Q?*4- 


tet 


Columbia  2tlnitier0itp 

mtlifCttpofJtogark 

College  of  ^fjpfiictans;  anb  burgeons 
Utorarp 


GIFT  OF 

Frederick  S.  Lee 


(on  the  flat)         (»»<!«  view)  Birtl 


' 


Plate    I. 


Fvih 


Mammal 


m 


Frog's  Corpuscle 
after  addition  of  water 


Mammalian 
after  addition  of  syrup 


Main,. 


1.  Red  blood-corpuscles. 


Nectunii.  Nucleus 
'  swollen;  nuclear  nm, 
corpuscular  envelope? 
ruptured. 


9 


II 


if 


c 


2.  The  colourless  corpuscles  of  human  blood,  x  1000.  a,  eosinophile  cells  ; 
b,  finely  granular  oxyphile  cells  ;  c,  hyaline  cells ;  d,  lymphocyte ; 
e,  polymorphonuclear  neutrophile  cells  (Kanthack  and  Hardy).  The 
magnification  is  much  greater  than  in  1 . 


3.  Cover-glass  preparation  of  spinal  cord  of  ox,   x  250. 
{Stained  with  methylene  blue). 

Dendritic  processes 


Q; 


Detached       • 
axis-cylinder 
process 


Bipolar  nerve-cells 


4.  Potassium  in  a,  frog's  erythrocyte  (Mark 
b,  nerve  (black) ;  c,  striped  muscle  (black 
d,  cartilage  cells  (yellow)  (Macalluni), 


Capillary 


MANUAL  OF  PHYSIOLOGY 

Mith  practical  fiycrdscs 


G.  N.  STEWART,  M  A.,  D.Sc,  M.D.  Edin.,  D.P.H.  Camb. 

PROFESSOR   OF   EXPERIMENTAL    MEDICINE   IN   WESTERN    RESERVE    UNIVERSITY,    CLEVELAND  ; 

FORMERLY      PROFESSOR     OF      PHYSIOLOGY     IN     THE     UNIVERSITY     OF     CHICAGO; 

PROFESSOR    OF    PHYSIOLOGY    IN    THF.    WESTERN    RESERVE    UNIVERSITY-, 

GEORGE    HENRY    LEWES   STUDENT; 

EXAMINER    IN    PHYSIOLOGY    IN    THE    UNIVERSITY   OF    ABERDEEN; 

SENIOR    DEMONSTRATOR   OF    PHYSIOLOGY    IN    THE    OWENS    COLLEGE,    VICTORIA    UNIVERSITY, 

ETC. 


WITH    COLOURED    PLATES    AND    4.5O    OTHER 
ILLUSTRATIONS 


SIXTH     EDITION 


NEW      YORK 
WILLIAM     WOOD     &     COMPANY 

MDCCCCX 


4 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 
Columbia  University  Libraries 


http://www.archive.org/details/manualofphysiolo1910stew 


^ 


PREFACE    TO    THE    SIXTH    EDITION 

In  the  present  edition  the  book  has  been  extensively 
revised,  and  in  many  parts  rewritten.  A  considerable 
amount  of  new  matter  has  been  added,  and  an  increase  in 
the  bulk  of  the  volume  has  been  found  unavoidable. 

G.  N.   STEWART. 

Cleveland, 

September,  1910. 


EXTRACT    FROM    THE    PREFACE    TO 
THE    FIRST    EDITION 

In  this  book  an  attempt  has  been  made  to  interweave 
formal  exposition  with  practical  work,  according  to  a  pro- 
gramme which  I  have  followed  for  some  time  past  in  teaching 
Physiology  to  medical  students  on  the  other  side  of  the 
Atlantic,  and  which  has,  it  is  believed,  proved  to  be  well 
adapted  to  their  needs  and  opportunities.  It  ought,  how- 
ever, to  be  explained  that,  for  various  reasons,  a  somewhat 
wider  range  of  experiment  is  open  to  the  student  in  America 
than  in  this  country.  But  as  nobody  will  use  this  book 
except  in  a  regular  laboratory  and  under  responsible 
guidance,  it  has  not  been  thought  necessary  to  mark  in  any 
special  manner  the  parts  of  the  exercises  which  the  English 
student  must  do  by  proxy  (that  is,  learn  from  demonstra- 
tions), and  the  parts  he  ought  to  perform  for  himself. 

An  arrangement  of  the  exercises  with  reference  to  the 
systematic  course  has  this  advantage— that  by  a  little  care 
it  is  possible  to  secure  that  practical  work  on  a  given  subject 
shall  actually  be  going  on  at  the  time  it  is  being  expounded 
in  the  lectures.  Cross-reference  from  lecture-room  to 
laboratory,  and  from  laboratory  to  lecture-room,  from  the 
detailed  discussion  of  the  relations  of  a  phenomenon  to  the 
living  fact  itself,  is  thus  rendered  easy,  natural,  and  fruitful. 

As  some  teachers  may  wish  to  know  how  a  course  such  as 
that  described  in  the  Practical  Exercises  may  be  conducted 
for  a  fairly  large  class,  a  few  words  on  the  method  we  have 
followed  may  not  be  out  of  place.  It  is  obvious  that  many 
of  the  exercises  require  more  than  one  person  for  their  per- 


vin      EXTRACT  FROM  THE  PR1  I   It  I    TO  Jill   FIRS1   I  DITIOU 

formance  ;  and  it  may  be  said  that,  excepl  in  the  •  ase  oi 
the  sinipU-r  experiments  and  the  chemical  work  as  a  whole. 
which  ea<  li  student  does  for  himself,  it  has  been  found 
convenient  to  divide  the  class  into  groups  of  four,  each  group 

remaining  together  throughout  the  session.  It  is  possible 
that  some  may  find  a  group  of  four  too  large  a  unit,  and  it 
is  certain  that  three,  or  perhaps  even  two.  would  he  better  ; 
but  in  a  large  school  so  minute  a  subdivision  is  hardly 
possible,  without  entailing  excessive  labour  on  the  teachers. 

The  systematic  portion  of  the  book  is  so  arranged  that 
it  can  equally  well  be  used  independently  of  the  practical 
work,  and  aims  at  being  in  itself  a  complete  exposition  of 
the  subject,  adapted  to  the  requirements  of  the  student  of 
medicine. 

As  to  the  matter  of  the  text,  it  is  hardly  necessary  to  say 
that  this  book  does  not  aspire  to  the  dubious  distinction  of 
originality;  and  it  is  literally  impossible  to  acknowledge 
all  the  sources  from  which  information  has  been  derived. 
In  many  cases  names  have  been  quoted,  but  names  no  less 
worthy  of  mention  have  often  been  of  necessity  omitted. 

G.  N.  STEWART. 
Cambridge, 

September,  1895. 


CONTENTS 


Introduction   - 

The  proteins 
Carbo-hydrates    - 
Fats         ... 
Structure  of  living  matter 
Functions  of  living  matter 


PAGE 
I 
I 

3 

4 
4 
6 


CHAPTER  I. 

The  Circulating  Liquids  of  the  Body 

Blood-corpuscles  ... 

Life-history  of  the  corpuscles     - 

Viscosity  of  blood  - 

Reaction  of  blood  - 

Specific  gravity  of  blood 

Electrical  conductivity  of  blood  - 

Relative  volume  of  corpuscles  and  plasma 

Haemolysis  - 

Precipitins  - 

Coagulation  of  blood        - 

Chemical  composition  of  blood  - 

Haemoglobin  and  its  derivatives 

Quantity  of  blood  - 

Lymph  and  chyle  - 

Functions  of  blood  and  lymph    - 


M 

15 
19 

22 

23 
25 

25 
26 
27 
30 
30 
41 
43 
47 
49 
5i 


CHAPTER  II. 

The  Circulation  of  the  Blood  and  Lymph 
Physiological  anatomy  of  vascular  system 
Flow  of  a  liquid  through  tubes   - 
The  beat  of  the  heart       - 
The  sounds  of  the  heart 
The  cardiac  impulse         - 
Endocardiac  pressure       - 
The  arterial  pulse  - 


72 
73 
75 
78 
80 
82 
84 
92 


x  CO  A  TENTS 

The  Circulation  ob  im    Blood  and  Lymph  [continued] — 

Arterial  blood-pressure    -----     ioo 

Measurement  of  the  blood-pressure  in  man        -  -     104 
Velocity  of  the  blood       - 

Measurement  of  velocity  of  blood           -            -  -     1 1 1 

The  volume-pulse            -            -            -            -  -116 

The  circulation  in  the  capillaries             -             -  1  I  9 

The  circulation  in  the  veins         -              -              -  i-'  1 

The  circulation-time         -              -              -              -  -     123 

Work  and  output  of  heart          -             -             -  -127 

The  relation  of  the  nervous  system  to  the  circulation  -     128 

Intrinsic  nerves  of  the  heart        -              -              -  -129 

Cause  of  the  heart-beat  -----     129 

Conduction  and  co-ordination  in  heart  -              -  -     134 

Auriculo-ventricular  bundle         ...  -      135 

Chemical  conditions  of  heart-beat            -             -  139 

Refractory  period  of  heart           -             -             -  -     141 

Extrinsic  nerves  of  the  heart       -              -              -  -     143 

Action  of  poisons  on  the  heart    -              -              -  -     150 

Normal  excitation  of  cardiac  nervous  mechanism  -     152 

Vaso-motor  nerves           -             -             -             -  -     157 

Yaso-motor  centres          -              -              -              -  -166 

Yaso-motor  refle-  -----     [6g 

Influence  of  gravity  on  the  circulation    -              -  -     173 

The  lymphatic  circulation            -             -             -  -     176 

CHAPTER   III. 

Respiration       -------     206 

Blood-supply  of  lungs     -----     207 

Mechanical  phenomena  of  respiration      -  -  -      209 

Types  of  respiration     "    -  -  -  -  -213 

Artificial  respiration         -  -  -  -  -      214 

Respiratory  sounds  -  -  -  -  -216 

Frequency  of  respiration  -  -  -  -     218 

Vital  capacity     -  -  -  -  -  - 

Intrathoracic  pressure     -  -  -  -221 

Respiratory  pressure        -  -  -  -  -jjj 

Relation  of  respiration  to  the  nervous  system  -  -22 

Apncea     -------     231 

Automaticity  of  respiratory  centre         -  -  - 

on  of  drugs  on  the  respiratory  centre  -  -     234 

Double  vagotomy  -  -  -  -  -     236 

Special  modifications  of  respiratory  movements 
Chemistry  of  respiration  -  -  -  - 

Ventilation  ------     243 

The  gases  of  the  blood     -  -  -  -  -     246 

Tension  of  blood-gases     -----     256 

Seats  of  oxidation  -  -  -  -  --59 


CONTEh  is  xi 

Respiration  (continued) —  PAG), 

Respiration  of  muscle     -----  261 

Nature  of  the  oxidative  process             -  264 

Influence  of  respiration  on  blood -pressure                         -  265 

Effects  of  breathing  condensed  and  rarefied  air             -  272 

Cutaneous  respiration      -----  275 

Voice  and  speech               -  276 


CHAPTER  IV. 

Digestion  -------  2gb 

Mechanical  phenomena  of  digestion         -  300 
Deglutition           -             -             -             -             -             -301 

Movements  of  stomach  and  intestines  -  -  -  304 

Influence  of  central  nervous  system  on  gastro-intestinal 

movements       ------  309 

Defalcation  -  -  -  -  -  -310 

Vomiting  -  -  -  -  -  -312 

Chemical  phenomena  of  digestion  -  -  -  314 

Ferments  -  -  -  -  -  -314 

Chemistry  of  the  digestive  juices  -  319 

Saliva        -  -  -  -  -  -319 

Gastric  juice  -----  322 

Antiseptic  function  of  the  gastric  juice  -  -  328 

Pancreatic  juice  -----  330 

Bile  -  -  -  -  -  -  334 

Succus  entericus   -----  341 

Secretion  of  the  digestive  juices  -  344 

Changes  in  pancreas  and  parotid  during  secretion  346 

Changes  in  gastric  glands  during  secretion  -  347 

Changes  in  mucous  glands  during  secretion  -  352 

Mode  of  formation  of  the  digestive  juices  -  354 

Why  the  stomach  does  not  digest  itself   -  -  359 

Influence    of    the    nervous    system    on    the    salivary 

glands  ------  302 

Reflex  secretion  of  saliva  -  -  -  -  36  j 

Influence  of  the  nervous  system  on  the  gastric  glands    -  372 

Influence  of  the  nervous  system  on  the  pancreas  -  378 

Secretin    -------  379 

Influence  of  the  nervous  system  on  the  secretion  of  bile  383 
Influence  of  the  nervous  system  on  the  secretion  of  intes- 
tinal juice          ------  336 

Action  of  drugs  on  digestive  secretions    -  387 

Secretion  of  the  digestive  juices  (summary)         -  -  388 

Digestion  as  a  whole        -  -  -  -  -  389 

Reaction  of  intestinal  contents    -  -  -  -  393 

Bacterial  digestion  -----  39^ 

Faeces       -------  396 


CONTENTS 


CHAPTER  V. 

PAGE 

Absorption        -------     398 

I  inhibition,  diffusion,  and  osmosis  ...     398 

Absorption  of  the  food     -----     401 

Theories  of  absorption     -  -.  -  -  -     404 

Formation  of  lymph        -----     406 

Absorption  of  fat  -  -  -  -  -412 

Absorption  of  carbo-hydrates      -  -  -  -     416 

Absorption  of  water  and  salts     -  -  -  -     417 

Absorption  of  proteins     -  -  -  -  -418 

CHAPTER  VI. 

Excretion          -------  435 

Excretion  by  the  kidneys             -  436 
Chemistry  of  urine            -              -              -              -              -436 

The  urine  in  disease         -----  447 

Secretion  of  urine             -             -             -             -             -  451 

Bloodvessels  and  tubules  of  kidney          ...  452 

Theories  of  renal  secretion           -             -             -  455 

Influence  of  the  circulation  on  the  secretion  of  urine    -  467 

Diuretics                ------  470 

Micturition           -             -             -             -             -             -  471 

Excretion  by  the  skin     -----  473 

CHAPTER  VII. 

Metabolism,  Nutrition  and  Dietetics         -  l<i<> 

Metabolism  of  proteins    -  -  -  -  -496 

Formation  of  urea  -----     ^00 

Formation  of  uric  acid     -----     ^05 

Formation  of  hippuric  acid  -  508 

Formation  of  kreatinin    -----     509 

Autolysis  ------     509 

Metabolism  of  carbo-hydrates — glycogen  -  -     511 

Glycogen-formers  -  -  -  -  -     513 

Extra-hepatic  glycogen   -  -  -  -  -514 

Fate  of  the  glycogen        -  -  -  -  -515 

Glycolysis  -  -  -  -  -  -516 

Diabetes  -  -  -  -  -     518 

Metabolism  of  fat  -  -  -  -  -522 

Formation  of  fat  from  carbo-hydrates    -  -  -     524 

Formation  of  fat  from  protein    -  -  -  -     .5-5 

Income  and  expenditure  of  the  body      -  -  -     528 

Nitrogenous  equilibrium  -  529 

Laws  of  nitrogenous  metabolism  ...     535 

Carbon  equilibrium  -  -  -  -  -     539 

The  oxygen  deficit  -  -  -  -  -     541 


C0NT1  \  rs  •.hi 

Mi  rABOLISM,   Nutrition  and  Dietetics  {continued) paoi 

Inorganic  salts  in  metabolism     -                         -             -  511 
Dietetics               -             -                                                       "543 

Stimulants           -                         -            -                         -  551 

I  Qternal  secrel  Ion                                                -            -  35- 

of  pancreas           -            -                                     -  553 

of  sexual  organs    -                                               -               -  .55'' 

of  thymus              -             -                          -  557 

of  thyroid  and  parathyroid                        -             -  558 

of  suprarenal         -----  563 

of  pituitary            -             -             -             -             -  566 

CHAPTER  VIII. 

Animal  Heat    -------  572 

Calorimetry          -             -             -             -             -             -  573 

Heat-loss               -             -             -             -             -             -  578 

Heat-production               -  579 

Seats  of  heat-production              -  583 

Thermotaxis         -              -              -              -              -              -  587 

Heat  centres         ------  595 

Fever       -------  597 

Distribution  of  heat          -----  602 

Temperature  topography              ...              -  604 

Normal  variations  in  body  temperature               -             -  605 

CHAPTER  IX. 

Muscle  -  -  -  -  -  -  -  -615 

Physical  introduction      -----  615 

Physical  properties  of  muscle      -  630 

Stimulation  of  muscle     -----  632 

Direct  excitability  of  muscle        -                           -             -  633 
The  muscular  contraction            -             -             -             -637 

Optical  phenomena  of  (and  structure  of  muscle)  -  638 

Mechanical  phenomena  of  642 

Influence  of  fatigue  on     -             -             -             -  648 

Electrical  tetanus               -  656 

Voluntary  contraction      -  660 

Thermal  phenomena  of    -              -              -              -  663 

Chemical  phenomena  of  -              -              -              -  666 

Source  of  the  energy  of  muscular  contraction     -             -  669 
Rigor  mortis        -             -             -             -             -             -671 

CHAPTER  X. 

Nerve    --------  077 

The  nerve-impulse  ;  its  initiation  and  conduction           -  07(1 

Stimulation  of  nerve        -----  680 

Excitabilitv  of  nerve        -              -              -              -              -  681 


xiv  COS  TENTS 

Nerve  {continued) —  PAOE 

Electrotonus        -            -            -            -            -            -  ( 

Condui  Hon  in  t  he  nerve  -  -  -  -  - 

Velocity  oi  the  nerve-impulse     -  -  -  - 

Chemistry  of  nerve          -            -            -            -            -  < 

Degeneration  oi  nerve     -----  69] 

Regeneration  of  nerve    -  -  -  -  -694 

I  rophic  nerves    -  -  -  -  -  -     ' 

Classification  of  nerves     -----  702 


CHAPTER  XI. 

Electro-Physiology   ------  717 

Currents  of  rest  and  action          -  718 

Relation  between  action  current  and  functional  activity  725 

Polarization  of  muscle  and  nerve             -  726 

Electrotonic  currents       -----  728 

Heart-currents     ------  730 

Human  electro-cardiogram           -              -              -              -  731 

Glandular  currents          -----  734 

Eye-currents        -  -  -  -  -  -734 

Electric  fishes      ------  736 


<  II  API  ER  XII. 

The  Central  Nervous  System  -  744 

Structure  -  -  -  -  -  "7  11 

Development        -  -  -  -  -  -      7  1" 

Histology  -  -  -  -  -  "717 

Nutrition  of  the  neuron  -----      7^5 

General  arrangement  of  grey  and  white  matter  in  the 

central  nervous  system  -  -  -  "759 

Arrangement  of  grey  and  white  matter  in  the  spinal  cord      762 
Arrangement  of  grey  and  white  matter  in  the  upper  part 

of  the  cerebro-spinal  axis         -  767 

Functions  of  the  central  nervous  system  -  -     786 

Functions  of  the  spinal  cord        -  788 

Decussation  of  the  sensory  paths  -  -  702 

Reflex  action        ------ 

Influence  of  brain  on  spinal  reflexes        -  806 

Automatism  of  the  spinal  cord    -  -  -  -     812 

The  cranial  nerves  -  -  -  -  8  1  ^ 

The  functions  of  the  brain  -  827 

Functions  of  the  cerebellum        -  -  -  -8 

Co-ordination  of  movements       -  837 

Functions  of  the  cerebral  cortex  ...     840 

Motor  '  areas     -  -  -  -  -  -     844 

Sensory  areas       ------ 

Aphasia   -  -  -  -  -  -  - 


CONTENTS  xv 

1 11 1  Central  Nervous  System  {continued) —  paoi 

I  0(  alization  of  function  in  central  nervous  system        -     867 
Kr.M  t ion  time      -  -  -  ?2 

Sleep  and  fatigue  -  -  °J* 

Hypnosis'  -  -  7 

Cerebral  circulation  -  -  -  °7° 

Resuscitation  of  central  nervous  system 
Chemistry  of  nervous  activity    - 
Cerebro-spinal  fluid 
Autonomic  nervous  system 


CHAPTER  XIII. 


880 
882 
883 


890 
892 

802 


The  Senses       - 
Vision       - 

Physical  introduction 
Structure  of  the  eye 

Chemistry  of  the  refractive  media  -             -  901 

Refraction  in  the  eye        -  9°2 

Accommodation    -  "  9°5 

Iris             -             -             -  "             "             -  9o8 

Defects  of  the  eye              -  -             -             -912 

Ophthalmoscope  -             -  -  9I7 

Skiascopy               -  "  92° 

Diplopia   -  "  923 

Stereoscopic  vision             -  -              -              -  9^5 

Visual  judgments  and  illusions  -             -             -  926 

Purkinje's  figures               -  93° 

Blind  spot              -             -  -             "             "  93 1 

Rods  and  cones  in  vision  -                           "  932 

Talbot's  law                        -  -             "             "  938 

Colour  vision         -  "  939 

Contrast   -             -             -  -             "             "944 

Perimetry               -             -  -             "             "  94° 

Colour-blindness  -  948 

Movements  of  the  eyes     -  -             -             -  951 

Hearing  -  "  953 

Smell  and  taste   -             -             -  "             "             ~  A 

Tactile  senses       -             -             -  -             "             -  908 

Sensations  of  temperature           -  -             -  97 1 

Pain          -              -              -              "  "              "              "  973 

Phenomena  after  section  of  cutaneous  nerves     -             -  975 

Muscular  sense    -  "  9y2 

CHAPTER  XIV. 

Reproduction  -  "  IO°3 

Regeneration  of  tissues  -  "  IO°3 

Reproduction  in  the  higher  animals  -              -              -  IO°4 

Menstruation        ----'"  IO°5 


xvi  CONTENTS 

Reproduction  [continued) —  pace 

Development  <>f  the  ovum            -                            -              -  1006 

Physiology  oi  the  embryo           -                        -            -  ioio 

Km  hange  <>i  materials  in  1 1 1 « -  pla<  enta    -            -            -  1013 

Parturition            ...                                          -  * 

Milk          -              -                                                         -              -  i"-i 

Transplantation  oi  tissues           ...            -  1023 

Parabiosis              -              -                            -              -              -  1024 

Appendix            -------  1027 

Index     --------  1029 


PRACTICAL  EXERCISES 

INTRODUCTION 

General  reactions  of  proteins      -              -              -              -  -          7 

Colour  reactions  of  proteins        -              -  7 

Special  reactions  of  groups  of  proteins  -              -              -  -8 

Precipitation  reactions  of  proteins          -  8 

Reactions  of  derivatives  of  proteins        -             -             -  9 

Carbo-hydrates  -             -             -             -             -             -  -10 

Fats         -             -             -             -             -             -             -  -       11 

Scheme  for  testing  for  proteins  and  carbo-hydrates        -  -       13 

I  HAPTER  I. 

1.  Reaction  of  blood     -                           -  54 

2.  Specific  gravity  of  blood       -              -              -              -  54 

3.  Coagulation  of  blood             -                                          -  i4"57 

4.  Preparation  of  fibrin-ferment           -              -              -  57 

5.  Preparation  of  extracts  containing  thrombokinase  -  57 

6.  Serum            -              -              -              -              -              -  "57 

7.  Enumeration  of  the  blood-corpuscles          -             -  58 

8.  Haimatocrite             -             -             -             -             -  "59 

9.  Electrical  conductivity  of  blood      -             -             -  -       60 

10.  Opacity  of  blood      -             -             -             -             -  -       61 

11.  Laking  of  blood       ...              -  -       61 

12.  Haemolysis  and  agglutination           ...  -       it< 

13.  Osmotic  resistance  of  coloured  corpuscles  -             -  -       '■} 

14.  Blood-pigment           -              -              -              -              -  -       65 

(1)  Preparation  of  haemoglobin  1  rystals 

(2)  Spectroscopic  examination  of  haemoglobin  and 

its  derivath                  ...  65-67 

(3)  Guaiacum  test  for  blood              -  -       68 

(4)  Quantitative  estimation  <>i  haemoglobin  -       68 

(5)  Haemin  test  for  blood-pigment                 -  71 


t  OX  II    \  I  s 


CHAPTER   II. 

PACE 

i     Microscopic  examination  of  the  circulating  blood  -            -  177 

j    Anatomy  of  the  frog's  heart                                                   -  177 

3.    I  he  Ik, it  of  the  heart             -                                             -              -  178 

|.  Apex  of  the  heart    -                                      ...  ijg 

5.  Heart  tracings          ------  iy(j 

6.  Dissection  of  vagus  and  cardiac  sympathetic  in  frog            -  181 

7.  Stimulation  of  the  vagus  in  the  frog              ...  tq2 

8.  Stimulation  of  the  junction  of  the  sinus  and  auricles          -  183 

9.  Action  of  muscarine  and  atropia  on  the  heart           -              -  183 

10.  Stannius'  experiment            -  183 

11.  Stimulation  of  cardiac  sympathetic  in  frog              -             -  184 

12.  Action  of  inorganic  salts  on  heart-muscle    -              -              -  185 

13.  The  action  of  the  mammalian  heart                         -              -  186 

14.  Action  of  the  valves  of  the  heart    -  190 

15.  Sounds  of  the  heart  -  -  -  -  -191 

16.  Cardiogram                ------  igi 

17.  Sphygmographic  tracings    -----  192 

18.  Venous  pulse  tracing  from  jugular  -                                         -  193 

19.  Polygraph  tracings  -             -             -                           -  193 

20.  Plethysmography  tracings  -                           ...  jg^ 
2i.  Pulse-rate    -                                                                                   -  195 

22.  Blood-pressure  tracing         -             -                           -             -  195 

23.  Estimation  of  arterial  pressure  in  man        -                            -  198 

24.  Influence  of  position  of  the  body  on  blood-pressure             -  199 

25.  Effects  of  haemorrhage  and  transfusion  on  blood-pressure  -  200 

26.  The  influence  of  albumoses  on  blood-pressure         -             -  201 

27.  Effect  of  suparenal  extract  on  blood-pressure          -             -  201 

28.  Section  and  stimulation  of  cervical  sympathetic  in  rabbit  202 

29.  Determination  of  the  circulation-time          ...  203 


CHAPTER   III. 

1.  Tracing  of  the  respiratory  movements  in  man         -             -  287 

2.  Production  of  apncea  and  periodic  breathing  in  man           -  288 

3.  Tracing  of  the  respiratory  movements  in  animals  -             -  288 

4.  Heat-dyspncea          ------  290 

5.  Measurement  of  volume  of  air  inspired  and  expired             -  291 

6.  Cardio-pneumatic  movements          -  291 

7.  Auscultation  of  the  lungs     -----  291 

8.  Measurement  of  the  respiratory  pressure     -  292 

9.  Determination  of  carbon  dioxide  and  oxygen  in  inspired 

and  expired  air    -             -             -             -             -             -  292 

10.  Estimation  of  carbon  dioxide  and  water  given  off  by  an 

animal      -------  294 

11.  Muscular  contraction  in  the  absence  of  free  oxygen            -  295 

12.  Oxidizing  ferments  ------  295 


CONTENTS 


CHAPTERS   IV.   AND  V. 

PACE 

i.  Chemistry  and  digestive  action  of  saliva    -  \t.i 

i.  Stimulation  of  the  chorda  tympani             ...  (Jj 

3.  Effect  of  drugs  on  the  secretion  of  saliva     ...  )_•-, 

4.  Digestive  action  of  gastric  juice     -            -            -  .^i, 

5.  To  obtain  chyme  and  gastric  juice  -            ...  jjy 

6.  Digestive  action  of  pancreati*   juice             ...  ^28 
7    Chemistry  of  bile      -            -            -            -            -            - 

8.  Microscopical  examination  of  faeces             ...  ^2 

9.  Absorption  of  fat      -  -  -  -  -  -432 

10.  Time  required  for  digestion  and  absorption  of  food  sub- 

stances   -------  ,j}_> 

11.  Quantity  of  cane-sugar  inverted  and  absorbed  in  a  given 

time  -  -  -  -  -  -  -433 

i_\  Auto-digestion  of  the  stomach         ....  434 

CHAPTER   VI. 

1.  Specific  gravity  of  urine        -             -             -             -             -  \11 

2.  Reaction  of  urine     -  -  -  -  -  "477 

3.  Chlorides  in  urine    -  -  -  -  -  "-477 

4.  Phosphates  in  urine               -  478 

5.  Sulphates  in  urine  ------  479 

6.  Indoxyl  in  urine        ------  ^jg 

7.  Urea              -------  480 

8.  Total  nitrogen  in  urine         -----  482 

9.  Uric  acid      -------  484 

10.  Kreatinin     -------  485 

11.  Hippuric  acid            .__---  486 

12.  Proteins  in  urine      ------  486 

13.  Sugar  in  urine          ------  488 

Pentoses  in  urine     ------  490 

Acetone  in  urine       -             -                      ,     -             -             -  492 

Determination  of  the  freezing-point  of  urine            -             -  492 

Examination  of  urine          -----  494 

Urinary  sediments  ------  494 

CHAPTERS  VII.  AND  VIII. 

1.  Glycogen      -------  608 

2.  Catheterism               -             -             -             -             -             -  609 

3.  Experimental  glycosuria       -----  609 

(1)  Injection  of  sugar  into  the  blood            -             -  609 

(2)  Phloridzin  glycosuria      -  610 

(3)  Alimentary  glycosuria     -             -             -             -  610 

4.  Milk               -             -             -             -             -             -             -  610 

5.  Cheese  -  -  -  -  -  -  -611 

6.  Flour             -             -             -             -             -             -             -  612 


CONTENTS  -Nix 

PACE 

j.  Bread  -  -  -  -  -  -  -612 

8.  Excretion  of  urea  (and  total  nitrogen)  and  proteins  in  food  612 
,     Measurement  of  t lie  heal  given  oft  in  respiration    -              -  <>i  ; 

CHAPTERS   IX.   AND   X. 

1.  Difference  of  make  and  break  induction  shocks      -              -  702 

2.  Stimulation  by  the  voltaic  current  -              ...  704 

3.  Ciliary  motion           ------  705 

4.  Direct  excitability  of  muscle — curara           -  706 

5.  Graphic  record  of  '  twitch  '  -  706 
<>.  Influence  of  temperature  on  the  muscle-curve  -  706 
7.  Influence  of  load  on  the  muscle-curve  -  708 
S.    Influence  of  fatigue  on  the  muscle-curve    -              -              -  708 

9.  Seat  of  exhaustion  in  fatigue  of  the  muscle-nerve  prepara- 

tion            -------  708 

10.  Seat  of  exhaustion  in  fatigue  for  voluntary  contraction       -  709 

11.  Influence  of  veratrine  on  muscular  contraction        -              -  709 
1  j.   Measurement  of  the  latent  period   of  muscular  contrac- 
tion           -              -              -              -              -              -              -710 

13.  Summation  of  stimuli  -  -  -  -  -711 

14.  Superposition  of  contractions          -             -             -             -  711 

15.  Composition  of  tetanus         -  -  -  -  -711 

16.  Contraction  of  smooth  muscles        -             -             -             -  712 

17.  Velocity  of  the  nerve-impulse          -             -             -             -  713 

18.  Chemistry  of  muscle             -----  713 

19.  Reaction  of  muscle  in  rest,  activity,  and  rigor        -             -  715 

CHAPTER  XI. 

1.  Galvani's  experiment            -----  738 

2.  Contraction  without  metals              -             -             -             -  738 

3.  Secondary  contraction          -----  738 

4.  Demarcation  and  action  currents  with  capillary  electro- 

meter       -------  73Q 

5.  Action-current  of  the  heart               ...             -  740 

6.  Electrotonus             ------  740 

7.  Paradoxical  contraction       -             -             -             -             -  741 

8.  Alterations  in  excitability  and  conductivity  produced  in 

nerve  by  a  voltaic  current            -             -             -             -  741 

9.  Formula  of  contraction         -----  742 

10.  Formula  of  contraction  for  (human)  nerves  in  situ  -             -  743 

11.  Ritter's  tetanus        ------  743 

CHAPTER  XII. 

1.  Section  and  stimulation  of  nerve-roots        ...  884 

2.  Reflex  action  in  the  '  spinal  '  frog  -             -             -             -  885 

3.  Reflex  time               -             -             -             -             -             -  886 


xx  COS  TENTS 

tua 

\.   Inhibition  of  the  reflexes     -  -  886 

5.  Spinal  cord  ;m<l  must  ular  tonus      -  -  886 

6.  Spinal  cord  and  tonus  of  the  bloodvessels   -  -  886 

7 .  Action  of  si  i  \ '  hnine  -  -  -  886 

8.  Mammalian  spinal  preparation        -                                      -  886 
g.   Reflexes  in  man       -                         ....  888 

id.   Excision  of  cerebral  hemispheres  (frog)       -  -  888 

ii.   Excisi i  cerebral  hemispheres  (pigeon)  -  -  888 

!_'.  Stimulation  oJ  the  motor  areas  in  the  dog  -  -  889 


CHAPTER  XIII. 

1.  Dissection  of  the  eye  -             -             -             -             - 

2.  Formation  of  inverted  imago  on  retina      -  -             -986 

3.  Phakoscope  -                         ....  (),si, 

4.  Scheiner's  experiment  .....  987 

5.  Kiihne's  artificial  eye  .....  988 

6.  Astigmatism  (ophthalmometer)       -  989 

7.  Spherical  aberration  -             -             -             -             -  991 

8.  Chromatic  aberration  -                            ...  992 

9.  Measurement  of  the  field  of  vision  -  992 

10.  Mapping  the  blind  spot         -  -                                           -  992 

1 1 .  The  yellow  spot        -  ....  993 

12.  Ophthalmoscope       -  ....  994 

13.  Retinoscopy  -                            -                                           -  994 

14.  Pnpillo-dilator  and  constrictor  fibres  -                            -  996 

15.  Colour-mixin»  -                                                                       -  996 

16.  After-images  ------  996 

17.  Retinal  fatigue         ......  997 

18.  Visual  acuity  -                                          ...  997 

19.  Colour-blindness       ------  998 

20.  Talbot's  law  ------  gg% 

21.  Purkinje's  figures     ------  998 

22.  Relation  of  pitch  and  vibration  froquoncv  -  -              -  998 

23.  Beats  -             -                                         .             -             .  999 

24.  Sympathetic  vibration          ....  -  999 

25.  Galton's  whistle       -  -                           -             -             -  999 

26.  Cranial  conduction  of  sound  ....  qgg 

27.  Taste  -------  999 

28.  Smell  -------  999 

29.  Touch  and  pressure  ------  999 

30.  Temperature  sensations        -----  jooi 

31.  Pain  -------  1001 


(MAPI  I   R    XIV. 
Contractions  of  isolated  uterine  rings  -  -  -  1 


A    MANUAL   OF    PHYSIOLOGY 


INTRODUCTION 

LIVING  matter,  whether  it  is  studied  in  plants  or  in  animals, 
has  certain  peculiarities  of  chemical  composition  and  structure, 
but  especially  certain  peculiarities  of  action  or  function,  which 
mark  it  off  from  the  unorganized  material  of  the  dead  world 
around  it. 

Chemical  Composition  of  Living  Matter.  —  Although  we 
cannot  analyze  the  living  substance  as  such,  we  can  to  a  certain, 
but  limited,  extent  reconstruct  it,  so  to  speak,  from  its  ruins. 
When  subjected  to  analytical  processes,  which  necessarily  kill  it, 
living  matter  invariably  yields  bodies  of  the  class  of  proteins, 
exceedingly  complex  substances,  which  have  approximately  the 
following  composition  :  Carbon,  51-5  to  54*5  per  cent.  ;  oxygen, 
20" 9  to  23' 5  per  cent.  ;  nitrogen,  15-2  to  17  per  cent.  ;  hydrogen, 
6*9  to  7- 3  per  cent.,  with  small  quantities  of  sulphur.  Nucleo- 
proteins,  which  are  compounds  of  ordinary  proteins  with  nucleic 
acids,  a  series  of  sulphur-free  organic  acids  rich  in  phosphorus, 
are  constantly  met  with.  Certain  carbo-hydrates,  composed  of 
carbon,  hydrogen,  and  oxygen  (the  last  two  in  the  proportions 
necessary  to  form  water),  of  which  glycogen  (C6H10O5)n  may  be 
taken  as  a  type,  appear  to  be  always  present.  Fats,  which  con- 
sist of  carbon,  hydrogen,  and  oxygen,  and  of  which  tristearin,  a 
compound  of  stearic  acid  with  glycerin,  of  the  formula 
C3H5,3(C18H3502),  may  be  given  as  an  example,  are  often,  and 
certain  liquids,  e.g.,  lecithin  (p.  4),  are  always,  found.  Finally, 
water  and  certain  inorganic  salts,  such  as  the  chlorides  and  phos- 
phates of  sodium,  potassium,  and  calcium,  are  constantly  present. 

The  Proteins. — The  constitution  of  the  protein  molecule  is  still 
unknown  ;  but  when  proteins  are  broken  down  by  the  action  of 
ferments,  such  as  exist  in  gastric  and  in  pancreatic  juice,  or  by 
chemical  methods — for  example,  by  boiling  with  dilute  acids — the 
most  important  of  the  cleavage  products  are  various  amino-acids 
(p.  332).  It  has  therefore  been  suggested  that  proteins  are  built  up 
by  the  linking  together  of  amino-acids,  the  different  proteins 
differing  quantitatively  or  qualitatively  as  regards  the  amino-acids 
present  (E.  Fischer).      Thus  serum-albumin  and  egg-albumin  yield 

I 


2  A   MANUAL  Of  PHYSIOLOGY 

no  glycin  or  glvcocoll  (aminn-acctic  acid.  (II  Nil  .COOH),  while 
glycin  is  constantly  found  among  the  cleavage  products  of  serum- 
globulin.     And  while  leucin  (a-aminoisobutylacetic  acid)  is  present 

to  tin-  extent  of  about  2C5  per  cent,  in  the  cleavage  products  oi 
(horse's)  serum-albumin,  (hen's)  egg-albumin  yields  only  yi  percent. 

On  the  other  hand,  egg-albumin  yields  8'I  per  cent,  of  alanin 
(amino-propionic  acid.  C2H4.NHj.COOH),  while  serum-albumin 
yields  only  i"j  per  cent.  Of  the  aromatic  amino-acids — that  is. 
amino-acids  united  to  the  benzene  ring — phenyl-alanin  (amino- 
propionic  acid  in  which  one  atom  of  H  is  replaced  by  phenyl.  CgH 
is  obtained  to  the  extent  of  44  per  cent,  from  egg-albumin,  and  a 
little  over  3  per  cent,  from  serum-albumin.  Tyrosin  or  oxyphenyl- 
alanin  (amino-propionic  acid  in  which  a  H  atom  is  replaced  by 
oxyphenyl,  (',11,. oil)  appears  to  the  amount  of  15  per  cent,  among 
the  cleavage  products  of  egg-albumin,  and  to  the  amount  of  2*1  per 
cent,  among  those  of  serum-albumin.  It  is  an  interesting  point  in 
this  connection  that  gelatin,  which  yields  16-5  per  cent,  of  glycin. 
yields  no  tyrosin  at  all ;  tryptophane,  an  aromatic  amino-acid 
still  more  complex  than  tyrosin.  is  also  absent.  These  facts  afford 
an  explanation  of  certain  colour  reactions  of  proteins  long  known 
empirically,  but  only  recently  understood  (p.  7) .  The  process  by  which 
the  protein  molecule  is  thus  decomposed  is  called  hydrolysis — that 
is,  the  molecule  takes  up  water,  and  then  splits  into  smaller  mole- 
cules. The  hydrolysis  occurs  in  various  stages,  bodies  like  acid-  or 
alkali-albumin  (meta-  or  infra-proteins)  being  first  formed,  then 
proteoses,  then  peptones.  The  peptones  are  further  split  into  bodies 
containing  a  relatively  small  number  of  amino-acids  linked  together. 
These  bodies  are  called  peptides  or  polypeptides,  which  finally  are 
decomposed  so  as  to  yield  the  individual  amino-acids.  The  inverse 
process  can  also  be  carried  on  to  a  certain  extent,  and  Fischer  has 
taken  an  important  step  towards  the  eventual  synthesis  of  proteins 
by  showing  how  polypeptides  of  increasing  complexity  can  be  built 
up  by  linking  amino-acids  together.  Bodies  may  thus  be  formed  in  the 
laboratory  which  give  some  of  the  characteristic  reactions  of  peptones. 

The  numerous  substances  included  in  the  group  of  proteins  may 
be  classified  as  follows,  beginning  with  the  simplest  : 

1.  Protamins,  such  as  the  bodies  called  salmin  and  sturin 
present  in  fish-sperm. 

2.  Histones,  bodies  separated  from  blood-corpuscles.  Globin.  the 
protein  constituent  of  haemoglobin,  is  one  of  them.  Unlike  the  other 
groups  of  proteins,  they  are  precipitated  by  ammonia. 

3.  Albumins. 

4.  Globulins. 

5.  Sclero-proteins  or  albuminoids,  such  as  gelatin  and  keratin. 

6.  Phospho-proteins,  including  such  substances  as  vitellin.  a  body 
obtainable  from  egg-yolk,  and  caseinogen,  the  chief  protein  of  milk. 
They  are  rich  in  phosphorus,  but  arc  to  be  distinguished  from  nucleo- 
proteins,  which  also  contain  a  relatively  large  amount  of  phosphorus, 
by  the  fact  that  they  do  not  yield  the  purin  bases,  the  characteristic 
products  of  the  decomposition  of  nucleo-proteins. 

7.  Conjugated  proteins,  substances  in  which  the  protein  molecule 
is  united  to  another  constituent,  usually  spoken  of  as  a  '  prosthetic  ' 
group.  Thus  the  nucleo-proteins  consist  of  protein  united  with 
nucleic  acid,  the  chromo-proteins  (e.g.,  haemoglobin)  of  protein  united 
with  a  pigment,  and  the  gluco-proteins  (e.g.,  mucin)  of  protein  united 
with  a  carbo-hydrate  group. 


INTRODUCTION  3 

Among  the  derivatives  of  proteins,  the  most  important  arc  those 
already  mentioned  as  being  produced  in  protein-hydrolysis,  viz.  : 
/    Meta-proteins. 

(h)  Proteoses,  including  albumose,  the  proteose  derived  from 
albumin;  globulose,  thai  derived  from  globulin;  gelatose,  that 
derived  from  gelatin,  etc.     The  proteoses  may  be  further  subdivided, 

according   to   the  order  in  which  they  arc  formed  in  digestion  into 
proto-protcoses,  hetero-proteoses,  and  deutero-proteoses. 

Peptones. 
—  ((/)   Polypeptides.     The  majority  of  these  are  artificial  products, 
formed    by   the   synthesis   of   amino-acids,    although   some   can   be 
obtained  from  proteins  by  hydrolysis.     Only  a  few  of  those  hitherto 
prepared  give  the  biuret  test. 

However  formidable  the  above  list  may  appear  to  the  student,  it 
gives  an  inadequate  idea  of  the  extreme  complexity  of  the  protein 
class  and  its  richness  in  individuals.  For,  apart  from  the  fact  that 
the  list  has  been  purposely  left  incomplete,  especially  as  regards  the 
numerous  vegetable  proteins,  there  is  the  best  evidence  that  proteins 
of  the  same  name  from  different  animal  species  have  certain  pro- 
perties which  distinguish  them  from  each  other.  The  serum- 
albumins  can  be  crystallized  much  more  easily  in  some  animals  than 
in  others.  The  same  is  conspicuously  true  of  the  haemoglobins, 
which  differ  also  in  certain  animals  in  the  relative  proportion  of 
sulphur  and  iron  in  the  molecule,  as  well  as  in  the  crystalline  form. 
Even  when  no  chemical  or  physical  differences  have  as  yet  been  made 
out,  proteins  of  the  same  name  from  the  blood  or  organs  of  different 
species  show  notable  '  specific  '  differences  when  subjected  to  certain 
biological  tests  (see,  e.g.,  the  paragraph  on  '  Precipitins,'  p.  30). 

Carbo-hydrates. — -The  most  important  carbo-hydrates  in  their 
physiological  relations  are  dextrose,  levulose,  galactose,  lactose, 
maltose,  sucrose  (cane-sugar),  starch,  and  glycogen.  As  regards  their 
chemical  constitution,  the  simplest  carbo-hydrates  are  aldehydes  or 
ketones — that  is,  the  first  oxidation  products  of  primary  and 
secondary  alcohols  respectively.  Thus  dextrose  is  the  aldehyde  of 
sorbite,  a  hexatomic  alcohol  (an  alcohol  containing  six  OH  groups), 
while  levulose  is  the  ketone  of  the  isomeric  alcohol  called  mannite, 
and  galactose  the  aldehyde  of  the  isomeric  alcohol  called  dulcite. 
The  sugars  containing  six  carbon  atoms  are  termed  hexoses.  They 
include  dextrose,  levulose,  and  galactose.  The  empirical  formula 
of  these  three  simple  sugars  (or  monosaccharides)  is  the  same 
(QHj.,0,,),  but,  owing  to  the  different  arrangement  of  the  atoms 
or  groups  of  atoms,  they  have  each  their  characteristic  properties 
by  which  they  can  be  easily  distinguished.  For  example,  dextrose 
rotates  the  plane  of  polarization  to  the  right,  levulose  to  the  left. 
By  the  union  or  '  condensation  '  of  two  molecules  of  a  monosac- 
charide, with  loss  of  a  molecule  of  water,  a  disaccharide  is  formed. 
Cane-sugar,  maltose,  and  lactose,  all  with  the  same  empirical  formula, 
(C12H22Ou),  are  disaccharides.  Cane-sugar  yields  on  hydrolysis  a 
mixture  of  equal  parts  of  dextrose  and  levulose ;  lactose,  a  mixture 
of  dextrose  and  galactose ;  while  maltose  is  converted  into  dextrose. 
By  the  condensation  of  more  than  two  molecules  of  monosaccharide 
polysaccharides  are  formed,  such  as  starch,  dextrin,  and  glycogen. 
The  exact  molecular  weights  of  these  substances  are  unknown. 
Their  general  formula  can  be  written  (C,;H10O.-)n,  where  n  represents 
the  number  of  monosaccharide  molecules  condensed  to  form  the 
polysaccharide,  in  the  case  of  starch  probably  some  hundreds. 

I — 2 


I  A   MANUAL  OF  PHYSIOLOGY 

Fats  and  Lipoids. — The  fats  arc  compounds  of  higher  fatty  acids 
with  glycerin  (glycerin  esters).  The  ordinary  body-fat  consists  of 
a  mixture  of  three  neutral  fats  (palmitin,  stearin,  and  olein)  which 
differ,  both  chemically  and  physically  from  each  other  -e.g.,  in 
melting-point  and  in  the  so-called  iodine  value,  the  number  which 
represents  the  amount  of  iodine  taken  up  from  a  standard  solution. 
(  tlein  melts  at  -  50  C,  palmitin  at  450  C,  and  stearin  at  a  still  higher 
temperature.  It  is,  therefore,  the  presence  o\  olein  which  keeps  the 
body-fat  liquid  at  the  temperature  of  the  body.  The  fats  are  soluble 
in  ether,  in  hot  alcohol,  and  in  many  other  liquids,  but  insoluble  in 
water.  Besides  the  ordinary  fats,  the  tissues  and  liquids  of  the  body 
contain  lecithin  (C4.iH„4NPO.,),  a  fat-like  compound  which  yields  on  de- 
composition, in  addition  to  glycerin,  and  a  fatty  acid,  phosphoric  acid 
and  a  nitrogen-containing  substance  called  cholin  (p.  337).  Lecithin, 
though  found  in  all  cells,  is  especially  abundant  in  nervous  tissues. 
It  is  associated  with  cholcstcrin  and  with  other  substances  which, 
like  lecithin  and  cholesterin,  are  soluble  in  ether  and  similar  solvents 
of  fat.  For  this  reason  these  substances  are  often  grouped  together 
as  lipoids,  although  some  of  them  are  chemically  quite  different  from 
fat.  Cholesterin,  for  instance,  is  an  alcohol.  Although  usually 
present  only  in  small  amount,  the  lipoids  play  a  very  important  part 
in  the  structure  and  in  the  economy  of  the  cell. 

Structure  of  Living  Matter — The  Cell. — Protoplasm  or  living 
substance,  when  examined  in  its  most  primitive,  undifferentiated 
condition  in  such  cells  as  the  amoeba  or  the  white  blood-corpuscles, 
appears  on  first  view  a  homogeneous,  structureless  mass,  except 
for  certain  granules  embedded  in  it,  and  consisting  either  of 
products  formed  by  its  activity  or  of  food  materials.  But  even 
here  more  careful  study  reveals  a  certain  complexity  of  struc- 
ture. At  the  very  least,  an  external  layer,  or  ectoplasm,  can  be 
distinguished  from  the  interior  mass,  or  endopiasm.  There  is 
reason  to  believe  that  even  where  no  histological  demonstra- 
tion of  an  ectoplasmic  layer  or  a  definite  envelope  is 
possible,  the  surface  of  the  cell  is  physiologically  different  from 
its  interior.  In  many  cells  the  protoplasm  presents  the  appear- 
ance of  a  honeycomb  or  network,  with  granules  usually  situated 
at  the  nodes,  and  holding  in  its  vesicles  or  meshes  a  fluid,  perhaps 
containing  pabulum,  from  which  the  waste  of  the  living  frame- 
work is  made  good,  or  material  upon  which  it  works,  and  which 
it  is  its  business  to  transform.  Some  observers,  however,  main- 
tain that  the  network  is  an  artificial  appearance  produced  by  the 
precipitation  of  the  colloid  constituents  of  the  protoplasm  by  the 
fixing  reagent,  or  even  by  the  coagulative  processes  associated 
with  the  act  of  dying,  and  that  the  unaltered  living  substance  is 
a  homogeneous  fluid  or  jelly.  In  certain  respects  it  behaves  like 
a  liquid,  and  in  others  like  a  solid,  a  peculiarity  which  is  un- 
doubtedly associated  with  its  richness  in  colloids,  as  experiments 
with  such  substances  as  gelatin  and  agar  have  shown.  In 
building  up  our  typical  cell  we  start  with  a  piece  of  protoplasm. 
Somewhere  in  the  midst  of  this  we  find  a  body  which,  if  not 


INTROnUCTlox  5 

absolutely  different  in  kind  from  the  protoplasm  of  the  rest  of 
the  cell  or  cytoplasm,  is  yet  marked  off  from  it  by  very  definite 
morphological  and  chemical  characters. 

This  is  the  nucleus,  generally  of  round  or  oval  shape,  and 
bounded  by  an  envelope.  Within  the  envelope  lies  a  second  net- 
work of  fine  threads,  which  do  not  themselves  stain  with  nuclear 
dyes  such  as  hematoxylin.  Hut  in  or  on  these  '  achromatic  ' 
filaments  lie  small,  highly  refractive  particles,  staining  readily 
and  deeply  with  dyes,  and  therefore  described  as  consisting  of 
chromatin.  This  chromatin  is  either  made  up  of  nucleins  (nucleo- 
proteins  particularly  rich  in  nucleic  acid,  and  therefore  in  phos- 
phorus), or  yields  nucleins  by  its  decomposition  ;  and  it  seems  to 
owe  its  affinity  for  certain  staining  substances  to  the  presence  of 
nucleic  acid.  The  meshes  of  the  nuclear  reticulum  contain  a 
semi-fluid  material,  which  does  not  readily  stain.  The  nucleus 
is  distinguished  from  the  cytoplasm,  even  as  regards  its  inorganic 
constituents,  by  the  absence  of  potassium.*  Besides  the  nucleus, 
another  much  smaller  structure,  the  centrosome,  is  differentiated 
from  the  protoplasm  of  the  cell.  This  is  a  minute  dot  staining 
deeply  with  such  dyes  as  hematoxylin,  and  generally  situated 
near  the  nucleus.  Surrounding  it  is  a  clear  area,  the  attraction 
sphere,  in  and  beyond  which  fine  fibrils  radiate  out  into  the 
cytoplasm.  Both  the  attraction  sphere  and  the  nucleus  play  an 
important  part  in  division  of  the  cell  by  the  process  known  as 
karyokinesis,  or  mitosis,  or  indirect  division,  which  is  by  far  the 
most  common  mode. 

When  the  nucleus  is  about  to  divide,  the  chromatin  granules 
arrange  themselves  into  one  or  more  coiled  filaments  or  skeins, 
which  then  break  up  into  a  number  of  separate  portions  called 
chromosomes.  These  undergo  a  remarkable  series  of  transforma- 
tions, leading  eventually  to  the  segregation  of  the  nuclear 
chromatin  in  two  separate  daughter  nuclei,  each  surrounded  by 
a  portion  of  the  original  cytoplasm.  Apart  from  its  role  in  the 
division,  and  therefore  in  the  multiplication,  of  the  cell,  the 
nucleus  is  now  known  to  exert  an  influence  perhaps  not  less 
important  upon  those  chemical  changes  in  the  cytoplasm  which 
are  necessary  for  its  normal  nutrition  and  function. f  It  is  doubt- 
ful whether  any  portion  of  protoplasm  can  permanently  survive 

*  This  has  been  shown  microchemically.  The  potassium  is  precipitated 
by  a  solution  of  hexanitrite  of  sodium  and  cobalt  as  orange  yellow  crystals 
of  the  triple  salt,  hexanitrite  of  potassium,  sodium  and  cobalt.  Where 
very  minute  traces  of  potassium  are  present,  ammonium  sulphide  must 
be  added,  after  washing  out  the  excess  of  the  cobalt  reagent.  Black 
cobalt  sulphide  is  thus  formed  from  the  triple  salt  (Macallum,  Frontispiece). 

t  According  to  Hertwig,  a  precursor  of  chromatin,  '  prochromatin,'  a 
substance  without  characteristic  staining  reaction,  is  formed  in  the  cyto- 
plasm, taken  up  by  the  nucleus,  and  there  elaborated  into  chromatin. 
From  the  nucleus  chromatin  and  its  derivatives  return  to  the  cytoplasm 
to  be  used  in  its  function. 


6  A   MANUAL  OF  PHYSIOLOGY 

the  loss  of  its  nuclear  material.     It  must  t>e  remembered,  how- 

-.  that  nuclear  material  may  sometimes  be  present  in  difl 
form  in  cells  which  do  not  show  a  nucleus  in  the  histological  sense. 

When  we  carry  back  the  analysis  of  an  organized  body  as  far  as 
we  can,  we  find  that  every  organ  of  it  is  made  up  of  cells,  which 
upon  the  whole  conform  to  the  type  we  have  been  describing, 
although  there  are  many  differences  in  details.  Some  organisms 
there  are,  low  down  in  the  scale,  whose  whole  activity  is  con- 
fined  within  the  narrow  limits  of  a  single  cell.  The  amoeba  sets 
up  in  life  as  a  cell  split  off  from  its  parent.  It  divides  in  its  turn, 
and  each  half  is  a  complete  amoeba.  When  we  come  a  little- 
higher  than  the  amoeba,  we  find  organisms  which  consist  of 
several  cells,  and  '  specialization  of  function  '  begins  to  appear. 
Tims  the  hvdra,  the  '  common  fresh-water  polyp  '  of  our  ponds 
and  marshes,  has  an  outer  set  of  cells,  the  ectoderm,  and  an 
inner  set,  the  endoderm.  Through  the  superficial  portions  of 
the  former  it  learns  what  is  going  on  in  the  world  ;  by  the  con- 
traction of  their  deeply- placed  processes  it  shapes  its  life  to  its 
environment.  As  we  mount  in  the  animal  scale,  specialization 
of  structure  and  of  function  are  found  continually  advancing, 
and  the  various  kinds  of  cells  are  grouped  together  into  colonies 
or  organs.  In  some  organs  and  tissues  the  bond  of  union  is 
simple  juxtaposition  and  similarity  of  function  of  the  constituent 
cells.  But  in  others  the  union  is  protoplasmic,  processes  of  the 
cvtoplasm  actually  passing  from  cell  to  cell.  This  is  seen  in 
certain  epithelial  tissues,  and  conspicuously  in  the  cardiac  muscle. 

The  Functions  of  Living  Matter. — The  peculiar  functions  of 
living  matter  as  exhibited  in  the  animal  body  will  form  the 
subject  of  the  main  portion  of  this  book  ;  and  we  need  only  say 
here  :  (i)  That  in  all  living  organisms  certain  chemical  changes  go 
on,  the  sum  total  of  which  constitutes  the  metabolism  of  the 
body.  These  may  be  divided  into  (a)  integrative  or  anabolic 
changes,  by  which  complex  substances  (including  the  living 
matter  itself)  are  built  up  from  simpler  materials ;  and 
(b)  disintegrative  or  katabolic  changes,  in  which  complex  bodies 
(including  the  living  substance)  are  broken  down  into  com- 
parativelv  simple  products.  In  plants,  upon  the  whole,  it  is 
integration  which  predominates;  from  substances  so  simple 
as  the  carbon  dioxide  of  the  air  and  the  nitrates  of  the  soil  the 
plant  builds  up  its  carbo-hydrates  and  its  proteins.  In  animals 
the  main  drift  of  the  metabolic  current  is  from  the  complex 
to  the  simple;  no  animal  can  construct  its  own  protoplasm 
from  the  inorganic  materials  that  lie  around  it  ;  it  must  have 
ready-made  protein  in  its  food.  But  in  all  plants  there  is  some 
disintegration  ;  in  all  animals  there  is  some  synthesis.  (2)  The 
living  substance  is  excitable — that  is,  it  responds  to  certaii. 


INTRODUCTION  7 

tenia]  impressions,  or  stimuli,  by  actions  peculiar  to  each  kind 
of  cell.  (3)  The  living  substance  reproduces  itself.  All  the 
manifold  activities  included  under  these  three  heads  have  but 
one  source,  the  transformation  of  the  energy  of  the  food.  It  is 
not.  however,  upon  the  whole,  peculiarities  in  food,  but  in  mole- 
cular structure,  that  underlie  the  peculiarities  of  function  of 
different  living  cells.  A  locomotive  is  fed  with  coal  ;  a  steam- 
pump  is  fed  with  coal.  The  one  carries  the  mail,  and  the  other 
keeps  a  mine  from  being  flooded.  Wherein  lies  the  difference 
of  action  ?  Clearly  in  the  build,  the  structure  of  the  mechanism, 
which  determines  the  manner  in  which  energy  shall  be  trans- 
formed within  it,  not  in  any  difference  in  the  source  of  the 
energy.  So  one  animal  cell,  when  it  is  stimulated,  shortens  or 
contracts  ;  another,  fed  perhaps  with  the  same  food,  selects 
certain  constituents  from  the  blood  or  lymph  and  passes  them 
through  its  substance,  changing  them,  it  may  be,  on  the  way  ; 
and  a  third  sets  up  impulses  which,  when  transmitted  to  the 
other  two,  initiate  the  contraction  or  secretion.  In  the  living 
body  the  cell  is  the  machine  ;  the  transformation  of  the  energy 
of  the  food  is  the  process  which  '  runs  '  it.  The  structure  and 
arrangement  of  cells  and  the  steps  by  which  energy  is  trans- 
formed within  them  sum  up  the  whole  of  biology. 


PRACTICAL  EXERCISES. 

Reactions  of  Proteins. 

1.  General  Reactions  of  Proteins. — Egg-albumin  may  be  taken 
as  a  type.  Prepare  a  solution  of  it  by  adding  water  to  white  of 
egg,  which  consists  mainly  of  egg-albumin  with  a  little  globulin. 
In  breaking  the  egg,  take  care  that  none  of  the  yolk  gets  mixed 
with  the  white.  Snip  the  white  up  with  scissors  in  a  large  capsule, 
then  add  ten  or  fifteen  times  its  volume  of  distilled  water.  The 
solution  becomes  turbid  from  the  precipitation  of  traces  of  globulin, 
since  globulins  are  insoluble  in  distilled  water.  Stir  thoroughly, 
strain  through  several  layers  of  muslin,  and  then  filter  through 
paper. 

Colour  Reactions. 

(1)  Add  to  a  little  of  the  solution  in  a  test-tube  a  few  drops  of 
strong  nitric  acid.  A  precipitate  is  thrown  down,  which  becomes 
yellow  on  boiling.  Cool,  and  add  strong  ammonia  ;  the  colour 
changes  to  orange  (xantho-proteic  reaction).  The  reaction  depends 
upon  the  presence  of  aromatic  groups  in  the  protein  molecule,  which 
are  converted  into  nitro-compounds. 

(2)  To  a  third  portion  add  a  drop  or  two  of  very  dilute  cupric 
sulphate  and  excess  of  sodium  or  potassium  hydroxide  ;  a  violet 
colour  appears  {Piotrowski's  test).  Peptones  and  proteoses  (albu- 
moses)  give  a  pink  {biuret  reaction).*     See  p.  426. 

*  The  reaction  is  also  given,  although  more  faintly,  with  the  hydroxides  of 
lithium,  strontium,  and  barium.  It  is  given  by  all  substances  containing 
at  least  two  COXIL  groups  attached  to  one  another  (as  in  oxamide),  or 
to  the  same  nitrogen  atom  (as  in  biuret),  or  to  the  same  carbon  atom. 


8  ./   MANUAL  OF    PHYSIOLOGY 

|  j)  ID  another  portion  add  Milton's  reagent  ;*  a  white  pre<  ipitate 
comes  down,  which  is  turned  reddish  on  boiling.  If  only  trao 
protein  are  present,  no  precipitate  is  caused,  but  the  liquid  takes 
on  a  red  tinge.  The  reaction  is  due  to  tyrosin.  It  is  given  by  all 
aromatic  substances  which  contain  the  group  (J  I,,  with  at  least  one 
H  replaced  by  OH. 

(4)  Adamkiewicz's  reaction  [Hopkins's  modification). — To  a  small 
quantity  of  the  albumin  solution  add  the  same  bulk  of  dilute  gly. 
oxylic  acid.f  Mix,  and  to  the  mixture  add  an  equal  volume  ol 
strong  pure  sulphuric  acid.  A  purple  colour  is  obtained.  The 
substance  in  the  protein  molecule  which  gives  the  reaction  is  tryp- 
tophane (p.  332). 

(5)  The  Formaldehyde  Reaction. — Add  to  the  albumin  solution  a 
few  drops  of  a  very  dilute  solution  of  formaldehyde  (1  :  2,500),  and 
then  allow  some  strong  (commercial)  sulphuric  acid  to  run  from  a 
pipette  into  the  bottom  of  the  test-tube.  A  purple  ring  appears  at 
the  surface  of  contact.  This  reaction  depends  on  the  presence  of 
tryptophane  in  the  protein. 

Precipitation  Reactions. 

(6)  Acidify  another  portion  strongly  with  acetic  acid,  and  add  a 
few  drops  of  a  solution  of  potassium  ferrocyanide.  A  white  pre- 
cipitate is  obtained.     Peptones  do  not  give  this  reaction. 

(7)  Heat  a  portion  to  300  C.  on  a  water-bath.  Saturate  with 
crystals  of  ammonium  sulphate  ;  the  albumin  is  precipitated.  Filter, 
and  test  the  filtrate  for  proteins  by  (2).  None,  or  only  slight  traces, 
will  be  found.  The  sodium  hydroxide  must  be  added  in  more  than 
sufficient  quantity  to  decompose  all  the  ammonium  sulphate.  It 
will  be  best  to  add  a  piece  of  the  solid  hydroxide.  Peptones  arc  not 
precipitated  by  ammonium  sulphate,  but  all  other  proteins  are. 

(8)  Add  alcohol  to  a  small  quantity  of  the  solution.  The  protein 
is  precipitated.  It  can  be  redissolved  at  first,  but  rapidly  becomes 
insoluble. 

2.  Special  Reactions  of  Certain  Proteins — (1)  Heat-Coagulable 
Proteins  :  (a)  Albumins. — (a)  Heat  a  little  of  the  solution  of  egg- 
albumin  in  a  test-tube  ;  it  coagulates.  With  another  sample  deter- 
mine the  temperature  of  coagulation,  first  very  slightly  acidulating 
with  a  2  per  cent,  solution  of  acetic  acid. 

To  determine  the  Temperature  of  Coagulation.  —  Support  a  beaker 
by  a  ring  which  just  grips  it  at  the  rim.  -Nearly  till  the  beaker  with 
water,  and  slide  the  ring  on  the  stand  till  the  lower  part  of  the  beaker 
is  immersed  in  a  small  water-bath  (a  tin  can  will  do  quite  well).  In 
this  beaker  place  a  test-tube-,  and  in  the  test-tube  a  thermometer. 
both  supported  by  rings  or  clamps  attached  to  the  same  stand.  Put 
into  the  test-tube  at  least  enough  of  the  albumin  solution  to  com- 
pletely cover  the  bulb  of  the  thermometer,  ami  heat  the  bath,  stirring 

*  Millon's  reagent  consists  of  a  mixture  of  tin-  nitrates  oi  mercury  with 
nitric  acid  in  excess,  ami  some  nitrous  acid.  To  make  it,  dissolve  mercury 
in  its  own  weight  of  strong  nitric  acid,  and  add  to  the  solution  thus  obtained 
twice  its  volume  of  water.  Let  it  stand  for  a  short  tunc,  and  then  decant 
the  clear  liquid,  which  is  the  reagent. 

t  A  solution  containing  glyoxylic  acid  in  the  requisite  strength  can  be 
prepared  by  treating  half  a  litre  of  a  saturated  solution  ol  oxali(  acid  with 
40  grammes  of  2  per  cent,  sodium  amalgam  in  a  tall  cylinder.     When  all 

the  hydrogen  has  been  evolved,  the  solution  is  filtered,  and  diluted  with 
twice  its  volume  of  water.  Oxalic  acid  and  sodium  binoxalate  are  also 
present  in  the  solution. 


PRAi  IK    U    I  XI  RCISES 

the  water  in  the  beaker  occasionally  with  ;i  feather  or  .1  splinter  ol 
wood,  or  ;i  glass  rod,  the  end  ol  which  is  guarded  with  a  piece  ol 
indiarubber  tubing.  Note  the  temperature  at  which  the  solution 
becomes  turbid,  and  then  the  temperature  at  which  a  distinct 
coagulum  or  precipitate  is  formed.  Repeat  with  the  unacidulated 
albumin  solution. 

(/?)  A  similar  experiment  may  be  performed  with  serum-albumin 
obtained  as  on  p.  57. 

(b)  Globulins.  Use  serum-globulin  (p.  57),  <>r  myosinogen  (p.  672). 
Fibrinogen  is  also  a  globulin,  but  cannot  easily  be  obtained  in 
quantity.     Verify  the  following  properties  of  globulins  : 

(a)   They  coagulate  on  heating. 

(/3)   They  are  insoluble  in  distilled  water  (p.  57). 

(7)  They  are  precipitated  by  saturation  with  magnesium  sulphate 
or  sodium  chloride  (p.  57). 

They  give  the  general  protein  tests  (1)  to  (8). 

Both  the  heat-coagulated  proteins  and  such  proteins  as  the  solid 
librin  which  is  formed  from  fibrinogen  in  the  clotting  of  blood  give 
such  of  the  general  protein  tests,  (1),  (2),  (3)  (p.  7),  as  with  suitable 
modifications  can  be  instituted  on  solid  substances.  Thus,  in  per- 
forming (2),  a  flake  of  fibrin  or  a  small  piece  of  the  boiled  egg-white 
should  be  soaked  for  a  few  minutes  in  a  dilute  solution  of  cupric 
sulphate.  Then  the  excess  of  the  cupric  sulphate  should  be  poured 
off,  and  sodium  hydroxide  added,  when  the  coagulated  protein  will 
become  violet.  Heat-coagulated  proteins  are  insoluble  in  water, 
weak  acids  and  alkalies,  and  saline  solutions  ;  fibrin  is  slightly 
soluble  in  the  latter. 

(2)  Gelatin. — Add  some  pieces  of  gelatin  to  cold  water  in  a  test- 
tube.  It  does  not  dissolve.  Immerse  the  tube  in  a  boiling  water- 
bath  till  the  gelatin  goes  into  solution.  Then  cool  the  test-tube 
under  the  tap  ;  the  solution  sets  into  a  jelly.  On  heating  it  redis- 
solves. 

Try  the  general  protein  reactions  (p.  7)  on  a  dilute  solution.  In 
Piotrowski's  test  a  violet  colour  is  obtained.  The  tests  which  depend 
on  the  presence  of  tryosin  or  tryptophane  are  not  given  by  a  solution 
of  pure  gelatin,  since  these  amino-acids  are  absent  from  the  gelatin 
molecule.  Commercial  gelatin  may  give  a  slight  reaction  due  to 
traces  of  other  proteins. 

3.  Reactions  of  Certain  Derivatives  of  Native  Proteins — (1)  Meta- 
Proteins  :  (a)  Acid-albumin. — To  a  solution  of  egg-albumin  add  a 
little  04  per  cent,  hydrochloric  acid,  and  heat  to  about  body  tem- 
perature— say  400  C. — for  a  few  minutes.  Acid-albumin  is  formed. 
It  can  be  produced  from  all  albumins  and  globulins  by  the  action 
of  dilute  acid.     Make  the  following  tests  : 

(a)  Add  to  a  portion  of  the  solution  in  a  test-tube  a  few  drops  of 
a  solution  of  litmus  ;  the  colour  becomes  red.  Now  add  drop  by 
drop  sodium  carbonate  or  dilute  sodium  hydroxide  solution  till  the 
tint  just  begins  to  change  to  blue.  A  precipitate  of  acid-albumin  is 
thrown  down.  Add  a  little  more  of  the  alkali,  and  the  precipitate 
is  redissolved.  It  can  be  again  brought  down  by  neutralizing  with 
acid. 

(p)  Heat  a  portion  of  the  solution  to  boiling  ;  no  precipitate  is 
formed. 

(7)  Add  strong  nitric  acid  ;  a  precipitate  appears,  which  dissolves 
on  heating,  and  the  liquid  becomes  yellow. 

(b)  Alkali-albumin. — To  a  solution  of  egg-albumin  add  a  little 
sodium  hydroxide,  and  heat  gently  for  a  few  minutes.     Alkali-albumin 


ro  \  MANUAL  OF   PHYSIOLOGY 

is  produced.  It  can  be  derived  l>v  similar  treatment  from  any 
albumin  m-  globulin. 

(a)  Neutralize,  after  colouring  with  litmus  solution,  l>v  the  addition 
•  it  dilute  hydrochloric  or  acetic  acid.  Alkali-albumin  is  pre<  ipitated 
when  neutralization  has  been  reached.     It  is  redissolved  in  exi 

Of  the  acid. 

()    I'm  another  portion  of  the  solution  <>i  alkali-albumin  add  a  few 

drops  of  sodium  phosphate  solution,  then  litmus,  and  then  dilute  .i,  id 

till  the  alkali-albumin  is  precipitated.  More  of  the  dilute  acid  should 
now  be  required  to  precipitate  the  alkali-albumin,  since  tin-  sodium 
phosphate  must    first  be  changed  into  acid  sodium  phosphate 

(7)  On  heating  the  solution  of  alkali-albumin  there  is  no  coagula- 
tion. 

(2)  Proteoses.  -For  preparation  and  reactions,  sec  p.  4,26.  They 
differ  from  albumins  and  globulins  in  not  being  coagulated  by  he, it, 
and  from  meta-proteins  in  not  being  precipitated  by  neutralization. 
They  are  soluble  (with  the  exception  of  hetero-albumose)  in  distilled 
water,  and  are  not  precipitated  by  saturation  of  their  solutions  with 
magnesium  sulphate  or  sodium  chloride.  Saturation  with  ammonium 
sulphate  precipitates  them.  With  a  solution  of  commercial  '  pep- 
tone,' which  consists  chiefly  of  albumoses,  and  contains  only  a  little 
true  peptone,  perform  the  following  tests  : 

(a)   Boil  the  slightly  acidulated  solution  ;  there  is  no  coagulation. 

(.i)  Biuret  reaction,  p.  7. 

(7)  To  a  portion  of  the  solution  add  its  own  volume  of  saturated 
ammonium  sulphate  solution.  The  primary  albumoses  (proto-  and 
hetero-albumose)  are  precipitated.  Filter.  Add  a  drop  of  sulphuric 
acid  to  the  filtrate  and  saturate  it  with  ammonium  sulphate  crystals. 
The  secondary  or  dcutero-albumoses  arc  precipitated.  Filter.  The 
filtrate  still  contains  peptones.     Use  it  for  (3). 

(3)  Peptones. —For  preparation  and  tests,  see  p.  426.  They  differ 
from  heat-coagulable  proteins  and  meta-proteins  in  the  same  way  as 
proteoses,  and  they  differ  from  proteoses  in  not  being  precipitated  by 
ammonium  sulphate.  On  the  filtrate  from  (2)  perform  the  biuret 
test,  as  described  in  (7),  p.  8  ;  and  note  that  the  pink  colour  is  the 
same  as  that  given  by  proteoses. 

Carbo-hydrates. 

1.  Glucose  or  Dextrose.  -Make  a  solution  of  dextrose  in  water, 
and  apply  to  it  Trommer's  test  for  reducing  sugar.  1'nt  some  ot 
the  dextrose  solution  in  a  test-tube,  then  a  few  drops  of  cupric 
sulphate,  and  then  excess  of  sodium  or  potassium  hydroxide.  The 
blue  precipitate  of  cupric  hydroxide  which  is  first  thrown  down  is 
immediately  dissolved  in  the  presence  of  dextrose  and  many  Other 
organic  substances.  Now  boil  the  blue  liquid,  and  a  yellow  or  red 
precipitate  (cuprous  hydroxide  or  oxide)  is  formed. 

2.  Cane-sugar. --Perform  Trommer's  test  with  a  sample  of  a  solu- 
tion. A  blue  liquid  is  obtained,  which  is  not  changed  on  boiling. 
Now  put  the  rest  of  the  solution  in  a  flask.  Add  s'jjth  of  its  bulk  oi 
strong  hydrochloric  acid,  and  boil  for  ,1  quarter  of  an  hour.  Again 
perform  Trommer's  test.  Remember  that  excess  ot  alkali  must  be 
present  after  the  acid  is  neutralized.  The  test  now  shows  much 
reducing  sugar.  The  cane-sugar  has  been  '  inverted  '  -».*.,  changed 
into  a  mixture  of  dextrose  and   levulose. 

3.  Starch. — (1)  Cut  a  slice  from  a  well-washed  potato;  take  a 
scraping    from    it    with    a    knife,    and    examine    with    the    micros, 


PRACTICA1    EXERCISES  n 

Mote  the  starch  granules  with  their  concentric  markings,  using  a 

small  diaphragm.  \\\\n  a  drop  of  dilute  iodine  solution  under  the 
cover-slip,  and  observe  thai  the  grannies  become  bluish.  Examine 
also  with  a  polarization  microscope.     (2)  Rub  up  a  little  starch  in  ;i 

mortar  with  cold  water,  then  add  boiling  water  and  stir  thoroughly. 

Decant  into  a  capsule  or  beaker,  and  boil  for  a  few  minutes.  After 
the  liquid  has  cooled,  perform  the  following  experiments : 

(a)  Add  a  few  drops  of  iodine  solution  to  a  little  of  the  thin  starch 
mucilage  in  a  test-tube.  A  blue  colour  is  produced,  which  disappears 
on  heating,  returns  on  cooling,  is  bleached  by  the  addition  of  a  little 
sodium  hydroxide,  and  restored  by  dilute  acid. 

(b)  Test  the  starch  solution  for  reducing  sugar  by  Trommel's 
test.  Jf  none  is  found,  boil  some  of  the  mucilage  with  a  little 
dilute  sulphuric  acid  in  a  flask  for  twenty  minutes,  and  again 
perform  Trommer's  test.  Abundance  of  reducing  sugar  will  now  be 
present. 

4.  Dextrin. — Dissolve  some  dextrin  in  boiling  water.  Cool.  Add 
iodine  solution  to  a  portion  ;  a  reddish-brown  (port-wine)  colour 
results,  which  disappears  on  heating.  As  a  control,  the  same  amount 
of  iodine  should  be  added  to  an  equal  quantity  of  water  in  another 
test-tube.  The  colour  returns  on  cooling.  The  colour  is  also 
bleached  by  alkali,  restored  by  acid.  Excess  of  iodine  should  be 
added  for  the  bleaching  experiment  (i.e.,  more  than  enough  to  give 
the  maximum  depth  of  tint).  If  too  little  iodine  has  been  added 
there  may  be  no  restoration  of  the  colour  by  the  acid.  The  addition 
of  a  little  more  iodine  to  the  acid  solution  will  then  cause  the  port- 
wine  colour  to  return,  and  this  may  be  again  bleached  by  alkali,  and 
will  now  be  restored  by  acid. 

5.  Glycogen. —See  p.  608. 

6.  Molisch's  Test  for  Carbo-hydrates. — This  is  a  general  test  for 
carbo-hydrates.  It  is  also  given  by  proteins  which  contain  a  carbo- 
hydrate group.  Put  a  drop  of  dextrose  solution  in  a  test-tube. 
Add  a  drop  of  a  10  per  cent,  solution  of  o-naphthol  in  methyl  alcohol, 
and  then  o'5  c.c.  of  water.  Then  cautiously  allow  1  c.c.  of  pure 
concentrated  sulphuric  acid  to  run  under  the  mixture,  and  shake 
gently.     A  violet  or  reddish  colour  appears. 

Fats. 

1.  Take  a  little  lard  or  olive-oil,  and  observe  that  fat  is  soluble 
in  ether  or  warm  alcohol,  but  not  in  water.  Put  a  drop  of  the 
ethereal  solution  of  fat  on  a  piece  of  paper,  and  note  that  it  leaves 
a  greasy  stain. 

2.  Put  a  little  alcohol  in  a  test-tube,  and  then  a  drop  of  phenol- 
phthalein  solution  and  a  drop  or  two  of  dilute  sodium  hydroxide 
to  give  the  solution  a  red  colour.  Add  a  few  drops  of  an  ethereal 
solution  of  the  lard  or  olive-oil.  If  the  red  colour  persists  the  fat 
is  neutral  ;  if  it  disappears  the  fat  contains  free  fatty  acids. 

3.  Saponification. — Melt  some  lard  in  a  porcelain  dish,  and  pour 
it  into  an  alcoholic  solution  of  potassium  hydroxide  previously  heated 
on  a  water-bath  nearly  to  boiling.  Mix  well,  and  keep  the  mixture 
gently  boiling  on  the  bath  till  saponification  is  complete.  This 
only  takes  a  short  time.  Remove  a  little  of  the  soap  solution,  and 
drop  it  into  distilled  water  in  a  test-tube.  If  unsaponified  fat  is 
present  it  will  rise  to  the  top  as  drops  of  oil.  In  this  case  boiling 
should  be  continued.  If  all  the  fat  has  been  saponified  the  soap 
solution  will  mix  with  the  water  and  no  oil-drops  will  separate. 


12  A   Ml  M    II.  OF  I'll  YSIOLOGY 

I  Fatty  Acids.  Heat  some  20  per  cent.  sulphuri<  acid  in  a  in. ill 
Sash  nearly  to  boiling,  and  drop  into  it  some  oi  the  soap  obtained 
in  3.  The  fatty  acids  separate  out  and  rise  to  the  top  .is  an  oily 
layer.  Cool,  skim  oil  the  fatty  acid,  and  wash  n  with  distilled 
water  till  the  wash-water  is  no  Longer  acid. 

(a)  Dissolve  .1  little  of  the  washed  fatty  acid  in  ether.  Add  a  few 
drops  of  an  alkaline  solution  of  phenolphthalein  to  a   few   c.c,  oi 

\v;ilcr  in  a  test-tube.  Drop  into  this  the  ethereal  solution  ol  fatty 
acid.      The  red  colour  is  discharged. 

(h)  Put  a  small  portion  of  the  fatty  aeid  on  a  ^lass  slide  resting 
on  a  piece  of  white  paper.     Place  on  it  a  drop  or  two  of  a  1  percent 

solution  of  osmic  aeid  (osiniuni  tetroxide).  The  osmic  acid  is 
reduced  to  a  lower  oxide  (which  is  black)  by  the  action  ol  oleic  acid 
present  in  the  tatty  acid  mixture,  which  abstracts  some  ol  the  oxygen. 
Any  fat  which  contains  olein  or  oleic  acid,  as  body-fat  does,  is 
therefore  blackened  by  osmic  acid. 

(c)  Add  to  a  portion  of  the  fatty  acid  some  sodium  hydroxide 
solution,  and  warm.  Sodium  soap  is  formed.  Add  warm  water 
and  shake  up.  A  lather  is  produced.  Keep  the  soap  solution 
tor  6.      Keep  a  little  of  the  fatty  acid  for  5  (h)  and  6  [b). 

5.  Glycerin. — (a)  Add  to  a  little  glycerin  in  a  dry  test-tube  a 
lew  crystals  of  potassium  bisulphate  (  KHS<  >,).  and  heat  over  the  free 
flame.  Acrolein  is  given  oil.  which  is  recognised  by  its  pungent 
odour,  and  by  blackening  a  piece  of  filter-paper  moistened  with 
ammoniacaJ  silver  nitrate  solution,  and  held  over  the  mouth  ol  tin 
test-tube.  The  paper  is  blackened  owing  to  the  reducing  action  of 
the  vapour  on  the  silver  nitrate. 

(b)  Repeat  this  test  with  lard,  and  with  a  portion  of  the  fatty 
acid  from  4.  Acrolein  will  be  given  off  by  the  lard  because  glycerin 
is  contained  in  neutral  fat,  but  not  by  the  fatty  acid  if  it  has  been 
properly  separated  from  the  glycerin. 

6.  Emulsification. — (a)  Take  three  test-tubes  and  label  them  A, 
B,  and  C.  Put  a  few  c.c.  of  water  in  A,  a  solution  of  soap  in  B, 
ami  a  dilute  solution  of  sodium  carbonate  or  sodium  hydroxide  in  ('. 
To  eacli  add  a  lew  drops  of  fresh  olive-oil  and  shake.  An  emulsion 
will  be  formed  in  B,  but  not  in  A.  Probably  there  will  be  some 
emulsification  in  C  also,  owing  to  the  presence  in  the  oil  of  some 
fatty  acid,  which  forms  soap  with  the  alkali.  But  if  the  oil  is  free 
from  fatty  acid  no  emulsion  will  be  formed. 

(b)  Repeat  (a)  with  rancid  olive-oil,  which  contains  much  fatty 
acid,  or  with  fresh  olive-oil  to  which  some  of  the  fatty  acid  obtained 
in  4  has  been  added.  A  good  emulsion  will  be  produced  in  (  as 
well  as  in  B. 

7.  Melting-point  of  Fat. — Put  into  a  very  narrow  test-tube  or  .1 
short  piece  of  narrow  glass  tubing  some  finely  divided  mutton  tat. 
freed  as  far  as  possible  from  connective  tissue,  hasten  the  test-tub< 
on  to  the  bulb  of  a  thermometer  with  a  rubber  band,  and  imni 
the  thermometer  and  tube  in  a  beaker  filled  with  water  and  standing 
on  a  water-bath  which  is  gradually  heated.  Observe  the  temp 
ture  at  which  the  fat  melts.  Repeal  the  experiment  with  bog's  lard 
and  dog's  fat. 


PR  ICTH    II    EXERCISES 

SCHEME  FOR  TESTING  A  SOLUTION  FOR  THE  MORE 
COMMON  PROTEINS  A.ND  PROTEIN  -  DERIVATIVES, 
AND  FOR  CARBO-HYDRATES. 

i.  Nolt-  the  reaction,  and  whether  the  liquid  is  coloured  or  colourless, 
i  lear  or  opalescent.  A  reddish  colour  suggests  blood  ;  opalescence  suggests 
glycogen  in  starch  Try  one  or  more  of  the  general  protein  tests  (e.g., 
the  xanthoproteic  or  biuret).  II  the  result  is  positive,  proceed  as  in  2  ; 
ii  negative,  pass  to  3. 

2.  Test  for  Proteins.  —  (1)  If  the  reaction  is  acid  or  alkaline,  neutralize 
with  very  dilute  sodium  carbonate  or  sulphuric  acid.  A  precipitate  = 
acid-  or  alkali-albumin,  according  as  the  original  reaction  is  acid  or 
alkaline.  II  the  original  reaction  is  neutral,  no  acid-  or  alkali  albumin  can 
be  present  in  solution.      Filter  off  the  precipitate,  if  any. 

(2)  Boil  some  of  the  filtrate  from  (1)  (or  some  of  the  original  solution  if 
it  is  neutral),  acidulating  slightly  with  dilute  acetic  acid.  A  precipitate  = 
albumin  or  globulin.     Filter,  and  keep  the  filtrate. 

(3)  II  a  precipitate  has  been  obtained  in  (2),  (a)  saturate  some  of  the 
original  solution  with  magnesium  sulphate,  or  half  saturate  it  with  ammo- 
nium sulphate  (i.e.}  add  to  it  an  equal  volume  of  saturated  ammonium 
sulphate  solution).  If  there  is  no  precipitate,  globulin  is  absent,  and 
therefore  the  precipitate  obtained  in  (2)  must  be  albumin.  A  precipitate  = 
globulin.  But  albumin  may  also  be  present  in  the  solution.  To  see 
whether  this  is  so,  filter  off  the  globulin  and  boil  the  filtrate  after  acidulation 
with  acetic  acid.     A  precipitate  =  albumin. 

(b)  Half  saturate  the  filtrate  from  (2)  with  ammonium  sulphate  {i.e.,  add 
its  own  volume  of  a  saturated  solution  of  the  salt).  A  precipitate  = 
primary  proteoses.      Filter. 

(c)  Saturate  the  filtrate  from  (b)  with  ammonium  sulphate  crystals.  A 
precipitate  =  secondary  proteoses.      Filter. 

(d)  To  the  filtrate  from  (c)  add  excess  of  solid  sodium  hydroxide  in  small 
pieces  at  a  time.  Much  ammonia  is  given  off.  Allow  the  test-tube  to 
stand  fifteen  minutes,  shaking  it  at  intervals.  Then  add  dilute  cupric 
sulphate,  and  if  much  of  the  sodium  sulphate  formed  remains  undissolved, 
add  water  to  dissolve  it.     A  well-marked  rose  colour  =  peptone. 

(4)  If  no  precipitate  has  been  obtained  in  (2),  the  solution  contains 
neither  albumin  nor  globulin.  To  test  whether  primary  or  secondary 
proteose  or  peptone  is  present,  apply  (3)  (b),  (c),  and  (d). 

3.  Test  for  Carbo-hydrates. — Use  the  original  solution,  freed  from 
coagulable  proteins,  if  such  have  been  found,  by  acidulation  and  boiling. 

(1)  Add  iodine.  If  the  solution  is  alkaline  neutralize  it  before  adding 
the  iodine.  A  blue  colour  =  starch.  Confirm  by  boiling  with  dilute  sul- 
phuric acid  and  testing  for  reducing  sugar.  A  reddish-brown  colour  with 
iodine  =  glycogen  or  dextrin. 

Glycogen  gives  an  opalescent,  dextrin  a  clear,  solution.  Glycogen  is 
precipitated  by  basic  lead  acetate,  dextrin  is  not  (p.  608).  Both  are 
changed  into  reducing  sugar  by  boiling  with  dilute  acid. 

(2)  Add  to  some  of  the  original  solution  cupric  sulphate  and  excess  of 
sodium  hydroxide,  and  boil.     Yellow  or  red  precipitate  =  reducing  sugar. 

(3)  If  (1)  and  (2)  are  negative,  boil  some  of  the  liquid  with  one- twentieth 
of  its  volume  of  strong  hydrochloric  acid  for  fifteen  minutes,  and  test  as 
in  (2).  A  red  or  yellow  precipitate  shows  that  cane-sugar  was  originally 
present,  and  has  been  inverted. 


CHAPTER  I 

THE  CIRCULATING  LIQUIDS  OF  THE  BODY 

In  the  living  cells  of  the  animal  body  chemical  changes  are 
constantly  going  on  ;  energy,  on  the  whole,  is  running  down  ; 
complex  substances  are  being  broken  up  into  simpler  combina- 
tions. So  long  as  life  lasts,  food  must  be  brought  to  the  tissues, 
and  waste  products  carried  away  from  them.  In  lowly  forms 
like  the  amoeba  these  functions  are  performed  by  interchange 
at  the  surface  of  the  animal  without  any  special  mechanism  ; 
but  in  all  complex  organisms  they  are  the  business  of  special 
liquids,  which  circulate  in  finety  branching  channels,  and  are 
brought  into  close  relation  at  various  parts  of  their  course  with 
absorbing  organs,  with  eliminating  organs,  and  with  the  tissue 
elements  in  general. 

In  the  higher  animals  three  circulating  liquids  have  been 
distinguished  :  blood,  lymph,  and  chyle.  But  it  is  to  be  re- 
marked that  chyle  is  only  lymph  derived  from  the  walls  of  the 
alimentary  canal,  and  therefore,  during  digestion,  containing 
certain  freshly-absorbed  constituents  of  the  food  ;  while  both 
ordinary  lymph  and  chyle  ultimately  find  their  way  into  the 
blood,  and  are  in  their  turn  recruited  from  it.  The  blood 
contains  at  one  time  or  another  everything  which  is  about  to 
become  part  of  the  tissues,  and  everything  which  has  ceased  to 
belong  to  them.  It  is  at  once  the  scavenger  and  the  food- 
provider  of  the  cell.  But  no  bloodvessel  enters  any  cell  ;*  and 
if  we  could  unravel  the  complex  mass  of  tissue  elements  which 
essentially  constitute  what  we  call  an  organ,  we  should  see  a 
sheet  of  cells,  with  capillaries  in  very  close  relation  to  them,  but 
everywhere  separated  from  them  by  a  thin  layer  of  lymph. 
And  to  describe  in  a  word  the  circulation  of  the  food  substances 
we  may  say  that  the  blood  feeds  the  lymph,  and  the  lymph  feeds 
the  cell. 

*  Fine  intracellular  canaliculi,  communicating  with  the  blood-capillaries, 
and  probably  performing  a  nutritive  function,  since  they  seem  to  con- 
tain blood-plasma,  have  been  described  by  Schafer  and  others  in  the 
liver  cells. 

14 


TTIE  CIRCULATING  LIQUIDS  OF  THE  BODY 


l$ 


Morphology  of  the  Blood. 

The  blood  consists  essentially  of  a  liquid  part,  the  plasma, 
in  which  are  suspended  cellular  elements,  the  corpuscles.  When 
the  circulation  in  a  frog's  web  or  lung  or  in  the  tail  of  a  tadpole 
is  examined  under  the  microscope,  the  bloodvessels  are  seen  to 
be  crowded  with  oval  bodies — of  a  yellowish  tinge  in  a  thin 
layer,  but  in  thick  layers  crimson — which  move  with  varying 
velocity,  now  in  single  file,  now  jostling  each  other  two  or  three 
abreast,  as  they  are  borne  along  in  the  axis  of  an  apparently 
scanty  stream  of  transparent  liquid.  Nearer  the  walls  of  the 
vessels,  sometimes  clinging  to  them  for  a  little  and  then  being 
washed  away  again,  may  be  seen,  especially  as  the  blood-flow 
slackens,  a  few  comparatively  small,  round,  colourless  cells. 
The  oval  bodies  are  the  red  or  coloured  corpuscles,  or  erythro- 
cytes  ;  the  colourless  elements  are  the  white  blood-corpuscles, 
or  leucocytes  ;  the  liquid  in  which  the}'  float  is  the  plasma 
(Practical  Exercises,  p.  177). 

The  Red  Blood-corpuscles,  or  Erythrocytes,  differ  in  shape 
and  size  and  in  other  respects  in  different  animal  groups.  In 
amphibians,  such  as  the  frog  and  the.  :newt,  they  are  flattened 
ellipsoids  containing  a 
nucleus,  and  the  same  is 
true  of  nearly  all  the 
other  vertebrates,  except 
mammals.  In  mammals 
they  are  discs,  hollowed 
out  on  both  the  fiat  sur- 
faces, or  biconcave,  and 
possess  no  nucleus.  But 
the  red  corpuscles  of  the  FlG  r._DlAGRAM  SH0WING  Relative  Size  of 
llama      and      the      camel,         Red  Corpuscles  of  Various  Animals. 

although     non-nucleated, 

are  ellipsoidal  in  shape  like  those  of  the  lower  vertebrates.  As 
to  size,  the  average  diameter  in  man  is  between  7  and  8  /*.* 
In  the  frog  the  long  diameter  is  about  22  /j.,  while  in  Proteus  it 
is  as  much  as  60  /x,  and  in  Amphiuma,  the  corpuscles  of  which 
can  be  seen  with  the  naked  eye,  nearly  80  /x  (Plate  I.  frontispiece). 
As  regards  the  structure  of  the  red  corpuscles,  the  most  prob- 
able view  is  that  they  are  solid  bodies,  with  a  spongy  and  elastic 
structureless  framework,  denser  at  the  surface  of  the  corpuscle 
than  in  its  centre,  but  continuous  throughout  its  whole  mass 
(Rollett).  The  denser  peripheral  layer  constitutes  a  physio- 
logical envelope  which  permits  the  passage  of  certain  substances 
into  or  out  of  the  corpuscles,  and  hinders  the  passage  of  others. 

*  A  micro-millimetre,  represented  by  symbol  fi,  is  TTrV u  millimetre. 


1 

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16  A   M  I  \'i    II    <>/    PHYSIOLOGY 

Envelope  and  spongework  arc  sometimes  spoken  of  as  the 
stroma  of  the  corpuscle,  in  contradistinction  to  its  mosl  impor- 
tant constituent,  a  highly  complex   pigment,   the  haemoglobin, 

which,  not  in  solution  as  such,  but  cither  in  solution  as  a  com- 
pound with  some  other  unknown  substance,  or  more  probably 
bound  in  some  solid  or  semi-solid  combination  to  the  stroma, 
tills  up  the  space  within  the  envelope  in  the  intei>iireS  of  the 
spongework.  Since  there  is  good  reason  to  believe  that  the 
haemoglobin  as  obtained  artificially  from  the  corpuscles  is  not  quite 
the  same  substance  as  the  native  blood-pigment  wii  hin  them,  the 
latter  is  sometimes  distinguished  by  a  separate  name — haemo- 
chrome.  To  the  physical  properties  of  the  stroma  it  is  usual 
to  attribute  the  great  elasticity  of  the  corpuscles — that  is,  tin- 
power  of  recovering  their  original  shape  after  distortion — for 
their  elasticity  is  no  wise  impaired  by  the  removal  of  the  haemo- 
globin. 

Rouleaux  Formation. — When  blood  with  disc-shaped  corpuscles 
is  shed,  there  is  a  great  tendency  for  the  corpuscles  to  run  together 
into  groups  resembling  rouleaux,  or  piles  of  coin.  No  satisfactory 
expianation  of  this  curious  fact  has  yet  been  given. 

Crenation  of  the  corpuscles,  a  condition  in  which  they  become 
studded  with  fine  projections,  is  caused  by  the  addition  of  moderately 
strong  salt  solution,  by  the  passage  of  shocks  of  electricity  at  high 
potential,  as  from  a  Leyden  jar,  or  by  simple  exposure  to  the  air. 
Concentrated  saline  solutions,  which  abstract  water  from  the  cor- 
puscles and  cause  them  to  shrink,  make  the  colour  of  blood  a  brighter 
red,  because  more  light  is  now  reflected  from  the  crumpled  surfaces. 
On  the  other  hand,  the  addition  of  water  renders  the  corpuscles 
spherical  ;  more  of  the  light  passes  through  them,  less  is  reflected, 
and  the  colour  becomes  dark  crimson  (Plate  I.,  frontispiece). 

The  White  Blood-corpuscles,  or  Leucocytes. — The  red  cor- 
puscles are  peculiar  to  blood.  The  white  corpuscles  may  be 
looked  upon  as  peripatetic  portions  of  the  mesoderm  (see 
Chap.  XIV.),  and  some  of  them  ought  not  in  strictness  to  be 
called  blood-corpuscles.  They  are  more  truly  body  corpuscles. 
Similar  cells  are  found  in  many  situations,  and  wander  every- 
where in  the  spaces  of  the  connective  tissue.  They  pass  into 
the  bloodvessels  with  the  lymph,  and  may  pass  out  of  them  again 
in  virtue  of  their  amoeboid  power.  They  consist  of  protoplasm, 
less  differentiated  than  that  of  any  other  cells  in  the  body,  and 
under  the  microscope  appear  as  granular,  colourless,  transparent 
bodies,  spherical  in  form  when  at  rest,  and  containing  a  nucleus, 
often  tri-  or  multi-lobed.  Many  of  the  leucocytes  of  frog's  blood 
at  the  ordinary  temperature,  and  of  mammalian  blood  when 
artificially  heated  on  the  warm  stage,  may  be  seen  to  undergo 
slow  changes  of  form.  Processes  called  pseudo podia  are  pushed 
out  at  one  portion  of  the  surface,  retracted  at  another,  and  thus 
the  corpuscle  gradually  moves  or  '  flows '  from  place  to  place, 


THE  CIRCU1    ITING   LIQUIIJS  OF   THE  HODY 


<7 


.umI  envelopes  or  eats  up  substances,  such  as  grains  oi  carmine, 
which  conic  in  its  way.  This  kind  of  motion  was  first  observed 
in  the  amoeba,  and  is  therefore  called  amoeboid.  The  leucocytes 
of  human  blood  are  no1  all  of  the  same  size  and  differ  also  in 
ot  her  respects.  They  may  be  classified  according  to  the  pi  esem  e 
or  absence  of  granules  in  their  protoplasm,  and  the  fineness  or 
coarseness  of  the  granules;  according  to  the  chemical  nature 
ol  the  dyes  with  which  the  granules  most  readily  stain,  and 
according  to  the  form  of  the  nucleus.  Five  varieties  of  leuco- 
cytes may  thus  be  distinguished  in  normal  blood  (Plate  1.)  : 

i.  Polymorphonuclear  Neutrophile  Cells.— The  nucleus  assumes  a 
great  variety  of  tonus,  often  contorted  or  deeply  Lobed,  the  lobes 

being    united    bv    tine   strands  of  chromatin.      The   protoplasm   con- 
tains numerous  fine  refractive  granules,  which  stain  best  neither  with 
simple  acid  dyes  like-  eosin  nor  with  simple  basic  dyes  like  methylene 
blue,  but  with  mixtures  which  must  be  assumed  to  contain  '  neutral 
stains,  like  Ehrlich's  so-called  triacid  stain.*     These  cells  make  up 


Fig.  2. — Amceboid  Movement. 
A,  B.  C,  D,  successive  changes  in  the  form  of  an  amoeba. 

65  to  75  per  cent,  of  the  total  number  of  leucocytes.     Their  diameter 
is  10  to  12  ix. 

2.  Eosinophile  Cells  (12  to  15  fx  in  diameter),  much  less  numerous 
in  normal  blood  than  the  neutrophiles  (less  than  5  per  cent,  of  the 
whole),  but  found  in  considerable  numbers  in  the  serous  cavities, 
the  connective  tissue,  and  the  bone-marrow.  The  granules  in  the 
protoplasm  are  coarser  than  the  neutrophile  granules,  and  stain 
much  more  deeply  with  eosin.  The  nucleus  may  be  simple,  lobed, 
or  even  divided  into  fragments  between  which  no  connection  can  be 
traced.  It  is  less  rich  in  chromatin,  and  stains  less  easily  with  basic 
dyes,  like  methylene  blue,  than  the  nucleus  of  the  first  variety. 

3.  Hyaline  Cells,  or  Large  Mononuclear  Leucocytes,  with  a  diameter 
of  12  to  15  fj..  They  possess  a  large  simple  nucleus,  poor  in  chromatin, 
surrounded  by  a  relatively  great  amount  of  protoplasm,  with  no 
evident  granules.  They  constitute  3  to  5  per  cent,  of  the  total 
number  of  leucocytes. 

4.  Lymphocytes. — Smaller  cells  than  any  of  the  preceding  (diameter 
6  n),  possessing  a  single  large  nucleus,  surrounded  by  a  comparatively 
small  amount  of  protoplasm  ;  20  to  25  per  cent,  of  the  leucocytes  of 
the  blood  belong  to  this  group. 

*  A  mixture  of  orange  G.,  acid  fuchsin,  and  methyl  green. 

2 


iS  ./   .1/  ixr  ;/.  01    PHYSIOLOGY 

5.  'Mast  Cells,'  or  ' Basophiles,'  the  Leasl  aumerous  variety  (0-5 
per  cent,  oi  the  total  a  umber).  Very  few  are  to  be  found  in  the 
norma]  blood  of  adults,  but  more  in  children.  They  are  somewhat 
smaller  than  the  neutrophiles  (average  diameter  about  io  .»).  The 
nucleus  is  irregularly  trilobed.  The  protoplasm  shows  coi 
granules,  which  do  not  glitter  like  the  granules  oi  the  eosinophile 
cells,  and  are  therefore  less  conspicuous  in  the  unstained  condition. 
Unlike  the  eosinophile  granules,  they  stain  with  basic  dyes,  such  as 
methylene  blue. 

Blood-plates. — When  blood  is  examined  immediately  after 
being  shed,  small  colourless  bodies  (1  to  j  /t  in  diameter)  of 
various  shapes,  but  usually  round  or  oval,  may  be  seen.  These 
are  the  blood-plates  or  platelets.  They  can  be  collected  by 
placing  a  drop  of  blood  on  a  smooth  and  clean  pie<  e  oi  paraffin, 
and  keeping  it  in  a  moist  chamber.  Clotting  is  long  delayed, 
and  the  white  and  coloured  corpuscles  sink  to  the  bottom,  while 
the  platelets  rise  to  the  top  of  the  drop,  from  which  they  can  be 
removed  by  a  cover-slip.  They  can  be  best  studied  when  the 
blood  is  mixed  directly  with  some  fixing  solution,  such  as 
Hayem's  solution  (sodium  chloride,  1  grm.  ;  sodium  sulphate, 
5  grm.  ;  mercuric  chloride,  05  grm.  ;  water,  200  grm.),  or  osmic 
acid.  They  can  even,  like  leucocytes,  be  kept  alive  on  the 
warm  stage  in  an  appropriate  medium  (agar,  to  which  certain 
salts  have  been  added),  and  then  show  lively  amoeboid  move- 
ments (Deetjen).  While  some  observers  believe  that  they 
represent  the  remains  of  the  nuclei  of  the  erythroblasts,  it  is 
more  probable  that  they  are  independent  elements.  They 
have  even  been  described  as  nucleated  cells,  although  the 
nucleus  is  not  easy  to  stain.  They  are  not  produced  by  the 
breaking  up  of  other  elements  of  the  shed  blood,  for  they  have 
been  observed  within  the  freshly-excised,  and  therefore  still 
living,  capillaries — in  the  mesentery  of  the  guinea-pig  and  rat 
(Osier). 

Enumeration  of  the  Blood  -  corpuscles. — This  is  done  1  >y 
taking  a  measured  quantity  of  blood,  diluting  it  to  a  known 
extent  with  a  liquid  which  does  not  destroy  the  corpuscles, 
and  counting  the  number  in  a  given  volume  of  the  diluted 
blood  (p.  58). 

The  average  number  of  red  corpuscles  in  a  cubic  millimetre 
of  blood  is  about  5,000,000  in  a  healthy  man,  and  about  4,500,000 
in  a  healthy  woman,  but  a  variation  of  1,000,000  up  01  down 
can  hardly  be  considered  abnormal.  In  persons  suffering  from 
profound  anaemia  the  number  may  sink  to  1,000,000  per  cubic 
millimetre,  or  even  less,  while  in  new-born  children  and  in  tin- 
inhabitants  of  high  plateaus  or  mountains  it  may  rise  to  7,000,000, 
or  even  more.  In  the  latter  instance  a  residence  of  a  fortnight 
in   the   rarefied   air   is  sufficient    to    bring   about  the   increase, 


THE  CIRCULATING  LIQUIDS  01    llli    BODY  rg 

and   a  subsequent  residence  of  a  fortnight  in  the  lowlands  to 

annul  it.* 

The  number  of  white  blood-corpuscles  is  on  the  average  about 
10,000  per  cubic  millimetre  of  blood,  or  one  leucocyte*  for  every 
500  red  blood-corpuscles.  But  if  the  count  is  made  when 
digestion  is  relatively  inactive,  four  to  five  hours  after  a  meal, 
it  gives  no  more  than  7,000  to  the  cubic  millimetre.  In  new- 
born children  the  average  number  is  over  18,000  per  cubic 
millimetre.  In  leukaemia  the  number  of  white  corpuscle-,  is 
enormouslv  increased — on  the  average  to  about  300,000,  but  in 
extreme  cases  to  600,000  per  cubic  millimetre — while  at  the  same 
time  the  number  of  the  red  corpuscles  is  diminished  ;  and  the 
ratio  of  white  to  red  may  approach  1  :  4.  As  the  ana-mia 
rapidly  advances  towards  the  fatal  termination  of  an  acute  case, 
and  the  ervthrocyte  count  falls  to  1,000,000,  or  even  less,  the 
ratio  may  come  still  nearer  to  unity.  An  increase  in  the  number 
of  leucocytes  has  also  been  ob- 
served in  certain  infective  dis- 
eases as  part  of  the  inflamma- 
tory  reaction.  There  are  also 
physiological  variations,  even 
within  short  periods  of  time  ;  for 
example,  the  number  of  lympho- 
cytes is  increased  when  digestion 

is  going  on.     The  normal  num- 

,            r  %_i       ■,     1    .                        t  Fig.  3. —  Curve        showing        the 

ber   of    blood-plates    varies  from  XuMBER      OF    Red       Corpuscles 

a    quarter  to    half    a    million  to  at      Different       Ages       (after 

the    cubic    millimetre,    but    may  Sorenseh's  Estimations). 

be  greater  in  disease  and  at  high        The  &s»r^  along  the  horizontal 

.      °.      ..,  axis   are   years    of   age,    those   along 

16\  els   (Kemp).  tbe    vertical    axis    millions    oi 

Life-history  of  the  Corpuscles,      puscles  per  cubic  millimetre  of  blood. 
— The   corpuscles  of  the  blood, 

like  the  body  itself,  fulfil  the  allotted  round  of  life,  and  then  die. 
They  arise,  perform  their  functions  for  a  time,  and  disappear. 
But  although  the  place  and  mode  of  their  origin,  the  seat  of  their 
destruction  or  decay,  and  the  average  length  of  their  life,  have 
been  the  subject  of  active  research  and  still  more  active  discus- 
sion for  many  years,  much  yet  remains  unsettled. 

*  In  1 13  apparently  healthy  students  (male)  the  average  number  of  red 
corpuscles  was  5  per  cubic  millimetre.     In  104  of  these,  the  number 

ranged  from  4,000,000  to  6,400,000  ;  in  71  (or  63  per  cent,  of  the  whole), 
from  4,400,000  to  5,500,000  ;  in  3,  from  3,500,000  to  3,900,000  ;  in  5,  from 
,000  to  7,000,000.  In  one  observation  the  number  reached  7,300,000. 
In  the  new-born  child  the  average  is  over  6,000,000.  In  one  case  of  per- 
nicious anaemia,  only  143,000  corpuscles  per  cubic  millimetre  were  present, 
the  lowest  number  recorded.  Over  13,000,000  have  been  counted  in  a 
case  of  cyanosis  (imperfect  oxygenation  of  the  blood,  with  blueness  of 
the  lips,  etc.)  due  to  congenital  disease  of  the  heart. 

2 — 2 


»H  W-»>7' 


A  MANU  U    OF  PHYSIOLOGY 


In  the  embryo  the  red  corpuscles,  even  of  those  forms  (mam- 
mals) which  have  non-nucleated  corpuscles  in  adult  life,  are  at 
first  possessed  of  nuclei,  and  approximately  spherical  in  form. 
In  the  human  foetus,  at  the  fourth  week  all  the  red  corpuscles 
are  nucleated.  Later  on  the  nucleated  corpuscles  gradually 
diminish  in  number,  and  at  birth  they  have  almosl  01  altogether 
disappeared,  some  of  them,  at  least,  having  been  converted  by 
a  shrivelling  of  the  nucleus  into  the  ordinary  non-nucleated 
form.  In  the  newly-born  rat,  which  comes  into  the  world  in 
a  comparatively  immature  state,  many  of  the  red  corpuscles 
may  be  seen  to  be  still  nucleated.  The  first  corpuscles  formed 
in  embryonic  life  are  developed  outside  of  the  embryo  altogether. 

Even  before  the  heart  has  as  yet 
begun  to  beat,  certain  cells  of 
the  mesoderm  (see  Chap.  XIV.) 
in  a  zone  ('  vascular  area  ') 
around  the  growing  embryo  begin 
to  sprout  into  long,  anasto- 
mosing processes,  which  after- 
wards become  hollowed  out  to 
form  capillary  bloodvessels.  At 
the  same  time  clumps  of  nuclei, 
formed  by  division  of  the  original 
nuclei  of  the  cells,  gather  at  the 
nodes  of  the  network.  Around 
each  nucleus  clings  a  little  lump 
of  protoplasm,  which  soon  de- 
velops haemoglobin  in  its  sub- 
stance ;  and  the  new-made  cor- 
puscles float  away  within  the 
new-made  vessels,  where  they 
rapidly  multiply  by  mitosis.  In 
later  embryonic  life  the  nucleated  corpuscles  continue  in  part 
to  be  developed  within  the  bloodvessels  in  the  liver,  allantois, 
spleen,  and  red  bone-marrow,  and  in  certain  localities  in  the 
connective  tissue,  by  mitotic  division  of  previously  existing 
nucleated  corpuscles,  in  part  to  be  formed  endogenouslv  within 
special  cells  in  the  liver  and  perhaps  other  organs.  Still  later 
the  nucleated  corpuscles  give  place  in  the  blood  of  the  mammal 
to  non-nucleated  erythrocytes.  Many  of  these  are  doubtless 
derived  from  the  nucleated  corpuscles,  but  some  appear  to  be 
produced  in  the  interior  of  certain  cells  of  the  connective  tissue, 
and  are  non-nucleated  from  the  start. 

In  the  mammal  in  extra-uterine  life  the  chief  seat  of  forma- 
tion of  the  red  blood-corpuscles  is  the  red  marrow  of  the  bones 
of  the  skull  and  trunk,  and  of  the  ends  of  the  long  bones  of  the 


Fig.  4. — Curve  showing  Propor- 
tion of  White  Corpuscles  to 
Red  at  Different  Times  of  the 
Day  (after  the  Results  of 
Hirt). 

At  I  the  morning  meal  was  taken  ; 
at  II  the  mid-day  meal ;  at  III  the 
evening  meal.  During  active  diges- 
tion the  number  of  lymphocytes  in 
the  blood  is  greatly  increased,  both 
absolutely  and  relatively  to  the 
number  of  the  other  leucocytes. 


////    CIRCU1   ITING  LIQUIDS  OF    /III    BODY  ji 

1  mi  I  >s.  Special  nucleated  cells  in  the  marrow,  originally  colour- 
less, multiply  by  karyokinesis,  take  up  haemoglobin  or  form  it 

within  their  protoplasm,  and  are  transformed  by  various  stages 
into  the  ordinary  non-nucleated  red  corpuscles,  which  then  pass 
into  the  blood-stream.  These  blood-forming  cells  have  received 
the  name  of  er\  t  hroblasts  or  haematoblasts.  According  to  their 
size,  erythroblasts  have  been  distinguished  as  normoblasts, 
megaloblasts,  and  microblasts.  The  normoblasts  are  most 
numerous,  and  have  about  the  same  diameter  as  the  full-formed 
erythrocytes,  into  which  they  are  believed  to  develop.  The 
megaloblasts  are  larger,  and  the  microblasts  smaller,  and  they 
are  thought  to  be  the  precursors  of  those  aberrant  forms  of 
erythrocytes  sometimes  found  in  the  blood  in  certain  diseases. 
After  haemorrhage  rapid  regeneration  of  the  blood  takes  place, 
so  that  in  a  few  weeks  the  loss  of  even  as  much  as  a  third  of 
the  total  blood  is  made  good.  The  plasma  is  much  sooner 
restored  to  its  normal  amount  than  the  corpuscles.  Microscopical 
examination  shows  in  the  red  marrow  the  tokens  of  increased 
production  of  coloured  corpuscles.  Other  organs  also,  par- 
ticularly the  spleen,  may,  in  such  emergencies,  take  on  a  blood- 
forming  function. 

A  constant  destruction  of  red  blood-corpuscles  must  go  on, 
for  the  bile-pigment  and  the  pigments  of  the  urine  are  derived 
from  blood-pigment.  The  bile-pigment  is  formed  in  the  liver. 
It  contains  no  iron  ;  but  the  liver-cells  are  rich  in  iron,  and  on 
treatment  with  hydrochloric  acid  and  potassium  ferrocyanide, 
a  section  of  liver  is  coloured  by  Prussian  blue.  Iron  must, 
therefore,  be  removed  by  the  liver  from  the  blood-pigment  or 
from  one  of  its  derivatives  ;  and  there  is  other  evidence  that 
the  liver  is  either  one  of  the  places  in  which  red  corpuscles  are 
actually  destroyed,  or  receives  blood  charged  with  the  products 
of  their  destruction.  Although  it  cannot  be  doubted  that  in  all 
animals  whose  blood  contains  haemoglobin  the  iron  found  in  the 
liver  bears  an  important  relation  to  the  building  up  or  breaking 
down  of  the  blood-pigment,  the  injection  of  haemoglobin  or 
haemin,  indeed,  increasing  markedly  the  amount  of  iron  in  the 
liver,  as  well  as  in  the  spleen,  bone-marrow  and  other  tissues,  this 
does  not  seem  to  be  the  only  function  of  the  hepatic  iron,  for  the 
liver  of  the  crayfish  and  the  lobster,  which  have  no  haemoglobin 
in  their  blood,  is  rich  in  iron.  Destruction  of  erythrocytes  may 
also  take  place  in  the  spleen  and  bone-marrow.  Although  the 
statement  that  free  blood-pigment  exists  in  demonstrable  amount 
in  the  plasma  of  the  splenic  vein  is  incorrect,  red  corpuscles  have 
been  seen  in  various  stages  of  decomposition  within  large  amoeboid 
cells  in  the  splenic  pulp  ;  and  deposits  containing  iron  have  been 
found  there  and  in  the  red  bone-marrow  in  certain  pathological 


22  A   MANUAL  <>/    !■//)  SIOLOGY 

condition>.  Bui  there  is  no  good  foundation  for  the  statement 
sometimes  rather  fancifully  made  that  the  spleen  is  in  any  special 
sense  the  '  graveyard  of  the  red  corpuscle^.'  Some  of  the  coloured 
corpuscles  may  break  up  in  the  blood  itself,  forming  granules  of 
pigment,  which  may  then  be  taken  up  by  tin?  liver,  spleen,  and 
lymph  glands.  Indeed,  it  is  probable  that  a  large  proportion  of 
the  worn-out  erythrocytes  are  finally  destroyed  in  the  blood- 
stream. The  portal  circulation  may  be  more  than  other  vascular 
tracts  a  seat  of  this  natural  decay,  perhaps  in  virtue  of  the 
presence  of  substances  with  a  hemolytic  action  (p.  27)  absorbed 
from  the  alimentary  canal. 

The  lymphocytes  are  undoubtedly  derived  from  the  lymph. 
They  are  identical  with  the  small  lymph-corpuscles,  and  have 
little,  if  any.  power  of  amoeboid  movement.  They  are  formed 
largely  in  the  lymphatic  glands,  for  the  lymph  coming  to  the 
glands  is  much  poorer  in  corpuscles  than  that  which  leaves  them. 
The  lymphatic  glands,  however,  are  not  the  only  seat  of  forma- 
tion of  lymphocytes,  for  lymph  contains  some  corpuscles  before 
it  has  passed  through  any  gland  ;  and  although  a  certain  number 
of  these  may  have  found  their  way  by  diapedesis  from  the  blood, 
others  are  formed  in  the  diffuse  adenoid  tissue,  or  in  special  col- 
lections of  it,  such  as  the  thymus,  the  tonsils,  the  Peyer's  patches 
and  solitary  follicles  of  the  intestine,  and  the  splenic  corpuscles. 
The  hyaline  cells  are  possibly  developed  by  the  enlargement  of 
lymphocytes.  It  is  probable  that  the  eosinophile  cells,  the  poly- 
morphonuclear neutrophiles,  and  the  '  mast  '  cells  are  formed  in 
the  bone-marrow.  To  a  very  small  extent  white  blood-corpuscles 
may  multiply  by  karyokinesis  or  indirect  division  in  the  blood. 

The  fate  of  the  leucocytes  is  even  less  known  than  that  of 
the  red  corpuscles,  for  they  contain  no  characteristic  substance, 
like  the  blood-pigment,  by  which  their  destruction  may  be  traced. 
That  they  are  constantly  disappearing  is  certain,  for  they  are 
constantly  being  produced.  Not  a  few  of  them  actually  escape 
from  the  mucous  membranes  of  the  respiratory,  digestive,  and 
urinary  tracts.  The  remnants  of  broken-down  leucocytes  have 
been  found  in  the  spleen  and  lymph  glands.  It  must  be  assumed 
that  many  break  up  in  the  blood-plasma  itself. 

Physical  and  Chemical  Properties  of  the  Blood. 

Fresh  blood  varies  in  colour,  from  scarlet  in  the  arteries  to 
purple-red  in  the  veins.  It  is  a  somewhat  viscid  liquid,  with  a 
saline  taste,  and  a  peculiar  odour. 

Viscosity  of  Blood.  The  viscosity  of  normal  dog's  blood  is 
about  six  times  greater  than  that  of  distilled  water  at  body 
temperature.     It  can  be  determined  by  allowing  the  blood  to 


////    CIRCULATING  LIQUIDS  OF    THE  BODY  23 

flow  through  a  capillary  tube  of  known  dimensions  under  a 
definite  pressure,  and  measuring  the  amount  which  escapes  in 
a  given  time.  In  general  the  viscosity  and  specific  gravity  ol 
the  blood  vary  in  the  same  direction,  although  there  is  not  an 
exact  proportionality  between  them.  Tims,  sweating,  which  causes 
a  diminution  of  the  water  of  the  blood,  causes  also  an  increase 
in  its  viscosity.  With  increasing  temperature  the  viscosity  of 
the  blood  diminishes,  as  is  the  case  with  other  liquids  (Opitz). 

In  polycythemia,  where  the  number  of  erythrocytes  in  pro- 
portion to  plasma  is  greatly  increased,  the  viscosity  of  the  blood 
increases  in  an  equal  degree.  In  one  case  of  polycythemia, 
with  a  blood-count  of  8,300,000,  the  viscosity  was  0/4  times  that 
of  water  ;  in  a  case  of  marked  chlorosis  it  was  only  2-i4.  But 
the  importance  of  this  factor  in  causing  an  abnormal  blood- 
pressure  by  increasing  or  diminishing  the  resistance  to  the  blood- 
flow  has  been  exaggerated.  Although  it  has  been  shown  that  in 
the  living  vessels,  so  long  as  their  calibre  remains  constant,  the 
flow  is  affected  by  changes  in  the  viscosity  of  the  blood,  just  as 
in  glass  tubes,  compensation  by  adjustment  of  the  vascular 
calibre  is  so  ample  and  so  easy  that  even  the  greatest  alterations 
of  viscosity  produce  little  effect  on  the  mean  blood-pressure. 

Reaction  of  Blood. — In  the  sense  in  which  the  term  is  used  in 
physical  chemistry,  the  reaction  of  a  solution  depends  on  the 
proportion  between  its  content  of  hydrogen  (H  +  )  and  hydroxyl 
(OH  -  )  ions,  an  excess  of  hydrogen  ions  corresponding  to  an 
acid  and  an  excess  of  hydroxyl  ions  to  an  alkaline  reaction.  It 
has  been  shown  by  a  physical  method  (the  determination  of  the 
electromotive  force  of  a  cell  containing  blood  or  serum  as  one 
liquid)  that  hydroxyl  ions  are  present  only  in  small  excess,  and 
that  blood  is  really  but  a  little  more  alkaline  than  distilled  water. 
Practically,  it  may  be  regarded  as  a  neutral  liquid.  Under  a 
great  variety  of  conditions,  physiological  and  pathological,  its 
reaction  remains  almost  unchanged.  The  administration  of  large 
quantities  of  acid  or  alkali  causes  a  surprisingly  small  effect. 
In  diabetes,  even  when  it  can  be  shown  that  an  abnormal  pro- 
duction of  acid  substances  is  taking  place,  the  blood  shows  little, 
if  any,  diminution  in  the  proportion  of  hydroxyl  ions  ;  it  remains 
to  all  intents  and  purposes  a  neutral  liquid.  In  diabetic  coma, 
where  the  blood  may  in  extreme  cases  turn  blue  litmus  red,  the 
true  reaction  is  only  slightly  altered. 

The  manner  in  which  the  reaction  of  the  blood,  the  tissue 
liquids,  and  probably  the  protoplasm  itself,  is  regulated  within 
such  narrow  limits  is  a  subject  of  great  interest.  Although  it 
cannot  be  said  that  all  the  details  of  the  process  have  been  satis- 
factorily explained,  two  factors  have  been  shown  to  be  of  im- 
portance :  (1)  The  power  of  the  proteins  to  combine  either  with 


•I  I  MA  xr  u    OF    PHYSIOLOGY 

acids  in  wiiii  bases,  so  that,  when  excess  oi  base  is  added  to 
blood,  the  proteins  act  as  acids,  and  neutralize  the  base  ;  when 
cm  ess  (it  acid  is  added,  the  proteins  acl  as  bases,  and  neutralize 
the  acid.  (2)  The  equilibrium  of  certain  oi  the  inorganic  con- 
stituents of  the  blood  (carbon  dioxide,  the  carbonates,  and  the 
phosphates)  is  such  that  even  great  \  -an  at  ions  in  the  com  entration 
of  any  of  these,  such  as  ma5  normally  occur,  produ<  e  scarcelj  any 
effect  upon  the  concentrations  of  the  hydrogen  and  hydroxy]  ions. 

The  so-called  '  titratable  '  alkalinity  of  blood  or  serum,  measured 
by  the  amount  of  standard  acid  which  must  be  added  before  the 
colour  of  the  indicator  used  changes  from  alkaline  to  acid,  bears  no 
neeessary  or  fixed  proportion  to  the  actual  alkalinity.  When  blond, 
for  instance,  is  titrated  with  hydrochloric  acid,  with  methyl  orange 
as  indicator,  at  the  point  where  the  red  colour  appears  all  the  disodiiini 
phosphate  and  sodium  bicarbonate  will  have  been  changed  into 
monosodium  phosphate  and  carbon  dioxide,  all  the  alkali  removed 
from  combination  with  proteins,  a  certain  amount  of  acid-protein 
compounds  Eormed,  and  other  minor  react  inns  pri  iduced  1 1  tenderson). 
It  is  difficult  to  correlate  the  quantity  deduced  from  such  a  titration 
with  any  physiological  condition,  although  undoubtedly  it  bens 
some  relation  to  the  acid-neutralizing  power  of  the  blond,  and  some 
relation  to  its  real  reaction. 

What  is  estimated  here  is  the  quantity  of  acid  required  to  satisfy 
the  proteins  and  to  react  with  the  carbonates  and  phosphates 
before  thai  concentration  of  hydrogen  and  hydroxy!  ions  just 
necessary  to  cause  the  change  of  colour  is  established.  This  is  not 
the  same  for  different  indicators,  since  there  is  a  certain  minimum 
ratio  in  the  concentration  of  these  ions  at  which  each  indicator 
turns  in  one  or  the  other  direction,  none  turning  precisely  at  the 
neutral  point.  Thus  scrum  appears  to  be  acid  wh(  n  tested  with 
phenolphthalein.  and  alkali  must  be  added  to  the  scrum  before  the 
pink  colour  indicating  alkalinity  is  produced.  <  >n  the  other  hand. 
with  litmus  or  methyl  orange  it  gives  the  alkaline  reaction,  and  a 
considerable  amount  of  acid  must  be  added  before  the  colour  of  the 
indicator  which  denotes  acidity  appears.  The  true  reaction  of  the 
serum  is  not,  of  course,  at  one  and  the  same  time  both  alkaline  and 
acid  ;  but  it  is  so  near  neutrality  that  it  falls  just  below  the  degree 
of  alkalinity  necessary  to  give  the  pink  colour  with  phenolphthalein, 
and  just  below  the  degree  of  acidity  which  gives  the  pink  colour 
corresponding  to  an  acid  reaction  with  methyl  orange.  Certain 
indicators — for  example,  rosolic  acid — turn  so  as  to  give  sharp 
colour  reactions  at  about  the  concentration  of  hydrogen  and  hydroxy! 
ions  in  the  blood,  and  these  may  possibly  be  of  use  in  determining 
the  changes  in  the  true  reaction  for  clinical  purposes     \dleri. 

Much  more  closely  related  to  the  true  alkalinity  of  the  blood 
than  the  titratable  alkalinity  is  the  carbon  dioxide  content. 
This  follows  from  the  facts  thai  much  the  greatest  pari  of  the 
carbon  dioxide  is  united  with  bases,  chiefly  with  sodium,  and 
that  the  quantity  in  simple  solution  is  approximately  constant. 
The  estimation  of  the  total  carbon  dioxide  in  a  sample  ol  blood 
throws  light  upon  the  capacity  of  the  blood  to  perform  one  of 
its   most    important    functions — the    transportation    of   carbon 


////    CIRCULATING   LIQUIDS  OF    THl    BOD\  25 

dioxide  and  to  preserve  one  of  its  essential  properties  -an 
almosl  neutral  reaction     in  the  presence  of  an  excessive  intake 

01    production   of  acid   substances.      In    herbivorous  animals   th< 

carbon  dioxide  content  of  the  blood  is  easily  lessened  by  the 
administration  ol  acids,  but  in  carnivora  and  in  man  il  is  much 

more    difficult    to    bring   about    such    a    decided    effect,    the    acid 

being  neutralized  by  ammonia,  which  is  split  oh  from  the  pro- 
teins. In  many  diseases,  however,  and  particularly  in  those 
accompanied  by  fever,  this  protective  mechanism  breaks  down, 
and  the  alkalinity  of  the  blood,  as  measured  by  its  content  of 
carbon  dioxide,  becomes  seriously  reduced. 

Specific  Gravity  of  Blood.  The  average  specific  gravity  of 
blood  is  aboui  ro66  at  birth.  It  falls  during  infancy  to  about 
1050  in  the  third  year,  then  rises  till  puberty  is  reached  to  about 
1058  in  males  (at  the  seventeenth  year),  and  1055  in  females  (at 
the  fourteenth  year).  It  remains  at  this  level  during  middle 
life  in  males,  but  falls  somewhat  in  females.  In  chlorotic  anaemia 
of  young  women  it  may  be  as  low  as  1030  or  1035.  It  rises  in 
starvation.  Sleep  and  regular  exercise  increase  it  (Lloyd  Jones).* 
The  specific  gravity  of  the  serum  or  plasma  varies  from  1026  to 
1032. 

the  Electrical  Conductivity  of  Blood.— The  liquid  portion 
of  the  blood  conducts  the  current  entirely  by  means  of  the 
electrolytes  dissolved  in  it,  the  most  important  of  these  being  the 
inorganic  salts  ;  and  the  conductivity  of  the  serum  varies,  in 
different  specimens  of  blood,  within  a  comparatively  narrow 
range.  The  conductivity  of  entire  (defibrinated)  blood,  on  the 
contrary,  varies  within  wide  limits.  For  instance,  in  a  case  of 
pernicious  anaemia  the  conductivity  of  the  blood  was  found  to 
be  almost  double  that  of  normal  human  blood,  while  the  con- 
ductivity of  the  serum  was  normal.  The  most  influential  factor 
which  governs  this  variation  is  the  relative  volume  of  the  cor- 
puscles and  serum.  When  the  blood  is  relatively  rich  in 
corpuscles  and  poor  in  serum,  its  conductivity  is  low  ;  when  it 
is  poor  in  corpuscles  and  rich  in  serum,  its  conductivity  is  high. 
The  explanation  is  that  the  corpuscle  refuses  passage  to  the  ions 
of  the  dissociated  molecules,  which,  in  virtue  of  their  electrical 
charges,  render  a  liquid  like  blood  a  conductor  (p.  400),  or 
permits  them  only  to  pass  very  slowly,  so  that  the  intact  red 
corpuscles  have  an  electrical  conductivity  so  many  times  less 
than  that  of  serum,  that  they  may,  in  comparison,  be  looked 
upon  as  non-conductors  (Practical  Exercises,  p.  60). 

*  In  105  students  (male)  the  average  specific  gravity  of  the  blood,  as 
determined  in  the  writer's  laboratory  by  Hammerschlag's  method  (p.  54) 
was  1054*4.  In  149  of  these  the  variation  was  from  1050  to  [065  :  in  94 
(or  57  per  cent,  of  the  whole),  from  1054  to  1060  ;  in  4,  from  104c  to  1049  ; 
in  9,  from  1066  to  1070.     In  3  the  specific  gravity  was  only  1040  to  104 j. 


26  ./   .1/  /  XI    //.  OB   PHYSIOLOGY 

The  Relative  Volume  of  Corpuscles  and  Plasma  in  Unclotted 
Blood,  or,  whal  can  be  converted  into  this  by  a  small  correction, 
the  relative  volume  oi  corpuscles  and  serum  in  defibrinated 
blood,  can  be  easily  determined,  with  approximate  accuracy, 
by  comparing  the  electrical  conductivity  of  entire  Mood  with 
thai  ot  its  serum.*  Another  method,  more  suitable  Eoi  clinical 
work,  though  not  so  accurate,  is  the  so-called  haematocrite 
method.  A  small  quantity  of  blood  is  centrifugalized  in  a 
graduated  glass  tube  of  narrow  bore  until  the  corpuscles  have 
been  collected  into  a  solid  '  thread'  at  the  outer  extremity  oi 
the  tube.  Their  volume  and  that  of  the  clear  plasma  which  has 
been  separated  from  them  are  then  read  off  on  the  scale.  The 
haematocrite  must  rotate  at  such  a  high  speed  (10,000  turns  a 
minute)  that  separation  of  the  corpuscles  from  the  plasma  is 
accomplished  before  clotting  has  occurred.  Dilution  oi  the  blood 
with  liquids  which  prevent  clotting  is  not  permissible  for  exact 
work  (Practical  Exercises,  p.  59).  By  these  and  other  methods 
too  elaborate  for  description  here,  it  has  been  shown  that  the 
plasma  or  serum  usually  makes  up  rather  less  than  two-thirds, 
and  the  corpuscles  rather  more  than  one-third,  of  the  blood. 
But  this  proportion  is,  of  course,  liable  to  the  same  variations 
as  the  number  of  corpuscles  in  a  cubic  millimetre  of  blood.  It 
depends,  further,  the  number  of  corpuscles  being  given,  on  the 
average  volume  of  each  corpuscle.  For  instance,  when  the  mole- 
cular concentration,  and  therefore  the  osmotic  pressure  (p.  398), 
of  the  plasma  is  reduced,  as  by  the  addition  of  water  or  the 
abstraction  of  salts,  water  passes  into  the  corpuscles  and  they 
swell  ;  when  the  molecular  concentration  of  the  plasma  is  in- 
creased, by  the  abstraction  of  water  or  the  addition  of  salts, 
water  passes  out  of  the  corpuscles,  and  they  shrink.  In  human 
serum  the  average  depression  of  the  freezing-point  below  that 
of  distilled  water,  which  is  a  measure  of  the  molecular  concentra- 
tion and  of  the  osmotic  pressure,  is  about  0560  C.  (Practical 
Exercises,  p.  64).  For  clinical  purposes,  the  determination  of  the 
relative  volume  of  corpuscles  and  plasma  is  most  useful  in  cases 
where  the  average  size  of  the  erythrocytes  departs  from  the 
normal,  and  where,  accordingly,  the  enumeration  of  the  corpuscles 
would  give  an  erroneous  idea  of  their  total  mass. 

Laking  of  Blood,  or  Haemolysis. —Even  in  thin  layers  blood 
is  opaque,  owing  to  reflection  of  the  light  by  the  red  corpuscles. 

*  The  formula  p=  (iy^-\(b)),  where/?  is  the  number  of  c.c.  of 

serum  in  100  c.c.  of  blood  ;  \(b),  \(s),  the  conductivity  respectively  of 
the  blood  and  serum  (both  measured  at  or  reduced  to  50  C,  and  expressed 
in  reciprocal  ohms  multiplied  by  ioH),  may  be  used  in  the  calculation.  A 
reciprocal  ohm  is  the  conductivity  of  a  mercury  column  1*063  metres  long 
and  1  square  millimetre  in  section. 


I  III    (//,'<  /  /    [TING   I  lor  ins  OF  THE  BODY  27 

It  becomes  transparent  or  '  laky  '  when  by  any  means  the  pig- 
ment is  brought  oul  <>t  the  corpuscles  and  goes  into  true  solution. 
Repeated  freezing  and  thawing  of  the  blood,  the  addition  oi 
water,  the  passage  of  electrical  currents,  constant  and  induced,* 
putrefaction,  heating  the  blood  to  6o°  C,  and  many  chemical 
agents  (as  bile-salts,  ether,  saponin),  cause  this  change.  Certain 
complex  poisons  of  animal  origin,  such  as  snake-venoms,  bee- 
poison,  spider  -  poison  or  arachnolysin,  and  certain  toxins  pro- 
duced by  pathogenic  bacteria — for  instance,  tetanolysin,  formed 
by  the  tetanus  bacillus — also  possess  decided  haemolytic  power. 
The  blood-serum  of  certain  animals  acts  on  the  coloured  corpuscles 
of  others,  and  sets  free  their  pigment — for  example,  the  serum 
of  the  dog  or  ox  causes  haemolysis  of  rabbit's  corpuscles  ;  the 
serum  of  the  ox,  goat,  dog,  or  rabbit  lakes  guinea-pig's  corpuscles. 
But  rabbit's  serum  does  not  lake  dog's  corpuscles,  and  guinea- 
pig's  serum  is  inactive  towards  the  corpuscles  both  of  the  rabbit 
and  the  dog.  It  has  been  shown  that  in  haemolysis  by  foreign 
serum  two  bodies  are  concerned  :  one,  which  is  easily  destroyed 
by  heating  to  about  560  C,  the  so-called  complement,  and  another, 
the  intermediary  body  or  amboceptor,  which  is  not  affected  by  being 
heated  to  this  temperature.  Thus,  if  dog's  serum  be  heated  to 
560  C.  for  twenty  minutes,  no  amount  of  it  will  lake  rabbit's  washed 
corpuscles — that  is,  rabbit's  corpuscles  freed  from  their  own  serum 
by  repeated  washing  with  salt  solution  and  centrifugalization.  If, 
however,  serum  which  is  not  itself  haemolytic  for  rabbit's  blood 
{e.g. ,  rabbit's  or  guinea-pig's  serum)  be  added  to  the  washed  rabbit's 
corpuscles,  they  will  be  laked  by  the  heated  dog's  serum.  Unheated 
dog's  serum  will  lake  rabbit's  corpuscles,  whether  they  have  been 
washed  free  from  their  own  serum  or  not  (Practical  Exercises,  p.  63) . 
The  hypothesis  which  best  explains  these  facts  and  many 
similar  ones  is  that  dog's  serum  contains  both  of  the  bodies 
necessary  for  haemolysis  of  rabbit's  corpuscles.  When  the 
complement  has  been  rendered  inactive  by  heating,  the  ambo- 
ceptor cannot  cause  laking  by  itself.  Rabbit's  serum  contains 
complement,  but  not  the  specific  amboceptor  necessary  for  the 
laking  of  rabbit's  corpuscles.  Accordingly,  the  addition  of  fresh 
rabbit's  serum  to  heated  dog's  serum  restores  complement  to 
the  latter,  and  thus  it  is  again  rendered  active  for  rabbit's  cor- 
puscles. The  amboceptor  is  supposed  to  unite  on  the  one 
hand  with  certain  groups  in  the  corpuscle  and  on  the  other  with 
the  complement,  which  is  thus  enabled  to  develop  its  haemolytic 
action  upon  the  envelope  or  the  stroma.     The  complement  is 

*  The  laking  action  of  induced  currents  is  due  simply  to  the  heating  of 
the  blood.  Condenser  discharges,  which  cause  liberation  of  the  haemo- 
globin without  raising  the  temperature  of  the  blood  as  a  whole  to  the  point 
at  which  heat-laking  occurs,  possibly  act  in  the  same  way  by  causing  local 
heating  of  the  corpuscles  owing  to  their  high  resistance. 


/    \l  INUA1    OF   PHYSIOLOG  I 

incapable  ol  acting,  even  in  the  presence  ol  amboceptor,  if  the 
temperature  is  reduced  to  o  C.  Nevertheless  the  corpuscles 
take  up  amboceptor  a1  this  temperature,  and  on  this  fad  is 
based  .1  method  ol  freeing  serum  from  amboceptor.  For  ex- 
ample, it  dog's  serum  and  excess  oi  rabbit's  washed  corpus*  les, 

both  pie  vim  1  ly  Cooled  to  0°  < '.,  be  mixed  and  placed  at  0  C.  tin- 
some  hours,  and  the  serum  then  removed,  i1  will  be  found  thai  it 
lias  lost  the  power  of  laking  rabbit's  corpuscles,  washed  or.  un- 
washed, at  air  or  body  temperature,  although  h  will  still  do  so 
on  the  addition  of  dog's  serum  in  which  the  complement  has  been 
destroyed  by  heating  it  to  56°  C. 

\s  to  the  manner  in  which  haemolytic  agents  cause  the  liberation 
of  the  blood-pigment,  the  fad  thai  in  so  many  forms  oi  Laking  the 
corpuscles  swell   up  before   the   haemoglobin  escapes  indicates  thai 

the  entrance  of  water  is  an  important  step.  The  entrance  of  water 
is  favoured  l>v  changes  produced  in  the  chemical  and  physical  con- 
dition of  certain  constituents  of  the  superficial  layer  (envelop*  I  oi 
the  corpuscle,  as  well  as  by  changes  in  its  interior.  Saponin  and 
ether,  for  example,  are  known  to  1)''  solvents  ol  cholesterin  and 
lecithin,  and  cholesterin  and  lecithin  are  importanl  constituent 
the  stroma,  and  envelope  of  the  erythrocyte.  It  is  easy  to  under- 
stand that  if  a  portion  of  one  or  both  of  these  substances  is  dis- 
solved, or  altered  without  being  actually  dissolved,  profound  1  hai 
may  be  produced  in  the  permeability  of  the  corpuscle  to  water  and 
to  the  salts  dissolved  in  the  liquid  in  which  the  erythrocytes  are 
suspended.  In  addition  to  this  change  of  permeability,  many  laking 
agents,  perhaps  all,  exert  also  a  more  direct  influence  on  the  normal 
relations  of  the  native  blood-pigment  to  the  stroma.  Ether  and 
saponin,  for  instance,  seem  to  act  in  two  ways — by  disorganizing 
the  envelope  through  solution  of  its  lipoids,  and  thus  increasing  its 
permeability  to  water;  and  by  helping  to  dissociate  the  blood  - 
pigment-stroma  complex  by  exerting  a  pull  on  the  lipoids  of  the 
stroma,  while  the  water  .simultaneously  exerts  a  pull  on  the  pigment. 

The  conclusion  follows  from  this  view  of  haemolysis  that  the 
erythrocytes,  normally  so  perfectly  adapted  to  the  plasma  in  which 
they  float,  may,  when  the  conditions  on  which  their  equilibrium 
with  it  depends  are  altered,  be  rapidly  and  inevitably  destroyed  by 
that  very  plasma  itself.  It  is.  indeed,  the  very  fact  ol  the  exquisite 
adaptation  of  liquid  and  cell  for  a  strictly  regulated  exchange  of 
material  which  constitutes  the  danger  when  the  regulation  is  upset. 
A  liquid  like  mercury,  which  is  not  adapted  either  to  give  anything 
to  ervthrocytes  in  contact  with  it  or  to  take  anything  from  them, 
would  not  cause  haemolysis,  even  if  the  permeability  of  the  corpusi 
for  water  or  sodium  chloride  were  increased  to  any  extent.  The 
continued  survival  of  the  erythrocytes  in  an  aqueous  solution  of 
salts  and  proteins  like  the  plasma  miv.  more,  the  protection  of  the 
corpuscles  up  to  a  certain  point  l>v  the  plasma  against  the  attack 
of  extraneous  haemolytic  agents  are  facts  we  are  prone  to  take  so 
much  for  granted  as  to  forget  that  they  depend  entirely  upon  a  most 
delicate  adjustment  of  the  permeability  ot  tin  1  orpus(  les  tor  essential 
constituents  of  the  plasma.  Disturb  these  relations  to  a  sufficient 
degree,  and  the  plasma  becomes  a  poison  to  the  erythrocytes  not 
much  less  deadly  than  distilled  water. 

When  we  add  to  blood   a  haemolytic   substance,   and   see   that 


THE  CIRCU1   [TING   LIQUIDS  OF    Ml    BODY  29 

presently  the  blood-pigmenl  has  Kit  the  corpuscles,  we  are  apt  on 
inst  impulse  to  attribute  the  whole  effecl  to  the  foreign  material 
added.  We  arc  apt  to  say  thai  the  saponin,  the  ether,  the  alien 
serum,  has  laked  the  blood.  In  a  certain  sense  this  is  true,  but  it 
is  not  the  whole  truth.  In  reality  the  haemolytic  agent  lias  acted 
in  an  essential  degree,  although  not  exclusively,  by  overthrowing 
tlu-  equilibrium  between  the  corpuscles  and  the  aqueous  solution  oi 
eei  tain  substances  in  which  they  are  suspended.  To  say  that  the 
Eoreign  substance  alone  causes  the  haemolysis  is  no  more  accurate 
than  it  would  be  to  say  that  a  man  swimming  strongly  in  a.  rough 
sea.  who  sinks  when  hit  and  stunned  by  a  piece  of  wreckage,  was 
drowned  by  the  blow,  and  not  by  the  sea'.  No  doubt  it  is  true  that. 
but  for  the  blow,  be  would  have  continued  to  swim  ;  yet,  in  reality, 
he  loses  his  lite  because  he  is  environed  by  a  medium  deadly  to  linn 
as  soon  as  his  power  of  adjustment  to  it  has  been  too  much  diminished. 
On  land,  the  blow  would  have  stunned,  but  would  not  have  killed 
him.  In  like  manner,  to  glance  at  one  phase  of  the  natural  decay 
of  the  corpuscles  within  the  body,  an  erythrocyte  may  float  secure 
in  its  watery  environment  through  many  rounds  of  the  circulation. 
But  its  security  is  not  static,  like  that  01  a  log  floating  on  the  water. 
It  is  dynamic,  a  triumph  of  perfect  physico-chemical  poise,  as  the 
security  of  the  swimmer,  still  more  of  the  tight-rope  dancer,  is 
dynamic,  a  triumph  of  perfect  neuromuscular  poise.  The  time, 
however,  arrives  when,  either  through  changes  in  the  corpuscle 
itself  (the  changes  of  cellular  senility,  as  we  may  call  them),  or 
through  changes  in  the  environing  medium,  or  through  a  combina- 
tion of  the  two,  the  adjustment  is  upset,  and  the  erythrocyte  is  now 
destroyed  by  the  plasma  in  which  it  has  so  long  lived. 

In  general  haemolysis  by  foreign  serum  is  preceded  by  agglu- 
tination or  aggregation  of  the  corpuscles  into  groups.  Agglutina- 
tion may  be  obtained  without  haemolysis  by  heating  the  haemo- 
lytic serum  to  the  temperature  at  which  the  complement  is 
destroyed,  since  the  agglutinating  agents,  or  agglutinins,  are 
relatively  resistant  to  heat.  When  the  corpuscles  of  one  animal 
are  injected  intraperitoneally  or  subcutaneously  into  an  animal 
of  a  different  kind,  the  serum  of  the  latter  acquires  the  property 
of  agglutinating  and  laking  the  corpuscles  of  an  animal  of  the 
same  kind  as  that  whose  corpuscles  have  been  injected.  This  is 
especially  marked  if  the  injection  is  several  times  repeated  at 
intervals  of  a  few  days.  If,  for  instance,  dog's  corpuscles  are 
injected  into  a  rabbit,  the  rabbit's  serum  after  a  time  becomes 
strongly  haemolytic  for  dog's  corpuscles.  It  also  agglutinates 
them.  This  is  due  to  the  appearance  in  the  rabbit's  serum  of 
an  amboceptor  and  an  agglutinin  which  have  a  specific  action  on 
dog's  corpuscles.  Many  other  cells  besides  the  coloured  blood- 
corpuscles  give  rise,  when  injected,  to  similar  specific  substances 
(cytolysins),  which  cause  destruction  of  cells  of  the  same  kind — 
e.g.,  leucocytes  and  spermatozoa.  The  process  of  haemolysis  is 
more  easily  followed  than  the  cytolysis  of  ordinary  cells.  Yet 
in  its  main  features  it  is  essentially  similar.  Hence  it  has  been 
studied  not  only  for  its  own  interest,  but  even  more  for  the  light 


30  A  MANUAL  OF  PHYSIOLOGY 

it  throws  upon  that  peculiar  and  specific  response  which  the  body 
makes  to  the  presence  of  foreign  cells  or  juices,  and  which  con- 
stitutes an  attempt  to  render  itself  '  immune  '  to  them. 

In  each  cast'  the  specific  antibody  seems  to  be  produced  in  n  sponse 
to  the  presence  of  some  particular  constituent  of  the  foreign  cell. 
The  substances  which  on  injection  give  rise  to  antibodies  are  spoken 
of  as  antigens.  In  the  case  of  the  erythrocytes  there  is  evidence 
that  the  antigens  (both  the  haemolysinogen,  which  causes  the  pro- 
duction of  specific  amboceptor,  and  the  agglutininogen,  the  substance 
which  gives  rise  to  specific  agglutinin)  are  lipoids,  or  are  so  closely 
associated  with  the  lipoids  of  the  corpuscles  that  they  are  extracted 
by  the  same  solvents.  Thus  ethereal  extracts  of  erythrocytes  cause 
the  production  of  hemolysin  and  agglutinin,  just  as  the  entire  cor- 
puscles do.  Indeed,  the  response  of  the  animal  body  to  the  presence 
of  foreign  substances  is  so  catholic,  and  at  the  same  time  so  exquisitely 
specific,  that  many  artificially  isolated  proteins,  even  those  of  vege- 
table origin,  after  as  careful  purification  as  possible,  occasion,  when 
injected,  the  production  of  antibodies  which  will  precipitate  from  a 
solution  only  the  variety  of  protein  injected. 

Precipitins. — When  the  serum  of  one  animal  is  injected  into 
another  of  a  different  group,  the  serum  of  the  latter  acquires 
the  property  of  causing  a  precipitate  in  the  normal  serum  of 
animals  of  the  same  group  as  that  whose  serum  was  injected, 
but  not  in  the  serum  of  any  other  kind  of  animal.  Thus,  if 
human  blood  or  serum  is  repeatedly  injected  into  a  rabbit, 
the  serum  of  the  rabbit  will  cause  a  precipitate  in  diluted  human 
blood  or  serum,  but  not  in  the  blood  or  serum  of  other  animals, 
except  that  of  monkeys,  where  a  slight  reaction  may  be  obtained. 
The  specific  bodies  which  cause  the  precipitation  are  termed 
precipitins.  The  phenomenon  has  been  made  the  basis  of  a 
method  of  distinguishing  human  blood  for  forensic  purposes. 

Since  changes  begin  in  the  blood  as  soon  as  it  is  shed,  having 
for  their  outcome  clotting  or  coagulation,  we  have  to  gather 
from  the  composition  of  the  stable  factors  of  clotted  blood,  or 
of  blood  which  has  been  artificially  prevented  from  clotting, 
some  notion  of  the  composition  of  the  unaltered  fluid  as  it 
circulates  within  the  vessels.  The  first  step,  therefore,  in  the 
study  of  the  chemistry  of  blood  is  the  study  of  coagulation. 

Coagulation  of  the  Blood. — When  blood  is  shed,  its  viscidity 
soon  begins  to  increase,  and  after  an  interval,  varying  with  the 
kind  of  blood,  the  temperature  of  the  air,  and  other  conditions, 
but  in  man  seldom  exceeding  ten,  or  falling  below  three,  minutes, 
it  sets  into  a  firm  jelly.  This  jelly  gradually  shrinks  and 
squeezes  out  a  straw-coloured  liquid,  the  serum.  Under  the 
microscope  the  serum  is  seen  to  contain  few  or  no  red  corpuscles  ; 
these  are  nearly  all  in  the  clot,  entangled  in  the  meshes  of  a  kind 
of  network  of  fine  fibrils  composed  of  fibrin.  In  uncoagulated 
blood  no  such  fibrils  are  present  ;  they  have  accordingly  been 


THE  CIRCULATING  LIQUIDS  OF  THE  HODY  31 

formed  by  a  change  in  some  constituent  or  constituents  of  the 
normal  blood.     Now,  it  has  been  shown  that  there  exists  in  the 
plasma — the  liquid  portion  of  unclotted  blood — a  substance  from 
which  fibrin  can  be  derived,  while  no  such  substance  is  present 
in  the  corpuscles.     In  various  ways  coagulation  can  be  prevented 
or  delayed,  and  the  plasma  separated  from  the  corpuscles.     For 
example,  the  blood  of  the  horse  clots  very  slowly,  and  a  low 
temperature  lessens  the  rapidity  of  coagulation  of  every  kind 
of  blood.     If  horse's  blood  is  run  into  a  vessel  surrounded  by 
ice  and  allowed  to  stand,  the  corpuscles,  being  of  greater  specific 
gravity  than  the  plasma,   gradually  sink  to  the  bottom,   and 
the    clear    straw  -  yellow    plasma    can    be    pipetted    off.       Or 
the  addition  of  neutral  salts  to  blood  may  be  used  to  delay 
coagulation,  the  blood  being  run  direct  from  the  animal  into, 
say,   a  third  of  its  volume  of  saturated  magnesium   sulphate 
solution.      The    plasma   may    then    be   conveniently   separated 
from  the  corpuscles  by  means  of  a  centrifugal  machine.     Again, 
two  ligatures  may  be  placed  on  a  large  bloodvessel,  so  that  a 
portion  of  it  can  be  excised  full  of  blood  and  suspended  vertically 
(the  so-called  experiment  of  the  '  living  test-tube  ')  ;  coagula- 
tion is  long  delayed,  and  the  corpuscles  sink  to  the  lower  end. 
In  these  and  many  other  ways  plasma  free  from  corpuscles  can 
be  got  ;  and  it  is  found  that  when  the  conditions  which  restrain 
coagulation  are  removed^when,  for  instance,  the  temperature 
of  the  horse's  plasma  is  allowed  to  rise  or  the  magnesium  sulphate 
plasma  is  diluted  with  several  times  its  bulk  of  water — clotting 
takes  place,  with  formation  of  fibrin  in  all  respects  similar  to 
that  of  ordinary  blood-clot.     The  corpuscles  themselves  cannot 
form  a  clot.*     From  this  we  conclude  that  the  essential  process 
in  coagulation  of  the  blood  is  the  formation  of  fibrin  from  some 
constituent  of  the  plasma,  and  that  the  presence  of  corpuscles 
in  ordinary  blood-clot  is  accidental.      In  accordance  with  this 
conclusion,  we  find  that  lymph  entirely  free  from  red  corpuscles 
clots  spontaneously,  with  formation  of  fibrin  ;  and  when  fibrin 
is  removed  from  newly-shed  blood  by  whipping  it  with  a  bundle 
of  twigs  or  a  piece  of  wood,  it  will  no  longer  coagulate,  although 
all  the  corpuscles  are  still  there. 

What,  now,  is  the  substance  in  the  plasma  which  is  changed 
into  fibrin  when  blood  coagulates  ?  If  plasma,  obtained  in  any 
of  the  ways  described,  be  saturated  with  sodium  chloride,  a 
precipitate  is  thrown  down.  The  filtrate  separated  from  this 
precipitate  does  not  coagulate  on  dilution  with  water  ;  but  the 
precipitate  itself — the   so-called  plasmine   of   Denis — on   being 

*  Bird's  corpuscles,  however,  washed  free  from  plasma,  will  form  a  clot 
when  laked  in  various  ways,  as  by  addition  of  water  or  by  freezing  and 
thawing. 


I    MANX    II    OF  PHYSIOLOGY 

dissolved  in  a  little  water,  does  form  a  clot.  Fibrin  is  therefore 
derived  from  something  in  this  precipitate.  Now,  '  plasmine ' 
contains  two  protein  bodies  fibrinogen,  which  coagulates  by 
heal  .it  aboul  56  C,  and  serum-globulin,  which  coagulates 
.it  aboul  75  ('.,  and  it  was  at  one  time  believed  thai  both  of 
these  entered  into  the  formation  oi  fibrin  (Schmidt).  Hammer- 
sten.  however,  lias  shown  that  fibrinogen  alone  is  a  precursor 
of  fibrin;  pme  serum-globulin  neither  helps  noi  hinders  its 
formation.  This  observer  isolated  fibrinogen  from  blood- 
plasma  by  adding  sodium  chloride  till  about  1  ;  per  cent,  was 
present.  With  this  amount  the  fibrinogen  is  precipitated, 
while  serum-globulin  is  not  precipitated  till  20  per  cent,  ol 
salt  is  reached.  Alter  precipitation  of  the  fibrinogen  the  plasma 
no  longer  coagulates  ;  and  a  solution  of  pure  fibrinogen  can 
be  made  to  clot  and  to  form  fibrin,  while  a  solution  ol  serum- 
globulin  cannot.  Blood-serum,  too,  which  contains  abundance 
of  serum-globulin,  but  no  fibrinogen,  will  not  coagulate. 

So  far,  then,  we  have  reached  the  conclusion  that  fibrin  is 
formed  by  a  change  in  a  substance,  fibrinogen,  which  can  be 
obtained  by  certain  methods  from  blood-plasma.  It  may  be 
added  that  there  is  evidence  that  fibrinogen  exists  as  such  111 
the  circulating  blood  ;  for  if  unclotted  blood  be  suddenly  heated 
to  about  560  C,  the  temperature  of  heat-coagulation  of  fibrinogen, 
the  blood  for  ever  loses  its  power  of  clotting.  The  liver  sen ims 
to  be  an  important  place  of  origin  of  fibrinogen,  which  may  also 
be  formed  in  the  bone-marrow.  Since  fibrinogen  is  readily 
soluble  in  dilute  saline  solutions,  and  fibrin  only  soluble  with 
great  difficulty,  we  may  say  that  in  coagulation  of  the  blood  a 
substance  soluble  in  the  plasma  passes  into  an  insoluble  form. 

How  is  this  change  determined  when  blood  is  shed  ?  We 
have  said  that  a  solution  of  pure  fibrinogen  can  be  made  to 
coagulate,  but  it  does  not  coagulate  of  itself.  The  addition  ol 
another  substance  in  minute  quantity  is  necessary.  This  other 
substance  does  not  itself  seem  to  be  used  up  in  the  process,  nor 
to  enter  bodily  into  the  fibrin  formed  ;  a  small  quantity  of  it 
can  cause  an  indefinitely  large  amount  of  fibrinogen  to  clot  ;* 
its  power  is  abolished  by  boiling.  For  these  reasons  it  is  con- 
sidered to  be  a  ferment  (p.  _;i  |),  and  is  spoken  ol  as  fibrin- 
ferment  or  thrombin. 

Two  forms  of  fibrin-ferment  have,  been  distinguished  by  some 
writers:  « -thrombin,  which  exists  in  serum  before  anything  has 
been  added  to  it,  and  /^-thrombin,  or  Schmidt 's  fibrin-ferment,  in 

*  According  to  Rettger's  recent  work  this  is  erroneous.  He  states  tli.it 
the  quantity  oi  fibrin  formed  is  proportional  to  the  amount  oi  thrombin 
present,  and  that  thrombin  does  uol  acl  like  a  ferment.  The  inquirj  is 
complicated  by  the  fad  thai  fibrin,  once  formed,  tends  to  adsorb  the 
remaining  thrombin  and  so  to  interfere  with  its  furthei  action. 


////    CIRCU1   ITING   LIQUIDS  OF   I  III    BODY 

a  solution  which  can  be  obtained  by  precipitating  blood-serum, 
or  defibrinated  blood,  with  fitteen  to  twenty  times  its  hulk  of 
alcohol,  letting  the  whole  stand  for  a  month  or  more,  and  then 
extracting  the  precipitate  with  water.  All  the  ordinary  proi< 
of  the  blood  having  been  rendered  insoluble  by  the  alcohol,  the 
fibrin-ferment  passes  into  solution  in  the  water,  and  the  addition  of 
a  1 1  ace  of  the  extract  to  a  solution  of  fibrinogen  causes  coagulation. 
The  supposed  distinction  between  this  form  of  thrombin  and  the 
other  is  not  so  well  established  that  we  need  take  account  of  it  here. 

The  action  of  fibrin-ferment  on  fibrinogen  helps  to  explain 
many  experiments  in  coagulation.  Thus,  transudations  like 
hydrocele  fluid  do  not  clot  spontaneously,  although  they  contain 
fibrinogen,  which  can  be  precipitated  from  them  by  a  stream  of 
carbon  dioxide  or  by  sodium  chloride.  But  the  addition  of  a 
little  fibrin- ferment  causes  hydrocele  fluid  to  coagulate.  So  does 
the  addition  of  serum,  not  because  of  the  serum-globulin  which 
it  contains,  as  was  once  believed,  but  because  of  the  fibrin- 
ferment  in  it.  The  addition  of  blood-clot,  either  before  or  after 
the  corpuscles  have  been  washed  away,  or  of  serum-globulin 
obtained  from  serum,  also  causes  coagulation  of  hydrocele  fluid, 
and  for  a  similar  reason,  the  fibrin-ferment  having  a  tendency 
to  cling  to  everything  derived  from  a  liquid  containing  it.  On 
the  other  hand,  serum,  which,  although  fibrin-ferment  is  present 
in  it,  does  not  of  itself  clot,  because  the  fibrinogen  has  all  been 
changed  into  fibrin  during  coagulation  of  the  blood,  can  be  made 
to  coagulate  by  the  addition  of  hydrocele  fluid,  which  contains 
fibrinogen.  We  have  thus  arrived  a  step  farther  in  our  attempt 
to  explain  the  coagulation  of  the  blood  :  it  is  essentially  due  to 
the  formation  of  fibrin  from  the  fibrinogen  of  the  plasma  under  the 
influence  of  fibrin-ferment. 

The  Formation  of  Fibrin- ferment  from  its  Precursors. — 
There  is  good  reason  to  believe  that  thrombin  is  formed  by 
the  interaction  of  three  factors  :  (i)  A  substance  which,  since 
it  is  a  precursor  of  thrombin,  is  called  thrombogen,  or  pro- 
thrombin. It  is  already  present  in  the  circulating  plasma. 
(2)  A  substance  liberated  from  the  formed  elements  of  the  shed 
blood,  but  which  can  be  obtained  also  from  the  cells  of  all  tissues. 
Since  it  has  been  supposed  to  act  upon  thrombogen,  changing  it 
into  fully-formed  thrombin,  much  in  the  same  way  as  entero- 
kinase  (p.  331)  acts  upon  trypsinogen,  changing  it  into  fully- 
formed  trypsin,  it  is  called  thrombokinase  (Morawitz).*     (3)  Cal- 

*  Others  believe,  however,  that  the  substances  in  tissue  extracts  which 
favour  coagulation  do  so  not  by  activating  prothrombin,  but  by  a  direct 
action  upon  fibrinogen  similar  to,  but  not  necessarily  identical  with,  that 
exerted  by  thrombin,  and  speak  of  them  as  coagulins  (L.  Loeb).  It  is 
possible  that  the  tissues  yield  both  activating  substances  (kinases)  and 
coagulins. 

3 


34  A   MAM    \l    or    PHYSIOLOGY 

cium  ions.  The  following  experiments  illustrate  the  role  of  these 
three  factors  : 

The  plasma  obtained  by  drawing  oil  birds  blood  e.g.,  tin- 
blood  of  a  fowl  or  goose — through  a  perfectly  clean  cannula  into 
a  perfectly  clean  vessel,  without  contact  with  the  tissues,  and 
then  rapidly  centrifugalizing  off  the  formed  elements,  can  be 
kept  unclotted  for  days  and  even  weeks.  The  addition  of  a 
small  amount  of  tissue  extract  (procured  by  rubbing  up  blood- 
free  liver,  thymus,  muscle,  or  other  organs  with  sand,  and  ex- 
tracting for  several  hours  with  salt  solution)  to  the  bird's  plasma 
causes  rapid  coagulation.  The  plasma  contains  thrombogen 
and  calcium  salts,  but  is  lacking  in  thrombokinase,  which  is 
supplied  by  the  tissue  extract.  A  solution  of  fibrinogen  con- 
taining calcium  will  clot  if  serum,  in  which  fibrin-ferment  is  always 
present,  be  added.  It  will  not  clot  on  addition  of  tissue  extra*  I 
alone,  nor  on  addition  of  bird's  plasma  alone  (obtained  as  above), 
but  will  readily  coagulate  if  both  tissue  extract  and  bird's 
plasma  be  added.  Therefore,  something  in  the  bird's  plasma 
(thrombogen),  plus  something  in  the  tissue  extract  (thrombo- 
kinase), produce  in  the  presence  of  calcium  the  same  effect  as 
the  thrombin  of  serum.  It  can  be  shown  that  calcium  is  only 
necessary  for  the  formation  of  the  fibrin-ferment,  but  not  for  its 
action  on  fibrinogen.  For  instance,  a  calcium-free  solution  of 
fibrinogen  can  be  made  to  clot  by  serum  from  which  the  calcium 
has  been  removed. 

If  a  soluble  oxalate  (potassium  or  ammonium  oxalate)  is 
mixed  with  freshly-drawn  dog's  blood  to  the  amount  of  02  or 
03  per  cent.,  the  blood  remains  unclotted.  The  plasma  separated 
from  this  oxalated  blood  contains  both  thrombogen  and  throm- 
bokinase, but  it  does  not  coagulate,  because  the  calcium  has 
been  precipitated  out  in  the  form  of  insoluble  calcium  oxalate. 
In  the  absence  of  calcium  the  reaction  of  the  thrombogen  and 
thrombokinase  which  leads  to  the  formation  of  thrombin  does 
not  take  place.  All  that  is  necessary  to  bring  about  coagulation 
is  to  add  calcium  chloride  in  somewhat  greater  quantity  than  is 
required  to  combine  with  any  excess  of  oxalate  present.  If  more 
than  a  certain  amount  of  calcium  be  added  clotting  is  hindered 
instead  of  being  helped,  so  that  it  is  only  within  certain  limits  of 
concentration  that  calcium  favours  coagulation.  From  oxalate 
plasma  a  nucleo-protein  or  a  mixture  of  nucleo-proteins  can  be 
separated  which  contains  thrombogen  and  thrombokinase,  but 
little  or  no  calcium,  and  does  not  cause  clotting,  but  which  on 
treatment  with  a  calcium  salt  acquires  the  properties  of  fibrin- 
ferment.  In  the  curious  hereditary  disease  known  as  haemo- 
philia, a  deficiency  of  calcium  seems  occasionally  to  be  responsible 
lor  the  diminished  coagulability  of  the  blood  ;  and  the  internal 


////    (//,'<  I  I   ITING   LIQUIDS  OF   I  III    BODY  35 

administration  o\  .1  solution  of  calcium  chloride  has  sometimes 
been  thoughl  to  lessen  the  tendency  to  haemorrhage,  or  its  local 
application  to  cut  short  .111  actual  attack.  It  is  possible  thai  in 
some  cases  there  may  be  a  want  of  thrombokinase  in  the  blood 
or  in  the  cut  tissues,  and  that  the  application  of  normal  tissue 
extract  (extract  of  thymus,  for  example)  or  of  a  solution  con- 
taining fibrin-ferment  may  be  of  benefit.  The  injection  of 
normal  scrum  into  the  circulation,  or  the  transfusion  of  normal 
blood,  have  also  been  used  with  temporary  advantage. 

When  sodium  fluoride  is  added  to  freshly-drawn  blood  to  the 
amount  of  0*3  per  cent.,  coagulation  is  also  prevented.  But 
there  is  this  difference  between  oxalate  and  fluoride  plasma — 
that,  although  the  calcium  has  been  precipitated  in  both,  the 
addition  of  calcium  chloride  to  fluoride  plasma  is  not  sufficient 
to  induce  clotting.  Tissue  extract  containing  thrombokinase 
must  be  supplied  as  well.  In  some  way  or  other  sodium  fluoride 
interferes  with  the  liberation  of  thrombokinase  from  the  formed 
elements  of  the  blood,  although  in  the  concentration  mentioned 
it  does  not  hinder  the  action  of  fully-formed  thrombin,  as  is 
shown  by  the  fact  that  fluoride  plasma  coagulates  on  the  addition 
of  a  little  serum,  which  supplies  fibrin-ferment.  The  fluoride 
blood  clots  readily  if  it  is  diluted  with  water,  and  at  the  same 
time  mixed  with  calcium  chloride  solution,  for  the  water  damages 
the  formed  elements,  and  thus  favours  the  liberation  of  thrombo- 
kinase. 

When  proteoses  (or  peptones)  are  injected  into  the  circulation 
of  a  dog  or  goose,  the  blood  is  deprived  of  the  power  of  coagulation. 
The  peptone  plasma  must  be  assumed  to  contain  both  thrombogen 
and  thrombokinase,  since  it  can  be  made  to  clot  in  various  ways 
{e.g.,  by  dilution  with  water  or  by  slight  acidulation  with  acetic 
acid)  without  the  addition  of  anything  which  could  supply  either 
of  these  factors.  Yet  a  little  tissue  extract  causes  it  to  clot 
much  more  rapidly  than  simple  dilution  or  acidulation,  and  more 
rapidly  than  the  addition  of  serum.  So  that  either  the  throm- 
bokinase already  present  in  peptone  plasma  is  present  in  an 
unavailable  form,  or  in  some  way  the  formation  of  thrombin 
from  its  precursors  is  hindered.  But  this  is  not  the  only  cause 
of  the  incoagulability  of  peptone  plasma.  It  may  be  shown 
to  contain  an  antithrombin,  a  body  which  antagonizes  the 
action  of  fully-formed  thrombin,  and  which  does  not  seem  to 
be  a  ferment,  since  it  acts  quantitatively  in  proportion  to  the 
amount  present.  This  is  the  reason  why,  although  peptone 
plasma  can  always  be  made  to  clot  by  the  addition  of  fibrin- 
ferment,  in  serum,  for  instance,  relatively  large  quantities  of 
it  must  be  supplied  (Practical  Exercises,  pp.  56,  57). 

An  extract  of  the  head  of  the  medicinal  leech  in  salt  solution 

3—2 


A   MANUAL  OF  PHYSIOLOC  Y 

prevents  the  clotting  oi  blood  both  in  the  test-tube  and  when 
inje<  ted  into  the  circulation.  The  plasma  obtained  differs  from 
peptone  plasma  in  refusing  to  coagulate  unless  tissue  extract 
is  , Milled.  It  is  therefore  deficienl  in  thrombokinase,  or,  rather, 
as  lias  been  shown,  the  kinase  present  is  unable  to  ai  t,  because 
neutralized  by  antikinase  present  in  the  leech-extract.  Leech- 
extrad  also  contains  an  antithrombin,  which  can  be  neutralized 
by  a  sufficient  amount  of  thrombin.  In  the  small  wound  from 
which  the  leech  sucks  blood  this  sufficient  amount  is  not 
present,  and  the  blood  remains  unclotted,  as  it  also  docs  in 
the  alimentary  canal  of  the  leech.  The  anticoagulant  sub- 
stance, hirudin,  has  been  isolated,  and  gives  the  reactions  of 
an  albumose. 

Sources  of  Thrombogen  and  Thrombokinase. — It  has  already 
been  stated  that  thrombogen  exists  in  the  circulating  plasma. 
This  is  shown  by  the  fact  that  fluoride  plasma  obtained  from 
M' Mid  drawn  directly  through  a  wide  cannula  into  sodium  fluoride 
solution,  with  all  precautions  to  prevent  alteration  of  the  blood, 
and  immediately  separated  from  the  formed  elements  by  tin- 
centrifuge,  will  clot  on  the  addition  of  tissue  extract.  The  source 
oi  the  thrombogen  has  been  thought  to  be  the  blood-plates,  but 
this  has  not  been  proved.  Thrombokinase  is  not  present  in  the 
circulating  plasma.  In  shed  and  clotting  blood  which  has  nol 
been  allowed  to  come  into  contact  with  cut  tissues  the  only 
possible  sources  of  thrombokinase,  so  far  as  we  know,  are  the 
corpuscles  and  the  blood-plates.  The  red  corpuscles  we  may 
at  once  dismiss,  for  although  the  stromata,  especially  of  nucleated 
corpuscles,  contain  thrombokinase,  or  can  under  artificial  con- 
ditions be  made  to  develop  that  action  on  coagulation  by  which 
we  recognize  its  presence,  not  only  do  they  remain  intact  under 
ordinary  circumstances  during  coagulation,  but  there  is  strong 
evidence,  as  has  already  been  pointed  out,  that  they  do  not 
make  any  essential  contribution  to  the  process.  We  have  hit 
over  the  leucocytes  and  the  platelets,  and  it  is  highly  probable 
that  tioin  both  thrombokinase  is  liberated  in  the  first  moments 
after  blood  is  drawn,  and,  acting  on  the  thrombogen  already 
present  in  the  plasma,  changes  it  into  actual  fibrin-ferment. 
This  surmise  is  strengthened  by  the  fact  that  in  freshly-shed 
mammalian  blood  extensive  destruction  of  blood-plato  takes 
place.  It  has  also  been  shown  that  the  blood  of  the  crayfish, 
which  coagulates  with  extreme  rapidity,  contains  certain  colour- 
less corpuscles  which,  immediately  it  is  withdrawn,  break  up 
with  explosive  suddenness,  and  that  substances  which  hinder  the 
breaking  up  of  these  corpuscles  restrain  coagulation  (Hardy). 
In  the  blood  of  another  crustacean  Lunulas,  the  kingcrab, 
coagulation  is  preceded  by  an  agglutination  oi   the   leucocytes 


THE  CIRCU1   \TING  LIQUIDS  01     till    BOD"i  37 

which  exhibil   amoeboid  movements.     They  become  entangled 
by   the   interlacing  of    the    pseudopodia   which    they   protrude 
(I..  Loeb).     In  the  blood  of  some  mammals  (rabbit)  many  leuco 
cytes,  especially  the  polymorphonuclear  leucocytes,  disappear, 

but  in  man,  the  pig,  and  the  OX  this  is  not  the  case  It  must  be 
remembered,  however,  that  t lie  leucocytes  in  shed  blood,  with- 
out actually  being  destroyed,  may,  under  the  influence  of  what 
is  tor  them  a  foreign  environment,  undergo  changes  which  permit 
the  escape  of  thrombokinase  and  other  substances.  Further, 
the  white  layer  or  '  bully  coat  '  which  tops  the  tardily-formed 
clot  of  horse's  blood,  and  consists  of  the  lighter,  and 
therefore  more  slowly  sinking,  platelets  and  white  corpuscles, 
causes  clotting  in  otherwise  incoagulable  liquids  like  hydrocele 
fluid  much  more  readily  than  the  red  portion  of  the  clot,  and 
yields  far  more  of  Schmidt's  fibrin-ferment  on  treatment  with 
alcohol. 

In  blood  collected  in  paraffined  vessels,  so  as  to  delay  clotting, 
and  immediately  centrifugalized,  coagulation  is  seen  to  begin  in 
and  around  the  layer  of  white  elements,  and  then  to  spread 
upwards  in  the  stratum  of  plasma  and  downwards  in  the  stratum 
of  erythrocytes. 

Thrombokinase  has  not  only  been  shown  to  exist  in  the 
leucocytes,  the  platelets,  and  the  stromata  of  the  coloured 
corpuscles,  but,  as  already  stated,  in  all  tissues  hitherto  examined. 
Under  ordinary  circumstances  it  appears  that  a  larger  amount 
of  thrombogen  is  liberated  or  is  already  present  in  shed  blood 
than  can  be  changed  into  thrombin  by  the  thrombokinase  set 
free,  since  serum  contains  a  surplus  of  thrombogen  in  addition 
to  the  fully-formed  ferment.  This  is  shown  by  the  fact  that  the 
activity  of  a  given  quantity  of  serum  in  causing  the  coagulation 
of  a  plasma  not  spontaneously  coagulable  or  of  a  fibrinogen 
solution  is  increased  by  the  addition  of  tissue  extract  (containing 
thrombokinase). 

The  thrombin  of  any  particular  kind  of  vertebrate  blood  has 
no  marked  specific  action — that  is,  will  cause  coagulation  in 
solutions  of  fibrinogen  or  plasma  of  very  different  origin.  For 
example,  the  sera  of  all  vertebrates  hitherto  investigated  induce 
clotting  in  goose's  plasma.  On  the  other  hand,  it  appears  that 
a  greater  degree  of  specificity  exists  in  the  case  of  the  thrombo- 
kinase and  thrombogen,  the  specificity  being  absolute  in  some 
cases,  relative  in  others.  That  is  to  say,  the  thrombokinase  of 
one  animal  may  activate  the  thrombogen  of  an  animal  of  another 
group,  while  it  may  fail  to  activate  the  thrombogen  of  an  animal 
belonging  to  a  third  group.  But  it  will  always  activate  the 
thrombogen  of  an  animal  of  the  same  kind. 

To  sum  up,  we  may  say  that  when  blood  is  shed  fibrin-ferment 


,S8  I    1/  /  \v  //.  OF  PHYSIOLOGY 

[thrombin)  is  rapidly  formed  by  the  action  of  thrombokinase, 
liberated  from  the  leucocytes,  the  blood-plates,  and  possibly  to  some 
extent  from  the  erythrocytes,  upon  thrombogen,  already  present  in 
the  circulating  plasma.  Further  and  this  is  of  great  practical 
importance  since  no  vessel  is  opened  under  ordinary  circumstances 
except  through  a  wound  in  the  overlying  structures,  the  cut  tissues 
supply  a  store  of  thrombokinase  at  the  point  where  it  is  required  to 
aid  in  the  stanching  of  the  wound.  Calcium  is  essential  to  the  reac- 
tion by  which  thrombogen  and  thrombokinase  form  fibrin-ferment. 
l>ut  is  not  necessary  for  that  action  of  fibrin-ferment  on  fibrinogen 
by  which  fibrin  is  produced  (Practical  Exercises,  pp.  55-57). 

Both  thrombogen  and  thrombokinase  have  close  relations  with 
a  substance  or  substances  belonging  to  the  group  of  nucleo- 
proteins.  If  they  are  not  actually  nucleo-proteins,  they  cling 
to  them  with  such  tenacity  that  it  is  not  easy  by  ordinary  means 
to  separate  them.  Thus  nucleo-protein  can  be  obtained  from 
solutions  of  fibrin-ferment,  and,  by  appropriate  treatment  and 
in  the  presence  of  proper  conditions,  solutions  of  nucleo-protein 
can  be  made  to  influence  coagulation  in  the  way  characteristic 
of  fibrin-ferment.  Nucleo-proteins  are  contained  in  the  nuclei 
and  protoplasm  of  cells,  and  have  been  prepared  from  the 
thymus,  testis,  kidney,  lymphatic  glands,  and  other  organs,  by 
precipitating  their  watery  extracts  with  dilute  acetic  acid  (Wool- 
dridge),  or  by  extracting  with  sodium  chloride  and  then  pre- 
cipitating with  excess  of  water  (Halliburton).  The  precipitated 
nucleo-protein  can  be  dissolved  in  dilute  sodium  carbonate 
solution.  When  it  is  injected  slowly  or  in  small  amount  into 
the  veins  of  an  animal,  it  abolishes  for  a  time  the  power  of  coagula- 
tion of  the  blood  ;  and  when  this  '  negative  phase,'  as  it  is  called, 
has  been  once  established,  even  a  very  large  and  rapid  injection 
produces  no  further  effect,  possibly  because  an  antibody  which 
neutralizes  the  action  of  thrombokinase  has  been  produced. 
If,  however,  a  considerable  quantity  of  the  solution  lias  been 
injected  at  the  first,  the  result  is  very  different  :  extensive 
intravascular  clotting  instantly  ensues  ;  the  animal  dies  in  a  few 
minutes;  and  the  right  side  of  the  heart,  the  venae  cavae,  the 
portal  vein,  and  perhaps  the  pulmonary  arteries,  may  be  found 
choked  with  thrombi.  Here  the  injected  thrombokinase  is 
responsible  for  the  clotting,  thrombogen  and  calcium  being 
already  present.  Curiously  enough,  intravascular  coagulation 
fails  to  be  produced  in  a  certain  proportion  of  cases  when  albino 
animals  are  injected  with  nucleo-protein  from  pigmented  animals. 
while  there  is  no  absolute  failure  of  coagulation  when  albinos 
are  injected  with  nucleo-protein  from  albino-,,  and  no  failure 
when  pigmented  animals  are  injected  with  material  either 
from  other  pigmented  animals  or  from  albinos.     Intravascular 


THE  CIRCU1   ITING  LIQUIDS  OF  THE  BODY  v> 

[illation  is  especially  striking  in  birds  on  injection  <>l   tis 
extracts. 

To  a  certain  extent  the  action  of  nncleo-protein  in  coagula- 
tion can  be  imitated  by  other  substances  of  animal  origin,  such 
as  the  venoms  of  some  vipers  (Martin),  and  even  by  certain 
artificial  products  of  the  laboratory,  the  synthesized  colloids  of 
Grimaux,  which,  when  injected  into  the  blood,  produce  the  same 
phenomena  of  intravascular  coagulation  down  to  the  finest  detail 
and  including  the  negative  phase.  It  is  not  known  whether  these 
substances  act  on  the  blood-plates,  leucocytes,  or  other  cells, 
and  thus  cause  an  increased  production  or  an  increased  liberation 
of  one  or  more  of  the  precursors  of  fibrin-ferment,  or  whether 
they  take  part  directly  in  its  formation.  But  there  is  some 
evidence  that  the  venoms  which  favour  coagulation  do  so  in 
virtue  of  their  containing  a  kinase.  On  the  other  hand,  cobra- 
venom  prevents  coagulation  by  means  of  an  antikinase — that  is, 
a  substance  which  antagonizes  the  action  of  kinase,  and  so 
hinders  the  formation  of  fibrin-ferment.  It  does  not  contain 
an  antithrombin — that  is,  a  body  which  will  prevent  the  action 
of  fibrin-ferment  already  formed  (Mellanby). 

So  far  we  have  been  considering  the  problem  of  coagulation 
as  if  all  the  data  for  its  solution  could  be  obtained  by  a  study  of 
the  blood  itself.  In  other  words,  our  main  business  up  to  this 
point  has  been  the  explanation  of  coagulation  in  the  shed  blood  ; 
it  has  been  only  incidentally,  and  with  the  object  of  casting  light 
on  the  question  of  extravascular  clotting,  that  we  have  touched 
on  the  coagulation  of  the  blood  within  the  living  vessels.  It  is 
not  possible  here  to  adequately  discuss,  nor  even  to  define,  the 
differences  between  the  two  problems.  All  we  can  do  is  to  warn 
the  student,  and  to  emphasize  our  warning  by  one  or  two  illus- 
trations, that  valuable  as  is  the  knowledge  derived  from  experi- 
ments on  extravascular  coagulation,  it  would  be  totally  mis- 
leading if  applied  without  modification  to  the  circulating  blood. 
For  instance,  we  have  recognized  in  the  leucocytes  and  blood- 
plates  an  important  source  of  the  thrombokinase  which  plays  so 
great  a  part  in  the  clotting  of  shed  blood  ;  but  we  may  be  sure 
that  leucocytes  and  blood-plates  are  constantly  breaking  down 
in  the  lymph  and  the  blood,  and  we  have  to  inquire  how  it  is 
that  coagulation  does  not  occur,  except  in  disease,  within  the 
vessels.  Calcium  is  not  wanting  to  the  circulating  plasma, 
fibrinogen  is  not  wanting,  and  it  has  already  been  mentioned 
that  thrombogen  exists  in  perfectly  fresh  and,  as  we  may  say, 
still  living  blood.  Why,  then,  does  it  not  coagulate  ?  Some 
have  said  that  coagulation  is  '  restrained  '  by  the  contact  of  the 
living  walls  of  the  bloodvessels  ;  but  although  it  is  certain  that 
the  contact  of  foreign  matter — and  all  dead  matter  is  foreign  to 


40  I   M  INUAL  OF  PHYSIOLOGY 

Living  cells    does  hasten  the  destruction  of  leucocytes  and  blood- 

plates  or  thai  alteration  in  them  on  which  the  liberation  of  the 

precursors  oi  the  fermenl  depends,  it  is  evident  thai  it  is  just  this 

restraining'  influence  oi   the  vessels,  if  it  is  due  to  anything 

more  than  the  mere  smoothness  of  their  endothelial  lining,  which 
has  to  be  explained.      The  best  answer  which  <  an  he  given  to  the 

question  is:  First,  that  the  quantity  of  thrombokinase  free  in 

the  plasma  at  any  given  time  must  he  small,  since  no  evidence 
oi  its  presence  in  fluoride  plasma  can  he  obtained.  If  thrombo- 
kinase is  liberated  in  the  circulating  blood,  we  may  assume  that 
it  is  changed  into  some  inactive  substance  or  quickly  eliminated. 
And  it  appeals  that,  unlike  the  true  ferments,  thrombokinase 
acts  quantitatively — i.e.,  in  proportion  to  its  amount — -upon 
thrombogen.  Second,  an  antithromhin  exists  in  the  circulating 
plasma,  and  even  if  fully  formed  fibrin-ferment  were  present,  it 
could  not  cause  coagulation  until  the  antithromhin  had  been 
neutralized.  This  antithromhin  is  probably  not  manufactured 
in  the  blood,  or  at  least  not  exclusively  in  the  blood,  but  in  the 
tissues,  and  there  is  no  reason  to  deny  the  vessels  themselves  a 
share  in  its  production,  even  if  its  presence  has  not  hitherto  been 
demonstrated  in  the  internal  coat  (L.  Loeb).  So  that  living 
Mood  within  the  living  vessels  may  be  said  to  be  acted  upon  by 
two  sets  of  influences,  one  tending  to  favour  coagulation,  the 
other  to  oppose  it.  Under  normal  conditions,  the  processes  that 
make  for  coagulation  never  obtain  the  upper  hand.  But  anything 
which  interrupts  the  circulation,  and  consequently  the  free  inter- 
change between  blood  and  tissues,  interferes  with  the  elimination 
or  neutralization  of  the  precursors  of  fibrin-ferment,  and  with 
the  entrance  of  the  substances  that  render  the  fully-funned 
ferment  inactive.  In  the  clotting  of  extravascular  plasma,  free 
from  corpuscles,  we  may  indeed  see  the  continuation,  under 
modified  conditions,  of  a  normal  process  always  going  on  within 
the  bloodvessels.  In  the  lungs  it  would  seem  that  the  forces 
which  favour  coagulation  are  feeble,  or  the  forces  thai  resisl  it 
strong,  for  blood,  after  passing  many  times  through  the  pul- 
monary circulation  without  being  allowed  to  enter  the  systemic 
vessels,  loses  its  power  of  clotting. 

The  liver  is  another  organ  whose  relations  to  the  coagulation 
of  the  blood  are  peculiar.  We  have  already  mentioned  that  the 
injection  of  commercial  peptone,  which  consists  chiefly  of  pro- 
teoses, into  the  blood  of  dogs  causes  it  to  lose  its  coagulability. 
The  effect  gradually  passes  away,  till  after  some  hours  the  01  iginal 
power  of  coagulation  is  restored  (p.  55).  The  liver  is  known 
to  be  intimately  concerned  in  the  production  of  this  remarkable 
resultj  for  if  the  circulation  through  it  be  interrupted,  the  injec- 
tion ot  proteose  is  ineffective.     Further,  if  a  solution  oi  proteose 


THE  CIRCULATING  LIQUIDS  OF  im    BODY  41 

Is  artificially  circulated  through  an  excised  liver,  a  substance 
[perhaps  an  antithrombin)  Ls  formed  which  is  capable  oi  sus 
pending  the  coagulation  of  blood  outside  of  the  body,  a  property 
which  proteoses  themselves  do  not  possess,  or  possess  only  in 
slight  degree.  It  is  not  believed  that  the  proteose  is  actually 
changed  into  this  anticoagulant  substance,  but  rather  that  the 
liver  cells  produce  it  as  a  '  reaction  '  to  the  presence  of  the  foreign 
substance,  being  perhaps  stimulated  in  some  way  by  the  cir- 
culating proteose.  In  part  the  abnormally  great  alkalinity  oi 
the  peptone  blood,  due  to  the  excess  of  alkali  secreted  by  the 
liver,  is  responsible  tor  its  slow  coagulation.  Under  certain  con 
ditions,  some  of  which  are  known  and  others  not,  the  injection 
even  of  one  or  other  of  the  purified  proteoses  causes  not  retarda- 
tion, but  hastening,  of  coagulation  ;  and  if  this  has  been  the 
result  of  a  first  injection,  a  second  is  equally  unsuccessful.  It 
is  possible  that  by  an  effort  of  the  organism  to  restore  the 
normal  coagulability  of  the  blood,  on  which  its  very  existence 
depends,  substances  which  favour  coagulation  are  produced,  and 
that  the  result  of  an  injection  of  proteose  is  determined  by  the 
relative  amount  of  coagulant  and  anticoagulant  secreted  in  a 
given  time.  Protamins  (products  obtained  from  the  ripe  milt  of 
certain  fishes,  and  believed  to  be  the  simplest  proteins)  exert, 
when  injected  intravenously,  a  retarding  influence  on  coagula- 
tion, and  lower  the  blood-pressure,  just  as  albumoses  do  (Thomp- 
son). Even  serum  -  albumin  and  serum  -  globulin  possess  this 
property  in  some  degree.  All  these  substances  also  cause  a 
diminution  in  the  number  of  leucocytes  in  the  blood  owing,  in 
the  case  of  albumose  at  any  rate,  to  their  accumulation  in  the 
abdominal  vessels,  and  not  to  any  actual  destruction  of  them. 

The  Chemical  Composition  of  Blood. 

The  serum  of  coagulated  blood  represents  the  plasma  minus 
fibrinogen  ;  the  clot  represents  the  corpuscles  plus  fibrin.     Thus  : 

Plasma  —  Fibrin  (ogen)  =  Serum. 

Corpuscles+  Fibrin=Clot. 

Plasma+  Corpuscles  =  Serum  +  Clot= Blood. 

Bulky  as  the  clot  is,  the  quantity  of  fibrin  is  trifling  (02  to  0-4  per 
cent,  in  human  blood).  The  plasma  contains  about  10  per  cent. 
of  solids,  the  red  corpuscles  about  40  per  cent.,  the  entire  blood 
about  20  per  cent. 

Serum  contains  8  to  9  per  cent,  of  proteins,  about  o-8  per  cent. 
of  inorganic  salts,  and  small  quantities  of  neutral  fats,  soaps, 
cholesterin  esters,  lecithin,  urea,  kreatin,  dextrose,  lactic  acid, 
and  other  substances.  The  chief  proteins  are  serum-all  nun  in  and 
serum-globulin.     In  the  rabbit  the  former,  in  the  horse  the  latter. 


42  A   MANUAL  OF  PHYSIOLOGY 

is  the  more  abundant  ;  in  man  they  exist  in  no1  far  from  equal 
amount.  A  small  quantity  of  nucleo-frotein  (which  is  either  the 
fibrin-ferment  <>r  is  closely  united  with  it)  and  of  fibrino-globulin 
(which  some  consider  a  soluble  product  formed  from  fibrinogen 
in  clotting)  is  also  present.  Ferments  which  cause  hydrolysis 
oi  proteins  and  carbohydrates,  possibly  a  fermenl  (lipase)  which 
acts  upon  fats,  and  certain  oxidizing  ferments  (oxydases),  have 
also   hem  demonstrated.     The  chemical  nature  of  the   bodies 


Fig.  5. — Diagram  showing  Relative  Quantity  of  Solids  and  W"  x  i  1  r  in  Red 

Corpuscles  and  Plasma. 

which  confer  on  serum  or  plasma  its  specific  hemolytic,  agglu- 
tinating, precipitating,  and  bactericidal  properties  has  not  been 
definitely  determined. 

The  quantitative  composition  of  serum,  especiallv  as  regards  the 
inorganic  salts,  is  remarkably  constant  in  animals  of  the  same 
species,  and  even  in  animals  of  different  species  belonging  to  the 
same,  or  to  not  very  widely-separated,  natural  groups.  In  cold- 
blooded animals  the  serum-albumin  is  scantier  than  in  mammals, 
the  globulin  relatively  more  plentiful. 

Serum-albumin  belongs  to  the  class  of  native  albumins.  It  has 
been  obtained  in  a  crystalline  form  from  the  serum  of  horse's  blood. 
It  is  soluble  in  distilled  water,  and  is  not  precipitated  by  saturating 
its  solutions  with  certain  neutral  salts.  Heated  in  neutral  or 
slightly  acid  solution,  it  coagulates  first  at  73  °,  then  at  77  .  then  at 
840  C.  Although  this  is  not  of  itself  sufficient  proof,  there  is  other 
evidence  that  it  consists  of  a  mixture  of  proteins. 

Serum-globulin  belongs  to  the  globulin  group  of  proteins.  When 
heated,  it  coagulates  at  about  750  C.  (p.  8).  It  is  insoluble  in  dis- 
tilled water,  and  is  precipitated  by  saturation  with  such  neutral 
salts  as  magnesium  sulphate  or  by  half-saturation  with  ammonium 
sulphate.  It  has  been  shown  that,  as  thus  obtained,  it  is  uol  a 
single  substance,  but  a  mixture  of  at  least  two  proteins  —eu-globulin, 
which  can  be  precipitated  from  its  saline  solution  by  dialyzing  off 
the  salts,  and  pseudo-globulin,  which  cannot  be  so  precipitated. 

Of  the  inorganic  salts  of  serum,  the  most  important  are  sodium 
chloride  and  sodium  carbonate.  Small  amounts  o\  potassium, 
calcium,  and  magnesium,  united  with  phosphoric  acid  or  chlorine. 
and  a  trace  of  a  fluoride,  are  also  present.  A  portion  of  the  sails  is 
loosely  combined  with  the  proteins. 

The  Red  Corpuscles  consist  of  rather  less  than  60  per  cent, 
of  water  and  rather  more  than  40  per  cent,  of  solids.  Of  the 
solids  the  pigment  haemoglobin  makes  up  about  90  per  cent.  ; 
the  proteins  and  nucleo-protein  of  the  stroma  about  7  per 
cent.  ;  lecithin  and  cholesterin  2  to  3  per  cent.  ;  inorganic  salts 
(which   vary  greatly   in   their  relative  proportions  in  different 


THE  CIRCV1   ITING  LIQUIDS  OF  THE  BODY  43 

animals,  but  in  man  consist  chiefly  of  phosphates  and  chloride 
of  potassium,  with  a  much  smaller  amount  of  sodium  chloride) 
about  1  ]  ><  1  cent.  There  is  evidence  thai  a  portion  of  the  salts  is 
more  firmly  combined  than  the  rest,  so  1  hat,  even  after  the  action 
of  the  most  energetic  taking  agents,  this  fraction  remains  attached 
to  the  stroma. 

Hemoglobin.    -Of  all  the  solid  constituents  of  the  blood,  haemo- 
globin is  present  in  greatest  amount,  constituting,  as  it  does,  no  less 

than  [3  per  cent.,  by  weight,  of  that  liquid.  It  is  an  exceedingly 
complex  body,  containing  carbon,  hydrogen,  nitrogen,  and  oxygen  in 
much  the  same  proportions  in  which  they  exist  in  ordinary  proteins 
(p.  1).  Iron  is  also  present  to  the  extent  of  almost  exactly  one-third 
of  1  per  cent.,  and  there  is  also  a  little  sulphur,  the  amount  of  which 
stands  in  a  very  simple  relation  to  the  quantity  of  iron  (1  atom  of 
iron  to  3  of  sulphur  in  dog's  haemoglobin,  and  1  atom  of  iron  to 
2  of  sulphur  in  the  ha-moglobin  of  the  horse,  ox,  and  pig).  Haemo- 
globin is  made  up  of  a  protein  element  which  contains  all  the  sulphur 
and  a  pigment  which  contains  all  the  iron,  the  protein  constituting 
by  far  the  larger  portion  of  the  gigantic  molecule,  whose  weight  has 


Fig.  6. — Diagram  of  Spectroscope. 

A,  source  of  light  ;  B,  layer  of  blood  ;  C,  collimator  for  rendering  rays  parallel  ; 
D,  prism  :  E,  telescope. 

been  estimated  at  more  than  16,000  times  that  of  a  molecule  of 
hydrogen.  Since  its  percentage  composition  is  still  undetermined 
with  absolute  precision,  it  is  impossible  to  give  an  empirical  formula 
that  is  more  than  approximately  correct.  For  dog's  haemoglobin 
Jaquet  gives  C768H120sN19SSsFeO2i8,  which  would  make  the  molecular 
weight  16,669. 

The  most  remarkable  property  of  haemoglobin  is  its  power 
of  combining  loosely  with  oxygen  when  exposed  to  an  atmo- 
sphere containing  it,  and  of  again  giving  it  up  in  the  presence  of 
oxidizable  substances  or  in  an  atmosphere  in  which  the  partial 
pressure  of  oxygen  (pp.  248,  254),  has  been  reduced  below  a 
certain  limit.  It  is  this  property  that  enables  haemoglobin  to 
perform  the  part  of  an  oxygen-carrier  to  the  tissues,  a  function 
of  the  first  importance,  which  will  be  more  minutely  considered 
when  we  come  to  deal  with  respiration. 

The  bright  red  colour  of  blood  drawn  from  an  artery  or  of 
venous  blood  after  free  exposure  to  air  is  due  to  the  fact  that  the 


44 


A   M.WI     1/    ()!■•   PlIYSIOUHA 


haemoglobin  is  in  the  oxidized  state — in  the  state  <>i  oxyhemo- 
globin, as  it  is  called.  If  the  oxygen  is  removed  by  means  oi 
reducing  agents,  such  ;is  ammonium  sulphide,  or  h\  exposure 
to  the  vacuum  of  an  air-|>nin]>.  the  colour  darkens,  the  blood- 
pigment  being  now  in  the  form  of  reduced  haemoglobin.  In 
ordinary  venous  blood  a  large  proportion  of  the  pigment  is  in 
this  condition,  but  there  is  always  oxyhaemoglobin  presenl  as 
well.  In  asphyxia  (p.  331),  however,  nearly  the  whole  of  the 
oxyhemoglobin  may  disappear. 


B    C 


E   b 


1 

1  II 

"  111 

!'■■'. 

111 

r 

Ill    1 

iiiiii 

11 

ill    111 

Liiiiii 

!■ 

in         in 

III!  ill! 

lUm 

1 

I 

llllllll 

III    N 

111 

1 

■ 

r  13 

IT  1 

iff 

( ).\yli:i'moglol)in 


Reduced  haemoglobin 


Carbonic  oyide 
haemoglobin 


Methaemoglpbin  (in 
ai  id  solution) 


Acid-haematin  (in 
ethereal  solution) 


Alkaline-haematin 


H.-emodn 


Haematoporphyrin 
(in  ai  iii  solution) 


1 1  i  matoporphyrin 
(in  alkaline  solu- 
tion) 

B     C  D~"  "I  4>™~       "~^~ 

Fir,.  7. — Table  of  Spectra  of  H/emoglobin  and  its  Derivatives. 

Crystallization  of  Hemoglobin.  —  In  the  circulating  blood  the 
haemoglobin  is  related  in  such  a  way  to  the  stroma  of  the  corpu 
that,  although  the  latter  are  suspended  in  a  liquid  readily  1  apable  oi 
dissolving  the  pigment,  it  yet  remains  under  ordinary  circumstances 
strictly  within  them.  In  a  few  invertebrates,  however,  it  is  normally 
in  solution  in  the  circulating  liquid.  As  a  rare  occurrence  haemo- 
globin may  form  crystals  inside  the  corpuscles  (p.  63).  When  it  is  in 
any  way  brought  into  solution  outside  the  body,  it  shows  in  many 
animals,  but  not  in  the  same  degree  in  all,  a  tendency  to  crystalliza- 
tion ;  and  the  ease  with  which  crystallization  can  be  induced  is  in 
inverse  proportion  to  the  solubility  of  the  haemoglobin.     Thus,  it  is 


THE  CIRCUL  ITING  LIQUIDS  OF   THE   BODY 


far  more  difficult  to  obtain  crystals  of  oxyhemoglobin  from  human 
blood  than  from  the  blood  of  the  rat,  guinea-pig,  or  dot;,  whose  blood 
pigment   is  less  soluble  than  that  of  man,  and  for  a  like  reason   the 
oxyhemoglobin  of  the  bird,  the  rabbit,  or  the  frog  crystallizes  ^till 
less  readily  than  that  of  human  blood. 

As  to  the  form  of  the  crystals,  in  the  vast  majority  oi  animals 
they  are  rhombic  prisms  or  needles,  but  in  the  guinea-pig  they  are 
tetrahedra  belonging  to  the  rhombic  system,  and  in  the  squirrel 
six-sided  plates  of  the  hexagonal  system  (Fig.  8). 

Reduced  haemoglobin  can  also  be  caused  to  crystallize,  though 
with  more  difficulty  than 
oxyhemoglobin,  since  it  is 
more  soluble.  Crystals  of  re- 
duced hemoglobin  were  first 
prepared  from  human  blood 
by  Hiifncr,  who  allowed  it 
to  putrefy  in  sealed  tubes 
for  several  weeks. 


When  a  solution  of  oxy- 
hemoglobin of  moderate 
strength  is  examined  with 
the  spectroscope,  two  well- 
marked  absorption  bands 
are  seen,  one  a  little  to  the 
right  of  Fraunhofer's  line 
D,  and  the  other  a  little  to 
the  left  of  E.  A  third 
band  exists  in  the  extreme 
violet  between  G  and  H. 
It  cannot  be  detected  with 
an  ordinary  spectroscope, 
but  has  been  studied  by  the 
aid  of  a  fluorescent  eye- 
piece, by  projecting  the 
spectrum  on  a  fluorescent 
screen,  and  by  photograph- 
ing the  spectrum.  The  ad- 
dition Of  a  reducing  agent,  «■&.  from  ^an; C,  from  cat;  d, from  gmnea-pig 
.  °     °  e,  from  hamster;  /,  lrom  squirrel  (Frev). 

such  as  ammonium  sul- 
phide, causes  the  bands  in  the  visible  spectrum  to  disappear, 
and  they  are  replaced  by  a  less  sharply-defined  band,  of  which 
the  centre  is  about  equidistant  from  D  and  E.  This  is  the 
characteristic  band  of  reduced  haemoglobin.  The  spectrum  of 
ordinary  venous  blood  shows  the  bands  of  oxyhemoglobin. 

Carbonic  oxide  hcemoglobm  is  a  representative  of  a  class  of  haemo- 
globin compounds  analogous  to  oxyhaemoglobin,  in  which  the  loosely- 
combined  oxygen  has  been  replaced  by  other  gases  (carbon  monoxide, 
nitric  oxide)  in  firmer  union.  Its  spectrum  shows  two  bands  very 
like  those  of  oxy haemoglobin,  but  a  little  nearer  the  violet  end. 
Carbonic  oxide  haemoglobin  is  formed  in  poisoning  with  coal-gas. 


Fig.  8. — Oxyhemoglobin  Crystals. 


46 


./   MANUAL  OF   PHYSIOLOGY 


Owing  to  the  great  stability  of  the  compound,  the  haemoglobin  can 
no  longer  be  oxidized  in  the  lungs,  and  death  may  take  place  from 
asphyxia.  It  is.  however,  gradually  broken  up,  and  therefore  arti- 
ficial respiration  may  be  of  use  in  such  cases.  Inhalation  of  oxygen 
.uul  especially  transfusion  of  blood  arc  also  of  great  value. 

Meth  n  is  a  derivative  of  oxyhemoglobin  which  can    be 

formed  from  it  in  various  ways,  e.g.,  by  the  addition  of  ferricyanide 


Oxijllb 

Carbonic  c  x  /  </.•  Hb  I  T, 

Ha i nicch  rcmcift  n  \bana 

i  Htitmalt/ii  i/i/ii/iiiifac/dj] 
Mitlintiiu  tjlfbin  ^ 

ftciiJ '  Ha,  urn  tin  I   Ont, 

Alkaline  Haemal  in    fx     4 
Reduced  Hb.  \ba"d 


Fig.  9. — Diagram  to    show,  the    Chief   Characteristics    by    which    Haemo- 
globin   AND   SOME   OF   ITS    DERIVATIVES    MAY   Bl     RECOGNIZ1  D   Sl'ECTROSCOPI- 

cally.     The  Position  of    the    Middle    of    Each    Band    i-    indk  ah  d 
roughly   BY  a  Vertical  Line. 


of  potassium  or  nitrite  of  amyl  (Gamgee),  by  electrolysis  (in  the 
neighbourhood  of  the  anode),  or  by  the  action  of  the  oxidizing  fer- 
ment '  echidnase  '  in  the  poison  of  the  viper  (Phisalix).  It  very 
often  appears  in  an  oxyhemoglobin  solution  which  is  exposed  to 
the  air.  It  has  been  found  in  the  urine  in  cases  of  hemoglobinuria, 
in  the  fluid  of  ovarian  cysts,  and  in  haematocelcs.  The  stron, 
band  in  its  spectrum  is  in  the  red.  between  C  and  D.  but  nearc 
nearly  in  the  same  position  as  the  band  of  acid-haematin.      Reducing 


J 

Liver  29.5 
Muscles         29-2 

GreatVessc/sHeartklunas  227 
Btnes                 S-2 

Intt  stint  skgenital  crqans  6-3 
Skin  21 
Kidneys  1-6 
Nerve  Centres  t2 
Sp.lt  en               02 

■ 

gp^ 

'                                                ' 

Fig. 


io.     Diagram  to  illustrate  the  Distribution  of  the  Blood  in 
Various  Organs  of  a  Rabbit  (after  Ranke's  Measuri  mi 

The  numbers  are  per  I  the  total  blood. 


agents,  such  as  ammonium  sulphide,  change  methaemoglobin  first 
into  oxyhemoglobin  and  then  into  reduced  haemoglobin.  It  has  by 
some  been  regarded  as  a  more  highly  oxidized  haemoglobin  than 
oxyhemoglobin.  Rebutting  evidence  has.  however,  been  offered  to 
the  effect  that  the  same  quantity  of  oxygen  is  required  to  saturate 
both  pigments,  and  this  evidence  appears  to  be  sound.  The  differ- 
ence lies  rather  in  the  manner  in  which  the  oxygen  is  united  to  the 


nil    <  TRCUL  in.VG  LIQUIDS  <>/■    THE  HODY  47 

haemoglobin  in  the  methaemoglobin  molecule,  than  in  the  quantity 

of  oxygen  which  it  contains.  For  methaemoglobin,  unlike  oxy- 
baemoglobin,  parts  with  no  oxygen  to  the  vacuum,  while,  <>n  the 
Other  hand,  in  the  presence  of  reducing  agents  it  yields  up  its  oxygen 
even  more  readily  than  oxyhemoglobin  docs  (Haldanc)  (p.  251), 

By  the  action  of  acids  or  alkalies  oxyhemoglobin  is  split  into 
a  pigment,  haematin  and  protein  bodies,  of  which  much  the  most 
importanl  is  globin,  a  substance  belonging  to  the  histon  group.  It 
is  easily  precipitated  from  solution  by  ammonia.  As  to  the  pig- 
ment moiety,  when  haemoglobin  is  acted  on  by  acids  in  the  absence 
of  oxygen,  hamochromogen  is  first  formed,  which  then  gradually 
loses  its  iron  and  is  changed  into  haematoporphyrm.  If  oxygen  be 
present,  haematin  is  the  final  product.  By  the  action  of  alkalies 
reduced  haemoglobin  yields  luemochromogcn,  which  is  stable  in  alkaline 
solution,  and  gives  a  beautiful  spectrum  with  two  bands,  bearing 
some  resemblance  to  those  of  oxyhaemoglobin,  but  placed  nearer 
the  violet  end.  The  band  next  the  red  end  is  much  sharper  than 
the  other  (p.  68). 

Hcematin,  the  most  frequent  result  of  the  splitting  up  of  haemo- 
globin, is  generally  obtained  as  an  amorphous  substance  with  a 
bluish-black  colour  and  a  metallic  lustre,  insoluble  in  water,  but 
soluble  in  dilute  alkalies  and  acids,  or  in  alcohol  containing  them. 
In  addition  to  the  iron  of  the  haemoglobin,  haematin  contains  the 
four  chief  elements  of  proteins — carbon,  hydrogen,  nitrogen,  and 
oxygen  (Practical  Exercises,  pp.  67,  68). 

H cematopoy phyriti,  or  iron-free  haematin,  may  be  obtained  from 
blood  or  haemoglobin  by  the  action  of  strong  sulphuric  acid.  Its 
spectrum  in  acid  solution  shows  two  bands,  one  just  to  the  left  of  D, 
the  other  about  midway  between  D  and  E.  Like  oxy haemoglobin,  re- 
duced haemoglobin,  carbonic  oxide  haemoglobin,  methaemoglobin  and 
other  derivatives  of  haemoglobin,  it  also  has  a  band  in  the  ultra-violet. 

Hcemin  is  a  compound  of  haematin  and  hydrochloric  acid,  which 
crystallizes  in  the  form  of  small  rhombic  plates,  of  a  brownish  or 
brownish-black  colour  (Fig.  16,  p.  67).  They  are  insoluble  in  water, 
but  readily  soluble  in  dilute  alkalies  (Practical  Exercises,  p.  71). 

Chemistry  of  the  White  Blood-corpuscles. — The  composition  of 
pus-cells  and  the  leucocytes  of  lymphatic  glands  has  alone  been 
investigated.  The  chief  constituents  of  the  latter  are  a  globulin 
coagulating  by  heat  at  480  to  500  C.  ;  a  nucleo-protein  coagulating 
in  5  per  cent,  magnesium  sulphate  solution  at  750  C,  and  causing 
coagulation  of  the  blood  on  injection  into  the  veins  of  rabbits  ;  an 
albumin  coagulating  at  730  C.  ;  and  a  ferment  with  powers  like  the 
pepsin  of  the  gastric  juice.  In  pus-cells  glycogen  has  been  found, 
and  it  can  be  demonstrated  microchemically  in  the  leucocytes  of 
blood  by  the  iodine  reaction  in  various  conditions.  Fats,  cholesterin, 
and  lecithin  are  also  present,  as  well  as  the  so-called  protagon.  The 
ordinary  inorganic  constituents  have  been  demonstrated — namely, 
potassium,  sodium,  calcium,  magnesium,  and  iron,  united  with  chlorine 
and  phosphoric  acid.     The  total  solids  amount  to  11  to  12  per  cent. 

The  Quantity  of  Blood. — The  quantity  of  blood  in  an  animal 
is  most  accurately  determined  by  the  method  of  Welcker.  The 
animal  is  bled  from  the  carotid  into  a  weighed  flask.  When  blood 
has  ceased  to  flow  the  vessels  are  washed  out  with  water  or  physio- 
logical saline  solution,  and  the  last  traces  of  blood  are  removed 
by  chopping  up  the  body,  after  the  intestinal  contents  have  been 


P  A   MANUAL  OF  PHYSIOLOGY 

cleared  away,  .mil  extracting  it  with  water.  The  extract  and 
washings  are  mixed  and  weighed  ;  a  given  quantity  o\  t  he  mixture 
is  placed  in  a  haematinometer  (a  glass  trough  with  parallel 
sides,  e.g.),  and  a  weighed  tjnaiitity  of  the  unmixed  blood  diluted 
in  a  similar  vessel  till  the  tint  is  the  same  in  both.  From  the 
amount  of  dilution  required,  the  quantity  oi  Mood  in  the  watery 
solution  can  be  calculated.  This  is  added  to  the  amount  ot 
unmixed  blood  directly  determined.  Since  haemorrhage  is  imme- 
diately followed  by  the  entrance  of  liquid  into  the  bloodvessels 
from  the  lymph  and  tissue  fluids,  somewhat  too  high  a  result 
will  be  obtained  if  the  bleeding  is  at  all  prolonged.  It  is  well, 
therefore,  to  take  only  a  moderate  amount  of  blood  for  direct 
estimation,  and  to  compute  the  balance  by  the  colorimetric 
method. 

Many  other  methods  have  been  devised  on  the  principle  of 
injecting  a  known  quantity  of  some  substance  into  the  circulating 
blood,  and  then,  after  an  interval  has  been  allowed  for  mixture, 
determining  the  change  produced  in  a  sample.  Thus,  the  specific 
gravity  of  a  drop  of  blood  having  been  measured,  a  certain 
quantity  of  a  solution  of  sodium  chloride  isotonic  with  the 
plasma  may  be  injected  into  a  vein,  and  the  specific  gravity 
again  determined.  Or  the  electrical  resistance  of  a  small  sample 
of  blood  may  be  measured  before  and  after  injection  of  a  given 
quantity  of  isotonic  salt  solution. 

The  quantity  of  blood  in  the  body  was  greatly  overestimated 
by  the  ancient  physicians.  Avicenna  put  it  at  25  lb.,  and  many 
loose  statements  are  on  record  of  as  much  as  20  lb.  being  losl 
by  a  patient  without  causing  death.  The  proportion  of  blood 
to  body-weight  has  been  found  to  be  in  the  dog  1 :  13,  new-born 
child  1  :  19,  cat  1  :  14,  horse  1  :  15,  frog  1  :  17,  rabbit  1  :  19, 
fowl  1  :  20.  The  total  mass  of  the  blood  in  a  living  man  has  been 
estimated  by  causing  the  person  to  inhale  a  known  volume  oi 
carbon  monoxide  mixed  with  oxygen  or  air,  and  then  determining 
in  a  sample  of  blood  taken  from  the  finger  the  percentage  amount 
to  which  the  haemoglobin  has  become  saturated  with  carbon 
monoxide.  All  that  remains  is  to  estimate  the  volume  of  carbon 
monoxide  (or,  what  is  precisely  the  same  thing,  the  volume  of 
oxygen)  which  100  c.c.  of  blood  will  take  up.  This  latter 
quantity  is  called  the  percentage  oxygen  capacity.  From  these 
data  the  total  volume  of  the  blood  can  be  calculated.  If  the 
volume  is  multiplied  by  the  specific  gravity  the  mass  is  obtained. 

Thus,  if  the  haemoglobin  was  found  to  be  25  per  cent,  saturated 
with  carbon  monoxide  after  the  person  had  absorbed  150  c.c.  of  that 
gas,  the  whole  of  the  blood  would  require  000  c.c.  of  carbon  monoxide 
to  saturate  it  completely.  If  the  percentage  oxygen  capacity  was 
20,  20  c.c.  of  oxygen  or  carbon  monoxide  would  be  needed  to  saturate 


////    CIRCU1   ITING   LIQUIDS  OF   THE   BODY  \g 

too  c.c.  of  blood.     Therefore  the  total  volume  oJ  the  blood  would  be 

6oo>  '""     1,000  c.c.     And   the  mass,   d   the  specific  gravity  was 
20 

1-055.  would  be  3,000x1*055  =  3,165  grammes.  According  to  this 
method  the  blood  on  the  average  in  man  constitutes  only  49  per 
rent.,  or  .,,)-,  of  the  body-weight  (say,  3i  kilogrammes  in  a  70  kilo 
man),  varying  in  fourteen  persons  between  ..}■„  and  fc.  Probably 
these  results  are  somewhat  too  small.  The  amount  has  recently- 
been  estimated  at  ,',,  of  the  body-weight  (Plesch).  But,  upon  the 
whole,  the  method  is  sufficiently  accurate,  as  shown  by  control 
experiments  with  Welcker's  method  on  animals.  In  chlorosis  and 
pernicious  anaemia  the  quantity  of  blood  is  markedly  increased.     In 

one  case  of  pernicious  anaemia  it  amounted  to  —  of  the  body-weight. 
This  is  due  solely  to  increase  in  the  plasma. 

Fig.  10  (p.  46)  illustrates  the  distribution  of  the  blood  in  the 
various  organs  of  a  rabbit.  The  liver  and  skeletal  muscles  each 
contain  rather  more  than  one-fourth  ;  the  heart,  lungs,  and  great 
vessels  rather  less  than  one-fourth;  and [ the  rest  of  the  body 
about  one-fifth,  of  the  total  blood.  Thejddney  and  spleen  of 
the  rabbit  each  contain  one-eighth  of  their  own  weight  of 
blood,  the  liver  between  one-third  and  one-fourth  of  its  weight, 
the  muscles  only  one-twentieth  of  their  weight. 

Lymph  and  Chyle. 

Lymph  has  been  defined  as  blood  without  its  red  corpuscles 
(Johannes  Miiller)  ;  it  resembles,  in  fact,  a  dilute  blood-plasma, 
containing  leucocytes,  some  of  which  (lymphocytes)  are  common 
to  lymph  and  blood,  others  (coarsely  granular  basophile  cells) 
are  absent  from  the  blood.  The  reason  of  this  similarity  appears 
when  it  is  recognised  that  the  plasma  of  tissue-lymph  (p.  407) 
is  derived,  in  large  part  at  any  rate,  from  the  plasma  of  blood 
by  a  process  of  physiological  filtration  (or  secretion)  through  the 
walls  of  the  capillaries  into  the  lymph-spaces  that  everywhere 
occupy  the  interstices  of  areolar  tissue,  while  the  lymph  of  the 
lymphatic  vessels  is  in  turn  derived  from  the  tissue  fluid.  But 
in  addition  to  the  constituents  of  the  plasma,  lymph  appears  to 
contain  certain  substances  produced  in  the  metabolism  of  the 
tissues  which  pass  into  it  directly.  Lymph,  as  collected  from  one 
of  the  large  lymphatic  vessels  of  the  limbs,  or  from  the  thoracic 
duct  of  a  fasting  animal,  is  a  colourless  or  sometimes  yellowish  or 
slightly  reddish  liquid  of  alkaline  reaction.  Its  specific  gravity  is 
much  less  than  that  of  the  blood  (1015  to  1030).  It  coagulates 
spontaneously,  but  the  clot  is  always  less  firm  and  less  bulky  than 
that  of  blood.  The  plasma  contains  fibrinogen,  from  which  the 
fibrin  of  the  clot  is  derived.  Serum-albumin  and  serum-globulin 
are  present  in  much  the  same  relative  proportion  as  in  blood, 
although  in  smaller  absolute  amount.     Neutral  fats,  urea,  and 

4 


50 


A   MANUAL  01    PH\  SIOLOG\ 


sugar  are  also  found  in  small  quantities.  The  inorganic  salts 
are  the  same  as  those  ol  the  blood-serum,  and  exist  in  aboul  the 
same  amount,  sodium  preponderating  among  the  bases,  as  it 
does  in  serum.     The  following  table  shows  the  results  of  anal 

of  lymph  from  man  and  the  horse  (Munk)  : 


Man. 

Horse. 

Water 

95  o  per  cent. 

95'8  per  cent 

[  Fibrin 

o'i      \ 

OI 

( Hher  proteins 

4'1 

2'9 

Solids  > 

Fat 

trace 

r  5'° 

trace      4  J 

Extractives*    - 

o*3 

OI 

Salts 

°'5     J 

ri      i 

Chyle  is  merely  the  name  given  to  the  lymph  coming  from 
the  alimentary  canal.  The  fat  of  the  food  is  absorbed  by  the 
lymphatics,  and  during  digestion  the  chyle  is  crowded  with  fine 
fatty  globules,  which  give  it  a  milky  appearance.  There  may 
also  be  in  chyle  a  few  red  blood-corpuscles,  carried  into  the 
thoracic  duct  by  a  back-flow  from  the  veins  into  which  it  opens. 
Chyle  clots  like  ordinary  lymph,  the  size  of  the  clot  varying 
according  to  the  quantity  of  fat  present  and  enmeshed  by  the 
fibrin.  Wounds  of  the  thoracic  duct  or  of  lymphatics  opening 
into  it  are  occasionally  produced  in  operations  on  the  neck,  and 
when  these  remain  open  chyle  may  be  readily  collected.  In 
samples  obtained  from  a  patient  only  a  week  alter  the  section  of 
a  branch  of  the  duct  during  an  operation  for  the  removal  of 
tubercular  glands,  water  constituted  928-90  parts  in  1,000,  total 
solids  7i'io,  inorganic  solids  6-04,  organic  solids  05-00,  proteins 
18-52,  ether  extract  (fatty  substances)  19-30  (Sollmann).  The 
following  is  the  composition  of  a  sample  analyzed  by  Patorr,  and 
obtained  from  a  fistula  of  the  thoracic  duct  in  a  man  : 


Water 

Solids 

Inorganic 
Organic 

I  Yotrills 

Fate  - 
Cholestei  in 

Lecithin 


9534 

65 

4°' ' 

137 

24*06 

0  6 


The  quantity  of  chyle  flowing  from  the  fistula  was  estimated 
at  as  much  as  3  to  4  kilos  per  twenty-four  hours,  or  nearly  as 

*  The  term  'extractives'  is  somewhat  loosely  applied  to  organic 
substances  which  exisl  in  so  small  an  amount,  or  have  such  indefinite 
chemical  characters  that  they  cannot  be  separately  estimated. 


////    CIRCU1   ITING   LIQUIDS  OF    THE   /;<)DY  51 

much  as  the  whole  of  the  blood.  The  flow  has  been  calculated 
in  various  animals  at  one-eighteenth  to  one-seventh  of  the  l>'><lv- 

weight  in  the  twenty-four  hours.  The  quantity  of  lymph  in 
the  body  is  unknown,  hut  it  must  he  very  great — perhaps  two 
or  three  times  that  of  the  hlood. 

Allied  to  tissue-lymph,  hut  not  identical  with  it,  are  the  fluids 
present  in  health  in  very  small  amount  in  such  serous  cavities 
as  the  pericardium.  The  synovial  fluid  of  the  joints  differs  from 
lymph  especially  in  containing  a  small  amount  of  a  mucin-like 
suhstance. 

The  gases  of  the  blood  and  lymph  will  be  treated  of  in 
Chapter  III.,  the  formation  of  lymph  in  Chapter  V. 

The  Functions  of  Blood  and  Lymph. 

We  have  already  said  that  these  liquids  provide  the  tissues 
with  the  materials  they  require,  and  carry  away  from  them 
materials  which  have  served  their  turn  and  are  done  with. 
These  materials  are  gaseous,  liquid,  and  solid.  Oxygen  is 
brought  to  the  •  tissues  in  the  red  corpuscles  ;  carbon  dioxide 
is  carried  away  from  them  partly  in  the  erythrocytes,  but  chiefly 
in  the  plasma  of  the  blood  and  lymph.  The  water  and  solids 
which  the  cells  of  the  body  take  in  and  give  out  are  also,  at 
one  time  or  another,  constituents  of  the  plasma.  The  heat 
produced  in  the  tissues,  too,  is,  to  a  large  extent,  conducted 
into  the  blood  and  distributed  by  it  throughout  the  body. 
It  is  not  known  whether  the  leucocytes  play  any  part  in  the 
normal  nutrition  of  other  cells,  although  it  is  probable  that 
they  exercise  an  influence  on  the  plasma  in  which  they  live  ; 
but  they  have  important  functions  of  another  kind,  to  which 
it  is  necessary  to  refer  briefly  here. 

Phagocytosis. — Certain  of  the  amoeboid  cells  of  blood  and 
lymph,  and  the  cells  of  the  splenic  pulp,  are  able  to  include 
or  '  eat  up  '  foreign  bodies  with  which  they  come  in  contact,  in 
the  same  way  as  the  amoeba  takes  in  its  food.  Such  cells  are 
called  phagocytes  ;  and  it  is  to  be  remarked  that  this  term 
neither  comprises  all  leucocytes  nor  excludes  all  other  cells, 
for  some  fixed  cells,  such  as  those  of  the  endothelial  lining  of 
bloodvessels,  are  phagocytes  in  virtue  of  their  power  of  sending 
out  protoplasmic  processes,  while  the  small,  immobile,  uninuclear 
leucocyte,  or  lymphocyte,  is  not  a  phagocyte. 

Although  it  is  not  at  present  possible  to  assign  a  physiological 
value  to  all  the  phenomena  of  phagocytosis,  either  as  regards 
the  phagocytes  themselves  or  as  regards  the  organism  of  which 
they  form  a  part,  there  seems  little  doubt  that  under  certain 
circumstances  the  process  is  connected  with   the  removal  of 

4—2 


52  A   M.l.Xi    11.  <)/■   PHYSIOLOGY 

Structures  which  in  the  course  oi  development  have  become 
obsolete,  or  with  the  neutralization  or  elimination  <>!  harmful 

substances  introduced  from  without,  or  formed  by  the  activity 
«ii  bacteria  within  the  tissues.  Dining  the  metamorphosis  oi 
some  larvae,  groups  of  cilia  and  muscle-fibres  may  be  absorbed 
and  eaten  up  by  the  leucocytes.  In  the  metamorphosis  of 
maggots,  for  example,  the  muscular  fibres  of  the  abdominal 
wall,  which  are  used  in  creeping,  and  are  therefore  not  required 
in  the  adult,  degenerate,  and  are  devoured  by  swarms  of  leuco- 
cytes winch  migrate  into  them.  In  the  human  subject  an 
example  of  absorption  of  tissue  by  the  aid  of  leucocytes  is  the 
removal  of  the  necrosed  decidua  rerlexa,  the  fold  of  uterine 
mucous  membrane  which  envelops  the  ovum  (Minot). 

The  behaviour  of  phagocytes  towards  pathogenic  micro- 
organisms is  of  even  greater  interest  and  importance.  Metschni- 
koff  laid  the  foundation  of  our  knowledge  of  this  subject  by  his 
researches  on  Daphnia,  a  small  crustacean  with  transparent 
tissues,  which  can  be  observed  under  the  microscope.  When 
this  creature  is  fed  with  a  fungus,  Monospora,  the  spores  of  the 
latter  find  their  way  into  the  body-cavity.  Here  they  an-  at 
once  attacked  by  the  leucocytes,  ingested,  and  destroyed.  But 
after  a  time  so  many  spores  get  through  that  the  leucocytes  are 
unable  to  deal  with  them  all  ;  some  of  them  develop  into  the 
first  or  '  conidium  '  stage  of  the  fungus  ;  the  conidia  poison  the 
leucocytes,  instead  of  being  destroyed  by  them,  and  the  animal 
generally  dies.  Occasionally,  however,  the  leucocyte  are  able 
to  destroy  all  the  spores,  and  the  life  of  the  Daphnia  is  preserved. 
This  battle,  ending  sometimes  in  victory,  sometimes  in  defeat, 
is  believed  by  Metschnikoff  to  be  typical  of  the  struggle  which 
the  phagocytes  of  higher  animals  and  of  man  seem  to  engage 
in  when  the  germs  of  disease  are  introduced  into  the  organism. 
He  supposes  that  the  immunity  to  certain  diseases  posse^ 
naturally  by  some  animals,  and  which  may  be  conferred  on 
others  by  vaccination  with  various  protective  substances,  is, 
to  a  large  extent,  due  to  the  early  and  complete  success  of  the 
phagocytes  in  the  fight  with  the  bacteria  ;  and  that  in  rapidly- 
fatal  diseases — such  as  chicken-cholera  in  birds  and  rabbits, 
and  anthrax  in  mice — the  absence  of  any  effective  phagocyt<>>i> 
is  the  factor  which  determines  the  result.  Others  have  laid 
stress  on  the  action  of  protective  substances  supposed  to  exist 
in  the  living  plasma  itself,  although  only  as  yet  demonstrated  in 
the  scrum.  It  is  possible  that  such  substances  are  manufactured 
by  the  leucocytes,  and  either  given  nil  by  them  to  the  plasma  by 
a  process  of  '  excretion,'  or  liberated  by  their  complete  solution. 

The  most  recent  investigations  go  to  show  that  Mctschnikoffs 
phagocytic  theory  of  immunity  requires  modification,  at  any 


THE  CIRCU1   ITING  LIQUIDS  GF  THE  BODY  53 

rate  in  the  case  of  the  higher  animals  and  man,  although  the 
brilliant  biological  observations  on  which  i(  was  originally  buiU 
retain  all  their  value.  He  supposed  that  in  the  immunizing 
process  the  leucocytes  underwent  certain  changes,  acquired,  so 
to  speak,  a  sort  of  '  education  '  that  enabled  them  to  cope  with 
bacteria  against  which  they  were  previously  powerless.  It  seems 
more  probable  that  in  the  presence  of  the  substances  that  confer 
immunity,  not  only  the  leucocytes,  but  other  cells,  are  stimulated 
to  produce  bodies  which  cut  short  the  life,  or  inhibit  the  growth, 
of  the  bacteria  (alexins),  or  prepare  them  for  being  taken  up  by 
the  phagocytes  (opsonins).  It  has  been  shown  that  bacteria 
which  have  been  in  contact  with  serum  containing  the  appro- 
priate opsonins  are  taken  up  readily  by  leucocytes  washed  free 
from  serum  constituents  by  physiological  salt  solution,  whereas 
the  washed  leucocytes  either  do  not  ingest  bacteria  which  have 
not  been  acted  on  by  serum,  or  take  them  up  in  much  smaller 
numbers.  There  is  some  evidence  that  in  certain  bacteiial 
infections — for  example,  chronic  furunculosis,  a  condition  in 
which  crops  of  boils  continue  to  appear — the  grip  of  the 
bacteria  on  the  body  is  perpetuated  by  a  deficiency  in  the 
amount  or  in  the  activity  of  opsonins  capable  of  acting  specifi- 
cally upon  the  micro-organisms  in  question.  A  numerical  ex- 
pression, which  in  certain  cases,  perhaps,  gives  a  measure  of  the 
patient's  resistance  to  the  infection,  has  been  worked  out  by 
Wright  under  the  name  '  opsonic  index.'  This  index  is  the  ratio 
between  the  average  number  of  bacteria  taken  up,  under  certain 
fixed  conditions,  by  each  polymorphonuclear  leucocyte  in  an 
emulsion  made  with  the  patient's  serum,  and  the  average  number 
taken  up  by  similar  leucocytes  in  an  emulsion  made  with  normal 
serum.  The  significance  of  this  index,  and  even  the  practicability 
of  the  methods  used  to  ascertain  it,  are  still  the  subject  of 
lively  discussion. 

Diapedesis. — The  fact  that  leucocytes  can  pass  out  of  the 
bloodvessels  into  the  tissues  has  a  very  important  bearing  on 
the  subject  of  phagocytosis.  The  phenomenon  is  called  diape- 
desis, and  is  best  seen  when  a  transparent  part,  such  as  the 
mesentery  of  the  frog,  is  irritated.  The  first  effect  of  irritation 
is  an  increase  in  the  flow  of  blood  through  the  affected  region. 
If  the  irritation  continues,  or  if  it  was  originally  severe,  the 
current  soon  begins  to  slacken,  the  corpuscles  stagnate  in  the 
vessels,  and  inflammatory  stasis  is  produced.  The  leucocytes 
adhere  in  large  numbers  to  the  walls  of  the  capillaries,  and 
particularly  of  the  small  veins,  and  then  begin  to  pass  slowly 
through  them  by  amoeboid  movements,  the  passage  taking  place 
at  the  junctions  between,  or  it  may  be  through  the  substance  of, 
the  endothelial  cells.     Plasma  is  also  poured  out  into  the  tissues. 


S4  A  MANUAL  Of  PHYSIOLOGY 

the  whole  forming  an  inflammatory  exudation.  Even  red  blood- 
corpuscles  may  pass  out  of  the  vessels  in  small  numbers.  The 
exudation  may  he  gradually  reabsorbed,  or  destruction  of  tissue 
may  ensue,  and  a  collection  of  pus  he  formed.     The  cells  of  pus 

are  emigrated  leucocytes  (Practical  Exercises,  Chap.  II..  p.  1771. 
Their  emigration  is  connected  with  the  defence  of  the  organism 
against  the  entrance  of  certain  forms  of  bacteria  at  the  seat  of 
injury,  and  with  the  repair  of  the  injured  tissue,  but  the  nature 
of  the  summons  which  gathers  them  there  is  not  yet  clearly 
understood.  It  is  probably  some  sort  of  chemical  attraction 
(chemiotaxis)  between  constituents  of  the  bacteria  or  decom- 
position products  of  the  injured  tissue  on  the  one  hand,  and 
constituents  of  the  leucocytes  on  the  other. 


PRACTICAL  EXERCISES  ON  CHAPTER   I. 

X.B. — In  the  following  exercises  all  experiments  on  animals  which 
would  cause  the  slightest  pain  are  to  be  done  under  complete  ancesthesia. 

1.  Reaction  of  Blood. — (1)  Put  a  drop  of  fresh  dog's  or  ox  blood 
on  a  piece  of  glazed  neutral  litmus  paper  (the  litmus  paper  can  be 
glazed  by  dipping  it  into  a  neutral  solution  of  gelatin  and  allowing 
it  to  dry).  Wash  the  blood  off  in  10  to  30  seconds  with  distilled 
water.  A  bluish  stain  will  be  left,  showing  that  fresh  blood  is  alkaline. 
(2)  Repeat  with  dog's  or  ox  serum.  It  is  not  necessary  to  wash  the 
serum  off,  as  it  does  not  obscure  the  change  of  colour.  (3)  Repeat 
(1)  with  human  blood.  With  a  clean  suture-needle  or  a  good-sized 
sewing-needle  which  has  been  sterilized  in  the  flame  of  a  Bunsen 
burner,  prick  one  of  the  fingers  behind  the  nail.  Bandaging  the 
finger  with  a  handkerchief  from  above  downwards,  so  as  to  render 
its  tip  congested,  will  often  facilitate  the  getting  of  a  good-sized 
drop,  but  for  quantitative  experiments,  like  2,  7,  and  14  (4),  this 
should  not  be  done. 

2  Specific  Gravity  of  Blood — Hammer schlag's  Method. — (1)  Put 
a  mixture  of  chloroform  and  benzol  of  specific  gravity  I'ooo  into  a 
small  glass  cylinder.  Put  a  drop  of  dog's  or  ox  defibrinated  blood 
into  the  mixture  by  means  of  a  small  pipette.  If  the  drop  sinks  add 
chloroform,  if  it  rises  add  benzol,  till  it  just  remains  suspended 
when  the  liquid  has  been  well  stirred.  Then  with  a  small  hydrometer 
measure  the  specific  gravity  of  the  mixture,  which  is  now  equal  to 
that  of  the  blood.  Filter  the  liquid  to  free  it  from  blood,  and  put 
it  back  into  the  stock-bottle.  (2)  Obtain  a  drop  of  human  blood  as 
in  1,  and  repeat  the  measurement  of  the  specific  gravity. 

3.  Coagulation  of  Blood.* — (1)  Take  three  tumblers  or  beakers, 
label  them  o,  /3,  and  7,  and  measure  into  each  100  c.c.  of  water. 
Mark  the  level  of  the  water  by  strips  of  gummed  paper,  and  pour  it 
out.  (If  a  sufficient  number  of  graduated  cylinders  is  available,  they 
may  of  course  be  used,  and  this  measurement  avoided.)  Into  a  put 
25  c.c.  of  a  saturated  solution  of  magnesium  sulphate,  into  /3  25  c.c. 
of  a  1  per  cent,  solution  of  potassium  or  ammonium  oxalate  in 
oq  per  cent,  solution  of  sodium  chloride,  and  into  7   25  c.c.  of  a 

*  This  experiment  requires  two  laboratory  periods,  the  various  blood 
mixtures  being  obtained  during  the  first  and  worked  up  during  the  second. 


PR  \CTH    II    EXERi  TSES  $5 

i  _•  per  cent,  solution  of  sodium  fluoride  in  eg  per  cenl .  sail  solution. 
It  tin-  dog  provided  is  a  large  one,  these  quantities  may  be  .ill 
doubled  ;  for  a  small  dog  they  may  be  all  halved. 

(_')  Insert  a  cannula  into  the  central  end  of  the  carotid  artery  of  a 
dog  anaesthetized  with  morphine*  and  ether,  or  A.C.F.  mixture. t 

/■>  put  a  Cannula  into  an  Artery.  Select  a  glass  cannula  of 
suitable  size,  feel  for  the  artery,  make  an  incision  in  its  course 
through  tlie  skin,  then  isolate  about  an  inch  of  it  with  forceps  or  a 
blunt  needle,  carefully  clearing  away  the  fascia  or  connective  tissue. 
Next  pass  a  small  pair  of  forceps  under  the  artery,  and  draw  two 
ligatures  through  below  it.  If  the  cannula  is  to  be  inserted  into  the 
central  end  of  the  artery,  tie  the  ligature  which  is  farthest  from  the 
heart,  and  cut  one  end  short.  Then  between  the  heart  and  the  other 
ligature  compress  the  artery  with  a  small  clamp  (often  spoken  of  as 
bulldog  '  forceps).  Now  lift  the  artery  by  the  distal  ligature,  make  a 
transverse  slit  in  it  with  a  pair  of  fine  scissors,  insert  the  cannula,  and 
tie  the  ligature  over  its  neck.  Cut  the  ends  of  the  ligature  short. 
If  the  cannula  is  to  be  put  into  the  distal  end  of  the  artery,  both 
ligatures  must  be  between  the  clamp  and  the  heart,  and  the  bulldog 
must  be  put  on  before  the  first  ligature  (the  one  nearest  the  heart) 
is  tied,  so  that  the  piece  of  bloodvessel  between  it  and  the  ligature 
may  be  full  of  blood,  as  this  facilitates  the  opening  of  the  artery. 

(3)  Run  into  a,  /3,  and  7  enough  blood  to  fill  them  to  the  mark. 
Shake  the  vessels,  or  stir  up  once  or  twice  with  a  glass  rod,  to  mix 
the  blood  and  solution. 

(4)  Take  a  small  thin  copper  or  brass  vessel,  and  place  it  in  a 
freezing  mixture  of  ice  and  salt.  Run  into  it  some  of  the  blood 
from  the  artery.  It  soon  freezes  to  a  hard  mass.  Now  take  the 
vessel  out  of  the  freezing  mixture  and  allow  the  blood  to  thaw.  It 
will  be  seen  that  it  remains  liquid  for  a  short  time  and  then  clots. 

(5)  Run  some  of  the  blood  into  a  porcelain  capsule,  stirring  it 
vigorously  with  a  glass  rod.  The  fibrin  collects  on  the  rod  ;  the 
blood  is  defibrinated  and  will  no  longer  clot. 

(6)  Now  let  some  blood  run  into  a  small  beaker  or  jar.  Notice  that 
the  blood  begins  to  clot  in  a  few  minutes,  and  that  soon  the  vessel 
can  be  tilted  without  spilling  it.  Note  the  time  required  for  clotting 
to  occur.  Set  the  coagulated  blood  aside  in  a  cool  place,  and  observe 
next  day  that  some  clear  yellow  serum  has  separated  from  the  clot. 

(7)  Weigh  out  a  quantity  of  Witte's  '  peptone  '  equivalent  to 
o"5  gramme  for  every  kilo  of  body- weight  of  the  dog.  Dissolve  the 
peptone  in  about  twenty  times  its  weight  of  o'o.  per  cent,  salt  solution. 
Put  a  cannula  into  the  central  end  of  a  crural  vein  (p.  200).  Fill  the 
cannula  with  the  peptone  solution  and  connect  it  with  a  burette.  Put 
15  drops  of  the  peptone  solution  into  a  test-tube  labelled  '  Peptone  A.' 
Put  the  rest  into  the  burette  and  see  that  the  connecting  tube  is 
filled  with  the  solution  and  free  from  air.  Run  into  the  test-tube 
about  5  c.c.  of  blood  from  the  cannula  in  the  carotid.  Now  let  the 
peptone  solution  flow  from  the  burette  into  the  vein.  Feel  the 
pulse  over  the  heart  as  the  solution  is  running  in.  If  the  heart 
becomes  very  weak,  stop  the  injection  ;  otherwise  the  animal  may 
die  from  the  great  lowering  of  blood-pressure  (p.  201).     As  soon  as  the 

*  One  to  2  centigrammes  of  morphine  hydro-chlorate  per  kilogramme  of 
body-weight  should  be  injected  subcutaneously  about  half  an  hour  before 
the  operation.  Ten  c.c.  of  a  2  per  cent,  solution  is  sufficient  for  a  dog  of 
good  size.  Note  that  diarrhoea  and  salivation  are  caused  by  such  a  dose. 
For  directions  for  fastening  the  dog  on  the  holder,  see  footnote  on  p.  1S6. 

t  A  mixture  of  1  part  of  alcohol,  2  of  ether,  and  3  of  chloroform. 


56 


A   M  \NV  11    OF  PHYSIOLOGY 


injection  is  finished,  draw  oil  a  sample  of  5  c.c.  of  blood  into  a  test- 
tube  labelled  '  Peptone  IV  and  let  ii  stand.  In  ten  minutes  collect 
five  further  samples  of  5  c.c.  ('Peptone  C,  D,  E,  F.  <•  '),  and  a 
large  one,  H  ;  in  half  an  hour  another  set  of  five  small  samples, 
and  al  as  long  ;m  interval  as  possible  thereafter  five  more.  Now 
letting  the  dog  bleed  to  death,  observe  thai  the  flow  of  blood  is 
temporarily  increased  by  pressure  on  the  abdominal  walls,  which 
squeezes  it  towards  the  heart,  by  passive  movements  oi  the  hind- 
legs,    and    also    during    the    convulsions    of    asphyxia,    which    soon 

appear.  Add  to  the  peptone 
blood  D  5  c.c.  of  scrum,  to 
little  sodium  chloride  extract  of 
liver,  to  F  a  little  extract  of 
muscle,  and  to  G  1 r,  drops  of  a 
_>  per  cent,  solution  of  calcium 
chloride,  and  put  C,  1).  E,  F.  and 
G  into  a  water  hath  at  400  C. 
Treat  the  other  sets  of  small 
samples  in  the  same  way.  Note 
how  long  each  specimen  takes 
to  clot,  and  report  your  results.* 

(8)  Observe  that  the  blood  in 
a,  ji,  and  >  has  not  coagulated. 
Label  four  test-tubes  '  Oxalate 
A,  B,  C,  D,'  and  put  into  each 
about  5  c.c.  of  the  oxalated 
blood.  Add  to  A  and  B  5  or 
6  drops  of  a  2  per  cent,  solution 
of  calcium  chloride,  to  C  12 
drops,  and  to  I)  as  much  as  there 
is  of  the  blood.  Leave  A  at  the 
ordinary  temperature,  put  the 
other  test-tubes  in  a  water-bath 
at  400  C.,  and  note  when  clotting 
occurs. 

(9)  To  10  c.c.  of  the  fluoride 
blood  add  a  little  more  CaClg 
than  is  required  to  combine  with 
the  excess  of  fluoride  present. 
Label  four  test-tubes  '  Fluoride 
A,  B,  C,  D,'  and  into  each  put 
about  2  c.c.  of  this  '  rccalcified 
fluoride  blood.  To  F.  add  1  c.c. 
liver  extract  ;  to  C  1  c.c.  muscle 
extract,  and  to  D  4  c.c.  water. 
Label  two  more  test-tubes '  Flu- 
oride E  and  1".'      Into  each  put 

2  c.c.  of  the  fluoride  blood  without  CaCl2.  Add  also  to  F  1  c.c.  liver 
extract  and  to  F  i  c.c.  scrum.  Put  all  the  tubes  in  a  bath  at  aboul 
40°C.,  and  observe  in  which  and  in  what  time  coagulation  takes  place. 
(10)  By  means  of  a  centrifuge  (Fig.  11)  separate  the  plasma 
*  Sometimes  the  injection  of  peptone  hastens  coagulation  instead  of 
hindering  it.  It  has  been  asserted  that  this  is  only  the  case  when  small 
doses  are  used  (less  than  0*02  gramme  per  kilo  of  body-weight).  But  in  2 
dogs  out  of  11  a  dose  of  0*5  gramme  per  kilo  has  been  seen  to  hasten  coagu- 
lation, and  in  1  out  of  12  to  leave  it  unaffected  ;  in  the  other  o  coagulation 
was  markedly  retarded. 


Fig.   11. — Centrifuge  (Jung). 
The  four  cylinders  shown  at  the  top  of 
the  figun   are  so  swung  that  they  become 
horizoiit.il  as  soon  as  speed  is  got  up. 


PR  ICTIC  U    EXERCISES  57 

from  the  corpuscles  in  «.  (8,  and  7,  and  also  from  the  peptone 
blood. 

With  the  oxalate  plasma  from  /9,  and  the  fluoride  plasma  from  7, 
repeat  the  observations  in  (8)  and  (9),  using  smaller  quantities  of 
the  plasma,  if  necessary,  in  small  f  est -tubes.  With  the  plasma  from 
a  perform  the  following  experiments:  Put  a  small  quantity  of  the 
plasma  (1  c.c.)  into  four  test-tubes,  labelling  them  '  Magnesium 
Sulphate  A,  B,  C,  D.'  Dilute  B  with  four  times,  C  with  eight  times, 
and  D  with  twenty  times  as  much  distilled  water  as  was  taken  of 
the  plasma.  Observe  in  which,  if  any,  coagulation  occurs,  and  the 
time  of  its  occurrence,  and  report  the  result. 

(n)  With  peptone  plasma  from  H  and  from  the  peptone  blood 
obtained  later  repeat  the  experiments  done  in  (7).  In  addition 
dilute  1  c.c.  of  the  plasma  with  three  volumes  of  water  and  1  c.c. 
of  it  with  ten  volumes  of  water,  and  put  in  the  bath  at  400  C.  Observe 
whether  clotting  occurs. 

If  no  centrifuge  is  available,  the  various  blood-mixtures  must  be 
left  standing  in  a  cool  place  for  12  to  24  hours  till  the  corpuscles 
settle.  The  plasma  can  then  be  siphoned  or  pipetted  off.  Instead 
of  dog's  blood,  the  blood  of  an  ox  or  pig  may  be  obtained  at  the 
slaughterhouse. 

4.  Preparation  of  Schmidt's  Fibrin-ferment. — Precipitate  blood- 
serum  with  ten  times  its  volume  of  alcohol.  Let  it  stand  for  several 
weeks,  then  extract  the  precipitate  with  water.  The  water  dissolves 
out  the  fibrin-ferment,  but  not  the  coagulated  serum  proteins. 

5.  Preparation  of  Tissue  Extracts  containing  Thrombokinase.— 
In  a  dog  or  rabbit  killed  by  bleeding  insert  a  cannula  into  the  lower 
end  of  the  thoracic  aorta.  Fill  the  cannula  with  o-g  per  cent,  salt 
solution  or  water,  and  connect  it  with  a  bottle  also  containing  salt 
solution  or  water.  Wash  out  the  vessels  of  the  lower  portion  of 
the  body,  making  an  opening  in  the  inferior  vena  cava  above  the 
diaphragm  to  allow  the  liquid  to  escape.  For  the  sake  of  cleanli- 
ness, a  cannula  armed  with  a  piece  of  rubber  tubing  should  be 
inserted  for  this  purpose  into  the  inferior  vena  cava.  Continue 
the  injection  till  the  liquid  issues  colourless.  Then  remove  portions 
of  liver  and  muscle.  Mince  each  separately.  Rub  up  with  sand  in 
a  mortar.  Add  o'o.  per  cent,  sodium  chloride  solution  and  rub  up 
again.  Put  into  bottles  and  keep  in  the  ice-chest.  For  use  take 
off  some  of  the  liquid  from  the  top  with  a  pipette,  or  strain  through 
cheese-cloth. 

6.  Serum. — Test  the  reaction,  and  determine,  both  by  the  hydro- 
meter and  the  pyenometer,  or  specific  gravity  bottle,  the  specific 
gravity  of  the  serum  provided,  or  of  the  serum  obtained  in  experi- 
ment 3. 

Serum  Proteins. — (1)  Saturate  serum  with  magnesium  sulphate 
crystals  at  300  C.  The  serum-globulin  is  precipitated.  Filter  off. 
Wash  the  precipitate  on  the  filter  with  a  saturated  solution  of  mag- 
nesium sulphate.  Dissolve  the  precipitate  by  the  addition  of  a 
little  distilled  water,  and  perform  the  following  tests  for  globulins  : 

(a)  Saturate  with  magnesium  sulphate.     A  precipitate  is  obtained. 

(b)  Drop  into  a  large  quantity  of  water,  and  a  ffocculent  precipitate 
falls  down,  (c)  Heat.  Coagulation  occurs.  Determine  the  tempera- 
ture of  coagulation  (p.  8). 

(2)  To  a  portion  of  the  filtrate  from  (1)  add  sodium  sulphate  to 
saturation.  The  serum-albumin  is  precipitated.  (Neither  mag- 
nesium   sulphate   nor   sodium    sulphate   precipitates   serum-albumin 


58 


A   MANUAL  OF  PHYSIOLOGY 


alone,  but  the  double  salt  sodio-magnesium  sulphate   precipit 
it,  and  this  is  formed  when  sodium  sulphate  is  added  to  magnesium 
sulphate.) 

(3)  Dilute  another  portion  of  the  filtrate  from  (1)  with  its  own 
hulk  of  water.  Very  slightly  acidulate  with  dilute  acetic  a*  id,  and 
determine  the  temperature  oi  heat  coagulation. 

(4)  Precipitate  the  serum-globulin  from  another  portion  of  serum 
by  adding  to  it  an  equal  volume  of  saturated  solution  oi  ammonium 
sulphate.  Filter.  Precipitate  the  scrum-albumin  from  the  filtrate 
by  saturating  with  ammonium  sulphate  crystals. 

(5)  Dilute  scrum  with  ten  to  twenty  times  its  volume  of  distilled 
water,  and  pass  through  it  a  stream  of  carbon  dioxide.  The  serum- 
globulin  is  partially  precipitated.  This  is  the  si  art  ing-point  of  a 
method  said  to  be  the  best  for  obtaining  pure  serum-globulin. 

(6)  Acidulate  some  scrum  with  dilute  acetic  acid  and  boil.  Filter 
off  the  coagulum,   and  to  the  filtrate  add  silver  nitrate.     A  non- 


-A 


0.100  mm. 

,—  ilium. 
400  I 


C  Zeiss 

Jena. 


Fig.   12. — Thoma-Zeiss  H.emocytometer. 

M,  mouth-piece  of  tube  G,  by  which  blood  is  sucked  into  S  ;  E,  bead  f< >r  mixing  ; 
a,  view  of  slide  from  above  ;  b,  in  section  ;  c,  squares  in  middle  of  B,  as  seen  under 
microscope. 

protein  precipitate  insoluble  in  nitric  acid  but  soluble  in  ammonia 
indicates  the  presence  of  chlorides. 

7.  Enumeration  of  the  Blood-corpuscles. — Use  the  Thoma-Zeiss 
apparatus  (Fig.  12).  (1)  Suck  a  drop  of  ox  or  dog's  blood  up  into 
the  capillary  tube  S  to  the  mark  1.  Wipe  off  any  blood  which 
may  adhere  to  the  end  of  the  tube.  Then  fill  it  with  Eiayem's 
solution  (p.  18)  or  3  per  cent,  sodium  chloride  to  the  mark  iox. 
This  represents  a  dilution  of  100  times.  Mix  the  blood  and  solution 
thoroughly,  then  blow  out  a  drop  or  two  of  the  liquid  to  remove 
all  the  solution  which  remains  in  the  capillary  tube.  Now  till  the 
shallow  cell  B  with  the  blood  mixture.  Put  the  cover-glass  on, 
taking  care  that  it  does  not  float  on  the  liquid,  but  that  the  cell  is 
exactly  filled.  Put  the  slide  under  the  microscope  (say  Leitz's 
oc.  III.,  obj.  5),  and  count  the  number  of  red  corpus*  les  in  not  less 
than  ten  to  twenty  squares.  Sixteen  squares  is  a  good  routine 
number.  The  greater  the  number  of  squares  counted,  the  nearer 
will  be  the  approximation  to  the  truth.  Now  take  the  average 
number  in  a  square.      The  depth  of  the  cell  i->   , ', (  mm.,  the  area   oi 


PRACTJC  II    EX1  RCTSES  $g 

each  Bquare  ,,',,,  sq.  mm.  The  volume  of  the  column  oi  liquid 
standing  upon  a  square  is  ,,,',,,,  cub.  mm,  One  cub.  nun.  of  the 
diluted  blond  would  therefore  contain  4,000  times  as  many  corpuscles 
.is  one  square.  Hut  the  blood  has  been  diluted  too  times,  there- 
fore 1  cub.  mm.  of  the  undiluted  blood  would  contain  400,000  times 
the  number  of  corpuscles  in  one  square.  Suppose  the  average  for 
.1  square  is  found  to  be  13.  This  would  correspond  to  5,200,000 
corpuscles  in  1  cub.  mm.  of  blood.  Compare  your  result  with  the 
true  number  supplied  by  the  demonstrator.  (2)  Prick  the  finger 
to  obtain  a  drop  of  blood,  and  repeat  the  count  as  in  (1).* 

To  Count  the  While  Corpuscles.  Add  to  r  part  of  blood  9  parts 
of  £  per  cent,  acetic  acid,  in  order  to  lake  the  coloured  corpuscles 
and  render  it  easy  to  see  the  leucocytes. 

8.  Relative  Volume  of  Corpuscles  and  Plasma  by  Haematocrite. — 
(1)  For  practice,  fill  the  two  graduated  glass  tubes  with  the  de- 
fibrinated  blood  of  an  animal.  The  rubber  tube  with  mouthpiece 
supplied  with  the  apparatus  is  to  be  attached  to  the  glass  tube,  and 
the  blood  sucked  up.  Press  the  tip  of  the  index-finger  against  the 
pointed  end,  and  carefully  remove  the  rubber  tube.     Place  the  tube 


Fig.    13. — H.^MATOCRITE. 

A,  hagmotocrite  attachment  with  graduated  tubes  ;  B,  automatic  pipette  for 
filling  the  tubes  (Daland). 


in  the  haematocrite  frame,  blunt  end  outwards — -that  is,  farthest 
from  the  axis  of  rotation — and  then  slip  the  pointed  end  down  into 
position  against  the  spring.  Instead  of  the  rubber  tube,  a  special 
suction  pipette  for  automatically  filling  the  graduated  tubes  may  be 
employed  (Daland).  Attach  the  haematocrite  frame  to  the  centri- 
fuge, and  rotate  till  the  volume  of  sediment  (corpuscles)  ceases  to 
diminish.  The  graduations  are  best  read  with  a  hand  lens.  The 
leucocytes  will  be  seen  to  form  a  thin  whitish  line  proximal  to  the 
column  of  red  corpuscles. 

(2)  Prick  the  finger  or  the  lobe  of  the  ear,  fill  the  tubes  as  in  (1), 
and  centrifugalize.  Everything  must  be  done  as  rapidly  as  possible, 
so  that  the  blood  may  not  clot  till  the  separation  of  plasma  and  cor- 
puscles is  completed.  The  centrifuge  must  rotate  very  rapidly 
(about  10,000  revolutions  a  minute)  for  two  or  three  minutes.  For 
clinical  purposes  it  is  best  to  rotate  the  centrifuge  always  at  the 
same  speed  for  the  same  length  of  time  rather  than  to  aim  at  reaching 
a  constant  length  of  the  column  of  corpuscles.     In  this  way  useful 

*  If  the  tube  has  not  been  properly  filled,  blow  the  blood  out  immedi- 
ately.     On  no  account  permit  it  to  clot  in  the  capillary  tube 


6o  A    MANUA1    OF  PHYSIOLOGY 

comparative  results  can  be  obtained.  K  is  well,  to  avoid  the  risk 
of  accident,  to  rotate  the  centrifuge  under  a  guard. 

9.  Electrical  Conductivity  of  Blood.  -(1)  Fill  a  small  U-tube  with 
blood   u])  to  a  mark.     In  each  limb  insert  a  platinum  electrode* 

connected  with  a  holder,  which  insures  thai  the  electrodi  shall 
always  dip  to  the  same  depth  into  the  tube.  Arrange  the  U-tube 
SO  that  it  is  immersed  at  Leasl  to  the  mark  in  water  ol  constant 
temperature.     Water  running  freely  from  the  cold-water  tap  into 

and  out  of  a  large  vessel  will  have  a  sufficiently  constanl  temperature 
lor  the  purpose.  A  thermometer  must  be  fixed  in  the  water  with 
its  bulb  in  contact  with  the  U-tubc.  Connect  the  electrodes  with  a 
resistance-box  in  the  Wheals!  one's  bridge  arrangemenl  (Fig.  204, 
p.  617),  so  that  the  U-tube  occupies  the  position  ot  the  unknown 
resistance  CD.  Instead  of  the  battery  F,  connect  the  poles  ol  the 
secondary  of  a  small  induction-coil,  arranged  for  an  interrupted 
current,  with  A  and  C,  and  instead  of  the  galvanometer  ( '.  insert  a 
telephone.  The  resistances  AB  and  AD  (the  arms  of  the  bridge) 
will  be  obtained  by  taking  out  two  plugs  from  the  appropriate  part 
of  the  resistance-box.  Whether  the  arms  should  be  equal  (say, 
10  :  10,  100  :  100,  or  1,000  :  1,000  ohms)  or  unequal  (say,  to  :  100, 
or  100  :  1,000,  or  10  :  1,000  ohms)  will  depend  upon  the  resistance 
of  the  tube  of  liquid  to  be  measured.  Take  out  from  the  part  of  the 
box  corresponding  to  BC  a  plug  representing  a  resistance  some- 
thing like  that  which  the  tube  of  blood  is  expected  to  have.  Close 
the  primary  circuit  of  the  induction-coil,  and  apply  the  telephone  to 
the  ear.  A  buzzing  sound  will  be  heard,  which  will  be  louder  the 
farther  from  the  true  resistance  of  the  tube  the  resistance  taken 
out  of  the  box  is.  Go  on  altering  the  resistance  in  the  box  by  taking 
out  or  putting  in  plugs  till  the  sound  disappears,  or  is  reduced  to  a 
minimum.  The  temperature  of  the  water  should  now  be  read  off. 
The  resistance  of  the  tube  of  blood  for  this  temperature  can  easily 
be  calculated  from  the  formula  on  p.  Or;.  It  increases  about 
2  per  cent,  for  each  degree  Centigrade  of  diminution  of  temperature. 
The  conductivity  is  the  reciprocal  of  the  resistance.  By  determining 
once  for  all  the  resistance  of  the  tube  when  filled  with  a  standard 
solution  of  a  salt  whose  conductivity  is  known,  the  specific  conduc- 
tivity of  the  blood  can  be  expressed  in  definite  units,  but  this  is  not 
necessary  for  the  purposes  of  the  student.  Compare  the  resistances 
of  defibrinated  blood,  serum,  o'o.  per  cent,  sodium  chloride  solution, 
and  a  sediment  of  blood-corpuscles  separated  by  centrifugalization. 

(2)  Instead  of  the  resistance-box  a  wire  mounted  on  a  scale  may 
be  used  for  the  bridge  arms  AB,  AD,  the  ends  of  the  wire  being 
connected  at  B  and  D.  A  slider  with  an  insulated  handle  moving 
along  the  graduated  wire  is  joined  by  a  flexible  wire  with  one  pole 
of  the  secondary  coil,  the  other  pole  being  connected  a1  C.  The 
resistance  BC  is  constituted  by  a  rheostat  from  which  a  fixed  resist- 
ance can  be  taken  out.  Instead  of  obtaining  the  minimum  sound  in 
the  telephone  by  varying  the  resistance  BC  in  the  box,  the  measure- 
ment is  made  by  varying  the  position  of  the  slider  ;  in  other  words, 
by  changing  the  ratio  AB  :  AD. 

(3)  If  no  rheostat  is  available  instructive  comparative  measure- 
ments may  still  be  made  with  the  graduated  wire  by  substituting 
for  the  resistance  BC  a  U-tubc  of  another  liquid. 

*  If  the  platinum  electrodes  areoi  good  size  and  the  resistance  oi  the  tube 
of  liquid  considerable,  it  is  not  necessary  to  platinize  them  -/.<•.,  to  cover 
them  by  electrolysis  of  a  solution  of  platinic  chloride  with  a  layer  of 
platinum  black. 


PRAi   IK    III  XI  ff<  TSES  61 

[f  the  tubes  axe  of  the  same  dimensions,  and  the  liquids  with  which 
they  are  filled  are  approximately  a1  the  same  initial  temperature, 
it  is  not  necessary  to  immerse  them  in  water  at  constanl  temperature. 
Ii  is  sufficient  to  place  them  side  by  side  in  the  air.  Perform  the 
following  experiments  in  this  way  : 

(a)  Label  the  lubes  A  and  B.  Fill  them  both  to  the  mark  with 
o"g  percent.  NaCl  solution.  Conned  .is  in  the  figure,  and  move  the 
slider  along  the  wire  till  the  sound  is  a  minimum.  Probably  the  two 
t  ulns  are  not  exactly  of  the  same  dimensions,  and  therefore  the  slider 
will  not  be  exactly  in  the  middle  of  the  wire.  Suppose  it  is  a1 
49*0,   the   total   length  of  the   wire  being   100.     Then  resistanee  of 

49 
A  :  resistance  of  B  :  :  40/0  :  51*0,  i.e.,  resistance  of  A=       resistanee 

of  B.  5i 

(b)  Fill  A  with  defibrinated  blood,  keeping  B  filled  with  NaCl  solu- 
tion, and  repeat  the  measurement.  The  slider  must  now  be  moved 
much  farther  away  from  the  zero  of  the  scale.  Suppose  the  mini- 
mum sound  is  obtained  with  the  slider  at  70' o.     Then  resistance  of 

7     51 
blood  =    x       resistance  of  the  NaCl  solution. 
3     49 

(c)  Compare  in  the  same  way  the  resistance  of  serum  with  that 
of  the  NaCl  solution.  It  will  be  found  much  less  than  that  of  the 
blood. 

(d)  Ccntrifugalize  some  of  the  blood  for  as  long  as  is  convenient, 
and  compare  the  resistance  of  the  blood  from  the  top  of  the  tubes 
and  from  the  bottom  of  the  tubes  with  that  of  the  NaCl  solution. 
The  resistance  of  the  blood  from  the  bottom  of  the  tubes  will  be 
found  much  greater  than  that  of  the  blood  from  the  top. 

10.  Opacity  of  Blood. — Smear  a  little  fresh  blood  on  a  glass  slide, 
and  hold  the  slide  above  some  printed  matter.  It  will  not  be  possible 
to  read  it,  because  the  light  is  reflected  from  the  corpuscles  in  all 
directions,  and  little  of  it  passes  through. 

11.  Laking  of  Blood  by  Chemical  and  Physical  Agents. — (1)  Put  a 
little  fresh  blood  into  three  test-tubes,  A,  B  and  C.  Dilute  A  with  an 
equal  volume,  B  with  two  volumes,  and  C  with  three  volumes,  of 
distilled  water,  and  repeat  experiment  9.  The  print  can  now  be  read 
probably  through  a  layer  of  A,  but  certainly  through  B  and  C,  since 
the  haemoglobin  is  dissolved  out  of  the  corpuscles  by  the  water  and 
goes  into  solution,  the  blood  becoming  transparent  or  laked.  That 
the  difference  is  not  due  merely  to  dilution  can  be  shown  by  putting 
an  equal  quantity  of  blood  in  two  test-tubes,  and  gradually  diluting 
one  with  distilled  water  and  the  other  with  a  o'o.  per  cent,  solution 
of  sodium  chloride,  which  does  not  dissolve  out  the  haemoglobin. 
Print  can  be  read  through  the  first  with  a  smaller  degree  of  dilution 
than  through  "the  second.  Examine  the  laked  blood  with  the 
microscope  for  the  '  ghosts,'  or  shadows  of  the  red  corpuscles.  The 
addition  of  a  drop  or  two  of  methylene  blue  will  render  them  some- 
what more  distinct. 

(2)  Heat  a  little  dog's  or  ox  blood  in  a  test-tube  immersed  in  a 
water-bath.  Put  a  thermometer  in  the  test-tube,  taking  care  that 
there  is  enough  blood  to  cover  the  bulb.  Keep  the  temperature 
about  6o°  C.  In  a  few  minutes  the  blood  becomes  dark  and  laking 
occurs. 

(3)  (a)  Put  a  little  blood  into  each  of  four  test-tubes.  To  one  add 
a  little  ether,  to  another  a  little  chloroform,  to  the  third  dilute 
acetic  acid  in  09  per  cent.  NaCl,  and  to  the  fourth  a  dilute  solution 


62  A   MANUAL  OF   PHYSIOLOGY 

of  bile  salts  (or  of  sodium  taurocholate)  in  09  per  cent.  Na<  1  solution. 
Laking  occurs  in  all. 

(6)  To  5  c.c.  of  blood  add  05  c.c.  of  a  3  per  cent,  solution  of  saponin 
in  eg  per  cent.  NaCl  solution,  and  put  the  mixture  at  400  C.  Laking 
soon  occurs. 

(c)  Using  a  10  per  cent,  dilution  of  blood  (blood  to  which  nine 
volumes  of  NaCl  solution  have  been  added)  or  a  5  per  cent,  suspension 
of  washed  corpuscles  in  NaCl  solution  (i.e.,  a  suspension  of  corpuscles 
which  have  been  washed  free  from  serum  by  being  repeatedly  mixed 
with  NaCl  solution  and  ccntrifugalized),  determine  the  minimum 
dose  of  o"3  per  cent,  saponin  solution  which  will  just  cause  complete 
laking.  Keep  the  tubes  at  about  400  C,  and  observe  them  from 
time  to  time.  Now  add  to  some  of  the  10  per  cent,  dilution  or  the 
5  per  cent,  suspension  of  blood  an  equal  volume  of  serum  from  the 
same  kind  of  blood,  and  repeat  the  determination  of  the  minimum 
dose  of  saponin  necessary  for  laking.  It  will  be  found  that  more 
is  now  required.  The  cholesterin  in  the  serum  neutralizes  the  action 
of  some  of  the  saponin. 

(4)  (a)  Put  1  c.c.  of  blood  into  each  of  two  test-tubes.  To  one  add 
1  c.c.  of  2  per  cent,  aqueous  solution  of  urea,  and  to  the  other  3  c.c. 
Laking  will  take  place  in  the  second,  whether  this  has  been  the  case 
in  the  first  or  not. 

(b)  Repeat  the  experiment  with  a  2  per  cent,  solution  of  urea  in 
o-9  per  cent.  NaCl  solution.  Laking  does  not  occur.  This  shows 
that  the  urea  in  the  first  experiment  did  not  act  as  a  hemolytic  agent. 
Laking  occurred  because  urea  penetrates  the  corpuscles  easily,  and 
therefore,  although  the  freezing-point  of  the  urea  solution  is  not  very 
different  from  that  of  the  NaCl  solution,  its  actual  osmotic  pressure, 
in  relation  to  the  envelopes  of  the  corpuscles,  is  very  much  less, 
and  the  laking  is  really  water-laking. 

(5)  Put  some  blood  into  a  flask  or  test-tube,  cork  up,  and  let  it  stand 
till  it  begins  to  putrefy.  It  becomes  laked.  The  same  occurs  when 
the  blood  is  collected  aseptically  in  a  sterile  tube  and  scaled  up, 
although  it  takes  a  longer  time  for  the  laking  to  become  complete. 

(6)  With  blood  containing  nucleated  corpuscles  (necturus,  frog 
or  chicken)  diluted  with  isotonic  salt  solution,  perform  the  following 
experiments  under  the  microscope  : 

(a)  With  a  glass-rod  drawn  to  a  fine  point  put  a  small  drop  of  blood 
on  a  slide,  and  near  it  a  drop  of  distilled  water.  Carefully  lower  the 
cover-slip  and  observe  the  interface  with  the  microscope,  first  with 
the  low  and  then  with  the  high  power.  Then  mix  and  sec  complete 
laking.     Add  a  little  methylene  blue.     Note  that  the  nuclei  still  stain. 

(b)  Place  a  small  drop  of  a  3  per  cent,  solution  of  saponin  in 
isotonic  salt  solution  on  a  slide,  and  near  it  a  small  drop  of  blood. 
Observe  as  in  (a).  Repeat  with  a  2  per  cent,  solution  of  sodium 
taurocholate  in  salt  solution.  If  necturus  corpuscles,  which  arc 
splendid  objects  for  such  experiments  on  account  of  their  great  size, 
have  been  used,  intracorpuscular  crystallization  of  the  haemoglobin 
may  be  observed. 

(c)  Repeat  (a)  and  (b)  with  mammalian  blood.  Note  that  the 
corpuscles  swell  before  being  laked  by  the  saponin.  If  any  of  the 
corpuscles  are  crenated,  it  may  be  seen  that  before  being  laked  by 
the  saponin  the  crenations  disappear,  the  corpuscles  becoming  round, 
while  in  the  taurocholate  solution  they  may  remain  crenated  till 
laking  has  occurred.  This  indicates  that  the  permeability  of  the 
envelopes  is  not  affected  in  the  same  way  by  the  two  laking  agents. 


PR  \illi     II     I  XERi  IS  US 

i  j.  Haemolysis  and  Agglutination  by  Foreign  Serum,  di  To  a 
small  quantity  of  rabbit's  blood  add  an  equal  volume  of  dog's  serum. 
Mix  and  let  stand  at  .40°  ('.  The  colour  of  the  blood  is  soon  darker 
than  before,  and  it  can  be  seen  to  be  laked.  Examine  microscopi- 
cally. 

(2)  Place  a  small  drop  of  rabbit's  blood  and  a  somewhat  larger 
drop  of  the  dog's  scrum  on  a  slide,  near,  but  not  quite  in  contact 
with,  each  other.  Now  put  on  a  cover-slip,  so  that  the  drops  just 
come  together,  and  examine  at  once  with  the  microscope  with  a 
moderately  high  power.  Where  the  two  drops  mingle,  the  red 
corpuscles"  will  be  seen  first  to  become  agglutinated  into  groups,  and 
then  to  fade  out,  leaving  only  their  '  ghosts.'  A  few  of  the  corpuscles 
which  come  into  contact  with  the,  as  yet,  undiluted  serum  may  be 
entirely  dissolved. 

(3)  Heat  some  of  the  dog's  serum  to  6o°  C.  for  ten  minutes,  and 
repeat  (1)  and  (2).  No  laking  will  now  be  produced  in  the  rabbit's 
corpuscles,  but  agglutination  may  be  observed  as  before. 

(4)  Repeat  (1)  and  (2)  with  dog's  blood  and  rabbit's  serum.  The 
blood  will  not  be  laked,  although  sometimes  the  dog's  corpuscles 
may  become  crcnatcd.     There  will  be  no  agglutination. 

(5)  With  a  5  per  cent,  suspension  of  rabbit's  washed  corpuscles 
perform  the  following  experiments  :* 

Put  into  each  of  six  small  test-tubes  1  c.c.  of  the  suspension. 
Label  the  tubes  A,  A',  B,  B',  C,  C. 

(a)  To  A  and  A'  add  respectively  o'l  c.c.  and  0-5  c.c.  ox  serum. 

(b)  To  B  and  B'  add  respectively  o'i  c.c.  and  0-5  c.c.  dog's  serum. 

(c)  To  C  and  C  add  respectively  o- 1  c.c.  and  0*5  c.c.  of  o"o,  per  cent, 
sodium  chloride  solution. 

Put  all  the  tubes  in  a  bath  at  400  C.  Compare  the  amount  of 
laking  and  agglutination  in  the  various  tubes  at  intervals  of  two 
minutes  or  less.  Repeat  (a),  (b),  and  (c)  with  guinea-pig's  washed 
corpuscles  and  serum  of  ox  and  dog.  Determine  which  of  these 
sera  has  the  strongest  haemolytic  power. f 

(6)  Heat  1  c.c.  of  ox  and  dog's  serum  respectively  to  560  C,  keeping 
it  at  that  temperature,  or  not  more  than  a  couple  of  degrees  above 
it,  for  ten  $  minutes,  and  repeat  experiment  (5),  labelling  the  tubes 

*  The  material  obtained  from  one  medium-sized  dog,  two  rabbits,  and 
one  guinea-pig  is  enough  for  fifty  or  sixty  students,  working  together  in 
sets  of  two,  to  perform  experiments  (5)  to  (8).  In  order  to  obtain  a  serum 
more  strongly  ha-molytic  for  rabbit's  corpuscles  than  normal  dog's  serum, 
a  dog  may  be  '  immunized  '  by  previous  injection  of  all  the  washed  cor- 
puscles obtainable  from  a  rabbit.  The  injection  should  be  made  under 
the  skin  or,  better,  into  the  peritoneal  cavity — of  course,  with  aseptic 
precautions.  It  should  be  repeated  not  less  than  twice,  with  an  interval 
of  ten  days  between  the  successive  injections,  and  the  dog's  blood  should 
be  drawn  off  about  ten  days  after  the  last  injection. 

f  To  determine  the  amount  of  laking  at  any  given  moment,  drop  the 
small  test-tubes  into  the  metallic  centrifuge  cups  after  shaking  them  up, 
and  centrifugalize.  A  very  short  time  is  sufficient  to  separate  a  clear 
supernatant  liquid,  from  the  tint  of  which  the  extent  of  the  haemolysis 
can  be  deduced.  Before  replacing  the  tubes  in  the  thermostat,  they  should, 
of  course,  be  shaken  up.  Small  test-tubes  of  about  8  mm.  internal  diameter 
and  short  enough  to  go  conveniently  into  the  centrifuge  cups  are  the  most 
serviceable. 

X  For  exact  work  a  longer  time  is  recommended.  But  for  the  student 
the  time  is  made  as  short  as  possible,  and  it  is  only  in  exceptional  cases 
that  ten  minutes  is  not  enough. 


64  A   MANUAL  OF  PHYSIOLOGY 

D,  D'.  E,  E',  F,  F'.  Save  the  rest  of  the  heated  sera  for  (8).  There 
is  no  taking  in  any  of  the  tubes,  but  probably  agglutination  in  I ),  I )'. 

anil  E,  E'.  (The  complement  is  destroyed,  but  not  the  intermediary 
body  or  amboceptor,  or  the  agglutinin — p.  27.) 

(7)  Put  half  of  the  contents  of  tubes  D,  D\  E,  E',  into  four  separate 

test-tubes,  ami  add  to  each  o'2  c.c.  of  rabbit's  serum.  II  there  is 
hiking  now  it  is  because  the  rabbit's  serum  contains  complement. 
Save  the  balance  of  D,  D',  E  and  E'  for  (8). 

(8)  Allow  u'5  c.c.  of  ox  serum  to  act  at  o°  C.  on  the  rabbit's 
washed  corpuscles  contained  in  5  c.c.  of  the  5  per  cent,  suspension 
alter  removal  of  the  sodium  chloride  solution.  The  ox  serum  and 
rabbit's  corpuscles  are  separately  cooled  to  o°  C.  before  being  mixed, 
and  the  mixture  is  then  kept  at  o°  C.  for  one  hour.  Centrifugalize  the 
serum  off  rapidly.     Label  it  '  Serum  S.'     To  02  c.c.  of  the  original 

5  per  cent,  suspension  of  rabbit's  washed  corpuscles  add  o'l  c.c.  of 
this  serum  (labelling  the  tube  G),  and  put  at  400  C.  with  a  control-tube 
containing  the  same  amount  of  suspension  plus  salt  solution  instead 
of  serum.  Add  the  rest  of  the  serum  S.  cooled  to  o°  C,  to  the  same 
cooled  rabbit's  corpuscles,  and  leave  for  a  further  period  at  o°  C. 
Then  centrifugalize  rapidly,  and  to  o-2  c.c.  of  the  original  suspension 
of  washed  rabbit's  corpuscles  add  o' r  c.c.  of  serum  S  (labelling  the 
tube  H),  and  put  at  400  C.  with  a  sodium  chloride  tube  as  control. 
There  may  be  no  hiking  in  cither  G  or  H,  or  if  there  is  hiking  it  may 
be  greater  in  G  than  in  H.  The  amboceptor  has  been  removed 
from  serum  S  by  the  rabbit's  corpuscles.  Add  o*  1  c.c.  of  this  '  in- 
activated '  serum  to  the  balance  of  D,  D',  and  E,  E'  (left  from  6). 
Laking  will  occur  because  the  scrum  S  contains  complement,  and  the 
heated  serum  added  in  (6)  to  these  tubes  contains  amboceptor. 
Wash  the  rabbit's  corpuscles  which  have  been  treated  with  ox  serum 
at  o°  C.  with  cooled  sodium  chloride  solution.  Add  to  them  some  of 
serum  S  (that  from  the  top  of  tube  H  will  do  if  no  more  is  left),  and 
put  at  400  C.  Laking  will  occur,  showing  that  the  amboceptor  was 
fixed  by  the  rabbit's  corpuscles  at  o°  C.  To  a  further  portion  of 
the  washed  rabbit's  corpuscles  wliich  were  treated  with  ox  serum  at 
o°  C.  add  normal  rabbit's  serum,  and  put  at  40°  C.  if  laking  occurs 
it  is  because  the  rabbit's  scrum  contains  complement. 

Dog's  serum  may  be  used  instead  of  ox  serum  tor  experiment   (8  , 
13.  Osmotic  Resistance  of  the  Coloured  Corpuscles. — Fill  a  burette 
with  a  1  per  cent,  solution  of  sodium  chloride  and  another  with  dis- 
tilled water.     Take  a  series  of  ten  test-tubes  and  run  into  the  first 

6  c.c.  of  the  NaCl  solution,  into  the  second  5' 8  c.c,  into  the  third 
5'(>  c.c,  and  so  on,  always  making  a  difference  of  o"2  c.c.  between 
each  two  successive  test-tubes.  From  the  other  burette  run  in 
enough  distilled  water  to  make  up  10  c.c.  of  solution  in  each  tube — 
that  is,  4  c.c  of  distilled  water  for  the  first  tube,  42  c.c.  for  the  second, 
and  so  on.  Shake  up.  The  tubes  now  contain  a  scries  of  solutions 
of  salt  differing  in  strength  by  002  per  cent,  in  successive  tubes,  the 
strongest  being  06  per  cent.,  and  the  weakest  042  per  cent.  Number 
the  tubes  1  to  10,  beginning  with  the  strongest  solution.  Put  into 
each  tube  one  drop  of  perfectly  fresh  blood.  Shake  moderately  so  as 
to  mix  the  blood  and  salt  solution,  and  allow  the  tubes  to  stand  for 
ten  to  thirty  minutes.  Observe  the  colour  of  the  clear  liquid  above 
the  sediment  of  corpuscles.  Determine  in  which  tube  the  lust  tinge 
of  haemoglobin  appears.  The  next  higher  concentration  of  the  salt 
solution  is  that  in  which  all  the  corpuscles  are  just  able  to  retain  their 
haemoglobin,   and   is  a  measure  of  the   minimum   osmotic  resistance 


PRACTICAL  EXERCISES  65 

of  i  he  corpuscles,  or  the  resistance  of  the  weakesl  corpuscles.  Repeal 
with  blood  which  has  stood  at  room  temperature  for  twelve  to 
twenty-four  hours.  For  clinical  purposes  tubes,  each  containing 
5  c.c.  of  salt  solution,  may  be  used.  A  single  drop  of  blood  can  then 
be  distributed  between  the  tubes  with  a  fine  pipette  or  a  glass  rod, 
beginning  with  the  most  concentrated  solution,  and  passing  down 
to  the  less  concentrated.  The  blood  must  be  distributed  rapidly 
before  coagulation  occurs.  Only  such  concentrations  of  the  s.ill 
solution  as  are  known  to  correspond  to  the  possible  variations  of  the 
osmotic  resistance  for  any  particular  disease  or  for  any  particular 
variety  of  blood  need  be  employed. 

14.  Blood-pigment  (1)  Preparation  of  Haemoglobin  Crystals. — (a) 
To  a  little  dog's  blood  in  a  narrow  test-tube  add  its  own  volume  or 
twice  its  volume  of  chloroform.  Invert  the  tube  ten  or  twelve  times 
so  as  to  allow  the  chloroform  to  act  on  the  blood,  but  avoid  violent 
shaking.  When  the  tube  is  now  allowed  to  stand  for  a  few  minutes 
the  laked  blood  all  rises  to  the  top.  Remove  a  little  of  the  layer 
of  blood  without  taking  with  it  any  of  the  chloroform  layer,  and 
examine  the  oxyhemoglobin  crystals  with  the  microscope.  They 
form  long  rhombic  prisms  and  needles  (Fig.  8,  p.  45). 

(b)  Add  a  little  crude  saponin  to  dog's  blood  in  a  test-tube.     Shake 


B 

Fig.  14. — Direct  Vision  Spectroscope  of  Simple  Type. 
A,  slot  in  which  a  pin  on  the  eyepiece  C  slides  in  focussing  the  spectrum; 
B,  milled  head,  by  the  rotation  of  which  the  slit  is  narrowed  or  widened. 

up  well,  and  allow  it  to  stand  till  the  colour  becomes  dark.  Then 
shake  vigorously,  and  a  mass  of  haemoglobin  crystals  will  be  formed. 

(c)  Put  a  small  drop  of  guinea-pig's  blood  on  a  slide.  Mix  with  a 
drop  of  Canada  balsam  and  cover.  Tetrahedral  crystals  of  oxy- 
hemoglobin will  form  after  a  time.     The  slide  may  be  kept. 

(2)  Spectroscopic  Examination  of  Haemoglobin  and  its  Derivatives. 
— (a)  With  a  small,  direct-vision  spectroscope  look  at  a  bright  part  of 
the  sky  or  a  white  cloud.  Focus  by  pulling  out  or  pushing  in  the  eye- 
piece until  the  numerous  fine  dark  lines  (Fraunhofer's  lines),  running 
vertically  across  the  spectrum,  are  seen.  Narrow  the  slit  by  moving 
the  milled  edge  till  the  lines  are  as  sharp  as  they  can  be  made.  Note 
especially  the  line  D  in  the  orange,  the  lines  E  and  b  in  the  green, 
and  F  in  the  blue.  Always  hold  the  spectroscope  so  that  the  red  is 
at  the  left  of  the  field.  Now  dip  an  iron  or  platinum  wire  with  a 
loop  on  the  end  of  it  into  water,  and  then  into  some  common  salt  or 
sodium  carbonate,  and  fasten  or  hold  it  in  the  flame  of  a  fishtail 
burner.  On  examining  the  flame  with  the  spectroscope,  a  bright 
yellow  line  will  be  seen  occupying  the  position  of  the  dark  line  D  in 
the  solar  spectrum.  This  is  a  convenient  line  of  reference  in  the 
spectrum,  and  in  studying  the  spectra  of  haemoglobin  and  its  deri- 
vatives, the  position  of  the  absorption  bands  with  regard  to  the  D 
line  should  always  be  noted.     The  dark  lines  in  the  solar  spectrum 

5 


A   MANUA1    OF  1'IIYSIOI.OGY 


are  due  to  the  absorption  of  light  of  a  definite  range  of  wave-lengths 
by  metals  in  a  state  of  vapour  in  the  sun's  atmosphere,  and  of  course 
no  dark  lines  are  seen  in  the  spectrum  of  a  gas-flame.  Put  some 
defibrinated  blood  into  a  test-tube.  Fasten  it  vertically  in  a  clamp 
in  front  of  the  flame  and  examine  it  with  the  spectroscope,  holding 
the  latter  in  one  hand  with  the  slit  close  to  the  test-tube,  and  focus- 
sing the  eyepiece  with  the  other.  Or  arrange  the  spectroscope,  test- 
tube  and  gas-flame  on  a  stand  as  in  Fig.  15.  Nothing  can  be  seen  till 
the  blood  is  diluted.  Pour  a  little  of  the  blood  into  another  test- 
tube,  and  go  on  diluting  till,  on  focussing,  two  hands  of  oxyhemoglobin 
are  seen  in  the  position  indicated  in  Fig.  7.  Draw  the  spectrum  ; 
then  dilute  still  more,  and  observe  which  of  the  bands  first  dis- 
appears.     Now  put  5  c.c.  of  the  blood  into  another  test-tube,  and 


Fig.   15. — Spectroscopic  Examination  of  Blood-pigment. 


dilute  it  with  four  times  its  volume  of  water.  Take  5  c.c.  of  this 
dilution,  and  again  add  four  times  as  much  water,  and  so  on  till  the 
solution  is  only  faintly  coloured.  Note  with  what  degree  of  dilution 
the  bands  disappear.  Then  examine  each  of  the  solutions  with  the 
spectroscope  and  draw  its  spectrum. 

{b)  Make  a  solution  of  blood  which  shows  the  oxyhemoglobin 
bands  sharply.  Add  some  ammonium  sulphide  solution  to  reduce 
the  oxyhemoglobin.  Heat  gently  to  about  body  temperature.  \ 
single,  ill-defined  band  now  appears,  occupying  a  position  midway 
between  the  oxyhemoglobin  bands,  and  the  latter  disappear.  This 
is  the  band  of  reduced  hemoglobin  (Fig.  7). 

(c)  Carbonic  Oxide  Hemoglobin. — Pass  coal-gas  through  blood  for 
a  considerable  time.  Examine  some  of  the  blood  (after  dilution) 
with  the  spectroscope.  Two  bands,  almost  in  the  position  of  the 
Oxyhemoglobin  bands,  are  seen  ;  but  no  change  is  caused  by  the 


/'/,'  ICTICAL  EXERCISES  67 

addition  of  ammonium  sulphide,  since  carbonic  oxide  bae lobin 

is  ,1  more  stable  compound  than  oxyhemoglobin. 

(d)  MethmcBOglobin. — Put  some  blood  into  a  test-tube,  add  a  few 
drops  of  a  solution  oi  ferricyanide  of  potassium,  and  heat  gently.  On 
diluting  a  well-marked  band  will  be  seen  in  the  red.  On  addition 
of  ammonium  sulphide  this  band  disappears  ;  the  oxyhemoglobin 
bands  are  seen  for  a  moment,  and  then  give  place  to  the  band  of 
reduced  ha  moglobin  (Fig.  7). 

(e)  Acid  Hcematin.  To  a  little  diluted  blood  add  strong  acetic  acid 
and  heat  gently.  The  colour  becomes  brownish.  The  spectrum 
shows  .1  hand  in  the  red  between  C  and  D,  not  far  from  the  position 
of  the  band  of  methaemoglobin.  The  addition  of  a  drop  or  two  of 
ammonium  sulphide'  causes  no  change  in  the  spectrum,  and  this  is  a 
me ins  of  distinguishing  acid-haematin  from  methaemoglobin.  If 
more  ammonium  sulphide  be  added,  haematin  will  be  precipitated 
when  the  acid  solution  has  been  rendered  neutral,  and  a  further 
addition  of  ammonium  sulphide  or  sodium  hydroxide  will  cause  the 
haematin  to  be  again  dissolved,  a  solution  of  alkaline  haematin  being 
formed.  This  in  its  turn  maybe  reduced  by  an  excess  of  ammonium  sul- 
phide, and  the  spectrum  of  haemochromogen  maybe  obtained  (Fig.  7). 

Since  the  watery  solution  of  acid 
haematin  obtained  as  above  is  usually 
somewhat  turbid,  a  solution  in  acid 
ether  is  sometimes  employed  for 
spectroscopic  examination.  Add  to 
a  little  undiluted  defibrinated  blood 
about  half  its  volume  of  glacial 
acetic  acid,  and  then  not  less  than 
an  equal  volume  of  ether.  Mix  well, 
pour  off  the  ethereal  extract  and 
examine  it  with  the  spectroscope, 
diluting,  if  necessary,  with  ether 
and  glacial  acetic  acid.  It  shows  a  FlG  i6._Crystals  of  ELemin 
strong  band    in  the  red   somewhat  (Frey) 

farther  from  the    D    line   than    the 

methaemoglobin  band.     On  dilution,  three  additional  fainter  bands 
may  be  seen. 

(/)  Alkaline  Hcematin. — To  diluted  blood  add  strong  acetic  acid 
and  warm  gently  for  a  few  minutes.  Then,  when  the  spectroscopic 
examination  of  a  sample  shows  that  acid-haematin  has  been  formed, 
neutralize  with  sodium  hydroxide.  A  brownish  precipitate  of  haematin 
is  thrown  down,  which  dissolves  in  an  excess  of  sodium  hydroxide, 
giving  a  solution  of  alkaline  haematin  (or  alkali-haematin). 

Or  add  sodium  hydroxide  to  blood  directly,  and  warm  for  a  couple  of 
minutes  after  the  colour  has  changed  decidedly  to  brownish-black. 
The  spectrum  of  alkaline  haematin  is  a  broad  but  ill-defined  band 
just  overlapping  the  D  line,  and  situated  chiefly  to  the  red  side  of  it 
(Fig.  7).  The  solution  should  be  shaken  up  with  air  before  being 
examined,  as  some  of  the  alkali-haematin  is  changed  into  haemo- 
chromogen by  reducing  substances  formed  by  the  action  of  the  alkali 
on  the  blood. 

(g)  Hcemochromogen. — To  a  solution  of  alkaline  haematin  add  a 
drop  or  two  of  ammonium  sulphide.  The  band  near  D  disappears, 
and  two  bands  make  their  appearance  in  the  green  (Fig.  7). 

(h)  H  CBmato  porphyrin . — Put  some  strong  sulphuric  acid  in  a  test- 
tube.     Add  a  few  drops  of  blood,  agitate  the  test-tube  till  the  blood 

5—2 


68 


A   MANUAL  OF  PHYSIOLOGY 


dissolves,  and  examine  the  purple  liquid,  diluting  it.  if  necessary, 
with  sulphuric  acid.  Its  spectrum  shows  two  well-marked  bands, 
one  just  to  the  lefi  of  D,  and  the  other  midway  between  \>  and  E 
(Fig-  ?)• 

(3)  Guaiacum  Test  for  Blood.  A  lest  for  blood  much  used  in 
hospitals,  and,  indeed,  a  delicate  one,  bu1  no1  always  trustworthy 
unless  certain  precautions  be  taken  is  the  guaiacum  test.  A  drop 
of  freshly-prepared  tincture  of  guaiacum  is  added  to  the  liquid  to 
be  tested,  and  then  peroxide  of  hydrogen.  If  blood  !><■  present,  the 
guaiacum  strikes  a  blue  colour.  The  decomposition  of  the  peroxide 
by  the  blood  is  due  mainly  to  tin-  haemoglobin  oi  the  corpuscles. 
Any  derivative  of  haemoglobin  which  still  contains  the  iron  will 
and  boiling  does  not  abolish  this  power.  On  tin-  other  hand,  oxy- 
dases or  oxidizing  ferments  present  not   only  in  the  formed  elements 


Fig.  17. — Haldane's  Modification  01  Gowers'  II  i.mim.i  omvomi.tkr. 

of     blood     but     elsewhere,     e.g.,    in     fresh    vegetable    protoplasm, 

milk,   seminal   fluid,    ami    pus.    will  cause  the  same  colour  (p. 

but  not  if  they  have  been   previously  boiled*     The  test  has  been 

*  The  formed  elements  oi  blood  really  contain  no  less  than  thtei 
ments  oi   interesi    in   this  connection      in    \   catalase  which   decom] 
peroxide  oi  hydrogen  into  water  and  molecular  oxygen  [i.e.,  oxygen  not 
in   the  atomic    oi    aa  cenl     tate).      I  in-  reaction  1-  given  by  both  Mood 
and  [his.     (2)  An  oxyda  1  »  lied  oxidase),  which  oxidises  guaiacum 

and  similar  substance    withoui  the  presence  oi  hydrogen  peroxide.     This 
reaction  is  obtainable  even  from  aqueous  extracts  oi  leui 
peroxydase  (also  spelled  peroxidase)  which  causes  the  oxidation  oi  these 
substances  only   in   the   presence  oi   hydrogen    peroxide,  a    reaction   .il-'> 
given    l>y   leucocytes.     These    ferments    are    all    inactivated    l>\     Koiling 


PR  ICTIl    II    I  XERCISES 


69 


1  onsidered  chiefly  o\  value  as  a  negative  test.     When  the  blue  colour 

is  not  obtained,  we  have  good  evidence  thai  blood  is  absent.     But, 

•rding  to  Buckmaster,  if  the  precaution  of  first  boiling  the  liquid 

suspect  eel  to  contain  blood  be  adopted,  it  is  also  a  good  positive  test. 
Quantitative  Estimation  of  Haemoglobin  [a)  By  Haldane's 
Modification  of  Gowers'  Hamoglobinometer.  Place  in  the  graduated 
tube  B  (Fig.  17)  an  amount  of  water  less  than  will  ultimately  be 
required  to  dilute  the  blood  to  the  required  tint.  Puncture  the 
finger  or  lobe  of  the  ear  with  one  of  the  small  lancets  in  F,  and  fill 
the  capillary  pipette  D  to  a  little  beyond  the  mark  jo.  Wipe  the 
punt  ol  the  pipette  and  dab  it  on  a  piece  of  filter-paper  till  the 
blood  stands  exactly  ai  the  mark.  Blow  the  blood  into  the  water 
in  B,  and  rinse  the  pipette  with  the  water.  Attach  the  cap  of  tube 
(i  to  .1  gas-burner.  Introduce  the  rubber  tube  into  B  nearly  to  the 
level  of  the  water,  and  allow  gas  to  pass  for  a  few  seconds.      With- 


Fig.   18. — Fleischl's  H.emometer. 


draw  the  tube  while  the  gas  is  still  passing.  Immediately  close  the 
end  of  B  with  the  finger,  and  move  the  tube  so  that  the  liquid 
passes  from  end  to  end  of  it  at  least  a  dozen  times,  to  saturate  the 
haemoglobin  with  carbonic  oxide.  While  this  is  being  done,  the 
tube  should  be  held  in  a  cloth,  otherwise  it  will  become  heated,  and 
liquid  will  spurt  out  when  the  finger  is  removed.  Water  is  now 
added  drop  by  drop  with  the  pipette  stopper  of  the  bottle  E,  which 
is  used  for  holding  the  water,  the  tube  being  inverted  after  each 
addition,  till  the  tint  in  B  is  the  same  as  that  in  A.  In  comparing 
the  tubes,  they  should  be  held  against  the  light  from  the  sky  or 
from  an  opal  glass  lamp-shade.  It  is  necessary  to  transpose  the 
tubes  repeatedly.  The  level  at  which  the  tints  are  equal  is  read 
off  on  B  half  a  minute  after  the  addition  of  the  last  drop  of  water. 
Water  is  now  again  added  by  drops  till  the  tint  in  B  is  just  notice- 
ably weaker  than  in  A,  and  the  mean  of  the  two  readings  is  taken. 


70 


I     \l  IXi  ,11    oh    IIIYSIOLOG  \ 


I  In  resull  is  the  percentage  actually  presenl  of  the  average  propor- 
tion  of  haemoglobin  in  tin-  blood  oi  healthy  adull  males.  Healthy 
women  give  an  average  oi  only  89  per  cent.,  and  healthy  children 
.m  average  oi  only  >s7  per  cent.,  01  the  proportion  in  men.  The 
liquid  in  A  is  a  1  per  cent,  solution  of  blood  containing  the  av< 
percentage  of  haemoglobin  found  in  the  blood  of  healthy  adull  m 
and  having  an  oxygen  capacity  of  1  s •  5  per  cent,     i.e.,   100  c.c.  of 

the    blood    with    which    the    standard    was    made    would    take    1 1 J >    in 
combination   from   air    [8*5   c.c.   of  oxygen.      The  solution   in    A   lias 

Been  saturated   witli  carbonic 

oxide. 

This  method  is  probably 
more  accurate  than  any  other 
used  in  clinical  work,  the 
error,  in  the  hands  of  an  ex- 
perienced observer,  not  ex- 
ceed in g   1   per  cent. 

d>\  By  /■'//  ist  hl's  HcemomeU  > 
(Fig.  1S1.  Fill  with  distilled 
water  that  compartment  a' of 
the  small  cylinder  (above  the 
which  is  over  t  he  tinted 
w<  dge.  I  'lit  a  little  distilled 
water  into  the  other  compart- 
in  nt  a.  Now  prick  the  finger 
and  fill  one  of  the  small 
capillary  tubes  with  blood 
Sec  that  none  of  the  blood  is 
smeared  on  t  he  outside  of  the 
tube.  Then  wash  all  the  blood 
into  the  water  in  compartment 
a,  and  fill  it  to  the  brim  with 
distilled  water.  By  means  of 
the  milled  head  T  move  the 
tinted  wedge  K  till  the  depth 
of  colour  is  tin'  same  in  tin- 
two  compartments.  The  per- 
centage of  the  normal  quantit  y 
of  haemoglobin  is  given  by 
the  graduated  scale  P.  For 
example,  it  tin  reading  is  90, 
the  blood  contains  90  percent . 
of  the  normal  amount  ;  if  100. 
it  contains  the  normal  quan- 
tity. The  observations  should 
be  made  in  a  dark  room. 
the  white  surface  S,  arranged  below  the  compartments  a  and  a'. 
being  illuminated  by  a  lamp.  I  >r  t  he  insl  rument  max-  lie  placed  in  a 
small  box.  Lighted  by  a  candle.  It  is  best  that  each  result  should  be 
the  mean  of  two  readings,  one  just  too  large  and  the  other  just  too 
small.  In  any  case  the  instrument  does  not  -i\c  readings  accurate 
to  less  than  5  per  cent. 

(c)  Hoppc-Seylcv's  Method.  Two  parallel-sided  Ldass  troughs  arc 
used.  In  one  is  put  a  standard  solution  oi  oxyhaemoglobin  oi 
known  strength,  in  the  other  a  measured  quantity  oi  tin-  blood  to  be 
tested.      The  latter  is  diluted   with  water  until  its  tint    appears  the 


Fig.  19.  —  Diagram  oi  Primitive  Verte- 
brate Heart,  combining  Features 
pound  in  Tin:  Eel,  Dogfish,  and  Frog 
(Flack,  after  Keith). 

a.  Sinus  venosus ;  b,  auricular  canal ; 
1.  auricle;  </.  ventricle;  e,  bulbus  cordis  ; 
/,  aorta  ;  i-i,  sino-auricular  junction  and 
venous  valves ;  2-2,  junction  of  canal  and 
auricle  ;  3-3,  annular  part  of  auricle;  5,  bulbo- 
ventricular  junction. 


PR  /<   /  /<    //.   EXERi  ISI.S  7r 

sameas  thai  of  the  standard  solution,  when  the  troughs  are  placed  side 
l>\  side  on  white  paper.  From  the  quantity  of  water  added  it  is  easy 
to  calculate  the  proportion  oi  haemoglobin  in  the  undiluted  blood. 
Greater  accuracy  is  obtained    if   the   haemoglobin  in   the  standard 

solution  and  that  of  the  blood  are  converted  into  carbonic  oxide 
haemoglobin  by  passing  a  stream  of  coal-gas  through  them. 

(</)  Tallquist's  Method.  —  In  this  method  the  tint  produced  by  a 
drop  of  blood  on  a  piece  of  white  filter-paper  is  compared  with  a 
scale  representing  10  percentages  of  haemoglobin  (from  10  to  ioo  pei 
cent.).  The  standard  filter-paper  is  supplied  in  the  form  of  a  book 
with  the  scale.  To  make  an  estimation,  all  that  is  necessary  is  to 
touch  a  drop  of  blood  with  a  piece  of  the  filter-paper,  and  allow  the 
blood  to  diffuse  slowly  through  the  paper,  so  as  to  give  an  even  stain. 
The  position  of  the  stain  is  then  determined  by  the  scale  ;  e.g.,  it 
may  be  deeper  than  qo,  but  fainter  than  ioo,  in  which  case  the  per- 
centage of  haemoglobin  lies  between  90  and  100.  The  method  is  by 
no  means  a  very  accurate  one,  but  more  accurate  than  it  appears  at 
first  sight. 

(5)  Microscopic  Test  for  Blood-pigment. — Put  a  drop  of  blood  on 
a  slide.  Allow  the  blood  to  dry.  or  heat  it  gently  over  a  flame,  so  as  to 
evaporate  the  water.  Add  a  drop  of  glacial  acetic  acid  ;  put  on  a 
cover-glass,  and  again  heat  slowly  till  the  liquid  just  begins  to  boil. 
Take  the  slide  away  from  the  flame  for  a  few  seconds,  then  heat  it 
again  for  a  moment  ;  and  repeat  this  process  twro  or  three  times. 
Now  let  the  slide  cool,  and  examine  with  the  microscope  (high  power). 
The  small  black,  or  brownish-black,  crystals  of  haemin  will  be  seen 
(Fig.  16,  p.  67) .  This  is  an  important  test  where  only  a  minute  trace  of 
blood  is  to  be  examined,  as  in  some  medico-legal  cases.  If  a  blood- 
stain is  old,  a  minute  crystal  of  sodium  chloride  should  be  added  along 
with  the  glacial  acetic  acid.  Fresh  blood  contains  enough  sodium 
chloride. 

A  blood-stain  on  a  piece  of  cloth  may  first  of  all  be  soaked  in  a 
small  quantity  of  distilled  water,  and  the  liquid  examined  with  the 
spectroscope  or  the  micro-spectroscope  (a  microscope  in  which  a 
small  spectroscope  is  substituted  for  the  eyepiece).  Then  evaporate 
the  liquid  to  dryness  on  a  water-bath,  and  apply  the  haemin  test. 
Or  perform  the  haemin  test  directly  on  the  piece  of  cloth.  In  a  fresh 
stain  the  blood-corpuscles  might  be  recognized  under  the  microscope. 
Very  few  liquids,  however,  are  available  for  washing  out  the  blood, 
as  all  ordinary  solutions,  and  even  serum  itself,  cause  laking  of  dried 
corpuscles  (Guthrie).  Absolute  alcohol,  or  35  per  cent,  potassium 
hydroxide,  may  be  used  to  soak  and  rub  up  the  cloth  in. 


CHAPTER  II 

THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH 

The  blood  can  only  fulfil  its  functions  by  continual  movement. 
This  movement  implies  a  constant  transformation  of  energy  ; 
and   in    the   animal    body   the   transformation   of   energy   into 

mechanical  work  is  almost  entirely  allotted  to  a  spei  ia]  form  of 
tissue,  muscle.  In  most  animals  there  exist  one  or  more  rhyth- 
mically contractile  muscular  organs,  or  hearts,  upon  which  the 
chief  share  of  the  work  of  keeping  up  the  circulation  falls. 

Comparative. — In  Echinus  a  contractile  tube  connects  the  two 
vascular  rings  that  surround  the  beginning  and  end  ol  i  he  alimentary 
canal,  and  plays  the  part  of  a  heart.  In  the  lower  i  rusta<  ea  .md  in 
inserts  the  heart  is  simply  the  contractile  and  generally  sacculated 
dorsal  bloodvessel  ;  in  the  higher  Crustacea,  such  as  the  lobster,  it  is 
a  well-defined  muscular  sac  situated  dorsally.  A  closed  vascular 
system  is  the  exception  among  invertebrates.  In  most  of  them  the 
blood  passes  from  the  arteries  into  irregular  spaces  or  lacunas  m  tin 
tissues,  and  thence  finds  its  way  back  to  the  heart.  In  the  primitive 
vertebrate  heart  five  parts  can  be  distinguished  as  we  proceed  from 
the  venous  to  the  arterial  end  :  (i)  The  sinus  venosus.  into  which  the 
great  veins  open  ;  (2)  the  auricular  canal,  from  the  dorsal  wall  of 
which  is  developed — (3)  the  auricle  ;  (4)  the  ventricle ;  (5)  the  bulbus 
arteriosus,  from  which  the  chief  artery  starts  (Fit;.  [9,  p.  70  \mphi- 
oxus,  the  lowest  vertebrate,  has  a  primitive  lacunar  vascular  system  ; 
a  contractile  dorsal  bloodvessel  serves  as  arterial  or  systemic  heart,  a 
contractile  ventral  vessel  as  venous  or  respiratory  heart.  Prom  the 
latter,  vessels  go  to  the  gills.  Fishes  possess  only  a  respiratory  heart, 
consisting  of  a  venous  sinus,  auricle,  ventricle,  and  bulbus  arteriosus. 
This  drives  the  blood  to  the  gills,  from  which  it  is  gathered  into  the 
aorta  ;  it  has  thence  to  find  its  way  without  further  propulsion 
through  the  systemic  vessels.  Amphibians  have  a  venous  sinus. 
two  auricles,  a  single  ventricle,  and  an  arterial  bulb;  reptiles,  two 
auricles  and  two  incompletely-separated  ventricles.  In  birds  and 
mammals  the  respiratory  and  systemic  hearts  an-  completely 
irated.  The  former,  consisting  of  the  right  auricle  and  ventrii  le, 
propels  the  blood  through  the  lungs;  the  latter,  consisting  oi  the 
left  auricle  and  ventricle,  receives  it  from  the  pulmonary  veins,  and 
sends  it  through  the  systemic  vessels. 

The  sinus  venosus  seems  1m  be  represented  in  the  mammalian 
heart  by  certain  small  portions  oi  t  i-^iie.  espe<  ially  the  so-called  sino- 
auricular  node,  a  little  knot  of  primitive  fibres  at  the  mouth  of  the 

7- 


////    (//,'(  /'/.  \TION  OF   I  III    BLOOD  AND  LYMPH 


73 


superior  vena  cava.  The  auricular  canal  is  probably  represented  by 
the  auriculo-ventricular  bundle,  which  will  again  bs  referred  to  in 
relation  to  the  conduction  of  the  heart-beat  from  auricles  to  vent  ri(  l( 
(p.  [35).  This  bundle  starts  from  a  clump  of  primitive  tissue,  the 
auriculo-ventricular  node  at  the  base  of  the  interauricular  septum 
on  the  right  side,  bslow  and  to  the  right  of  the  coronary  sinus,  and 
runs  down  the  interventricular  septum.  The  sino-auricular  and  the 
auriculo-ventricular  nodes  arc  connected  by  fibres  which  run  in  the 
interauricular  septum,  so  that  it  may  be  considered  that  the  primi- 
tive cardiac  tube  is  si  ill  represented  from  base  to  apex  of  the  adult 
mammalian  heart,  although  only  by  very  slender  threads  of  tissue, 
amidst  the  massive  secondary 
developments  of  auricular  and 
ventricular  muscle  (Keith  and 
Flack). 

General  View  of  the  Circulation 
in  Man.  -The  whole  circuit  of  the 
blood  is  divided  into  two  portions, 
very  distinct  from  each  other,  both 
anatomically  and  functionally — 
the  respiratory  or  lesser  circula- 
tion, and  the  systemic  or  greater 
circulation.  Starting  from  the  left 
ventricle,  the  blood  passes  along 
the  systemic  vessels  —  arteries, 
capillaries,  veins — and,  on  return- 
ing to  the  heart,  is  poured  into  the 
right  auricle,  and  thence  into  the 
right  ventricle.  From  the  latter 
it  is  driven  through  the  pul- 
monary artery  to  the  lungs, 
passes  through  the  capillaries  of 
these  organs,  and  returns  through 
the  pulmonary  veins  to  the  left 
auricle  and  ventricle.  The  portal 
system,  which  gathers  up  the 
blood  from  the  intestines,  forms 
a  kind  of  loop  on  the  systemic 
circulation.  The  lymph-current 
is  also  in  a  sense  a  slow  and  stag- 
nant side-stream  of  the  blood- 
circulation  ;  for  substances  are 
constantly  passing  from  the  blood- 
vessels into  the  lymph-spaces,  and  returning,  although  after  a  com- 
paratively long  interval,  into  the  blood  by  the  great  lymphatic  trunks. 

Physiological  Anatomy  of  the  Vascular  System. — The  heart  is  to  be 
looked  upon  as  a  portion  of  a  bloodvessel  which  has  been  modified  to 
act  as  a  pump  for  driving  the  blood  in  a  definite  direction.  Morpho- 
logically it  is  a  bloodvessel  ;  and  the  physiological  property  of  auto- 
matic rhythmical  contraction  which  belongs  to  the  heart  in  so 
eminent  a  degree  is,  as  has  been  mentioned  (p.  72),  an  endowment 
of  bloodvessels  in  many  animals  that  possess  no  localized  heart. 
Even  in  some  mammals  contractile  bloodvessels  occur  ;  the  Veins 
of  the  bat's  wing,  for  example,  beat  with  a  regular  rhythm,  and 
perform  the  function  of  accessory  hearts. 

The  whole  vascular  system  is  lined  with  a  single  layer  of  endo- 


Fig.   20. — Diagram  of  the    General 
Course  of  the  Circulation. 

RA,  LA,  right  and  left  auricles  ;  RV 
LV,  right  and  left  ventricles. 


74  '    M  \Nl    1/    "/    /7M  SIOLOGl 

thelial  colls.  In  the  capillaries  nothing  cist-  is  present  ;  the  endo 
i1mIi.iI  layer  forms  the  whole  thickness  of  the  wall.  In  young 
animals,  at  any  rale,  the  endothelial  cells  of  the  capillaries  an 
capable  of  contract  Jul;  when  stimulated  ;  and  changes  in  the  calibre 
"i  these  vessels  can  be  brought  about  in  this  way.  The  walls  ol  the 
arteries  and  veins  arc  chiefly  made  up  of  two  kinds  of  tissue,  which 
render  them  distensible  and  elastic  :  non-striped  muscular  fibres  and 
yellow  clastic  fibres.  The  muscular  fibres  arc  mainly  arranged  as  a 
circular  middle  coat,  which,  especially  in  the  smaller  arteries,  is 
relatively  thick.  One  conspicuous  layer  of  clastic  fibres  marks  the 
boundary  between  the  middle  and  inner  coats.  In  the  larger 
arteries  elastic  lamina?  arc  also  scattered  freely  among  the  muscular 
fibres  of  the  middle  coat.  The  outer  coat  is  composed  chiefly  of 
ordinary  connective  tissue.  The  veins  differ  from  the  arteries  in 
having  thinner  walls,  with  the  layers  less  distinctly  marked,  and 
containing  a  smaller  proportion  of  non-striped  muscle  and  elastic 
tissue  ;  although  in  some  veins,  those  of  the  pregnant  uterus,  for 
instance,  and  the  cardiac  ends  of  the  large  thoracic  veins,  there  is 
a  greater  development  of  muscular  tissue.  Further,  and  this  is  of 
prime  physiological  importance,  valves  are  present  in  many  veins. 
These  arc  semilunar  folds  of  the  internal  coat  projecting  into  the 
lumen  in  such  a  direction  as  to  favour  the  flow  of  blood  towards 
the  heart,  but  to  check  its  return.  In  some  veins,  as  the  venae  cavae, 
the  pulmonary  veins,  the  veins  of  most  internal  organs,  and  of  bone, 
there  arc  no  valves  ;  in  the  portal  system  they  are  rudimentary  in 
man  and  the  great  majority  of  mammals.  The  valves  are  especially 
well  marked  in  the  lower  limbs,  where  the  venous  circulation  is  uphill. 
When  a  valve  ceases  to  perform  its  function  of  supporting  the  column 
of  blood  between  it  and  the  valve  next  above,  the  foundation  of 
varicose  veins  is  laid  ;  the  valve  immediately  below  the  incompetent 
one,  having  to  bear  up  too  great  a  weight  of  blood,  tends  to  yield  in 
its  turn,  and  so  the  condition  spreads.  The  smallest  veins,  or 
venules,  are  very  like  the  smallest  arteries,  or  arterioles,  but  somewhat 
wider  and  less  muscular.  The  transition  from  the  capillaries  to  the 
arterioles  and  venules  is  not  abrupt,  but  may  be  considered  as  marked 
by  the  appearance  of  the  non-striped  muscular  fibres,  at  first  scattered 
singly,  but  gradually  becoming  closer  and  more  numerous  as  we  pass 
away  from  the  capillaries,  until  at  length  they  form  a  complete  layer. 

In  the  heart  the  muscular  clement  is  greatly  developed  and 
differentiated.  Both  histologically  and  physiologically  the  fibres 
seem  to  stand  between  the  striated  skeletal  muscle  and  the  smooth 
muscle.  In  the  mammal  the  cardiac  muscular  fibres  are  generally 
described  as  made  up  of  short  oblong  cells,  devoid  of  a  sarcolemma, 
often  branched,  and  arranged  in  anastomosing  rows,  each  cell  having 
a  single  nucleus  in  the  middle  of  it.  But  it  has  recently  been  shown 
that  the  muscle  fibrils  run  right  through  the  apparent  cell  boundaries, 
and  form  a  continuous  sheet  of  tissue  anastomosing  in  every  direc- 
tion. The  fibres  are  transversely  striated,  but  the  stria'  are  not  so 
distinct  as  in  skeletal  muscle.  A  sarcolemma  is  not  absent,  although 
it  is  more  delicate  than  in  skeletal  muscle,  and  perhaps  of  a  different 
nature.  Many  fibres  pass  from  one  auricle  to  the  other,  and  from 
one  ventricle  to  the  other. 

In  the  frog's  heart  the  muscular  fibres  are  spindle-shaped,  like 
those  of  smooth  muscle,  but  transversely  striated,  like  those  of 
skeletal  muscle.  From  the  sinus  to  the  apex  of  the  ventricle  there  is 
a  continuous  sheet  of  muscular  tissue. 


////    (  //,',  /  /    I770A   OF    I  III    BLOOD    IND  LYMPH  75 

The  problems  of  the  circulation  arc  partly  physical,  partly 
vital.     Some  o!   the  phenomena  observed  in  the  blood-stream 
n!  .i  living  animal  can  be  reproduced  on  an  artificial  model  ; 
and  they  may  justly  be  tailed  the  physical  phenomena  of  the 
circulation.     Others    are    essentially   bound    up   with   the    pro- 
pel tics  of   living  tissues;   and  these  maybe  classified  as  the 
vital  or  physiological  phenomena  of  the  circulation.     The  dis- 
tinction, although  by  no  means  sharp  and  absolute,  is  a  con- 
venient one — at  least,  for  purposes  of  description  ;  and  as  such 
we  shall  use  it.     But  it  must  not  be  forgotten  that  the  physio- 
logical  factors   play  into   the  sphere  of  the  physical,   and   the 
physical   factors  modify  the   physiological.     Considered  in   its 
physical  relations,  the  circulation  of  the  blood  is  the  flow  of  a 
liquid  along  a  system  of  elastic  tubes,  the  bloodvessels,  under 
the  influence  of  an  intermittent  pressure  produced  by  the  action 
of  a  central   pump,   the   heart.     But  the  branch  of  dynamics 
which  treats  of  the  movement  of  liquids,  or  hydrodynamics,  is 
one  of  the  most  difficult  parts  of  physics,  and,  in  spite  of  the 
labours  of  many  eminent  men,  is  as  yet  so  little  advanced  that 
even  in  the  physical  portion  of  our  subject  we  are  forced  to  rely 
chiefly  on  empirical  methods.     It  would,  therefore,  not  be  pro- 
fitable to  enter  here  into  mathematical  theory,  but  it  may  be 
well  to  recall  to  the  mind  of  the  reader  one  or  two  of  the  simplest 
data  connected  with  the  flow  of  liquids  through  tubes  : 

Torricelli's  Theorem. — Suppose  a  vessel  filled  with  water,  the  level 
of  which  is  kept  constant  ;  the  velocity  with  which  the  water  will 
escape  from  a  hole  in  the  side  of  the  vessel  at  a  vertical  depth  h 
below  the  surface  will  be  v=  J  2.gh,  where  g  is  the  acceleration  pro- 
duced by  gravity.*  In  other  words,  the  velocity  is  that  which  the 
*  water  would  have  acquired  in  falling  in  vacuo  through  the  distance  h. 
This  formula  was  deduced  experimentally  by  Torricelli,  and  holds 
only  when  the  resistance  to  the  outflow  is  so  small  as  to  be  negligible. 
The  reason  of  this  restriction  will  be  easily  seen,  if  we  consider  that 
when  a  mass  m  of  water  has  flowed  out  of  the  opening,  and  an  equal 
mass  m  has  flowed  in  at  the  top  to  maintain  the  old  level,  everything 
is  the  same  as  before,  except  that  energy  of  position  equal  to  that 
possessed  by  a  mass  m  at  a  height  h  has  disappeared.  If  this  has  all 
been  changed  into  kinetic  energy  E,  in  the  form  of  visible  motion 
of  the  escaping  water,  then  ~E  =  :hmv2  =  mgh,  i.e.,  v=  \'2gh.  If,  how- 
ever, there  has  been  any  sensible  resistance  to  the  outflow,  any 
sensible  friction,  some  of  the  potential  energy  (energy  of  position), 
will  have  been  spent  in  overcoming  this,  and  will  have  ultimately 
been  transformed  into  the  kinetic  energy  of  molecular  motion,  or  heat. 
Flow  of  a  Liquid  through  Tubes. — Next  let  a  horizontal  tube  of 
uniform  cross-section  be  fitted  on  to  the  orifice.  The  velocity  of 
outflow  will  be  diminished,  for  resistances  now  come  into  play. 
When  the  liquid  flowing  through  a  tube  wets  it,  the  layer  next  the 
wall  of  the  tube  is  prevented  by  adhesion  from  moving  on.  The 
*  I.e.,  the  amount  added  per  second  to  the  velocity  of  a  falling  body 
(g  =  32  feet). 


7" 


A   MANUAL  OF  PHYSIOLOGY 


particles  nexl  this  stationary  layer  rub  on  it.  so  to  speak,  and  arc 
retarded,  although  not  stopped  altogether.  The  nexl  layer  rubs  on 
the  comparatively  slowly  moving  particles  outside  it,  and  is  also 
delayed,  although  not  so  much  as  thai  in  contact  with  the  immovable 
layer  on  the  walls  oi  the  tube.  In  this  way  it  comes  about  thai  every 
particle  of  the  liquid  is  hindered  by  its  friction  against  others  those 
hid  he  axis  of  the  tube  least,  those  near  the  periphery  most  and  part 
of/the'energy  of  position  of  the  water  in  the  reservoir  is  used  up  in  o\  er- 
coming  this  resistance,  only  the  remainder  being  transformed  Into  t he 
visible  kinetic  energy  of  the  liquid  escaping  from  the  open  end  of  the  tube. 
If  vertical  tubes  be  inserted  at  different  points  of  the  horizontal 
tube,  it  will  be  found  that  the  water  stands  at  continually  decreasing 
heights  as  we  pass  away  from  the  reservoir  towards  the  open  end  oi 
the  tube.  The  height  of  the  liquid  in  any  of  the  vertical  tubes 
indicates  the  lateral  pressure  at  the  point  at  which  it  is  insetted  ;  in 
other  words,  the  excess  of  potential  energy,  or  energy  oi  position, 
which  at  that  point  the  liquid  possesses  as  compared  with  the  watei 
at  the  free'  end,  where  the  pressure  is  zero.      If  the  centre  of  the  cross- 


FlG.    21. 


Diagram  ro  illustrate  Flow  of  Water  along  a  Horizontal  1 1  bi 

CONNECTED    WITH    A    RESERVOIR. 


section  ol  the  free  end  of  the  tube  be  joined  to  the  centres  of  all  the 
menisci,  it  will  be  found  that  the  hue  is  a  straight  lute.  The  lateral 
pressure  at  any  point  of  the  tube  is  therefore  proportional  to  its 
distance  from  the  free  end.  Since  the  same  quantity  of  water  must 
pass  through  each  cross-section  of  the  horizontal  tube  in  a  given  time 
as  Hows  out  at  the  open  end.  the  kinetic  energy  of  the  liquid  at  every 
cross-section  must  be  constant  and  equal  to  i;»,-'.  where  v  is  the 
mean  velocity  (the  quantity  which  escapes  in  unit  of  time  divided  by 
the  cross-section)  of  the  water  at  the  tree  end. 

Just  inside  the  orifice  the  total  energy  ol  a  mass  m  of  water  is 
mgh  ;  just  beyond  it  at  the  first  vertical  tube,  mgh'-i  h*nv2,  where  /;' 
is  the  later, d  pressure.  On  the  assumption  th.it  between  the  inside 
of  the  orifice  and  the  first  tube,  no  energy  has  been  transformed  into 
he.it  (an  assumption  the  more  nearly  correct  the  smaller  the  distant  e 
between  it  and  the  inside  of  the  orifice  i>  made),  we  have  mgh  — mgh' 
+  lmr-,  i.e.,  \n/r'-- -mg(h  h').  In  other  words,  the  portion  ol  the 
energy  oi  position  of  the  water  in  the  reservoir  which  is  transformed 
into  the  kinetic  energy  of  the  water  flowing  along  the  horizontal  tube 
is  measured  by  the  difference  between  the  heighl  oi  the  level  of  the 
reservoir  and  the  Literal  pressure  at  the  beginning  "t  the  horizontal 
tube-that  is,  the  height  at  which  the  straight  hue  joining  the 
menisci  of  the  vertical  tubes  intersects  the  column  of  watei  in  the 
reservoir.     Let  11  represent  the  height  corresponding  to  that  part  of 


THE  CIRCU1   ITION  OF   THE  BLOOD  AND  LYMPH  77 

the  energy  of  position  which  is  transformed  into  the  kinetic  energy 

ni  the  flowing  water.     II  is  easily  calculated  when  the  mean  velocity 

di  efflux   is  known.     For  v=  J  >g\\   by  Torricelli's  theorem    (since 

nunc  of  the  energy  corresponding  to  II  is  supposed  to  be  used  up  in 

v'2 
overcoming    friction),   or    11=  — .     At   the   second    tube   the  lateral 

2g 

pressure  is  only  h".  The  sum  of  the  visible  kinetic  and  potential 
energy  here  is  therefore  \mv2+mgK'.  A  quantity  of  energy  mg{h'  -h") 
must  have  been  transformed  into  heat  owing  to  the  resistance  caused 
by  fluid  friction  in  the  portion  of  the  horizontal  tube  between  the  Inst 
two  vertical  tubes.  In  general  the  energy  of  position  represented  by 
the  lateral  pressure  at  any  point  is  equal  to  the  energy  used  up  in 
overcoming  the  resistance  of  the  portion  of  the  path  beyond  this  point. 

Velocity  of  Outflow. — It  has  been  found  by  experiment  that  v,  the 
mean  velocity  of  outflow,  when  the  tube  is  not  of  very  small  calibre, 
varies  directly  as  the  diameter,  and  therefore  the  volume  of  outflow 
as  the  cube  of  the  diameter.  In  fine  capillary  tubes  the  mean 
velocity  is  proportional  to  the  square,  and  the  volume  of  outflow  to 
the  fourth  power  of  the  diameter  (Poiseuille).  If,  for  example,  the 
linear  velocity  of  the  blood  in  a  capillary  of  10  \t  in  diameter  is  \  mm. 
per  sec,  it  will  be  four  times  as  great  (or  2  mm.  per  sec.)  in  a  capillary 
of  20  /<  diameter,  and  one-fourth  as  great  (or  £  mm.  per  sec.)  in  a 
capillary  of  5  /<  diameter,  the  pressure  being  supposed  equal  in  all. 
The  volume  of  outflow  per  second  is  obtained  by  multiplying  the 
cross-section  by  the  linear  velocity.  The  cross-section  of  a  circular 
capillary,  10  /<  in  diameter,  is  ■*  (5  x -10Vo)2  =  '  saY>  12500  scl-  mm. 
The  outflow  will  be  Ttt1oo  x  i~  25000  curj-  mm-  Per  sec-  The  outflow 
from  the  capillary  of  20  \i  diameter  would  be  sixteen  times  as  much, 
from  the  5  /<  capillary  only  one-sixteenth  as  much.  Some  idea  of 
the  extremely  minute  scale  on  which  the  blood-flow  through  a  single 
capillary  takes  place,  may  be  obtained  if  we  consider  that  for  the 
capillary  of  10  /(  diameter  a  flow  of  tt-^qq  cub.  mm.  per  sec.  would 
scarcely  amount  to  1  cub.  mm.  in  six  hours,  or  to  1  c.c.  in  250  days. 

When  the  initial  energy  is  obtained  in  any  other  way  than  by  means 
of  a  '  head  '  of  water  in  a  reservoir — say,  by  the  descent  of  a  piston 
which  keeps  up  a  constant  pressure  in  a  cylinder  filled  with  liquid — 
the  results  are  exactly  the  same.  Even  when  the  horizontal  tube  is 
distensible  and  elastic,  there  is  no  difference  when  once  the  tube  has 
taken  up  its  position  of  equilibrium  for  any  given  pressure,  and  that 
pressure  does  not  vary. 

Flow  with  Intermittent  Pressure. — When  this  acts  on  a  rigid  tube, 
everything  is  the  same  as  before.  When  the  pressure  alters,  the 
flow  at  once  comes  to  correspond  with  the  new  pressure.  Water 
thrown  by  a  force-pump  into  a  system  of  rigid  tubes  escapes  at  every 
stroke  of  the  pump  in  exactly  the  quantity  in  which  it  enters,  for 
water  is  practically  incompressible,  and  the  total  quantity  present 
at  one  time  in  the  system  cannot  be  sensibly  altered.  In  the 
intervals  between  the  strokes  the  flow  ceases  ;  in  other  words,  it  is 
intermittent.  It  is  very  different  with  a  system  of  distensible  and 
elastic  tubes.  During  each  stroke  the  tubes  expand,  and  make 
room  for  a  portion  of  the  extra  liquid  thrown  into  them,  so  that  a 
smaller  quantity  flows  out  than  passes  in.  In  the  intervals  between 
the  strokes  the  distended  tubes,  in  virtue  of  their  elasticity,  tend  to 
regain  their  original  calibre.  Pressure  is  thus  exerted  upon  the 
liquid,  and  it  continues  to  be  forced  out,  so  that  when  the  strokes  of 
the  pump  succeed  each  other  with  sufficient  rapidity,  the    outflow 


78  A   M  \NV  \L  OF  PHYSIOLOGY 

becomes  continuous.  This  is  the  state  oi  affairs  in  the  vascular 
system.  The  intermittent  action  <>t  the  bead  is  tuned  down  in  the 
elastic  vessels  to  a  continuous  steady  flow. 

The  Beat  of  the  Heart. — In  the  frog's  heart  the  contrac- 
tion can  be  seen  to  begin  aboul  the  mouths  oi  the  great  veins 
which  open  into  the  sinus  venosus.  Thence  it  spreads  in  suc- 
cession ovei  the  sinus  and  auricles,  hesitates  for  a  momenl  at 
the  auriculo-ventricular  junction,  and  then  with  a  certain  sud- 
denness invades  the  ventricle.  In  the  mammalian  hearl  the 
starting-point  of  the  contraction  is  likewise  the  mouths  of  the 
veins  opening  into  the  auricles  (especially  the  superior  vena  cava), 
which  are  richly  provided  with  muscular  fibres  akin  to  those  oi 
the  heart.  But  the  wave  advances  so  rapidly  that  it  is  difficult 
to  trace  in  its  course  a  regular  progress  from  base  to  apex, 
although  the  ventricular  beat  undoubtedly  follows  that  of  the 
auricle,  and  the  capillary  electrometer  indicates  that,  in  a  heart 
beating  normally,  the  electrical  change  associated  with  contrac- 
tion begins  at  the  base,  then  reaches  the  apex  (p.  730),  and  finally 
passes  towards  the  orifices  of  the  great  arteries. 

The  most  conspicuous  events  in  the  beat  of  the  heart,  in  their 
normal  sequence,  are  :  (1)  the  auricular  contraction  or  systole, 
(2)  the  ventricular  contraction  or  systole,  each  followed  by  relaxa- 
tion, (3)  the  pause.  The  auricles,  into  which,  and  beyond  which 
into  the  ventricles,  blood  has  been  flowing  during  the  pause  from  the 
great  thoracic  veins,  contract  sharply,  the  right,  perhaps,  a  little 
before  the  left.  The  contraction  begins  in  the  muscular  tissue 
that  surrounds  the  orifices  of  the  veins,  so  that  these,  destitute 
of  valves  as  they  are,  are  functionally,  at  least,  if  not  anatomi- 
cally, sealed  up  for  an  instant,  and  regurgitation  of  blood  into 
them  is  to  a  great  extent,  if  not  entirely,  prevented.  Apparently, 
complete  closure  of  the  inferior  cava  is  unnecessary,  the 
pressure  of  the  blood  in  it  being  sufficiently  high  to  hinder  any 
important  back  flow.  The  action  of  the  circular  fibres  of  the 
veins  in  closing  their  orifices  is  reinforced  by  the  contraction  of 
a  band  of  muscle  (the  tenia  terminal  is)  in  the  roof  of  the  right 
auricle.  This  band  compresses  especially  the  mouth  oi  the 
superior  vena  cava.  The  filling  of  the  ventricles  is  thus  com- 
pleted ;  their  contraction  begins  either  simultaneously  with  the 
relaxation  of  the  auricles  or  a  little  later.*  The  mitral  and 
tricuspid  valves,  whose  strong  but  delicate  curtains  have  during 
the  diastole  been  hanging  down  into  the  ventricles  and  swinging 

*  It  has  often  been  debated  whether  any  appreciable  interval  exists 
between  the  end  of  the  auricular  and  the  beginning  <>i  the  ventricular 
systole  of  the  warm-blooded  hearl.  According  to  Chauveau,  not  only  is 
this  period  (the  intersystole)  well  marked  and  sharply  delimited  (in  the 
horse),  but  it  is  occupied  by  a  definite  series  oi  events,  including  the  con- 
traction oi  the  papillary  muscles. 


THE  CIRCUL  ITTON  OF   I  III    moon  AND  LYMPH         79 

freely  in  the  entering  current  of  blood,  are  floated  up  as  the 
intraventricular  pressure  begins  to  rise,  so  that,  in  the  firsl 
momenl  of  the  sudden  and  powerful  ventricular  systole,  the  free 
edges  of  their  segments  come  together,  and  the  auriculo-ven- 
tricular  orifices  are  completely  closed  (Fig.  85,  p.  190).  In  the 
measure  in  which  the  pressure  in  the  contracting  ventricles 
increases,  the  contact  of  the  valvular  segments  becomes  closer 
and  more  extensive  ;  and  their  tendency  to  belly  into  the  auricles 
is  opposed  by  the  pull  of  the  chordae  tendineae,  whose  slender 
cords,  inserted  into  the  valves  from  bonier  to  base,  are  kept 
taut,  in  spite  of  the  shortening  of  the  ventricles  by  the  contrac- 
tion of  the  papillary  muscles.  The  arrangement  and  connections 
of  the  muscular  fibres  of  the  heart  are  such  that  during  the 
auricular  systole  the  auriculo-ventricular  groove  moves  towards 
the  base  of  the  heart,  while  during  the  systole  of  the  ventricles 
it  moves  towards  the  apex,  which  constitutes  a  relatively  fixed 
point  on  account  of  the  mutual  action  of  the  numerous  fibres 
which  converge  here  and  constitute  the  "  whorl."  The  line  joining 
the  apex  and  the  origin  of  the  aorta  does  not  shorten  when  the 
ventricles  contract,  but  all  parts  of  the  heart  are  drawn  towards 
this  line.  The  apex  is,  therefore,  pushed  forwards,  while  the  rest 
of  the  ventricular  surface  is  being  drawn  inwards.  During  the 
systole,  the  ventricles  change  their  shape  in  such  a  way  that  their 
combined  cross-section — which  in  the  relaxed  state  is  a  rough 
ellipse  with  the  major  axis  from  right  to  left — becomes  approxi- 
mately circular,  and  they  then  form  a  right  circular  cone.  As 
soon  as  the  pressure  of  the  blood  within  the  contracting  ventricles 
exceeds  that  in  the  aorta  and  pulmonary  artery  respectively,  the 
semilunar  valves,  which  at  the  beginning  of  the  ventricular 
systole  are  closed,  yield  to  the  pressure,  and  blood  is  driven  from 
the  ventricles  into  these  arteries. 

The  ventricles  are  more  or  less  completely  emptied  during  the 
contraction,  which  seems  still  to  be  maintained  for  a  short  time 
after  the  blood  has  ceased  to  pass  out.  The  contraction  is  fol- 
lowed by  sudden  relaxation.  The  intraventricular  pressure  falls. 
The  lunules  of  the  semilunar  valves  slap  together  under  the 
weight  of  the  blood  as  it  attempts  to  regurgitate,  the  corpora 
Arantii  seal  up  the  central  chink,  and  the  aorta  and  pulmonary 
artery  are  thus  cut  off  from  the  heart.  Then  follows  an  interval 
during  which  the  whole  heart  is  at  rest,  namely,  the  interval 
between  the  end  of  the  relaxation  of  the  ventricles  and  the 
beginning  of  the  systole  of  the  auricles.  This  constitutes  the 
pause.  The  whole  series  of  events  is  called  a  cardiac  cycle  or 
revolution  (see  Practical  Exercises,  p.  186). 

It  will  be  easily  understood  that  the  time  occupied  by  any 
one  of  the  events  of  the  cardiac  cycle  is  not  constant,  for  the 


8o  A   MANUAL  OF  PHYSIOLOGY 

rate  of  the  heart  is  variable.  If  we  take  about  70  beats  a  minute 
.is  the  average  normal  rate  in  a  man,  the  ventricular  systole  will 
tipy  about  0-3  second  ;  the  diastole,*  including  the  ventricular 
relaxation,  about  0-5  second.  The  systole  of  the  auricle  is  one- 
third  as  long  as  that  of  the  ventricle. 

This  rhythmical  beat  of  the  heart  is  the  ground  phenomenon 
of  the  circulation.  It  reveals  itself  by  certain  tokens — sounds, 
surface-movements  or  pulsations,  alterations  of  the  pressure  and 
velocity  of  the  blood,  changes  of  volume  in  parts-  all  periodic 
phenomena,  continually  recurring  with  the  same  period  as  the 
heart-beat,  and  all  fundamentally  connected  together.  And  it 
we  hold  fast  the  idea  that  when  we  take  a  pulse-tracing,  or  a 
blood-pressure  curve,  or  a  plethysmography  record,  we  are 
really  investigating  the  same  fact  from  different  sides,  we  shall 
be  able,  by  following  the  cardiac  rhythm  and'its  consequences 
as  far  as  we  can  trace  them,  to  hang  upon  a  single  thread  manv  of 
the  most  important  of  the  physical  phenomena  of  the  circulation. 

The  Sounds  of  the  Heart. — When  the  ear  is  applied  to  the 
chest,  or  to  a  stethoscope  placed  over  the  cardiac  region,  two 
sounds  are  heard  with  every  beat  of  the  heart  ;  they  follow 
each  other  closely,  and  are  succeeded  by  a  period  of  silence. 
The  dull  booming  '  first  sound  '  is  heard  loudest  in  a  region 
which  we  shall  afterwards  have  to  speak  of  as  that  of  the  '  cardiac 
impulse  '  (p.  82)  ;  the  short,  sharp,  '  second  sound  '  over  the 
junction  of  the  second  right  costal  cartilage  with  the  sternum. 

There  has  been  much  discussion  as  to  the  cause  of  the  first 
sound.  That  a  sound  corresponding  with  it  in  time  is  heard 
in  an  excised  bloodless  heart  when  it  contracts,  is  certain  ;  and 
therefore  the  first  sound  cannot  be  exclusively  due,  as  some 
have  asserted,  to  vibrations  of  the  auriculo-ventricular  valves 
when  they  are  suddenly  rendered  tense  by  the  contraction  of 
the  ventricles,  for  in  a  bloodless  heart  the  valves  are  not  stretched. 
Part  of  the  sound  must  accordingly  be  associated  with  the 
muscular  contraction  as  such. 

Again,  the  fact  that  the  first  sound  is  heard  during  the  whole, 

or  nearly  the  whole,  of  the  ventricular  systole  is  against  the 

idea  that  it  is  exclusively  due  to  the  vibrations  of  membranes 

like  the  valves,  which  would  speedily  be  damped  by  the  blood 

and  rendered  inaudible.     But  while  there  is  good  reason  to  believe 

that  the  vibration  of  the  suddenly-contracted  ventricles  is  the 

fundamental   factor,  the  shock  sets  up  vibrations  also  in  the 

blood,  the  chest -wall,  and  perhaps  the  resonant  tissue  of  the  lungs. 

Further,  as  we  shall  see  later  on  (p.  660),  the  sound  caused  by  a 

contracting  muscle  readily  calls  forth  sympathetic  resonance  in 

*  The  term  '  diastole  '  is  variously  used,  as  meaning  the  pause,  the 
pause  plus  the  period  during  which  relaxation  is  occurring,  or  the  period 
of  relaxation  alone.     We  shall  employ  it  in  the  second  sense. 


////    CIRCULATIOh   OF   THE   BLOOD  AND  LYMPH         81 

the  ear,  and  the  peculiar  booming  character  of  the  first  sound 
may  be  due  to  the  superposition  of  these  various  resonance  tones 
upon  the  muscular  note.  But,  in  addition,  the  vibration  of  the 
auriculo-ventricular  valves  undoubtedly  contributes  to  the  pro- 
duction of  the  sound,  and  some  observers  have  been  able  to 
distinguish  in  the  first  sound  the  valvular  and  the  muscular 
elements,  the  former  being  higher  in  pitch  than  the  latter,  but 
a  minor  third  below  the  second  sound.  In  the  excised  empty 
heart  the  deeper  tone  of  the  first  sound  is  alone  heard,  while 
the  higher  note  is  elicited  when  in  a  dead  heart  the  auriculo- 
ventricular  valves  are  suddenly  put  under  tension  (Haycraft). 
When  the  mitral  valve  is  prevented  from  closing  by  experimental 
division  of  the  chordae  tendinese,  or  by  pathological  lesions,  the 
first  sound  of  the  heart  is  altered  or  replaced  by  a  '  murmur.' 
This  evidence  is  not  only  important  as  regards  the  physiological 
question,  but  of  great  practical  interest  from  its  bearing  on  the 
diagnosis  of  cardiac  disease.  It  may  be  added  that  the  point 
of  the  chest-wall  at  which  the  first  sound  is  most  easily  recog- 
nised is  also  the  point  at  which  a  changed  sound  or  murmur 
connected  with  disease  of  the  mitral  valve  is  most  distinctly 
heard.  The  sound  is,  therefore,  best  conducted  from  the  mitral 
valve  along  the  heart  to  the  point  at  which  it  comes  in  contact 
with  the  wall  of  the  chest.  Changes  in  the  first  sound  con- 
nected with  disease  of  the  tricuspid  valve  are  heard  best,  in 
the  comparatively  rare  cases  where  they  can  be  distinctly 
recognised,  in  the  third  to  the  fifth  interspace,  a  little  to  the 
right  of  the  sternum. 

The  second  sound  is  caused  by  the  vibrations  of  the  semi- 
lunar valves  when  suddenly  closed,  '  the  recoiling  blood  forcing 
them  back,  as  one  unfurls  an  umbrella,  and  with  an  audible 
check  as  they  tighten  '  (Watson).  The  sharpness  of  its  note  is 
lost,  and  nothing  but  a  rushing  noise  or  bruit  can  be  heard,  when 
the  valves  are  hooked  back  and  prevented  from  closing.  It 
is  altered,  or  replaced  by  a  murmur  when  the  valves  are  diseased. 
As  there  is  a  mitral  and  a  tricuspid  factor  in  the  first  sound,  so 
there  is  an  aortic  and  a  pulmonary  factor  in  the  second.  The 
place  where  the  second  sound  is  best  heard  (over  the  junction 
of  the  second  right  costal  cartilage  and  sternum)  is  that  at  which 
any  change  produced  by  disease  of  the  aortic  valves  is  most 
easily  recognised.  The  sound  is  conducted  up  from  the  valves 
along  the  aorta,  which  comes  nearest  to  the  surface  at  this 
point.  Changes  connected  with  disease  of  the  pulmonary 
valves  are  most  readily  detected  over  the  second  left  intercostal 
space  near  the  edge  of  the  sternum,  for  here  the  pulmonary  artery 
most  nearly  approaches  the  chest-wall.  The  first  sound  is 
'  systolic  ' — that  is,  it  occurs  during  the  ventricular  systole  ;  the 

6 


82 


I    .1/  \NUAI.  ()!■    /■//)  SIo/jh,) 


second  is  '  diastolic,'  beginning  at   the  commencement    <>f  the 
diastole. 
The  Cardiac  Impulse.-    A   surface-movement    is  seen,   or  an 

impulse  felt,  at  every  cardiac  contraction  in  various  situations 
where  the  heart  or  arteries  approach  the  surface.  The  pulsa- 
tion, or  impulse,  of  the  heart,  often  styled  the  apex-beat,  is 
usually  most  distinct  to  sight  and  touch  in  a  small  area  lying  in 
the  fifth  left  intercostal  space,  between  the  mamma  ry  and  the  para- 
sternal line,*  and  generally,  in  an  adult,  about  an  inch  and  a  half 
to  the  sternal  side  of  the  former.  It  is  due  to  the  systolic 
hardening  of  the  ventricles,  which  are  heir  in  contact  with  the 
chest- wall,  the  contact  being  at  the  same  time  rendered  closer 
by  their  change  of  shape,  and  by  a  slight  movement  of  rotation  "1 
the  heart  from  left  to  right  during  the  contraction  (Practical  Exer- 
cises, p.  191).  When 
the  left  ventricle  is  in 
contact  with  the  chest 
at  the  position  of  the 
apex-beat,  as  is  usually 
the  case,  an  important 
element  in  the  impulse 
is  the  actual  forward 
thrust  of  the  apex. 
When  the  apex  -  beat 
corresponds  in  position 
with  the  right  ventricle, 
there  is  no  actual  for- 
ward movement,  al- 
though the  hardening 
of  the  ventricle  may  be 
felt  as  a  thrust  by  tin- 
finger.  Even  in  health  the  position  of  the  impulse  varies  some- 
what with  the  position  of  the  body  and  the  respiratory  move- 
ments. In  children  it  is  usually  situated  in  the  fourth  intercostal 
space.  In  disease  its  displacement  is  an  important  diagnostic 
sign,  and  may  be  very  marked,  especially  in  cases  of  effusion  ot 
fluid  into  the  pleural  cavity.  It  is  sometimes,  though  not  in- 
variably, a  little  lower  in  the  standing  than  in  the  sitting  position, 
and  shifts  an  inch  or  two  to  the  left  or  right  when  the  person  lies 
on  the  corresponding  side. 

Various  instruments,  called  cardiographs,  have  been  devised  for 
magnifying  and  recording  the  movements  produced  bythe  cardiac 
*  The  mammary  line  is  an  imaginary  vertical  line  supposed  to  be  drawn 
on  the  chest  through  the  middle  point  of  the  clavicle.  It  usually,  but  not 
necessarily,  passes  through  the  nipple.  The  parasternal  line  is  the  vertical 
line  lying  midway  between  the  mammary  line  and  the  corresponding 
border  of  the  sternum. 


Fig.  22.— Diagram  of  Marey's  Cardiograph. 


THE  CIRCULATION  OF  THE  moon    IND  l.VMril 


83 


Lmpulse.  Marey's  cardiograph  (Fig.  22)  consists  essentially  of  .1  small 
chamber,  or  tambour,  filled  with  air,  and  closed  a1  one  end  by  a 
flexible  membrane  carrying  a  button,  which  can  be  adjusted  to  the 
wall  of  the  chest.      This  receiving  tambour  is  connected   by  a  tube 

with  a  recording  tambour,  the  flexible  plate  of  which  acts  upon  a 
lever  writing  on  a  travelling  surface — a  uniformly-rotating  drum,  for 
example — covered  with  smoked  paper.  Any  movement  communi- 
cated to  the  button  forces  in  the  end  of  the  tambour  to  which  it  is 
attached,  and  thus  raises  the  pressure  of  the  air  in  it  and  in  the 
recording  tambour  ;  the  flexible  plate  of  the  latter  moves  in  response, 
and  the  lever  transfers  the  movement  to  the  paper.  The  tracing, 
or  cardiogram,  obtained  in  this  way  shows  a  small  elevation  corre- 
sponding to  the  auricular  systole,  succeeded  by  a  large  abrupt  rise 
i  .  n  responding  to  the  beginning  of  the  first  sound,  and  caused  by  the 
ventricular  systole.  This  ventricular  elevation  is  the  essential  por- 
tion of  the  curve  ;  it  is  alone  felt  by  the  palpating  hand,  and  the 
auricular  elevation  is  often  absent  from  the  cardiogram  in  man. 
The  rise  is  maintained,  with  small  secondary  oscillations,  for  about 
03  of  a  second  in  a  tracing 
from  a  normal  man,  then 
gives  way  to  a  sudden  de- 
scent, that  marks  the  relax- 
ation of  the  ventricles,  the 
beginning  of  the  second  sound. 
and  the  closure  of  the  semi- 
lunar valves.  An  interval  of 
about  o'5  second  elapses  be- 
fore the  curve  begins  again 
to  rise  at  the  next  auricular 
contraction. 

Such  was  the  interpretation 
which  Chauveau  and  Marey 
put  upon  their  tracings.  Al- 
though neither  their  results 
nor  their  deductions  from 
them  have  escaped  the  criti- 
cism of  succeeding  investiga- 
tors,  it   is   doubtful  whether 

any  adequate  reason  has  been  brought  forward  for  discarding 
them,  and  Chauveau  has  recently  furnished  fresh  proofs  of  their 
accuracy.  The  difficulties  that  beset  the  subject  are  great,  for 
the  cardiogram  is  a  record  of  a  complex  series  of  events.  The 
very  rapid  variation  of  pressure  within  the  ventricles,  the  change 
of  volume  and  of  shape  of  the  heart,  the  slight  change  of  position  of 
its  apex,  must  all  leave  their  mark  upon  the  curve,  which  is  besides 
distorted  by  the  resistance  of  the  elastic  chest-wall,  the  inertia  of  the 
recording  lever,  and  the  compression  of  the  air  in  the  connecting 
tubes.  It  is  only  by  comparing  in  animals  the  cardiographic  record 
with  the  changes  of  blood-pressure  in  the  heart  and  arteries  that  our 
present  degree  of  knowledge  of  the  human  cardiogram  has  been 
attained.  Could  we  register  directly  the  fluctuations  of  pressure  in 
the  interior  of  the  human  heart,  the  cardiographic  method  would  be 
rarely  employed.  For  clinical  purposes  the  receiving  tambour  can  be 
advantageously  replaced  by  a  small  glass  funnel  or  a  small  metal  cup, 
the  open  end  of  which  is  applied  without  a  membrane  over  the  cardiac 
impulse,  the  stem  being  connected  with  the  recording  tambour.     In 

6—2 


Fig. 


23. — Cardiogram  taken  with 
Marey's  Cardiograph. 


A,  auricular  systole  ;  V,  ventricular  sys- 
tole ;  D,  diastole.  The  arrow  shows  ^the 
direction  in  which  the  tracing  is  to  be  read. 


s4 


A   MANUAL  OB   PHYSIOLOGY 


cases  in  which  the  right  ventricle  is  in  contact  with  the  chest-wall  at 
the  position  of  the  apex-beat  the  cardiogram  is  '  inverted  '  that  is 
to  say.  the  chest-wall  is  drawn  in  <luring  systole  and  protruded  during 
diastole  of  the  ventricles.  Inversion  of  the  cardiogram  is.  I 
not  an  infallible  sign  of  the  pathological  condition  known  as  adherent 
pericardium  (Macken/i 

^Endocardiac  Pressure.  —  The  function  of  the  heart  is  to 
maintain  an  excess  of  pressure  in  the  aorta  and  pulmonary 
artery  sufficient  to  overcome  the  friction  of  the  whole  vascular 
channel,  and  to  keep  up  the  flow  of  blood.  So  long  as  the 
semilunar  valves  are  closed,  most  of  the  work  of  the  contracting 
ventricles  is  expended  in  raising  the  pressure  of  the  blood  within 
them.  At  the  moment  when  blood  begins  to  pass  into  the 
arteries,  nearly  all  the  energy  of  this  blood  is  potential  ;  it  is 


P«G.   -4. — Curves  of  Endocardiac  Pressure  taken  with  Cardiac    Sc 

A  in..  auri«  ular  curve  :  Vent.,  ventricular  curve  ;  AS,  period  of  auricular  systole, 
including  relaxation  :  VS.  of  ventricular  systole,  including  relaxation  ;  D,  pause. 

the  energy  of  a  liquid  under  pressure.  During  a  cardiac  cycle 
the  pressure  in  the  cavities  of  the  heart,  or  the  endocardiac 
pressure,  varies  from  moment  to  moment,  and  its  variations 
afford  important  data  for  the  study  of  the  mechanics  of  the 
circulation. 

For  the  study  of  the  endocardiac  pressure,  the  ordinary  mercurial 
manometer  (p.  ion  is  unsuitable,  since,  owing  to  the  relatively  great 
amount  of  work  required  to  produce  a  given  displacement  of  the 
mercury,  it  does  not  readily  follow  rapid  changes  of  pressure,  and  the 
mercurial  column,  once  displaced,  continues  for  a  time  to  execute 
vibrations  of  its  own.  which  arc  compounded  with  the  true  oscilla- 
tions of  blood-pressure.  Hut  bv  introducing  in  the  connection 
between  the  manometer  and  the  heart  a  valve  so  arranged  as  to 
oppose  the  passage  of  blood  towards  the  heart,  while  it  favours  its 


Till-   CIRCULATION  OF  THE  BLOOD  AND  F.YMP1I 


Ss 


passage  towards  the  manometer,  the  maximum  pressure  attained  in 
the  cardiac  cavities  during  the  cycle  may  be  measured  with  consider- 
able accuracy.  When  the  valve  is  reversed  the  apparatus  becomes 
.1  minimum  manometer.  In  this  way  it  has  been  found  that  in  I 
dogs  the  pressure  in  the  Left  ventricle  may  rise  as  high  as  230  to 
J41)  mm.  of  mercury,  and  sink  as  low  as  —30  to  —50  mm.  ;  while  in 
the  right  ventricle  it  may  be  as  much  as  70  mm.,  and  as  little  as 
—  25  mm.  In  the  right  auricle  a  maximum  pressure  of  20  mm.  of 
mercury  has  been  recorded,  and  a  minimum  pressure  of  —10  mm. 
or  even  less.  But  these  results  were  obtained  under  somewhat 
exceptional  experimental  conditions,  and  the  normal  maximum 
pressures  in  the  heart 
cavities  in  man  are  prob- 
ably not  so  high,  especi- 
ally in  the  right  auricle 
and  ventricle. 

Our  knowledge  of  the 
maximum  and  minimum 
pressure  attained  in  the 
cavities  of  the  heart,  even 
if  it  were  far  more  precise 
than  it  actually  is,  would 
only  carry  us  a  little  way 
in  the  study  of  the  endo- 
cardiac  pressure  -  curve, 
for  it  would  merely  tell  us 
how  far  above  the  base- 
line of  atmospheric  pres- 
sure the  curve  ascends, 
and  how  far  below  the 
base  -  line  it  sinks.  To 
exhaust  the  problem,  we 
require  to  have  tracings 
of  the  exact  form  of  the 
curve  for  each  of  the 
cavities  of  the  heart,  and 
to  know  the  time-relations 
of  the  curves  so  as  to  be 
able  to  compare  them 
with  each  other,  and  with 
the  pressure-curves  of  the 
great  arteries  and  great 
veins.  To  obtain  satis- 
factory   tracings    of    the 

swiftly-changing  endocardiac  pressure  is  a  task  of  the  highest  tech- 
nical difficulty,  and  it  is  only  in  very  recent  years  that  it  has 
been  accomplished  with  any  approach  to  accuracy  by  the  use 
of  elastic  manometers,  in  which  the  blood-pressure  is  counter- 
balanced, not  by  the  weight  of  a  column  of  liquid,  as  in  the  mer- 
curial manometer,  but  by  the  resistance  to  compression  of  a  small 
column  of  air  or  the  tension  of  an  elastic  disc  or  of  a  spring.  One 
of  the  earliest  of  these  was  the  now  somewhat  obsolete  C-spring 
manometer  of  Fick,  of  which  a  diagram  is  given  in  Fig.  25 .  Examples 
of  the  most  perfect  elastic  manometers  of  the  modern  type  are  the 
improved  instrument  of  Fick  (Fig.  26),  with  the  various  modifications 
it  has  undergone,  and  especially  the  manometers  of  Hurthle. 


Fig.  25. — Diagram  of  Fick's  C-spring 
Manometer. 

A,  hollow  spring  filled  with  alcohol.  Its  open 
end  B  is  covered  with  a  membrane  and  is  fixed 
to  the  upright  F  ;  the  other  end  C  is  free  to  move, 
and  is  connected  with  a  system  of  levers,  which 
move  the  writing  point  D  ;  E  is  the  cannula, 
which  is  connected  with  the  bloodvessel.  When 
the  pressure  in  the  spring  is  increased  it  tends 
to  straighten  itself. 


86 


A    MANUAL  OF  I'l I  YSlnl.OGY 


Hiirthlc's  spring  manometer  consists  of  a  small  drum  covered  with 
an  indiarubber  membrane,  loosely  arranged  so  as  no1  to  \  ibrate  with 
a  period  oi  its  own.     The  drum  is  connected  with  the  near!  or  with 

a  vessel,  and  the  blood-pressure  is  transmitted  to  a  steel  spring  by 
means  of  a  light  metal  disc  fastened  on  the  membrane.  The  Spring 
acts  on  a  writing  lexer.  The  instrument  is  so  constructed  that  for  a 
given  change  of  pressure  the  quantity  of  liquid  displaced  is  as  small 
as  possible,  and  it  is  on  this  that  its  capacity  to  follow  sudden 
variations  of  pressure  chiefly  depends.  The  manometer  is  connected 
with  the  cavity  of  the  heart  by  an  appropriately  curved  cannula  oi 
metal  or  glass,  which,  after  being  filled  with  some  Liquid  that  prevents 
coagulation  (Practical  Exercises,  p.  195),  is  pushed  through  the 
jugular  vein  into  the  right  auricle  or  ventricle,  or  through  the  carotid 
artery  and  aorta  into  the  left  ventricle.  Some  observers  fill  only 
the  cannula  with  fluid,  and  leave  the  capsule  of  the  elastic  manometer 
and  as  much  of  the  connections  as  possible  full  of  air.  Others  fib 
the  whole  system  with  liquid.  And  around  the  question  of  the 
relative  merits  of  '  transmission  '  by  liquid  and  by  air  has  raged  a 


l;i 


>6. — Fick's  Elastic  Manomj  11  r. 


a,  a  is  a  metal  piece  tunnelled  by  a  narrow  canal  of  about  1  nun.  in  diameter 
which  enlarges  below  to  a  shallow  saucer-shaped  space  b.  The  wide  opening  of  b  is 
covered  by  a  thin  piece  of  indiarubber  c,  to  the  centre  of  which  an  ivory  button  d 
is  attached.  The  button  presses  on  a  strong  steel  spring  /,  which  is  attached  at  one 
end  to  the  brass  frame  c.  e,  and  at  the  other,  by  means  of  an  intermediate  piece  g, 
to  the  lexer  It  .•  b  is  filled  with  1  few  drops  of  water,  but  the  canal  a  contains  only 
air.  When  a  is  connected  with  the  interior  of  the  heart  or  of  an  artery,  the  changes 
of  pressure  are  transmitted  to  the  spring,  and  recorded  by  the  writing-point  of  the 
lever. 


controversy  which,  however,  now  shows  signs  of  coming  to  an  end. 
For  there  is  reason  to  suppose  that  the  character  of  the  curves 
obtained  is  modified  among  other  circumstances  by  the  manner  in 
which  the  pressure  is  transmitted. 

Thus,  the  pressure-curve  of  the  ventricle,  according  to  most 
of  those  who  have  employed  manometers  with  liquid  trans- 
mission and  small  inertia  of  the  moving  parts  (Fig.  27),  remains 
after  the  first  abrupt  rise,  which  undoubtedly  corresponds  to 
the  ventricular  systole,  almost  parallel  to  the  abscissa  line  for  a 
considerable  time,  and  then  descends  somewhat  less  suddenly  than 
it  rose.  This  systolic  '  plateau,'  although  usually  broken  by  minor 
heights  and  hollows,  which  may  be  partly  due  to  inertia  oscilla- 
tions of  the  liquid  or  the  recording  apparatus,  would  indicate 


I  III'  CIRCULATION  Ol     I  III    BLOOD   AND  LYMPH 


87 


thai  the  ventricular  pressure,  after  reaching  its  maximum, 
maintained  itself  there  throughout  the  greater  pari  of  the 
systole.  The  tracings  yielded  by  most  of  the  manometers  with 
.111  transmission  (Fig.  28)  show  the  same  suddenness  in  the  fust 
pari  ol'  the  upstroke  and  the  last  part  of  the  descent — that  is, 
die  same  abruptness  in  the  beginning  of  the  contraction  and  the 
>nd  of  the  relaxation.  Hut  they  differ  totally  in  the  inter- 
mediate portion  of  the  curve, which, climbing  ever  more  gradually 
as  it  nears  its  apex,  remains  hut  a  moment  at  the  maximum, 
t  hen  immediately  descending  forms  a  '  peak,'  and  not  a  plateau. 
Without  entering  further  into  a  technical  discussion,  we  may 
say  the  bulk  of  the  evidence  goes  to  show  that  the  plateau  is 


wMwVW\MfvWV\^ 


Fig.  27. — Simultaneous  Record  of  Pressure    in  Left  Ventricle  (V)  and 
Aorta  (A).     (Hurthle.) 

The  tracings  were  taken  with  elastic  manometers  ;  o  indicates  a  point  just  before 
the  closure  of  the  mitral  valve  ;  i,  the  opening  of  the  semilunar  valve  ;  2,  begin- 
ning of  the  relaxation  of  the  ventricle  ;  3,  the  closure  of  the  semilunar  valve  ; 
4,  the  opening  of  the  mitral  valve.     The  ventricular  curve  shows  a  '  plateau.' 

not,  as  the  advocates  of  the  peak  have  claimed,  an  artificial 
phenomenon,  but  does  in  reality  correspond  to  that  continuation 
of  the  systole  of  the  ventricle,  that  dogged  grip,  if  we  may  so 
phrase  it,  which  it  seems  to  maintain  upon  the  blood  after  the 
greater  portion  of  it  has  been  expelled. 

This  conclusion  is  essentially  in  accordance  with  the  results  of 
Chauveau  and  Marey,  obtained  long  ago  by  means  of  their  'cardiac 
sound,'  which  was  in  principle  an  elastic  manometer  (Fig.  29). 

It  consisted  of  an  ampulla  of  indiarubber,  supported  on  a  frame- 
work, and  communicating  with  a  long  tube,  which  was  connected 
with  a  recording  tambour.  The  ampulla  was  introduced  into  the 
heart  through  the  jugular  vein  or  carotid  artery  in  the  way  already 
described.  Sometimes  a  double  sound  was  employed,  armed  with 
two  ampullae,  placed  at  such  a  distance  from  each  other  that  when 


88 


A  MANUAL  OF  PHYSIOLOGY 


one  was  in  the  right  ventricle  the  other  was  in  the  auricle  of  the  same 
side  Each  ampulla  communicated  by  a  separate  tube  in  the  common 
stem  nt  the  instrument  with  a  recording  tambour,  and  the  writing 
points  of  the  two  tambours  were  arranged  in  the  same  vertical  line. 

When  any  change  in  the  blond-pressure  lakes  place,  the  degree  of 
compression  of  the  ampullae  is  altered,  and  the  change  is  transmitted 
along  the  air-tight  connections  to  the  recording  tambours.  Simul- 
taneous records  of  the  changes  in  the  blood-pressure  in  the  righi 
auricle  and  ventricle  obtained  in  this  way  indicate  a  Midden  rise  of 
the  auricular  pressure  corresponding  with  the  auricular  systole, 
followed  by  a  sudden  fall  (Fig.  24).     This  is  represented  on  the  vcn- 

tricular    curve    by    a 

smaller  elevation, 
which  shows  that  the 
pressure  in  the  ven- 
tricle has  been  raised 
somewhat  by  the 
blood  driven  into  it 
from  the  auricle. 
Then  follows  imme- 
diately a  great  and 
abrupt  increaseof  ven- 
tricular pressure,  the 
result  of  the  systole 
of  the  ventricle.  The 
beginning  of  this  ele- 
vation is  synchronous 
with  the  beginning  of 
the  first  sound  ;  it  re- 
mains for  some  time 
at  the  maximum,  and 
then  the  curve  sud- 
denly sinks  as  the 
ventricle  relaxes.  (  )n 
the  descending  limb 
there  is  a  slight  ele- 
vation, due,  as  Marey 
supposed,  to  the  clo- 
sure of  the  semilunar 
valves,  which  causes 
a  better-marked  and 
simultaneous  eleva- 
tion in  the  curve  of 
aortic  pressure  when 
this  is  registered  by  means  of  a  sound  passed  into  the  aorta 
through  the  carotid  artery.  Both  the  auricular  and  ventricular 
curves  now  begin  again  to  rise  slowly,  showing  a  gradual  increase 
of  pressure  as  the  blood  flows  from  the  great  veins  into  the  auricle, 
and  through  the  tricuspid  orifice  into  the  ventrii  le.  This  slow  rise 
continues  till  the  next  auricular  systole. 


Fig.  28. — Comparison  of  Pressure  -  curves  op- 
Left  Auricle,  Left  Ventricle,  and  Aorta 
(v.  Frey). 

Recorded  by  elastic  manometers  with   air  trans- 
mission.    The  ventricular  curve  shows  a  '  peak.' 


It  is  probable  that  some  of  the  smaller  elevations  on  the  curves 
of  Chauveau  and  Marey.  and  particularly  that  which  they 
associated  with  the  closure  of  the  semilunar  valves,  were  due  to 
the   oscillations  of   their   apparatus.      For   it   is   a   remarkable 


THE  CTRCU1   ITION  OF  THE  BLOOD  AND  LYMPH 

fad  that  on  most  of  the  endocardiac  pressure  tracings  of  the 
besl  modern  manometers,  whether  the  curves  belong  to  the  type 
nt  thf  peak  or  of  the  plateau,  no  sudden  change  of  curvature,  no 

nick,  or  crease,  or  undulation  reveals  the  moment  of  opening  or 
closure  of  any  valve.  But  by  experimentally  graduating  a  pair 
of  elastic  manometers,  and  obtaining  with  them  simultaneous 
records  of  the  pressure  in  auricle  and  ventricle,  or  by  using  a 
'  differential  '  manometer,  in  which  the  pressures  in  two  cavities 
arc  opposed  to  each  other,  so  that  the  movement  of  the  membrane 
corresponds  to  their  difference,  we  can  calculate  at  what  points 
of  the  ventricular  curve  the  pressure  is  just  greater  than  and 
just  less  than  the  pressure  in  the  auricle.  The  first  point,  it  is 
evident,  will  correspond  to  the  instant  at  which  the  mitral  or 
tricuspid  valve,  as  the  case  may  be,  is  closed,  and  the  second  to 
the  instant  at  which  it  is 
opened.  And  in  like  man- 
ner, by  comparing  the 
pressure-curve  of  the  aorta 
with  that  of  the  left  ven- 
tricle, the  moment  of  open- 
ing and  closure  of  the  semi- 
lunar   valves    may    be    de- 

. „•       j    /-TV  _         j      o\       Fig.   29. — Diagram  of  Cardiac  Sound  for 

teimined  (FlgS.  27  and  28).  Simultaneous  Registration  of  Endo- 
According    to    the    best    ob-  cardiac  Pressure  in  Auricle  and  Ven- 

servations,    the    closure    of       tricle. 

the    semilunar    valves  takes         A-  elastic  ampulla  for  auricle  ;  V,  for  ven- 

,o„„„  „*  „   a: j       tricle;    T,   tubes  connected  with   recording 

place  at  a  time  correspond-    tambours. 

ing  to  a  point  on  the  upper 

portion  of  the  descending  limb  of  the  intraventricular  curve. 

On  the  blood-pressure  curve  of  the  aorta,  simultaneously  registered, 
the  corresponding  point  is  near  the  bottom  of  the  so-called  '  aortic  ' 
notch  (p.  96)  which  precedes  the  dicrotic  elevation.  For  clinical 
purposes,  in  man  the  moment  of  closure  of  the  semilunar  valves 
(denoted  by  the  abbreviation  S.C.  point)  may  be  taken  as  0^03  second 
before  the  bottom  of  the  aortic  notch  in  sphygmographic  tracings 
from  the  carotid,  this  being  approximately  the  average  time  taken 
by  the  pulse- wave  in  travelling  from  the  aorta  to  the  carotid.  The 
S.C.  point,  the  A.O.  point,  or  moment  of  opening  of  the  auriculo- 
ventricular  valves,  and  the  beginning  of  the  ventricular  systole,  are 
three  important  points  of  reference  in  the  measurement  and  inter- 
pretation of  pulse-tracings  in  clinical  work.  The  A.O.  point  in  man 
may  be  taken  as  a  point  '003  second  in  advance  of  the  summit  of 
the  dicrotic  wave  '  on  the  carotid  pulse-tracing  (Lewis).  But  this 
is  the  most  difficult  of  the  three  standard  points  to  determine 
clinically  with  anything  like  accuracy. 

The  study  of  the  curves  of  endocardiac  pressure  enables  us  to 
add  precision  in  certain  points  to  the  description  of  the  events 


go  A   MANUAL  OF  PHYSIOLOGY 

of  the  cardiac  cycle  which  we  have  already  given,  and,  as  regards 
the  ventricles,  to  divide  the  cycle  into  four  periods  : 

(i)  A  period  during  which  the  pressure  is  lower  in  the  ventricles 
than  cither  in  the  auricles  or  the  arteries,  and  the  auriculo-ven- 
tricular  valves  are  consequently  open,  and  the  semilunar  valves 
closed.     This  is  the  period  of  '  filling  '  of  the  heart,  or  the  pause. 

(2)  A  period,  beginning  with  the  ventricular  systole,  during 
which  the  pressure  is  increasing  abruptly  in  the  ventricles,  while 
they  are  as  yet  completely  cut  off  from  the  auricles  on  the  one  hand 
and  the  arteries  on  the  other  by  the  closure  of  both  sets  of  valves. 
This  is  the  period  of  '  rising  pressure'  during  which  the  ventricles 
arc,  so  to  say,  '  getting  up  steam.'  The  interval  between  the  be- 
ginning of  the  ventricular  systole  and  the  opening  of  the  semilunar 
valves  is  termed  the  '  presphvgmic  '  interval. 

(.',)  A  period  during  which  the  pressure  in  the  ventricles  overtops 
that  in  the  arteries,  and  the  semilunar  valves  are  open,  while  the 
auriculo-ventricular  valves  remain  shut.  This  is  the  period  of 
'  discharge  '  or  '  sphygmic  '  period. 

(4)  A  period  during  which  the  pressure  in  the  ventricles  is  a  git  in 
less  than  the  arterial,  while  it  still  exceeds  the  auricular  pressure,  and 
both  sets  of  valves  are  closed.  This  is  the  period  of  rapid  relaxation. 
The  interval  between  the  closure  of  the  semilunar  and  the  opening 
of  the  auriculo-ventricular  valves  is  sometimes  called  the  '  post- 
sp/ivgmic  '  interval. 

( M  the  four  periods,  the  second  and  fourth  are  exceedingly 
brief.  The  third  is  relatively  long  and  constant,  being  but 
slightly  dependent  on  either  the  pulse-rate  or  the  pressure  in 
the  arteries.  The  duration  of  the  first  period  varies  inversely 
as  the  frequency  of  the  heart  ;  with  the  ordinary  pulse-rate  it 
is  the  longest  of  all. 

From  records  taken  in  a  person  with  a  defect  in  the  chest-wall 
which  rendered  the  heart  accessible  the  following  results  were 
obtained  as  to  the  duration  of  the  various  events  of  the  cardiac 
cycle  :  First  and  fourth  periods  together,  0*445  ;  third  period,  0*254  '• 
second  period  (presphygmic  interval),  0-051  second,  the  pulse-rate 
being  80  a  minute  (Tigerstedt).  In  another  case  with  a  similar 
defect  the  first  period  lasted  0*32,  the  fourth  period  (post-sphygmic 
interval)  o-o6,  the  second  and  third  periods  together  0*4,  and  the 
auricular  systole  o- 1  second,  the  pulse-rate  being  66. 

The  fluctuations  of  pressure  in  the  auricles,  although  confined 
within  narrower  limits  than  in  the  ventricles,  are  of  equal 
interest.  They  have  been  studied  of  late  years  in  considerable 
detail  both  in  animals  and  by  indirect  methods  in  man.  No 
fewer  than  three  distinct  elevations  or  '  positive  waves,'  separated 
or  followed  by  three  depressions  or  '  negative  waves,'  have  been 
described  on  the  curve  of  intra-auricular  pressure  (Fig.  24).     The 


THE  CIRCUl   iTION  OF   THE  BLOOD  AND  LYMPH  91 

firsi  elevation  corresponds  to  the  systole  of  the  auricle  The 
•  lid  coincides  with  the  onset  of  the  ventricular  systole,  and 
is.  perhaps,  due  to  the  sudden  bulging  o\  the  auriculo-ventricular 
valve  into  the  auricle,  or  even  to  a  slight  regurgitation  of  blood 
from  the  ventricle  through  the  valve  before  it  has  completely 
closed.  The  cause  of  the  third  elevation,  which  occurs  during 
the  period  occupied  in  the  ventricular  pressure-curve  by  the 
plateau,  is  less  clearly  made  out.  En  man,  the  events  taking  place 
in  the  right  auricle  during  its  systole  can  be  followed  to  some 
extent  by  recording  the  \-enous  pulse  in  the  jugular  veins, 
especially  the  internal  jugular,  at  the  root  of  the  neck  (Fig.  30). 
Successful  tracings  can  be  obtained,  not  only  in  certain  pathological 
conditions,  but  in  many  normal  individuals,  and  it  is  probably 


Fin.   30. — Simultaneous  Record  of  Jugular  Pulse,  Ventricular  Contrac- 
tion, Auricular  Contraction,  and  Carotid  Pulse  in  Dog  (Cushny  and 

Grosh). 

a.  c.  v.  the  three  elevations  of  the  jugular  pulse.     Time-trace,  fifths  of  a  second. 

only  a  matter  of  improved  technique  to  obtain  them  in  all.  The 
jugular  venous  pulse-tracing,  like  the  intra-auricular  pressure- 
curve,  shows  in  general  three  well-marked  elevations  and  three 
depressions,  and  there  is  good  evidence  that,  broadly  speaking, 
these  features  of  the  jugular  curve  correspond  as  regards  their 
origin  with  the  changes  of  pressure  in  the  auricle.  Some  differ- 
ence of  opinion  exists  as  to  how  the  changes  of  pressure  in  the 
auricle  are  propagated  into  the  veins,  although  there  seems  to 
be  little  reason  to  suppose  that  in  normal  persons  any  actual 
regurgitation  of  blood  takes  place.  It  is  also  a  debatable  ques- 
tion how  far  pulsation  transmitted  from  the  great  arteries  of  the 
thorax  and  neck  may  affect  the  jugular  tracing.  But  be  this  as 
it  may,  the  jugular  curve,  when  properly  interpreted,  affords 
valuable  information  as  to  the  action  of  the  auricle,  information 
of  the  same  kind  as  that  afforded  by  the  arterial  pulse-tracing 
and   the   cardiogram   as   to   the   action  of  the   ventricle.     The 


02  A    M  \  \l     U    <>!■    PHYSIOLOGY 

student  must,  however,  be  warned  that  the  proper  interpreta- 
tion of  such  tracings  in  the  study  of  cardiac  disease  requires 
special  knowledge  and  training.* 

We  have  already  said  that  a  negative  pressure  may  be  detected  in 
the  cardiac  cavities  by  means  of  a  special  form  of  mercurial  mano- 
meter. This  is  confirmed  by  an  examination  of  the  tracings  written 
by  good  elastic  manometers,  for  the  curves  of  both  ventricles  may 
often  descend  below  the  line  of  atmospheric  pressure.  The  cause  ot 
this  negative  pressure  has  been  much  discussed.  In  part  it  may  be 
ascribed  to  the  aspiration  of  the  thoracic  cage  when  it  expands  during 
inspiration  (p.  210).  But  since  the  pressure  in  a  vigorously-beating 
heart  may  still  become  negative,  when  the  thorax  has  been  opened, 
and  the  influence  of  the  respiratory  movements  eliminated,  we  must 
conclude  that  the  recoil  of  the  somewhat  narrowed,  or  at  least  dis- 
torted, auriculo- ventricular  rings,  and  of  elastic  structures  in  the 
walls  of  the  ventricles,  exerts  of  itself  a  certain  suction  upon  the 
blood.  This,  however,  is  not  an  important  factor  in  the  maintenance 
of  the  circulation. 

The  Arterial  Pulse. — At  each  contraction  of  the  heart  a  quan- 
tity of  blood,  probably  varying  within  rather  wide  limits  (p.  127), 
is  forced  into  the  already  full  aorta.  If  the  walls  of  the  blood- 
vessels were  rigid,  it  is  evident  (p.  77)  that  exactly  the  same 
quantity  would  pass  at  once  from  the  veins  into  the  right  auricle. 
The  work  of  the  ventricle  would  all  be  spent  within  the  time  of 
the  systole,  and  only  while  blood  was  being  pumped  out  of  the 
heart  would  any  enter  it.  Since,  however,  the  vessels  are  exten- 
sible, some  of  the  blood  forced  into  the  aorta  during  the  systole 
is  heaped  up  in  the  arteries,  beyond  which,  in  the  narrow  arterioles 
and  in  the  capillary  tract,  with  its  relatively  great  surface,  the 
chief  resistance  lies.  The  arteries  are  accordingly  distended  to 
a  greater  extent  than  before  the  systole,  and,  being  elastic,  they 
keep  contracting  upon  their  contents  until  the  next  systole 
over-distends  them  again.  In  this  way,  during  the  pause  the 
walls  of  the  arteries  are  executing  a  kind  of  elastic  systole,  and 
driving  the  blood  on  into  the  capillaries.  The  work  done  by 
the  ventricle  is,  in  fact,  partly  stored  up  as  potential  energy  in 
the  tense  arterial  wall,  and  this  energy  is  being  continually 
transformed  into  work  upon  the  blood  during  the  pause,  the 
heart  continuing,  as  it  were,  to  contract  by  proxy  during  its 
diastole.  Thus,  the  blood  progresses  along  the  arteries  in  a 
series  of  waves,  to  which  the  name  of  '  blood-waves  '  or  '  pulse- 
waves  '  may  be  given.  Wherever  the  pulse-wave  spreads  it 
manifests  itself  in  various  ways — by  an  increase  of  blood-pres- 
sure, an  increase  in  the  mean  velocity  of  the  blood-flow,  an 
increase  in  the  volume  of  organs,  and  by  the  visible  and  palpable 
signs  to  which  the  name  of  pulse  is  commonly  given  in  a  restricted 

*  The  necessary  details  must  be  sought  in  such  works  as  Mackenzie's 
'  Diseases  of  the  Heart.' 


I  III    CIRCULATION  OF   I  III.  BLOOD  AND  I.YMDII 


93 


sense.  The  intermittence  in  the  flow  with  which  the  pulse- 
wave  is  necessarily  associated  is  at  its  height  at  the  beginning  of 
the  aorta.  In  middle-sized  arteries,  such  as  the  radial,  it  is  still 
well  marked,  but  it  dies  away  as  the  capillaries  are  reached,  and 
only  under  special  conditions  passes  on  into  the  veins,  where, 
however,  as  has  just  been  mentioned,  pulsatory  phenomena  of  a 
different  origin  may  be  detected. 

The  pulse  was  well  known  to  the  Greek  physicians,  and  used 
by  them  to  a  certain  extent  as  an  indication  in  practical  medicine. 
Harvey  demonstrated  with  some  clearness  the  relation  of  the 
pulse  to  the  contraction  of  the  heart,  but  Thomas  Young  was 
the  hrst  to  form  a  proper  conception  of  it  as  the  outward  token 
of  a  wave  propagated  from  heart  to  periphery. 

When  the  finger  is  placed  over  a  superficial  artery  like  the 
carotid,  the  radial  or  the  temporal,  a  throb  or  beat  is  felt,  which, 
without  measurement, 
seems  to  be  exactly 
coincident  with  the 
cardiac  impulse.  In 
certain  situations  the 
pulse  can  be  seen  as 
a  distinct  rhythmical 
rise  and  fall  of  the 
skin  over  the  vessel. 
The  throbbing  of  the 
carotid,  especially 
after  exertion,  is 
familiar  to  everyone, 
and  the  beat  of  the 
ulnar    artery    can   be 

easily  rendered  visible  by  extending  the  hand  sharply  on  the  wrist. 
When  the  pulse  is  felt  by  the  finger,  it  is  not  the  expansion, 
but  the  hardening  of  the  wall  of  the  vessel,  due  to  the  increase  of 
arterial  pressure,  that  is  perceived  ;  and  even  a  superficial  artery, 
when  embedded  in  soft  tissues  so  that  it  cannot  be  compressed, 
gives  no  token  of  its  presence  to  the  sense  of  touch.  Sometimes 
an  artery  is  longitudinally  extended  by  the  pulse-wave,  and  this 
extension  may  be  far  more  conspicuous  than  the  lateral  dilata- 
tion. This  is  particularly  seen  when  one  point  of  the  vessel  is 
fixed  and  a  more  distal  point  offers  some  obstruction  to  the  blood- 
flow,  as  at  a  bifurcation  or  in  an  artery  which  has  been  ligatured 
and  divided. 

By  means  of  the  sphygmograph,  the  lateral  movements  of 
the  arterial  wall,  or,  rather,  in  man,  the  movements  of  the  skin 
and  other  tissues  lying  over  the  bloodvessel,  can  be  magnified 
and  recorded. 


Fig.   31. — Scheme  of  Marey's  Sphygmograph. 

A,  toothed  wheel  connected  with  axle  H,  and 
gearing  into  toothed  upright  B  ;  C,  ivory  pad 
which  rests  over  bloodvessel  and  is  pressed  on  it 
by  moving  G,  a  screw  passing  through  the  spring  J  ; 
E,  writing-lever  attached  to  axle  H,  and  moved  by 
its  rotation.  E  writes  on  D,  a  travelling  surface 
moved  by  clockwork  F. 


94 


A   MANV  II    OF   PHYSIOLOGY 


It  would  be  very  unprofitable  to  enumerate  all  the  sphygmographs 
which  ingenuity  lias  invented  and  found  uames  for.  The  first  rude 
attempt  to  magnify  the  movements  of  the  pulse  was  made  by  loosely 
attaching  a  thin  fibre  of  glass  or  wax  to  the  skin  with  a  little  lard,  in 
order  to  demonstrate  the  venous  pulse  which  appears  under  certain 
conditions.  Vierordt  improved  on  this  by  usmg  a  counterpoised 
lever  writing  on  a  blackened  surface.  But  the  inertia  of  the  l< 
was  so  great  that  the  I;  ares  of  the  pulse  wen-  obscured.      In 

all  modern  sphygmographs  there  is  a  part,  usually  button-shaped, 
which  is  pressed  over  the  artery  by  means  of  a  spring,  as  in  .Marey's 
and  Dudgeon's  sphygmographs.  or  by  a  weight,  or  by  a  column  of 
liquid.  In  .Marey's  instrument,  the  button  acts  upon  a  toothed  rod 
gearing  into  a  toothed  wheel,  to  which  a  lever,  or  a  system  of  le\ 

is  attached.  The 
:  has  a  writing- 
point  which  records 
the  movement  on  a 
smoked  plate,  or  a 
plate  covered  with 
smoked  p  a  p  c  r , 
drawn  uniformly 
along  by  clockwork 
For 
many  clinical  pur- 
•cially  in 
the  study  of  dis- 
ordered cardiac 
function,  isolated 
records  of  the  ar- 
terial pulse  ar 
comparatively  little 
value.  Special 
forms  of  sphygmo- 
graphs (polygraphs) 
have,  therefore, 
been  devised, 
which,  by  the  ad- 
dition of  one  or 
more  recording 
tambours,  permit 
the  simultaneous 
record  of  move- 
ments from  two  or 
more  points  of  the  vascular  system — for  example,  the  radial  artery 
and  the  jugular  vein,  or  the  radial  or  carotid  artery,  jugular  vein, 
and  the  apex  of  the  heart.  In  rare  cases,  with  defect  of  the  chest 
wall,  a  tracing  may  be  obtained  even  from  the  aorta  (Fig.  33). 

In  a  normal  arterial  pulse-tracing  (Fig.  32)  the  ascent  is  abrupt 
and  unbroken  ;  the  descent  is  more  gradual,  and  is  interrupted 
by  one,  two,  or  even  three  or  more,  secondary  wavelets.  The 
most  important  and  constant  of  these  is  the  one  marked  j.  which 
has  received  the  name  of  the  dicrotic  wave.  Usually  less  marked, 
and  sometimes  absent,  is  the  wavelet  2  between  the  dicrotic 
elevation  and  the  apex  of  the  curve.     It  is  generally  termed  the 


Fig.   32. — Pulse-trai  1 

1,  primary  elevation;  2,  predicrotic  or  first  tidal 
wave  ;  3,  dicrotic  wave.  The  depression  between  2  and 
3  is  the  dicrotic  or  aortic  notch  :  3  is  better  marked 
in  B  than  in  A.  C,  dicrotic  pulse  with  low  arterial 
pressure  ;  D,  pulse  with  high  arterial  pressure — summit 
of  primary  elevation  in  the  form  of  an  ascending  plateau. 
Stolic  anacrotic  pulse  ;  the  secondary  wavelet  a 
occurs  during  the  upstroke  corresponding  to  tin  ven- 
tricular systole.  F,  presystolic  anacrotic  pulse  ;  a  1 
just  before  the  systole  of  the  ventricle.  In  this  rarer 
form  of  anacrotism,  a  may  sometimes  be  due  to  the 
auricular  systole  when  the  aortic  valves  are  incompetent. 


////    CIRCU1    ITION  OB    THE  BLOOD    I ND  LYMPH         95 

predicrotic  wave.  Oscillations,  due  to  vibrations  of  the  record- 
ing apparatus,  appear  on  many  pulse-tracings,  and  it  is  importanl 
to  recognise  their  cause,  so  that  no  weight  may  be  given  to  them. 

In  the  explanation  of  the  pulse-tracing,  a  fundamental  fact  to  be 

borne  in  mind  is  the  elasticity  of  the  vessels.  When  an  incompres- 
sible fluid  like  water  is  injected  by  an  intermittent  pump  into  one  end 
.it  ,tn  elastic  tube  a  wave  is  set  up,  which  is  transmitted  to  the  other 
end  of  the  tube.  It  is  a  positive  wave — that  is,  it  causes  an  increase 
of  pressure  and  an  expansion  of  the  tube  wherever  it  arrives  ;  and  if 
.1  series  of  lexers  be  placed  in  contact  with  the  tube,  they  will  rise 
and  sink  in  succession  as  the  wave  passes  them.  After  the  passage  of 
t  Ins  primary  wave  the  walls  of  the  tube,  instead  of  coming  instantly  to 
rest  in  their  original  position,  regain  it  by  a  series  of  oscillations,  lust 
shrinking  too  much,  then  expanding  too  much,  but  at  each  move- 
ment coming  nearer  to  the  position  of  equilibrium.  Each  vibration 
of  the  elastic  wall  is  of  course  accompanied  by  a  change  of  pressure 
in  the  contents  of  the  tube.  This  change  of  pressure  runs  along  the 
tube  as  a  wave  ;  and  such  waves,  succeeding  the  primary  one,  may 
be  called  secondary  waves  of  oscillation.  These  secondary  waxes  will 
be  set  up  in  an  clastic  system  whether 
the  distal  end  of  the  system  be  closed 
or  open.  But  if  it  is  closed,  or  suffi- 
ciently obstructed  without  being  actually 
closed,  secondary  waves  of  another  kind 
may  also  be  generated,  the  primary  wave 
on  arriving  at  the  distal  end  being  re- 
flected there.  The  reflected  wave  running 
back  towards  the  central  end  may  there 
again  undergo  reflexion,  and  pass  out 
once  more  towards  the  distal  end  as  a 
centrifugal,  twice-reflected  wave.  When 
the  liquid  ceases  to  enter  the  tube  at  the  Fig.  33. — Pulse-curve  from 
end  of  the  stroke,  a  wave  of  diminished  Human     Aorta     (after 

pressure — a  negative  wave — is  generated  Tigerstedt). 

at  the  central  end,   and  is  propagated 

to  the  distal  end,  where  it  may  be  reflected  just  like  the  positive 
wave. 

Although  under  certain  conditions  the  dicrotic  wave  is  so 
marked  that  the  double  beat  of  the  pulse  was  discovered  and 
named  by  physicians  long  before  the  invention  of  any  sphygmo- 
graph,  perhaps  no  physiological  question  has  been  more  dis- 
cussed or  is  less  understood  than  the  mechanism  of  its  production. 
Two  points,  however,  seem  to  be  clear  :  (1)  That  it  is  a  centri- 
fugal, and  not  a  centripetal,  wave — that  is  to  say,  it  travels 
away  from,  and  not  towards,  the  heart  ;  (2)  that  the  aortic 
semilunar  valves  have  something  to  do  with  its  origin. 

It  is  not  a  centripetal  wave,  for  in  tracings  taken  at  all  parts 
of  the  arterial  path,  no  matter  what  the  distance  from  the  heart 
and  the  capillaries  (e.g.,  the  origin  of  the  carotid  and  the  radial 
at  the  wrist),  the  dicrotic  wave  is  separated  by  the  same  interval 
from  the  beginning  of  the  primary  elevation.  This  can  only  be 
explained  by  supposing  that  it  has  the  same  point  of  origin,  and 


g6  ./   MANUAl    OB   PHYSIOLOGY 

travels  with  the  same  velocity  and  in  the  same  dire»  tion  as  the 
primary  wave.  It  is  not,  then,  a  wave  reflected  directly  from  t  In- 
peripheral  distribution  of  the  artery  from  which  the  pulse-tracing 
is  taken. 

Sonic  writers  have  contended  that  it  is  a  centrifugal  twice-reflected 
wave,  and,  indeed,  traces  of  such  waves  may  be  dete<  ted  in  the 
vessels  of  newly-killed  animals  when  changes  of  pressure  of  the  same 
order  of  magnitude  as  the  arterial  pulse  are  artificially  produced  by 
a  pump  and  recorded  by  clastic  manometers  connected  with  the 
interior  of  an  artery.  It  has  been  supposed  that  these  secondary 
waves  are  reflected  first  from  peripheral  points  at  which  the  blood- 
flow  is  particularly  obstructed  (the  bifurcations  of  the  larger  arteries, 
and  the  small  arteries  and  capillaries  in  general),  and  that  running 
towards  the  heart,  they  are  again  reflected  outwards  from  the  semi- 
lunar valves.  It  has  been  urged  in  support  of  this  view  that  in  very 
small  animals  (guinea-pigs)  no  dicrotic  elevation  occurs  on  the  pulse- 
tracing,  since  the  path  which  the  reflected  wave  has  to  follow  is  so 
short  that  it  arrives  at  the  root  of  the  aorta  before  the  primary 
elevation  is  over.  But  this  argument  is  by  no  means  conclusive, 
and,  indeed,  the  great  difference  in  the  distance  from  the  heart  of 
the  numerous  points  at  which  reflection  must  take  place  is  one  of 
the  chief  difficulties  of  the  hypothesis.  For  it  is  not  easy  to  under- 
stand how  the  reflected  fragments  of  the  primary  wave,  arriving  at 
different  intervals  at  the  heart,  can  be  integrated  into  the  single 
considerable  dicrotic  elevation. 

The  explanation  that  best  takes  account  of  the  facts  and 
renders  most  clear  the  role  of  the  semilunar  valves  is  some- 
what as  follows  :  When  the  systole  abruptly  comes  to  an  end  and 
the  outflow  from  the  ventricle  ceases,  the  column  of  blood 
in  the  aorta  tends  still  to  move  on  in  virtue  of  its  inertia,  and  a 
diminution  of  pressure,  accompanied  by  a  corresponding  con- 
traction of  the  aorta,  takes  place  behind  it,  just  as  a  negative 
wave  is  set  up  in  the  central  end  of  the  elastic  tube  when  the 
stroke  of  the  pump  is  over.  At  the  same  moment,  and  while 
the  semilunar  valves  are  still  for  an  instant  incompletely  closed, 
the  diminution  of  pressure  in  the  beginning  of  the  aorta  is 
intensified  by  the  aspiration  of  the  relaxing  ventricle,  which  sucks 
the  blood  back  against  the  valves,  and  draws  them  a  little 
way  into  its  cavity.  A  negative  wave,  therefore — a  wave  of 
diminished  pressure,  represented  in  the  pulse  -  curve  by  the 
'  aortic  notch  '  —  travels  out  towards  the  periphery.  The 
diminution  of  pressure  is  quickly  followed  by  a  rebound,  as 
always  happens  in  an  elastic  system.  The  recoiling  blood  meets 
the  closed  semilunar  valves.  The  aorta  expands  again,  and  the 
expansion  is  propagated  once  more  along  the  arteries  as  the 
dicrotic  elevation.  It  is  possible  that  this  elevation  may  be  re- 
inforced by  a  reflected  wave  produced  in  the  manner  described. 

When  the  semilunar  valve  becomes  incompetent  in  disease,  or  is 
rendered  insufficient  in  animals  by  the  artificial  rupture  of  one  or 


THE  CIRCULATION  OF   THE  BLOOD  AND  LYMPH  97 

more  of  its  segments,  the  dicrotic  wave,  as  will  be  readily  understood 
from  the  manner  in  winch  it  is  produced,  either  disappears  altogether 
or  is  markedly  enfeebled.  But  apart  from  any  anatomical  Lesion  or 
functional  defect  in  the  aortic  valves,  the  prominence  of  the  wave 
varies  with  a  great  number  of  circumstances,  some  of  which  are  in  a 
measure  understood,  while  others  remain  obscure.  It  varies  in 
particular  with  the  abruptness  of  discharge  of  the  ventricle  and  the 
extensibility  of  the  arteries.  The  conditions  are  usually  favourable 
when  the  arterial  pressure  is  low,  for  the  blood  then  passes  quickly 
from  the  ventricle  into  the  arteries,  which,  already  only  moderately 
tense,  are  easily  dilated  by  the  primary  wave,  then  sharply  collapse, 
and  are  again 'abruptly  distended  when  the  dicrotic  wave  arrives. 
And.  in  fact,  an  exaggeration  of  the  dicrotic  wavelet  may  be  artifi- 
cially  produced  by  nitrite  of  amyl  (Fig.  89,  p.  193),  a  drug  which 
lessens  the  blood-pressure  by  dilating  the  small  arteries.  Muscular 
exercise  (Fig.  88,  p.  193),  running  or  bicycling,  for  instance,  has  a 
similar  effect  on  the  sphygmogram,  although  the  explanation  can 
scarcely  be  the  same,  since  the  blood-pressure  mounts  rapidly  when 
moderate  exercise  begins  and  only  gradually  falls  during  its  con- 
tinuance, with  an  abrupt  decline  to  normal  or  below  it  on  cessation 
of  work  (Bowen).  The  increase  in  the  pulse-rate  may  have  some- 
thing to  do  in  this  case  with  the  exaggeration  of  the  dicrotism,  which 
is  very  frequently,  although  by  no  means  invariably,  associated  with 
a  rapidly-beating  heart,  and  therefore  is  often  seen  in  fever.  On 
the  other  hand,  in  certain  diseases  associated  with  a  high  arterial 
pressure  the  dicrotic  elevation  almost  disappears.  Atheromatous 
arteries,  being  very  inextensible,  do  not  allow  a  dicrotic  pulse. 

Since  the  pulse  represents  a  periodical  increase  and  diminution  in 
the  amount  of  distension  of  an  artery  at  any  point,  the  line  joining 
all  the  minima  of  the  pulse-curve  will  vary  in  its  height  above  the 
base-line,  or  line  of  no  pressure,  according  to  the  amount  of  per- 
manent distension,  i.e.,  permanent  blood-pressure,  which  the  heart 
in  any  given  circumstances  is  able  to  maintain.  Any  circumstance 
that  tends  to  lessen  the  permanent  distension  will  cause  a  fall  of  the 
line  of  minima,  and  any  circumstance  tending  to  increase  the  disten- 
sion will  cause  that  line  to  rise.  If,  for  example,  the  arm  be  raised 
while  a  pulse-tracing  is  being  taken  from  the  wrist,  the  line  of 
minima  falls  because  the  permanent  pressure  in  the  radial  artery  is 
diminished. 

The  form  of  the  pulse-curve  varies  in  the  different  arteries, 
and  therefore  in  making  comparisons  the  same  artery  should  be 
used.  When  the  wave  of  blood  only  enters  an  artery  slowly, 
the  ascending  part  of  the  curve  will  be  oblique.  This  is  normally 
the  case  in  a  pulse-curve  of  a  distant  artery,  such  as  the  posterior 
tibial.  The  height  of  the  wave  is  also  less  than  in  an  artery 
nearer  the  heart,  such  as  the  carotid,  or  even  the  axillary,  where 
the  primary  elevation  is  relatively  abrupt  (Fig.  90,  p.  193). 

Anacrotic  Pulse. — As  a  rule,  the  ascent  of  the  tracing  is 
unbroken  by  secondary  waves,  but  in  certain  circumstances 
these  may  appear  on  it.  This  condition,  which,  when  well 
marked  at  any  rate,  may  be  considered  pathological,  is  called 
anacrotism  (Fig.  32).  It  is  seen  when  the  discharge  of  the  left 
ventricle  into  the  aorta  is  slow  and  difficult — e.g.,  in  old  people 

7 


93  A  MANUAL  OF  PHYSIOLOGY 

whose  arteries  have  been  rendered  less  extensible  by  the  deposit 
of  lime-salts  in  their  walls  (atheroma),  and  in  cases  where  the 
orifice  of  the  aorta  has  been  narrowed  from  disease  of  the  semi- 
lunar valves  (aortic  stenosis).  Since  these  conditions  are  in 
general  associated  with  hypertrophy  and  dilatation  of  the  left 
ventricle,  the  slow  emptying  of  the  ventricle  is  partly  due  to  the 
greater  quantity  of  blood  which  it  contains.  In  whatever  way 
the  delay  in  the  emptying  of  the  ventricle  is  brought  about,  the 
most  probable  explanation  of  the  anacrotic  pulse  is  that  the 
delay  affords  time  for  one  or  more  secondary  waves  to  be  de- 
veloped in  the  arterial  system  before  the  summit  of  the  curve 
has  been  reached,  and  that  these  are  superposed  upon  the  long- 
drawn  primary  elevation.  In  aortic  insufficiency,  where  the  left 
side  of  the  heart  is  never  cut  off  entirely  from  the  aorta,  the 
auricular  impulse  is  sometimes  marked  on  the  pulse-curve  as  a 
distinct  elevation  ;  and  tins  gives  rise  to  a  peculiar  kind  of 
anacrotic  pulse,  especially  in  the  arteries  nearest  the  heart 
(Fig.  32,  F). 

Frequency  of  the  Pulse. — In  health,  the  working  of  the  cardiac 
pump  is  so  smooth  and  apparently  so  self-directed,  that  it 
needs  a  certain  degree  of  attention  to  perceive  that  the  rate  of 
the  stroke  is  not  absolutely  constant.  It  is.  in  reality,  affected 
by  many  internal  conditions  and  external  influences. 

At  the  end  of  foetal  life  the  rate  is  given  as  144  to  133;  from 
birth  till  the  end  of  the  first  year,  140  to  123  ;  from  10  to  15  years, 
91  to  76  ;  from  20  to  25  years,  j$  to  69.  It  remains  at  this  till  60 
years,  and  increases  again  somewhat  in  old  age.*  At  all  ages 
the  pulse  is  somewhat  quicker  in  the  female  than  in  the  male, 
the  excess  amounting  to  about  8  beats  a  minute.  So  that  if 
we  take  the  average  rate  for  a  man  (in  the  sitting  position)  as 
-_  the  average  for  a  woman  will  be  80.  The  difference  is  partly- 
due  to  the  fact  that  the  average  man  is  taller  than  the  average 
woman  ;  and  it  is  known  that  in  persons  of  the  same  sex  and  age 
the  pulse-rate  has  an  inverse  relation  to  the  stature.  But 
there  may  be,  in  addition,  a  real  sexual  difference.  It  must  not 
be  forgotten  that  a  small  number  of  perfectly  healthy  persons 
have  an  habitually  slow  pulse,  not  above  50  in  the  minute.  The 
position  of  the  body  exercises  a  slight,  but  relatively  constant, 

*  It  must  be  remembered  that  these  numbers  are  merely  averages. 
Some  healthy  individuals  have  a  much  lower  pulse-rate  than  72  per  minute, 
and  some  a  rate  considerably  greater.  Thus,  while  the  average  pulse-rate 
(taken  in  the  sitting  position)  of  S7  healthy  (male)  students  (in  the  writer's 
laboratory),  whose  ages  ranged  from  iS  to  36  years,  was  73,  the  extreme 
variation  was  from  54  to  9S.  In  the  standing  position  the  average  was 
8o,  and  the  variations  64  to  105.  In  the  supine  position,  average  69,  and 
variations  48  to  9S.  After  a  short  spell  of  muscular  exercise  (generally 
running  up  and  down  some  flights  of  stairs)  the  average  in  the  standing 
position  was  119,  the  variations  j^  to  104,  and  the  average  increase 


THE  CIRCULATIOX  OF    llll     Ill.ool)  .1X1)  LYMPH         <><> 

influence  on  the  rate,  which  is  greater  in  the  standing  than  in  the 
sitting  posture,  and  greater  in  the  latter  than  in  the  recumbent 
position.  And  this  is  true  even  when  muscular  action  is  as  far 
as  possible  eliminated  by  fastening  the  person  to  a  board.  The 
pulse  is  further  affected  by  the  respiratory  movements,  especially 
when  they  are  exaggerated  in  forced  breathing,  being  accelerated 
during  each  inspiration  (p.  269).  It  is  also  increased  by  the 
taking  of  food,  and  especially  of  alcoholic  stimulants,  by  muscular 
exercise,  in  fever  and  many  other  pathological  conditions,  and 
by  a  high  external  temperature.  A  warm  bath,  for  example, 
causes  a  very  distinct  acceleration  of  the  heart  ;  and  Delaroche 
found  that  in  air  at  the  temperature  of  650  C.  his  pulse  went  up 
to  160.  A  cold  bath  may  depress  the  pulse-rate  to  60,  or  even 
less.  During  sleep  it  may  fall  to  50.  It  is  greatly  influenced  by 
psychical  events,  and  that  in  the  direction  either  of  an  increase 
or  a  decrease.  Finally,  it  ought  to  be  remembered  as  of  some 
practical  importance  that  the  pulse-rate  in  women  and  children, 
but  particularly  in  the  latter,  is  less  steady  than  in  men,  and 
more  apt  to  be  affected  by  trivial  causes.  And  it  is  a  good  general 
rule  to  let  a  short  interval  elapse  after  the  finger  is  laid  on  the 
artery  before  beginning  to  count  the  pulse,  so  that  the  acceleration 
due  to  the  agitation  of  the  patient  may  have  time  to  subside. 

Rate  of  Propagation  of  the  Pulse-wave.  —  When  pulse- 
tracings  are  taken  simultaneously  at  two  points  of  the  arterial 
system  unequally  distant  from  the  heart,  by  two  sphygmographs 
whose  writing-points  move  in  the  same  vertical  straight  line, 
it  is  found  that  the  ascent  of  the  curve  begins  later  at  the  more 
distant  than  at  the  nearer  point.  Since  waves  like  the  pulse- 
wave  travel  with  approximately  the  same  velocity  in  different 
parts  of  an  elastic  system  like  the  arterial  '  tree,'  this  '  delay  ' 
must  be  due  to  the  difference  in  the  length  of  the  two  paths. 
The  difference  in  length  can  be  measured  ;  the  time-value  of 
the  '  delay  '  can  be  deduced  from  the  rate  of  movement  of  the 
recording  surface  ;  dividing  the  length  by  the  time,  we  arrive 
at  the  rate  of  propagation  of  the  pulse-wave.  The  average  rate 
has  been  found  to  be  about  7  metres  per  second  in  man  in  the 
arteries  of  the  upper  limb,  and  8  metres  in  those  of  the  lower 
limb,  the  difference  being  due  to  the  smaller  distensibility  of 
the  latter.  In  sleep  the  velocity  diminishes  almost  a  metre  a 
second.  It  increases  in  arterio-sclerosis,  where  the  distensibility 
of  the  arteries  is  diminished,  and  in  chronic  nephritis  with  hyper- 
trophy of  the  heart,  in  which  the  blood-pressure  is  increased. 
The  mean  velocity  of  the  pulse-wave  is  about  the  same  as  the 
speed  of  a  moderately  fast  steamship  (say,  17  miles  an  hour), 
but  less  than  that  of  a  wave  of  the  sea  in  a  strong  gale.  The 
velocity  of  the  pulse-wave  must  not  be  confounded  with  that 

7—2 


ioo  A   MANUAL  OF  PHYSIOLOGY 

of  the  blood-stream  itself,  which  is  not  one-thirtieth  as  great. 
A  ripple  passes  oxer  the  surface  of  a  river  at  its  own  rate — a 
rate  thai  is  independent  of  the  velocity  of  the  current.  The 
passage  of  the  ripple  is  not  a  bodily  transference  of  the  particles 
of  water  of  which  at  any  given  moment  the  wave  is  composed, 
but  the  propagation  of  a  change  of  relative  position  of  the  par- 
ticles. The  mere  fact  that  the  ripple  can  pass  upstream  as 
well  as  down  is  sufficient  to  illustrate  this.  The  pulse-wave 
does  not,  however,  correspond  in  every  respect  to  a  ripple  on  a 
stream,  for  the  bodily  transfer  of  the  blood  depends  upon  the 
series  of  blood-waves  which  the  heart  sets  travelling  along  the 
arteries.  Every  particle  of  blood  is  advanced,  on  the  whole, 
by  a  certain  distance  with  every  pulse-wave  in  which  for  the 
time  it  takes  its  place.  But  no  particle  continues  in  the  front 
of  the  pulse-wave  from  beginning  to  end  of  the  arterial  system. 
The  '  delay  '  or  '  retardation  '  of  the  pulse  (the  interval,  say. 
between  the  beginning  of  the  ascent  of  the  carotid  and  radial 
curves)  is  practically  constant  in  the  same  individual,  not  only 
in  health,  but  also  in  most  diseases.  But  the  retardation  is 
markedly  increased  when  the  pulse-wave  has  to  pass  through 
a  portion  of  an  artery  whose  lumen  is  either  greatly  widened 
(in  aneurism),  or  greatly  constricted  (in  endarteritis  obliterans). 
The  Blood-pressure  Pulse. — In  man  it  is  only  possible  to 
trace  the  pulse-wave  along  the  arteries  by  movements  of  the 
walls  of  the  vessels  transmitted  through  the  overlying  tissues. 
In  animals  the  changes  of  pressure  that  occur  in  the  blood  itself 
can  be  directly  registered,  and  these  changes  may  be  spoken  of 
as  the  blood-pressure  pulse.  At  bottom,  as  already  pointed 
out,  the  phenomenon  is  exactly  the  same  as  that  we  have  been 
dealing  with  in  our  study  of  the  external  pulse.  We  are  only 
now  to  follow,  by  a  more  direct,  and  in  some  respects  a  more 
perfect  method,  the  same  wave  of  blood  along  the  same  channel. 

Measurement  of  the  Blood-pressure. — Hales  was  the  first  to 
measure  the  blood-pressure.  This  he  did  by  connecting  a  tall  glass 
tube  with  the  crural  artery  of  a  horse.  The  height  to  which  the  blood 
rose  in  the  tube  indicated  the  pressure  in  the  vessel.  Poiseuille. 
nearly  half  a  century  later,  applied  the  mercury  manometer,  which 
had  already  been  used  in  physics,  to  the  measurement  of  blood- 
pressure.  Ludwig  and  others  improved  this  method  by  making  the 
manometer  self-registering  by  means  of  a  float  in  the  open  limb,  sup- 
porting a  style  which  writes  on  a  revolving  drum,  or  kymograph. 
(For  the  method  of  taking  a  blood-pressure  tracing,  see  p.  195.) 

For  reasons  already  mentioned  the  mercurial  manometer  is  better 
suited  for  measuring  the  mean  blood-pressure,  or  for  recording 
changes  in  the  pressure  which  last  for  some  time,  than  for  following 
the  rapid  variations  of  the  pulse-wave.  For  the  latter  purpose,  one 
of  the  class  of  elastic  manometers  is  required  (p.  86). 

A  blood-pressure  tracing  taken  from  an  artery  with  a  manometer 
of  this  sort  yields  the  truest  picture  of  the  pulse- wave  which  it  is 


////    (  //,(  ri   ITION  OF   THE  BLOOD  AND  LYMPH       roi 

possible  to  obtain,  because  the  reproduction  oi  it  is  the  mosl  direct. 
ihr  t.ut  th.it  such  .1  tracing  shows  a  close  agreement  with  the  trace 
,,t  .1  good  sphygmograph  properly  applied  to  the  corresponding  artery 
on  the  other  side,  is  .1  striking  proof  of  the  genera]  accuracy  oi  the 
Bphygmographic  method  for  physiological  purposes,  and  enables  us  to 
guide  1  »urselves  in  transferring  to  man,  in  whom,  of  course,  the  sphyg- 
mograph can  alone  be  used,  the  information  derived  from  direct 
manometric  observations  in  animals. 

For  the  same  reason  it  is  unnecessary  to  discuss  the  mano- 
metric tracings,  as  regards  the  pulsatory  phenomena,  in  all  then 


Fig.  34. — Arrangement  for  taking  a  Blood-pressure  Tracing. 

M,  manometer  ;  Hg,  mercury  ;  F,  float  armed  with  writing-point ;  A,  thread 
attached  to  a  wire  projecting  from  the  drum  and  supporting  a  small  weight.  The 
thread  keeps  the  writing-point  in  contact  with  the  smoked  paper  on  the  drum. 
B  is  a  strong  rubber  tube  connecting  the  manometer  with  the  artery  ;  C,  a  pinch- 
cock  on  the  rubber  tube,  which  is  taken  off  when  a  tracing  is  to  be  obtained. 

details.  It  will  be  sufficient  to  say  that  while  the  form  of  the 
blood-pressure  pulse-curve  varies  with  the  mean  blood-pressure, 
the  dicrotic  wave  is  always  marked  on  it,  preceded  by  one  or 
more  oscillations  falling  within  the  period  of  the  systole,  and 
followed  by  one  or  more  within  the  period  of  the  diastole.  When 
the  blood-pressure  is  low,  the  first  or  primary  elevation  is  the 


./    Ml  XT  II    ()/■    rilYSIOLOGY 


highest  of  the  whole  curve  (Fig.  35).  When  the  blood-pressure 
is  high,  the  maximum  falls  later,  coinciding  with  one  of  the 
secondary  systolic  waves,  but  always  preceding  the  dicrotic 
wave  ;  and  the  curve  assumes  an  anacrotic  character. 

That  all  the  secondary  oscillations,  including  the  dicrotic  wavelet, 
are  centrifugal,  and  not  centripetal,  may  be  shown,  just  as  in  the 
sphygmographic  method,  by  recording  the  blood-pressure  simul- 
taneousfy  at  two  points  of  the  arterial  system  at  different  distances 
from  the  heart — e.g.,  in  the  crural  and  carotid  arteries.  The 
secondary  waves  are  found,  by  measuring  the  tracings,  to  reach  t he- 
more  distal  point  later  than  the  more  central. 

The  increase  of  pressure  during  the  systole,  as  indicated  by  the 

height  of  the  primary 
elevation,  is  always  very 
large,  much  larger  than 
it  appears  in  a  tracing 
taken  with  a  mercury 
manometer.  In  the  rab- 
bit this  pulsatory  varia- 
tion is  one-third  to  one- 
fourth  of  the  minimum 
pressure.  In  the  dog  it 
is  still  greater,  owing  to 
the  slower  rate  of  the 
heart,  and  often  amounts 
to  50  mm.  of  mercury, 
while  under  favourable 
conditions(low  minimum 
pressure  and  slowly  beat- 
ing heart)  the  systolic 
increase  of  pressure  may 
be  actually  more  than 
double  the  minimum 
(I  hirthle).  Pick  found 
also,  by  means  of  his 
spring  manometer,  that 
the  pulsatory  variations 
of  blood  -  pressure  were 
greater  than  the  respira- 
tory variations  (p.  103), 
although  in  the  records 
of  the  mercury  manometer  the  reverse  appears  often  to  be  the 
case.  Landois,  too,  in  the  course  of  experiments  in  which  a  divided 
artery  was  allowed  to  spout  against  a  moving  surface,  and  to 
trace  on  it  a  sort  of  pulse-curve  painted  in  blood  (a  ha?mautogram 
as  it  is  called),  observed  that  the  rate  of  escape  of  the  blood  was 
nearly  50  percent,  greater  during  the  systole  than  during  the  pause 
of  the  heart.  The  existence  of  the  dicrotic  wave  on  this  tracing 
was  long  looked  on  as  the  best  proof  that  it  was  not  an  artificial 
phenomenon. 

The  wave  of  increased  pressure,  as  it  runs  along  the  arterial 
system,  carries  with  it  wherever  it  arrives  an  increase  of  potential 
energy.     But  this  excess  of  potential  energy  is  continually  being 


Fig.  35. — Curves  of  Blood-pressure  taken 
with  a  Spring  Manometer  from  the 
Carotid  Artery  of  a  Dog  (Hurthle). 

When  1  was  taken  the  blood-pressure  was  high  ; 
2  corresponds  to  a  medium,  3  to  a  low,  and  4  to  a 
very  low,  blood-pressure  ;  p  is  the  primary  eleva- 
tion— this  and  the  succeeding  elevations  between 
p  and  a  arc  railed  systolic  waves  ;  tin'  systolic 
waves  are  followed  by  a  marked  elevation  </.  which 
corresponds  to  the  dicrotic  wave. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH       103 

worn  down,  owing  to  the  friction  of  the  vascular  bed  ;  and 
although  in  the  comparatively  large  arteries  the  loss  of  energy  is 
not  great,  it  rapidly  increases  as  the  arteries  approach  then  ter- 
mination, and  begin  to  break  up  into  the  narrow  arterioles  which 
feed  the  capillary  network.  For  not  only  is  the  total  surface,  and 
therefore  the  friction,  increased  with  every  bifurcation,  but  the 
mere  change  of  direction  and  division  of  the  wave  cannot  take 
place  without  loss  of  energy.  For  this  reason  the  fluctuations  of 
blood-pressure  are  greater  in  the  large  arteries  near  the  heart 
than  in  arteries  smaller  and  more  remote.  In  the  wide  and  much- 
branched  capillary  bed  the  pulse-wave  disappears  altogether,  and 
the  blood-pressure  becomes  relatively  constant  or  permanent. 
And  it  is  for  some  purposes  convenient  to  look  upon  the  blood- 
pressure  in  the  arteries  as  made  up  of  a  permanent  element,  with 
pulsatory  oscillations  superposed  on  it.  Since  no  portion  of  the 
arterial  system  is  more  than  partially  emptied  in  the  interval 
between  two  blood-waves,  the  minimum  or  permanent  pressure 
is  always  positive — i.e.,  always  above  that  of  the  atmosphere, 
the  beats  of  the  heart  succeeding  each  other  so  rapidly  that  the 
successive  waves  overlap  or  '  in- 
terfere,' and  are  only  separated 
at  their  crests. 

If  the  heart  is  stopped  while 
a  blood-pressure  tracing  is  being 
taken — and  we  shall  see  later  on 
how  this  can  be  done  (p.  143)-      FlG"  36-Blood-pressure  Tracing. 
the  minimum  line  of  the  tracing  ™e  horizontal  straight  line  inter- 

b      secting  the  curves  is  the  line  of  mean 
goes  on  falling  towards  the  zero-     pressure. 

line.      When    the    heart    begins 

beating  again,  the  pressure-curve  rises,  not  by  a  continuous 
ascent,  but  by  successive  leaps,  each  corresponding  to  a  beat  of 
the  heart,  and  each  overtopping  its  predecessor,  till  the  old  line 
of  minimum  or  of  mean  pressure  is  again  reached. 

The  mean  arterial  blood-pressure  is  the  permanent  pressure 
plus  one-half  of  the  average  pulsatory  oscillation.  In  a  blood- 
pressure  tracing  the  line  of  permanent  pressure  joins  all  the 
minima  ;  the  line  of  maximum  pressure  joins  all  the  maxima  ; 
the  line  of  mean  pressure  is  drawn  between  them  in  such  a  way 
that  of  the  area  included  between  it  and  the  blood- pressure 
curve  as  much  lies  above  as  below  it  (Fig.  36).  As  has  been 
said,  a  tracing  taken  with  a  mercury  manometer  gives  approxi- 
mately the  mean  blood-pressure.  Each  beat  of  the  heart  is 
represented  on  it  by  a  single  elevation  of  variable  size,  sometimes 
not  amounting  to  more  than  one-twentieth  of  the  height  of  the 
curve  above  the  line  of  zero  or  atmospheric  pressure,  but  some- 
times much  larger.     The  oscillations  due  to  the  heart-beatjare 


104  A    MANUAL  OF  PHYSIOLOGY 

superposed  upon  much  longer,  and  often,  as  registered  in  this 
way,  larger  waves,  caused  by  the  movements  of  respiration.  So 
much  having  been  said  by  way  of  definition,  we  have  now  to 
consider  the  amount  of  the  mean  arterial  pressure,  the  varia- 
tions which  it  undergoes,  and  the  factors  on  which  its  maintenance 
depends. 

As  to  its  amount,  it  will  be  sufficiently  accurate  to  say  that 
in  the  systemic  arteries  of  warm-blooded  animals  in  general 
(including  birds),  and  of  man  in  particular,  the  mean  pressure 
does  not,  under  ordinary  conditions,  descend  much  below  ioo  mm. 
of  mercury,  nor  rise  much  above  200  mm.  ;  while  in  cold-blooded 
animals  it  seldom  exceeds  50  mm.,  and  may  fall  as  low  as  20  mm. 

It  does  not  seem  possible,  at  least  with  our  present  data,  to  further 
subdivide  these  two  great  groups  ;  nor  do  \vc  know  precisely  whether 
the  distinction  depends  mainly  on  morphological  or  mainly  on 
physiological  differences,  whether,  that- is  to  say.  the  warm-blooded 
animal  has  a  higher  blood-pressure  than  the  cold-blooded  chiefly 
because  its  vascular  system  (and  especially  its  heart)  is  anatomically 
more  perfect,  or  because  its  heart  beats  faster  and  works  harder.  It 
may  be  that  it  is  for  both  of  these  reasons  that  the  birds,  which  in 
certain  other  respects  are  more  nearly  related  to  the  reptiles  than 
to  the  mammals,  mount,  as  regards  the  pressure  of  the  blood,  into 
the  mammalian  class,  and  that  a  manometer  in  the  carotid  of  a  goose 
will  rise  as  high,  or  almost  as  high,  as  in  the  carotid  of  a  horse,  a 
sheep,  or  a  dog,  while  the  pressure  in  the  aorta  of  a  tortoise  is  no 
higher  than  in  the  aorta  of  a  frog.  But  we  know  that  the  mere 
average  rate  of  the  heart  has  of  itself  comparatively  little  influence 
on  the  blood-pressure  within  either  group,  for  the  heart  of  a  rabbit 
beats,  on  the  average,  very  much  faster  than  the  heart  of  a  dog,  and 
yet  the  arterial  pressure  in  the  dog  is  certainly  at  least  as  great  as  in 
the  rabbit.  Nor  does  the  size  of  the  body  seem  to  have  any  definite 
relation  to  the  mean  pressure,  even  in  animals  of  the  same  species  ; 
and  there  is  no  reason  to  suppose  that  the  pressure  is  materially  less 
in  the  radial  artery  of  a  dwarf  than  in  the  radial  artery  of  a  giant. 

Measurement  of  the  Blood-pressure  in  Man. — In  man  the  blood- 
pressure  has  been  estimated  by  adjusting  over  an  artery  an 
instrument  known  as  a  sphygmomanometer  or  sphygmometer, 
which,  in  its  most  modern  form,  consists  essentially  of  a  hollow 
rubber  pad  or  bag  containing  liquid  or  air,  and  connected  with 
a  metallic  pressure  gauge  or  a  mercurial  manometer. 

The  sphygmomanometer  of  Erlanger  (Fig.  37)  is  arranged  to  obtain 
graphic  records  of  the  pulse,  from  which  both  the  maximum  and 
the  miminum  blood-pressures  may  be  deduced.  The  mean  pressure 
cannot  be  directly  measured,  but  must  lie  much  nearer  to  the  mini- 
mum than  to  the  maximum,  since  the  line  of  mean  pressure  bisects 
the  area  enclosed  by  the  pulse-curve,  and  this  area  is  broad  at  the 
base  and  narrow  at  the  apex.  The  rubber  bag  is  applied  in  the 
form  of  a  cuff  or  armlet  to  the  arm  above  the  elbow  over  the  brachial 
artery.  It  communicates  with  a  mercury  manometer,  which  gives 
the  pressure  exerted  upon  the  arm.     It  is  also  connected  with  a 


THE  CIRCULATION  OF  THE   BLOOD  AND  LYMPH        [05 


rubber  bulb,  B,  enclosed  in  a  glass  bulb,  G,  and  through  .1  stopcock 
with  a  syringe  bulb,  V,  provided  with  a  valve.  The  space  between 
B  .md  (i  communicates  (1)  with  the  tambour  ;  (2)  with  the  exterior 
through  the  stopcock  by  the  tube  E,  and  also  through  a  pin-point 

opening  in  the   membrane   of  the  tambour.     While   the   armlet   is 
being  adjusted  the  stopcock  is 
turned  so  that  the  rubber  bag 
is  in  communication  with  the 
external  air  through   F.     The 
same  is  true  of  the  space  TS 
in  the  glass  bulb.     The  tam- 
bour is  thus  protected  against 
undue    strain    during    adjust- 
ment.    The   stopcock   is  now 
rotated   so  as  to  cut   off  the 
armlet  from  the  exterior  and 
to  permit  the  entrance 
of  air  through  F  from  V, 
which  is  used  as  a  pump 
to  raise  the  pressure,  the 
space  TS  and  the  tam- 
bour being  still  in  com- 
munication with  the  ex- 
terior.    When    the    de- 
sired pressure  has  been 
reached,  the  stopcock  is 
turned  into  an  interme- 
diate    position,     which 
cuts  off  both  the  armlet 
and  the  space  TS  from 
the    exterior,    and    the 
pulse       is    then    trans- 
mitted to  the  tambour 
and     recorded    on    the 
drum.     By   certain   ad- 
justments of  the   stop- 
cock air  can  be 
allowed    to    es- 
cape    more     or 
less   rapidly 
from  the  armlet. 
To  determine 
the     maximum 
or      systolic 
blood -pressure, 
the  air-pressure 
in  the  armlet  is 
raised  consider- 
ably  (about   50 
mm.  Hg)  above 
what    it   is   ex- 
pected   to     be. 

While  the  lever  is  writing  on  the  drum  the  small  oscillations  due 
to  the  impact  on  the  bag  of  the  pulse-waves  in  the  central  portion 
of  the  obliterated  artery,  the  pressure  is  gradually  diminished  by 
allowing  air  to  escape.     At  the  moment  when  the  pressure  upon  the 


Fig.  37. — Sphygmomanometer  of  Erlanger. 


io6 


A   MANUAL  OF  PHYSIOLOGY 


arm  falls  below  the  maximum  blood-pressure,  and  the  pulse-wave  is 
first  able  to  break  through  the  brachial  artery,  the  oscillations  of  the 
lever  will  more  or  less  abruptly  increase  in  amplitude.  The  pressure 
shown  by  the  manometer  at  this  point  is  the  systolic  blood -pressure. 
To  obtain  the  minimum  or  diastolic  pressure,  the  air-pressure  in 
the  armlet  is  raised  somewhat  (10  to  15  mm.  Hg)  above  the  pressure 
expected.  The  pressure  is  diminished  by  5  mm.  Hg  at  a  time, 
records  of  the  oscillations  being  taken  on  the  drum.  The  manometer 
reading  at  the  point  at  which  the  oscillations,  after  reaching  the 
maximum,  begin  abruptly  to  diminish,  corresponds  to  the  minimum 
blood-pressure. 

In  using  the  sphygmometer  of  Hill  and  Barnard  (Fig.  38), 
the  bag  is  inflated  with  air  till  the  pulsation  indicated  by  the 
index  of  the  pressure  gauge  reaches  a  maximum.  The  mean 
pressure  shown  by  the  gauge  at  this  point  is  approximately 
equal  to,  or  somewhat  greater  than,  the  minimum  arterial  pressure. 
With  this  instrument  it  has  been  found  that  in  the  brachial  artery 
the  normal  arterial  pressure  in  most  healthy  young  men  is  no  to 
130  mm.  of  mercury  in  the  sitting  posture.     When  the  person  is 

resting  in  the 
recu  m  bent 
posture,  the 
pressure  may 
be  as  low  as 
05  mm.  of  mer- 
cury. Hard 
work  and  ner- 
vous strain 
may  raise  the 
pressure  to 
140  or  145 
mm.  of  mer- 
cury. 

The  effect 
of  muscular 
exercise  upon 
the  pressure 
is  influenced 
by  the  nature 
of  the  work. 
Such  an  effort 
as  the  lifting 
of  a  heavy  weight  causes  a  sudden  and  great  increase,  which  is 
very  transient.  Thus,  the  average  arterial  pressure  in  a  number 
of  men  was  in  before,  180  during,  and  no  two  to  three  minutes 
after  the  lift  (McCurdy).  The  rise  of  pressure  in  this  case  is  due 
largely  to  the  marked  diminution  of  the  calibre  of  the  bloodvessels 
mechanically  produced  by  the  strong  and  sustained  contraction 
of  the  muscles.  This  increases  the  resistance  to  the  passage  of 
the  blood  along  the  arteries,  while  the  veins  arc  emptied  by  the 
pressure,  and  more  blood  thus  reaches  the  right  side  of  the  heart. 
It  is  obvious  that  the  heart  and  vessels  may  easily  be  exposed  to 
an  injurious  strain  during  such  efforts.  In  such  an  exercise  as 
running,  while  the  pressure  mounts  to  some  extent  at  first,  as 
already  mentioned,  the  rise  is  not  maintained,  owing  to  the  dilata- 
tion of  the  cutaneous  vessels.     In  the  anterior  tibial  artery  of  a 


Fig.  38. — Sphygmometer  of  Hill  and  Barnard. 

It  consists  of  a  broad  armlet,  A,  which  is  strapped  round  the 
upper  arm.  On  the  inside  of  the  armlet  is  a  thin  rubber  bag 
containing  air,  and  connected  by  a  "["•tu'H>-  B,  with  a  pressure 
gauge,  C,  and  a  small  compressing  air-pump.  I),  fit  ted  wit  ha  valve. 


THE  CIRCULATION  Oh'  THE  BLOOD  AND  l.YMI'U        1..7 

boy  whose  leg  was  to  be  amputated,  the  blood-pressure,  measured 
by  means  of  a  manometer  connected  directly  with  the  artery,  was 
found  to  vary  from  100  to  160  mm.,  according  to  the  position  of  the 
body  and  other  circumstances.  In  a  woman  sixty  years  old,  in 
good  health,  the  following  readings  were  obtained  with  a  sphygmo- 
manometer : 

June  28     -----      126 — 130  mm.  of  mercury. 

„     29     -                                       -      126—136 
Aug.      3 132—144 

„       7    -  -  134—140  „ 

„     12  -     136—144 

Such  measurements  on  man  show  that  the  mean  blood-pressure 
under  similar  conditions  in  one  and  the  same  artery,  and  in  one 
and  the  same  individual,  may  vary  for  a  considerable  time  only 
within  comparatively  narrow  limits. 

This  relative  constancy  of  the  general  arterial  pressure  is  the 
result  of  a  delicate  adjustment  between  the  work  of  the  heart, 
the  resistance  of  the  vessels,  and  the  volume  of  the  circulating 
liquid.  The  quantity  of  the  blood  is  tolerably  steady  in  health, 
and  considerable  changes  may  be  artificially  produced  in  it 
(p.  174)  without  affecting  the  pressure  in  any  great  degree.  On 
the  other  hand,  the  work  of  the  heart  and  the  peripheral  resist- 
ance are  highly  variable  and  vastly  influential.  A  narrowing 
of  the  arterioles  throughout  the  body  or  in  some  extensive 
vascular  tract  increases  the  peripheral  resistance  ;  and  if  the 
heart  continues  to  beat  as  before,  the  pressure  must  rise.  If  the 
arterioles  are  widened,  while  the  heart's  action  remains  un- 
changed, the  pressure  must  fall.  In  like  manner  an  increase 
or  a  decrease  in  the  activity  of  the  heart,  in  the  absence  of  any 
change  in  the  peripheral  resistance,  will  cause  a  rise  or  a  fall  in 
the  blood-pressure.  But  if  a  slowing  of  the  heart  is  accompanied 
by  an  increase  in  the  peripheral  resistance,  or  a  dilatation  of  the 
arterioles  by  an  increase  in  the  activity  of  the  heart,  the  one 
change  may  be  partially  or  completely  balanced  by  the  other, 
and  the  pressure  may  vary  within  narrow  limits  or  not  at  all. 

Not  only  is  the  mean  pressure,  as  measured  in  a  large  artery, 
tolerably  constant,  but  if  recorded  simultaneously  in  two  arteries 
at  different  distances  from  the  heart,  it  is  seen  to  decrease  very 
gradually  so  long  as  the  arteries  remain  large  enough  to  hold  a 
cannula.  It  is  nearly  as  high,  for  instance,  in  the  crural  artery 
of  a  dog  as  in  the  carotid.  It  is  easy  to  see  that  this  must  be 
so,  for  the  resistance  of  the  arteries  between  the  point  where 
the  arterioles  are  given  off  and  the  heart  is  only  a  small  fraction 
of  the  total  resistance  of  the  vascular  path  ;  and  we  have  said 
(p.  76)  that  the  lateral  pressure  at  any  cross-section  of  a  system 
of  tubes  through  which  liquid  is  flowing  is  proportional  to  the 
resistance  still  to  be  overcome.  This  is  also  the  reason  why 
the  pressure  is  always  much  lower  in  the  pulmonary  artery  and 


A   MANUAL  OF  PHYSIOLOGY 

right  ventricle  than  in  the  aorta  and  left  ventricle  (onlv  one- 
third  to  one-sixth  as  great),  for  the  total  resistance  of  the  vas- 
cular path  through  the  lungs  is  much  less  than  that  of  the 
systemic  circuit.  In  dogs  with  natural  respiration  the  pressure 
in  the  pulmonary  artery  was  found  to  vary  between  14  and 
26  mm.  of  mercury,  averaging  about  20  mm. 

The  Velocity-pulse.  We  have  seen  that  the  blood  is  pro- 
pelled through  the  arteries  in  a  series  of  waves  that  travel  from 
the  heart  towards  the  periphery.  The  particles  in  the  front  of 
the  pulse-wave  are  constantly  changing,  but  since  every  section 
of  the  arterial  tree  is  successively  distended,  every  section  con- 
tains more  blood  while  the  pulse-wave  is  passing  over  it  than 
it  contained  immediately  before.  And  since  there  is  always  a 
fairly  free  passage  for  this  blood  towards  the  periphery,  there 
is  a  bodily  transfer  on  the  whole  of  a  certain  quantity  with 
every  wave. 

The  translation  of  the  blood,  instead  of  being  entirely  inter- 
mittent, as  it  would  be  in  a  rigid  tube  or  in  an  elastic  system 
with  a  slow  action  of  the  central  pump,  is  to  some  extent  con- 
stantly going  on  ;  for  a  portion  of  a  blood-wave  is  always  passing 
through  every  section  of  the  arterial  channel.  Thus,  we  arrive 
at  the  same  distinction  as  to  the  onward  movement  of  the  blood 
itself  as  we  previously  reached  in  regard  to  the  blood-pressure, 
the  distinction  between  the  constant  or  permanent  factor  of 
the  velocity  and  the  periodic  factor,  which  we  may  call  the 
velocity-pulse. 

The  Velocity  of  the  Blood. — By  the  velocity  or  rate  of  flow  of  a  river 
we  should  mean,  if  the  flow  were  uniform  throughout  the  whole 
cross-section,  the  rate  of  movement  of  any  given  portion  or  particle 
of  the  water.  If  we  could  identify  a  portion  of  the  water,  we  could 
determine  the  velocity  by  measuring  the  distance  travelled  over  by 
that  portion  in  a  given  time.  If  the  velocity  was  uniform  over  the 
channel,  we  could  predict  the  actual  time  which  would  be  required 
to  traverse  any  fractional  part  of  the  measured  distance.  If.  how- 
ever, the  velocity  of  the  current  changed  from  point  to  point,  then 
we  could  onlv  deduce  from  our  observation  the  mean  rate  of  the  river 
for  the  measured  distance.  To  determine  the  actual  rate  for  any 
given  portion  of  this  distance  over  which  the  rate  was  uniform,  we 
should  have  to  make  a  separate  observation  for  this  portion  alon< 

But  as  soon  as  we  pass  from  an  ideal  frictionless  river  to  an  actual 
stream,  in  which  the  water  at  the  bottom  and  near  the  banks  flows 
more  slowly  than  that  in  the  middle  and  on  the  surface,  we  arc  in 
even,-  case  restricted  to  the  notion  of  mean  velocity.  We  may 
distinguish  between  the  velocity  of  different  parts  of  the  current, 
between  that  of  the  mid-stream  and  the  side  current,  the  bottom  and 
the  surface  layers  ;  but  when  we  consider  the  river  as  a  whole,  we 
take  cognizance  only  of  the  mean  or  average  velocity.  And  at  any 
cross-section  this  may  be  defined  as  the  volume  of  water  passing  per 
hour,  or  whatever  the  unit  of  time  may  be.  divided  by  the  cross- 
section  of  the  current.      It  is  evident  that  this  does  not  enable  us  to 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH       109 

determine  the  actual  velocity  oi  any  given  particle  of  the  water  at  any 
given  moment  within  a  measured  interval  ;  nor  docs  it  tell  us  whether 
or  not  the  average  velocity  ol  bhe  current  has  itself  undergone 
variations  within  the  period  of  observation. 

We  have  dwelt  upon  this  point  because  the  measurement  of 
the  velocity  of  the  blood,  to  which  we  must  now  turn,  involves 
the  same  considerations.  Within  the  smaller  arteries,  as  the 
microscope  shows  us,  and  as  we  should  in  any  case  expect  from 
what  we  know  of  fluid  motion,  the  blood-current,  apart  from 
the  periodical  variations  in  its  velocity,  due  to  the  action  of  the 
heart,  varies  in  speed  from  point  to  point  of  the  same  cross- 
section.  The  layer  next  the  periphery  of  the  vessel,  the  so- 
called  peripheral  plasma-layer  or  Poiseuille's  space,  moves  more 
slowly  than  the  central  portion,  the  axial  stream.  In  fact,  we 
must  suppose  that  in  the  large  as  well  as  in  the  small  vessels 
the  layer  just  in  contact  with  the  vessel-wall  is  at  rest,  while  the 
stratum  internal  to  this  slides  on  it  and  has  its  velocity  diminished 
by  the  friction.  The  next  layer  again  slides  on  the  last,  but 
since  this  is  already  in  motion,  its  velocity  is  not  so  much 
diminished,  and  so  on.  The  velocity  must  therefore  increase 
as  we  pass  towards  the  axis  of  the  bloodvessel,  and  reach  its 
maximum  there  (p.  177). 

Again,  the  velocity  must  be  altered  wherever  an  alteration 
occurs  in  the  width  of  the  bed,  that  is,  in  the  total  cross-section 
of  the  vascular  system  ;  for  since  as  much  blood  comes  back 
in  a  given  time  to  the  right  side  of  the  heart  as  leaves  the  left 
side,  the  same  quantity  must  pass  in  a  given  time  through  every 
cross-section  of  the  circulation.  Wherever  the  total  section  of 
the  vascular  tree  increases,  the  blood-current  must  slacken  ; 
wherever  it  diminishes,  the  current  must  become  more  rapid. 
Now,  the  total  section,  increasing  somewhat  as  we  pass  from  the 
heart  along  the  branching  arteries,  undergoes  an  abrupt  augmen- 
tation, and  reaches  its  maximum  in  the  capillary  region.  It 
suddenly  diminishes  again  at  the  venous  end  of  the  capillary 
tract,  and  then  more  gradually  as  we  pass  heartwards  along  the 
veins,  but  never  becomes  so  small  as  in  the  arterial  tract.  We 
must,  therefore,  expect  the  mean  velocity  to  be  greatest  in  the 
large  arteries,  less  in  the  veins,  and  least  in  the  arterioles,  capil- 
laries, and  venules.  It  must,  of  course,  be  remembered  that  the 
total  section  varies  from  time  to  time  at  any  given  distance  from 
the  heart.  The  capillary  tract  is  especially  variable  in  its  area, 
and  capillaries  full  of  blood  at  one  moment  may  be  collapsed  and 
empty  at  another,  according  to  the  changes  of  calibre  and  pressure 
in  the  arteries  which  feed  and  the  veins  which  drain  them. 

Although  in  strictness  we  are  only  at  present  concerned  with  the 
arteries,  it  will  be  well  to  consider  here  what  a  change  of  velocity  at 


no  A    MAS  UAL  OF  PHYSIOLOGY 

any  pari  of  the  vascular  channel  really  implies,  In  iay  that  when 
the  channel  widens  the  velocity  diminishes,  is  not  to  explain  the 
meaning  of  this  diminution.  A  diminution  of  veloi  itv  implies  a 
diminution  of  kinetii  energy,  and  it  is  necessary  to  know  what 
becomes  of  the  energv  tint  disappears.  The  stock  of  energy  im- 
parted by  the  contraction  of  the  heart  to  a  given  mass  of  blood 
constantly  diminishes  as  it  passes  round  from  the  aorta  to  the  right 
side  of  the  heart,  for  friction  is  constantly  being  overcome  and  heat 
generated.  This  energy,  as  we  have  seen,  exists  in  a  moving  liquid 
in  two  forms,  potential  and  kinetic,  the  former  bein^  measured  by  the 
lateral  pressure,  the  latter  varying  directly  as  the  square  of  the 
velocity.  Whenever  the  velocity,  and  therefore  the  kinetic  energy, 
of  a  given  mass  of  the  blood  is  diminished  without  a  corresponding 
increase  in  the  potential  energy,  some  of  the  total  stock  of  energy 
must  have  been  used  up  to  overcome  resistance  (p.  76). 

In  a  uniform,  rigid,  horizontal  tube,  as  has  been  already  remarked, 
the  velocity  (and  consequently  the  kinetic  energv)  is  the  same  at 
every  cross-section  of  the  tube,  while  the  potential  energy,  repre- 
sented by  the  lateral  pressure,  diminishes  regularly  along  the  tube. 
When  the  calibre  of  the  tube  varies,  it  is  different.  Suppose,  for 
instance,  that  the  liquid  passes  from  a  narrower  to  a  wider  part,  the 
velocity  must  diminish  in  the  latter.  The  kinetic  energy  of  visible 
motion  which  has  disappeared  must  have  left  something  in  its  room. 
Here  there  are  three  possibilities  :  ( 1 )  The  kinetic  energy  that  has 
disappeared  may  be  just  enough  to  overcome  the  extra  friction 
in  the  wider  part  of  the  tube  due  to  eddies  and  consequent  change  of 
direction  of  the  lines  of  flow  ;  in  this  case  the  potential  energy  of  a 
given  mass  of  the  liquid  will  be  the  same  at  the  beginning  of  the 
wider  part  as  in  the  narrower  part.  The  lost  kinetic  energy  will 
have  been  transformed  into  heat.  (2)  The  kinetic  energy  which  has 
disappeared  may  be  greater  than  is  enough  to  overcome  the  extra 
resistance  ;  a  portion  of  it  must,  therefore,  have  gone  to  increase  the 
potential  energy,  and  the  lateral  pressure  will  be  greater  in  the  wide 
than  in  the  narrow  part.  (3)  The  lost  kinetic  energy  may  be  less 
than  enough  to  overcome  the  extra  resistance  ;  in  this  case  both  the 
lateral  pressure  and  the  velocity  will  be  less  in  the  wide  than  in  the 
narrow  part.  It  has  been  experimentally  shown  that  when  a  narrow 
portion  of  a  tube  is  succeeded  by  a  considerably  wider  portion,  and 
this  again  by  a  narrow  part,  case  (2)  holds  ;  and  the  liquid  may. 
under  these  conditions,  actually  flow  from  a  place  of  lower  to  a  place 
of  higher  lateral  pressure. 

In  the  vascular  system  the  conditions  are  not  the  same.  The 
widening  of  the  bed  which  takes  place  as  we  proceed  in  the 
direction  of  the  arterial  current  is  not  due  to  the  widening  of  a 
single  trunk,  but  to  the  branching  of  the  channel  into  smaller 
and  smaller  tubes.  In  the  larger  arteries  the  increase  of  resist- 
ance is  so  gradual  that  both  the  potential  and  the  kinetic  energy 
diminish  only  slowly,  and  the  lateral  pressure  and  velocity  are  not 
much  less  in  the  femoral  artery  than  in  the  aorta  or  carotid.  But 
in  the  arterirles  the  friction  increases  so  greatly  that  although  the 
velocity,  and  therefore  the  kinetic  energy,  in  the  capillary  region 
is  much  less  than  in  the  arteries,  the  amount  of  kinetic  energy  lost 
is  not  upon  the  whole  equivalent  to  the  energy  consumed  in  over- 


THE  CIRCULATION  OF  THE  BLOOD  ASD  LYMPH        III 

coming  the  extra  resistance;  the  potential  energy  oi  the  blood 
is  also  drawn  upon,  and  the  lateral  pressure  tails  sharply  in  the 
capillary  region,  as  well  as  the  velocity.  Where  the  capillaries 
open  into  the  veins,  the  Lateral  pressure  again  sinks  abruptly, 
while  the  velocity  begins  to  increase,  till  in  the  largest  veins  it 
is  probably  about  half  as  great  as  in  the  aorta. 

Where  does  the  extra  kinetic  energy  of  the  blood  in  the  veins 
come  from  3  To  say  that  the  vascular  channel  again  contracts 
as  the  blood  passes  from  the  capillaries  into  the  veins,  and  that, 
since  the  same  quantity  must  flow  through  every  cross-section 
of  the  channel,  the  velocity  must  necessarily  be  greater  in  the 
narrower  than  in  the  wider  part,  does  not  answer  the  question. 
The  greater  portion  of  the  kinetic  energy  of  the  arterial  blood 
is,  as  we  have  seen,  destroyed,  or,  rather,  changed  into  an  un- 
available form,  into  heat,  in  the  capillary  region.  The  mean 
velocity  of  the  blood  in  the  capillaries  is  not  more  than  ^i^  to 
ttJ^  of  the  velocity  in  the  aorta  ;  the  kinetic  energy  of  a  given 
mass  of  blood  in  the  capillaries  cannot  therefore  be  more  than 
(^(7o)"'  or  Ttjffoo  °f  i*s  kinetic  energy  in  the  aorta.  In  the  veins, 
taking  the  velocity  at  half  the  arterial  velocity,  the  kinetic  energy 
of  the  mass  would  be  one-fourth  of  that  in  the  aorta,  or  at  least 
10,000  times  as  great  as  in  the  capillary  region.  This  extra 
kinetic  energy  comes  partly  from  the  transformation  of  some 
of  the  potential  energy  of  the  blood.  The  resistance  in  the 
veins  is  very  small  compared  with  that  in  the  capillaries  ;  less 
of  the  potential  energy  represented  by  the  lateral  pressure  at 
the  end  of  the  capillary  tract  is  required  to  overcome  this  re- 
sistance, and  some  of  it  is  converted  into  the  kinetic  energy  of 
visible  motion,  the  lateral  pressure  at  the  same  time  falling 
somewhat  abruptly.  Contributory  sources  of  kinetic  energy  in 
the  veins  are  the  aspiration  caused  by  the  respiratory  move- 
ments and  the  pressure  caused  by  muscular  contraction  in  general, 
which,  thanks  to  the  valves,  always  aids  the  flow  towards  the 
heart.  From  these  two  sources  new  energy  is  supplied,  to  rein- 
force the  remnant  due  to  the  cardiac  systole  (p.  121). 

Measurement  of  the  Velocity  of  the  Blood. — i.  Direct  Observation. 
— (a)  This  method  can  be  applied  to  transparent  parts  by  observing 
the  rate  of  flow  of  the  corpuscles  under  the  microscope.  But  it  is 
only  where  the  blood  moves  slowly,  as  in  the  capillaries,  that  the 
method  is  of  use.  (b)  Part  of  the  path  of  the  blood  through  a  large 
vessel  may  be  artificially  rendered  transparent  by  the  introduction 
of  a  glass  tube,  of  approximately  the  same  bore  as  the  vessel  (Volk- 
mann).  The  tube  is  filled  with  salt  solution,  and  the  blood  admitted 
bv  means  of  a  stopco;k  at  the  moment  of  observation.  The  time 
which  the  blood  takes  to  pass  from  one  end  of  the  tube  to  the  other 
is  noted,  and  the  length  divided  bv  the  time  gives  the  velocity  of  the 
blood  in  the  tube.  If  the  calibre  of  the  tube  is  the  same  as  that  of  the 
artery,  this  is  also  the  velocity  in  the  vessel  ;  but  if  the  calibre  is 


A  M  ixr  !/   OF   PHYSIOLOGY 


different,  a  correction  would  have  to  be  made.  I  he  method  is  not  a 
good  one,  for  the  reason,  among  others,  ih.a  the  long  tube  introduces 
.in  extra  resistance. 

2.  Ludwig's  Stromuhr.  —This  instrument  measures  the  quantity 

of  blood  which  passes  in  a  given  time 
through  the  vessel  at  the  cross  section 
where  it  is  inserted.  M  i  onsists  of  a 
U  shaped  tube,  with  the  limbs  widened 
into  bulbs,  but  narrow  .it  the  free  ends, 
which  are  connei  ted  with  a  metal  di»  . 
By  rotating  the  instrument,  these 
ends  can  be  placed  alternately  in 
communication  with  a  i  annula  in  the 
central,  and  another  in  the  peripheral 
portion  of  a  divided  artery;  or  they 
can  be  placed  so  that  none  of  t la- 
blood  passes  through  the  bulbs,  but 
all  goes  by  a  short-cut.  One  limb  of 
the  instrument  is  filled  with  oil,  and 
the  other  with  defibrinated  blood. 
The  limb  containing  the  oil  is  first 
put  into  communication  with  the 
central  end.  and  that  containing  the 
blood  with  the  peripheral  end  of  the 
artery.  The  blood  from  the  artery 
rushes  in  and  displaces  the  oil  into 
the  other  limb,  the  defibrinated  blood 
passing  on  into  the  circulation.  As 
soon  as  the  blood  has  reached  a 
certain  height,  indicated  by  a  mark, 
the  instrument  is  reversed,  and  the 
oil  is  again  displaced  into  the  limb  it 
originally  occupied.  This  process  is 
repeated  again  and  again,  the  time 
from  beginning  to  end  of  an  experi- 
ment being  carefully  noted.  The 
number  of  times  the  blood  has  filled 
a  bulb  in  that  period,  the  capacity  of 
the  bulb  and  the  (  ross  se<  tion  <>f  the 
vessel  being  known,  all  the  data 
required  for  calculating  the  velocity 
of  the  blood  in  the  vessel  have  been 
obtained. 

Suppose,  for  example,  that  the 
capacity  of  the  bulb  up  to  the  mark 
is  5  c.c,  and  thai  it  is  filled  twelve 
times  in  a  minute,  the  quantity 
flowing  through  the  cross-section  of 
the  artery  is  i  c.c,  or  1,000  cub.  mm. 
per  second.  Let  the  diameter  of  the 
vessel  be  3  mm.,  then  its  sectional  area 

/  i\*     r  i4X(>  tm  ,  IOOO 

is  7r  x  (  "   )  =  —  =  706  sq.   mm.      The  velocity  is        -    =141  mm. 

V  j  '  4  n  7-1.0 

per  second. 

Various  improvements  in  this  method  have  been  made,  such  as  a 

graphic  registration  of  the  reversals  oi  the  stromuhr. 


Fig.  39* — Stromuhr  of  Ludwig 
and  Dog  1  el. 
A,  B,  glass  bulbs  ;  a,  a  metal 
disc,  to  which  A  and  G  are  at- 
tached, and  which  can  be  rotated 
on  the  disc  b ;  E,  F,  cannulas 
attached  to  b,  and  connected  with 
the  peripheral  and  central  end; 
oi  a  iln  ided  bli ><  ><l\ essel.  At  the 
beginning  of  the  experiment,  A 
and  the  juni  tion  between  A  and  B 
are  filled  with  oil  ;  B  is  filled  with 
physiological  sit  solution  or  de- 
fibrinated blood  :  a  being  turned 
into  the  position  sb  wn  in  the 
figure,  the  blood  passes  through  F 
and  I  I  into  A.  anil  the  oil  U  6  m  ed 
into  B.  As  soon  as  the  blood  has 
reached  the  mark  m,  the  disc  a, 
witli  the  bulbs,  is  rapidly  rotated, 
so  1  hat  C  1-  now  opposite  I-'.  The 
blood  ii' iw  pas-.es  intu  B,  and  the 
oil  is  again  driven  into  A.  When 
the  oil  has  re  1  lud  I  >.  reversal  is 
again  made,  and  so  on. 


THE  CIRCUl   ITION  OF  THE  BLOOD  AND  LYMPH       nj 


j,  A  tube  or  l">\.  in  which  swings  a  small  pendulum,  is  inserted 
in  the  course  of  the  vessel,  ["he  pendulum  is  deflc  ted  by  the  blood, 
.uid  the  amount  of  the  deflection 
beai  s  .1  rela  I  ion  to  I  be  veloi  it  y 
(it  the  stream  (Vierordt's  hcema- 
tachometer  ;  C  ha  u  vea  u  and 
Lortct's  much  more  perfect 
dromograph)  (Fig.  4  1 ). 

4.  Pilot's  lulus.  —  If  two 
\  nil'  .'l  t  ubc  i,  <>  and  b,  of  the 
form  shown  in  Fig.  40,  be  inserted 
into  a  horizontal  lube  in  which 
liquid  is  (lowing  in  the  direction 
of  tin-  arrow,  the  level  will  be 
higher  in   «<    than   would   be   the  Fig.  40.— Piror-s  Tubes. 

m    an   ordinary    side-lube 
without  an  elbow  ;   in  h  it  will  be  lower.     For  the  moving  liquid  will 
r\crt  .1  push  on  the  column  in  a,  and  a  pull  on  that  in  b.     The 
amount  of  this  push  and  pull  will  vary  with  the  velocity,  so  that  a 
change  in  the  latter  will  correspond 
to  an  alteration  in  the  difference  of 
level  in  the  two  tubes.    Instruments 
on    this    principle   have  been    con- 
structed by  Marey  and  Cybulski,  the 
former   registering   the    movements 
of    the    two   columns    of    blood    by 
connecting    the   tubes  to  tambours 
provided    with    writing    levers,   the 
latter  by  photography  (Fig.  44). 

5.  The  electrical  method,  described 
on  p.  123,  for  the  measurement  of 
the  circulation  time,  can  also  be 
applied  to  the  estimation  of  the 
mean  velocitv  of  the  blood  between 
two  cross  -  sections  of  the  arterial 
path  which  arc  separated  by  a 
sufficient  distance.  For  example, 
salt  solution  can  be  injected  into 
the  left  ventricle  or  the  beginning 
o.f  the  aorta,  and  the  interval  which 
it  takes  to  reach  a  pair  of  electrodes 
in  contact  with,  say,  the  femoral 
artery  determined.  Knowing  the 
distance  between  the  point  of  injec- 
tion and  the  electrodes,  we  can  then 
calculate  the  mean  velocity. 

Of  these  methods,  3  and  4  are 
alone  suited  for  the  study  of  the 
velocity-pulse,  that  is,  the  change 
of  velocity  occurring  with  every 
beat  of  the  heart.  The  curves 
obtained  by  Chauveau's  dromo- 
graph show  a  general  agreement 
with  blood- pressure  tracings  taken 


-Chauveau's 
graph. 


Dromo- 


A,  tube  connected  with  blood- 
vessel ;  B,  metal  cylinder  in  com- 
munication with  A.  The  upper  end 
of  B  has  a  hole  in  the  centre,  which  is 
covered  by  a  membrane,  m,  through 
which  a  lever,  C,  passes  ;  C  has  a 
small  disc.  />,  at  its  end,  which  pro- 
jects in'.o  the  lumen  of  A,  and  is  d  - 
fleeted  in  the  direction  of  the  blood- 
stream through  A.  The  deflection  is 
registered  by  a  recording  tambour  in 
communication  by  the  tube  E  with  a 
tambour  D,  the  flexible  membrane 
of  which  is  connected  with  the  lever 
or  pendulum  C. 

s 


Il4 


I   .1/  INVAL  OF  PHYSIOLOGY 


by  a  spring  manometer,  and  with  records  of  the  external  pulse 
obtained  by  a  sphygmograph.  There  is  a  primary  increase  of 
velocity   corresponding   with    the   ventricular    systole,    and    a 


Plethysmocj  ram 


QphycfiTiocfrCLTll 


Fig.    13. 

Fig.  42. — The  highest  of  the  three  curves  is  a  pic  thysmographic  record  taken 
from  the  hand  ;  the  second  curve  is  a  sphygmogram  taken  simultaneously  from 
the  corresponding  radial  artery  ;  the  lowest  (interrupted)  curve  is  the  curve  of 
velocity  deduced  from  a  comparison  of  the  first  two  (Fick). 

Fig.  43. — Simultaneous  plethysmography  and  sphygmographic  tracings. 

secondary  increase  corresponding  with  the  dicrotic  wave  (Fig.  45). 

Like  all  the  other  pulsatory  phenomena,  the  velocity-pulse  disap- 
pears in  the  capillaries, 
and  is  only  present 
under  exceptional  cir- 
cumstances in  the  veins. 
Fick,  from  a  com- 
parison  of  sphygmo- 
graphic and  plethys- 
mography tracings 
(p.  117),  taken  simul- 
taneously from  the 
radial  artery  and  the 
hand,  has  demon- 
strated that  in  man 
the  velocity-pulse  ex- 
hibits the  same  gener.il 
char  a  c  t  e  r  s  as  i  n 
animals  (Figs.  42  and 
43).  And  v.  Kries  has 
confirmed  Kick's  con- 
clusions by  actual  re- 
cords of  the  velocity- 
pulse  obtained  by 
means  of  an  arrange- 
ment called  a  gas 
tachograph  (Fig.  46). 


Fig.    44.— CybulSKI's    Arrangement    eor    Re- 
cording  Variations   in    the   Velocity   of 
the  Blood. 
A,   tube  connected  with  central,  B  with  peri 
plural    end    of    divided    bloodvessel.     The    blood 
stands  highei  in  the  tube  *   than  in  I >.     A  beam  "t 
light  passing  through  the  meniscus  in  both  tubes  is 
focussed  by  the  lens  l    on  tin-  travelling  photo- 
graphii    plate  1'.-     The  velocity  at  any  moment  is 
deduced  from  tin-  height  of  the  meniscus  in  the  two 
tubes  C  and  D. 


Tin:  CIRCULATION    OF   I  III'  II.OOD  AND  LYMPH        115 

This  consists  <>f  a  plethysmograph  connected  with  the  lube  of 
a  gas-burner.  When  the  part  enclosed  in  the  plethysmograph 
expands,  air  issues  Erom  the  connecting  tube,  and  causes  an 
increase  in  the  heighl  oi  Hie  Same.  When  the  part  shrinks,  air 
is  drawn  in  from  the  flame,  which  is  depressed.     Since  the  speed 


[    i/fii. 


!  T^j^sscfZ'O 


Fig.    45. — Simultaneous    Tracings    of    the    Velocity    (Upper    Curve)    ant 
Pressure  (Lower  Curve)  (Lortet). 

The  tracings  were  taken  from  the  carotid  artery  of  a  horse.  The  curve  of 
velocity  was  obtained  by  the  dromograph.  The  dicrotic  wave  is  marked  on  it. 
The  slightly  curved  ordinates  drawn  through  the  curves  indicate  corresponding 
points. 

of  the  blood  in  the  veins  may  be  considered  constant  during  the  time 
of  an  experiment,  the  rate  at  which  the  volume  of  the  part  alters  at 
any  moment  is  a  measure  of  the  pulsatory  change  of  velocity  in  the 
arteries  of  the  part.  And  by  photographing  the  movements  of  the 
flame  on  a  travelling  sensitive  surface,  the  velocity-pulse  is  directly 
recorded. 


Fig.   -id. — Photographic   Record  of  the   Velocity-pulse  obtained  by   the 
Gas  Tachograph  (v.   Kries). 

The  upper  curve  is  the  photographic  representation  of  the  movements  of  the 
flame,  and  corresponds  to  the  curve  of  velocity. 

The  mean  velocity,  like  the  mean  blood-pressure,  is  more 
variable  in  the  large  arteries  near  the  heart  than  in  the  smaller 
and  more  distant  arteries.  Dogiel  found  in  measurements  taken 
with  the  stromuhr  (a  good  instrument  for  the  estimation  of  mean 
speed),  within  a  period  of  two  minutes,  velocities  ranging  from 

S—2 


i  16 


A  MANUAL  OF  PHYSIOLOGY 


over  200  mm.  to  under  ioo  mm.  per  second  in  the  carotid  of  the 
rabbit,  and  from  over  500  mm.  to  less  than  250  nun.  in  the 
carotid  of  the  dog.  Chauveau,  with  the  dromograph,  found  the 
velocity  in  the  carotid  of  a  horse  to  be  520  mm.  per  second  during 
systole,  150  mm.  during  the  pause,  220  mm.  during  the  period 
of  the  dicrotic  wave. 

It  is  probable,  however,  that  if  these  numbers  are  at  all 
rate  for  bloodvessels  in  the  immediate  neighbourhood  of  the 
heart,  there  must  be  a  rapid  diminution  in  the  veloi  ltv  even 
while  the  arteries  are  still  of  considerable  calibre.  For  it  has 
been  found  by  the  electrical  method  that,  in  anaesthetized 
at  any  rate,  as  is  shown  in  the  following  table,  the  mean  velocity 
between  the  origin  of  the  aorta  and  the  crural  artery  in  the 
middle  of  the  thigh  is  usually  less  than  100  mm.  per  second. 


No.  of 
Experi- 
ment. 

1 

Body- 
weight 

in  Kilos. 

Distance  between 

Point  of  Injection 

and  Electrodes, 

in  Millimetres. 

Average  Time  be- 
tween Injection          Average 

and  Arrival  of  the       Pulse-rate 
Salt  Solution,  in      per  Minute. 
Seconds. 

Averag< 

1 
in  Milli- 
metres. 

Av  rage 
Distance 
traversed  per 
beat,  in 

Millimetres.  1 

I. 
II. 

III. 

IV. 
V. 

1 

34' 5  5 
i7-5 
14-99 
10*32 
7*165 

420 

495 
400 
470 

330 

4*62 

57 
5-0 

7*12 
7-83 

105 

69 

102 

74'5 
46*3 

(weak  beat) 

90-9 

86-8 
80 

;-•'' 
42T 

5I'9 

7? '4 
47  'O 
587 
54'5 

In  I.  the  injecting  cannula  was  in  the  descending  part  of  the 
thoracic  aorta,  in  V.  at  the  very  origin  of  the  aorta,  and  in  II.,  III., 
and  IV.  in  the  left  ventricle. 

As  to  the  speed  of  the  blood  in  the  arteries  of  man,  our  data 
are  insufficient  for  more  than  a  loose  estimate.  But  it  does  not 
seem  likely  that  the  mean  velocity  of  a  particle  of  blood  in 
moving  from  the  heart  to  the  femoral  artery  can  exceed  150  mm. 
per  second  for  the  whole  of  its  path.  This  would  correspond  to 
rather  more  than  a  third  of  a  mile  per  hour.  In  the  arch  of  the 
aorta  the  average  speed  may  be  twice  as  great.  '  The  rivers  of 
the  blood  '  are,  even  at  their  fastest,  no  more  rapid  than  a 
sluggish  stream.  A  red  corpuscle,  even  if  it  continued  to  move 
with  the  velocity  with  which  it  set  out  through  the  aorta,  would 
only  cover  about  15  miles  in  twenty-four  hours,  and  would 
require  five  years  to  go  round  the  world. 

The  Volume-pulse.  —  When  the  pulse-wave  reaches  a  part  it 
distends  its  arteries,  increases  its  volume,  and  gives  rise  to  what 
may  be  called  the  volume- pulse. 

This  may  be  readily  recorded  bv  means  of  a  plethysmograph,  an 
instrument  consisting'cssentidly  of  a  chamber  with  rigid  walls  which 


THE  CIRCULATION  OF  THE  HI  mm    IND  I  YMPH       117 

enclose  the  organ,  the  intervening  space  being  filled  up  with  liquid 
(Fig.  47).  The  movements  of  the  liquid  are  transmitted  either 
through  a  tube  tilled  with  air  to  a  recording  tambour,  or  directly  to 
.1  piston  or  floal  acting  upon  ;i  writing  lever.  Special  names  have 
been  given  to  plethysmogra.phs  adapted  to  particular  organs;  for 
example,  Koy's  oncometer  lor  the  kidney.  The  method  has  been 
successfully  applied  to  the  invest  igat  ion  of  circulatory  changes  in 
man,  a  finger,  a  hand  or  an  entire  limb  being  enclosed  in  the  plethys- 
mograph.  With  a  fairly  sensitive  arrangement,  every  beat  of  the 
heart  is  represented  on  the  tracing  by  a  primary  elevation  and  a 
dicrotic  wave  (Fig.  48). 

The  general  appearance  of  the  curve  is  very  similar  to  that  of 
an  ordinary  pulse-tracing,  though  there  are  some  differences  of 
detail,  especially  in  the  time  relations.  A  volume-pulse  has 
been  actually  observed  not  only  in  limbs  and  portions  of  limbs, 
but  also  (in  animals)  in  the  spleen,  kidney  and  brain,  and  other 
organs,  and  in'the'orbit. 

The    so-called    cardio-pneumatic    movements    also    constitute 


Fig.  47. — Plethysmograph  for  Arm. 

F,  float  attached  by  A  to  a  lever  which  records  variations  of  level  of  the  water  in 
B,  and  therefore  variations  in  the  volume  of  the  arm  in  the  glass  vessel  C.  Or  the 
plethvsmograph  may  be  connected  to  a  recording  tambour.  The  tubulure  at  the 
upper  part  of  C  is  closed  when  the  tracing  is  being  taken. 

a  volume-pulse,  although  of  complex  origin.  This  name  is  given 
to  the  rhythmical  changes  of  pressure  accompanying  the  beat  of 
the  heart,  which  can  be  detected  in  the  air  of  the  respiratory 
passages  when  one  nostril  is  connected  with  a  recording  tambour, 
or  water  manometer,  the  other  nostril  and  the  mouth  being  closed, 
and  the  respiration  suspended  in  inspiration,  with  the  glottis  open. 
Or  the  mouth  may  be  connected  with  the  recording  apparatus, 
the  nostrils  being  closed.  One  factor  in  the  production  of  these 
movements  may  be  the  change  of  blood-volume  in  the  soft 
tissues  of  the  mouth,  naso-pharynx,  and  perhaps  also  in  the 
lower  respiratory  passages  accompanying  the  heart-beat.  Another 
factor,  and  a  more  influential  one,  is  the  rhythmical  alteration  of 
pressure  caused  directly  by  the  alternate  systole  and  diastole  of 


I  IS 


A    M  I  \T  II    OF   PHYSIOLOGY 


the  heart  in  the  air  contained  in  the  lung-tissue  surrounding  it, 
which  acts  as  a  kind  of  air  plethysmograph.  One  interesting  wax- 
in  which  the  cardio-piuuimatic  movements  may  reveal  themselves 
is  by  a  variation  with  each  beat  of  the  heart  in  the  intensity  of  a 
note  prolonged  in  singing,  especially  after  fatigue  has  set  in. 
Upon  the  whole,  the  air-pressure  falls  during  systole,  owing  to  the 
expulsion  of  blood  from  the  chest,  and  rises  during  diastole. 
The  main  cardio-pneumatic  movement  is,  therefore,  a  systolic 
inspiration  and  a  diastolic  expiration  (Practical  Exercises,  p.  291). 

Doubtless  the  weight  of  an  organ  would  also  show  a  pulse  corre- 
sponding to  the  beat  of  the  heart,  and  so  would  the  temperature — 
at  least,  of  the  superficial  parts.  For  the  amount  of  heal  given  off 
by  the  blood  to  the  skin  increases  with  its  mean  velocity,  and.  there- 
fore, although  the  difference  may  not  in  general  be  measurable,  more 
heat  is  presumably  given  off  during  the  systolic  increase  of  velocity 
than   during  the  diastolic  slackening.     And  this,  along  with  other 


Fig.  48. — Plethysmograph  Tracing  from   Arm. 

The  tracing  was  taken  by  means  of  a  tambour  c lected  with  the  plethysmo- 
graph.    The  dicrotic  wave  is  distinctly  marked. 

considerations,  suggests  that,  at  any  rate  in  certain  situations  and 
under  certain  conditions,  there  may  even  be  a  pulse  of  chemical 
change  ;  that  is.  a  slight  and  as  yet  doubtless  inappreciable  ebb  and 
flow  of  metabolism  corresponding  to  the  rhythm  of  the  heart. 

The  Circulation  in  the  Capillaries. — From  the  arteries  the 
blood  passes  into  a  network  of  narrow  and  thin-walled  vessels, 
the  capillaries,  which  in  their  turn  are  connected  with  the  finesl 
rootlets  of  the  veins.  Physiologically,  the  arterioles  and  venules 
must  for  many  purposes  be  included  in  the  capillary  tract,  but 
the  great  anatomical  difference — the  presence  of  circularly- 
arranged  muscular  fibres  in  the  arterioles,  their  absence  in  the 
capillaries — has  its  physiological  correlative.  The  calibre  of  the 
arterioles  can  be  altered  by  contraction  of  these  fibres  under 
nervous  influences  ;  the  calibre  of  the  capillaries,  although  it 
varies  passively  with  the  blood-pressure,  and  is  possibly  to  some 
extent  affected  by  active  contraction  of  the  endothelial  cells, 
cannot  be  under  the  control  of  vasomotor  nerves  acting  on 
muscular  fibres  (but  see  p.  157). 


THE  Cmt  Ul   \TION  OF  THE  !:/<><>/>  AND  LYMPH       riy 

Harvey  had  deduced  from  his  observations  the  existence  of 
channels  between  the  arteries  and  the  veins.  Malpighi  was  the 
firsl  i"  observe  the  capillary  Mm  id-stream  with  the  microscope, 
and  thus  to  give  ocular  demonstration  of  the  truth  of  Harvey's 
brilliant  reasoning.  He  used  the  lungs,  mesentery  and  bladder 
of  the  frog.  The  web  of  the  frog,  the  tail  of  the  tadpole,  the 
wing  of  the  bat,  the  mesenteiy  of  the  rabbit  and  rat,  and  other 
transparent  parts,  have  also  been  frequently  employed  for  such 
investigations.  From  the  apparent  velocity  of  the  corpuscles 
and  the  degree  of  magnification,  it  is  easy  to  calculate  the 
velocity  of  the  capillary  blood-stream.  It  lias  been  estimated 
at  from  o-2  to  o-8  mm.  per  second  in  different  parts  and'different 
animals.  \ 

The  comparative  slowness  of  the  current  and  the  disappear- 
ance of  the  pulse  are  the  chief  characteristics  of  the  capillary 


Fig.  49. — Diagram  to  illustrate  the  Slope  of  Pressure  along  the  Vascular 

System. 

A,  arterial ;  C,  capillary  ;  V,  venous  tract.  The  interrupted  line  represents  the 
line  of  mean  pressure  in  the  arteries,  the  wavy  line  indicating  that  the  pressure 
varies  with  each  heart-beat.  The  line  passes  below  the  abscissa  axis  (line  of  zero 
or  atmospheric  pressure)  in  the  veins,  indicating  that  at  the  end  of  the  venous 
system  the  pressure  becomes  negative. 

circulation.  The  explanation  we  have  already  found  in  the 
great  resistance  of  the  narrow  arterioles  and  the  much-branched 
capillary  vessels.  Although  the  average  diameter  of  a  capillary 
is  only  about  10  /x  (5  to  20  //.  in  different  parts  of  the  body),  the 
number  of  branches  is  so  prodigious  that  the  total  cross-section 
of  the  systemic  capillary  tract  has  been  estimated  at  500  to  700 
times  that  of  the  aorta.  Such  estimates  are,  of  course,  by  no 
means  exact. 

The  total  cross-section  of  the  vascular  channel  gradually 
widens  as  it  passes  away  from  the  left  ventricle.  In  the  capillary 
region  it  undergoes  a  great  and  sudden  increase.  At  the  venous 
end  of  this  region  the  cross-section  is  again  somewhat  abruptly 
contracted,  and  then  gradually  lessens  as  the  right  side  of  the 


A   MANUAL  OF  PHYSIOLOGY 


heart  is  approached  :  bu1  the  united  sectional  area  of  the  large 
thoracic  veins  is  greater  than  that  of  the  aorta. 

Attempts  have  been  made  to  measure  the  blood-pressure  in  the 
capillaries  by  weighting  a  small  plate  of  glass  laid  on  the  ba<  l<  of 
of  the  fingers  behind  the  nail,  until  the  capillaries  are  just  emptied, 
as  shown  by  the  paling  of  the  skin  (v.  Kries),  or  by  observing  the 

height  of  a  column  of  liquid  that  just  stops  the  circulation  in  a  i  rans- 
parcnt  part  (Roy  and  Graham  Brown).  The  last-named  observers 
found  that  a  pressure  of  ioo  to  150  mm.  of  water  (about  7  to  1  1  mm. 
of  Hg)  was  needed  to  bring  the  blood  to  a  standstill  in  the  1  apillaries 
and  veins  of  the  frog's  web;  that  is,  about  a  third  of  the  blood- 
pressure  in  the  frog's  aorta.  The  pressure  in  the  capillaries  at  the 
root  of  the  nail  in  man  varies  from  30  to  50  mm.  of  mercury,  as 
estimated  by  the  method  of  v.  Kries.  But  the  method  is  exposed 
to  serious  errors. 

Under  certain  conditions  the  pulse-wave  may  pass  into  the 
capillaries  and  appear  bevond  them  as  a  venous  pulse.     Thus, 

we  shall  see  that 
when  the  small 
arteries  of  the  sub- 
maxillary gland 
are  widened,  and 
the  vascular  re- 
sistance lessened. 
by  the  stimulation 
of  the  chorda  tym- 
pani  nerve,  the 
pulse  passes 
through  to  the 
veins.  And,  nor- 
mally, a  pulse  may 
be  seen  in  the  wide 
capillaries  of  the 
nail-lied  especi- 
ally when  they  are  partially  emptied  by  pressure — as  a  flicker 
of  pink  that  comes  and  goes  with  every  beat  of  the  heart. 

We  have  seen  that  the  lateral  pressure  at  any  poinl  of  a  uniform 
rigid  tube  through  which  water  is  flowing  is  proportional  to  the 
amount  of  resistance  in  the  portion  of  the  tube  between  this  point 
and  the  outlet.  In  any  system  of  tubes  the  sum  of  the  potential  and 
kinetic  energy  must  diminish  in  the  direction  of  the  flow  .  and 
although  the  problem  is  complicated  in  the  vascular  system  by  the 
branching  of  the  channel  and  the  variation  in  the  total  cross-section, 
yet  theory  and  experiment  agree  that  in  the  larger  arteries  the 
lateral  pressure  diminishes  but  slowly  from  the  heart  to  the  periphery, 
the  resistance  being  small  compared  with  the  resistance  of  the  whole 
circuit.  In  the  capillary  region  the  vascular  resistance  abruptly 
increases;  the  velocity  (and  therefore  the  kinetic  energy)  abruptly 
diminishes,  and  the  lateral  pressure  falls  much  more  steeply  between 
the  beginning  and  the  end  of  this  region  than  between  the  heart  and 


Fig.  50. —  Relation  of  Blood-pressure,  Velocity, 
and  Cross-section. 

The  curves  P,  V,  and  S  represent  the  blood-pressure, 
velocity  of  the  blood,  and  total  cross-section  respect  iwlv 
in  the  arteries  A,  capillaries  C.  and  veins  V. 


THE  CIRCULATION  OF   THE  BLOOD  AND  LYMPH        121 

its  commencement.  In  the  veins  only  a  small  remnant  of  resistance 
remains  to  1>  ■  overcome,  and  the  lateral  pressure  must  sink  again 
rather  suddenly  about  the  end  of  the  capillary  tract.  Fig.  50  shows 
by  a  rough  diagram  the  manner  in  which  the  pressure,  velocity  and 

cross-section   probably  change   from    part    to   part  of  the  vascular 

system. 

The  Circulation  in  the  Veins.  The  slope  of  pressure,  as  we 
have  just  explained,  must  fall  rather  suddenly  near  the  beginning 

and  near  the  end  of  the  capillary  tract.  It  continues  falling  as 
we  pass  along  the  veins,  till  the  heart  is  again  reached.  In  the 
right  heart,  and  in  the  thoracic  portions  of  the  great  veins  which 
enter  it,  the  pressure  may  be  negative — that  is,  less  than  the 
atmospheric  pressure.  And  since  nowhere  in  the  venous  system 
is  the  pressure  more  than  a  small  fraction  of  that  in  the  arteries, 
its  measurement  in  the  veins  is  correspondingly  difficult,  because 
any  obstruction  to  the  normal  flow  is  apt  to  artificially  raise  the 
pressure.  A  manometer  containing  some  lighter  liquid  than  mer- 
cury, such  as  water  or  a  solution  of  sodium  citrate  or  magnesium 
sulphate,  is  usually  employed,  so  that  the  difference  of  level  may 
be  as  great  as  possible.  In  the  sheep  the  pressure  was  found  to 
be  3  mm.  of  mercury  in  the  brachial,  and  about  11  mm.  in  the 
crural  vein.  Opitz  obtained  the  following  pressures  in  dogs  (of 
about  15  kilos)  :  left  facial  vein,  5-1  ;  right  external  jugular, 
-oil  ;  central  end  of  superior  vena  cava,  — 2'8  ;  femoral  vein, 
5-4  ;  renal  vein,  109  ;  portal  vein,  8-o,  mm.  of  mercury. 

The  venous  pressure  being  so  low,  or,  in  other  words,  the 
potential  energy  which  the  systole  of  the  heart  imparts  to  the 
blood  being  so  greatly  exhausted  before  it  reaches  the  veins, 
other  influences  begin  here  appreciably  to  affect  the  blood- 
stream : 

1.  Contraction  of  the  Muscles. — This  compresses  the  neighbour- 
ing veins,  and  since  the  blood  is  compelled  by  the  valves,  if  it 
moves  at  all,  to  move  towards  the  heart,  the  venous  circulation 
is  in  this  way  helped. 

2.  Aspiration  of  the  Thorax. — In  inspiration  the  intrathoracic 
pressure,  and  therefore  the  pressure  in  the  great  thoracic  veins, 
is  diminished,  and  blood  is  drawn  from  the  more  peripheral  parts 
of  the  venous  system  into  the  right  heart  (p.  210). 

3.  Aspiration  of  the  Heart. — When  the  heart,  after  its  contrac- 
tion, suddenly  relaxes,  the  endocardiac  pressure  becomes  nega- 
tive, and  blood  is  sucked  into  it,  just  as  when  the  indiarubber 
ball  of  a  syringe  is  compressed  and  then  allowed  to  expand. 
But  we  cannot  attribute  any  great  importance  to  this  ;  and, 
of  course,  it  is  only  the  relaxation  of  the  right  ventricle  which 
could  directly  affect  the  venous  circulation. 

4.  Every  change  of  position  of  the  limbs,  as  in  walking,  aids 
the  venous  circulation  (Braune),  and  this  independently  of  the 


i22  A   MANUAL  OF  PHYSIOLOGY 

muscular  contracl  ion.  When  the  thigh  of  a  dead  body  is  rotated 
outwards,  and  at  the  same  time  extended,  a  manometer  con- 
nected with  the  femoral  vein  shows  a  negative  pressure  of  5  to 
10  mm.  of  water.  When  the  opposite  movements  are  made, 
the  pressure  becomes  posit ive. 

It  follows  from  the  number  of  casually-acting  influences  which 
affect  the  blood-flow  in  the  veins  that  it  cannot  be  very  regular 
or  constant.  We  have  seen  that  in  the  great  arteries  there  is  a 
considerable  variation  of  velocity  and  of  pressure  with  every 
discharge  of  the  ventricle,  and  although  this  variation  is  absent 
from  the  veins,  since  normally  the  pulse,  due  to  the  ventricular 
discharge,  does  not  penetrate  into  them,  the  venous  flow  is, 
nevertheless,  as  a  matter  of  fact,  more  irregular  than  the  arterial. 
So  that  if  it  is  difficult  to  give  a  useful  definition  of  the  term 
'  velocity  of  the  blood  '  in  the  case  of  the  arteries,  it  is  still  more 
difficult  to  do  so  in  the  case  of  the  veins.  Where  voluntary 
movement  is  prevented,  one  potent  cause  of  variation  in  the 
venous  flow  is  eliminated  ;  and  in  curarized  animals  certain 
observers  have  found  but  little  difference  between  the  mean 
velocitv  in  the  veins  and  in  the  corresponding  arteries.  Others 
have  found  the  velocitv  in  the  veins  considerably  less,  which  is 
indeed  what  we  should  expect  from  the  fact  that  the  average 
cross-section  of  the  venous  system  is  greater  than  that  of  the 
arterial  system.  Opitz,  by  means  of  a  stromuhr,  obtained  a  mean 
velocity  of  147  mm.  per  second  in  the  external  jugular  vein  of  a 
13-kilo  dog. 

To  sum  up,  we  may  conclude  that,  upon  the  whole,  the  blood 
passes  with  gradually-diminishiug  velocity  from  the  left  ventricle 
along  the  arteries  ;  it  is  greatly  and  somewhat  suddenly  slowed 
in  the  broad  and  branching  capillary  bed  ;  but  the  stream 
gathers  force  again  as  it  becomes  more  and  more  narrowed  in 
the  venous  channel,  although  it  never  acquires  the  speed  which 
it  has  in  the  aorta. 

Venous  Pulse. — To  complete  the  account  of  the  circulation 
in  the  veins,  it  may  be  recalled  that,  in  addition  to  the  venous 
pulse  described  on  p.  120,  which,  as  an  occasional  phenomenon, 
may  travel  through  widened  arterioles  and  capillaries  from  the 
arteries  into  the  veins,  and  therefore  in  the  direction  ol  the  blood- 
stream, a  so-called  venous  pulse,  travelling  from  the  heart  against 
the  blood-stream  and  depending  on  variations  of  pressure  in  tin- 
right  auricle,  may  be  detected  in  the  jugular  vein  in  healthy 
persons,  and  far  more  distinctly  in  certain  disorders  of  the  1  ii  - 
dilation.  In  animals  a  venous  pulse  of  this  nature*  has  been 
demonstrated  in  the  venae  cavae,  the  jugular  vein,  and  with  a 
delicate  manometer  even  in  the  large  veins  of  the  limbs.  It 
moves  with  a  speed  of  1  to  3  metres  a  second  (Morrow).     It  is  most 


Till    CIRCULATION  OF  THE  BLOOD  AND  LYMPH       123 

easily  observed  in  the  jugular  veins  in  man,  because  of  their 
proximity  to  the  heart.  We  have  already  pointed  out  the  signili- 
ce  of  the  study  of  this  venous  pulse  for  the  analysis  of  cardiac 
events  (p.  91).  A  jugular  venous  pulse  of  a  perfectly  different 
origin  is  seen  in  cases  of  incompetence  of  the  tricuspid  valve. 
Here  the  chief  elevation  is  synchronous  with  the  ventricular 
systole,  and  is  caused  by  the  regurgitation  of  blood  from  the 
right  ventricle  through  the  auricle  into  the  veins.  The  so-called 
'  communicated  venous  pulse  '  is  simply  due  to  the  proximity 
of  some  large  arterv,  especiallv  when  enclosed  in  a  common 
sheath,  whose  pulsations  are  directly  transmitted  to  the  vein. 
The  changes  of  pressure  in  the  great  veins  accompanying  the 
respiratory  movements  (p.  266)  are  also  sometimes  spoken  of  as 
a  venous  pulse,  but  they  are  produced  in  an  entirely  different 
way — namely,  by  the  rhythmical  alteration  in  the  intrathoracic 
pressure,  which  alternately  favours  and  hinders  the  venous  return 
to  the  heart. 

The  Circulation-time. — Hering  was  the  first  who  attempted  to 
measure  the  time  required  by  the  blood,  or  by  a  blood-corpuscle,  to 
complete  the  circuit  of  the  vascular  system.  He  injected  a  solution 
of  potassium  ferrocvanide  into  a  vein  (generallv  the  jugular),  and 
collected  blood  at  intervals  from  the  corresponding  vein  of  the  oppo- 
site side.  After  the  blood  had  clotted,  he  tested  for  the  ferrocvanide 
by  addition  of  ferric  chloride  to  the  serum.  The  first  of  the  samples 
that  gave  the  Prussian  blue  reaction  corresponded  to  the  time  when 
the  injected  salt  had  just  completed  the  circulation.  This  method 
was  improved  by  Yierordt,  who  arranged  a  number  of  cups  on  a 
revolving  disc  below  the  vein  from  which  the  blood  was  to  be  taken. 
In  these  cups  samples  of  the  blood  were  received,  and  the  rate  of 
rotation  of  the  disc  being  known,  it  was  possible  to  measure  the 
interval  between  the  injection  and  appearance  of  the  salt  with 
considerable  accuracy.  Hermann  made  a  further  advance  by 
allowing  the  blood  to  play  upon  a  revolving  drum  covered  with 
paper  soaked  in  ferric  chloride,  and  by  using  the  less  poisonous 
sodium  ferrocyanide  for  injection. 

Even  as  thus  modified,  the  method  laboured  under  serious  defects. 
It  was  not  possible  to  make  more  than  a  single  observation  on  one 
animal,  at  least  without  allowing  a  considerable  interval  for  the 
elimination  of  the  ferrocyanide,  and,  further,  the  method  was  un- 
suited  for  the  estimation  of  the  circulation-time  in  individual  organs. 
In  both  of  these  respects  the  more  recently  introduced  electrical 
method  presents  considerable  advantages  ;  for  by  its  aid  we  can  not 
onlv  obtain  satisfactory  measurements  of  the  circulation-time  in 
such  organs  as  the  lungs,  liver,  kidney,  etc.,  but  we  can  repeat  them 
an  indefinite  number  of  times  on  the  same  animal. 

A  cannula,  connected  with  a  burette  (or  a  Mariotte's  bottle,  or  a 
syringe),  containing  a  solution  of  sodium  chloride  (usually  a  1*5  to 
2  per  cent,  solution),  is  tied  into  a  vessel — say,  the  jugular  vein. 
Suppose  that  the  time  of  the  circulation  from  the  jugular  to  the 
carotid  is  required — that  is,  practically  the  time  of  the  lesser  or 
pulmonary  circulation.     A  small  portion   of  one  carotid  artery  is 


124 


./   MANUA1    OF  PHYSIOLOGY 


isolated,  and  laid  on  a  pair  of  hook-shaped  platinum  electrodes,* 
pi  on  til-  concave  side  of  the  hook,  with  a  layer  of 
insulating  varnish.  To  further  secure  insulation,  a  hit  of  very  thin 
sheet-indiarubber  is  slipped  between  the  artery  and  the  tissues  By 
means  of  the  electrodes  the  piece  oi  artery  lying  between  them, 
with  the  blood  that  flows  in  it.  is  connected  uj>  as  one  oi  the  resist- 
ances in  a  Wheatstone's  bridge  (p.  617).  The  secondary  <  oil  ..t  a 
small  inductorium,  arranged  for  giving  an  interrupted  current,  and 
with  a  single  Daniel!  or  dry  cell  in  its  primary,  is  substituted  for  the 
battery,  and  a  telephone  for  the  galvanometer,  according  to  Kohl- 
rausch's  well-known  method  for  the  measurement  of  the  n 
of  electrolytes.  It  is  well  to  have  the  induction  machine  se1  up  in  a 
rate  room  and  connected  to  the  resistance-box  by  long  wire-,, 


TKtTvr-       I    >"    ' 


m  ^ 
^ 


Fig.  51. 


-Measi  01    mi    Pulmonary  Circulation-timi    in  Rabbit  by 

Injection  "i    Mi  1  hyli  n i    Bi 


so  that  the  noise  of  the  Neef's  hammer  may  be  inaudible.  The 
bridge  is  balanced  by  adjusting  the  resistant  es  until  the  sound  heard 
in  the  telephone  is  at  its  minimum  intensity,  the  s.(  ondary  coil  being 
placed  at  such  a  distance  from  the  primary  that  there  is  no  sign  ol 
stimulation  of  muscles  or  nerves  in  the  neighbourhood  of  the  elec- 
trodes when  the  current  is  closed.  A  definite,  small  quantity  oi  the 
salt  solution  is  now  allowed  to  run  into  the  vein  by  turning  the 
stop-i  oci  Of  the  burette.  It  moves  on  with  the  velcK  ity  of  the  blood, 
and  reaching  the  artery  on  the  elei  trodes  causes  a  diminution  of  its 

*  The  electrodes  can  easily  he  made  by  beating  out  one  end  of  a  piece 
of  thick  platinum  wire  to  a  breadth  of  ;  or  6  mm.,  and  then  bending  the 
flattened  part  into  a  hook,  or  by  bending  pi«  es  oi  stout  platinum  foil. 


////    (  //>'<  [  /    I770A    OF    III!    BLOOD     IND  I  )   \ITII        125 

(In  iiu.il  resistance  (p.  25).  This  disturbs  the  balance  oi  the  bridge, 
and  the  sound  m  the  telephone  becomes  louder.  The  time  from  the 
beginning  <>t  the  injection  to  the  alteration  in  the  sound  is  the  cir<  ula 
tion  time  between  jugular  and  carotid.  It  can  be  read  oil  by  a 
stop  watch,  or  more  accurately  by  an  electric  time-maker  writing  on 
a  revolving  drum  (Fig.  52).  Instead  oi  the  telephone  a  galvanometer 
may  be  used,  the  equal  and  oppositely  directed  induction  shocks  being 
replaced  by  a  weak  voltaic  currenl  and  the  platinum  by  unpolarizable 
electrodes  (p.  625).     Bu1   this  is  less  convenient. 

The  circulation-time  oi  an  organ  like  the  kidney  can  be  measured 
l>\  adjusting  a  pair  of  electrodes  under  the  renal  artery  and  another 
under  the  renal  vein,  and  reading  oft  the  interval  required  by  the  salt 
solution  to  pass  I  roil  1  the  point  of  injection  first  to  the  artery  and  then 
tot  he  vein.     'The  difference  is  the  circulation-time  through  the  kidney. 

For  certain  purposes,  and  particularly  for  measurements  on  small 
animals  like  the  rabbit,  or  on  organs  whose  \  esse  Is  are  too  delicate  to 
be  placed  on  electrodes  without  the  risk  of  serious  interference  with 
the  circulation,  another  method  may  be  employed  with  advantage. 
It  depends  on  the  injection  of  a  pigment,  like  methylene  blue,  which 
at  first  overpowers  the  colour  of  the  blood  and  shows  through  the 
walls  of  the  bloodvessels,  but  is  soon  reduced  to  a  colourless  sub- 
stance (Fig.  51).  The  details  of  the  method  are  given  in  the 
Practical  Exercises  (p.  203). 

It  may  be  said  in  general  terms  that  in  one  and  the  same  animal 
the  time  of  the  lesser  circulation  is  short  as  compared  with  the  total 
circulation-time,  relatively  constant,  and  hat  little  affected  by  changes 
of  temperature.     In  animals  of  the  same  species  it  increases  with 

the  size,  hut  more  slowly,  and  rather  in  proportion  to  the  increase 
of  surface  than  to  the  increase  of  weight. 

Thus  a  dog  weighing  2  kilogrammes  had  an  average  pulmonary 
circulation-time  of  4*05  seconds,  while  that  of  a  dog  weighing 
11S  kilos  was  8' 7  seconds,  and  that  of  a  dog  with  a  body- weight 
of  1 8' 2  kilos  only  104  seconds.  It  is  probable  that  in  a  man  the 
pulmonary  circulation-time  is  not  usually  much  less  than  12  seconds, 
nor  much  more  than  15  seconds. 

The  circulation-time  in  the  kidney,  spleen  and  liver  is  rela- 
tively long  and  much  more  variable  than  that  of  the  lungs, 
being  easily  affected  by  exposure  and  changes  of  temperature 
(increased  by  cold,  diminished  by  warmth). 

In  a  dog  of  i3-3  kilos  weight  the  average  circulation-time  of 
the  spleen  was  10*95  seconds  ;  kidney,  13*3  seconds  ;  lungs, 
8*4  seconds.  The  circulation-time  of  the  stomach  and  intes- 
tines is  (in  the  rabbit)  comparatively  short,  not  exceeding  very 
greatly  that  of  the  lungs,  but  it  is  lengthened  by  exposure.  The 
circulation-time  of  the  retina  and  that  of  the  heart  (coronary 
circulation)  are  the  shortest  of  all. 

The  total  circulation-time  is  properly  the  time  required  for  the 
whole  of  the  blood  to  complete  the  round  of  the  pulmonary  and 
systemic  circulation.  But  there  arc  many  routes  open  to  any  given 
particle  of  blood  in  making  its  systemic  circuit.  If  it  passes  from  the 
aorta  through  the  coronary  circulation  it  takes  an  exceedingly  short 


126  A  MANUAL  OF  PHYSIOLOGY 

route.  II  it  passes  through  the  intestines  and  liver,  or  through  tli'- 
kidney.  or  through  the  lower  Limbs,  it  takes  .1  long  route.  So  thai 
to  determine  the  total  circulation-time  by  direel  measurement  we 
must  know  (1)  the  quantity  of  blood  thai  passes  on  the  average  by 
each  path  in  a  given  time,  and  (2)  the  average  circulation-time  ol 
each  path.  It  the  average  weight  of  blood  in  each  organ  be  repre- 
sented by  "',.  <>'..  <v;.  etc.;  and  the  average  circulation-times  by 
/,.    /.,.    /;.   etc.  ;    and   /  be  the   total    systemic   circulation-time  .    then 

,.'t    .  w-      w-   .   etc.,   will   represent   the  quantity  ol   blood   passing 

'1        h       '  '3 
through  each  organ  in  /  seconds,  since  in  the  average  circulation- 
time  of  an  organ  the  whole  of  the  blood  in  it  at  the  beginning  of 
the  period  of  observation  will  have  been  exchanged  for  fresh  blood. 


j\_jl_JLJLJUri_ILJLJLJLJl_n_JlJ^ 


II 


JLJLJLJIJLJLJLJUUUULJUUU 

m        , 


^^j\-ji-fLJLJLJi-jULJiJi-JL-n-n..D  .n-n-OJi 

pIG    52 — Time  of  the  Lesser  Circulation.     Cat  anaesthetized 
with    Ether. 

Time-trace,  seconds.  The  line  above  the  time-trace  was  written  by  an  electro- 
magnetic si&ial,  the  circuit  of  which  was  closed  at  the  moment  when  injection 
,,1  methylene  blue  into  the  jugular  vein  was  begun,  and  opened  at  the 
moment  when  the  change  of  colour  in  the  carotid  was  observed.  1.  normal 
circulation-time;  II,  circulation-time  after  section  ol  both  vagi  (much 
diminished);  III,  circulation-time  during  stimulation  ol  the  peripheral  end  oi 
one  vagus  (much  increased). 

But  the  whole  of  the  blood  in  the  body,  which  we  may  call  \\  . 
passes  once  round  the  systemic  circulation  in  t  seconds.      Therefore. 

w: — haVj   +i0»   ,   etc.,=  W.      In    this   equation    everything   can   be 

determined  by  experiment  except  /,  and  therefore  /  can  be  calculated. 
Adding  I  to  the  pulmonary  circulation-time,  we  arrive  at  the  total 
circulation-time. 

Although  our  experimental  data  are  ,b  yet  too  meagre  to  make  the 
calculation  more  than  a  rough  approximation,  it  appears  probable 
that  in  certain  animals  the  total  circulation-time  is  five  or  six  times 
as  great  as  the  pulmonary  circulation-time.  It  the  same  ratio  holds 
good  in  man,  the  total  circulation-time  is  unlikely  to  be  much  less 
than  a  minute  or  much  greater  than  a  minute  and  a  quarter.     We 


////    CIRCULATIOh   OB    I  ill    BLOOD  AND  LYMPH       127 

shall  see  directly  thai  tins  estimate  is  confirmed  by  data  derived  from 
.1  different  source.  In  the  meantime,  we  may  use  it  provisionally  to 
calculate  the  work  done  by  the  heart.  Lei  us  take  Eor  simplicity  the 
total  circulation-time  as  1  minute  in  a  70-kilo  man.  the  quantity  oi 

blood  as  |l  kilos.*  and  the  mean  pressure  in  the  aorta  as  150  mm. 
ol  mercury.  Up  to  the  tune  when  the  semilunar  valves  are  opened, 
the  work  done  by  the  left  ventricle  is  spent  in  raising  the  intra 
ventricular  pressure  till  it  is  sufficient  to  overcome  the  pressure  in 
the  aorta.  If  a  vertical  tube  wen-  connected  with  the  left  ventricle, 
the  blood  would  rise  till  the  column  was  of  the  same  weight  as  a 
column  of  mercury  of  equal  section  and  150  mm.  high.  This  column 
of  blood  would  be  about  1*92  metres  in  height.  If  a  reservoir  were 
placed  in  communication  with  the  tube  at  this  height,  a  quantity  oi 
Blood  equal  to  that  ejected  from  the  ventricle  would  at  each  systole 
p.i>s  into  the  reservoir  ;  and  the  work  which  the  blood  thus  collected 
would  be  capable  of  doing,  if  it  were  allowed  to  fall  to  the  level  of 
the  heart,  would  be  equal  to  the  work  expended  by  the  heart  in 
forcing  it  up.  Thus,  in  1  minute  tin-  work  of  the  left  ventricle  would 
be  equal  to  that  done  in  raising  4J  kilos  of  blood  to  a  height  of 
1*92  metres— that  is.  about  8*64  kilogramme-metres;  in  24  hours  it 
w  ould  be.  say,  12,450  kilogramme-metres.  Taking  the  mean  pressure 
in  the  pulmonary  artery  at  one-third  of  the  aortic  pressure,  we  get 
for  the  daily  work  of  the  right  ventricle  about  4,150  kilogramme- 
metres.  The  work  of  the  two  ventricles  is  thus  about  16,600 
kilogramme-metres,  t  which  is  enough  to  raise  a  weight  of  nearly 
4  pounds  from  the  bottom  of  the  deepest  mine  in  the  world  to  the 
top  of  its  highest  mountain,  or  to  raise  the  man  himself  to  1^  times 
the  height  of  the  spire  of  Strasburg  Cathedral,  or  twice  the  height 
of  the  loftiest  '  skyscraper  '  in  New  York.  By  friction  in  the 
bloodvessels  this  work  is  almost  all  changed  into  its  equivalent 
of  heat,  nearly  40  calories  (p.  584).  Further,  since  the  contraction 
of  the  heart  is  always  maximal  (p.  141),  and  there  is  reason 
to  believe  that  the  quantity  of  blood  ejected  at  a  single  systole 
by  the  left  ventricle  (being  dependent  upon  the  inflow  from  the  pul- 
monarv  veins,  and  therefore  upon  the  inflow  into  the  right  side  of  the 
heart  from  the  svstemic  veins)  varies  widely,  some  of  the  mechanical 
effect  of  the  contraction  must  be  wasted  when  the  quantity  is  less 
than  the  ventricle  is  capable  of  expelling. 

Output  of  the  Heart. — If  4^  kilos  of  blood  pass  through  the  heart 
in  1  minute  with  the  average  pulse-rate  of  72  per  minute,  the  quantity 

ejected  by  either  ventricle  with  every  systole  will  be  *£?-  6r5  grm., 

or  a  little  less  than  60  c.c.  This  is  much  less  than  the  amount 
assigned  by  Vierordt,  which  at  one  time  gained  great  vogue  in  physio- 
logical text-books,  but  all  recent  observers  who  have  directly 
measured  the  output  are  agreed  that  Vierordt 's  estimate  is  too  high. 
Thus,  in  a  series  of  experiments  on  more  than  twenty  dogs,  ranging  in 
weight  from  5  to  nearly  35  kilos,  it  has  been  shown  that  the  output, 
or  contraction  volume,  as  it  is  sometimes  called,  of  the  left  ventricle 
per  kilo  of  body-weight  diminishes  as  the  size  of  the  animal  in- 
creases ;  and  the  relation  between  body-weight  and  output  is  such 
that  in  a  man  weighing  70  kilos  we  can  hardly  suppose  that  the 

*  The  mean  oi  the  5J  kilos  given  by  most  writers,  and  of  the  3-.',-  kilos 
obtained  by  Haldanc  and  Smith  (p.  49). 

f  Since  the  blood  on  expulsion  is  moving  with  a  certain  velocity,  an 
addition  might  be  made  for  its  kinetic  energy.  But  this  would  only 
increase  the  total  work  by  a  small  fraction  (about  1  per  cent.). 


us  /    m  ixr  II.  OF  PHYSIOLOG  Y 

ventricle  discharges  more  than  105  grm.  of  blood  per  second,  or 
87  grm.  (80  c.c.)  per  heart  bc.it  with  a  pulse-rate  ol  7 2.  Putting  this 
resull  along  with  thai  deduced  from  the  circulation  time,  we  can 
pretty  safely  conclude  that  the  average  amounl  ol  blood  thrown  out 
by  each  ventricle  at  each  beat  is  nut  more  than  7"  or  80  c.c.  Zuntz 
from  the  quantity  of  oxygen  absorbed  bv  the  blood  in  the  lungs,  has 
estimated  the  output  at  60  c.c.  But  according  to  him  this  may  be 
doubled  during  severe  muscular  work,  when,  as  a  matter  ol  tact,  by 
ili-  aid  of  the  Rontgen-rays  or  by  percussion  of  the  chest,  the  volume 
oi  the  In-art  may  be  shown  to  be  considerably  increased.  In  the 
middle  of  the  eighteenth  century,  Passavant  calculated  the  output 
at  jo  5  grm.,  which  is  certainly  too  low.  Tigerstedt  puts  it  at  50  to 
100  c.c.   I  'leseh  at  59  c.c. 

The  Relation  of  the  Nervous  System  to  the  Circulation. 

So  far  we  have  been  considering  the  circulation  as  a  purely 
physical  problem.  We  have  spoken  of  the  action  ol  the  heart 
as  that  of  a  force-pump,  and  perhaps  to  a  small  extent  that  ol  a 
suction-pump  too.  We  have  spoken  of  the  bloodvessels  as  a 
system  of  more  or  less  elastic  tubes  through  which  the  blood  is 
propelled.  We  have  spoken  of  the  resistance,  which  the  blood 
experiences  and  the  pressure  which  it  exerts  in  this  system  of 
tubes,  and  we  have  considered  the  causes  of  this  resistance,  the 
interpretation  of  this  pressure,  and  the  physical  changes  in  the 
vascular  system  that  may  lead  to  variations  of  both.  But  so 
far  we  have  not  at  all,  or  only  incidentally  and  very  briefly, 
dealt  with  the  physiological  mechanism  through  which  the 
physical  changes  are  brought  about.  We  have  now  to  see  that 
although  the  heart  is  a  pump,  it  is  a  living  pump  ;  that  although 
the  vascular  system  is  an  arrangement  of  tubes,  these  tubes  are 
alive  ;  and  that  both  heart  and  vessels  are  kept  constantly  in 
the  most  delicate  poise  and  balance  by  impulses  passing  from 
the  central  nervous  system  along  the  nerves. 

In  mam'  respects,  and  notably  as  regards  the  influence  of 
nerves  on  it,  we  may  look  upon  the  hear!  as  an  expanded. 
thickened  and  rhythmically  -  contractile  bloodvessel,  s;>  that 
an  account  ol  its  innervation  may  fitly  precede  the  description 
of  vaso-motor  action  in  general. 

The  Relation  of  the  Heart  to  the  Nervous  System.  A  very 
simple  experiment  is  sufficient  to  prove  that  the  beat  ol  the 
heart  does  not  depend  on  its  connection  with  the  central  nervous 
system,  for  an  excised  frog's  heart  may,  under  favourable  con- 
ditions, of  which  the  most  important  ate  a  moderately  low 
temperature,  the  presence  of  oxygen  and  the  prevention  of 
evaporation,  continue  to  beat  lor  days.  The  mammalian  heart 
also,  after  removal  from  the  body,  beats  for  a  time,  and  indeed, 
if  defibrinated  blood  be  artificially  circulated  through  t  he  coronary 
vessels,   for  several  or  even  many   hours.     But   although   this 


THE  CIRCU1   ITION  OF   llll    BLOOD     IND  LYMPH       [29 

proves  that  the  heart  can  heat  when  separated  from  the  central 
nervous  system,  it  does  no1  prove  that  nervous  influence  is  not 
essential  to  its  action,  for  in  the  cardiac  substance  nervous 
elements,  both  cells  and  fibres,  are  to  be  found. 

The  Intrinsic  Nerves  of  the  Heart.  In  the  heart  of  the 
frog  numerous  nerve-cells  occur  in  the  sinus  venosus,  especially 
near  its  junction  with  the  right  auricle  (Remak's  ganglion). 
A  branch  from  each  vagus,  or  rather  from  each  vago-sympathetic 
nerve  (for  in  the  frog  the  vagus  is  joined  a  little  below  its  exit 
from  the  skull  by  the  sympathetic),  enters  the  heart  along  the 
superior  vena  cava  (pp.  143,  182). 

Running  through  the  sinus,  with  whose  ganglion-cells  the  true 
vagus  fibres,  or  some  of  them,  are  believed  to  make  physiological 
junction  (p.  149).  the  nerves  pursue  their  course  to  the  auricular 
septum.  Here  they  form  an  intricate  plexus,  studded  with  ganglion- 
cells.  From  the  plexus  nerve-fibres  issue  in  two  main  bundles, 
which  pass  down  the  anterior  and  posterior  borders  of  the  septum 
to  end  in  two  clumps  of  nerve-cells  (Bidder's  ganglia),  situated  at 
the  auriculo-ventricular  groove.  These  ganglia  in  turn  give  off 
fine  nerve-bundles  to  the  ventricle,  which  form  three  plexuses — -one 
under  the  pericardium,  another  under  the  endocardium,  and  a  third 
in  the  muscular  wall  itself,  or  myocardium.  From  the  last  of  these 
plexuses  numerous  non-medullated  fibres  run  in  among  the  muscular 
fibres  and  end  in  close  relation  with  them.  Similar  plexuses  of 
nerve-fibres  exist  in  the  mammalian  ventricle.  But  while  scattered 
ganglion-cells  are  found  in  the  upper  part  of  the  ventricular  wall, 
most  observers  have  been  unable  to  demonstrate  any  either  in  the 
mammal  or  the  frog  in  the  apical  half.  In  the  rat's  heart,  accord- 
ing to  the  careful  observations  of  Schwartz,  true  ganglion-cells 
are  confined  to  an  area  on  the  posterior  surface  of  the  auricles, 
lying  always  under  the  visceral  pericardium.  Other  writers,  how- 
ever, have  stated  that  ganglion-cells  do  exist  in  the  apex  both  of 
the  cat's  and  of  the  frog's  heart.  In  connection  with  the  whole 
question  it  must  be  borne  in  mind  that  in  other  organs  improved 
histological  methods  have  brought  typical  nerve-cells  to  light  in 
situations  where  they  were  not  suspected  or  were  denied  to  exist, 
and,  further,  that  all  investigators  are  not  agreed  upon  the  histological 
criteria  by  which  ganglion-cells  are  to  be  distinguished. 

Cause  of  the  Rhythmical  Beat  of  the  Heart. — Scarcely  any 
physiological  question  has  excited  greater  interest  for  many 
years  than  the  mechanism  of  the  heart-beat.  Several  properties 
of  the  cardiac  tissue  ought  to  be  distinguished  in  discussing  this 
question  :  (1)  Its  automatism — i.e.,  its  power  of  beating  in  the 
absence  of  external  stimuli ;  (2)  its  rhythmicity — i.e.,  its  power  of 
responding  to  continuous  stimulation  by  a  series  of  rhythmically 
repeated  contractions  ;  (3)  its  conductivity — i.e.,  its  power  of 
conducting  the  contraction  wave  or  the  impulse  to  contraction 
once  it  has  been  set  up  ;  and  (4)  the  power  of  co-ordination,  in 
virtue  of  which  the  various  parts  of  the  heart  beat  in  a  regular 
sequence. 

9 


130  A   MANUAL   >>/    PHYSIOLOGY 

The  excitability  of  Hie  cardiac  tissue — that  is,  its  power  of 
appropriate  response  (namely,  by  contraction)  to  a  suitable 
stimulus — does  not  particularly  concern  us  here,  since  it  is  in  no 
wise  a  property  special  to  the  heart.  Only,  as  we  shall  see  in 
the  sequel,  the  time-relations  of  this  excitability  are  of  interest, 
for  the  existence  of  a  refractory  period — that  is,  an  interval 
during  which  the  cardiac  muscle  refuses  to  respond  to  excitation 
— throws  light  upon  the  rhythmicity  of  the  heart-beat.  The 
tonicity  of  the  heart — i.e.,  its  power  of  remaining  contracted  to  a 
certain  extent  in  the  intervals  between  successive  beats — is 
another  property  of  great  importance  in  certain  aspects,  but 
which  only  needs  to  be  mentioned  at  present. 

That  the  heart-beat  is  automatic,  is  sufficiently  shown  by 
the  fact  that,  as  already  mentioned,  an  excised  and  empty 
heart  will  go  on  beating  for  a  time,  for  many  hours  or  even 
for  days  in  the  case  of  cold-blooded  animals.  When  blood, 
or  even  a  suitable  solution  of  such  inorganic  salts  as  exist 
in  serum,  is  caused  to  circulate  through  the  coronary  vessels  of 
the  excised  heart  of  a  warm-blooded  animal,  it  also  continues 
to  contract  for  a  long  time.  But  where  the  cause  of  the 
automatism  resides,  in  the  muscular  tissue  or  in  the  intrinsic 
nervous  apparatus,  cannot  be  decided  offhand,  because  in 
nearly  all  animals  hitherto  investigated  the  muscular  tissue, 
ganglion-cells,  and  nerve-fibres  are  inseparably  intermingled. 
In  Limulus,  however,  the  horseshoe  or  king  crab,  the  cardiac 
ganglion-cells  are  collected  in  a  nerve-cord  running  longi- 
tudinallv  in  the  median  line  along  the  dorsal  surface  of  the 
segmented  heart,  and  sending  off  at  intervals  branches  to  two 
lateral  cords,  and  also  branches  which  enter  the  heart  muscle 
directly  (Fig.  53).  When  the  median  nerve-cord  is  removed, 
as  can  be  done  without  injuring  the  muscle,  the  heart 
ceases  for  ever  to  beat  spontaneously.  It  still  contracts  when 
directlv  stimulated,  mechanically  or  electrically,  but  the  con- 
traction never  outlasts  the  stimulation.  The  automatic  power 
therefore  resides  in  the  nerve-cord  alone,  and  not  in  the  muscle. 
The  same  is  true  of  the  rhythmical  power,  for  excitation  of  the 
nerves  that  pass  from  the  median  cord  to  the  muscle  produces, 
'  not  a  rhythmical  series  of  beats  in  the  resting,  and  an  accelera- 
tion of  the  rhythm  in  the  pulsating  heart,  but  a  tetanus  closely 
resembling  that  produced  in  skeletal  muscle  on  stimulation  of  a 
motor  nerve  '  (Carlson).  Conduction  and  co-ordination  are  also 
effected  in  this  heart  through  the  nervous  mechanism,  and 
essentially  through  the  median  nerve-cord;  for  section  of  the 
longitudinal  nerves  in  any  segment  of  the  heart  abolishes  the 
co-ordination  of  the  two  ends  of  the  heart  on  either  side  of  the 
lesion,  while  division  of  the  muscle  in  any  segment  does  not 


THE  CIRCULATION  OF  Till'  BLOOD  AND  LYMPH       131 

.1  licet  the  co-ordination.  Tt  is  not  permissible  to  transfer  these 
results  wholesale  to  higher  hearts,  and  especially  the  conclusions 
as  to  rhythm,  conduction,  and  co-ordination.  But  in  the  case 
of  the  higher  animals  also  facts  may  be  adduced  in  favour  of  the 
neurogenic  origin  of  t  he  beat.  The  isolated  auricular  appendices 
of  the  mammalian  heart,  in  which  no  ganglion-cells  have  been 
found,  refuse  to  beat  spontaneously.  If  in  the  frog  we  divide 
the  sinus,  which  is  conspicuously  rich  in  ganglion-cells,  from  the 
lower  portion  of  the  heart,  it  continues  to  pulsate.  A  fragment 
from  t  lie  base  of  the  ventricle  will  go  on  contracting  if  it  includes 
Bidder's  ganglion,  but  not  otherwise.  We  cut  off  the  lower 
two-thirds  of  the  frog's  ventricle,  the  so-called  apex  preparation, 
which  either  contains  no  ganglion- cells  or  is  relatively  poor  in 
them,  and  it  remains  obstinately  at  rest.  Further,  if,  without 
actually  cutting  off  the  apex,  we  dissever  it  physiologically 
from   the  heart   by  crushing  a  narrow  zone  of  tissue  midway 


08  mnc  In  la  ' 

Fig.  53.  —  The  Heart  and  the  Heart  Nerves  of  Limulus  :  Dorsal  View 

(Carlson). 

(The  heart  is  figured  one-half  the  natural  size  of  a  large  specimen.) 

aa.  Anterior  artery ;  la,  lateral  arteries ;  In,  lateral  nerves ;  mnc,  median  nerve- 
cord  ;  os,  ostia. 


between  it  and  the  auriculo-ventricular  groove,  we  abolish  for 
ever  its  power  of  spontaneous  rhythmical  contraction.  The  frog 
may  live  for  many  w^eeks,  but  in  general  the  apex  remains  in 
permanent  diastole.  It  can  be  caused  to  contract  by  an  artificial 
stimulus,  but  it  neither  takes  part  in  the  spontaneous  contraction 
of  the  rest  of  the  heart,  nor  does  it  start  an  independent  beat  of 
its  own. 

What  can  be  simpler  than  to  assume  that  the  sinus  beats 
because  it  has  numerous  ganglion-cells  in  its  walls,  and  that 
the  apex  refuses  to  beat  because  it  has  comparatively  few  or 
none  ?  Could  we  pick  out  the  nerve-cells  from  the  sinus,  without 
injuring  the  muscular  tissue,  as  easily  as  we  can  extirpate  the 
median  nerve-cord  in  Limulus  we  may  well  suppose  that  it  would 
lose  its  power  of  automatic  contraction.  And  although,  if  we 
pursue  our  investigations  a  little  farther,  facts  may  emerge  which 
seem  to  contradict  the  neurogenic  hypothesis,  the  contradiction 
is  usually  only  apparent.     Let    us  inquire,  for  instance,   what 

9—2 


132  A   MANUAL  OF  PHYSIOLOGY 

happens  to  the  auricles  and  ventricle  of  the  frog's  heart  when 
the  sinus  is  cut  off.  The  answer  is  that,  as  a  rule,  while  the  sinus 
goes  on  beating,  the  rest  of  the  heart  comes  to  a  standstill,  in 
spite  of  the  numerous  ganglion-cells  in  the  auricular  septum  and 
the  auriculo-ventricular  groove.  Not  only  so,  bul  if  the  ventricle 
be  now  severed  from  the  auricles  by  a  section  carried  through 
the  groove,  it  is  the  former,  poor  in  nerve-cells  though  it  be, 
which  will  usually  first  begin  to  beat.  We  shall  again  have  to 
discuss  this  experiment  (p.  151).  It,  at  any  rate,  cannot  be 
interpreted  as  proving  that  the  automaticity  of  the  heart  does  not 
depend  upon  the  presence  of  ganglion-cells.  For  although  a 
portion  of  the  heart  rich  in  ganglion-cells  may,  under  the  cir- 
cumstances mentioned,  refuse  for  a  time  to  beat,  there  is  good 
evidence  that  this  is  due  either  to  a  peculiar  condition  called  inhibi- 
tion into  which  the  muscular  tissue  or  the  nerve-cells  of  the  lower 
portions  of  the  heart  have  been  thrown  by  the  first  section,  or  more 
probably  to  the  loss  of  the  accustomed  impulses  from  the  sinus 
which  normally  give  the  signal  for  the  auricular  contraction.  A 
stronger  argument  in  favour  of  the  myogenic  theory  is  the  fact 
that  the  embryonic  heart  beats  with  a  regular  rhythm  at  a 
time  when  as  yet  no  ganglion-cells  have  settled  in  its  walls. 
But  it  may  well  be  that  this  primitive  automatic  power  of  the 
cardiac  muscle,  absolutely  necessary  at  first,  since  the  early 
establishment  of  the  circulation  is  essential  for  the  development 
of  the  tissues  in  general  and  of  the  nervous  system  in  particular, 
falls  into  abeyance  when  the  intrinsic  cardiac  nervous  mechanism 
is  completed,  or  at  least  becomes  subordinated  to  the  latter. 
The  advocates  of  the  myogenic  theory  further  state  that  the 
isolated  bulbus  aortae  of  the  frog,  and  even  tiny  fragments  of  it, 
will  pulsate  spontaneously,  and  that  the  same  is  true  of  small 
portions  of  the  great  veins  which  open  into  the  sinus.  The 
rhythmical  contraction  of  the  veins  of  the  bat's  wing  has  also 
been  considered  an  argument  in  favour  of  myogenic  automatism. 
In  none  of  these  cases,  however,  can  the  complete  absence  of 
ganglion-cells  be  considered  satisfactorily  demonstrated.  The 
statement  that  a  portion  of  the  apex  of  the  dog's  ventricle 
continues  for  a  considerable  time  to  beat  with  a  rhythm  of  its 
own  when  connected  with  the  rest  of  the  heart  by  nothing  but 
its  bloodvessels  and  the  narrow  isthmus  of  visceral  pericardium 
and  connective  tissue  in  which  they  lie  has  not  been  confirmed 
by  all  observers.  But  even  if  it  Ik-  accepted,  it  can  hardly  be 
used  as  a  decisive  argument  against  the  neurogenic  theory  so 
long  as  the  absence  of  ganglion-cells  from  such  a  ventricular  strip 
has  not  been  demonstrated. 

The   fact    that    under    the   influence   of   a   constant    stimulus 
portions  of  the  heart    can   be  made  to   beal    rhythmically  has 


Till    CIRCULATION  OF  THE  BLOOD  AND  LYMPH       133 

been  sometimes,  though  erroneously,  brought  forward  as  evident  e 
nl  myogenic  automatism.  Thus  the  supposedly  ganglion-free 
apex  of  the  frog's  heart,  lifeless  as  it  seems  when  left  to  itself, 
can  he  caused  to  execute  a  long  and  faultless  scries  of  pulsations 
when  its  cavity  is  distended  with  defibrinated  blood  or  serum, 
or  certain  artificial  nutritive  fluids,  or  even  physiological  salt 
solution.  The  passage  of  a  constant  current  through  the 
preparation  may  also  start  a  regular  rhythm.  But  apart  from 
the  question  whether  nervous  elements  would  not  be  subjected 
to  the  constant  stimulus  impartially  with  the  muscular  elements 
(and  nerve-fibres,  at  any  rate,  are  acknowledged  to  be  present), 
tlu-  beat  here  produced  ought  not  to  be  considered  as  an  auto- 
matic beat,  but  as  a  contraction  evoked  by  an  external  stimulus. 
Such  experiments,  in  fact,  throw  no  light  upon  the  automatism 
of  the  heart,  but  prove  clearly  its  rhythmicity — i.e.,  its  power  of 
responding  to  a  continuous  stimulus  by  regularly  recurring 
contractions.  While  we  are  hardly  at  present  in  a  position  to 
discriminate  sharply  between  the  influence  of  constant  stimula- 
tion upon  the  nervous  and  upon  the  muscular  elements  of  the 
heart,  and  certainly  not  in  a  position  to  deny  to  the  nervous 
elements  the  power  of  responding  to  such  stimulation  by  rhyth- 
mical discharges,  it  can  hardly  be  doubted  that  the  cardiac  muscle 
itself  possesses  rhythmical  power.  This  is  a  property  which  also 
belongs  to  the  smooth  muscle  of  such  tubes  as  the  ureter,  whose 
rhythmical  contraction  is  affected  by  distension  much  as  that  of 
the  heart  is,  and  in  a  smaller  degree  even  to  ordinary  skeletal 
muscle,  which  can  contract  with  a  kind  of  rhythm  under  the 
stimulus  of  a  certain  tension  and  in  certain  saline  solutions. 
But  just  as  the  primitive  automatism  of  the  cardiac  muscle  may 
have  become  subordinated  in  the  course  of  development  to  the 
automatism  of  the  nervous  elements,  so  the  primitive  rhythmical 
power  of  the  muscle  may  under  ordinary  conditions  remain  in 
abeyance  and  yet  be  capable  of  asserting  itself  in  favourable 
circumstances,  and  when  the  normal  rhythmical  impulses  from 
the  nervous  apparatus  are  withdrawn.  In  any  case,  in  the 
normally  beating  heart  the  opportunity  for  the  exercise  of  the 
rhythmical  power  of  the  muscle  does  not  arise,  at  least  in  the 
case  of  the  lower  portions  of  the  heart.  For  the  impulses  which 
(in  the  frog's  heart),  descending  from  the  sinus,  liberate  the 
contraction  of  the  auricles,  and  the  impulses  which,  descending 
from  the  auricles,  liberate  the  contraction  of  the  ventricle  appear 
to  be  discrete,  and  not  continuous  ;  in  other  words,  the  lower 
portions  of  the  heart  do  not  receive  from  the  upper  portions  a 
continuous  stream  of  stimuli  to  which  they  respond  by  rhyth- 
mical contractions,  but  a  series  of  rhythmically  repeated  impulses, 
each  of  which  evokes  a  single  contraction.     One  of  the   best 


i34  A   MANUAL  OF    PHYSIOLOGY 

proofs  of  this  i>  that,  if  the  sinus  is  heated  the  ventricle  beats 

much  more  rapidly  in  unison  with  the  rapidly  beating  sinus  and 
auricles,  while  if  the  ventricle  itself  is  heated  no  change  takes  place 
in  its  rhythm.  Now,  if  the  ventricle  responds  to  a  constant 
stimulus  by  rhythmical  beats,  the  condition  of  the  ventricular 
tissue  ought  to  affect  the  rate  of  its  beat.  In  the  mammalian 
heart,  too,  an  alteration  in  the  temperature  of  a  definite  area  of 
the  wall  of  the  right  auricle  lying  between  the  mouths  of  the 
venae  cava;,  produces  a  change  in  the  rate  of  the  whole  heart, 
while  no  effect  is  caused  by  altering  the  temperature  of  any  other 
portion  of  the  heart.  It  has  already  been  stated  that  the 
impulses  from  the  nerve-cord  which  maintain  the  rhythm  in  the 
Limulus  heart  are  also  discontinuous. 

Conduction  and  Co-ordination. — The  question  of  the  con- 
duction of  the  excitation  over  the  heart  and  the  co-ordination 
of  its  parts  is  in  the  same  position  as  the  question  of  the 
automatism  and  rhythmicity.  In  the  horseshoe  crab,  as  already 
remarked,  the  mechanism  appears  to  be  a  nervous  one.  In 
higher  hearts,  on  the  other  hand,  facts  have  been  discovered 
which  favour  each  of  the  rival  hypotheses.  In  the  frog's 
heart  the  probability  that  the  contraction  wave  is  propagated 
from  fibre  to  fibre  of  the  muscle  without  the  intervention 
of  nerves  has  been  much  insisted  upon,  since  the  muscular 
tissue,  although  presenting  certain  variations  in  its  character 
in  the  different  divisions  of  the  heart  and  at  their  junctions, 
forms  a  practically  continuous  sheet  over  the  whole  organ  from 
base  to  apex.  In  support  of  this  view  has  been  brought  forward 
the  observation  that  the  delay  of  the  wave  at  the  auriculo- 
ventricular  groove  is  much  greater  than  it  ought  to  be  if  the 
excitation  were  transmitted  by  nerves,  since  the  velocity  of  the 
nerve-impulse  is  exceedingly  great  (p.  689)  ;  and  the  further 
observation  that,  when  the  ventricle  is  caused  to  contract 
by  artificial  stimulation  of  the  auricle,  this  delay  is  appreciably 
greater  when  the  stimulus  is  applied  as  far  from  the  ventricle 
as  possible  than  when  it  is  applied  as  near  to  it  as  possible.  The 
delay  has  been  attributed  to  the  '  embryonic  '  character  of  the 
muscular  tissue  at  the  junction  of  the  sinus  with  the  auricles 
and  of  the  auricles  with  the  ventricles.  But  it  has  never  been 
demonstrated  that  muscular  fibres  with  the  histological  characters 
described  do,  as  a  matter  of  fact,  conduct  the  contraction  wave 
so  much  more  slowly  than  the  other  cardiac  muscular  fibres.  It 
is  just  as  probable,  and  indeed  more  so,  that  whether  the  con- 
traction travels  in  any  particular  division  of  the  heart  directly 
from  muscle-fibre  to  muscle-fibre  or  not,  the  impulse  to  contrac- 
tion is  transferred  from  each  division  of  the  heart  to  the  next  by 
a  nervous  mechanism  whose  action  is  timed  with  the  very  object 


THE   CIRCUL  \TION  OB    THE   BLOOD  AND  LYMPH 


'35 


di  securing  a  certain  interval  between  the  systoles  of  successive 
divisions.  In  any  case;,  since  we  know  that  the  velocity  of  the 
nerve-impulse  is  very  different  in  different  varieties  of  nerves,  I  he 

question  cannot  be  decided  by  general  arguments  of  this  kind. 
In  Limnlns,  as  a  matter  of  fact,  the  velocity  in  the  intrinsic 
heart  nerves  is  only  one-tenth  as  great  as  in  the  ordinary  motor 
(limb)  nerves  of  the  animal  (Carlson). 

In  the  mammalian  heart  the  alleged  absence  of  muscular  con- 
nection between  the  auricles  and  ventricles  was  long  the  founda- 
tion  of  the  general  belief  that  the  link  was  a  nervous  one.  Cer- 
tainly there  is  no  dearth  of  nerves  which  might  serve  as  such  a 


Fig.    54. — Right   Auricle    and    Ventricle    of   Calf,    to    show   Auriculo- 
ventricular  band  (keith). 

1,  Central  cartilage  ;  2,  main  auriculo-ventricular  bundle  ;  3,  auriculo-ventriCular 
(A-V)  node  ;  4,  right  septal  division  of  the  bundle  ;  5,  moderator  band  ;  6,  medial  or 
septal  cusp  of  tricuspid  valve  ;  8,  coronary  sinus. 

bridge.  But  it  has  been  shown  (Kent,  His,  etc.)  that  in  the  mam- 
malian heart,  too,  a  slender  band  of  muscular  fibres,  arising  at  a 
definite  point  near  the  coronary  sinus  on  the  right  side  of  the 
interauricular  septum  below  the  fossa  ovalis,  passes  forwards 
and  downwards  through  the  fibrous  ring  between  the  auricles  and 
ventricles  under  the  septal  cusp  of  the  tricuspid  valve.  It  then 
divides  into  two  branches,  one  for  each  ventricle,  which  run 
down  the  interventricular  septum  towards  the  apex,  spreading  out 
as  the  Purkinje  fibres  or  their  equivalent,  to  blend  at  last,  with 
the  ordinary  muscle  of  the  ventricles,  and  particularly  of  the 


/   MANUAL  01    PHYSIOLOGY 

interventricular  septum.  The  fibres  of  the  bundle  are  narrower 
than  the  other  fibres  of  the  auricles,  very  rich  in  nuclei,  and  only 
slightly  differentiated  into  fibrillae.  They  seem  to  represent  the 
remains  of  the  primitive  cardiac  tube,  which  by  the  development 
of  certain  pouches  and  twists  becomes  transformed  into  a  multi- 
chambered  heart.  Their  resemblance  to  embryonic  nines  sug- 
gests that  they  may  have  retained  the  primitive  capacity  oi  the 
mesodermic  tissue  of  the  embryonic  heart  to  conduct,  and  even 
to  originate,  the  rhythmical  contraction.  But  while  there  is  no 
decisive  evidence  that  they  constitute  an  automatic  cardio-motor 
centre,  as  some  authors  have  supposed,  they,  or  at  least  the 
narrow  bridge  of  tissue  in  which  they  lie,  do  play  an  important 
part  in  the  conduction  of  the  contraction  from  the  auricles  to  the 
ventricles.  For  compression  of  the  band  produces  a  block,  just 
as  the  pressure  of  a  clamp  in  the  auriculo-ventricular  groove  does 
in  the  frog's  heart  (Kent).  With  a  certain  degree  of  pressure  the 
ventricle  beats  only  once  for  two  beats  of  the  auricle,  with  greater 
pressure  only  once  for  three  or  more  auricular  beats.  With  a  still 
greater  pressure  or  after  crushing  or  section  of  the  bundle  con- 
duction is  abolished,  and  the  ventricle  either  remains  at  rest  for 
a  time,  as  in  the  frog's  heart,  or,  what  is  much  more  common,  im- 
mediately starts  beating  with  an  independent  rhythm,  which  is 
slower  than  that  of  the  auricles  (Erlanger).  It  can  be  considered 
certain  that  in  these  observations  nerves  may  have  been  involved 
in  the  block  as  well  as  the  muscle  of  the  auriculo-ventricular 
hand,  since  this  band  is  richly  provided  with  nerve-fibres  as  well 
as  ganglion-cells  (Wilson).  Yet  it  is  unlikely  that  all  the  nerves 
capable  of  conducting  the  impulses  to  contraction  should  be 
gathered  into  such  a  narrow  compass,  and  therefore  the  experi- 
ment supports  the  view  that  the  conduction  is  carried  out  in  the 
muscular  tissue.  And  if  the  conduction  of  the  excitation  from 
auricles  to  ventricles  is  accomplished  bv  a  muscular  connection, 
it  is  natural  to  suppose  that  the  co-ordination  of  symmetrical 
portions  of  the  heart  on  either  side  of  the  longitudinal  axis,  the 
co-ordination  in  virtue  of  which  the  two  auricles  contracl  together 
and  the  two  ventricles  together,  is  also  achieved  by  the  passage 
of  impulses  through  the  muscular  tissue.  In  accordance  with 
this,  it  lias  been  shown  that  the  ventricles  in  the  dog  and  cat 
continue  to  beat  in  unison,  after  the  attempt  has  been  mack'  to 
sever  any  nerves  connecting  them  by  extensive  zigzag  incisions. 
so  long  as  they  are  united  by  a  narrow  bridge  of  muscle  (Porter). 

In  disease,  interference  with  the  conduction  oi  the  stimulus  from 
auricles  to  ventricles  along  the  atrio-ventricular  bundle  is  a  not 
uncommon  phenomenon.  According  to  the  degree  oi  interference. 
the  ventricular  contraction  may  be  simply  delayed,  or  only  a  certain 
proportion  of  the  auricular  contractions  (every  second,  every  third. 
or  every  fourth'  may  be  conducted  to  the  ventricle,  or,  finally,  the 
block  may  be  complete,  and  the  ventricle  then  contracts  quite  inde- 


////    (  //,'<  /  /    ITION  nl     III!    BLOOD    \ND   I  YMPH 

pendently  oi  the  auricle,  the  stimulus  to  contraction  originating, 
perhaps,  in  the  uninjured  portion  oi  the  bundle  below  the  seal  oi 

the  block.     These  conditions  are  most  easily  recognised  by  com] ig 

tracings  simultaneously  obtained  from  the  jugular  vein  and  the 
radial  artery  or  apex-beal  (p.  82).  When  the  block  is  complete 
the  rate  oJ  the  ventricle  is  very  slow  (aboul  30  in  the  minute,  or  less), 


Fig.  55.— Jugular  (Upper)  and  Carotid  (Lower)  Pulsi  facing  from  a 
Casi  oi  Akterio-sclerosis,  showing  Partial  Failure  of  Conduction 
in  mi   Ai  rii  ulo-Ventricular  Bundle  (Cushny  and  Grosh). 

Tin;  ventricle  only  beats  once  to  two  beats  of  the  auricle.     Time-trace,  fifths 
.it  a  second. 

the  time  of  the  ventricular  beat  is  clearly  unrelated  to  that  of  the 
auricular,  and  the  stability  of  the  ventricular  rhythm  is  abnormally 
great,  such  circumstances  as  usually  cause  a  marked  increase  in  the 
pulse-rate — mental  excitement,  for  instance — affecting  it  little  or 
not   at   all.     This   is  the   condition   in  the   so-called   Stokes- Adams 


Fig.  56. — Tracing  of  Jugular  (Upper)  and   Radial  (Lower)  Pulse  from  a 
Man  with  Heart-Block  (Lewis  and  Macnaltv). 

In  the  cycles  marked  34,  35,  and  36  the  ventricular  contraction,  although  less 
frequent  than  the  auricular,  was  initiated  from  the  auricle.  In  the  last  two 
cycles  (37  and  38)  and  the  pause  of  36  complete  heart-block  was  present.  On  the 
jugular  trace  the  a-c  interval  (representing  the  interval  between  the  onset  of  the 
auricular  and  ventricular  contractions)  is  given,  and  on  the  radial  trace  the 
duration  of  a  cardiac  cycle,  both  in  fifths  of  a  second. 


disease.  In  some  of  these  cases  pathological  (syphilitic)  changes  in 
the  atrio- ventricular  bundle  have  actually  been  discovered  at  autopsy. 
In  others  there  is  some  reason  to  believe  that  abnormal  excitation 
of  the  cardio-inhibitory  nerves  may  be  responsible  even  for  long- 
continued  block,  especially  when  the  conductivity  of  the  bundle 
has  been  already  permanentlv  diminished. 


i  }8  /    MANl    !/.  <>/■   PHYSIOLOGY 

In  the  case  of  the  warm-blooded  heart  a  complete  breakdown 
of  co-ordination  occurs  under  certain  circumstances,  producing 
the  phenomenon  known  as  fibrillary  contraction,  or  delirium 
cordis,  a  condition  in  which  each  minute  portion,  perhaps  each 
fibre,  of  the  whole  heart,  or  of  a  portion  of  it,  goes  on  contracting 
in  a  disorderly  manner,  quite  independently  of  the  rest.  The 
condition  is  often  seen  in  a  heart  that  has  been  exposed  for  some 
time,  particularly  in  the  ventricle,  and  can  be  induced  by  stimu- 
lating it  with  strong  induction  shocks  or  by  ligation  of  the  coronary 
arteries.  There  is  no  reason  to  believe  that  fibrillarv  contraction 
is  connected  with  the  loss  of  impulses  from  any  special  co-ordinat- 
ing centre,  for  it  is  not  peculiar  to  the  heart,  but  is  typically  seen 
in  the  tongue  when  the  circulation  after  a  long  interruption  is 
restored.  The  peculiar  '  boiling  '  movement  is  exactly  similar 
to  that  observed  in  the  heart,  probably  because  the  tongue  also 
contains  fibres  running  in  several  directions. 

Without  entering  further  into  a  discussion  of  the  rival  hypo- 
theses, we  may  sum  up  by  saying  that  for  one  heart  {that  of 
Limulus)  the  automatism  and  the  rhythmical  power  hare  been 
clearly  shown  to  reside  in  the  local  nervous  apparatus  ;  for  the  hearts 
of  other  animals  full  and  formal  proof  of  the  neurogenic  theory,  so 
far  as  those  two  properties  of  the  cardiac  tissue  are  concerned,  has 
not  been  given.  It  is  probable,  but  not  proven.  As  regards  the 
conduction  and  co-ordination  of  the  contraction,  the  bulk  of  the 
evidence  {leaving  the  Limulus  heart  out  of  account)  points  to  the 
muscular  tissue  as  the  channel  through  which  the  effective  impulses 
pass.  The  normal  order  or  sequence  in  which  the  different  parts 
of  the  heart  contract  depends  upon  the  fact  that  the  automatism  of 
the  upper  portions  is  more  pronounced  than  that  of  the  lower,  so 
that  under  strictly  physiological  conditions  the  contraction  is  only 
propagated,  and  not  originated,  by  the  lower  parts  of  the  heart.  When. 
however,  the  signal  to  contraction  normally  given  by  the  basal 
region  is  prevented  from  reaching  the  lower  parts,  an  independent 
automatic  rhythm  of  the  latter  may  be  developed,  as  in  the  case 
of  the  mammalian  ventricle  mentioned  above.  Here  we  may 
suppose  that  the  automatic  mechanism  of  the  lower  portions  of 
the  heart  discharges  itself  as  soon  as  a  sufficient  accumulation 
of  energy  has  taken  place  in  it,  although  it  requires  a  longer 
time  to  reach  the  point  of  discharge  than  the  automatic 
mechanism  of  higher  parts,  and  therefore  is  normally  dis- 
charged from  above.  Under  certain  conditions  the  normal 
sequence  can  be  reversed.  In  the  heart  <>t  the  --k.ite  it  i- 
easy,  by  stimulating  the  bulbus  arteriosus,  to  cause  a  con- 
traction passing  from  bulbus  to  sinus.  The  power  of  propa- 
gating the  contraction  may  also  be  artificially  altered.  As 
already    mentioned,    it    may    be    diminished   or    abolished    by 


THE  CIRCU1   ITION  OF    THE  B.LOOD    iND  LYMPH       [39 

pressure.  The  same  effecl  may  be  produced  by  fatigue  oi 
cold,  while  heating  a  portion  of  the  heart  in  general  increases  its 
power  of  conducting  the  contraction. 

Chemical  Conditions  of  the  Beat. — When  we  have  localized 
the  essential  mechanism  of  the  rhythmical  beat  in  the  nervous 
or  in  the  muscular  elements,  the  question  may  still  be  asked 
what  the  chemical  and  physical  conditions  are  which  are 
necessary  to  its  maintenance.  While  it  is  known  that  a  supply 
of  arterial  blood  at  or  near  body-temperature,  and  under  a 
sufficient  pressure,  is  required  for  permanent  cardiac  contrac- 
tion, much  simpler  solutions  will  suffice  to  maintain  the  activity 
even  of  the  isolated  mammalian  heart  for  a  considerable  time. 
One  of  the  best  of  these  is  a  solution  containing  sodium  chloride, 
potassium  chloride,  calcium  chloride,  and  sodium  bicarbonate 
in  the  proportions  in  which  they  exist  in  blood-serum,  with 
the  addition  of  a  small  quantity  of  dextrose  (Locke).  When 
this  solution,  properly  oxygenated  and  warmed,  is  circulated 
through  the  coronary  vessels  of  an  excised  rabbit's  or  cat's 
heart,  strong  and  regular  beats  may  be  observed  for  many  hours. 
Some  investigators  have  claimed  for  sodium  chloride,  and  even 
for  sodium  ions,  others  for  calcium  salts  or  calcium  ions,  a  special 
role  in  the  origination  or  maintenance  of  the  rhythmical  beat. 
There  is  no  doubt  that  strips  from  the  ventricle  of  the  tortoise 
or  turtle,  which  after  isolation  have  ceased  beating,  and  if  left  to 
themselves  in  a  moist  chamber  do  not  develop  rhythmical  con- 
tractions, begin  after  a  while  to  beat  when  immersed  in  or  irri- 
gated with  a  solution  of  sodium  chloride  or  a  solution  of  cane- 
sugar  containing  a  little  of  that  salt.  They  refuse  to  beat  in  any 
solution  which  does  not  contain  sodium  chloride  (Lingle).  The 
addition  of  calcium  chloride  to  the  sodium  chloride  solution,  or 
preliminary  treatment  of  the  strip  with  a  solution  of  a  calcium 
salt  before  its  immersion  in  the  sodium  chloride  solution  hastens 
the  onset  of  the  contractions,  and  increases  the  length  of  time 
for  which  they  are  kept  up  (Erlanger).  It  is  unquestionable  that 
for  the  normal  beat  of  the  heart  the  presence  of  both  salts  is  one 
of  the  necessary  conditions,  but  there  is  at  present  no  sufficient 
foundation  for  the  view  that  either  the  one  or  the  other  acts  as 
a  special  chemical  excitant  of  the  automatic  contraction. 

Resuscitation  of  the  Heart. — Not  only  can  the  beat  of  the 
freshly-excised  mammalian  heart  be  long  maintained  by  artificial 
circulation,  but  many  hours  or  even  days  after  somatic  death 
pulsation  may  be  restored  by  the  perfusion  of  such  a  solution 
of  inorganic  salts  as  Locke's  through  the  coronary  vessels. 
Kuliabko  in  this  way  was  able  to  restore  a  rabbit's  heart  which 
had  been  kept  forty-four  hours  in  the  ice-chest.  Even  after  an 
interval  of  three  to  rive  days  from  the  death  of  the  animal, mother 


i4"  .J    MANUAL  OF  PHYSIOLOGY 

experiments,  pulsation  returned  in  certain  parts  of  the  In-art.  while 
twenty  hours  after  death  from  double  pneumonia  the  heart  of  a 
boy  three  months  old  was  restored,  and  went  ou  beating  for  over 
an  hour.     He  obtained  also  more  or  less  complete  restoration  of 
the  beat  in  the  hearts  of  persons  dead  from  bronchitis  combined 
with  peritonitis  or  meningitis,  and  from  cholera  infantum,  but  was 
unsuccessful  in  cases  of  diphtheria  complicated  with  septicaemia 
or  erysipelas,  and  in  cases  of  pleurisy  with  effusion.     It  is  to  be 
remarked,  however,  that  although  beats  of  a  kind  can  be  obtained 
a  long  time  after  death,  they  are  either  confined  to  the  auricles 
or  to  portions  of  them,  or,  if  they  involve  the  ventricles  too,  they 
are  only  shallow  and  local  contractions,  especially  seen  in  the 
neighbourhood  of  the  larger  coronary  vessels,  and  are  utterly 
inadequate  to  the  maintenance  of  an  efficient  circulation.     The 
heart  can  also  be  resuscitated  in  situ  for  some  time  after  complete 
stoppage  without  the  injection  of  any  solution  by  clamping  the 
aorta  in  the  thorax  and  practising  direct  cardiac  massage,  the 
lower  end  of  the  animal  at  the  same  time  being  elevated  to  allow 
blood  to  pass  out  of  the  engorged  abdominal  veins  to  the  right 
auricle.     The  clamping  of  the  aorta  permits  a  sufficient  pressure 
to   be   attained   for   the    filling  of  the  coronary  arteries.     The 
injection   of    adrenalin    into    the    blood    has   also    been   recom- 
mended as  a  means  of  raising  the  blood-pressure  by  constricting 
the  small  arteries,   and  stimulating  the  action  of  the  cardiac 
muscle.       The    possibility    of    restoration   of    the    mammalian 
heart  many  hours  after  somatic  death  has  been  considered  by 
some  a  strong  argument   for  the  myogenic  theory  of  cardiac 
automatism,  since,  they  say,  it  is  improbable  that  ganglion-cells, 
elsewhere  such  physiologically  fragile  structures,  should  in  the 
heart  retain  their  vitality  for  so  long  a  time.     But  it  is  easy  to 
overdo  this  argument,  and  we  must  not  assume  without  proof 
that  ganglion-cells  in  all  parts  of  the  body  have  an  equal  capacity 
of  survival.     Indeed,  we  know  that  there  are  great  differences. 
the    nervous   mechanism    concerned   in    respiration,    c.^.,    being 
capable   of   restoration   when   the  circulation    is    renewed    after 
total  anaemia  of  the  brain  and  cervical  cord  lasting  lor  as  much 
as  an  hour  (in  cats),  while  the  nervous  mechanism  concerned 
in   voluntary  movements  cannot    be   completely   restored  even 
after  a  much  shorter  interval.     It   is   very   probable   that   the 
cardiac  ganglia,  if  the  all-important  automatic  function  of  the 
heart  depends  upon  them,  are,  like  the  cardiac  muscle,  endowed 
with  exceptional  powers ol  resistance  to  those  changes  which  con- 
stitute death.     The  possibility  also  must  not  be  overlooked  that 
the  contractions  obtained  after  such  long  intervals  are  not  truly 
automatic,  but  similar  rather  to  the  rhythmical  beats  developed 
under  the  influence  of  pressure  in  the  frog's  apex  preparation  or 
by  immersion  in  salt  solutions  of  tortoise  ventricle  strips. 


THE  CIRCULATION  01    I  III    BLOOD    IND  LYMPH       141 

In  addition  to  its  marked  power  of  rhythmical  contraction, 
the  cardiac  muscle  is  distinguished  from  ordinary  skeletal  muscle 
l>v  other  peculiarities.  11  used  to  he  considered  the  most  striking 
of  these  peculiarities  thai  '  it  is  everything  or  nothing  with  the 
heart  ';  in  other  words,  that  the  heart  muscle,  when  it  contracts, 
makes  the  hest  effort  of  which  it  is  capable  at  the  time  ;  a  weak 
stimulus,  it  it  can  just  produce  a  beat,  causing  as  great  a  con- 
traction as  a  strong  stimulus.  Recent  work,  however,  has  indi- 
cated th.it  this  property  is  also  possessed  by  the  skeletal  muscle- 
fibre.  When  a  whole  skeletal  muscle  is  excited  either  directly 
or  through  its  motor  nerve,  it  is  true  that  throughout  a  con- 
siderable range  increase  of  stimulus  is  accompanied  by  an 
apparent  increase  in  the  strength  of  contraction.  But  there 
is  reason  to  believe  that  this  is  because  a  larger  and  larger 
number  of  fibres  become  involved  in  the  excitation  as  the  stimulus 
is  increased,  and  not  because  each  fibre  responds  more  and  more 
strongly  (Lucas).  In  skeletal  muscle  the  fibres  are  completely 
isolated  from  each  other  and  the  excitation  does  not  spread 
from  fibre  to  fibre,  as  happens  in  the  heart. 

A  more  characteristic  property  of  the  cardiac  muscle  than  the 
'  all  or  nothing  '  law  is  that  a  true  tetanus  of  the  heart  cannot 
be  obtained  at  all,  or  only  under  very  special  conditions.  When 
the  ventricle  of  a  normally  beating  frog's  heart  is  stimulated  by 
a  rapid  series  of  induction  shocks,  its  rate  is  generally  increased, 
but  there  is  no  definite  relation  between  the  number  of  stimuli 
and  the  number  of  beats.  Many  of  the  stimuli  are  ineffective. 
In  the  same  way  a  portion  of  the  heart,  such  as  the  apex  of  the 
ventricle,  when  stimulated  in  the  quiescent  condition  by  an 
interrupted  current,  responds  by  a  rhythmical  series  of  beats, 
and  not  by  a  tetanus.  It  is  evident  that  the  cardiac  muscle,  like 
ordinary  striped  muscle,  is  for  some  time  after  excitation  in- 
capable of  responding  to  a  fresh  stimulus — i.e.,  there  is  a  refractory 
period.  But  this  is  immensely  longer  in  cardiac  than  in  skeletal 
muscle.  When  the  phenomenon  is  analyzed,  it  is  found  that  a 
stimulus  falling  into  the  heart  muscle  between  the  moment  at 
which  the  contraction  begins  and  the  moment  at  which  it  reaches 
its  maximum,  produces  no  effect — is,  so  to  speak,  ignored.  When 
the  stimulus  is  thrown  in  at  any  point  between  the  maximum  of 
the  systole  and  the  beginning  of  the  next  contraction,  it  causes 
what  is  called  an  extra  contraction.  The  extra  contraction  is 
followed  by  a  longer  pause  than  usual — a  so-called  compensatory 
pause — which  just  restores  the  rhythm,  so  that  the  succeeding 
systole  falls  in  the  curve  where  it  would  have  fallen  had  there 
been  no  extra  contraction  (Fig.  57). 

In  man,  extra  systoles  followed  by  compensatory  pauses  may 
occur  under  pathological  conditions,   giving  rise  to  an  important 


142 


!    M  L\rn    <>/■  PHYSIOLOGY 


group  ot  cardiac  irregularities.  These  extra  systoles  may  be  either 
auricular  or  ventricular,  the  auricle  or  the  ventricle  contracting  pre- 
maturely without  waiting  for  the  signal  of  the  sinus  rhythm  normally 
originating  .it  the  mouths  of  the  great  veins.  The  analysis  of  pulse- 
tracings  showing  these  irregularities  has  led  to  results  of  great 
physiological  and  clinical  interest  (Cushny,  Mackenzie,  etc.),  but 
cannot  be  dwelt  on  here.  When  every  second  beat  is  an  extra 
systole,  generally  weaker  than  the  preceding  and  the  succeeding 
normal  beat,  the  condition  is  called  pulsus  bigeminus.  The  weaker 
beat  is  always  followed  by  a  compensatory  pause  of  greater  duration 
than  that  preceding  it.  From  the  pulsus  bigeminus  must  be  dis- 
tinguished that  form  of  alternating  pulse  termed  pulsus  alternans, 
in  which  every  second  beat  is  diminished  in  size,  but  the  intervals 

separating  the 
beats  are  of  uni- 
form length. 
This  form  of 
irregularity  in- 
dicates that  the 
power  of  the 
heart-muscle  to 
contract  is  fail- 


MMMWWMM 


Fig.  57. — Refractory  Period  and  Compensatory  Pause 
(Marey). 

A  frog's  heart  was  stimulated  at  a  point  corresponding  to 
the  nick  in  the  horizontal  line  below  each  curve.  In  1  and  2 
there  was  no  response  ;  in  3  and  4  there  was  an  extra  con- 
tr.n  tion,  succeeded  by  a  compensatory  pause. 


The  refrac- 
tory period  is 
shorter  for 
stronger  than 
lor  weak  stim- 
uli, and  is 
markedly  dim- 
inished by  rais- 
ing the  tempe- 
rature of  the 
heart.  So  that 
stimulation  of 
the  heated 
heart    with    a 

series  of  strong  induction  shocks  may  cause  a  tetaniform  condi- 
tion, if  not  a  typical  tetanus.  The  contraction  of  the  normally 
beating  heart  is  really  a  simple  contraction,  and  not  a  tetanus. 
The  capillary  electrometer  shows  only  the  electrical  changes 
corresponding  to  a  single  contraction  (p.  720)  ;  and  when  the 
nerve  of  a  nerve-muscle  preparation  is  laid  on  the  heart,  the 
muscle  responds  to  each  beat  by  a  simple  twitch,  and  not  by 
tetanus  (p.  188).  That  the  cardiac  muscle  itself,  apart  from  the 
intrinsic  nervous  mechanism,  shows  the  phenomenon  of  '  refrac- 
tory state  '  has  been  shown  in  the  Limulus  heart  after  extirpa- 
tion of  the  ganglion  (Carlson). 

Like  ordinary  skeletal  muscle,  the  cardiac  muscle  is  at  first 
benefited  by  contraction,  perhaps  by  an  '  augmenting  '  action  of 


THE  CIRCUl   I!  /<>X  OF  THE  BLOOD  AND  I  VMl'lI 


143 


fatigue-products  such  as  carbon  dioxide  (Lee),  so  that  when  the 
apex  is  stimulated  at  regular  intervals,  each  contraction  is  some- 
what stronger  than  the  preceding  one.  To  this  phenomenon  the 
name  of  the  staircase  or  '  treppe  '  has  been  given  from  the 
appearance  <>1  the  tracings  (p.  <>4<S). 

The  Extrinsic  Nervous  Mechanism  of  the  Heart.— -While, 
as  we  have  seen,  the  essential  cause  of  the  rhythmical  heat  <>t 
the  heart  resides  in  the  tissue  of  the  heart  itself,  it  is  constantly 
affected  by  impulses  that  reach  it  from  the  central  nervous 
system.  These  impulses  are  of  two  kinds,  or,  rather,  produce 
two  distinct  effects:  inhibition,  or 
diminution  in  the  rate  or  force  of 
the  heart-beat,  and  augmentation,  or 
increase  in  the  rate  or  force.  Both 
the  inhibitory  and  the  augmentor 
impulses  arise  in  the  medulla  ob- 
longata, and  perhaps  a  narrow  zone 
of  the  neighbouring  portion  of  the 
cord  ;  and  they  can  be  artificially  ex- 
cited by  stimulation  in  this  region. 
They  pursue  their  course  to  the  heart 
by  fibres  which  may  in  certain  animals 
be  mingled  together,  but  are  anatomi- 
cally distinct.  We  may,  therefore, 
divide  the  extrinsic  or  external  ner- 
vous mechanism  of  the  heart  into  a 
cardio-inhibitory  centre  with  its  effer- 
ent inhibitory  nerve  -  fibres  and  a 
cardio  -  augmentor  centre  with  its 
efferent  accelerator  or  augmentor 
fibres.  Both  of  those  centres,  as  we 
shall  see,  have  also  extensive  rela- 
tions with  afferent  nerve-fibres  from 
all  parts  of  the  body,  including  the 
heart  itself. 

It  was  in  the  vagus  of  the  frog  that  inhibitory  nerves  were  first 
discovered  by  the  brothers  Weber  more  than  sixty  years  ago,  and 
even  now  our  knowledge  of  the  cardiac  nervous  mechanism  is 
more  complete  in  this  animal  than  in  an)'  other.  We  shall, 
therefore,  first  describe  the  phenomena  of  inhibition  and  augmen- 
tation as  we  see  them  in  the  heart  of  the  frog,  and  then  pass  on 
to  the  mammal. 


Fig.  58.  —  Diagram  of  Ex- 
trinsic Nerves  of  Frog's 
Heart  (after  Foster). 

Ill,  3rd  spinal  nerve  ;  AV, 
annulus  of  Vieussens  ;  X,  roots 
of  vagus;  IX,  glosso-pharyngeal 
nerve  ;  VS,  combined  vagus  and 
sympathetic ;  1,  2,  and  3,  the  1st, 
2nd,  and  3rd  sympathetic  gang- 
lia. The  dark  line  indicates  the 
course  of  the  sympathetic  fibres. 
The  arrows  show  the  direction 
of  the  augmentor  impulses. 


In  the  frog  the  inhibitor)-  fibres  leave  the  medulla  oblongata  in 
the  vagus  nerve.  The  augmentor  fibres  come  off  from  the  upper 
part  of  the  spinal  cord  by  a  branch  from  the  third  nerve  to  the 
third  sympathetic  ganglion,   and  thence  find  their  way  along  the 


'4-1 


A   MANUAL  OF  PHYSIOLOGY 


sympathetic  cord  to  its  junction  with  the  vagus,  in  which  they  run, 
mingled  with  the  inhibitory  fibres,  down  to  the  heart. 

When  the  vagosympathetic  in  the  frog  or  toad  is  cut,  and  its 
peripheral  end  stimulated,  the  heart  in  the  vast  majority  of  cases 
is  stopped  or  slowed,  or  its  beat  is  distinctly  weakened  without,  it 
mav  be,  any  marked  slowing.  In  other  words,  the  rate  at 
which  the  heart  was  working  before  the  stimulation  is  greatly 
diminished,  or  reduced  to  zero.  Such  an  effect,  a  diminution  of 
the  rate  of  working,  we  call  Inhibition.  What  precise  form  the 
inhibition  shall  take,  whether  the  stoppage  shall  be  complete  or 
partial,    appears   to   depend   partly   upon   the   strength   of   the 


Fig.  59. — Tracing  from  Frog's  Heart. 
A.   auricular,  V,  ventricular  tracing.     Sinus  stimulated  (primary  oil  70  mm. 
from  secondary).     Heart   at   temperature   ir:°    C.     Complete   standstill.     The 
time-tracing  between  the  curves  marks  intervals  of  two  seconds. 

stimulus  used  and  partly  upon  the  state  of  the  heart  itself. 
Some  hearts  it  mav  be  impossible  to  stop  with  weak  stimulation, 
although  other  signs  of  inhibition  may  be  distinct,  while  tl 
are  readilv  stopped  by  stronger  stimulation.  In  other  cases 
the  strongest  stimulation  may  not  produce  complete  standstill. 
Again,  a  heated  heart  may  be  more  readily  brought  to  standstill 
by  stimulation  of  the  vagus  than  a  heart  at  the  ordinary  tem- 
perature or  a  cooled  heart. 

But  there  are  other  points  of  importance  to  be  noted  in  regard 
to  this  inhibition  :  (1)  It  does  not  begin  for  a  little  time  after 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH       [45 

stimulation  has  begun.  In  other  words,  there  is  a  distinct 
[atenl  period  ;  and  the  length  of  this  latenl  period  is  related  to 
the  phase  of  the  heart's  contraction  at  which  the  stimulus  is 

thrown  in,  and  to  the  rate  at  which  the  heart  is  beating.  As  a 
general  rule,  the  heart  makes  at  least  one  beat  before  it  stops. 

(2)  The  inhibition  does  not  continue  indefinitely,  even  if 
stimulation  of  the  nerve  is  kept  up.  Sooner  or  later,  and 
usually,  in  fact,  after  an  interval  of  a  few  seconds,  the  heart 
begins  again  to  beat  if  it  has  been  completely  stopped,  or  to 
quicken  its  beal  if  it  has  only  been  slowed,  or  to  strengthen 
it  if  the  inhibition  has  only  weakened  the  contraction,  and  it 


Fig.  60. — Frog's  Heart  :  Vagus  Stimulated. 

Temperature  of  heart  8°  G.  ;  78  mm.  between  the  coils.  Diminution  in  force  of 
auricle  and  ventricle,  but  not  complete  standstill.  Time-tracing  shows  two-second 
intervals. 

soon  regains  its  old  rate  of  working.  Not  only  so,  but  very 
often  there  follows  a  longer  or  shorter  period  during  which  the 
heart  works  at  a  greater  rate  than  it  did  before  the  inhibition, 
and  this  greater  rate  of  working  may  be  manifested  by  increased 
frequency  of  beat,  or  increased  strength  of  beat,  or  by  both. 
When  the  temperature  of  the  heart  is  low,  increased  frequency  ; 
when  it  is  high,  increased  strength,  is  generally  seen  during  this 
period  0}  secondary  augmentation*  The  cause  of  this  secondary 
augmentation,  and  of  the  primary  augmentation  sometimes  seen 
in  fresh  preparations  and  often  in  hearts  that  have  been  long 

*  Augmentation  is  termed  '  secondary  '  when  it  is  preceded  by  inhibi- 
tion, '  primary  '  when  it  is  not  so  preceded. 

10 


t46  A   MANUAL  OF  PHYSIOLOGY 

exposed  (Fie;.  6i),  excited  much  speculation  before  it  was  known 
that  sympathetic  fibres  existed  in  the  vagus.    There  is  no  longer 
any  doubt  that  it  is  due  to  the  stimulation  of  these  accelerator 
or,  as  it  is  better  to  call  them  (since  mere  acceleration  is  not  the 
only  consequence  of  their  stimulation),  augmentor  fibres  in  the 
mixed  nerve.     For  (i)  excitation  of  the  roots  of  the  vagus  proper 
within  the  skull,  and  therefore  above  the  junction  of  the  sympa- 
thetic fibres,  causes  no  secondary  augmentation,  or  very  little, 
and  the  inhibition  lasts  far  longer  than  when  the  mixed  trunk  is 
stimulated.     (2)  Excitation  of  the  upper  or  cephalic  end  of  the 
sympathetic  cord  before  it  has  joined  the  vagus  causes,  after  a 
relatively  long  latent  period,  marked  augmentation.     And  if  the 
contractions  of  the  heart  are  registered,  the  t raring  bears  a  1  lose 
resemblance  to  the  curve  of  secondary  augmentation  following 
excitation  of  the  mixed  nerve  on  the  other  side  with  an  equally 
strong  stimulus  and  for  an  equal  time.     (3)  When  the  vago-sym- 
pathetic  is  stimulated  weakly  there  is  little  or  no  secondary  aug- 
mentation.    Now,  it  is  known  that  the  augmentor  fibres  require 
a  comparatively  strong  stimulus  to  cause  any  effect  when  they 
are  separately  excited,  whereas  a  weak  stimulus  will  excite  the 
inhibitory  fibres. 

The  question  arises  at  this  point,  why  it  is  that,  when  the  inhibi- 
tory and  augmentor  fibres  are  stimulated  together  in  the  mixed 
nerve  (and  the  same  is  true  when  the  sympathetic  on  one  side  and 
the  vagus  on  the  other  are  stimulated  at  the  same  time),  the  inhibi- 
tory effect  always  comes  first,  when  there  is  any  inhibitory  effect, 
while  the  augmentation  always  has  to  follow.  The  answer  has 
sometimes  been  given,  that  the  latent  period  of  the  augmentor  fibres 
is  longer  than  that  of  the  inhibitory  fibres.  But  although  this  is 
certainly  the  case,  the  answer  is  insufficient.  For  the  period  of  post- 
ponement may  be  much  greater  than  the  latent  period  of  the  sym- 
pathetic fibres  when  stimulated  by  themselves.  The  inhibition 
apparently  runs  its  course  without  being  affected  by  the  simultaneous 
augmentor  effect,  which,  lying  latent  until  the  end  of  the  inhibition, 
then  bursts  out  and  completes  its  own  curve.  It  is  not  like  the 
passing  of  two  waves  through  each  other,  but  rather  like  the  stopping 
of  one  wave  until  the  other  has  passed  by.  It  seems  as  if  augmenta- 
tion cannot  develop  itself  in  the  presence  of  inhibition— at  least, 
until  the  latter  is  nearly  spent.  Like  a  musical-box  devised  to  play 
a  series  of  melodies  in  a  fixed  order,  and  from  which  a  particular 
tune  cannot  be  obtained  till  those  preceding  it  have  been  run 
through,  the  heart,  in  some  way  or  other,  is  arranged,  in  the  presence 
of  competing  impulses  from  its  extrinsic  nerves,  to  play  the  tune  of 
inhibition  before  the  tune  of  augmentation.  In  the  frog,  at  any 
rate,  the  two  processes  can  hardly  be  considered  as  antagonistic,  in 
the  sense  that  a  definite  amount  of  augmentor  excitation  can  over- 
come a  definite  amount  of  inhibitory  excitation.  Nor  is  it  the  case 
that  when  the  heart  is  played  upon  at  the  same  time  by  impulses  of 
both  kinds,  it  pits  them  against  each  other  and  strikes  the  balance 
accuratelv  between  them.  It  is  possible,  however,  that  when  the  in- 
hibitory fibres  are  very  weakly,  and  the  augmentor  fibres  very  strongly 
stimulated,  the  amount  of  inhibition  may  be  somewhat  diminished.  -In 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH       147 

mammals,  on  Hie  other  hand,  a  true  antagonism  seems  to  exist  ;  and 
stimulation  of  the  inhibitory  nerves  is  less  elfective  when  the  aug- 
mentors  are  excited  a1  the  same  time.  Thecardiac  nervesaffecl  not 
only  the  rate  and  force  of  the  contraction,  but  also  the  conductivity 
0f  the  heart.  Tims  in  the  frog's  heart  during  stimulation  of  the 
vagus,  the  contraction  passes  more  slowly,  and  during  stimulation  of 
the  sympathetic  more  quickly  from  auricles  to  ventricle. 

In  "mammals  (and  in  what  follows  we  shall  restrict  ourselves  chiefly 
to  the  dog,  cat,  and  rabbit,  as  it  is  in  these  animals  that  the  subject 
has  been  most  carefully  studied)  the  inhibitory  fibres  run  down  the 
vagus  in  the  neck  and  reach  the  heart  by  its  cardiac  branches.  They 
are  derived  from  the  bulbar  roots  of  the  spinal  accessory,  whose  inner 


Frog's  Heart. 


A.   auricular.   V,  ventricular  tracing.     Ventricle  beating  very  feebly.     Vagus 
stimulated  (60  mm.  between  oils).     Marked  augmentation  of  ventricular  beat. 

branch  joins  the  vagus.  The  augmentor  fibres  leave  the  spinal  cord  in 
the  anterior  roots  of  the  second  and  third  thoracic  nerves,  and  possibly 
to  some  extent  by  the  fourth  and  fifth.  Through  the  corresponding 
white  rami  communicantes  they  reach  the  sympathetic  cord,  and  run- 
ning up  through  the  stellate  ganglion  (first  thoracic),  and  the  annulus 
of  Vieussens,  which  surrounds  the  subclavian  artery,  to  the  inferior 
cervical  ganglion,  they  pass  off  to  the  heart  by  separate  '  accelerator 
branches,  taking  origin  either  from  the  annulus  or  from  the  inferior 
cervical  ganglion.  Some  augmentor  fibres  are  often,  if  not  always, 
present  in  the  dog's  vago-sympathetic  in  the  neck.  It  is  especially 
easy  to  demonstrate  their  presence  five  or  six  days  after  section  of  the 
nerve,  when  the  excitability  of  the  inhibitory  fibres  has  disappeared. 

10 — 2 


I4S 


A  MANUAL  "l    PHYSIOLOGY 


In  the  dog  the  vagus  and  cervical  sympathetic  are,  in  the  great 
majority  of  cases,  contained  in  a  strong  common  sheath,  and  pass 
ther  through  the  inferior  cervical  ganglion.  Upon  opening  this 
sheath  they  may  with  care  be  separated,  the  fibres  running  in  dis- 
tinct strands,  and  not  mixed  together  as  in  the  vago-sympathetic 
of  the  frog.  For  some  distance  below  the  superior  i  en  ical  ganglion 
the  cervical  sympathetic  is  not  connected  with  the  vagus,  and  here 
the   nerves  may  be  separately   stimulated    without    any   artificial 

isolation,  but  the  electrodes  must  be 
very  well  insulated,  as  the  available 
length  of  nerve  is  small. 

In  the  rabbit  and  some  other  mam- 
mals, including  man.  the  vagus  and 
sympathetic  run  a  separate  course  in 
the  neck. 

The  effects  of  stimulation  of  the 
vagus  or  vago-sympathetic  in  the 
mammal  are  very  much  the  same  as 
in  the  frog,  except  that  secondary 
augmentation  is  in  general  less 
marked,  though  often  present  in 
some  degree,  and  that  in  tliemanim.il 
the  inhibitory  fibres  have  a  smaller 
direct  action  on  the  ventricle.  It 
indeed  beats  more  slowly  when  the 
auricle  is  slowed,  but  this  is  only 
because  in  the  normally  beating 
heart  the  ventricle  takes  the  time 
from  the  auricle.  The  strength  of 
the  ventricular  contractions  may  be 
not  at  all  diminished,  even  when  the 
auricle  is  beating  very  feebly  during 
inhibition.  When  the  auricle  is  com- 
pletely stopped,  which  does  not  occur 
so  readily  as  in  the  frog,  the  ventricle 
also  stops  for  a  short  time,  but  soon 
begins  to  beat  again  with  an  inde- 
pendent rhythm  of  its  own.  In  the 
frog  the  ventricle  is  directly  affected 
by  stimulation  of  the  vagus,  and  the 


Fio.  62. — Diagram  01  Cardiac 
Nerves  in  im  J  )og  (after 
Foster). 

II,  III.  second  and  third  dor- 
sal nerves  ;  SA,  subclavian  ar- 
tery ;  AV,  annulus  of  Vieussens  ; 
I('<;.  inferior  cervical  ganglion  ; 
1  S.  c  ervii  al  sympathetic  :  1,  first 
thoracic  or  stellate  ganglion 
of  the  sympathetic  ;  2,  second 
thoracic  ganglion;  Ac,  accele- 
rator or  augmentor  fibres  pass- 
ing off  towards  the  heart  :  X. 
roots  of  vagus;  XI,  roots  of 
spinal  accessory:  JO.  jugular 
ganglion  ;  GTV,  ganglion  trunci 
vagi :  In.,  inhibitory  fibres  pass- 
ing off  towards  the  heart. 


force  of  its  beats  is  diminished  inde- 
pendently of  the  inhibitory  effects  in  the  auricles  (Practical 
Exercises,  pp.  182,  187). 

The  inhibitory  fibre-,  then,  influence  the  heart  particularly 
through  the  auricles;  they  are  par  excellence  auricular  nerves. 
On  the  other  hand,  the  accelcrantes  in  all  mammals  which  have 
been  investigated  nol  only  extend  to  the  ventricles,  but  are 
even  mainlv  distributed  to  them.     They  are  emphatically  \vn- 


/■///    (  TRt  I  I    I770A    OB    I  III    BLOOD    IND  I  )  \irn 


'  [9 


tricular  fibres,  and  in  accordance  with  its  greater  mass  the  lefl 
ventricle  receives  more  fibres  than  the  i  i  t<  1 1 1 . 

Stimulation  <>!   Lhe  accelerator  nerves  in  the  dog  causes  an 
increase  in  the  force  "l  both  the  auricular  and  ventricular  con 
traction,  and,  as  a  rule,  in  addition,  some  increase  in  the  rate  oi 
the  beat. 

As  to  the  nature  of  the  physiological  linkage  between  the 
cardiac  nerves  and  the  muscular  tissue  of  the  hear!  we  know  but 
little.  It  has  been  supposed  that  within  the  heart  itself  there 
may  exist  peripheral  nervous  mechanisms  which  mediate  between 
the  nerves  and  the  muscle.  We  have  already  given  reasons  for 
assigning  to  the  intrinsic  cardiac  nervous  mechanism  an  im- 
portant share  in  the 
maintenance  of  the 
rhythmical  heat.  It 
this  be  the  case,  it 
is  natural  to  assume 
that  the  extrinsic 
nerves  act  on  the 
heart  -  muscle  not 
directly,  bu1  through 
the  ganglion  -  cells. 
Some  of  these  cells 
lie  on  the  course  of 
the  vagus  fibres,  and 
although  the  view 
has  been  advocated 
that  they  are  simply 
stations  where  the 
inhibitory  impulses 
pass  from  medul- 
lated  to  non-medul- 
lated  fibres,  and 
where  possibly  other 
anatomical    changes 

and  rearrangements  occur,  they  may  just  as  well  be  impor- 
tant intermediate  mechanisms  which  essentially  modify  the 
physiological  impulses  falling  into  them  and  shape  the  visible 
results  that  follow  those  impulses.  The  nervi  accelerantes 
are  already  non-medullated  before  they  reach  the  heart, 
and  it  is  not  known  whether  they  make  connection  with  in- 
tracardiac ganglion-cells.  The  fact  that  the  action  of  the 
accelerantes  can  be  restored  by  perfusing  the  heart  with  a 
nutrient  solution  at  a  much  longer  interval  after  somatic  death 
than  the  action  of  the  vagus  strengthens  the  suggestion  that 
ganglion-cells  are  interposed  on  the  inhibitory  though  not  on 


Fig.  63. — Blood-pressure  Tracings  :  Rabbit. 
Vagus  stimulated  at    1.     Stimulus  stronger  in  B 
than  in  A  ( I  liirtlilc's  spring  manometer). 


150  A   MANI    ll    a/     I'llYSIOLOGY 

the  augment  or  path,  without,  however,  proving  ol  itself  thai 
such  a  difference  exists.  In  one  experimenl  the  hearl  oi  an 
anthropoid  ape  was  revived  when  three  successive  periods  viz., 
four  and  a  halt,  twenty-eighl  and  a  half,  and  fifty-three  hours 
respectively — had  elapsed  after  the  death  of  the  animal,  although 
during  the  last  period  the  heart  had  been  twice  frozen  haul.  The 
vagus  was  shown  to  be  still  capable  of  causing  some  inhibition 
six  hours  after  death,  and  the  accelerans  some  augmentation  as 
late  as  fifty-three  hours  after  death  (Hering). 

In  the  discussions  thai  have  arisen  over  the  relation  of  the  ex- 
trinsic to  the  intrinsic  cardiac  nervous  apparatus  appeal  has  fre- 
quently been  made  to  the  action  of  certain  poisons  on  the  heart. 

Thus,  after  nicotine  has  been  injected  subcutaneously,  or  painted 
directly  on  the  heart  of  a  frog,  stimulation  of  the  vago-sympathetic 
causes  no  inhibition  ;  it  may  cause  augm  intation.  Bu1  stimulation 
of  the  junction  of  the  sinus  and  auricle  sLill  can.  :s  inhibit!  m  as  in 
the  normal  heart. 

Atropine  and  its  allies,  such  as  daturine,  not  only  abolish  the  in- 
hibitory effect  of  stimulation  of  the  vagus  trunk,  but  also  thai  oi 
stimulation  of  the  junction  of  sinus  and  auricle. 

Muscarine,  a  poison  contained  in  csrtain  mushrooms  (p.  i 
causes  diastolic  arrest  of  the  heart,  which  when  the  circulation  is 
intact,  becomes  swollen  and  engorged  with  blood.  This  action 
takes  place  in  a  heart  already  poisoned  with  nicotine  or  one  of  its 
congeners)  but  not  in  a  heart  under  the  influent  :  oi  atropine  or  its 
allies.  And  a  heart  brought  to  a  standstill  by  muscarine  can  bo 
made  to  beat  again  by  the  application  of  atropine,  although  not  by 
nicotine. 

These  facts  may  be  explained  as  follows:  Nicotine  paralyzes  not 
the  very  ends  of  the  vagus,  but  the  ganglia  through  winch  its  fibres 
pass.  Stimulation  of  the  sinus,  which  is  practically  stimulation  oi 
the  vagus  fibres  hjtw.m  the  ganglion-cells  and  the  muscular  fibres, 
is  therefore  effective,  although  stimulation  of  the  nerve-trunk  is  not 
(Langley).  On  the  other  hand,  the  atropine  group  paralyzes  the 
nerve-endings  themselves,  or  interferes  with  the  reception  of  the 
inhibitory  impulses  by  acting  on  a  so-called  receptive  substance  in 
the  muscle  (p.  166),  SO  that  neither  stimulation  of  the  sinus  nor  ol 
the  nerve-trunk  can  cause  inhibition.  Muscarine,  on  the  contrary, 
stimulates  the  vagus  fibres  between  the  nerve-cells  and  the-  muscle. 
or  the  actual  nerve-endings,  or  exerts  an  inhibitory  action  on  the 
muscle  ilsell  through  the  appropriate  receptive  substance,  and  thus 
keeps  the  heart  in  a  state  oi  permanent  inhibition,  which  is  removed 
when  atropine  tuts  out  the  nerve-endings,  or  combines  with  the 
receptive  substance.  It  is  quite  in  accordance  with  this  that  mus- 
carine has  no  effect  on  a.  heart  whose  vagus  nerves,  .is  occasionally 
happens,  have  no  inhibitory  power.  Pilocarpine  has  very  much 
the  same  action  as  muscarine. 

The  view  that  muscarine  and  atropine  can  directly  affect  the 
cardiac  muscle  gains  a.  certain  amount  of  support  from  the  E; 
that  these  drugs  act  very  much  m  the  same  way  on  i  he  heart  ol  the 
mammalian  embryo  (rat.  rabbit,  etc.)  before  and  after  the  develop- 
ment of  its  intrinsic  nervous  system,  and  that  tin-  passage  oi  au 
interrupted  current  through  the  heart  of  very  young  embryos  causes 
distinct  inhibition.     But,  as  has  already  been  pointed  out.  it   is  not 


THE  CIRCU1   ITION  OF   THE  BLOOD  AND  I.V.MI'II       tsi 


legitimate  to  transfer  without  question  to  the  muscle  oJ  the  fully 
developed  heart  the  properties  of  the  embryonic  cardiac  ti 
And,  on  the  other  band,  muscarine  tails  to  affect  the  heart  in  many 
invertebrate  animals  for  instance,  in  the  Daphnia  (Pickering). 
Wt  it  is  probable  that,  while  the  various  tissues  in  the  tiearl  possess 
a  different  susceptibility  to  one  and  the  same  drug,  if  the  dose  is 
large  enough  it  may  affect  them  all.  In  the  Limulus  heart,  where 
the  question  can  be  most  easily  tested,  it  has  been  found  that  the 
selective  action  of  alkaloids,  anaesthetics,  and  various  other  sub- 
stances on  the  three  heart-tissues  (ganglion,  motor  nerve  plexus, 
and  muscle)  is  one  of  degree  only  (Meek). 

Stannius'  Experiment.  Another  series  of  phenomena,  intimately 
related  to  our  present  subject,  have  excited,  since  they  were  first 
made  known  by  Stannius,  an  enormous  amount  of  discussion.  The 
chief  factsof  this  classi- 
cal experiment  we  have 
already  mentioned  (p. 
[32),  and  they  are  also 
described  in  the  Prac- 
tical Exercises  (p.  C83). 
They  are  easy  to  verify, 
but  difficult  to  inter- 
pret. The  most  prob- 
abl  ■  explanation  of  the 
standstill  caused  by 
the  first  ligature  is 
that  the  lower  portion 
of  the  heart,  when  cut 
off  from  the  sinus  in 
which  the  beat  nor- 
mally originates,  needs 
some  time  for  the  de- 
velopment of  its  auto- 
matic power  to  the 
point  at  which  an  in- 
dependent rhythm  can 
be  maintained.  The 
effects  following  the 
second  Stannius  liga- 
ture are  supposed  by 
some  to  be  due  to 
stimulation  of  the  mus- 
cular tissue  in  the  auriculo-ventricular  groove  by  the  ligature. 

Another  view  is  that  the  first  ligature  stimulates  the  inhibitory 
mechanism  (vagus  fibres)  at  the  junction  of  the  sinus  and  right 
auricle,  a  position  in  which  it  is  specially  sensitive  to  stimuli.  This 
causes  inhibition  of  the  whole  of  the  heart  below  the  ligature.  The 
second  ligature  cuts  off  the  ventricle  from  the  inhibitory  impulses, 
while  leaving  the  auricle  still  under  their  influence.  The  Stannius 
experiment  does  not  succeed  in  the  mammalian  heart — or,  at  any 
rate,  only  imperfectly. 

Nature  of  Inhibition  and  Augmentation. — So  far  we  have  been 
discussing  the  phenomena  of  inhibition  and  augmentation  as  ultimate 
facts.  We  have  not  attempted  to  go  behind  them,  nor  to  ask  what 
it  is  that  really  happens  when  inhibitory  impulses  fall  into  a  heart, 
which  from  the  first  days  of  embryonic  life  has  gone  on  beating  with 
a  regular  rhythm,  and  in  the  space  of  a  second  01  two  bring  it  to  a 


Fig.  64. — Frog's  Heart. 

Sympathetic  stimulated  (30  mm.  between  the 
coils).  Temperature  120.  Marked  increase  in  force. 
Only  auricular  tracing  reproduced.  Time -trace, 
two-second  intervals. 


152 


A   M.I. xr  n    a/-   PHYSIOLOGY 


piifiiif|f||i 


28  "5 

a  30 


I  I II I  II II  I  I  I  I  I  I  1 1  I  II 


nrn  1 1 1 1  i  1 1 1 1 1 1  ■  i ' 


standstill.  The  question  (annul  fail  to  press  itsell  upon  the  mind  of 
anyone  who  lias  ever  witnessed  tins  most  beautiful  ol  physiological 
experiments  ;  but  as  ye1  there  is  no  answer  ex<  ep1  ingenious  specula- 
tions. The  most  plausible  of  these  is  the  trophic  theory  oi  Gaskell, 
who  sees  in  the  vagus  a  nerve  which  so  acts  upon  the  chemical  changes 
going  <m  in  the  heart  as  to  give  them  a  trophic,  or  anabolic,  or  i  on- 
structive  turn,  and  thus  to  lessen  for  the  time  the  destructive  changes 
underlying  the  inuseular  contraction.  The  augmentor  nerves,  on 
the  other  hand,  are  su])})osed  to  exert  a  katabolic  influence,  and  to 
favour  these  destructive  changes.  And  while,  according  to  Gaskell, 
the  natural  consequence  of  inhibition  is  a  stage  of  increased  efficiency 
and  working  power  when  the  inhibition  has  passed  away,  the  natural 

_  _       complement  of  aug- 
MHfflliill/lllillll|'\)  mentation  is  a  tem- 

porary exhaustion. 
But  it  must  be  re- 
membered that  this 
dist  inction  is  not  as 
yet  based  upon  any 
very  solid  founda- 
tion of  actually  ob- 
served  and  easily 
interpreted  facts, 
while  to  some  of  the 
facts  brought  for- 
ward in  its  favour 
undue  importance 
has  been  given. 

Whatever  the  ex- 
act mechanism  of 
augmentation  may 
be,  there  is  no  foun- 
dation for  the  state- 
ment th.it  the  car- 
dio-au g  m  entor 
nerves  have  an  ac- 
tion on  the  heart  so 
fundamentally  dif- 
ferent from  the  ac- 
tion of  motor  nerves 
on  skeletal  muscle 
that  they  cannot 
originate  contrac- 
tions in  a  heart  entirely  at  rest.  Excitation  oi  the  cardio-aug- 
mentor  nerves  can  cause  rhythniie.il  contractions  in  the  perfectly 
quiescent  heart  of  molluscs,  and  a  sudden  and  prolonged  outburst  of 
beats  of  great  force  in  the  frog's  heart,  which  has  been  brought  to  a 
standstill  by  cautiously  heating  it  to  40  to  13  C.  (Practical  Exer- 
cises, p.  178)  for  a  minute  or  two,  or  to  a  considerably  lower  tempera- 
ture, for  a  longer  time  (Fig.  65).  A  similar  effect  can  be  obtained  on 
the  quiescent  mammalian  heart  by  stimulation  of  the  nervi 
accelerantes. 

The  Normal  Excitation  of  the  Cardiac  Nervous  Mechanism. 
— We  have  now  to  inquire  how  this  elaborate  nervous  mechanism 

is  normally  set  into  action.      And  we  may  say  at  once  that, 


rr»vrrvoNsr^J 


Fig.  65. — Effect  of  Stimulation  of  Frog's  Cardiai 
Sympathetic  during  Complete  Standstill  <>i  mi 
Heart  at  28-5°  C. 

Upper  tracing,  auricle;  lower,  ventricle.     To  be  read 
from  right  to  left.     Time-trace,  two-second  intervals. 


////    (  //,•<  ll    I770A    OB    till    BLOOD  AND  I  \   \iril       [53 

striking  .is  are  the  effects  oi  experimental  stimulation  "l  the 
vagus  trunk  or  the  nervi  accelerantes  in  their  course,  ii  is  only 
under  exceptional  circumstances  thai  the  efferenl  nerve  fibres, 
at  any  rate  before  thej  have  entered  the  heart,  can  be  directly 
excited  in  t he  intact  body.  In  certain  cases  the  pressure  ol  a 
tumour  or  an  aneurism  on  the  nerve-trunks,  or,  in  the  case  ol 
the  accelerators,  the  progress  of  a  pathological  change  in  the 
sympathetic  ganglia  through  which  the  fibres  pass,  has  been 
thought  to  bring  about  by  direct  stimulation  a  slowing  or  a 
quickening  of  the  pulse.  In  some  individuals  the  vagus  may  be 
excited  by  compressing  it  against  the  vertebral  column  or  against 
a  bony  tumour  in  the  neck.  But  it  is  from  the  cardio-inhibitory 
and  cardio-augmentor  centres  in  the  medulla  oblongata  that  the 
impulses  which  regulate  the  activity  of  the  heart  are  normally 
discharged.  Inhibitory  impulses  are  constantly  passing  out 
from  the  medulla,  for  section  of  both  vagi  causes  almost  invari- 
ably an  increase  in  the  rate  of  the  heart,  at  least  in  mammals, 
although  the  increase  is  less  conspicuous  in  animals  like  the 
rabbit,  whose  normal  pulse-rate  is  high,  than  in  animals  like 
the  dog,  whose  pulse-rate  is  comparatively  low.  Section  of  one 
vagus  usually  causes  only  a  comparatively  slight  increase,  for 
the  other  is  able  of  itself  to  control  the  heart.  It  is  not  certainly 
known  whether  the  augmentor  centre  in  like  manner  discharges 
a  continuous  stream  of  impulses,  or  is  only  roused  to  occasional 
activity  by  special  stimuli.  For  the  results  of  section  of  the 
nervi  accelerantes,  or  the  extirpation  of  the  inferior  cervical  and 
stellate  ganglia,  are  dubious  and  conflicting.  But  if  it  does 
exert  a  tonic  influence  on  the  heart,  this  is  feebler  than  the  tone 
of  the  inhibitory  centre.  As  to  the  nature  of  this  inhibitory 
tone,  and  the  manner  in  which  it  is  maintained,  we  know  but 
little.  It  may  be  that  the  chemical  changes  in  the  nerve-cells 
of  the  inhibitory  centre  lead  of  themselves  to  the  discharge  of 
impulses  along  the  inhibitory  nerves.  But  there  is  some  evi- 
dence that,  in  the  complete  absence  of  stimulation  from  without, 
the  activity  of  the  centre  would  languish,  and  perhaps  be  ulti- 
mately extinguished.  For  when  the  greater  number  of  the 
afferent  impulses  have  been  cut  off  from  the  medulla  oblongata 
by  a  transverse  section  carried  through  its  lower  border,  division 
of  the  vagi  produces  little  effect  on  the  rate  of  the  heart.  Also, 
when  the  upper  cervical  cord  and  the  brain  are  resuscitated  after 
a  period  of  anaemia,  the  return  of  cardio-inhibitory  tone  is  tardy 
in  comparison  with  the  return  of  the  truly  automatic  function  of 
respiration,  and  does  not  seem  to  precede  the  opening  up  of  the 
afferent  paths  to  the  cardio-inhibitory  centre.  Indeed,  reflex 
inhibition  may  be  produced  at  a  time  when  the  inhibitory  centre 
has  regained  none  of  its  tone. 


i  5  i  A   MANUA1    OF   PHYSIOLOG  Y 

Tin4  suggestion  is  thai  the  normal  tone  oi  the  i  entre  is  largely 
dependent  upon  reflex  impulses.  Be  this  as  it  may,  we  know 
thai  the  activity  of  the  inhibitory  centre  is  profoundly  influenced 
— and  that  both  in  the  direction  of  an  increase  and  oi  a  diminu- 
tion by  impulses  that  fall  into  it  through  afferent  nerves  and 
by  stimuli  directly  applied  to  it.  And  we  may  assume  that  the 
same  is  true  of  the  augmentor  centre.  The  common  statement 
that  stimulation  of  the  central  end  of  one  vagus,  the  other  being 
intact,  produces  distinct  inhibition  does  not  hold  for  all  mammals. 
In  dogs  this  is  sometimes  the  case,  but  often  (under  anaesthesia, 
at  any  rate)  there  is  little  or  no  inhibition,  or  even  augmentation. 
In  etherized  cats,  on  the  other  hand,  some  inhibition  is  always 
seen.  Of  all  the  afferent  fibres  of  the  vagus,  the  pulmonary 
fibres  produce  the  most  marked  reflex  inhibition.  The  cardiac 
fibres  are  much  less  effective. 

These  pulmonary  nerves  also  influence  the  respiratory  and 
vaso-motor  centres.  The  respiration  is  temporarily  arrested, 
and  the  blood-pressure  falls  through  the  dilatation  oi  the  small 
arteries  when  they  are  excited.  As  will  be  again  pointed  out 
in  connection  with  the  subject  of  death  during  the  administration 
oi  anaesthetics,  the  afferent  vagus  fibres  coming  from  the  alveoli 
oi  the  lungs  can  be  chemically  stimulated  when  irritant  vapours, 
such  as  chloroform  or  ammonia,  are  inhaled  (p.  2.55). 

The  depressor  nerve,  a  branch  of  the  vagus,  which  is  easily 
found  in  the  rabbit  as  a  slender  nerve  running  close  to  the 
sympathetic  in  the  neck,  and  a  little  to  its  inner  side,  but  in  the 
dog  is  usually  blended  with  the  vago-sympathetic,  tails  into  the 
same  category  with  the  vagus  itself  as  regards  its  reflex  action 
on  the  heart,  to  which  it  bears  an  important  relation.  In  all 
mammals  some  of  its  fibres  end  in  the  wall  of  the  aorta,  but 
some  of  them  may  run  down  over  the  heart  to  the  ventricle. 
Stimulation  of  its  peripheral  end  has  no  effect,  for  the  fibres  in 
it  which  influence  the  circulation  are  afferent,  not  efferent. 
But  excitation  of  its  central  end  causes  a  marked  fall  of  blood- 
pressure  (p.  169),  accompanied  by,  but  not  essentially  due  to, 
a  distinct  slowing  of  the  heart,  [f  the  animal  isnol  anaesthetized, 
there  may  be  signs  of  pain,  and  for  this  reason  the  depressor 
has  sometimes  been  spoken  of,  somewhat  loosely,  as  the  sensory 
nerve  of  the  heart.  The  abdominal  sympathetic  (of  the  frog) 
also  contains  afferent  fibres,  through  which  reflex  inhibition  of 
the  heart  can  be  produced  when  they  are  excited  mechanically 
by  a  rapid  succession  oi  light  strokes  on  the  abdomen  with  the 
handle  oi  a  scalpel. 

On  the  other  hand,  when  the  central  end  of  an  ordinary 
peripheral  nerve  like  the  sciatic-  or  brachial  is  excited  the  common 
effect  is  pure  augmentation  (Fig.  66),  which  sometimes  develops 


Till    CIRCUL  ITION  OF   THE  BLOOD    \ND  LYMPH 

itself  with  even  greatei  suddenness  than  when  the  accelerator 
nerves  are  directly  stimulated.  Occasionally,  however  the 
augmentation  is  abruptly  followed  by  a  typical  vagus  action. 
Here  the  reflex  inhibitory  effect  seems  to  break  in  upon  and  cut 
short  the  reflex  augmentor  effect. 

These  examples  show  thai  certain  afferent  nerves  are  especially 
related  to  the  cardio-inhibitory3  and  others  to  the  cardio-aug- 
mentor,  centre,  or  at  Least  that  the  central  connections  of  some 
nerves  are  such  that  inhibition  is  the  usual  effect  of  their  reflex 
excitation,  while  the  opposite  is  the  case  with  other  nerves. 
But  it  is  improbable  that  the  effect  of  a  stream  of  afferent  im- 
pulses reaching  the  cardiac  centres  by  any  given  nerve  is  deter- 
mined  solely  by  anatomical   relations.     The  intensity  and  the 


nrvHhrvKnl  \nh\J\H'  ihWihhW-J  vHnnJ 


Ii    .   66. — Myocardiographic  Tracing  of  Cat's  Ventricle. 

Tin-  signal  line  shows  the  point  at  which  the  central  end  of  the  brachial  nerve 
stimulated  during  resuscitation  of  the  animal  after  a  period  of  cerebral  anaemia. 
Some  augmentatii  in  i  if  the  ventricular  beat  is  seen.     The  notches  in  the  ventricular 
tracing  are  due  to  the  artificial  respiration.     Time-trace,  seconds. 

nature  of  the  stimulus  seem  also  to  have  something  to  do  with 
the  result.  For  when  ordinary  sensory  nerves  are  weakly  stimu- 
lated, augmentation  is  said  to  be  more  common  than  inhibition, 
and  the  opposite  when  they  are  strongly  stimulated.  And  while 
a  chemical  stimulus,  like  the  inhaled  vapour  of  chloroform  or 
ammonia,  causes  in  the  rabbit  reflex  inhibition  of  the  heart 
through  the  fibres  of  the  trigeminus  that  confer  common  sensa- 
tion on  the  mucous  membrane  of  the  nose,  the  mechanical  ex- 
citation of  the  sensory  nerves  of  the  pharynx  and  oesophagus 
when  water  is  slowly  sipped  causes  acceleration.*  The  stimula- 
tion of  the  nerves  of  special  sense  is  followed  sometimes  by  the 
one  effect  and  sometimes  by  the  other.     To  complete  the  cata- 

*   In  78  healthy  students  the  average  pulse-rate  (in  the  sitting  position) 
was  increased  from  j$  to  85  per  minute  by  sipping  water. 


i  $6  I    \l  INV  II    OF    PHYSIOLOGY 

Logue  ol  the  nervous  channels  by  which  impulses  may  reach  the 
cardiac  centres  in  the  medulla,  we  may  add  that  then-  must  be 
an  extensive  connection  between  them  and  the  cerebral  cortex, 
since  every  passing  emotion  Leaves  its  trace  upon  the  curve  ol 
cardiac  action.  The  so-called  'reflex  cardiac  death,'  which  is 
an  occasional  consequence  of  intense  psychical  influences  (anxiety, 
fright,  etc.),  may  be  due  to  the  prolonged  excitation  ol  the 
cardio-inhibitory  centre,  as  well  as  to  the  disturbance  oi  other 
centres  in  the  bulb  by  the  cortical  storm.  It  is  a  remarkable 
fact,  too,  and  one  that  can  only  be  explained  by  such  .1  con- 
nection, that  although  in  the  vast  majority  ol  individuals  the 
will  has  no  influence  whatever  on  the  rate  or  force  ol  the  heart, 
except,  perhaps,  indirectly  through  the  respiration,  some  persons 
have  the  power,  by  a  voluntary  effort,  of  markedly  accelerating 
the  pulse.  In  one  case  of  this  kind  it  was  noticed  that  per- 
spiration broke  out  on  the  hands  and  other  parts  of  the  body 
when  the  heart  was  voluntarily  accelerated.  A  rise  ol  blood- 
pressure  clue  to  constriction  of  the  vessels  has  also  been  ob  served. 
The  effort  cannot  he  kept  up  for  more  than  a  short  time  and 
the  pulse-rate  quickly  goes  hack  to  normal.  It  has  been  recently 
shown  that  this  peculiar  power  is  more  common  than  has  been 
supposed,  and  that  where  it  is  present  in  rudiment,  it  can 
cultivated,  although  it  is  a  dangerous  acquisition. 

As  an  example  ol  the  direct  action  of  a  chemical  stimulus 
on  a  cardiac  centre,  we  may  cite  the  inhibition  produced  by 
injection  of  adrenalin  into  a  vein  (p.  201),  and  as  an  instance  ol 
the  direct  action  of  a  physical  change,  the  slowing  ol  the  hearl 
in  asphyxia  as  the  blond-pressure  rises  (p.  172).  The  variation 
in  the  pulse-rate  associated  with  changes  in  the  position  ol  the 
body,  to  which  we  have  already  referred  (p.  98),  is  brought  about 
by  direct  stimulation  of  the  inhibitory  centre  by  the  incn 
ol  blood-pressure  in  the  medulla  oblongata  when  a  person  who 
has  been  standing  assumes  the  supine,  or  even  the  sitting,  posture. 
But  it  is  also  due  in  pari  to  changes  in  the  amount  ol  muscular 

contraction,  since  muscular  exercise  causes  accelerate I   the 

heart  either  reflexly,  through  afferent  muscular  nerves,  or  by  a 
direct  effect  of  waste  products  ol  the  metabolism  ol  the  mus<  les 
on  the  cardiac  centres  in  the  bulb  or  on  the  hearl  itsell  (p.  229). 

Theoretically,  quickening  of  the  heart  mighl  be  caused  rather 
by  a  diminution  in  the  inhibitory  tone  oi  by  an  increase  in  the 
activity  of  the  augmentor  centre;  and  slowing  ol  the  hearl 
might  be  due  either  to  a  diminution  in  the  augmentor  tone,  il 
such  exists,  or  to  an  increase  in  the  activity  of  the  inhibitory 
centre.  So  that  it  is  not  always  easy  to  interpret  such  results 
as  we  have  quoted  above.  But  it  would  appear  that  under 
ordinary  conditions  the  rate  of  the  heart   is  mainly  regulated 


THE  CIRCUl   ITION  OF   I//I    moon    I ND  LYMPH       i;- 

by  the  inhibitory  centre,  which,  within  a  considerable  range, 
can  produce  variations  in  either  direction.  The  augmentor 
mechanism  is  perhaps  merely  auxiliary  to  the  inhibitory,  being 
called  into  action  only  in  emergencies. 

Vaso-motor  Nerves.  -Jus1  as  the  muscular  walls  of  the  hearl 
are  governed  l>v  two  sets  of  nerve-fibres,  a  set  which  keeps 
down  the  rate  of  working  and  a  set  which  may  increase  it,  the 
muscular  walls  of  the  vessels  are  under  the  control  of  nerves 
which  have  the  power  of  diminishing  their  calibre  (vaso-con- 
strictor), and  of  nerves  which  have  the  power  of  increasing  it 
[vaso-dilator).  All  nerves  that  affect  the  calibre  of  the  vessels, 
whether  vaso-constrictor  or  vaso-dilator,  are  included  under  the 
general  name  vaso-motor.  These  vaso-motor  nerves,  like  the 
augmentor  and  inhibitory  fibres  of  the  heart,  are  connected 
with  a  centre  or  centres,  which  in  turn  are  in  relation  with 
numerous  afferent  nerves.  It  is  convenient  to  distinguish  the 
afferent  nerves  which  cause  on  the  whole  a  vaso-constriction 
and  a  consequent  increase  of  arterial  pressure  as  pressor  nerves, 
and  those  which  cause  on  the  whole  vaso-dilatation,  with  fall 
of  pressure,  as  depressor  nerves,  reserving  the  terms  vaso-con- 
strictor and  vaso-dilator  for  the  efferent  portions  of  the  reflex 
arcs.  It  is  through  this  reflex  mechanism  that  the  bloodvessels 
an>  mainly  influenced,  although  the  endings  of  the  vaso-motor 
nerves  in  the  smooth  muscular  fibres  or  the  muscular  fibres 
themselves  are  sometimes  directly  affected  by  substances 
circulating  in  the  blood.  Albumose,  for  instance,  causes  by 
peripheral  action  dilatation  of  the  vessels  and  a  fall  of  blood- 
pressure  (p.  201)  ;  suprarenal  extract,  or  its  active  principle, 
adrenalin,  constriction,  with  a  rise  of  pressure  (p.  201).  Apoco- 
deine  paralyzes  the  vaso-motor  nerve-endings  after  a  preliminary 
stimulation,  and  now  adrenalin  causes  no  constriction.  Chryso- 
toxin,  an  active  principle  of  ergot,  causes  a  marked  rise  of  blood- 
pressure  by  stimulating  the  sympathetic  ganglion-cells  or  the 
pre-ganglionic  fibres  of  the  vaso-constrictor  path.  Vaso-motor 
nerves  control  chiefly  the  small  arteries.  They  have  no  direct 
influence  on  the  capillaries.*  Nor  has  the  existence  of  an  effec- 
tive vaso-motor  regulation  of  the  calibre  of  the  veins,  except  in 
the  portal  system,  been  proved  up  to  this  time  by  any  clear  and 

*  It  is  usually  taught  that  the  capillaries,  being  devoid  of  muscular 
fibres  in  their  walls,  are  not  supplied  with  vaso-motor  fibres,  and  that  the 
only  kind  of  active  contraction  of  which  they  are  capable  is  due  to  a  process 
analogous  to  the  turgescence  of  vegetable  cells,  the  thickness  of  the  wall 
being  increased  at  the  expense  of  the  lumen,  while  the  total  cross-section 
of  the  vessel  remains  unchanged.  It  has  recently  been  asserted,  however, 
that  a  true  contraction,  in  which  both  the  total  section  and  the  lumen  are 
diminished,  may  be  caused  in  the  capillaries  of  the  nictitating  membrane 
oi  the  frog  either  by  direct  stimulation  or  by  excitation  of  vaso-motor 
fibres  in  the  sympathetic^ (Steinach  and  Kahn). 


i;x  A   M  INV  u    OF  PHYSIOLOG  Y 

unambiguous  experiment,  although  there  are  grounds  on  which 
it  lias  been  surmised  thai  the  nervous  system  docs  influence  the 
'  tone  '  of  the  whole  venous  tract.  These  grounds  will  be  men- 
tioned in  the  proper  place.  Meanwhile,  before  describing  the 
distribution  of  the  best-known  tracts  of  vaso-motor  fibres  and 
defining  the  position  of  the  vaso-motor  centres,  we  must  glance 
at  the  methods  by  which  our  knowledge  has  been  attained. 

( i )  In  translucent  parts  inspection  is  sufficient.  Paling  oi  the  pari 
indicates  constriction;  flushing,  dilatation  of  the  small  vessels. 
This  method  has  been  much  used,  sometimes  in  conjunction   with 

(2),  in  such  parts  as  the  balls  of  the  toes  of  dogs  or  cats,  the  ear  oi 
the  rabbit,  the  conjunctiva,  the  mucous  membrane  of  the  mouth  and 
gums,  the  web  of  the  frog,  the  wing  of  the  bat,  the  intestines.  1  1. 

(2)  Observation  of  changes  in  the  temperature  of  parts.  This 
method  has  been  chiefly  employed  in  investigating  the  vaso-motor 
nerves  of  the  limbs,  the  thermometer  bulb  being  fixed  between  the 
toes.  In  such  peripheral  parts  the  temperature  "I  the  blood  is 
normally  less  than  thai  of  the  blood  in  the  internal  organs,  because 
the  opportunities  of  cooling  are  greater,  The  effecl  of  a  freer  cir- 
culation of  blood  (dilatation  of  the  arteries)  is  to  raise  the  tempera- 
ture ;  of  a  more  restricted  circulation  (constriction  of  the  art<  I 

to  lower  it. 

(3)  Measurement  of  the  blood-pressure.  If  we  measure  the 
arterial  blood-pressure  at  one  point,  and  find  that  stimulation  of 
certain  nerves  increases  it  without  affecting  the  action  of  tin  heart, 
we  can  conclude  that  upon  the  whole  the  tone  of  the  small  vessels 
has  been  increased.  But  we  cannot  tell  in  what  region  or  regions 
the  increase  has  taken  place  ;  nor  can  we  tell  whether  it  has  not  been 
accompanied  by  diminution  of  tone  in  other  tracts. 

But  if  we  measure  simultaneously  the  blood-pressure  in  the  chief 
artery  and  chief  vein  of  a  part  such  as  a  limb,  we  can  tell  from  the 
changes  caused  by  section  or  stimulation  of  nerves  whether,  and  in 
what  sense,  the  tone  of  the  small  vessels  within  tins  area  has  been 
altered.  For  example,  if  we  found  that  the  lateral  pressure  in  the 
artery  was  diminished,  while  at  the  same  time  it  was  increased  in 
the  vein,  we  should  know  that  the  '  resistance  '  between  artery  and 
vein  had  been  lessened,  and  that  the  blood  now  found  its  way  more 
readily  from  the  artery  into  the  vein.  If.  on  the  other  hand,  the 
venous  pressure  was  diminished,  and  the  arterial  pressure  simul- 
taneously increased,  we  should  have  to  conclude  thai  the  vascular 
resistance  in  the  part  was  greater  than  before.  M  the  pressure  both 
in  artery  and  vein  was  increased,  we  could  not  come  to  any  con- 
clusion as  to  local  changes  of  resistance  without  knowing  how  the 
general  blood-pressure  had  varied. 

(4)  The  measurement  of  the  velocity  of  the  blood  in  the  vessels 
of  the  part.  This  may  be  done  by  the  stroinuhr  or  dromograph,  or 
by  allowing  the  blood  to  escape  from  a  small  vein  and  measuring  the 
outflow  in  a  given  time,  or,  without  opening  t  In-  \  essris.  by  esl  imal  ing 
the  circulation  time  (p.  123).  When  changes  in  the  general  arterial 
pressure  are  eliminated,  slowing  of  the  blood  stream  through  a.  part 
corresponds  to  increase  oi  vascular  resistance  m  it  ;  increase  in  the 
rate  of  flow  implies  diminished  vascular  resistance.  Sometimes  tin- 
red  colour  of  the  blood  issuing  from  a  cut  vein,  and  the  visible  pulse 
in  the  stream,  indicate  with  certainty  that  the  vessels  of  the  organ 
have  been  dilated. 


THE  CIRCULATION  OF  THE  BLOOD  AND  LYMPH        159 

(5)  Alterations  in  the  volume  of  an  organ  or  limb  are  often  taken 
.is  indications  of  changes  in  the  calibre  of  the  small  vessels  in  it. 
We  have  already  seen  howthese  alterations  arc  recorded  by  means 
Hi  a  plethy Sinograph  (p.  117).  The  brain  is  enclosed  in  the  skull  as 
in  a  natural  plethysmograph,  and  changes  in  its  volume  may  be 
registered  by  connecting  a  recording  apparatus  with  a.  trephine  hole. 

(6)  For  the  separation  of  the  effects  of  stimulation  of  vaso- 
constrictor and  vaso-dilator  fibres  when  they  are  mingled  together, 
as  is  the  case  in  many  nerves,  advantage  is  taken  of  certain  differences 
between  them.  for  exam  pie,  the  vaso-constrictors  lose  their  excita- 
bility sooner  than  the  vaso-dilators  when  cut  off  from  the  nerve-cells 
to  which  they  belong.  So  that  if  a  nerve  is  divided,  and  some  days 
.1  Mowed  to  elapse  before  stimulation,  only  the  dilators  will  be  excited. 
The  vaso-dilators  are  more  sensitive  to  weak  stimuli  repeated  at  long 
intervals  than  to  strong  and  frequent  stimuli,  and  the  opposite  is  true 


Fig.    67. — Plethysmograms  :    Hind-limb   of   Cat    (after    Bovvditch    and 

Warren). 

To  be  read  from  right  to  left.  On  the  left  hand  is  shown  the  effect  of  slow  stimu- 
lation of  the  sciatic  (1  per  second)  ;  on  the  right  hand  the  effect  of  rapid  stimula- 
tion (64  per  second).  In  the  first  case  the  limb  swelled  owing  to  excitation  of 
the  vaso-dilators  ;  in  the  second,  it  shrank  through  excitation  of  the  vaso-con- 
strictors. 

of  the  constrictors.  When  a  nerve  containing  both  kinds  of  fibres  is 
heated,  the  excitability  of  the  vaso-constrictors  is  increased  in  a 
greater  degree  than  that  of  the  dilators  ;  when  the  nerve  is  cooled, 
the  dilators  preserve  their  excitability  at  a  temperature  at  which  the 
constrictors  have  ceased  to  respond  to  stimulation  (Fig  67). 

The  Chief  Vaso-motor  Nerves.- — The  first  discovery  of  vaso- 
motor nerves  was  made  in  the  cervical  sympathetic.  When  this 
nerve  is  cut,  the  corresponding  side  of  the  head,  and  especially 
the  ear,  become  greatly  injected  owing  to  the  dilatation  of  the 
vessels.  This  experiment  can  be  very  readily  performed  on  the 
rabbit,  and  the  changes  are  most  easily  followed  in  an  albino. 
The  ear  on  the  side  of  the  cut  nerve  is  redder  and  hotter  than 
the  other  ;  the  main  arteries  and  veins  are  swollen  with  blood, 


)    1/  ]\r  \i    01    PHYSIOLOGY 

and  many  vessels  formerly  invisible  come  im<>  view.  The  slow 
rhythmical  changes  oi  calibre,  which  in  the  normal  rabbil  are 
very  characteristically  seen  in  the  middle  artery  ol  the  ear,  dis- 
;tp|)cai  I"!  .1  time  after  section  oi  the  sympathetic,  although  they 
ultimately  again  become  visible  (Practical  Exercises,  p.  2< 

Stimulation  ol  the  cephalic  end  "I  the  cul  sympathetic  causes 
a  marked  constri<  tion  ol  the  vessels  and  a  fall  ol  temperature  on 
the  same  side  ol  the  head.  From  these  facts  we  know  that 
the  cervical  sympathetic  in  mammals  contains  vaso-constrictor 
fibres  for  the  side  of  the  head  and  ear,  and  thai  these  fibres  are 
constantly  in  action.  Certain  parts  ol  the  eye,  and  the  salivary 
glands,  larynx,  oesophagus,  and  thyroid  gland,  are  also  supplied 
with  vaso-motor  (constrictor)  nerves  from  the  cervical  sym- 
pathetic. 

It  has  been  asserted  that  the  cervical  sympathetic  contains  some 
of  the  vaso-constrictor  fibres  that  supply  the  corresponding  half  of 
the  brain  and  its  membranes,  but  this  has  been  disputed,  and  some 
observers  deny  that  the  vessels  of  the  brain  have  any  vaso-motor 

nerves.  Xon-mediillated  nerve-fibres,  however,  may  be  seen  in 
and  around  the  walls  of  the  cerebral  and  spinal  bloodvessels,  and 
it  is  difficult  to  believe  thai  these  have  not  a  vaso-motor  function, 
although  this  has  not  as  yet  been  clearly  demonstrated  by  experi- 
mental methods. 

It  has  sometimes  been  argued  that  we  ought  not  to  expect  the 
brain  to  be  supplied  with  vaso-motors.  For  it  is  enclosed  in  a  rigid 
box,  and  the  quantity  of  blood  in  it  can  be  increased  or  diminished 
only  to  the  slight  extent  to  which  the  ccrebro-spinal  liquid  can  be 
displaced  into  the  vertebral  canal.  Important  changes  in  the 
cerebral  blood-supply  are  therefore  brought  about,  it  is  said,  not  by 
a  widening  or  narrowing  of  the  cerebral  vessels,  but  by  an  alteration 
in  the  velocity  of  the  blood  in  them  as  a  result  or  fall  of  the 

systemic  arterial  pressure.  This  argument,  however,  leaves  out  of 
account  the  consideration  that  in  general  the  brain  docs  not  function 
as  a  whole,  but  that  certain  parts  of  it  may  often  become  active  and 
relatively  hypenemic.  while  other  parts  are  inactive  and  relatively 
anaemic,  and  thai  important  changes  in  the  distribution  of  the 
blood  in  the  encephalon  ui.lv  be  effected,  although  the  total  mass  of 
blood  in  the  organ  undergoes  little  or  no  alteration.  It  is.  of  course, 
true  that  it  is  not  the  absolute  quantity  of  blood  in  an  organ  which 
is  a  function  of  its  activity,  but  the  rate  at  which  it  is  renewed. 
And  i1  is  theoretically  possible  that  an  organ  at  resl  should  contain 
as  much  blood  as  when  it  is  active,  or  even  more.  Bui  such  i 
it  they  exist,  are  certainly  rare.  The  retina,  which  from  the  stand- 
point of  development  is  a  portion  of  the  brain,  is  undoubtedly 
supplied  with  vaso-constrictor  fibres  which  run  in  the  cervical 
sympathetic. 

That  the  cervical  sympathetic  contains  some  dilator  fibres  is 
proved  by  the  fact  that  stimulation  of  the  cephalic  end  in  the 
dog  causes  flushing  of  the  mucous  membrane  of  the  mouth  on 
the  same  side.  Further,  after  division  of  the  nerve  on  one  side 
in  the  rabbit  it  may  be  observed  that  when  the  animal  is  excited 


////    CIRCU1    fT/OA   OF  THE  BLOOD    IND  LYMPH         161 

the  vessels  of  the  oar  whose  nerve  is  intact  may  become  still  more 
dilated  than  those  whose  constrictor  fibres  have  been  paralyzed. 
Ihc  only  explanation  is  that  vaso-dilatoi  -  are  being  excited  from 
the  central  nervous  system.  In  the  cat  the  cervical  sympathetic 
contains  vaso-dilators  tor  tin;  submaxillary  gland  (p.  367). 

The  vaso-motor  fibres  of  the  head  inn  up  in  the  cervical  sym- 
pathetic, and  then  pass  into  various  cerebral  nerves,  of  which  the 
fifth  or  trigeminus  is  the  most  important. 

The  trigeminus  nerve  contains  vasoconstrictor  nerves  for 
various  parts  of  the  eye  (conjunctiva,  sclerotic,  iris),  and  for 
the  mucous  membrane  of  the  nose  and  gums,  and  section  of 
it  is  followed  by  dilatation  of  the  vessels  of  these  regions.  The 
iiii^itti/  branch  of  the  trigeminus  supplies  vaso-motor  fibres  to  the 
tongue,  and  apparently  both  vaso-constrictor  and  vaso-dilator. 

In  some  animals  -the  rabbit,  for  instance — the  ear  derives  part 
of  its  vaso-motor  supply  through  the  great  auricular  nerve,  a 
branch  of  the  third  cervical  nerve,  which  they  reach  as  grey  rami 
from  the  stellate  ganglion. 

Another  great  vaso-motor  tract,  the  most  influential  in  the 
body,  is  contained  in  the  splanchnic  nerves,  which  govern  the 
vessels  of  many  of  the  abdominal  organs.  Section  of  these 
nerves  causes  an  immediate  and  sharp  fall  of  arterial  pressure. 
The  intestinal  vessels  are  dilated  and  overfilled  with  blood.  As 
a  necessary  consequence  of  their  immense  capacity,  the  rest  of 
the  vascular  system  is  underfilled,  and  the  blood-pressure  falls 
accordingly.  Stimulation  of  the  peripheral  end  of  the  splanchnic 
nerves  causes  a  great  rise  of  blood-pressure,  owing  to  the  con- 
striction of  vessels  in  the  intestinal  area.  We  therefore  conclude 
that  in  the  splanchnics  there  are  vaso-motor  fibres  of  the  con- 
strictor type,  and  that  impulses  are  constantly  passing  down  them 
to  maintain  the  normal  tone  of  the  vascular  tract  which  they 
command.  The  presence  of  dilator  fibres  (for  the  intestines  and  the 
kidney,  for  example)  has  also  been  demonstrated  in  the  splanchnic 
nerves,  although  the  constrictors  predominate,  and  special 
methods  have  to  be  employed  for  the  detection  of  the  dilators. 

The  same  is  true  of  the  nerves  of  the  extremities,  which  cer- 
tainly contain  vaso-dilator  fibres  in  addition  to  vaso-constrictors, 
although  the  difficulty  of  demonstrating  the  presence  of  the 
former  is  fully  as  great  as  it  is  in  the  splanchnics.  For  the 
investigation  is  complicated  by  the  fact  that  such  nerves  as 
the  sciatic  supply  with  vaso-motor  fibres  two  leading  tissues — 
skin  and  muscle  ;  and  these  are  not  necessarily  affected  in  the 
same  direction  or  to  the  same  extent  by  stimulation  of  their 
vaso-motor  fibres.  The  vaso-constrictors  under  ordinary  con- 
ditions preponderate,  so  that  section  of  the  sciatic  or  the  brachial 
is  generally  followed  by  flushing  of  the  balls  of  the  toes  and  rise 

n 


H)2  .(    MANX  AL  OF   PHYSIOLOG  ) 

of^temperature^of  the  feet,  stimulation  by  paling  and  fall  <>l 
temperature.  By  taking  advantage,  however,  ol  the  unequal 
excitability  of  dilators  and  constrictors  in  a  degenerating  nerve, 
ami  of  the  differences  between  the  two  kinds  of  fibres  in  their 
reaction  to  electrical  stimuli  (p.  159),  it  lias  been  shown  thai 
vaso-dilators  are  also  present,  and  come  to  the  front  when  the 
conditions  are  rendered  favourable  for  them  and  unfavourable 
for  the  constrictors. 

Vaso-motor  fibres  for  the  fore-limb  (dog)  issue  from  the  cord 
in  the  anterior  roots  of  the  third  to  the  eleventh  dorsal  tierves,  and 
for  the  hind-limb  in  the  anterior  roots  of  the  eleventh  dorsal  to  the 

thud  lumbar.  Stimulation  of  most  of  these  roots  causes  constric- 
tion of  the  vessels,  but  stimulation  of  the  eleventh  dorsal  may  cause 
dilatation  (Bayliss  and  Bradford). 

The  Vaso-motor  Nerves  of  Muscle. — When  the  motor  nerve  oi  the 
thin  mylo-hyoid  muscle  of  the  frog,  which  can  be  observed  under  the 
microscope,  is  cut,  and  the  peripheral  vm\  stimulated,  the  vessels  are 
seen  to  dilate  distinctly,  and  this  effect  is  not  abolished  when  con- 
traction of  the  muscle  is  prevented  by  a  dose  of  curara  insufficient 
to  paralyze  the  vaso-motor  nerves.  This  indicates  the  existence  in 
the  nerve  of  vaso-dilator  fibres.  But  we  must  be  cautious  in 
transferring  this  result  to  ordinary  skeletal  muscle,  for  the  mylo-hyoid 
is  more  closely  allied  to  the  muscles  of  the  tongue  than,  for  example, 
to  the  muscles  of  the  limbs,  and  in  the  mammal  the  tongue  muscles 
are  known  to  be  better  supplied  with  vaso-dilator  fibres  than  the 
limb  muscles.  The  average  flow  of  blood  through  a  mammalian 
muscle  is  indeed  increased  during  voluntary  contraction,  and  during 
rhythmically  repeated  artificial  tetanization  of  its  motor-nerve. 
The  outflow  of  blood  from  the  main  vein  of  the  levator  labii  superioris, 
one  of  the  muscles  used  in  feeding  in  the  horse,  was  found  to  be  in 
one  experiment  nearly  eight  times,  in  another  about  seven  times. 
and  in  a  third  three  and  a  half  times  as  great  during  voluntary  work 
with  it  (in  chewing)  as  in  rest.  But  as  no  increase  111  the  blood-flow 
through  the  skeletal  muscles  of  a  completely  curarized  mammal 
during  excitation  of  their  nerves  has  ever  been  satisfactorily  demon- 
strated, we  must  conclude  that  they  are  very  scantily  provided  with 
vaso-dilator  fibres  or  not  at  all.      It  is  uncertain   whether  they  are 

supplied  with  vaso-constrictors.    The  undoubted  increase  in  tin  hi I 

flow  in  contraction  may  therefore  be  connected  in  some  way  with  the 
mechanical  or  chemical  changes  in  the  muscular  fibres  themselves. 

It  has  been  suggested  that  the  muscular  vessels  are  widened  by 
the  direct  action  of  the  acid  products  ol  tin  active  muscle,  since 
very  dilute  acids  (lactic  acid,  e.g.)  cause  general  dilatation  of  the 
small  vessels.  A  similar  explanation  has  been  extended  to  the 
1  Ida  tat  ion  of  the  vessels  of  the  brain  during  cerebral  activity  by  some 
ol  t  hose  who  deny  the  existence  of  vaso-motor  nerves  for  thai  organ, 
but  here  the  evidence  is  by  no  means  satisfactory.  The  vagus  has 
been  stated  to  contain  vaso-constrictor,  ami  the  annul  us  oi  Vieussens 
vaso-dilator,  fibres  for  the  coronary  arteries  oi  the  heart.  Bui  this 
question  is  far  from  being  settled.     There  is  some  reason  t"  believe 

that    the    metabolic    products    liberated    m    the    heart     muscle,    and 

especially  carbon  dioxide,  govern  the  changes  in  the  calibre  ol  the 
.  oronary  arterioles.  A  .  lose  relationship  exists  between  the  output 
of  carbon  dioxide  ami  the  rate  of  tlow  through  the  coronary  circula- 
tion (I '.arc  1  oit  ami  Dixon). 


////    CIRCU1    ITION  01     THE    BLOOD    iND  LYMPH 

Vaso-motoi  Nerves  of  the  Lungs.  There  has  been  much  discussion 
as  to  the  course,  and  even  as  to  the  existence,  of  vaso-motor  fibn  . 
for  the  lungs.  The  problem  is  perhaps  the  most  difficult  in  the 
whole  range  oi  vaso-motor  topography,  for  the  pulmonary  circulation 
is  so  related  to  other  vascular  tracts,  thai  changes  produced  in  the 
vessels  of  distant  organs  bv  the  stimulation  or  section  of  nerves  may 
affect  the  quantity  of  blood  received  by  the  right  side  of  the  heart, 
and  therefore  the  quantity  propelled  through  the  lungs  and  the 
pressure  in  the  pulmonary  artery.  And  changes  in  the  systemic 
arterial  pressure  may  favour  or  hinder  the  discharge  of  the  left 
ventricle,  and  therefore  affect  the  pressure  in  the  left  auricle  and  the 
pulmonary  veins".  All  that  we  can  really  say  is  that  the  lungs  are 
probably  supplied  with  vaso-constrictor  fibres,  although  less  richly 
than  most  other  organs,  in  mammals  these  fibres  seem  to  pass  out 
from  the  upper  half  of  the  dorsal  spinal  cord,  ami  some  of  them  can  be 
detected  nearer  their  destination  in  the  annulus  of  Yieussens.*  The 
vago-sympathctic  of  the  tortoise  contains  vaso-constrictors  for  the 
lung  of  the  same  side  (Krogh). 

Vaso-dilator  Fibres. — In  most  of  the  peripheral  nerves  these 
are  mingled  with  vaso-constrictors  ;  but  in  certain  situations, 
for  an  anatomical  reason  that  will  be  mentioned  presently, 
nerves  exist  in  which  the  only  vaso-motor  fibres  are  of  the  dilator 
type.  Of  these,  the  most  conspicuous  examples  are  the  chorda 
tympani  and  the  nervi  erigentes  or  pelvic  nerves  ;  and,  indeed, 
it  was  in  the  chorda  that  vaso-dilators  were  first  discovered 
by  Bernard.  The  chorda  tympani  contains  vaso-dilator  and 
secretory  fibres  for  the  submaxillary  and  sublingual  salivary 
glands.  With  the  secretory  fibres  we  have  at  present  nothing 
to  do  ;  and  the  whole  subject  will  have  to  be  returned  to,  and 
more  fully  discussed  in  Chapter  IV.  But  a  most  marked 
vascular  change  is  produced  by  stimulation  of  the  peripheral  end 
of  the  divided  chorda  tympani  nerve.  The  glands  flush  red  ; 
more  blood  is  evidently  passing  through  their  vessels.  Allowed 
to  escape  from  a  divided  vein,  the  blood  is  seen  to  be  of  bright 
arterial  colour  and  shows  a  distinct  pulse.  The  small  arteries 
have  been  dilated  by  the  action  of  the  vaso-motor  fibres  in  the 
nerve.  The  resistance  being  thus  reduced,  the  blood  passes  in 
a  fuller  and  more  rapid  stream  through  the  capillaries  into  the 
veins,  and  on  the  way  there  is  not  time  for  it  to  become  com- 
pletely venous.  These  vaso-dilator  fibres  are  not  in  constant 
action,  for  section  of  the  nerve,  as  a  rule,  produces  little  or  no 
change.     Vaso-constrictor  fibres  pass  to  the  salivary  glands  from 

*  Brodie  and  Dixon,  perfusing  isolated  '  surviving  '  lungs  with  blood 
under  constant  pressure,  and  measuring  the  outflow,  came  to  the  conclu- 
sion that  no  pulmonary  vaso-motor  fibres  exist,  since  adrenalin  causes  no 
vaso-constriction.  They  assume  that  adrenalin  acts  upon  vaso-motor 
nerve-endings  (but  see  p.  564),  and  that  in  organs  in  which  this  drug  does 
not  produce  vaso-constriction  no  vaso-constrictor  fibres  are  present.  But 
Plunder,  working  independently  with  the  same  method,  saw  strong  con- 
striction of  the  pulmonary  vessels  under  the  influence  of  adrenalin,  and 
also  on  stimulation  of  the  annulus  of  Yieussens.  Wiggers  also  obtained 
constriction  with  adrenalin. 

II — 2 


mm  /    »/  l.xi    II    OF    /'//)  SIOLOC  \ 

the  cervical  sympathetic,  along  the  arteries,  and  stimulation  <>t 
that  nerve  causes  nai  rowing  oi  the  vessels  and  diminution  oi  the 
blood-flow,  sometimes  almosl  to  i  omplete  stoppage. 

rhe  nervi  erigentes  are  the  nerves  through  which  erection 
of  the  penis  is  caused.  When  they  are  divided  there  is  no 
effect,  but  stimulation  of  the  peripheral  end  causes  dilatation 
of  the  vessels  oi  the  erectile  tissue  of  the  organ,  whi<  h  be<  omes 
overfilled  with  blood.  During  stimulation  of  these  nerves,  the 
quantity  of  blood  flowing  from  the  cut  dorsal  vein  oi  the  penis 
may  be  fifteen  times  greater  than  in  the  absence  ol  stimulation. 
It  spurts  out  in  a  strong  stream,  and  is  brighter  than  ordinary 
venous  blood  (Eckhard).  -Stimulation  of  the  peripheral  end  of 
the  nervus  pudendus  causes  constriction  of  the  vessels  ol  the 
penis,  so  that  it  contains  vaso-constrictor  fibres  which  are  the 
antagonists  of  the  nervi  erigentes. 

Vaso-motor  Nerves  of  Veins. — Like  arteries,  veins  have  plexuses 
of  nerve-fibres  in  their  walls,  and  contract  in  response  to  various 
stimuli.  In  some  cases — e.g.,  in  the  wing  of  the  bat  -rhythmical 
contractions  of  the  veins  are  strikingly  displayed,  but  they  do 
not  depend  on  the  central  nervous  system,  as  they  persisl 
after  section  of  the  brachial  nerves.  The  first  clear  proof  of 
the  existence  of  vaso-motor  nerves  for  veins  was  furnished  by 
Mall,  who  showed  that  vaso-constrictor  fibres  for  the  portal  vein 
exist  in  the  splanchnic  nerves.  When  these  were  stimulated, 
alter  the  disturbing  effect  of  changes  in  the  circulation  through 
the  intestines  had  been  eliminated  by  compression  of  the  aorta 
in  the  thorax,  an  actual  shrinking  of  the  vein  could  be  observed. 
The  fibres  issue  from  the  spinal  cord  by  the  anterior  roots  of  the 
third  to  the  eleventh  dorsal  nerves,  but  chiefly  in  the  fifth  to  the 
ninth  dorsal.  When  the  liver  is  enclosed  in  a  plethysmograph, 
and  the  central  end  of  an  ordinary  sensory  nerve,  like  the  sciatic, 
excited,  reflex  vaso-constriction  takes  place  in  the  portal  area. 
the  volume  of  the  organ  diminishes,  and  the  blood-pressure  ri 
in  the  portal  vein  (Francois-Franck). 

The  vena  portae  and  its  branches  are  in  the  physiolo 
sense  arteries  rather  than  veins,  since  they  break  up  into  capil- 
laries, and  it  was  to  be  expected  that  the  regulation  of  the  blood- 
flow  in  them  would  be  carried  out  in  the  same  way  as  in  ordinary 
arteries,  namely,  by  means  oi  vaso-motor  nerves.  But  we  must 
not,  without  special  proof,  extend  the  results  obtained  in  the 
portal  system  to  ordinary  veins.  A  certain  amount  of  evidence, 
however,  exists  that  even  such  veins  as  those  oi  the  extremities 
are  supplied,  though  scantily,  with  vaso-(  onstri<  toi  (veno-motor) 
fibres.  After  ligation  oi  the  crural  artery  or  aorta,  stimulation 
of  the  peripheral  end  of  the  sciatic  has  been  seen  to  cause  con- 
traction of  short  portions  of  the  superficial  veins  of  the  leg. 


////    CIRCULATION  OF   llli    BLOOD    I ND  LYMPH       16$ 

Course  of  the  Vaso-motor  Nerves.  In  the  dog  the  vaso-constrii  tor  i 
pass  out  as  fine  medullated  fibres  (i*8  to  y6  n  in  diameter)  in  the 
anterior  runts  of  the  second  dorsal  t<>  about  the  second  lumbar 
nerves.  They  proceed  by  the  white  rami  communicantes  to  the 
Literal  sympathetic  ganglia,  where,  or  in  more  distal  ganglia  such 
as  the  interior  mesenteric,  they  lose  their  medulla,  and  their  axis- 
cylinder  processes  (Chap.  XII.)  break  up  into  fibrils  that  come  into 
close  relation  with  the  nerve-cells  ol  the  ganglia.  These  ganglion- 
cells  in  their  turn  send  oil  axis-cylinder  processes,  which,  enveloped 
by  a  neurilemma,  pass  as  non-medullated  fibres  by  various  routes 
to  their  final  destination,  the  unstriped  muscular  fibres  of  the  blood- 
vessels. Their  course  to  the  head  has  been  already  described.  To 
the  limbs  they  are  distributed  in  the  greal  nerves  (brachial  plexus, 
sciatic,  etc.).  which  they  reach  from  the  sympathetic  ganglia  by 
the  grey  rami  communicantes. 

'The  outflow  of  vaso-dilator  fibres  is  not  restricted  to  the  same 
portion  of  the  cord  from  which  the  outflow  of  constrictor  fibres 
takes  place.  Their  existence  is  indeed  most  easily  demonstrated  in 
nerves  springing  from  those  regions  of  the  cerebro-spinal  axis  from 
which  vaso-constrictor  fibres  do  not  arise,  and  where,  therefore,  we 
have  not  to  contend  with  the  difficulty  of  interpreting  mixed  effects. 
Vaso-dilators  for  the  external  generative  organs  and  the  mucous  mem- 
brane of  the  lower  end  of  the  rectum  pass  out  as  small  medullated 
fibres  of  the  anterior  roots  of  certain  of  the  sacral  nerves  (mainly  the 
second  and  third  in  the  cat)  into  the  pelvic  nerve  (nervus  erigens). 
They  end  in  relation  with  ganglion-cells  in  the  neighbourhood  of  the 
organs  which  they  supply.  The  seventh  and  ninth  cranial  nerves 
carry  vaso-dilator  fibres  which  are  distributed  by  way  of  the  lingual 
and  other  branches  of  the  fifth  to  the  salivary  glands,  the  tongue, 
1  he  mucous  membrane  of  the  floor  of  the  mouth,  and  part  of  the  soft 
palate.  Those  in  the  lingual,  passing  through  the  chorda  tympani.cnd 
in  ganglion-cells  near  the  submaxillary  and  sublingual  glands,  and  the 
axons  of  these  cells  continue  the  path  to  the  vessels  of  the  glands. 
It  is  supposed  that  the  vaso-dilators  distributed  in  other  branches 
of  the  fifth  also  have  ganglion-cells  on  their  course.  In  fact,  there 
is  good  evidence  that  every  efferent  vaso-motor  fibre  is  interrupted 
by  one,  and  only  by  one,  ganglion-cell  between  the  cord  and  the 
bloodvessels.  The  remarkable  statement  has  been  recently  made 
that  for  certain  regions  of  the  body,  especially  the  skin  of  the  limbs, 
the  vaso-dilator  nerves  are  contained,  not  in  the  anterior,  but  in  the 
posterior  roots.  And  these,  it  is  claimed,  are  not  aberrant  efferent  fibres 
which  have  strayed  in  the  course  of  development  into  the  wrong  roots, 
but  true  posterior  root-fibres  whose  cells  of  origin  lie  in  the  spinal 
ganglia,  and  which  conduct  efferent  vaso-dilator  impulses  in  the  wrong 
direction,  so  to  speak,  from  the  cord  to  the  periphery—'  antidromic  ' 
impulses  (Bayliss).     But  the  question  is  still  under  discussion. 

Effect  of  Nicotine  on  Nerve-cells. — A  method  which  has  been 
found  most  fruitful  in  studying  the  relations  of  sympathetic  ganglion- 
cells  to  the  vaso-motor  fibres,  as  well  as  to  the  pilo-motor*  and 
secretory  fibres  which  in  certain  situations  are  so  intricately  mingled 
with  them,  must  here  be  mentioned.  It  depends  upon  the"  fact  that 
when  a  suitable  dose  of  nicotine  (10  milligrammes  in  a  cat)  is  injected 
into  a  vein,  or  a  solution  is  painted  on  a  ganglion  with  a  brush,  the 
passage  of  nerve-impulses  through  the  ganglion  is  blocked  for  a  time 
(Langley).     The    nerve-fibres    peripheral    to    the    ganglion    are    not 

*  Pilo-motor  nerves   supply    the   smooth   director   pili   muscles,    whose 

contraction  causes  the  hair  to  '  stand  on  end.' 


i66  A   MANV  U    OF  PHYSIOLOGY 

affected.  The  question  whether  efferent  fibres  axe  connected  with 
nerve-cells  between  a  given  point  and  their  peripheral  distribution 
can.  therefore,  be  answered  by  observing  whether  any  effect  <>t  stimu- 
lation ia  abolished  by  meet  me.  If.  for  instance,  the  excitation 
nerve  caused  constriction  of  certain  bloodvessels  bet., re.  and  lias  ao 
effect  after,  the  application  of  nicotine  to  a  ganglion,  its  vaso-con- 
strictor  fibres,  or  some  ol  them,  must  be  connected  with  nerve 
in  that  ganglion.  Langley  lias  recently  brought  forward  evidence 
that  many  of  the  bodies  which  are  commonly  supposed  to  at  t  upon 
nerve-endings  (as  nicotine,  curara,  atropine,  pilocarpine,  adrenalin, 
etc.)  really  act  upon  'receptive'  substances  ,>t  tin  cells  in  connec- 
tion with  which  the  nerve-fibres  end.  These  receptive  substances 
are  conceived  to  be  capable  of  being  specincallv  affected  by  chemical 
bodies  and  by  nervous  stimuli,  and  in  their  turn  to  be  capable  of 
influencing  the  metabolism  of  the  main  cell  substance  on  which  its 
function  depends.  The  receptive  substances  thus  form  beyond  the 
histological  link  of  the  nerve-ending  a  kind  of  chemical  link  between 
the  nerve-fibre  and  the  cell  which  it  supplies. 

We  have  thus  traced  the  vaso-motor  nerves  from  the  cerebro- 
spinal axis  to  the  bloodvessels  which  they  control  ;  it  still  remains 
to  define  the  portion  of  the  central  nervous  system  to  w  hich  these 
scattered  threads  are  related,  which  holds  them  in  its  hand  and 
acts  upon  them  as  the  needs  of  the  organism  may  require. 

Vaso-motor  Centres. — Now.  experiment  has  shown  that  there 
is  one  very  definite  region  of  the  spinal  bulb  which  has  a  most 
intimate  relation  to  the  vaso-motor  nerves.  If  while  the  blood- 
pressure  in  the  carotid  is  being  registered,  say.  in  a  curarized 
rabbit,  the  central  end  of  a  peripheral  nerve  like  the  sciatic 
is  stimulated,  the  pressure  rises  so  long  as  the  bulb  is  intact. 
this  rise  being  largelv  due  to  the  reflex  constriction  of  the  vessels 
in  the  splanchnic  area.  If  a  series  of  transverse  sections  be  made 
through  the  brain,  the  rise  of  pressure  caused  by  stimulation  of 
the  sciatic  is  not  affected  till  the  upper  limit  of  the  bulb  is  almost 
reached.  If  the  slicing  is  still  carried  downwards,  the  blood- 
pressure  sinks,  and  the  rise  following  stimulation  of  the  sciatic 
becomes  less  and  less.  When  the  medulla  has  been  cut  away  to 
a  certain  level,  only  an  insignificant  rise  or  none  at  all  can  be 
obtained.  The  portion  of  the  medulla  the  removal  of  which 
exerts  an  influence  on  the  blood-] >ressmv.  and  its  increase  by 
reflex  stimulation,  extends  from  a  level  4  to  5  mm.  above  the 
point  of  the  calamus  scriptorius  to  within  1  to  _'  mm.  of  the 
corpora  quadrigemina.  Stimulation  of  the  medulla  causes  a 
rise,  destruction  of  this  portion  0!  it  a  severe  fall,  of  general 
blood-pressure.  There  is  evidently  in  this  region  a  nervous 
'centre'  so  intimately  related,  it  not  to  all  the  vaso-motor 
nerves,  at  least  to  such  very  important  tracts  as  to  deserve  the 
name  of  a  vaso-motor  centre.  Experimenl  lias  shown  that  this 
is  much  the  most  influential  centre,  and  it  is  usually  called  the 
chief   or   general    vaso-motor   centre.     Some    writers    prefer    to 


THE   <  TRCU1   tTTON  OF  THl    BLOOD  AND  LYMPH      167 

speak  of  it  as  the  vaso-constrictor  centre,  since  it  is  undoubtedly 
connected  with  most  or  all  of  the  vaso-constrictor  paths,  and 
has  nol  been  shown  to  be  similarly  connected  with  the  vaso- 
dilator paths.  There  is,  indeed,  not  the  same  solid  evidence  for 
the  existence  of  a  general  vaso-dilator  centre  in  the  bulb  as  for 
the  existence  of  the  general  vaso-constrictor  centre.  Yet  there 
are  facts  which  indicate  that  the  bulbar  vaso-motor  centre  or 
centres,  when  reflexly  stimulated,  can,  and  often  do,  respond  not 
merely  by  an  increase  or  a  remission  of  vaso-constrictor  tone, 
but  by  a  simultaneous  inhibition  of  vaso-constrictor  fibres  and 
excitation  of  vaso-dilators  leading  to  a  fall  of  pressure,  or  by  a 
simultaneous  inhibition  of  vaso-dilators  and  excitation  of  vaso- 
constrictors leading  to  a  rise  of  pressure. 

The  spinal  cells  of  origin  of  the  pre-ganglionic  segments  of  the 
vaso-constrictor  paths  constitute  subordinate  centres  which 
either  normally  support  a  certain  degree  of  vascular  tone,  or 
come  to  do  so  after  the  chief  vaso-motor  centre  has  been  cut  off. 
Thus,  in  the  frog  it  is  possible  to  go  on  destroying  more  and 
more  of  the  cord  from  above  downwards,  and  still  to  obtain 
reflex  vaso-motor  effects,  as  seen  in  the  vessels  of  the  web,  by 
stimulating  the  central  end  of  the  sciatic  nerve.  Although  these 
effects  indeed  diminish  in  amount  as  the  destruction  of  the  cord 
proceeds,  yet  a  distinct  change  can  be  caused  when  only  a  small 
portion  of  the  cord  remains  intact. 

.similarly,  in  the  mammal  evidence  has  been  obtained  of  the 
existence  of  '  centres  '  at  various  levels  of  the  cord,  capable  of 
acting  eventually,  if  not  at  once,  as  vaso-constrictor  centres  after 
the  loss  of  the  controlling  influence  of  the  bulb.  The  best  example 
of  a  vaso-dilator  centre  is  that  situated  in  the  lumbar  cord,  which 
controls  the  erection  of  the  penis.  After  total  section  of  the  cord 
at  the  upper  limit  of  the  lumbar  region,  erection,  which  is  known 
to  be  due  to  a  reflex  dilatation  of  the  arteries  of  the  organ  through 
the  nervi  erigentes,  can  still  be  caused  (in  dogs)  by  mechanical 
stimulation  of  the  glans  penis,  so  long  as  the  afferent  fibres  of  the 
reflex  arc  contained  in  the  nervus  pudendus  are  intact.  Destruc- 
tion of  the  lumbar  cord  abolishes  the  effect.  It  is  impossible  to 
avoid  the  conclusion  that  a  vaso-dilator  or  erection  centre, 
which  is  in  relation  on  the  one  hand  with  the  nervi  erigentes,  and 
on  the  other  with  the  nervus  pudendus,  exists  in  the  lower 
portion  of  the  spinal  cord.  Vaso-motor  centres  for  the  hind- 
limbs  have  also  been  located  in  the  same  region.  When  the  brain, 
the  bulb,  and  the  upper  portion  of  the  cord  have  been  eliminated 
by  ligation  of  all  the  arteries  from  which  blood  can  possibly 
reach  them,  a  sufficient  vascular  pressure  persists  to  permit  the 
circulation  to  go  on  in  the  lower  portion  of  the  body  for  hours. 
And  while  section — or  freezing  (Fig.  68) — of  the  cord  in  the  lower 


A   MANUA1    OF  PHYSIOLOGY 


cervical  region  causes  a  marked  fall  of  pressure,  this  i-  not  per- 
manent if  the  animal  is  allowed  to  survive.  Forty-one  days  after 
total  section  of  the  cord  al  the  seventh  cervical  segmenl  in  a  dog 
an  arterial  pressure  of  130  mm.  of  mercury  was  found.  A 
mechanism  for  the  maintenance  of  vascular  tone  exists  even 
beyond  the  limits  of  the  central  nervous  system.  Forwhen  the 
lower  portion  of  the  cord  is  completely  destroyed,  the  dilatation 
of  the  vessels  of  the  hind-limbs,  which  is  at  firsl  so  conspicuous, 
passes  away  after  a  time,  the  functions  of  vaso-motor  centre- 
having  perhaps  been  assumed  by  the  sympathetic  ganglia  (Goltz 
and  Ewald).  When  the  lumbo-sacral  sympathetic  chain  is  extir- 
pated, there  is  a  further  loss  of  vascular  tone  in  the  affected  regi<  »n. 
But  even  this  is  not  irremediable.  After  a  time  recovery  again 
occurs,  although  it  may  be  more  partial  and  tardy  than  before. 
This  mav  take  place  either  through  the  intervention  of  still  more 


^W*/*i 


^^^^fc^'li''*****'^ 


Fig.  68. — Effect  on  Blood-pressure  in  Dor.  of  Freezing  Spinal  (  1 

(Piki  ■). 

At  1  the  first  or  second  dorsal  segment  of  the  cord  was  frozen  with  liquid  air  ;  at 
2  and  3  central  end  of  sciatic  stimulated  without  effect  on  pit  -  '\\  ely  one 

and  a  half  and  three  minutes  after  freezing  of  cord).     (Four-fifths  of  original  - 

peripheral  ganglia,  or  through  the  development  of  a  certain  tonu-bv 
the  muscular  fibres  of  the  vessels  when  abandoned  to  themseh  es. 
As  to  the  nature  of  the  tone  of  the  general  vaso-motor  centre, 
the  same  question  may  be  asked  which  has  been  already  discussed 
for  the  cardio-inhibitory  centre.  Is  it  reflex,  or  does  it  depend 
upon  direct  excitation  of  the  centre  by  some  constituent  oi  the 
blood  or  lymph,  or  some  substance  produced  in  the  <  entre  itself  ? 
The  best  answer  which  can  at  present  be  made  is  that  a  constant 
central  excitation  by  the  carbon  dioxide  formed  in  the  centre  or 
circulating  in  the  blood  is  a  not  unimportant  factor  in  the  main- 
tenance of  the  vaso-motor  tone.  A  marked  diminution  in  the 
carbon  dioxide  tension  of  the  blood,  a  condition  which  is  termed 
'acapnia,'  may  indeed  contribute  to  the  severe  fall  oi  Mood- 
pressure  associated  with  surgical  shock  (p.  175)  (Henderson).  In 
addition  to  the  direct  influence  of  carbon  dioxide,  and  possibly  of 
other  substances,  the  arrival  of  afferent  impulses  at  the  centre 
seems  to  play  a  part  in  maintaining  that  continual  discharge 


////    CIRCU1   \TION  01     l/ll    BLOOD  AND  LYMPH 

i>\  efferent  impulses  along  the  vaso-motor  nerves  which  consti- 
tutes its  tone.  In  this  regard,  the  vaso-motor  centre  occupies 
an  intermediate  position  between  the;  respiratory  centre,  the 
most  purely  automatic,  and  the  cardio-inhibitory  centre,  tin- 
most  purely  reflex  of  the  three  great  bulbar  mechanisms. 

(if  the  anatomical  relations  of  the  nerve-cells  that  make  up  the 
bulbar  and  spinal  vaso-motor  centres,  little  more  is  known  than  may- 
be deduced  from  the  physiological  facts  we  have  been  reciting.  It 
has  been  surmised  on  histological  grounds  that  certain  cells  of  small 
size  scattered  up  and  down  the  thoracic  and  upper  lumbar  regions 
of  the  cord  in  the  lateral  horn  (intcrmedio-lateral  tract),  and  perhaps 
cropping  out  also  in  the  bulb,  are  vaso-motor  cells.  There  is  good 
evidence  that  the  pre-ganglionic  sympathetic  fibres,  including  the 
vaso-motor  fibres  which  we  have  already  discovered  emerging  from 
the  cord  in  the  spinal  roots,  arc  connected  with  these  cells.  And. 
indeed,  there  is  reason  to  believe  that  the  connection  is  made  with- 
out the  intervention  of  any  other  nerve-cells,  and  that  the  axis- 
cylinders  of  these  vaso-motor  fibres  are  the  axis-cylinder  processes  of 
the  vaso-motor  cells.  So  that  the  simplest  efferent  path  along  which 
vaso-motor  impulses  can  pass  may  be  considered  as  built  up  of  two 
neurons,  one  with  its  cell-body  in  the  cord,  and  the  other  in  a 
sympathetic  ganglion.  Less  is  known  of  the  elements  which  con- 
stitute the  bulbar  centre  and  of  their  connections.  But  since  it 
would  appear  that  the  spinal  vaso-motor  centres  are  under  the  con- 
trol of  the  chief  centre  in  the  bulb,  it  is  necessary  to  suppose  that 
the  axis-cylinder  processes  of  some  of  the  cells  of  the  bulbar  centre 
come  into  relation  with  the  spinal  vaso-motor  cells,  and  that  im- 
pulses passing,  let  us  say,  from  the  bulb  to  the  vessels  of  the  leg, 
would  have  to  traverse  three  neurons  (see  Chap.  XII.). 

Vaso-motor  Reflexes. — We  have  already  seen  that  the  cardiac 
centres  are  constantly  influenced  by  afferent  impulses,  and  that 
in  the  direction  either  of  augmentation  or  inhibition.  The  vaso- 
motor centre  in  the  bulb  is  equally  sensitive  to  such  impulses. 
They  reach  it  for  the  most  part  along  the  same  nerves,  and  by 
increasing  or  diminishing  its  tone  cause  sometimes  constriction 
and  sometimes  dilatation  of  the  vessels,  the  result  depending 
partly  upon  the  anatomical  connection  of  the  afferent  fibres,  but 
apparently  in  part  also  upon  the  state  of  the  centre. 

Of  the  afferent  nerves  that  cause  vaso-dilatation,  the  most 
important  is  the  depressor,  whose  reflex  inhibitory  action  on 
the  heart  has  been  already  described.  The  fall  in  the  arterial 
pressure  is  due  chiefly,  not  to  the  inhibition  of  the  heart,  but  to 
inhibition  of  the  vaso-constrictor  tone  of  the  bulbar  vaso-motor 
centre,  combined  with  stimulation  of  vaso-dilator  nerves,  and 
consequent  general  dilatation  of  the  arterioles  throughout  the 
hod}r.  That  the  depressor  action  involves  excitation  of  vaso- 
dilators follows  from  the  fact  that  vaso-dilatation  occurs  in  the 
limbs  on  stimulation  of  the  depressor  after  their  vaso-constrictor 
nerves  have  been  cut.  Stimulation  of  the  depressor  produces  its 
usual  result  after  section  of  the  vagi.     It  has  been  suggested  that 


i  7<  i 


A   M  INV  U    OF  PHYSIOLOG  V 


the  function  of  the  nerve  is  to  a<  I  as  an  automatic  check  upon 
the  blood-pressure  in  the  interest  both  of  the  heart  and  the  vessels, 

its   terminations   in    the   aorta    or   the   ventricular   wall    being 
mechanically  stimulated  when  the  pressure  tends  to  rise  towards 

the  danger  limit.     In  rare  rases,  efferent  inhibitory  fibres  tor  the 
heart  have  been  found  in  the  depressor  of  the  rabbit. 

Manx   of  the  peripheral  nerves  contain  fibres  whose  stimula- 
tion   is    followed    by    dilatation    of    the    bloodvessels     m     Special 

regions,  usually  the  areas  to  which  they  are  themselves  dis- 
tributed,  accompanied   by  constriction  of  distant    and,   it   may 


Fig.  69. — Diagram  of  De- 
pr]  -sun  Nerve  in  Rab- 


X.  vagus  :  SL,  superior 
laryngeal  branch  of  vagus  : 
1 ).  depressor  fibres.  The 
arrows  show  the  course  ol 
the  impulses  that  affect  the 
M l-pressure. 


Fig.    70. — Blood-pressur]     Tracing: 
(Mercury  M  inomi  i  i:k). 

Central  end   of    depressor    stimulated    at 
stimulation  stopped  at  2.     Time-trace,  seconds. 


be,  more  extensive  vascular  tracts.  Thus,  the  usual  local  eftect 
of  stimulating  the  afferent  fibres  of  the  lowesl  three  thoi 
nerves,  in  whose  anterior  roots  run  the  vaso-motor  fibres  for 
the  kidney,  is  a  dilatation  of  the  renal  vessels  (Bradford),  and 
the  usual  local  effect  of  stimulating  the  infra-orbital  or  supra- 
orbital nerve  a  dilatation  of  the  external  maxillary  artery. 
But  the  general  effect  in  both  cases  is  vaso-constriction  in  other 
regions  of  the  body,  which  more  than  compensates  the  local  dila- 
tation, so  that  the  arterial  blood-pressure  rises.  It  i^  not  difficult 
to  see  that  both  of  these  changes  render  it  easier  for  the  part  to 
obtain  an  increased  supply  of  blood. 

Sometimes  the  reciprocal  relation  between  vaso-dilatation  in  one 
part  of  the  body  and  vaso-constriction  in  another  is  only  apparent. 
For  example,  stimulation  of  the  cut  end  of  the  sciatic  causes,  as  we 
have  already  seen,  extensive  vaso-constriction  and  a  notable  rise  in 
the  blood-pressure.    The  constriction  certainly  involves  the  splanch- 


////    CIRCU1    \TIOh    OF   /III    BLOOD  AND  LYMPH        171 

11  ii-  area  :  hut  superficial  parts,  as  the  lips,  may  he  seen  to  be  flushed 
with  blood       In  asphyxia,  when  the  vaso-motor  centres  are  directs 

stimulated  l>v  the  venous  M I.  tins  apparenl  antagonism  is  slill 

better  marked:  the  cutaneous  vessels  are  widely  dilated  and 
engorged,  the  face  is  livid,  bu1  the  abdominal  organs  are  pale  and 
bloodless  (Heidenhain) .  The  blood-pressure  rises  rapidly,  reaches 
a  maximum,  and  then  gradually  falls  as  the  vasomotor  centre 
becomes  paralyzed  (Figs.  72  and  73).  It  haabeen  shown  that  in  both 
cases  vaso  constriction  <>i  the  skin  is  really  produced  as  well  as  vaso- 
constriction <il  the  internal  organs,  but  the  increased  blood-pressure 
mechanically  overcomes  the  constriction  of  the  cutaneous  vessels. 

The  kind  of  stimulus  seems  to  have  something  to  do  with  the 
direction  of  the  reflex  vaso-motor  change.  For  while  electrical 
stimulation  of  every  muscular  nerve,  even  of  the  very  finest 
twigs   that    can    be    isolated   and   laid   on   electrodes,    provokes 


Fie,.  71. — Pressor  Effect  of  Stimulation-   of  Central  End  of  Vagus  in   a 
Cat  during  Resuscitation  after  Cerebral  Anaemia. 

The  depressions  in  the  signal  line  ABC  indicate  the  duration  of  three  successive 
excitations  of  equal  strength,  sixty-five,  seventy-three,  and  seventy-nine  minutes 
respectively  after  restoration  of  the  circulation.  The  pressor  effect  increases  as 
resuscitation  proceeds.  Later  on  the  original  depressor  effect  was  again  obtained. 
The  upper  tracing  is  that  of  the  artificial  respiration.      (Two-thirds  original  size.) 

alwavs,  whether  the  shocks  follow  each  other  rapidly  or  slowly, 
a  rise  of  general  blood-pressure,  mechanical  stimulation  of  a 
muscle,  as  by  kneading  or  massage,  causes  a  fall.  The  condi- 
tion of  the  afferent  fibres  also  exerts  an  influence.  For  example, 
excitation  of  the  central  end  of  a  sciatic  nerve  that  has  been 
cooled  is  followed  by  vaso-dilatation  and  fall  of  pressure,  the 
opposite  of  the  ordinary  result.  These  and  similar  facts  have 
led  to  the  idea  that  most  afferent  nerves  contain  two  kinds  of 
fibres,  whose  stimulation  can  affect  the  activity  of  the  vaso- 
motor centres — '  reflex  vaso-constrictor,'  or  '  pressor  '  fibres,  and 
'  reflex  vaso-dilator,'  or  '  depressor  '  fibres.  The  branch  of  the 
vagus,  however,  to  which  the  name  '  depressor  '  has  been  specially 
given,  is  usually  described  as  the  only  peripheral  nerve  the  ex- 
citation of  which  is  in  all  circumstances  followed  by  a  general 


172  A  MANUAL  01    PHYSIOLOGY 

diminution  of  arterial  pressure.  But  this  is  not  strictly  correct, 
for  at  an  early  period  in  the  resuscitation  of  the  brain  after  anaemia 
excitation  of  the  rabbit's  '  depressor  '  causes  a  slight  rise  of 
pressure  not  followed  by  any  fall.  This,  perhaps,  indicates  the 
presence  in  the  '  depressor  '  of  a  small  number  of  pressor  ftl 
which  are  resuscitated  sooner  than  the  depressor  fibres  proper. 
The  same  phenomenon,  only  more  marked,  may  he  seen  when 
the  central  end  of  the  cat's  vagus,  containing  the  depressor 
fibres,  is  excited  at  intervals  during  resuscitation  (Fig.  71). 
Or  the  result  may  depend  upon  a  change  in  the  response  of  the 
altered  vaso-motor  centres  to  impulses  reaching  them  along  the 
depressor  fibres.  If  specific  'depressor'  fibres  exist  in  other 
nerves,  they  are  so  mingled  with  '  pressor  '  fibres  that  their  action 
is  masked  when  both  are  stimulated  together.     Th<  E  the 


Fig.  72. — Rise  of  Blood-pressure  in  Asphyxia  :   Rabbit. 

Respiration  stopped  at  1.      Interval  between  2  and  3  c  nds. 

during  whirh  the  blood-pressure  steadily  rose.    AtJ4,|respiration  r<  Time 

trace,  seconds. 

-motor  centre  is  unquestionably  a  factor  which  has  some 
importance  in  determining  the  result  of  reflex  v  t-<  i-mi  'tor  stimula- 
tion. For  instance,  in  an  animal  deeply  anaesthetized  with 
chloroform  or  chloral,  excitation  of  pressor  fibres  (in  an  ordinary 
sensory  nerve)  causes,  not  a  rise,  but  a  fall  of  blood-pressure; 
while  in  an  animal  fully  under  the  influence  of  strychnine  stimula- 
tion of  the  depressor  nerve  causes  not  a  fall,  but  a  r- 

These  facts  enable  us  to  some  extent  to  understand  the  manner 
in  which  the  distribution  of  the  blood  is  adjusted  to  the  require- 
ments of  the  different  parts  of  the  body,  so  that  to  a  certain 
degree  of  approximation  no  organ  has  too  much,  and  none  too 
little.  The  blood-supply  of  the  organs  is  always  shifting  with 
the  calls  upon  them.  Now,  it  is  the  actively-digesting  stomach 
and  the  actively-secreting  glands  of  the  alimentary  tract  which 
must  be  fed  with  a  full  stream  of  blood,  to  supply  waste  and  to 


Till    CIRCU1    \TION  OB    THE   BLOOD  AND  LYMPH       173 

carry  away  absorbed  nutriment.  Again,  it  is  the  working 
muscles  oi  the  legs  or  of  the  .inns  thai  need  the  chiel  blood- 
supply.  But  wherever  the  call  may  be,  the  vaso-motor  mechan- 
ism is  able,  in  health,  to  answer  it  by  bringing  aboul  a  widening 
oi  the  small  arteries  of  the  part  which  needs  more  blood,  and  a 
compensatory  narrowing  of  the  vessels  of  other  parts  whose 
needs  are  not  so  great. 

The  amount  of  blood  flowing  through  an  organ  in  a  given  time  is 
not,  of  course,  proportional  to  the  quantity  contained  in  it  at  any 
moment.  For  it  depends  also  upon  the  velocity  of  the  blood-stream, 
and  the  blood  flows  at  a  different  rate  in  different  organs  and  in  the 
same  organ  at  different  times.  The  flow  for  100  grammes  of  organ- 
substance  per  minute  under  certain  conditions  has  been  determined 
l>v  observations  with  the  stromuhr  in  dogs  as  follows  :  Posterior 
extremity,  5  c.c.  ;  skeletal  muscles,  12  c.c.  ;  head,  20  c.c.  ;  intestine, 
31  c.c.  ;  spleen,  58  c.c.  ;  brain,  136  c.c.  ;  kidney,  150  c.c.  ;  thyroid 
gland,  560  c.c.  (Opitz,  etc.). 

It  is  also  through  the  vaso-motor  system,  and  especially  by 
the  action  of  that  portion  of  it  which  governs  the  abdominal 
vessels,  and  of  the  nerves  that  regulate  the  work  of  the  heart, 
that  in  animals  to  which  the  upright  position  is  normal  (monkey) 
and  in  man  the  influence  of  changes  of  posture  on  the  circu- 
lation is  almost  completely  compensated.*  The  pressure  in  the 
upper  part  of  the  human  brachial  artery  has  been  measured  with 
a  sphygmomanometer,  first  in  the  horizontal  and  then  im- 
mediately afterwards  in  the  standing  posture,  and  in  health  it 
has  been  found  to  remain  practically  unchanged  (Hill).  But  if 
the  person  was  overworked  or  out  of  sorts,  the  compensation 
was  less  complete.  It  is  well  known  that  in  debilitated  persons, 
especially  if  long  confined  to  bed,  the  sudden  assumption  of  the 
upright  position  may  cause  vertigo,  and  even  syncope,  the  normal 
compensatory  mechanism  being  deranged.  In  such  animals  as 
the  rabbit  this  compensation  is  totally  inefficient.  When  a 
domesticated  rabbit,  which  has  been  kept  in  a  hutch,  is  sus- 

*  Two  factors  may  be  distinguished  in  the  blood-pressure,  the  hydro- 
static and  the  hydrodynamic  elements.  The  hydrostatic  portion  of  the 
pressure  is  due  to  the  weight  of  the  column  of  blood  acting  on  the  vessel  ; 
the  hydrodynamic  portion  of  the  pressure  is  due  to  the  work  of  the  heart. 
If  a  dog  be  securely  fastened  to  a  holder  arranged  in  such  a  way  that  the 
animal  can  be  placed  vertically,  with  the  head  up  or  down,  and  the  mean 
blood-pressure  in  the  crural  artery  be  measured  in  the  two  positions,  there 
will  be  a  considerable  difference.  For  when  the  legs  are  uppermost  the 
heart  has  to  overcome  the  weight  of  the  column  of  blood  rising  above  it 
to  the  crural  artery  ;  when  the  head  is  uppermost  the  action  of  the  heart 
is  reinforced  by  the  weight  of  the  blood.  And  if  no  change  were  produced 
in  the  action  of  the  heart,  or  in  the  general  resistance  of  the  vascular  path, 
by  the  change  of  position,  this  diflerence  would  be  equal  to  the  pressure 
of  a  column  of  blood  twice  as  high  as  the  straig!  t-line  distance  between 
the  cannula  and  the  point  of  the  arterial  system  at  which  the  pressure  is 
the  same  with  head  up  as  with  head  down  (indifferent  point). 


i/4  '    W  INI    II    OF   PHYSIOl  OG  ) 

pended  vertically  with  the  feel  down,  the  blood  drains  into  the 
abdominal  vessels,  syncope  speedily  ensues,  and  in  a  period  that 
ranges  from  less  than  a  quarter  to  three-quarters  ol  an  houi  the 
animal  dies  in  the  convulsions  of  acute  cerebral  ansmia  (Salathe\ 
Hill).  The  head-down  position  lias  no  ill  effects.  In  wild  rabbits, 
whose  abdominal  wall  is  more  tense  and  clastic,  these  fatal  symp- 
toms are  not  easily  produced,  and  the  same  is  true  ol  cats  and 
dogs.  But  in  all  animals,  when  the  compensation  is  destroyed, 
as  in  paralysis  ol  the  vaso-motor  centre  by  chloroform,  the  i  ir- 
culation  may  be  profoundly  influenced  by  the  position  ol  tin- 
body:  elevation  ol  the  head  may  had  to  cerebral  anaemia, 
syncope,  and  even  death  ;  elevation  of  the  legs,  and  parti*  nlarly 
the  abdomen,  may  restore  the  sinking  pulse  by  filling  the  heart 
and  the  vessels  of  the  brain.  It  a  chloralized  dog  be  fastened 
on  a  board  which  can  be  rotated  about  a  horizontal  axis  passing 
under  the  neck,  the  blood-pressure  in  the  carotid  artery  falls 
greatly  when  the  animal  is  made  to  assume  the  vertical  position 
with  the  head  up,  and  either  rises  a  little  or  remains  practically 
unchanged  when  the  head  is  made  to  hang  down.  So  great  may 
the  fall  of  pressure  be  in  the  former  position  that  death  may 
occur  if  it  be  long  maintained  (Practical  Exercises,  p.  199). 

Finally,  it  is  in  virtue  of  the  amazing  power  of  accommoda- 
tion possessed  by  the  vascular  system,  as  controlled  by  the 
vaso-motor  and  cardiac  nerves,  that  so  long  as  these  are  not 
disabled  the  total  quantity  of  blood  may  be  greatly  diminished 
or  greatly  increased,  without  endangering  life,  or  even  causing 
more  than  a  transient  alteration  in  the  arterial  pressure.  It  is 
not  until  at  least  a  quarter  of  the  blood  has  been  withdrawn 
that  there  is  any  notable  effect  on  the  pressure,  for  the  loss  is 
quickly  compensated  by  an  increase  in  the  activity  ol  the  heart 
and  a  constriction  of  the  small  arteries.  An  animal  may  recover 
after  losing  considerably  more  than  half  its  blood.*  Conversely, 
the  volume  of  the  circulating  liquid  may  be  doubled  by  the 
injection  of  blood  or  physiological  salt  solution  without  causing 
death,  and  increased  by  50  per  cent,  without  any  marked  in- 
crease in  the  pressure.  The  excess  is  promptly  stowed  away 
in  the  dilated  vessels,  especially  those  of  the  splanchnic  ar< 
the  water  passes  rapidly  into  the  lymph,  and  is  then  more 
gradually  eliminated  by  the  kidneys. 

From  these  facts  we  can  deduce  the  practical  lesson,  that  blood- 
letting, unless  fairly  copious,  is  useless  as  a  means  ot   lowering 

*  It  is  not  usually  possible  t<>  obtain  quite  two-thirds  oi  the  total  blood 
by  bleeding  a  dog  from  a  large  artery.  In  seven  dogs  bled  from  the  carotid 
in  the  laboratory  of  the  writer,  the  ratio  of  the  weight  ol  the  blood  obtained 
to  the  body  weight  was  1  :  24*7,  1  :  21*7,  '  :  -'"'7.  '  ;  -  '''•  '  :  ''', 

1  :  1 3-5 .  In  the  last  case,  the  blood  clotted  with  abnormal  slowness,  and 
the  animal  died  in  a  few  minutes. 


Till    (  //,•(  'I    ITION  "I     I  HI    BLOOD  AND  LYMPH        17- 


the  genera]  arterial  pressure,  while  it  need  nol  be  feared  thai 
transfusion  oi  .1  siderable  quantity  oi  blood,  or  oi  sail  solu- 
tion, in  cases  "t  severe  haemorrhage  will  dangerously  incn 
the  pressure.  And  from  the  physiological  point  oi  view  the 
term  '  haemorrhage  '  includes  more  than  it  does  in  its  ordinary 
sense.  For  as  dirt  to  the  sanitarian  is  '  matter  in  the  wrong 
place,'  haemorrhage  to  the  physiologist  is  blood  in  the  wrong 
place.  Not  a  drop  of  blood  may  be  lost  from  the  body,  and  yet 
death  may  occur  from  haemorrhage  into  the  pleural  or  the 
abdominal  cavity,  into  the  stomach  or  intestines.  Not  only  so, 
but  a  man  may  bleed  to  death  into  his  own  bloodvessels  ;  in 
surgical  shock,  as  well  as  in  ordinary  fainting  or  syncope,  the 
blood  which  ought  to  be  circulating  through  the  brain,  heart  and 
lungs  may  stagnate  in  the  dilated  vessels  of  the  splanchnic  and 


^mmm^ 


n\\\ 


«— « 


1  1  ■  1  1  1  1  1  i  1  1  1  1  1  1  1  1  1  I  1  1  1  1  I  1  t  1  1  1  1  1  1  1  1  1  1 1  1 1  1  1 1 1H1  1  t  1  11 


Second* 
Fig.    73- 


Blood-pressure  Tracing  from  a  Dog  poisoned 
with  Alcohol. 


The  respiratory  centre  being  paralyzed,  respiration  stopped,  and 
the  typical  rise  of  blood-pressure  in  asphyxia  took  place.  The  pres- 
sure had  again  fallen,  and  total  paralysis  of  the  vaso-motor  centre 
was  near  at  hand,  when  at  A  the  animal  made  a  single  respiratory  movement. 
The  quantity  i  if  oxygen  thus  taken  in  was  enough  to  restore  the  vaso-motor  centre, 
and  the  blood-pressure  again  rose.  This  was  repeated  five  or  six  times.  (Three - 
fourths  original  size.) 


other  areas.  The  rapid  feeble  pulse  in  shock  is  due  to  a  similar 
loss  of  activity  of  the  cardio-inhibitory  centre.  The  cause  of  the 
vascular  symptoms  of  surgical  shock  is  by  no  means  clear,  and 
is  probably  complex.  Some  observers  have  laid  stress  upon  the 
supposed  effect  of  excessive  stimulation  of  afferent  nerves  in 
producing  long-continued  inhibition  or  fatigue  of  the  vaso-motor 
centres.  In  favour  of  this  hypothesis  is  the  fact  that  in  experi- 
mental shock  in  animals  the  rise  of  blood- pressure  which  can  be 
obtained  by  stimulation  of  a  nerve  like  the  sciatic  is  not  so  great 
as  under  normal  conditions  (Crile,  Howell).  As  alreadv  men- 
tioned (p.  169),  a  diminution  of  the  carbon  dioxide  pressure  in 
the  blood  occasioned  by  increased  pulmonary  ventilation  due  to  the 
excitation  of  afferent  nerves,  or  in  the  case  of  abdominal  opera- 
tions or  wounds  by  the  direct  escape  of  carbon  dioxide  through 
the  peritoneum,  has  also  been  suggested  as  an  important  factor. 


i7"  A    M.IM    //.  OF    PHI  SIOLOG\ 

The  Lymphatic  Circulation.  \s  has  already  been  itated,  ome 
"i  the  constituents  oi  the  blood,  instead  oi  passing  back  to 
the  heart  from  the  capillaries  along  the  veins,  find  their  ■  >v  by 
a  much  more  tedious  route  along  the  lymphatics.  The  blood- 
capillaries  .hi  everywhere  in  very  intimate  relation  with  lymph- 
capillaries,  which,  completely  lined  with  epithelioid  cells,  h<-  in 
irregular  spaces  in  the  connective-tissue  that  everywhere  accom- 
panies and  supports  the  bloodvessels.  The  constituents  oi  the 
blood-plasma  are  filtered  through,  or  secreted  by  the  capillary  walls 
into  these  lymph  spaces,  and  mingling  there  with  waste  products 
discharged  i>y  the  cells  oi  the  tissues,  term  the  liquid  known  as 
tissue  liquid  or  tissue  lymph.  From  the  tissue  liquid  the  lymph 
capillaries  take  up  the  constituents  of  the  '  lymphatic  '  lymph, 
which  then  passes  into  larger  lymphatic  vessels,  with  lymphatic 
glands  at  intervals  on  their  course.  These  fall  into  still  larger 
trunks,  and  finally  the  greater  part  of  the  lymph  reaches  the  blood 
again  by  the  thoracic  duct,  which  opens  into  the  venous  system  at 
the  junction  of  the  left  subclavian  and  intern. d  jugular  veins.  The 
lymph  from  the  right  side  of  the  head  and  neck,  the  right  extremity, 
and  the  right  side  of  the  thorax,  with  its  viscera,  is  collected  l>v  t he 
right  lymphatic  duct,  which  opens  at  the  junction  oi  the  right  sub- 
clavian and  internal  jugular  veins.  The  openings  oi  both  duets  are 
guarded  by  semilunar  valves,  which  prevent  the  reflux  of  blood  from 
the  veins.  Serous  cavities  like  the  pleural  sacs,  although  differing 
from  ordinary  lymph  spaces,  are  connected  through  small  openings, 
called  stomata,  with  lymphatic  vessels. 

The  rate  of  flow  of  the  lymph  in  the  thoracic  duct  is  very  small 
compared  with  that  of  the  blood  in  the  arteries — only  about  4  mm. 
per  second,  according  to  one  observer.  Nevertheless,  a  substance 
injected  into  the  blood  can  be  detected  in  the  lymph  of  the  duct  in 
four  to  seven  minutes  (Tschirwinsky).  The  factors  which  contribute 
to  the  maintenance  of  the  lymph  flow  are  : 

(1)  The  pressure  under  which  it  passes  from  the  blood  capillaries 
into  the  lvmph  spaces  and  from  the  lvmph  spaces  into  the  lymph 
capillaries.  The  pressure  in  the  thoracic  duct  of  a  horse  may  be  as 
high  as  12  mm.  of  mercury  ;  in  the  dog  it  may  be  less  than  1  mm. 
The  difference  is  probably  due,  in  part  at  least,  to  a  difference  in  the 
experimental  conditions,  dogs  being  usually  anaesthetized  for  such 
measurements,  horses  not.  The  pressure  in  the  lymph  capillaries 
must,  of  course,  be  higher  than  in  the  thoracic  duct — how  much 
higher  we  do  not  know. 

(2)  The  contraction  of  muscles  increases  the  pressure  of  the 
lymph  by  compressing  the  channels  in  which  it  is  contained,  and 
the  valves,  with  which  the  lymphatics  are  even  more  richly  provided 
than  the  veins,  hinder  a  backward  and  favour  an  onward  flow.  The 
contractions  of  the  intestines,  and  especially  of  the  villi,  are  an 
important  aid  to  the  movement  of  the  chyle.     By  the  contri 

the  diaphragm,  substances  maybe  sucked  from  the  peritoneal  cavity 
into  the  lymphatics  of  its  central  tendon,  through  the  stomal. 1  in  the 
serous  layer  with  which  its  lower  surface  is  clad.  It  is  even  possible 
by  passive  movements  of  the  diaphragm  in  a  dead  rabbit  to  inject 
its  lymphatics  with  a  coloured  liquid  placed  on  its  peritoneal  surface. 
Passive  movements  of  the  limbs  and  massageof  the  muscles  are  also 
known  to  hasten  the  sluggish  current  of  the  lymph,  and  are  some- 
times employed  with  this  object  in  the  treatment  oi  dis 

(3)  The  movements  of  respiration  aid  tin-  flow.      At  every  inspira- 


PR  ICTIC  If    EXERCISES  177 

tion  the  pressure  in  the  great  veins  near  the  heart  becomes  negative, 
.uul  lymph  is  sucked  into  them  (p.  -to). 

(4)  Tn  some  animals  rhythmically-contracting  muscular  sacs  or 
hearts  exist  on  the  course  of  the  lymphatic  circulation.  The  frog 
lias  two  pairs,  an  anterior  and  a.  posterior,  of  these  lymph  heart  I, 
which  pulsate,  although  not  with  any  great  regularity,  at  an  average 
rate  of  sixty  to  seventy  beats  a  minute,  and  are  governed  by  motor 
and  inhibitory  centres  situated  in  the  spinal  cord.  The  beat  is  not 
directly  initiated  from  the  cord,  but  the  tonic  influence  of  the  cord 
is  necessary  inforder  that  the  Ivmph  heart  may  continue  to  beat 
(Tscheimak).  Such  hearts  are  also  found  in  reptiles.  It  is  possible 
that  in  animals  without  localized  lymph  hearts  the  smooth  muscle, 
which  is  so  conspicuous  an  clement  in  the  walls  of  the  lymphatic 
vessels,  may  aid  the  flow  by  rhythmical  contractions. 


PRACTICAL  EXERCISES  ON  CHAPTER  II. 

1.  Microscopic  Examination  of  the  Circulating  Blood. — -(1) '  Take 
a  tadpole  and  lay  it  on  a  glass  slide.  Cover  the  tail  with  a  large 
cover-slip,  and  examine  it  with  the  low  power  (Leitz,  oc.  III.,  obj.  3), 
Generally  the  tail  will  stick  so  closely  to  the  slide,  and  the  animal 
will  move  so  little,  that  a  sufficiently  good  view  of  the  circulation 
can  be  obtained.  If  there  is  any  trouble,  destroy  the  brain  with  a 
needle.  Observe  the  current  of  the  blood  in  the  arteries,  capillaries  and 
veins.  An  artery  may  be  easily  distinguished  from  a  vein  by  looking 
for  a  place  at  which  the  vessel  bifurcates.  In  veins  the  blood  flows 
in  the  two  branches  of  the  fork  towards  the  point  of  bifurcation,  in 
arteries  away  from  it.     Sketch  a  part  of  a  field. 

To  Pith  a  Frog. — -Wrap  the  animal  in  a  towel,  bend  the  head 
forwards  with  the  index-finger  of  one  hand,  feel  with  the  other  for 
the  depression  at  the  junction  of  the  head  and  backbone,  and  push  a 
narrow-bladed  knife  right  down  in  the  middle  line.  The  spinal  cord 
will  thus  be  divided  with  little  bleeding.  Now  push  into  the  cavity 
of  the  skull  a  piece  of  pointed  lucifer  match.  The  brain  will  thus 
be  destroyed.  The  spinal  cord  can  be  destroyed  by  passing  a  blunt 
needle  down  inside  the  vertebral  canal. 

(2)  Take  a  frog  and  pith  its  brain  only,  inserting  a  match  to 
prevent  bleeding.  Pin  the  frog  on  a  plate  of  cork  into  one  end  of 
which  a  glass  slide  has  been  fastened  with  sealing-wax.  Lay  the 
web  of  one  of  the  hind-legs  on  the  glass  and  gently  separate  two  of 
the  toes,  if  necessary  by  threads  attached  to  them  and  secured  to 
the  cork  plate.  Put  the  plate  on  the  microscope-stage  and  fasten 
by  the  clips  (see  pp.  15,  109). 

(3)  After  the  normal  circulation  has  been  studied  thoroughly  put 
a  very  small  drop  of  tincture  of  cantharides  on  the  portion  of  the  web 
which  is  in  the  field  of  the  microscope,  using  a  fine  pipette.  Observe 
the  process  of  inflammation,  including  stasis  and  diapedesis  (p.  53). 

2.  Anatomy  of  the  Frog's  Heart. — Expose  the  heart  of  a  pithed 
frog  by  pinching  up  the  skin  over  the  abdomen  in  the  middle  line, 
dividing  it  with  scissors  up  to  the  lower  jaw,  and  then  cutting  through 
the  abdominal  muscles  and  the  bony  pectoral  girdle.  The  external 
abdominal  vein,  which  will  be  observed  on  reflecting  the  skin,  can 
be  easily  avoided.  The  heart  will 'now  be  seen  enclosed  in  a  thin 
membrane,   the  pericardium,   which  should  be  grasped  with  fine- 

12 


i78 


A    MA  XI     U    <>/■    PHYSIOLOGY 


pointed  forceps  and  freely  divided.  Connecting  the  posterior 
surface  ol  the  heart  and  tin  pericardium  is  a  slender  band  of  con- 
nective tissue,  the  fraenum.  A  silk  ligature  may  be  passed  around 
tins  with  a  threaded  curved  needle,  or  curved  one-pointed  forceps, 
and  tied,  and  then  the  fraenum  may  be  divided  posterior  to  tne 
ligature.  The  anatomical  arrangement  of  the  various  parts  oi  the 
heart  should  now  be  studied.  Note  the  single  ventricle  with  the 
bulbus  arteriosus,  the  two  auricles,  and  the  sinus  venosus,  turning 
the  heart  over  to  see  the  latter  by  means  of  the  Ligature  (  observe 
the  whitish  crescent  at  the  junction  oi  the  sinus  venosus  and  the 
right  auricle  | Fig.  74). 

3.  The  Beat  of  the  Heart.-  Note  that  the  auricles  beal  first,  and 
then  the  ventricle.  The  ventricle  becomes  smaller  and  paler  during 
its  systole,  and  blushes  red  during  diastole.  Count  the  number  01 
beats  of  the  heart   in  a  minute      Now  excise  the  heart,  Lifting  it  by 

means'ot  I  he  ligal  ure, 


and  taking  1  are  to  cut 
w  ideol  t  he  sinus  veno- 
sus. Place  the  heart 
in  a  small  por<  elain 
capsule  on  a  little 
blotting-paper  moist- 
ened with  physiologi- 
cal salt  solut  ion.*  <  )b- 
serve  that  it  goes  on 
beating.  Put  a  little 
ice  or  snow  in  contact 
with  the  heart,  and 
count  the  number  of 
beats  in  a  minute  I  he 
rate  is  greatly  dimin- 
ished. Now  remove 
the  ice  and  blotting- 
paper,  cover  the  heart 
with  the  salt  solution, 
and  heat,  noting  the 
temperature  with  a 
thermometer.  Observe  that  the  heart  beats  faster  and  faster  as  the 
temperature  rises.  At  4O0  C.  to  13  C.  it  stops  beating  in  diastole 
(heat  standstill).  Now  at  once  pour  off  the  heated  liquid,  and  run 
in  some  cold  salt  solution.      The  heart  will  begin  to  beat  again. 

4.  Cut  ott  the  apex  of  the  ventricle  a  little  below-  the  auriculo- 
ventricular  groove.  The  auricles,  with  the  attached  portions  of  the 
ventricle,  go  on  beating.  The  apex  docs  not  contract  spontaneously, 
but  can  be  made  to  beat  by  stimulating  it  mechanically  (by  pricking 
it  with  a  needle)  or  electrically.  Divide  the  still  contracting  portion 
of  the  heart  by  a  longitudinal  incision.  The  two  halves  go  on 
beating. 

5.  Heart  Tracings. —  (1)  hasten  a  myograph-plate  (Fig.  75]  on  a 
stand.  Take  a  long  light  lever  consisting  of  a  straw  or  a  piece  "t 
thin  chip,  armed  at  one  end  with  a  writing-point  of  parchment-paper, 
supported  near  the  other  end  by  a  horizontal  axis,  and  pierced  not 
far  from  the  axis  by  a  needle  carrying  on  its  point  a  small  piece  of 
cork  or  a  ball  of  sealing-wax. 

*  For  frog's  tissues  this  should  be  07  to  075  per  cent,  sodium  chloride 
solution,  for  mammalian  tissues  a  little  stronger  (about  erg  per  cent.). 


Fig.  74. — Frog's  Heart  with  Stannius'  Ligatcrfs 
in   Position   (Cyon). 

Anterior  surface  of  heart  shown  on  the  left,  pos- 
terior surface  on  the  right,  a,  right  auricle  ;  h,  left 
auricle:  c,  ventricle;  </.  bulbus  arteriosus:  ,-.  /. 
aorta'  :  g,  sinus  venosus. 


PR  ICTICAL  EXERCISES 


179 


Ccu*ter/>oiSf 


75- — Arrangement   for   obtaining   a    Heart 
Tracing  from  a  Frog. 


A  counterpoise  is  adjusted  on  the  short  arm  of  the  liver  in  the 
form  <>t  .i  sn ial I  Leaden  weight.  Cover  a  drum  with  glazed  paper 
and  smoke  it.  The  paper  must  be  put  on  so  tightly  thai  it  will  not 
slip.     To  smoke  the  drum,  hold  it  by  the  spindle  in  both  hands  over 

a  fish-tail  burner,  de- 
press the  drum  in  the 
(lame,     and     rotate 

rapidly.  Avoid  put- 
ting on  a  heavy 
coating  of  smoke,  as 
a  more  delicate  trac- 
ing is  obtained  when 
the  paper  is  lightly 
smoked.  The  speed 
of  the  drum  can  be 
varied  by  putting  in 
or  taking  out  a  small 
vane.  Arrange  an 
electro -magnetic 
t  in)  e  -  ma  rker  for 
writing  seconds 
(Fig.  76).  Pith  a  frog 
(brain    only),  expose 

the  heart,  and  put  under  it  a  cover-slip  to  give  it  support.  Pin  the  frog 
on  the  myograph-plate,  and  adjust  the  foot  of  the  lever  so  that  it  rests 
on  the  ventricle  or  the  auriculo- ventricular  junction.  Bring  the 
writing-point  of  the  lever  and  that  of  the  time-marker  vertically  under 
each  other  on  the 
surface  of  the  drum. 
Set  off  the  drum  at 
the  slow  speed 
(say,  a  centimetre 
a  second) .  When 
the  lever  rests  on 
the  auriculo- ven- 
tricular junction, 
the  part  of  the 
tracing  correspond- 
ing to  the  contrac- 
tion of  the  heart 
will  be  broken  into 
two  portions,  repre- 
senting the  systole 
of  the  auricles  and 
ventricle  respec- 
tively. Cut  the 
paper  off  the  drum 
with  a  knife  (keep- 
ing the  back  of  the 
knife  to  the  drum 
to  avoid  scoring  it) 
and  carry  it  to  the 
varnishing-trough,  holding  the  tracing  by  the  ends  with  both  hands, 
smoked  side  up.  Immerse  the  middle  of  it  in  the  varnish,  draw 
first  one  end  and  then  the  other  through  the  varnish,  let  it  drip  for 
a  minute  into  the  trough,  and  fasten  it  up  with  a  pin  to  dry. 

12 — 2 


Fig.  76. — Electro-magnetic  Time-marker  connected 
with  Metronome. 

The  pendulum  of  the  metronome  carries  a  wire  which 
closes  the  circuit  when  it  dips  into  either  of  the  mercury 
cups,  Hg. 


i8o 


A   MANir.1L  OF  PHYSIOLOGY 


(2)  Heart  Tracing,  with  Simultaneous  Record  of  Auricular  and 
Ventricular  Contractions,  (a)  For  this  purpose  two  levers  may  be 
arranged,  one  resting  on  the  auricle,  the  other  on  the  ventricle,  the 
writing  points  being  placed  in  the  same  vertical  straight  line  on  the 
drum.     A  convenient  form  of  apparatus  is  shown  in  fig.  77. 

(6)  Gaskell's  Method  {a  modification  of). — Attach  a  silk  ligature  to 
the  very  apex  of  the  ventricle.  Divide  the  fraenum,  cut  the  aorta 
across  close  to  the  bulbus,  pinch  up  a  tiny  portion  of  the  auricle  and 
ligature  it.  Remove  the  intestines,  liver,  lungs,  etc.,  care  being 
taken  in  cutting  away  the  liver  not  to  injure  the  sinus.  Then 
remove  the  lower  jaw,  and  cut  away  the  whole  of  tin-  body  e»  epi 
the  head,  part  of  the  oesophagus,  and  the  tissue  connecting  it  with 
the  heart.  Fix  the  head  in  a  clamp  sliding  on  an  ordinary  stand. 
The  heart  is  held  at  the  auriculo-ventricular  junction  in  a  Gaskell's 
clamp  supported  on  a  separate  stand.  The  thread  connected  with 
the  ventricle  is  brought  round  a  pulley  and  attached  to  a  lever 
above  the  heart.     The  auricle  is  connected  with  another  lever.     The 


Fig.  77. —  Apparatus  for  obtaining  a  Simultaneous  Tracing  01 
Auricular  and  Ventricular  Contraction- 

writing-points  of  the  two  levers  are  arranged  in  a  vertical  line  on  the 
drum.  The  small  pulley  must  be  oiled  from  time  to  time  to  lessen 
the  friction  (Fig.  78). 

If  tortoises  or  turtles  are  available,  the  much  larger  heart  of  these 
animals  may  be  used  for  Experiments  5  (2)  (a)  and  (b).  The  animal 
having  been  killed  by  cutting  off  its  head,  the  ventral  portion  of  the 
carapace  is  detached  by  the  saw.  The  pericardium  can  now  be  slit 
open,  and  the  pads  of  the  levers  arranged  on  auricles  and  ventricle 
respectively,  as  in  Experiment  5  (2)  (a),  without  further  disturbing 
the  heart.  Or  the  heart  may  be  removed,  together  with  the  upper 
portion  of  the  body,  the  pericardium  opened,  and  the  liver  cut  away. 
The  aortic  trunk  is  then  divided,  and  the  portion  of  it  attached  to 
the  heart  grasped  by  a  small  forceps  clamp.  Fine  silk  ligatures  are 
attached  to  the  apex  of  the  ventricle  and  the  top  of  the  right  auricle. 
The  vagus  nerves  are  exposed  in  the  neck,  ligated,  and  divided. 
The  upper  portion  of  the  body  is  supported  on  a  stand.  The  forceps 
grasping  the  aorta  is  fixed  in  an  ordinary  holder,  and  the  threads  are 
attached  to  the  levers,  as  in  Experiment  5  (2)  (b). 


PRACTICAL  EXERCISES 


1S1 


UW 


With  the  vagi,  Experiment  7  may  be  performed.  It  must  be 
remembered  tli.it  the  activity  of  the  two  vagi  is  unequal  in  the 
tortoise,  the  right  being  the  more  active. 

6.  Dissection  of  the  Vagus  and  Cardiac  Sympathetic  Nerves  in 
the  Frog. — (1)  Put  the  tissues  in  the  region  of  the  neck  on  the 
stretch  by  passing  into 
the  gullet  a  narrow  test- 
tube  or  a  thick  glass  rod 
moistened  with  water, 
and  by  pinning  apart 
the  anterior  limbs.  Ex- 
pose the  heart  by  cut- 
ting through  the  pectoral 
girdle  in  the  way  de- 
scribed in  2  (p.  177).  On 
clearing  away  a  little 
connective  tissue  and 
muscle  with  a  seeker, 
three  large  nerves  will 
come  into  view.  The 
upper  is  the  glosso- 
pharyngeal, the  lower 
the  hypoglossal  ;  the 
vagus  crosses  diagonally 
between  them  (Fig.  79). 
Above  the  vagus  trunk, 
running  parallel  to  it, 
and  separated  from  it 
by  a  thin  muscle  and  a 
bloodvessel  (the  carotid 
artery),  lies  its  laryngeal 
branch.  The  vagus 
should  be  traced  up  to 
the  ganglion  situated  on 
it  near  its  exit  from  the 
skull. 

( 2 )  Then  cut  away  the 
lower  jaw,  dividing  and 
reflecting  the  membrane 
covering  the  roof  of  the 
mouth.  At  the  junction 
of  the  skull  and  the 
backbone  will  be  seen 
on  each  side  the  levator 
anguli  scapula?  muscle 
(Fig.  80).  Remove  this 
muscle  carefully  with 
fine  forceps.  Clear  away 
a  little  connective  tissue 
lying  just  over  the 
upper  cervical  vertebra?, 
and     the     sympathetic 

chain,  with  its  ganglia,  will  be  seen.  Pass  a  fine  silk  thread  beneath 
the  sympathetic  about  the  level  of  the  large  brachial  nerve,  by 
means  of  a  sewing-needle  which  has  been  slightly  bent  in  a  flame 
and  fastened  in  a  handle.     Tie  the  ligature,  divide  the  sympathetic 


:B=  —  B 

pIG.  76. — Arrangement  for  recording  Auricu- 
lar and  Ventricular  Contractions  (and 
Studying  the  Influence  of  Temperature 
on  the  Heart). 

C,  clamp  holding  the  heart  at  the  auriculo 
ventricular  groove ;  P,  pulley  round  which  a 
thread  attached  to  the  apex  of  the  ventricle  passes 
to  the  lever  L'  ;  L,  lever  connected  with  auricle. 
(The  rest  of  the  arrangement  is  for  studying  the 
influence  of  temperature  on  the  heart  and  its 
nerves,  G  being  a  vessel  filled  with  physiological 
salt  solution  in  which  the  heart  is  immersed ;  R,  an 
inflow  tube  from  a  reservoir  containing  salt  solu- 
tion at  the  temperature  required  ;  O',  an  outflow 
tube  by  which  G  may  be  emptied  into  the  beaker 
B'  ;  O,  a  tube  passing  to  the  beaker  B  to  prevent 
overflow  from  G  ;  T,  a  thermometer.) 


!■>-' 


A   MANUAL  OF  PHYSIOLOGY 


G/ass  rod 
Glo  sso/inart/n  yea/ 


m       \r  i 

^^§§k     \  \Larynifeal 


below  it,  and  isolate  it   i   irefully  with  fine  scissors  up  to  its  junction 
with  tin  vagus  ganglion. 

Batteries — To  set  up  a  Daniell  Cell.—  Fill  the  porous  pol  (Fig.  j<>3, 
p.  615)  previously  well  soaked  in  water,  with  dilute  sulphuric 
(1  part  of  commercial  acid  to  10  or  15  parts  of  water)  to  within 
i£  inches  of  the  brim,  and  place  in  it  the  piece  of  amalgamated 
zinc.  If  the  zinc  is  not  properly  amalgamated,  leave  it  in  the  pot 
for  a  minute  or  two  to  clean  its  surface.  Then  lift  it  out,  pour  over 
it  a  little  mercury,  and  rub  the  mercury  thoroughly  over  it  with  a 
cloth.  Put  the  pot  into  the  outer  vessel,  which  contains  the  copper 
plate,  and  is  filled  with  a  saturated  solution  of  sulphate  of  copper, 

with  some  undis- 
solved crystals  to 
keep  it  saturated. 
After  using  the 
Daniell.  it  must  al- 
wavs  be  taken  down. 
The  outer  pot  is  left 
with  the  copper  plate 
and  the  sulphate 
solution  in  it.  The 
zinc  is  washed  and 
brushed  bright.  The 
sulphuric  acid  is 
poured  into  the 
stock  bottle,  and  the 
porous  pot  put  into 
a  large  jar  of  water 
to  soak. 

The  Bichromate 
Cell  contains  only 
one  liquid — a  mix- 
ture of  1  part  of 
sulphuric  acid  with 
4  parts  of  a  10  per 
cent,  solution  of  po- 
tassium bichromate. 
In  this  is  placed  one, 
or  in  some  forms  two, 
carbon  plates  and  a 
plate  of  am  algam  ated 
zinc.  After  usinp  the 
battery,  take  the 
zincoutof  the  liquid. 
The  Leclanchc  battery  consists  of  a  porous  pot  filled  with  a 
mixture  of  manganese  dioxide  and  carbon  packed  around  a  carbon 
plate,  which  forms  the  positive  pole.  The  pot  stands  in  an  outer 
jar  of  k'lass  filled  with  a  saturated  solution  of  ammonium  chloride, 
into  which  dips  an  amalgamated  zinc  rod,  which  constitutes  the 
negative  pole.  Various  fcrms  of  dry  batteries  can  be  conveniently 
used  for  running  induction-coils  or  time-markers,  but  are  not 
adapted  for  yielding  constant  currents  of  long  duration. 

7.  Stimulation  of  the  Vagus  in  the  Frog.  Make  the  same  arrange- 
ments as  in  ;  (1)  (p.  17N).  but,  in  addition,  set  up  an  induction 
machine  arranged  for  an  interrupted  current  (Fig.  81),  with  a 
Daniell,  a  bichromate,   a   Leclanche,   or  a  dry  cell  in  the  primary 


hit/ft  og '/ess at.  V 
Vafus-f" 


KMffeoH 

Zu  n  a 


Fig.  79. — The  Relations  of  the  Vagus  in  the 
Frog. 


PRACTICAL  EXERCISES 


Gancjiion-  nf°Vaqu  s 


»     AW/ 


circuit,  which  should  also  include  a  simple  key.  Insert  a  short- 
uiting  key  in  the  secondary  circuit.  Attach  the  electrodes  to  the 
ihorl  <  ircuiting  key,  push  the  secondary  coil  up  tow;  in  is  the  primary 
until  the  shocks  are  distinctly  felt  on  the  tongue  when  the  N< 
hammer  is  set  going  and  the  short-circuiting  key  opened.  Pith  the 
brain  of  a  frog,  expose  the  heart,  dissect  out  the  vagus  on  one  side, 
ligature  it  as  high  up  as  possible,  and  divide  above  the  ligature. 
Fasten  the  electrodes  on  the  cork  plate  by  means  of  an  indiarubbei 
band,  and  lay  the  vagus  on  them.  Set  the  drum  off  (at  slow  speed). 
Alter  a  dozen  heart-beats  have  been  recorded,  stimulate  the  vagus 
for  two  or  three  seconds  by  opening  the  short-circuiting  key.  If  the 
nerve  is  active,  the  heart 
will  be  slowed,  weakened, 
or  stopped.  In  the  last 
case  the  lever  will  trace  em 
unbroken  straight  line  ; 
but  even  if  the  stimulation 
is  continued  the  beats  will 
again  begin. 

8.  Stimulation  of  the 
Junction  of  the  Sinus  and 
Auricles. — Aftera  sufficient 
number  of  the  observations 
described  in  7  have  been 
taken  with  varying  time 
and  strength  of  stimula- 
tion, take  the  writing- 
points  off  the  drum,  apply 
the  electrodes  directly  to 
the  crescent  at  the  junction 
of  the  sinus  venosus  with 
the  right  auricle,  and 
stimulate.  The  heart  will 
be  affected  very  much  in 
the  same  way  as  by  stimu- 
lation of  the  vagus,  except 
that  during  the  actual 
stimulation  its  beats  may 
be  quickened  and  the  in- 
hibition may  only  begin 
after  the  electrodes  have 
been  removed  (Fig.  59, 
p.  144). 

9.  Effect  of  Muscarine  (or 
Pilocarpine)  and  Atropine. 
— Paint  on  the  sinus  veno- 
sus with  a  small  camel's-hair  brush  a  very  dilute  solution  of  muscarine 
(or  of  pilocarpine).  The  heart  will  soon  be  seen  to  beat  more 
slowly,  and  will  ultimately  stop  in  diastole.  Now  apply  a  dilute 
solution  of  sulphate  of  atropine  to  the  sinus.  The  heart  will  again 
begin  to  beat.  Stimulation  of  the  vagus  will  now  cause  no  in- 
hibition of  the  heart,  because  its  endings  have  been  paralyzed  by 
atropine.  (Muscarine  or  pilocarpine  has  also  been  applied  to  the 
heart,  but  it  could  be  shown  by  a  separate  experiment  that  atropine 
by  itself  has  the  same  effect  on  the  vagus  endings — p.  150). 

10.  Stannius'  Experiment. — Pith  a  frog.     Expose  the  heart  in  the 


"'ell         d'i/fA 


Muscle 


Fig.   8 


Sympathetic]  7     ^\ 


o.— Relation  cf  the  Sympathetic 
to  the  Vagus  in  the  Frog. 

1,  2,  3,  4  are  spinal  nerves. 


184 


A   MANUAL  OF  PHYSIOLOGY 


way  described  under  2  (p,  1 77).  Ligature  the  fnenum  with  a  fine  silk 
thread,  and  use  the  thread  to  manipulate  the  heart.  With  a  curved 
needle  pass  a  moistened  silk  thread  between  the  aorta  and  the 
Superior  vena  cava,  and  tie  it  round  the  junction  of  the  sinus  and 
right  auricle  (Fig.  74,).  The  auricles  and  ventricle  stop  beating  as 
soon  as  the  ligature  is  tightened.  The  sinus  venosus  goes  on  lx  it  Lng. 
Now  separate  the  ventricle  from  the  rest  of  the  heart  by  an  incision 
through  the  3 uriculo- ventricular  groove,  or  tie  a  second  ligature  in 
the  groove.  The  ventricle  begins  to  beat  again,  the  auricle  remaining 
quiescent  in  diastole  (p.  151).  Occasionally  both  auricle  and 
ventricle,  or  only  the  auricle,  may  begin  to  beat. 

11.  Stimulation  of  Cardiac  Sympathetic  Fibres  in  the  Frog. — 
(1)  In  the  vago-sympathetic  after  the  inhibitory  fibres  have  been  cut  out 
by  atropine. — Arrange  everything  as  in  7  (p.  182).  Assure  yourself, 
by  stimulating    the  vagus,  that  it   inhibits  the  heart,   and  take  a 


Fig.  Si. — Arrangement  of  Induction  Machine  for  Tetanus. 

B,  battery  ;  K,  simple  key  ;  P,  primary  coil  ;  S,  secondary  coil  ;  A,  C,  binding 
screws  to  be  connected  with  battery  for  single  shocks  ;  F,  G,  binding  screws  for 
tetanizing  current;  N,  Neef's  hammer;  D,  short-circuiting  key  in  secondary; 
E,  electrodes.  D  and  E  are  drawn  to  a  much  larger  scale  than  the  rest  of  the 
figure. 

tracing  during  stimulation.  Then  paint  a  dilute  solution  of  atropine 
on  the  sinus.  Stimulation  of  the  vagus,  which  is  really  the  vago- 
sympathetic (see  Fig.  80),  will  now  cause,  not  inhibition,  but  aug- 
mentation (increase  in  rate  or  force,  or  both),  since  the  endings  of 
the  inhibitory  fibres  have  been  paralyzed  by  atropine.  The  strength 
of  the  stimulating  current  required  to  bring  out  atypical  augmentor 
effect  is  greater  than  that  needed  to  stimulate  the  inhibitory  fibres. 
Take  a  tracing  to  show  augmentation  produced  by  stimulating  the 
nerve. 

(2)  By  direct  stimulation  of  the  cervical  sympathetic. — Make  the 
same  arrangements  as  in  11  (1),  but,  instead  of  isolating  the  vagus, 
dissect  out  the  sympathetic  on  one  side  in  the  manner  described  in 
6  (2)  (p.  181),  and  do  not  apply  atropine  to  the  heart.  Lay  the  upper 
(cephalic)  end  of  the  sympathetic  on  very  fine  and  well-insulated 
electrodes,  and  stimulate  (Fig.  64,  p.  151).  (To  insulate  electrodes 
the  points  may  be  covered  with  melted  paraffin.     When  the  paraffin 


PRAi   I  h    II    I  XERi  ISES  185 

has  cooled,  a  narrow  groove,  just  sufficient  to  Lay  bare  the  wires  on 
the  upper  side,  is  made  in  it.  and  the  nerve  is  laid  in  this  groove.) 

Experiments  7.  11  (i)  and  11  (2)  will  be  rendered  more  exact 
by  connecting  .1  second  ele<  0   tic  signal  with  a  Pohl's  com- 

mutator without  cross-wires  (Fig.  82),  in  such  a  way  that  the  circuit 
is  interrupted  at  the  instant   when  stimulation  begins. 

i-\  The  Action  of  Inorganic  Salts  on  Heart-muscle. — Expose  and 
remove  the  heart  of  a  tortoise  or  turtle  (p.  180).  Cut  off  the  apical  two- 
thirds  of  the  ventricle  by  an  incision  parallel  to  the  auriculo-  ventricular 
groove.  By  a  second  parallel  cut  remove  a  ring  of  tissue  2  or  3  milli- 
metres wide  from  the  upper  end  of  this  portion  of  the  ventricle. 
Divide  the  ring  at  opposite  ends  of  a  diameter,  so  as  to  form  two 
strips.  Tic  a  fine  silk  thread  to  each  end  of  one  strip.  Attach  one 
of  the  threads  to  the  short  limb  of  a  glass  rod  bent  at  right  angles, 
so  that  it  can  be  immersed  at  will  in  a  beaker.  The  other  end  of  the 
rod  is  fixed  in  a  holder  sliding  on  a  stand.  Attach  the  second  thread 
to  the  short  arm  of  a  counterpoised  lever  arranged  to  write  on  a 


Fig.   82. — Arrangement  for  recording  the  Beginning  and  End  of 
Stimulation. 

C,  Pohl's  commutator  without  cross-wires  ;  B,  battery  in  circuit  of  primary 
coil  P  ;  B',  battery  in  circuit  of  electro-magnetic  signal  T  ;  K,  simple  key  in 
primary  circuit  ;  S,  secondary  coil.  When  the  bridge  of  the  commutator  is 
tilted  into  the  position  shown  in  the  figure,  the  primary  circuit  is  closed  and  the 
circuit  of  the  signal  broken. 

slowly-moving   drum.     If   the   strip   is   still   beating,    wait   till   the 
contractions  have  ceased  ;  then 

(1)  Immerse  the  strip  in  a  beaker  filled  with  0-7  per  cent,  solution 
of  sodium  chloride.  After  a  time  it  begins  to  beat  rhythmically. 
The  contractions  become  rapidly  stronger,  and  then  after  a  while 
diminish,  and  gradually  cease.  The  tone  or  tonus  of  the  strip  is 
diminished  by  the  solution. 

(2)  Arrange  the  other  strip  in  the  same  way,  and  immerse  it  in  a 
solution  of  calcium  chloride  (about  1  per  cent.)  isotonic  with  the 
sodium  chloride  solution  used  in  (1).  If  the  strip  is  contracting, 
the  contractions  will  cease.  Rhythmical  contractions  will  not 
appear  as  in  the  sodium  chloride  solution.  The  tone  of  the  strip 
may  be  increased. 

(3)  Remove  most  of  the  calcium  chloride  solution  from  the  beaker. 
and  fill  it  up  with  o-7  per  cent,  sodium  chloride  solution.  The 
rhythmical  contractions  will  appear  after  a  longer  or  shorter  latent 


186  A   M  l\r  \i    on  I'llYSloi.oCY 

period,  and  will  be  stronger  and  last  for  a  longer  time  than  in  the 
sodium  chloride  solution  alone. 

(4)  Immerse  a  fresh  strip  in  a  solution  containing  sodium  chloride 
(o"7  per  cent.),  calcium  chloride  (0^025  per  cent.),  and  potassium 
chloride  (o-o3  per  cent.)  (a  modified  Ringer's  solution).  A  longer 
series  of  rhythmical  contractions  will  be  obtained  than  in  either  (1) 
or  (3).  That  this  is  not  due  to  the  potassium  chloride  acting  alone 
can  be  shown  by  immersing  a  strip  in  a  solution  of  potassium  chloi  Lde 
(about  09  per  cent.)  isotonic  with  the  sodium  chloride  solution  used 
in  (1).     No  contractions  will  be  caused. 

13.  The  Action  of  the  Mammalian  Heart. — Inject  under  the  skin  of  a 
dog  (preferably  a  small  one)  1  c.c.  of  a  2  per  cent,  solution  of  morphine 
hydrochlorate  for  every  kilo  of  body-weight.  As  soon  as  the  morphine 
has  taken  effect  (in  15  to  30  minutes,  but,  better,  after  an  hour),  fasten 
the  animal  back  down  on  a  holder  (as  in  Fig.  129,  p.  288),  pushing  the 
mouth-pin  behind  the  canine  teeth  and  screwing  the  nut  home*  In 
the  meantime  select  a  tracheal  cannulat  of  suitable  size,  and  get  ready 
instruments  for  dissection — one  or  two  pairs  of  artery- forceps,  a  pair 
of  artery-clamps  (bulldog  pattern),  two  or  three  glass  cannula?  of 
various  sizes  for  bloodvessels,  ten  strong  waxed  ligatures,  sponges, 
hot  water,  a  towel  or  two,  and  a  pair  of  bellows  to  be  connected 
with  the  tracheal  cannula  when  the  chest  is  opened.  Arrange  an 
induction-coil  and  electrodes  for  a  tetanizing  current  (  Fig.  8  1 ,  p.  1 84 ) . 
With  scissors  curved  on  the  flat  clip  away  the  hair  from  the  trout  of 
the  neck.  Put  the  hair  carefully  away,  and  remove  all  the  loose 
hairs  with  a  wet  sponge  so  that  they  may  not  get  into  the  wounds. 
Give  ether,  or  pour  into  the  stomach  by  a  tube  5  c.c.  of  a  05  per 
cent,  solution  of  chloroform  in  10  per  cent,  alcohol  per  kilo  of  body- 
weight,  diluted  before  administration  with  3  or  4  volumes  of  water 
(Grehant's  method). 

To  put  a  Cannula  in  the  Trachea. — The  hair  having  been  clipped  in 
the  middle  line  of  the  neck  and  the  skin  shaved,  a  mesial  incision 
is  to  be  made,  beginning  a  little  below  the  cricoid  cartilage,  which 
can  be  felt  with  the  finger.  The  trachea  is  then  cleared  from  its 
attachments  by  forceps  or  a  blunt  needle,  and  two  strong  ligatures 
are  passed  beneath  it.  A  single  loop  is  placed  on  each  of  these 
but  is  not  drawn  tight.  Raising  the  trachea  by  means  of  the  upper 
ligature,  the  student  makes  a  longitudinal  incision  through  two  or 
three  of  the  cartilaginous  rings,  inserts  the  cannula,  and  ties  the 

*  A  simple  but  efficient  and  convenient  holder  for  a  dog  may  be  easily 
constructed  as  follows.  Take  a  board  of  the  length  required  (2  J  to  5  feet, 
according  to  the  size  of  the  dog).  At  one  end  fasten  two  short  upright 
wooden  pins,  with  a  clear  space  of  4  to  6  inches  between  them.  These 
are  pierced  from  side  to  side  with  four  or  live  holes  at  different  heights. 
An  iron  pin  passes  behind  the  canine  teeth  of  the  animal  through  two 
corresponding  holes  in  the  uprights,  and  the  muzzle  is  tied  over  this  by 
a  cord  which  secures  the  head.  For  a  large  dog  an  upper  pair  of  holes 
is  used,  for  a  small  dog  a  lower  pair.  The  feet  arc  listened  by  cords 
to  staples  inserted  into  the  sides  of  the  board,  the  fore-legs  being  draws 
tailwards  for  all  operations  on  the  neck  or  head,  headwards  for  operations 
on  the  thorax.     A  rabbit-holder  can  be  made  in  exactly  the  same  way. 

t  A  tracheal  cannula  is  easily  made  by  heating  a  piece  of  glass  tubing, 
about  6  inches  long,  a  short  distance  from  one  end,  and  drawing  it  oul 
slightly  so  as  to  form  a  '  neck.'  The  tubing  is  then  bent  about  its  middle 
to  an  obtuse  angle,  and  the  end  next  the  neck  is  ground  obliquely  on  a 
stone.  The  diameter  of  the  cannula  should  be  about  the  same  as  that  of 
the  trachea,  into  which  it  is  to  be  inserted  by  its  oblique  end. 


rh'.lCTICAL  EXERCISES  187 

lower  ligature  firmly  around  its  neck.     The  upper  ligature  can  now 
be  withdrawn. 

Clip  off  the  hair  on  each  side  of  the  sternum.  Make  an  incision 
OD  each  side  through  the  skin  and  down  to  the  costal  cartilages  about 
2  inches  from  the  edge  of  the  breast-bone,  and  long  enough  to 
expose  about  four  costal  cartilages  (say,  3rd  to  6th).  With  a  curved 
needle  pass  waxed  ligatures  round  the  cartilages,  and  tic  firmly  to 
compress  the  intercostal  vessels.  The  bellows  should  now,  or  earlier 
if  any  symptoms  of  impeded  respiration  have  appeared,  be  connected 
with  one  end  of  the  horizontal  limb  of  a  glass  T-piece,  the  other  end 
of  which  is  similarly  connected  with  the  tracheal  cannula.  The 
stem  of  the  T-piecc  is  provided  with  a  short  piece  of  rubber  tubing, 
which,  when  artificial  respiration  is  being  carried  on,  is  to  be  alter- 
nately closed  and  opened — closed  during  inflation  of  the  lungs,  and 
opened  when  the  air  is  to  be  allowed  to  escape  from  them.  Or  a 
screw-clamp  may  be  adjusted  on  the  piece  of  tubing  so  that  the 
opening  is  sufficiently  narrow  to  permit  the  lungs  to  be  properly 
inflated  when  the  bellows  are  compressed,  and  yet  sufficiently  wide 
to  permit  easy  escape  of  the  air  and  collapse  of  the  lungs  at  the  end 
of  each  inflation.  Ether  may,  when  necessary,  be  administered,  by 
inserting  between  the  T-piece  and  the  tube  from  the  bellows  an  ether 
bottle  with  two  tubes  passing  through  the  cork  to  within  an  inch 
or  two  of  the  ether.  If  the  cannula  has  a  side-opening,  as  is  usually 
the  case  with  metal  cannulas,  the  T-piece  may  be  dispensed  with. 
One  student  should  take  sole  charge  of  the  artificial  respiration, 
which  ought  to  be  begun  as  soon  as  the  chest  has  been  opened,  and 
continued  at  the  rate  of  about  twenty  inflations  per  minute.  The 
costal  cartilages  are  rapidly  cut  through  with  strong  scissors  just  on 
the  sternal  side  of  the  ligatures,  the  artificial  respiration  being 
suspended  for  an  instant,  as  each  cut  is  made,  to  avoid  wounding 
the  lungs.  The  sternum  is  divided  at  its  lower  end  and  turned  up. 
If  there  is  much  bleeding  a  ligature  should  be  tied  round  its  upper 
end.  With  a  curved  needle  a  ligature  is  passed  below  the  internal 
mammary  arteries  as  they  approach  the  sternum.  That  bone  may 
now  be  removed,  and  the  heart,  enclosed  in  the  pericardium,  comes 
into  view.  A  thread  is  passed  with  a  suture-needle  through  each  side  of 
the  pericardium,  which  is  then  stitched  to  the  chest- wall  and  opened. 

(a)  Note  the  various  portions  of  the  heart,  right  and  left  ventricles, 
right  and  left  auricles,  with  the  auricular  appendices.  Feel  the 
heart  with  the  hand,  and  observe  that  the  right  ventricle  is  softer 
and  has  thinner  walls  than  the  left,  and  that  the  auricles  are  softer 
than  the  ventricles.  Note  how  all  the  parts  of  the  heart  harden  in 
the  hand  during  systole  and  soften  during  diastole  (pp.  78,  82). 

(b)  Dissect  out  the  vago-sympathetic  on  one  side  in  the  neck 
of  the  dog.  The  guide  to  the  nerve  is  the  carotid  artery.  These 
two  structures  and  the  internal  jugular  vein  lie  side  by  side 
in  a  common  sheath.  Feel  for  the  artery  a  little  external  to  the 
trachea,  cut  down  on  it,  open  the  sheath,  isolate  the  vago-sympathetic 
for  about  an  inch,  pass  two  ligatures  under  it,  tie  them,  and  divide 
between  the  ligatures.  The  peripheral  and  central  ends  of  the 
nerve  may  now  be  successively  stimulated.  Stimulation  of  the 
peripheral  end  causes  slowing  of  the  heart,  or  stoppage  in  diastole. 
Feel  that  it  softens  when  it  stops.  It  soon  begins  to  beat  again. 
Stimulation  of  the  central  end  of  the  vago-sympathetic  may  or  may 
not  cause  inhibition.  If  it  does,  expose  the  other  vago-sympathetic, 
divide  it,  and  repeat  the  stimulation  of  the  central  end.     There  will 


[88 


/    1/  I  \i    ll    ol    PHYSIOLOG  1 


B 


I 


\yF 


Fig.  S3. — Myocardiograph  of  Adami  a\i>  Ro\ 

(MODIFIED    BY    Ct'SIIN'Y    AND    MATTHEWS). 

AB,  a  perpendicular  rod  descending  ton  a 
universal  joint,  which  is  not  shown  in  the  figure; 
CD,  a  brass  sheath,  moving  easily  on  the  co  1.  and 
bearing  0:1  i!s  upper  end  an  ivory  pulley,  ami  a 
its  lower  end  a  horizontal  bar,  which  is  inter- 
rupted l>v  a  plate  of  hard  rubber,  I.  The  per- 
pendicular rod  EF  moves  0:1  the  horizontal  1  a- 
by  the  hinge-joint,  J.  EF  is  hooked  at  o:n  end 
for  attachment  to  the  heart,  and  bored  at  the 
other  for  a  thread  which,  passing  over  the  pulley 
at  C,  passes  through  the  universal  joint  aid 
moves  a  writing  lever  not  shown  in  the  figure. 
CD  is  prevented  from  moving  up  AB  by  a  ring  o! 
brass.  G,  which  is  screwed  to  AB,  b  it  i;  not 
attached  to  CI) ;  the  hook  F  can  therefore  move 
to  and  bom  AB,  and  can  rotate  round  i  .  whil 
it  enno'.  move  up  or  down.  The  hooks  I-  and  M 
are  insulated  from  each  other  by  the  hard  rubber,  I. 
H  is  a  binding  post  through  which,  and  thro  gli 
ano  her  connected  with  A,  induction  s 
maybe  sent  at  will  through  the  portion  oi  the 
heart  lying  between  the  hooks. 


now  be  no  inhibition  ol 
1  In-  In-art.  Iin  identally 
it  may  be  seen  1  ha1  stimu- 
lation of  the  cent  1  .il  end 
of  the  vago-sympathetic 
causes  si  rong,  though,  oi 
course,  with  opened  1  hesl . 
abortive,  respirat  ory 
movements. 

(/  i  I  'itli  ;i  frog  (brain 
and  cord),  disse<  1  out 
the  sciatic  nerve  on  one 
side     up    to    Hi-     sa<  raJ 

plexus.  (  ul  oil  the  whole 
leg.  Drop  the  cut  end  ol 
the  nerve  on  the  heart, 
and  hold  the  preparation 
so  that  the  in  r\  e touches 
the  hearl  also  by  its  longi- 
tudinal surface.  A' 
cardiac  beat  the  nerve 
is  stimulated  by  the  ac- 
tion current  (("hap.  XI.), 
and  the  muscles  of  the 
leg  contract. 

[,/\  Raise  t  he  In  >.ird  so 
that:  the  head  ol  the  ani- 
mal isdow n  and  the  hind- 
feet  up.  and  note  w  hot  her 
there  is  any  effed  on  the 
action  and  filling  ol  the 
heart.  Repeat  the  ob- 
servation with  head  up 
ami   leet  down. 

(e)  Compress  the  aorta 
with  the  fingers,  and 
observe  tin  effe<  1  on  the 
degree  of  dilatation  of 
the  various  cavities  of 
the  heart.  Repeat  the 
experiment  with  the  in- 
terior vena  cava,  and 
compare  the  results. 

(/)    Smoke    .1     d  rum  . 
Insert    the    hooks    ol    the 
myocardiograph  (1  > 
into  the  \  ant  hi  le,  taking 
care     no1     to     penetrate 

deepl  v    into   the    wall. 

Arrange  the  le\  ei  t"  w  rite 
on  tire  drum.  While  a 
tracing  is  being  taken 
stimulate  the  peripheral 
end  oi  the  vagus.  Un- 
hook the  cardiograph. 
(g)   Stop    the    artificial 


PR  ICTK    II    EXERCISES 


189 


respiration,  and  observe  the  changes  which  take  place  in  the  am 
and   ventricles,  comparing  particularly  the  righl   side  oi   the  hearl 
with  the  left.     Before  the  near!  has  slopped   beating,  recomrn 
t  he  arl  ificial  respiral  ion. 

(//)  Connect  a  cylinder  of  oxygen  with  a  "good-sized  rubber  catheter, 

and  pass  the  catheter  down  the 
tracheal  cannula  or  through  a 
separate  opening  in  the  trachea. 
Allow  a  small  stream  of  oxygen 
to  flow  into  the  lungs.  Artificial 
respiration  is  now  unnecessary. 
The  lungs  remain  at  rest,  yet  the 
blood  is  sufficiently  oxygenated, 
and  the  heart  goes  on  beating. 
The  myocardiographic  tracing 
thus  goes  on  undisturbed  by 
respiratory  movements. 

Stop  the  oxygen,  and 
resume  the  artificial  respira- 
tion. Make  a  small  penetrat- 
ing wound  with  a  scalpel  in 
the  left  ventricle.     Observe  the 


0  !C 

Fig.  84. — Arrangement  to  illustrate  Action  of  Cardiac  Valves  in  the 
Heart  of  an  Ox  (Gad). 
C,  glass  window  in  left  auricle ;  D,  window  in  aorta ;  E,  tube  inserted  through 
apex  of  heart  into  left  ventricle  and  connected  with  pump  P  ;  A,  side  tube  on 
E,  through  which  wires  are  connected  with  a  tiny  incandescent  lamp  in  the 
ventricle  ;  W.  water  in  bottle  B  ;  T,  T",  tubes. 

course   of  the  haemorrhage,   and  note   especially  the   difference   in 
systole  and  diastole. 

(/)  Lay  the  electrodes  on  the  heart,  and  stimulate  it  with  a  strong 
interrupted  current.  The  character  of  the  contraction  soon  becomes 
profoundly  altered.     Shallow,  irregular  contractions  flicker  over  the 


190 


./    .1/  /  vr  A  I.  OF  PHYSIOLOGY 


surface,  with  a  kind  of  simmering  movement  suggestive  of  a  boiling 
pot  (delirium  cordis,  fibrillar  contraction).  Now  kill  the  animal  by 
stopping  the  artificial  respiration.  Observe  how  long  the  heart 
continues  to  beat,  and  which  of  its  divisions  stop-,  Lasl 

(At  Make  a  dissection  of  the  cervical  sympathetic  up  to  the  superior 
cervical  ganglion,  and  down  through  the  inferior  cervical  i;an<dion 
to  the  stellate  or  first  thoracic  ganglion.  Make  out  tin-  annulus  of 
Vieussens  and  the  cardiac  sympathetic  (accelerator)  branches  e;oing 
off  from  the  annulus  or  the  inferior  cervical  ganglion  to  the  cardiac 
plexus  (Fig.  62,  p.  [48). 

14.  Action  of  the  Valves  of  the  Heart. — (1)  Study  the  action  of 
the  valves  of  the  ox-heart,  connected  with  the  pump  P  and  bottle 
B  in  the  artificial  scheme,  as  shown  in  Fig.  84.  The  cavity  of  the 
heart  is  illuminated  by  means  of  a  small  electric  lam]),  the  wires 
of  which  pass  in  at  A.     When  the  piston  of  the  pump  is  pushed  down, 

water  is  forced  through 
the  aorta  D  along  the  tube 
T  into  the  bottle,  and  flows 
back  again  into  the  left 
auricle  by  the  tube  T'. 
During  each  stroke  of  tin- 
pump  the  auriculo  -  ven- 
tricular valve  is  seen 
through  the  glass  disc  in- 
serted into  C  to  close,  and 
the  semilunar  valve  is  seen 
through  the  glass  in  D  to 
open.  When  the  piston  is 
raised,  the  semilunar  valve 
is  seen  to  be  closed  and 
the  auriculo  -  ventricular 
valve  to  be  opened.  For 
comparison,  a  human 
heart  with  a  valvular 
lesion  might  be  used. 

(2)  With  the  sheep's  or 
dog's  heart  provided,  per- 
form the  following  experi- 
ments : 

(a)  Open  the  pericar- 
dium and  notice  how  it  is 
reflected  around  the  great  vessels  at  the  base  of  the  heart.  Distin- 
guish the  pulmonary  artery,  the  aorta,  the  superior  and  interior 
vena  cavae,  and  the  pulmonary  veins.  The  trachea  and  portions  of 
the  lungs  may  also  be  attached.  If  so.  remove  them  carefully 
without  injuring  the  heart. 

(b)  Take  two  wide  glass  tubes,  drawn  slightly  into  a  neck  at  one 
end.  One  of  the  tubes  should  be  about  10  cm.  long,  and  the  other 
about  50  cm.  Tic  the  short  tube  A  firmly  by  its  neck  into  the 
superior  vena  cava,  the  long  tube  B  into  the  pulmonary  artery. 
Ligature  the  inferior  vena  cava.  Connect  A  by  a  small  piece  of 
rubber  tubing  with  a  funnel  supported  in  a  ring  on  a  stand.  Pour 
water  into  the  funnel  till  the  right  side  of  the  heart  is  full.  It  will 
escape  from  the  left  azygos  vein,  which  must  be  tied.  Put  on  any 
additional  ligatures  that  may  be  needed  to  render  the  heart  water- 
tight.    Support  B  in  the  vertical  position  by  a  clamp.     Fill  the 


Fig.  85. — Diagram  of  Valves  of  the  Heart. 

The  valves  are  supposed  to  be  viewed  from 
above,  the  auricles  having  been  partially  re- 
moved. A,  aorta  with  semilunar  valve  :  I),  posi- 
tion of  corpora  Arantii ;  P,  pulmonary  arterj  ; 

B,  wall  of  left  auricle  ;  M,  mitral  valve,  with 
1  and  2,  its  posterior  and  anterior  segments  ; 

C,  wall  of  right  auricle  ;  T,  tricuspid  valve,  with 
1,  its  posterior  ;  2,  its  anterior  ;  and  3.  its  external 
segment. 


PR  U  I  /<    //    /  XERCIS1  S  191 

funnel  with  water,  and  it  will  rise  in  B  to  the  same  level  as  in  the 
tunnel.  Now  compress  the  righl  ventricle  with  the  hand,  and  the 
water  will  rise  higher  in  B.  Relax  the  pressure,  and  notice  that  the 
water  remains  at  the  higher  level  in  B.  being  prevented  by  tin-  semi 
lunar  valves  from  flowing  back  into  the  ventricle.  By  alternately 
compressing  the  ventricle  and  allowing  it  to  relax,  water  can  be 
pumped  into  B  till  it  escapes  from  its  upper  end,  and  if  this  is  SO 
Curved  th.it  the  water  tails  into  the  funnel,  a  'circulation'  which 
imitates  that  ot  the  blood  can  be  established.  Note  that  during  the 
1  hi m ping  the  sinuses  of  Valsalva,  behind  the  semilunar  valves  at  the 
origin  of  the  pulmonary  artery,  become  prominent. 

(<  1  Take  out  B  and  tear  out  one  of  the  segments  of  the  semilunar 
valve.  Kepi. ice  B,  and  notice  that  while  compression  of  the  ventricle 
has  the  same  effect  as  before,  the  water  no  longer  keeps  its  level  on 
relaxation,  but  regurgitates  into  the  ventricle.  This  illustrates  the 
condition  known  as  insufficiency  or  incompetence  of  the  valves.  But 
if  the  injury  is  not  too  extensive,  it  is  still  possible,  by  more  vigorously 
and  more  rapidly  compressing  the  heart,  to  pump  water  into  the 
funnel.  This  illustrates  the  establishment  of  compensation  in  cases 
of  valvular  lesion. 

(d)  Now  remove  both  tubes.  Tic  the  pulmonary  artery.  Cut 
away  the  greater  part  of  the  right  auricle.  Pour  water  into  the 
auriculo-vcntricular  orifice,  and  notice  that  the  segments  of  the 
tricuspid  valve  are  floated  up  so  as  to  close  the  orifice.  Invert  the 
heart,  and  the  ventricle  will  remain  full  of  water.  Open  the  right 
ventricle  carefully,  and  study  the  papillary  muscles,  and  the  chordae 
tendinese,  noting  that  the  latter  are  inserted  into  the  lower  surface 
of  the  segments  of  the  tricuspid  valve,  as  well  as  into  their  free  edges. 

(e)  Repeat  (b),  (c),  and  (d)  on  the  left  side  of  the  heart,  tying  tube 
B  into  the  aorta  as  far  from  the  heart  as  possible,  and  A  into  the  left 
auricle. 

(/)  Separate  the  aorta  from  the  left  ventricle,  cutting  wide  of  its 
origin  so  as  not  to  injure  the  semilunar  valves,  and  tie  a  short  wide 
tube  into  its  distal  end.  Fill  the  tube  with  water,  and  notice  that 
the  valves  support  it.  Cut  open  the  aorta  just  between  twro  adjacent 
segments  of  the  valve,  and  notice  the  pockets  behind  the  segments, 
and  how  they  are  related  to  each  other,  and  connected  to  the  wall  of 
the  vessel. 

15.  Sounds  of  the  Heart. — {a)  In  a  fellow-student  notice  the 
position  of  the  cardiac  impulse,  the  chest  being  well  exposed.  Use 
both  a  binaural  and  a  single-tube  stethoscope.  Place  the  chest-piece 
of  the  stethoscope  over  the  impulse,  and  make  out  the  two  sounds 
and  the  pause,  (b)  With  the  hand  over  the  radial  or  brachial  artery, 
try  to  determine  whether  the  beat  of  the  pulse  is  felt  in  the  period 
of  the  sounds  or  of  the  pause,  (c)  Listen  with  the  stethoscope  over 
the  junction  of  the  second  right  costal  cartilage  with  the  sternum, 
and  compare  the  relative  intensity  of  the  two  sounds  as  heard  here 
with  their  relative  intensity  as  heard  over  the  cardiac  impulse. 

16.  Cardiogram. — Smoke  a  drum,  and  arrange  a  recording  tam- 
bour and  a  time-marker  beating  half  or  quarter  seconds  to  write 
on  it  (Fig.  76,  p.  179).  Apply  the  button  of  a  cardiograph  (Fig.  22, 
p.  82)  over  your  own  cardiac  impulse,  and  fasten  it  round  the  body 
by  the  bands  attached  to  the  instrument.  Connect  the  cardiograph 
by  an  indiarubber  tube  with  a  recording  tambour  (Fig.  86).  Set  the 
drum  off  at  a  fast  speed,  take  a  tracing,  and  varnish  it.  Compare 
with  Fig.  23  (p.  83),  and  if  the  tracing  is  sufficiently  typical,  as  is 


IQC 


A    V  INU  //    <>/■■  PHYSIOLOGY 


often  not  the  case  with  human  cardiograms,  measure  oul  the  time- 
value  of  the  various  events  in  the  cardiac  revolution. 

For  the  cardiograph,  a  small  glass  funnel,  or  thistle  tube,  the  stem 
of  which  is  connected  with  the  recording  tambour,  may  be  sub- 
stituted, the  broad  end  <>!  the  funnel  being  pressed  over  the  apex-beat. 

17.  Sphygmographic  Tracings. — Attach  a  Marey's  sphygmograph 
(Fig.  31,  p.  93)  tn  t  In-  arm.  Fasten  a  smoked  paper  on  the  plat  I » 
Apply  the  pad  C  of  the  sphygmograph  to  the  wrist  over  the  point 


Fig.  86. — Marey's  Tambour. 


where  the  pulse  of  the  radial  artery  can  be  most  distinctly  felt. 
Adjust  the  pressure  by  moving  the  screw  G.  The  writing-point  of 
the  lever  E  will  rise  and  fall  with  every  pulse-beat.  When  every- 
thing is  satisfactorily  arranged,  set  off  the  clockwork  which  moves 
the  plate  D.  and  a  pulse  tracing  will  be  obtained.  Study  the 
changes  which  can  be  produced  in  the  pulse  curve — (a)  by  altering 
the  position  of  the  body  (sitting,  standing,  and  lying  down)  ;  (b)  by 

exercise  (Fig.  88)  ;  (7 1  by 
inhalation  of  2  drops  of 
amyl  nitrite  poured  on  a 
handkerchief  by  the  de- 
monstrator (Fig.  89)  ;  (d) 
by  raising  the  arm  above 
the  headland  letting  it 
hang  at  the  side  ;  (e)  by 
compression  of  the  brach  ial 


Fig.  87. — Dudgeon's  Sphygmograph. 

artery  at  the  bend  of  the  elbow  ;  (/)  by  altering  the  pressure  of  the 
pad.  Varnish  the  tracings  alter  marking  on  them  the  conditions 
under  winch  they  were  obtained. 

A  Dudgeon's  sphygmograph  (Fig.  87)  may  also  be  employed. 
Or  a  small  glass  funnel  or  thistle  tube  connected  with  a  recording 
tambour  may  !>'■  pressed  over  the  carotid  artery.  The  lever  of  the 
tambour  writes  on  a  drum,  on  which  at  the  same  time  half  or  quarter 
si  conds  are  marked  by  an  eled  ro-magnetic  signal. 


PRA(  I  h  AL  EXERCISES 


■93 


SJ  V. 


[8.  Venous    Pulse    Tracing    from    the    Jugular    Vein.     An 
recording  tambour  to  write  on  a  drum.     Connect  the  tambour  with 

t  he  stem  of  a  small  glass  thistle-1  abe  (or  with  a  small  metal  cup)  by  a 

piece  of  narrow  rubber  tubing,  and  apply  the  cup-shaped  end  of  the 

thistle-tube  over  the  right  jugular  bulb  of  a  fellow-student.     This 

lies  about   i   inch  external  to  the 

right  sterno-clavicular  articulation, 

and  a  little  above  it.      The  n 

may   have  to  be  moved  about  a 

little    until    the    best    pulsation    is 

obtained.     The  '  patient  '  should  be 

lying  down,  the  shoulders  slightly 

raised,  the  head  on   a  pillow    and 

turned  slightly  to  the  right,  in  order 

to  relax   the  right   sterno-mastoid 

muscle  (Mackenzie). 

19.  Polygraph  Tracings. — 
Arrange  the  polygraph  over  the 
radial  artery,  as  with  an  ordinary 
sphygmograph.  so  that  the  lever  will 
record  the  radial  pulse  when  the 
strip  of  paper  is  set  moving.  If  the 
instrument  has  only  one  tambour,  connect  the  tambour  to  a  receiver 
or  thistle-tube  over  the  jugular  bulb,  and  arrange  the  writing-point 
of  the  tambour  immediately  below  the  writing-point  connected  with 
the  radial.  If  the  polygraph  is  provided  with  clockwork  to  record 
time,  set  off  the  time-marker  writing  fifths  of  a  second.     When  it  is 


MUMJUWUVAA 


Fig.   88. — Effect  of  Exercise  on 
the  Pulse  (Marey). 

Upper     tracing,     normal ;     lower, 
after^running. 


Fig.   &<j. — Effect  of   Amyl   Nitrite   on   thk 
Pulse   (Marey). 

Upper  tracing,  normal ;  lower,  after  inhala- 
tion of  amyl  nitrite. 


Fig.    90.  —  Pulse    Tracings 
from  Different  Arteries. 

T,  temporal  ;   R,  radial ;  P, 
artery  of  foot  (v.  Frey). 


seen  that  the  writing-points  are  marking  properly,  start  the  clockwork 
which  moves  the  strip  of  smoked  paper.  Repeat  the  observation 
with  the  tambour  connected  with  the  apex-beat.  Letter  the  curves 
as  far  as  possible  as  in  Figs. 355  and;'56  (p.  137) -without  at  present 
attempting  their  exact  analysis. 

If  the  polygraph  has  two  tambours,  simultaneous  tracings  of  the 

13 


194 


A   M  IM    //.  OF  PHYSIOLOGY 


radial  pulse,  the  jugular  pulse,  and  the  cardiac  impulse,  or  oi  the 
carotid  pulse,  the  jugular  pulse,  and  the  apex-beat,  may  be  taken, 
and  other  combinations  as  well.  If  no  polygraph  is  available,  a 
drum  may  be  employed,  the  tracings  being  all  taken  with  thistle- 
tubes  connected  with  recording  tambours.  The  lexers  of  the 
tambours  must  be  arranged  to  write  on  the  drum  in  the  same 
\  erticaJ  straight  line,  or,  without  making  the  adjustment  quite  exact, 
vertical  lines  of  reference  may  be  drawn  through  each  curve,  with  the 
drum  at  rest,  indicating  the  relative  positions  of  the  writing-points. 

20.  Plethysmographic  Tracings. — Connect  the   vessel   C  (Fi 
p.  117)  with  B,  place  the  arm  in  it,  and  adjust  the  indiarubber  band 
to  make  a  watertight  connection.     Support  C  so  that  the  arm  rests 
easily  within  it,  and  fill  it  with  water  at  body  temperature.      Adjust  a 

writing-point,  carried  by  the  float 
A,  to  write  on  a  drum,  and  close 
the  upper  tubulurc  of  C  with  a 
cork.  The  quantity  of  blood  in 
the  arm  is  increased  with  every 
systole  of  the  left  ventricle, 
diminished  in  diastole  The  float 
will  therefore  rise  when  the  ven- 
tricle contracts,  and  sink  when  it 
relaxes.  Or  C  may  be  conn< 
by  a  rubber  tube  with  a  record- 
ing tambour  writing  on  the  drum . 


Fig.  91. — Plethysmograph  (Mosso). 

.1/,  balanced  test-tube,  in  communication  with  I>.  Winn  water  passes  from 
vessel  D  to  M,  or  from  M  to  D,  M  moves  down  or  up,  and  its  movements  are  re- 
corded by  the  writing-point  N.     M  is  steadied  by  the  liquid  in  P,  into  which  it  dips. 

No  water  must  get  into  the  tambour,  and  it  is  well  to  insert  a 
piece  of  glass  tubing  in  the  connection  between  it  and  the  plethys- 
mograph, so  that  it  may  be  seen  when  the  water  is  rising  too  high. 
A  T-piece  with  a  short  piece  of  rubber  tubing  on  the  stem  should 
be  inserted  in  the  course  of  the  tube  leading  to  the  tambour.  All 
adjustments  are  made  with  the  T-piccc  open,  and  when  a  tracing  is 
to  be  taken  the  short  rubber  tube  is  closed  by  a  clip.  Arrange  a 
time-marker  to  write  half  or  quarter  seconds  (Fig.  76,  p.  179). 
Mosso's  arm  plethysmograph  (Fig.  91)  may  also  be  used. 


PRACTICAL  EXERCISES  195 

(1)  Take  tracings  with  the  arm  (a)  horizontal,  (b)  hanging  down. 

(2)  With   the   arm    horizontal,   take   tracings  to   show  the   effect 

(a)  of  closing   and   opening   the   fist   inside  the   plethysmograph  ;* 

(b)  of  applying  a  tight   bandage  round  the  arm  a  little  way  above 
tin   indiarubber  band  ;  (c)  of  inhaling  2  drops  of  amyl  nitrite. 

Instead  of  the  arm  plethysmograph  a  small  plethysmograph  to 
hold  a  finger  may  be  employed.  It  consists  of  a  glass  tube  drawn 
out  at  one  end.  The  wide  end  is  provided  with  a  rubber  collar. 
The  narrow  end  is  connected  by  a  small  rubber  tube  with  a  very 
small  and  sensitive  recording  tambour,  a  T-piece  being  inserted  on 
the  connection  as  before.  With  the  T-picce  closed  fill  the  tube  with 
water.  Then,  holding  up  the  wide  end  of  the  tube,  the  tip  of  the 
finger  is  put  in  so  as  just  to  close  the  tube.  The  T-piece  is  then 
raised  and  opened,  and  the  finger  pushed  in  as  far  as  it  will  go. 
The  collar  must  fit  the  linger  so  as  to  form  a  watertight  joint.  Now 
get  the  proper  pressure  in  the  tambour  by  blowing  into  the  T-piece, 
and  close  the  clamp.     A  time-tracing  can  be  taken  as  before. 

21.  Pulse-rate. — (1)  Count  the  radial  pulse  for  a  minute  in  the 
sitting,  supine,  and  standing  positions.  Use  a  stop-watch,  setting 
it  off  on  a  pulse-beat  and  counting  the  next  beat  as  one.  Make 
three  observations  in  each  position. 

(2)  Count  the  pulse  in  a  person  sitting  at  rest,  and  then  again  in 
the  sitting  position  immediately  after  active  muscular  exertion. 
Note  how  long  it  takes  before  the  pulse-rate  comes  back  to  normal. 

(3)  Count  the  pulse  in  a  person  sitting  at  rest.  Repeat  the 
observation  while  water  is  being  slowly  sipped,  and  note  any  change. 

(4)  With  one  hand  over  the  thorax  of  a  rabbit,  count  its  pulse. 
Then  notice  the  effect  (a)  of  suddenly  closing  its  nostrils,  (b)  of 
bringing  a  small  piece  of  cotton- wool  sprinkled  with  ammonia  or 
chloroform  in  front  of  the  nose  (reflex  inhibition  of  the  heart). 

22.  Blood-pressure  Tracing. — (a)  Put  a  dog  under  morphine  (p.  55). 
Set  up  an  induction  machine  arranged  for  an  interrupted  current 
(Fig.  81,  p.  184).  Fill  the  U-shaped  manometer  tube  (if  this  has 
not  already  been  done)  with  clean  mercury  to  the  height  of  10  to 
12  cm.  in  each  limb.  If  the  float  tends  to  stick,  half  an  inch  of  oil 
may  be  put  above  the  mercury  in  the  distal  (straight)  limb  before 
putting  in  the  float.  But  where  the  mercury  is  clean  and  dry,  and  the 
size  of  the  float  properly  adjusted  to  that  of  the  tube,  this  is  not 
necessary,  and  is  to  be  avoided.  Then,  tilting  the  tube  carefully, 
fill  the  proximal  limb  (i.e.,  the  limb  which  is  to  be  connected  with 
the  bloodvessel)  with  a  saturated  solution  of  sodium  carbonate  or 
a  half-saturated  solution  of  magnesium  sulphate,  or  what  is  better 
for  most  purposes,  a  2  per  cent,  solution  of  sodium  citrate.  This  is 
easily  done  by  means  of  a  pipette  furnished  with  a  long  point.  Now 
attach  a  strong  rubber  tube  to  the  proximal  end  of  the  manometer, 
and  fill  it  also  with  the  solution.  All  air  must  be  got  out  of  the 
manometer  and  its  connecting-tube.  Raise  the  end  of  the  rubber 
tube  and  blow  into  it,  so  as  to  cause  a  difference  of  about  10  cm.  in 
the  height  of  the  mercury  in  the  two  limbs  of  the  manometer,  and, 
without  releasing  the  pressure,  clamp  the  tube  with  a  pinchcock  or 
screw  clamp  (Fig.  34,  p.  10 1). 

Now  smoke  a  drum,  and  arrange  the  writing-point  of  the  mano- 
meter-float so  that  it  will  write  on  it.  Suspend  a  small  weight  by  a 
piece  of  silk  thread  from  a  support  attached  to  the  stand  of  the 

*  Closing  the  fist  causes  a  fall  in  the  curve,  i.e.,  a  diminution  in  the 
volume  of  the  arm.     On  opening  the  hand,  the  curve  regains  its  level. 

13—2 


I't't 


;    i/  i  vr  //    OF    PHI  SIOLOGY 


drum,  so  that  it  hangs  down  outside  of  the  writi 
manometer-floal  and  always  keeps  it  in  contact  w 
surface  withoul  undue  friction.  Or  a 
piece  of  ul<'ss  rod  drawn  out  to  a  fine 
tlire.nl  in  the  blowpipe  flame  answers 
very  well.  Below  the  writing-point  of 
the  float,  and  in  the  same  vertical  line  __ 
with  it,  adjust  the  writing-point  of  ag 
time-marker  beating  seconds   (Fig.    76, 

p.   [79). 

Next,  fasten  the  animal  on  a  holder, 
back  down.  Give  ether  and  insert  a 
tracheal  cannula  (p.  186).  (The  tracheal 
cannula  is  not  absolutely  required  for 
the  experiment,  but  it  is  convenient,  as 
the  animal  is  more  under  control,  and 
artificial  respiration  can  be  begun  at  any 
moment,  should  this  be  necessary.) 
Insert  a  glass  cannula,  armed  with  a 
short  piece  of  rubber  tubing,  into  the 


ng-poin 
ith  the 


t    of   the 
smoked 


T HRE  E  -  W  A  Y    C  A  N  N  e  1.  A . 


central  (cardiac)  end  of  the  carotid 
artery  (p.  55).  Leaving  the  bulldog 
forceps  on  the  artery,  fill  the  cannula 
and  tube  with  the  sodium  citrate  or 
one  of  the  other  solutions.  Slip  the 
rubber  tube  over  a  short  glass  come,  1 
ing-tube.  Fill  this  also  with  the  solu- 
tion, and  connect  it  with  the  mano- 
meter-tube, seeing  that  both  are  quite 
full  of  liquid,  so  that  no  air  may  be 
enclosed. 

Where  a  permanent  working  place  is 
provided  for  blood-pressure  experiments 
it  is  convenient  to  connect  the  cannula 
and  manometer  with  a.  pressure-bottle 
containing  the  sodium  citrate  solution, 
and  to  use  a  three-way  cannula  lor 
the  bloodvessel  (Fig.  92).  The  cannula 
has  a  bulbous  enlargement,  which  hinders  clotting 


I'n..     93.  — Manometi  r    with 
Side-tube  (Guthrii  i. 

A,  il". it  ;  li.  collar  through 
winch  the  wire  C  '>f  the  Boat 
moves  ;  1),  vertical  win-  fixed 
to  manometer  -  holder,  which 
keeps  the  writing-point  on  the 
drum  :  E,  limb  ol  manometer 
connected  with  cannula,  with 
its  side-piece,  F. 


The  end  of  the 
cannula'is  connected  with  the  tube  from  the  pressure-bottle,  which 


PRACTICAL  EXERCISES 


"<; 


is  closed  by  a  clip,  and  the  side-tube  is  connected  with  one  Limb,  E, 
of  the  manometer  shown  in  Fig.  93-  E  is  itself  provided  with  a 
side-tube,  F,  armed  with  a  short  piece  of  rubber  tubing.  I/he 
cannula  does  no1  require  to  be  idled  with  liquid  before  being  insert <■. I 
into  the  artery.  By  opening  F  arid  releasing  the  clip  on  the  tube 
from  the  pressure-bottle  the  cannula  and  the  tube  connects 
with  the  manometer  can  be  filled,  and  any  blood-clots  can  be  easily 
washed  out  in  the  course  of  an  experiment.  Before  the  bulldog 
forceps  is  taken  oil  the  artery  to  obtain  a  blood-pressure  tracing, 
V  must  be  closed,  and  the  clip  on  the  tube  from  the  pressure-bottle 
opened.  The  bottle  is  attached  to  a  strong  cord  passing  over  a 
pulley  by  which  it  is  raised  to  a  height  sufficient  to  balance  approxi- 
mately the  pressure  in  the  artery.     The  tube  to  the  pressure-bottle 


Stimulation  of 
central  end.  stopped 


I  Peripheral   end  ^ 

stimulated     J^ 


Fig.  94. 


-Blood-pressure  Tracing  from  a  Dog  :  Stimulation  of  Central 
and  Peripheral  Ends  of  Vagus. 


The  other  vagus  was  intact.  Stimulation  of  the  peripheral  end  caused  stoppage 
of  the  heart  and  a  marked  fall  of  pressure.  Stimulation  of  the  central  end  pro- 
duced a  great  rise  of  pressure,  with,  perhaps,  a  slight  acceleration  of  the  heart. 

is  then  clipped.  If  no  manometer  with  side-tube  is  available,  a 
T-piece  can  be  inserted  in  the  connection  between  the  cannula 
and  the  manometer,  and  the  cannula  can  be  washed  out  through 

this.  ,      , 

Now  take  the  bulldog  forceps  off  the  artery,  and  allow  the  drum  to 
revolve  at  slow  speed.  The  writing-point  of  the  manometer-float 
will  trace  a  curve  showing  an  elevation  for  each  heart -beat,  and 
longer  waves  due  to  the  movements  of  respiration. 

(b)  Isolate  the  vago-sympathetic  nerve  in  the  neck.  Ligature 
doubly,  and  cut  between  the  ligatures.  Stimulate  the  peripheral 
(lower)  end  ;  the  heart  will  be  slowed  or  stopped,  and  the  blood- 
pressure  will  fall.     Stimulate  the  central  (upper)  end  ;  there  may  be 


.'98  A   MANUAL  OF  PHYSIOLOGY 

inhibition  of  the  heart  or  acceleration,  and  the  pressure  may  fall 

Or  rise  (p.    [54). 

(c)  Expose  and  divide  the  other  vagosympathetic  while  a  trai  ing 

is  being  taken.     Again  stimulate  the  central  end  of  the  nerve  and 
observe  whether  there  is  any  effect. 

(d)  Expose  the  sciatic  nerve  in  one  leg,  as  follows  :  The  leg  having 
been  loosened  from  the  holder,  the  foot  is  seized  by  one  hand  and 
lifted  straight  up,  so  as  to  put  the  skin  of  the  thigh  on  the  stretch. 
An  incision  is  now  made  in  the  middle  line  on  the  posterior  aspei  1 
of  the  thigh,  through  the  skin  and  subcutaneous  tissue.  The 
muscles  are  separated  in  the  line  of  the  incision  with  the  fingers, 
and  the  sciatic  nerve  comes  into  view  lying  deeply  between  them. 
Place  a  double  ligature  on  it,  and  divide  between  the  ligature-,. 
Stimulate  the  upper  (central  end)  ;  the  blood-pressure  probably 
rises,  and  the  heart  may  be  accelerated.  Stimulate  the  peripheral 
end  of  the  nerve  ;  there  is  little  change  in  the  blood-pressure  and 
none  in  the  rate  of  the  heart. 

(e)  Note,  incidentally,  that  stimulation  of  the  central  end  of  the 
sciatic  or  the  upper  (cephalic)  end  of  the  vago-sympat hetic  may 
cause  increase  in  the  rate  and  depth  of  the  respiratory  movements. 
Dilatation  of  the  pupil  is  also  caused  by  stimulation  of  the  upper 
end  of  the  vago-sympathetic  through  the  sympathetic  (pupillo-dilator) 
fibres  that  supply  the  iris. 

(/)  Again  stimulate  the  peripheral  end  of  one  vagus,  or  of  both 
at  the  same  time,  while  a  tracing  is  being  taken,  and  see  how  long 
it  is  possible  to  keep  the  heart  from  beating.  Sometimes,  but 
rarely,  in  the  dog  inhibition  can  be  kept  up  so  long  that  the  animal 
dies. 

(g)  Close  the  tracheal  cannula  so  that  air  can  no  longer  enter  the 
lungs.  In  a  very  short  time  the  blood-pressure  curve  begins  to  rise 
(rise  of  asphyxia).  After  some  minutes  the  pressure  falls,  and  finally, 
when  the  circulation  has  stopped  completely  and  the  pressure  has 
become  equalized  throughout  the  whole  vascular  system,  a  residual 
pressure  of  only  a  few  mm.  (usually  about  10  mm.  Hg)  is  indicated. 
In  order  to  get  the  true  zero  pressure,  disconnect  the  arterial  can- 
nula from  the  manometer,  and  allow  the  writing-point  to  trace  a 
horizontal  straight  line  (line  of  zero  pressure)  on  the  drum  (Figs.  72 
and  73). 

23.  Estimation  of  the  Arterial  Blood-pressure  in  Man.  With  the 
Erlanger  sphygmomanometer  estimate  the  systolic  and  diastolic 
pressures  in  the  brachial  artery  of  a  fellow-student  as  described  on 
p.  105.     Begin  with  the  observed  person  in  the  sitting  position. 

Compare  the  results  with  those  obtained  on  the  same  artery  with 
any  other  sphygmomanometer  which  may  be  available,  especial  lv 
with  one  like  the  Riva-Rocci,  with  which  the  systolic  pressure  is 
obtained  by  observing  the  height  of  the  mercurial  manometer  at 
the  moment  when  the  pressure  in  the  cuff  over  the  brachial  has 
fallen  to  the  point  at  which  the  pulse  at  the  wrist  is  just  obliterated. 
By  compressing  rapidly  the  rubber  bulb  the  mercury  is  first  raised 
to  a  height  somewhat  greater  than  that  necessary  to  completely 
obliterate  the  radial  pulse.  Then  the  bulb  is  kept  compressed,  and 
the  mercury  allowed  to  fall  steadily,  the  point  being  noted  at  which 
the  fingers  over  the  radial  just  perceive  the  returning  pulse.  The 
observer's  left  hand  may  be  used  for  palpating  the  pulse,  and  the 
right  for  working  the  bulb.  Repeat  the  observations  with  the 
person  standing  up  and  lying  down.  Investigate  the  effect  of 
muscular  exercise  on  the  blood-pressure. 


PRACTICAL  EXERCISES  199 

24.  The  Influence  of  the  Position  of  the  Body  on  the  Blood- 
pressure.  Inject  into  the  rectum  of  a  dog  3  to  4  grm.  of  chloral 
hydrate  dissolved  in  a  little  water.  See  thai  LI  does  not  run  out 
again  immediately  after  injection.  In  ten  minutes  anaesthetize  the 
animal  fully  with  a  mixture  of  equal  parts  of  alcohol,  chloroform,  and 
ether  (one  ot  the  so  called  A..C.E.  mixtures),  or  with  chloroform,  and 
tie  i1  \  ery  securely,  back  downward,  on  a  board,  which  can  be  rotated 
around  a  horizontal  axis,  corresponding  in  position  to  the  point  at 
which  the  cannula  is  to  be  inserted.*  Set  up  a  drum  and  manometer 
as  in  -•_•  (p.  195),  but  with  a  rubber  connecting-tube  of  such  length 
as  will  allow  free  rotation  of  the  board.  Put  a  cannula  in  the 
trachea.  Insert  a  cannula  into  the  central  end  of  the  carotid 
artery  at  a  point  immediately  above  the  axis  of  rotation  of  the  board, 
and  connect  it  with  the  manometer. 

(a)  Take  a  blood-pressure  tracing  with  the  board  horizontal, 
\b)  Whilst  the  tracing  is  being  taken,  rotate  the  board  so  that 
the  position  of  the  animal  becomes  vertical,  with  the  feet  down. 
Mark  on  the  tracing  the  moment  when  the  change  of  position 
takes  place.  The  pressure  falls.  Replace  the  dog  in  the  hori- 
zontal position.  The  manometer  regains  its  former  level.  Now 
rotate  the  board,  till  the  animal  is  again  vertical,  but  with  feet 
up  and  head  down,  and  observe  the  effect  on  the  blood-pressure. 
The  respiratory  variations  in  the  pressure  ar.e  usually  greater  with 
feet  down  than  with  head  down.  Notice  in  both  cases  whether 
there  is  any  change  in  the  rate  of  the  heart. 

(c)  Take  the  board  off  the  stands,  lay  it  on  a  table,  expose  the 
femoral  artery,  and  insert  a  cannula  into  it.  Shift  the  axis  so 
that  it  now  lies  below  this  cannula.  Replace  the  board  on  the 
stands,  and  repeat  (a)  and  (£>).  The  fall  of  pressure  will  now 
take  place  in  the  head-down  position. f  In  the  feet-down  position 
(with  the  cannula  in  the  femoral  artery)  a  rise  of  pressure  in 
general  takes  place.  But  sometimes  this  is  very  small,  and  lasts 
only  a  few  seconds,  being  succeeded  by  a  fall,  during  which  the 
heart-beats  on  the  tracing  are  much  weaker  than  before,  since 
enough  blood  is  not  reaching  the  heart  to  enable  it  to  maintain 
the  pressure.  In  the  feet-down  position  see  whether  the  corneal 
reflex  can  be  got.  If  not,  as  is  likely,  turn  the  animal  into  the 
head-down  position.  The  reflex  may  now  soon  be  obtained,  and 
it  may  again  disappear  on  putting  the  animal  in  the  feet-down 
position.  If  the  chloroform  anaesthesia  is  light  the  reflex  may  not 
be  abolished  in  the  feet-down  position,  although  strong  respiratory 

*  A  simple  arrangement  for  this  purpose  is  a  board  with  a  number  of 
staples  fastened  in  pairs  into  its  lower  surface,  so  that  an  iron  rod  can  be 
pushed  through  any  pair,  and  form  a  horizontal  axis  at  right  angles  to 
the  length  of  the  board.  The  dog  having  been  tied  down,  the  rod  is 
pushed  through  the  pair  of  staples  corresponding  to  the  position  of  the 
cannula  in  the  artery  that  is  to  be  connected  with  the  manometer.  The 
projecting  ends  of  the  rod  rest  in  two  ordinary  clamp-holders,  fastened  at 
a  convenient  height  on  two  strong  stands,  whose  bases  are  clamped  to  the 
end  of  a  table.  The  other  end  of  the  board  is  supported  by  a  piece  of 
wood  that  rests  on  the  floor,  and  can  be  removed  when  the  board  is  to  be 
rotated. 

f  In  16  dogs  the  fall  of  pressure  in  the  carotid  in  the  feet-down  posi- 
tion varied  from  12  to  100  mm.  of  mercury  ;  average  fall,  44*4  mm.  In 
12  out  of  the  16  animals  the  rise  of  pressure  in  the  head-down  position 
varied  from  2  to  36  mm.  ;  in  1  there  was  no  change  ;  in  3  there  was  a  fall 
of  5  to  24  mm. 


2oo  A   M  INV  II    01    PHYSIOLOG  Y 

movements    may    occur,    owing    to   anaemia    oi    the    medulla    ob- 
longata. 

25.  Effects  of  Haemorrhage  and  Transfusion  on  the  Blood- 
pressure.-—  An, i'si  lict ize  .1  dog  with  morphine  and  ether,  and  insert  a 
cannula  into  the  trachea.     Pu1  a  cannula  into  the  central  end  oi  the 

carotid  artery  and  am  it  her  into  the  central  end  oi  the  femoral  artery. 
Ilicn  insert  a  cannula,  which  should  have  a  piece  of  indiarubber 
tubing  2  to  3  inches  in  length  on  its  wide  end.  into  the  i  entral  end 
of  the  femoral  vein  on  the  opposite  side.  In  doing  this  more  i  are 
is  necessary  than  in  putting  a  cannula  into  an  artery.  Feel  for  the 
femora]  artery,  cut  down  oxer  it,  and  with  forceps  or  a  blunt  needle 
separate  the  femoral  vein  from  it  for  about  an  inch.  I 'ass  two 
ligatures  under  the  vein,  and  tie  a  loose  loop  on  each.  I'ut  a 
pair  of  bulldog  forceps  on  the  veil!  between  the  ligatures  and  the 
heart.  Now  tie  the  lower  (distal)  ligature,  and  cut  one  end  short. 
The  piece  of  vein  between  it  and  the  bulldog  forceps  is  thus  dis- 
tended with  blood,  and  this  facilitates  the  next  step.  With  tine- 
pointed  scissors  make  a  snip  in  the  wall  of  the  vein.  The  cannula 
is  now  pushed  through  the  slit  in  the  vein,  and  the  upper  Ligature 
tied  firmly  round  its  neck.  By  the  aid  of  a  pipette,  made  by  drawing 
a  piece  of  glass  tubing  out  to  a  long  point,  the  cannula  and  rubber 
tube  are  then  completely  filled  with  09  per  cent,  salt  solution.  Be 
sure  to  pass  the  point  of  the  pipette  right  down  to  the  point  of  the 
cannula,  so  as  to  dislodge  any  bubble  of  air  that  may  tend  to  cling 
there.  Then,  holding  up  the  open  end  of  the  rubber  tube,  close  it. 
without  allowing  any  air  to  enter,  by  means  of  a  screw  clamp  or 
bulldog  forceps,  or  a  small  piece  of  glass  rod.  Connect  the  cannula 
in  the  carotid  with  a  manometer,  arranged  to  write  on  a  drum  as 
in  experiment  22  (p.  195).  Take  the  bulldog  off  the  carotid,  and 
measure  the  difference  in  the  level  of  the  mercury  in  the  two  limbs 
of  the  manometer  with  a  millimetre  scale. 

(1)  (a)  While  a  tracing  is  being  taken,  draw  off  about  10  c.c.  of 
blood  from  the  femoral  artery,  and  observe  whether  there  is  any 
eilect  on  the  tracing.  Mark  on  the  tracing  the  moment  when  the 
removal  of  the  blood  begins  and  ends. 

(b)  Repeat  (a),  but  run  off  about  100  c.c*  of  blood,  and  let  this 
be  immediately  defibrinated.  Then  draw  off  portions  of  100  c.c* 
at  short  intervals  until  a  distinct  fall  of  blood-pressure  has  been 
produced.  All  the  samples  of  blood  should  be  defibrinated  and 
strained  through  cheese-cloth. 

(2)  (a)  Now,  while  a  tracing  is  being  taken,  inject  the  Whole  "I 
the  defibrinated  blood  slowly  through  the  cannula  in  the  femoral 
vein  by  means  of  a  funnel  supported  by  a  stand  at  such  a  height  that 
the  blood  runs  in  easily.  A  pinchcock  should  be  put  on  the  tube 
connecting  the  funnel  and  the  cannula,  and  this  should  be  closed 
before  the  funnel  is  quite  empty,  so  as  to  obviate  any  risk  of  air 
getting  into  the  vein.  Of  course,  the  cannula  and  connecting-tubes 
must  all  be  freed  from  air  before  injection  is  begun.  Again  measure 
the  difference  in  the  level  of  the  mercury  and  compare  the  pressure 
with  that  observed  before  the  first  haemorrhage. 

(//)  Inject  into  the  vein,  while  a  tracing  is  being  obtained,  about 
100  c.c*  of  09  per  cent,  salt  solution  heated  to  400  (.'..  and  go  on 
injecting  portions  of  100  c.c.  until  a  distinct  rise  of  pressure  has  taken 
place,  keeping  a  record  of  the  total  amount  injected,  and  marking  the 
time  of  each  injection  on  the  curve. 

*  200  c.c.  for  a  large  dog. 


PRACTlCAl    EXERCISES  201 

\itcr  an  interval  of  thirty  minutes,  again  measure  the  heighl  ol 
tlie  mercury  in  the  manometer.  Then  bleed  the  dog  to  death  while 
.1  t  racing  is  being  recorded. 

20.  The  Influence  of  Albumoses  (and  Peptones)  on  the  Blood- 
pressure.  Set  up  the  apparatus  for  taking  a  blood  pressure  tracing 
as  in  experiment  22  (p.  105).  but  omit  the  induct  ion-coil.  Weigh 
a  dot;.  Weigh  out  a  quantity  oi  Witte's  peptone  equivalent  to 
o-5  grm.  for  every  kilo  of  body-weight.  Dissolve  the  peptone  in 
about,  ten  times  its  weight  ol  O'g  per  cent .  salt  solution.  Amcsthc- 
ti/c  the  dog  with  morphine  and  ether  or  A.C.E.  mixture.  Insert  a 
cannula  into  the  trachea.  Put  cannula'  into  the  central  end  of 
one  carotid  and  of  one  femoral  vein  (p.  200).  Connect  the  carotid 
with  the  manometer,  and  the  femoral  vein  with  a  burette  or  large 
syringe  containing  the  peptone  solution.  Take  care  that  the 
connecting-tube  and  cannula  are  free  from  air.  Now  commence 
to  take  a  blood-pressure  tracing,  and  while  it  is  going  on  inject 
the  peptone  solution.  The  pressure  falls  owing  largely  to  a  dilata- 
tion of  the  small     arteries  through  the  direct   action  of  the   peptone 


■  Peptone   injected. 


^ww^"* 


Fig.  95. — Effect  of  Injection  of  Peptone  on  the  Blood-pressure 
in  a  Dog. 

(To  be  read  from  right  to  left.) 


on   their    muscular    tissue    or   on   the    endings   of   the    vaso-motor 
nerves.* 

27.  Effect  of  Suprarenal  Extract  on  the  Blood-pressure. — Make 
the  arrangements  for  a  blood-pressure  tracing  from  a  dog  as  in  22, 
p.  195.  Put  a  cannula  in  the  carotid  and  another  in  the  femoral  vein 
or  one  of  its  branches  (p.  200).  Expose  both  vagi  in  the  neck,  and 
pass  threads  loosely  under  them.  Connect  the  carotid  with  the 
manometer  and  take  a  tracing.  Then,  while  the  tracing  is  continued, 
inject  slowly  into  the  femoral  vein  an  amount  of  watery  extract 
corresponding  to  about  0*2  grm.  of  suprarenal,  or,  what  is  more 
convenient,  a  few  c.c.  of  a  solution  of  adrenalin  chloride  of  the 
strength  of  1  to  50,000  in  o'g  per  cent,  sodium  chloride  solution, 
the  dose  depending,  of  course,  on  the  size  of  the  animal.     The  blood- 

*  In  12  dogs  the  blood-pressure  always  fell,  the  amount  of  the  fall 
varying  from  81  to  21  mm.  of  mercury  (average,  60  mm.).  It  sometimes 
returned  to  normal  in  twenty  to  thirty  minutes,  but  usually  required  a 
longer  time.  In  some  dogs,  after  the  injection  of  the  whole  of  this  amount 
oi  peptone,  death  occurs  before  there  has  been  any  considerable  recovery 
of  the  pressure. 


A   MANUAL  OF  PHYSIOLOGY 

pressure  rises*  owing  to  constriction  of  the  arterioles  by  direct 
excitation  of  the  junction  between  their  yaso-constrictor  nerves 
and  their  muscular  tissue.  The  heart  is  slowed,  but  its  beat  is 
strengthened.     At  once  cu1  both  vagi  while  a  tracing  is  being  taken  ; 

the  blood-pressure  rises  still  more  (p.  [56).  The  rise  of  pressure  is 
sometimes  so  great  that  to  prevent  the  mercury  from  being  forced 
out  of  the  manometer  the  tube  must  be  clipped.  The  rise  is  not  long 
maintained,  but  a  second  injection  causes  a  renewed  increase  of 
pressure. 

28.  Section  and  Stimulation  of  the  Cervical  Sympathetic  in  the 
Rabbit.  Set  up  an  induction-coil  arranged  for  an  interrupted 
current  (Fig.  81,  p.  184),  and  connect  it  through  a  short-circuiting 
key  with  electrodes.  The  preparations  necessary  for  an  operation 
with  antiseptic  precautions  are  supposed  to  have  been  previously 
made  the  instruments,  sponges,  and  ligatures  boiled  in  water  ; 
the  instruments  then  immersed  in  a  5  per  cent,  solution  (ri  carbolic 
acid,  the  sponges  and  ligatures  in  corrosive  sublimate  solution  (o- 1  per 
cent.),  [nstead  of  sponges  swabs  of  sterile  gauze  or  cotton  may  be 
used,  and  until  the  observations  on  the  nerve  have  been  made  it  is 
better  to  use  sterile  09  per  cent,  salt  solution  for  such  slight  sponging 
as  the  wound  may  require  rather  than  the  antiseptic  solutions.  The 
hands  are  to  be  thoroughly  washed,  with  diligent  use  of  the  nail- 
brush, in  soap  and  water  before  the  cutting  operation  begins,  and  t  hen 
soaked  successively  in  alcohol  and  in  the  corrosive  sublimate  solution. 

Fasten  the  rabbit  on  a  holder,  back  downwards,  as  in  Fig.  s  1 . 
Keep  the  animal  warm  by  covering  it  with  a  cloth,  and  do  not  handle 
or  wet  its  ears.  Clip  off  the  hair  on  the  anterior  surface  of  the  neck. 
Remove  loose  hairs  with  a  wet  sponge,  shave  the  neck,  and  wash  it 
thoroughly,  first  with  soap  and  water  and  then  with  corrosive 
sublimate.  Give  ether.  Make  a  longitudinal  incision  in  the 
middle  line  over  the  trachea,  beginning  a  little  below  ths  thyroid 
cartilage  and  extending  downwards  for  an  inch  and  a  half.  Feel  for 
the  carotid  artery,  expose,  and  raise  it  up.  Two  nerves  will  now  be 
seen  coursing  beside  the  artery.  The  larger  is  the  vagus,  the  smaller 
the  sympathetic.  A  third  and  much  finer  nerve  (the  depressor,  or 
superior  cardiac  branch  of  the  vagus)  may  also  be  seen  in  the  same 
position,  but  the  student  should  neglect  this  for  the  present.  Pass 
a  ligature  under  the  sympathetic,  and  tic  it.  the  ear  being  held  up  to 
the  tight  while  this  is  being  done,  so  that  its  vessels  may  be  clearly 
seen.  A  transient  constriction  of  the  arteries  may  be  seen  at  the 
moment  when  the  nerve  is  ligatured.  This  is  due  to  stimulation 
of  the  vaso-constrictor  fibres.  Then  follows  a  marked  dilatation 
of  the  bloodvessels,  due  to  paralysis  of  these  fibres.  The  car  is 
flushed  and  hot.  Note  also  that  the  pupil  is  probably  narrower  on 
the  side  on  which  the  nerve  has  been  tied.  On  stimulation  of  the 
upper  (cephalic)  end  of  the  sympathetic  with  the  electrodes,  the 
vessels  are  markedly  constricted,  the  car  becomes  pale  and  cold, 
and  the  pupil  dilates.     Cut  the  nerve  above  and  below  the  ligature 

*  The  amount  of  the  initial  rise  of  pressure  is  very  variable,  since  the 
slowing  of  the  heart  tends  to  diminish  the  pressure,  while  the  constriction 
of  the  arterioles  tends  to  increase  it.  Thus,  in  one  experiment  the  in<  I 
of  pressure  on  injection  of  the  extract  was  only  '>  mm.  of  mercury,  while 
in  another  it  was  ='  mm.  On  section  of  the  vagi  in  this  second  experi- 
ment, there  was  an  additional  rise  ol  64  mm.,  and  altera  second  injection 
a  further  rise  of  70  mm.,  making  an  increase  of  190  mm.  in  all  above  t he- 
original  pressure. 


PR  ICTIC  II.  EXERCISES 


~<  »3 


and  lake  out  the  ligature.  Wash  the  wound  thoroughly  with  cor- 
rosive sublimate,  then  with  sterile  (boiled)  water,  and  close  it,  the 
muscles  being  first  broughl  together  l>v  a  row  of  interrupted  sutures 

and  then  the  skin  bv  another  row.  Since  it  is  difficult  to  thoroughly 
disinfect   the  hair-follicles,  and  a  suture  passed   through  a  septic 

follicle  is  apt  to  give  rise  to  suppuration,  subcutaneous  stitches — 
/.(.,  stitches  passed  by  a  curved  needle  through  the  deep  layer  of  the 
skin  without  coming  through  to  the  surface — -may  be  employed. 
The  wound  is  to  be  protected  by  a  coating  of  collodion.  ,  No  other 
dressing  is  required.  The  animal  is  now  removed  from  the  holder 
and   put   bark  to   its  hutch.      The  student  must  examine  it  at  least 


Fig.   96. — Artificial  Scheme  to  illustrate  a  Method   of  Measuring  the 
Circulation-time. 

B,  bottle  containing  water,  the  rate  of  outflow  of  which  is  regulated  by  screw- 
clamp  a  ;  S,  syringe  filled  with  methylene-blue  solution,  connected  with  T-piece 
A;  M,  beakor  containing  methylene-blue  solution;  b,  c,  screw-clamps;  C,  T- 
piece,  inserted  in  the  course  of  the  flexible  tube  E,  and  connected  with  the  glass 
tube  T,  which  is  filled  with  beads  ;  F,  outflow  tube.  The  clamp  c  having  been 
closed  and  b  opened,  the  syringe  is  filled  with  the  methylene-blue  solution  ;  b  is 
then  closed,  c  opened,  and  a  definite  quantity  of  the  solution  injected  into  the 
system.  The  time  from  the  beginning  of  injection  till  the  appearance  of  the  blue 
at  G  is  measured  with  the  stop-watch. 


once  a  day  for  the  next  week,  and  study  the  differences  between  the 
two  ears  (p.  159)  and  the  two  pupils. 

29.  Determination  of  the  Circulation-time. — (a)  Begin  with  an 
artificial  scheme  (Fig.  96).  Fill  the  syringe  with  a  o-2  per  cent, 
solution  of  methylene  blue.  Allow  the  water  to  flow  from  the  bottle 
by  loosening  the  clamp.  Inject  a  definite  quantity  of  the  methylene- 
blue  solution,  and  with  a  stop-watch  observe  how  long  it  takes  to 
pass  from  the  point  of  injection  to  the  end  of  the  glass  tube  filled 
with  beads.  Make  ten  readings  of  this  kind  and  take  the  mean. 
Then  raise  the  bottle  so  as  to  increase  the  rate  of  flow  of  the  water, 


2U4  A   MANUAL  OF  PHYSIOLOGY 

and  repeal  the  observations.  The  'circulation-time  '  will  be  found 
to  be  diminished.  This  corresponds  to  an  increase  oi  blood-pressure 
due  to  increased  activity  of  the  heart,  without  i  hange  in  the  calibre 
of  the  bloodvessels.  Next,  leaving  the  bottle  in  its  present  position, 
diminish  the  outflow  by  tightening  the  clamp  ;  the  circulation-time 
will  be  increased.  This  corresponds  to  an  increase  of  blood-pressure 
due  to  diminution  in  the  calibre  of  the  small  artei  i 

(b)  Fill  the  syringe*  with  methylene-bluc  solution  (o'2  per  cent,  in 
09  per  cent,  salt  solution),  as  in  (a).  Keep  the  solution  warmed  to 
400  C.  by  immersing  the  small  beaker  containing  it  in  a  water-bath, 
or  heating  it  over  a  bunsen  with  a  small  flame.  Weigh  a  rabbit  or 
cat.  In  the  case  of  the  rabbit,  inject  \  grm.  chloral  hydrate  into 
the  rectum,  and  later  on  give  ether  if  necessary.  II  a  cat,  give 
ether  alone.  Fasten  it  on  a  holder,  back  downwards 
p.  [24).  Cover  it  with  a  towel  to  keep  it  warm.  Clip  oil  the 
hair  on  the  front  of  the  neck,  and  make  an  incision  i£  inches 
long  in  the  middle  line,  beginning  a  little  way  below  the  cricoid 
cartilage.  Reflect  the  skin  and  isolate  the  external  jugular 
vein,  which  is  quite  superficial.  Carefully  separate  about  J  inch 
of  the  vein  from  the  surrounding  tissue,  and  pass  two  Ligatures 
under  it,  but  do  not  tie  them.  Compress  the  vein  with  a  pair  of 
bulldog  forceps  between  the  heart  and  the  ligatures.  Now  tie  the 
uppermost  of  the  two  ligatures  (that  next  the  head),  but  only  put 
a  single  loose  loop  on  the  other.  The  piece  of  vein  between  the 
upper  ligature  and  the  bulldog  is  now  distended  with  blood.  With 
fine-pointed  scissors  make  a  small  slit  in  the  win.  taking  great  care 
not  to  divide  it  completely,  insert  the  cannula,  and  tie  the  loose 
ligature  firmly  over  its  neck.  Fill  the  cannula  and  the  small  piece 
of  rubber  tubing  attached  to  it  with  00,  per  cent,  salt  solution  by 
means  of  a  pipette  with  a  long  point.  Expose  the  carotid  on  the 
other  side,  isolate  it  for  J  inch,  clear  it  carefully  from  its  sheath, 
slip  under  it  a  strip  of  thin  sheet  indiarubber.  and  between  this  and 
the  artery  a  little  piece  of  white  glazed  paper.  Connect  the  cannula 
in  the  jugular  with  the  T-piece  attached  to  the  syringe.  Care  must 
be  taken  that  no  air  remains  in  the  cannula  or  its  connecting-tube, 
as  a  rabbit  not  unfrequently  dies  instantaneously  when  a  bubble 
of  air  is  injected  into  the  right  heart,  although  a  considerable 
quantity  of  air  can  generally  be  injected  into  the  jugular  of  a  dog 
without  killing  it. 

Xow  take  off  the  bulldog  from  the  vein,  and  make  a  series  of 
observations  on  the  pulmonary  circulation-time.  The  animal  must 
be  so  placed  that  a  good  light  falls  on  the  carotid.  If  necessary,  the 
light  of  a  gas-flame  may  be  concentrated  on  it  by  a  lens.  The 
student  holds  the  stop-watch  in  one  hand,  and  injects  a  measured 
quantity  of  the  methylene-blue  solution  with  the  other.  Uniformity 
in  the  quantity  injected  is  secured  by  fastening  on  the  piston  of  the 
syringe  a  screw-clamp,  which  stops  the  piston  at  the  desired  point. 
The  observation  consists  in  setting  off  the  watch  at  the  moment 
when  injection  begins  and  stopping  it  when  the  blue  appears  in  the 
carotid.     After  each  injection  the  screw-clamp  or  pinchcock  on  the 

*  A  burette,  sloped  so  as  to  make  a  small  angle  with  the  horizontal, 
may  be  substituted  for  the  syringe.  The  burette  is  supported  on  a  stand 
at  such  a  height  that  the  methylene-blue  solution  runs  without  great  force 
into  the  jugular  (say  10-15  cm.  above  the  level  of  the  cannula).  The 
danger  of  producing  an  abnormal  result  by  suddenly  raising  the  pressure 
in  the  right  side  of  the  heart  is  thus  avoided. 


PRACTICAL  I  XI  RCISES 
tube  connected    with   the  cannula  must   be   tightened,   the  othei 

opened,  and  the  syringe  refilled,      ('.real  care  must  be  taken  never  to 

open  the  two  clamps  ;it  the  same  time,  as  in  that  case  blood  may 
regurgitate  through  the  jugular  and  fill  the  syringe,  or  methylene 
blue  may  be  sucked  into  the  circul.it ion.  As  many  observations  ;is 
possible  should  be  taken,  and  the  mean  determined.  The  circula- 
tion-time observed  is  approximately  that  of  the  lesser  circulation, 
the  time  taken  by  the  blood  to  pass  from  the  left  ventricle  to  the 
carotid  being  negligible  for  the  purposes  of  the  student. 

The  specific  gravity  of  the  blood  may  also  be  tested  at  the 
beginning  and  end  of  the  experiment  by  Hammerschlag's  method 
(p.  54).  If  a  large  number  of  injections  have  been  made  in  quick 
succession,  the  specific  gravity  will  be  loss  than  normal;  but  if  a 
considerable  interval  has  been  allowed  to  elapse  after  the  last 
injection,  little  or  no  difference  may  be  found,  as  the  surplus  liquid 
readily  passes  out  of  the  bloodvessels. 

Autopsy. — Observe  particularly  the  state  of  the  lungs,  whether  the 
bladder  is  distended  or  not,  and  whether  any  of  the  serous  cavities 
or  the  intestines  contain  much  liquid  ;  so  as  to  determine,  if  possible, 
by  what  channel  the  water  injected  into  the  blood  may  have  been 
eliminated.  Study  the  distribution  of  the  methylene  blue  in  such 
organs  as  the  kidneys  and  the  muscles  immediately  after  death,  and 
notice  that  the  blue  colour  becomes  more  pronounced  after  exposure 
for  a  time  to  the  air.  Make  a  longitudinal  section  through  a  kidney, 
and  observe  that  the  pigment  is  found  especially  in  the  cortex  and 
around  the  pelvis  at  the  apices  of  the  pyramids,  or  it  may  be  only  in 
the  cortex.  The  urine  is  greenish.  If  some  methylene  blue  has  been 
injected  after  the  heart  ceased  to  beat,  the  bloodvessels,  particularly 
in  the  mesentery,  may  be  beautifully  mapped  out  by  the  pigment. 
This  is  not  the  case  if  the  last  injection  took  place  before  death, 
since  the  methylene  blue  is  rapidly  reduced  by  living  tissues  to  a 
colourless  substance,  leuco-methylene  blue. 


CHAPTER  III 

RES  PIRATION 

Respiration  in  its  widest  sense  is  the  sum  total  of  the  processes 
by  which  the  ultimate  elements  of  the  body  gain  the  oxygen 
they  require,  and  get  rid  of  the  carbon  dioxide  they  produce. 

Comparative. — In  a  unicellular  organism  no  special  mechanism  of 
respiration  is  needed  ;  the  oxygen  diffuses  in,  and  the  carbon  dioxide 
diffuses  out,  through  the  general  surface.  The  simple  wants  of  such 
multicellular  animals  as  the  ccelenterates,  the  group  to  which  the 
sea-anemone  belongs,  are  also  supplied  by  diffusion  through  the 
ectoderm  from  and  into  the  surrounding  water,  and  through  the 
endoderm  from  and  into  the  contents  of  the  body-cavity  and  its 
ramifications. 

But  in  animals  of  more  complex  structure  special  arrangements 
become  necessary,  and  respiration  is  divided  into  two  stages  : 
(i)  External  respiration,  an  interchange  between  the  air  or  water 
and  a  circulating  medium  or  blood  as  it  passes  through  richly 
vascular  skin,  gills,  tracheae,  or  lungs;  and  (2)  internal  respiration, 
an  interchange  between  the  blood,  or  lymph,  and  the  cells. 

In  the  lower  kinds  of  worms  respiration  goes  on  solely  through  the 
skin,  under  which  plexuses  of  bloodvessels  often  exist,  but  in  some 
higher  worms  there  are  special  vascular  appendages  that  play  the 
part  of  gills.  The  Crustacea  also  possess  gills,  while  in  the  other 
arthropoda  respiration  is  carried  on  either  by  the  general  surface  of 
the  body  (in  some  low  forms),  or  more  commonly  by  means  of 
tracheae,  or  branched  tubes  surrounded  by  blood  spaces  and  com- 
municating externally  with  the  air  and  internally  by  their  finest 
twigs  with  the  individual  cells.  Most  of  the  mollusca  breathe  by 
gills,  but  a  few  only  by  the  skin. 

Among  vertebrates  the  fishes  and  larval  amphibians  breathe  by 
gills,  but  most  adidt  amphibians  have  lungs.  The  skin,  too,  in  such 
animals  as  the  frog  has  a  very  important  respiratory  function,  more 
of  the  gaseous  exchange  taking  place  through  it  in  some  conditions 
than  through  the  lungs. 

One  small  group  of  fishes,  the  dipnoi,  has  the  peculiarity  of  pos- 
sessing both  gills  and  a  kind  of  lungs,  the  swim-bladder  being  sur- 
rounded with  a  plexus  of  bloodvessels  and  taking  on  a  respiratory 
function. 

In  all  ths  higher  vertebrates  the  respiration  is  carried  on  by  lungs  ; 
the  trifling  amount  of  gaseous  interchange  which  can  possibly  t  dee 
place  through  the  skin  is  not  worth  taking  in  1  1  account.  The  lungs 
are  to  be  regarded  as  developed  from  outgrowths  of  the  alimentary 
canal,  beginning  near  the  mouth. 

206 


RESPIR  I  I  ION  207 

riic  objecl  "i  .ill  special  respiratory  arrangement  in  the 

first  instance,  to  facilitate  the  gaseous  exchange  between  the  sur- 
rounding medium  (air  or  water)  and  the  blood,  a  primi  m  1 1  ity  of 
.1  respiratory  organ,  be  it  skin,  gill,  trachea,  or  lung,  is  a  tree  supply 
of  Modi!,  m  vessels  so  fine  and  thin  thai  diffusion  readily  takes  pla<  e 
into  them  and  out  of  them.  But  a  tree  supply  of  blood  would  be  <>i 
in  1  avail  ii  the  medium  to  which  the  blood  gave  up  its  carbon  dioxide 
and  from  which  it  drew  its  oxygen  was  ao1  bemg  constantly  and 
sufficiently  renewed. 

Sometimes  the  natural  currents  of  the  water  or  the  air  are  oi 
themselves  sufficient  to  secure  this  renewal  ;  in  other  cases,  artificial 
currents  arc  set  up  by  cilia,  or  special  bailing  organs,  like  the  scapho- 
gnathites  of  the  Lobster.  In  all  the  higher  animals,  active  move- 
ments, by  which  air  or  water  is  brought  into  contact  with  the 
respiratory  surfaces,  are  necessary  ;  and  it  is  possible  that  such 
movements  take  place  even  in  the  trachea?  of  insects  and  other 
air-breathing  arthropoda.  Fishes,  by  rhythmical  swallowing  move- 
ments, take  in  water  through  the  mouth  and  pass  it  over  the  gills 
and  out  by  the  gill-slits,  while  the  frog  distends  its  lungs  by  swal- 
lowing air. 

Physiological  Anatomy  of  the  Respiratory  Apparatus. — -In  man 
the  respiratory  apparatus  consists  of  a  tube  (the  trachea)  widened  at 
its  upper  part  into  the  larynx,  which  contains  the  special  mechanism 
of  voice,  and  communicates  through  the  nose  or  mouth  with  the 
external  air.  Below,  the  trachea  divides  dendritically  into  innumer- 
able branches,  the  ultimate  divisions  of  which  are  called  bronchioles. 
Each  bronchiole  breaks  up  into  several  wider  passages,  or  inf undibula, 
the  walls  of  wmich  are  everywhere  pitted  with  recesses  or  alcoves, 
called  alveoli.  The  infundibula  constitute  the  essential  distensible 
elements  of  the  lung,  by  the  alternate  stretching  and  relaxation  of 
which  the  respiratory  changes  in  the  volume  of  the  organ  are  mainly 
brought  about.  The  trachea  and  larger  bronchi  are  strengthened  by 
hyaline  cartilage  in  the  form  of  incomplete  rings,  connected  behind 
by  non-striped  muscular  fibres,  which  also  exist  in  the  intervals  be- 
tween the  rings.  The  middle-sized  bronchi  within  the  lungs  have  the 
cartilage  in  the  form  of  detached  pieces  in  the  outer  portion  of  the 
wall,  while  nearer  the  lumen  lies  a  complete  ring  of  non-striped  muscle. 

In  the  bronchioles,  no  cartilage  is  present,  but  the  circularly- 
arranged  muscular  fibres  still  persist,  and  also  form  a  thin  layer  in 
the  infundibula.  In  the  air-cells,  or  alveoli,  however,  there  are  no 
muscular  fibres.  Their  walls  consist  essentially  of  a  network  of 
elastic  fibres,  continuous  with  a  similar  layer  in  the  infundibula  and 
bronchioles,  and  covered  on  the  side  next  the  lumen  by  a  single 
layer  of  large,  clear  epithelial  scales,  with  here  and  there  a  few 
smaller  and  more  granular  polyhedral  cells. 

From  the  larynx  to  the  bronchioles  the  mucous  membrane  is 
ciliated  on  its  free  surface,  the  cilia  lashing  upwards  so  as  to  move 
the  secretion  towards  the  larynx  and  mouth.  In  the  infundibula  the 
ciliated  epithelium  begins  to  disappear,  and  is  absent  from  the  alveoli. 
Part  of  the  nasal  cavity  and  the  upper  part  of  the  pharynx  are  also 
lined  with  ciliated  epithelium.  Mucous  glands  are  present  in 
abundance  in  the  upper  portions  of  the  respiratory  passages,  but 
disappear  in  the  smaller  bronchi. 

Blood-supply  of  the  Lungs. — The  quantity  of  blood  traversing  the 
lungs  bears  no  proportion  to  the  amount  required  for  their  actual 
nourishment.     Small,  however,  as  this  latter  quantity  is,  it  cannot 


A   MANUAL  OF  PHYSIOLOGY 

apparently  be  derived  from  the  vitiated  blood  of  the  right  ventricle, 

but  is  obtained  directly  from  the  aortic  system  by  the  bronchia] 
arteries.  These  are  distributed  with  the  bronchi,  which  they  supply 
as  well  as  the  connective-tissue  of  the  interlobular  septa  running 
through  the  substance  of  the  lung,  the  pleura  lining  it  and  the  walls 
of  the  large  bloodvessels.  Most  of  the  blood  from  the  bronchial 
arteries  is  returned  by  the  bronchial  veins  into  the  systemic  venous 
system,  but  some  of  it  finds  its  way  by  anastomoses  into  the  pul- 
monary veins. 

The  branches  of  the  pulmonary  artery  are  also  distributed  with 
the  bronchi,  and  break  up  into  a  dense  capillary  network  around  the 
alveoli.  From  the  capillaries  veins  arise  which,  gradually  uniting,  f<  inn 
the  large  pulmonarv  veins  that  pour  their  blood  into  the  left  auricle. 

The  same  quantity  of  blood  must,  on  the  whole,  pass  per  unit  of 
time  through  the  lesser  as  through  the  greater  circulation,  otherwise 
equilibrium  could  not  exist,  and  blood  would  accumulate  either  in 
the  lungs  or  in  the  systemic  vessels.  But  it  does  not  follow  that  at 
each  heart-beat  the  output  of  the  two  ventricles  is  exactly  equal.  If, 
indeed,  the  capacity  of  the  lesser  circulation  were  constant,  the 
quantity  driven  out  at  one  systole  by  the  right  ventricle  would  be 
the  same  as  that  ejected  at  the  next  by  the  left  ventricle.  But  it  is 
known  that  the  capacity  of  the  pulmonary  vessels  is  altered  by  the 
movements  of  respiration  and  probablv  in  other  ways,  so  that  it  is 
only  on  the  average  of  a  number  of  beats  that  the  output  of  the  two 
ventricles  can  be  supposed  equal. 

The  time  required  bv  a  given  small  portion  of  blood,  e.g.,  by  a 
single  corpuscle,  to  complete  the  round  of  the  lesser  circulation,  is. 
as  we  have  seen  (p.  125),  much  less  than  the  average  time  needed  to 
complete  the  systemic  circulation.  In  the  rabbit  the  ratio  is  prob- 
ably about  1:5.  Since  all  the  blood  in  a  vascular  tract  must  : 
out  of  it  in  a  period  equal  to  the  circulation  time,  the  average  quantity 
of  blood  in  the  lungs  and  right  heart  of  a  rabbit  must  be  about  one- 
fifth  of  that  in  the  systemic  vessels.  On  the  assumption  that  the 
same  proportion  holds  for  a  man.  not  less  than  700  grm.  out  of  the 
4§  kilos*  of  blood  in  a  70  kilo  man  must  be  contained  in  the 
lesser  circulation,  and  about  3f  kilos  in  the  greater.  This  corre- 
sponds sufficientlv  well  with  calculations  from  other  d  ita. 

For  example,  the  average  weight  of  the  lungs  in  three  persons, 
executed  by  beheading,  was  457  grm.  (Gluge).  The  average  weight 
of  the  lungs  in  a  great  number  of  persons  who  h"\d  died  a  natural 
death  was  1024  grm.  (Juncker).  The  weight  of  the  pulmonary 
tissue  alone  in  the  first  set  of  cases  must  be  less  th  in  1.57  grm..  for 
the  lungs  of  a  person  who  has  bled  to  death  are  never  bloodless. 
In  a  dog  killed  bv  bleeding  from  the  carotid,  one-quarter  of  the 
weight  of  the  lungs  consisted  of  blood.  Assuming  the  same  propor- 
tion for  the  decapitated  individuals,  we  get  343  grm.  as  the  net 
weight  of  the  blood-free  lungs.  Deducting  this  from  1024  grm.. 
we  arrive  at  681  grm.  as  the  average  quantity  of  blood  in  the  lungs. 
Adding  to  this  the  quantity  in  the  right  side  of  the  heart  (p.  1^), 
we  get,  in  round  numbers,  750  grm.  as  the  amount  in  the  lesser  cir- 
culation. It  is  true  that  in  the  living  body  the  conditions  are  not 
the  same  as  after  death  ;  but  it  is  probable  that  in  a  large  number 
of  cases  taken  at  random  the  differences  would  be  approximately 
equalized. 

It  has  been  further  calculated  that  the  total  area  of  the  alveolar 

*  See  footnote  on  p.  127. 


RESPIRATION 


209 


surface  of  the  lungs  of  a  man  is  about  100  square  metres  (sixty 
times  greater  than  the  area  of  the  skin),  of  which,  perhaps,  75  square 
metres  are  occupied  by  capillaries.  The  average  thickness  of  this 
immense  sheet  of  blood  has  been  reckoned  to  be  equal  to  the  diameter 
of  a  red  blood-corpuscle,  or,  say,  8  m-  This  would  give  600  c.c. 
(630  grm.)  as  the  quantity  of  blood  in  the  lungs,  which  is  probably 
somewhat  too  low  an  estimate. 

If  we  take  the  pulmonary  circulation-time  as  13  seconds  (p.  125), 

and  the  quantity  of  blood  in  the  lungs  as  700  grm.,  then  — 

=  104  kilos  of  blood  will  pass  through  the  lungs  in  an  hour,  or 
4,656  kilos  (say,  4,400  litres)  in  twenty-four  hours.  This  would  rill 
a  cubical  tank  in  which  the  man  could  almost  stand  upright  with  the 
lid  closed. 

Mechanical  Phenomena  of  Respiration. 

The  lungs  are  enclosed  in  an  air-tight  box,  the  thorax  ;  or  it 
may  be  said  with  equal  truth  that  they  form  part  of  the  wall 
of  the  thoracic  cavity,  and  the  part  which  has  by  far  the  greatest 
capacity  of  adjustment.  The  alveolar  surface  of  the  lungs  is  in 
contact  with  the  air.  The  pleura,  which  covers  their  internal 
surface,  is  reflected  over  the  chest-walls  and  diaphragm,  so  as  to 
form  two  lateral  sacs,  the  pleural  cavities.  In  health  these  are 
almost  obliterated,  and  the  visceral  and  parietal  pleurae, 
separated  and  lubricated  by  a  few  drops  of  lymph,  glide  on  each 
other  with  every  movement  of  respiration.  But  in  disease  the 
pleural  cavities  may  be  filled  and  their  walls  widely  separated  by 
exudation,  as  in  pleurisy,  or  by  blood,  as  in  rupture  of  an  aneurism, 
or  by  air  in  the  condition  known  as  pneumo-thorax.  Between 
the  two  pleural  sacs  lies  a  mesial  space,  the  mediastinum, 
commonly  divided  into  an  anterior  mediastinum  in  front  of  the 
heart,  and  a  posterior  mediastinum  behind  it.  The  pleural  and 
pericardial  sacs  and  the  mediastinum  constitute  together  the 
thoracic  cavity.  The  external  surface  of  the  chest-wall  and  the 
alveolar  surface  of  the  lungs  are  subjected  to  the  pressure  of  the 
atmosphere,  to  which  the  pressure  in  the  thoracic  cavity  (intra- 
thoracic pressure)  would  be  exactly  equal  if  its  boundaries  were 
perfectly  yielding.  But  in  reality  the  intra-thoracic  pressure  is 
always  normally  something  less  than  this.  For  even  the  lungs, 
the  least  rigid  part  of  the  boundary,  oppose  a  certain  resistance 
to  distension,  and  so  hold  off,  as  it  were,  from  the  thoracic  cavity 
a  portion  of  the  alveolar  pressure  ;  and  in  any  given  position  of 
the  chest  the  intra-thoracic  pressure  is  equal  to  the  atmospheric 
pressure  minus  this  elastic  tension  of  the  lungs. 

The  object  of  the  respiratory  movements  is  the  renewal  of  the 
air  in  contact  with  the  alveolar  membrane — in  other  words,  the 
ventilation  of  the  lungs.  Two  main  methods  are  followed  by 
sanitary  engineers  in  the  ventilation  of  buildings  :  they  force  air 

H 


A    MANUAL  OF  PHYSIOLOGY 


in,  or  they  draw  it  in.  In  both  cases  the  movement  of  the  air 
depends  on  the  establishment  of  a  slope  of  pressure  from  the 
inlet  to  the  interior.  In  the  first  method,  this  is  done  by 
increasing  the  pressure  at  the  inlet  ;  in  the  second,  by  diminishing 
the  pressure  at  the  outlet.  In  certain  animals  Nature,  in 
solving  its  problem  of  ventilation,  has  made  use  of  the  first 
principle.  Thus,  the  frog  forces  air  into  its  lungs  by  a  swallowing 
movement.     In  artificial  respiration,  as  practised  in  physiological 

experiments,  the  same  method 
is  usually  employed  :  air  is 
driven  into  the  lungs  under 
pressure.  But  in  the  vast 
majority  of  air-breathing 
animals,  including  man,  the 
opposite  principle  has  been 
adopted  ;  and  the  '  indraught  ' 
of  air  from  nose  and  pharynx 
to  alveoli  is  not  set  up  by  in- 
creasing the  pressure  in  the 
former,  but  by  diminishing  it 
in  the  latter.  This  '  indraught,' 
or  inspiration,  is  brought 
about  by  certain  movements  of 
the  chest-wall,  which  increase 
the  capacity  of  the  thoracic 
cage  and  lower  the  pressure  in 
the  thoracic  cavity.  The  ex- 
pansion of  the  highly-distensible 
lungs  keeps  pace  with  the 
diminution  of  pressure  in  the 
pleural  sacs,  and  they  follow  at 
every  point  the  retreating  chest- 
wall  and  diaphragm,  although 
they  do  not  expand  equally  in  all 
directions.  The  dorsal  surface 
in  contact  with  the  vertebral  column,  the  mediastinal  surface  in 
contact  with  the  pericardium  and  the  contents  i  if  the  mediastinum, 
and  the  surface  of  the  apex,  move  but  little.  The  surfaces  in 
contact  with  the  diaphragm,  ribs,  and  sternum  have  the  greatest 
range  of  movement.  Intermediate  portions  of  the  parenchyma  of 
the  Lungs  expand  in  a  degree  determined  by  their  distance  from  the 
relatively  stationary  and  mobile  surfaces.  The  pressure  of  the 
air  in  the  alveoli  during  the  rapid  expansion  of  the  lungs  neces- 
sarily sinks  below  that  of  the  atmosphere,  and  air  rushes  in 
through  the  trachea  and  bronchi  till  the  difference  is  equalized. 
Then  commences  the  movement  of  expiration.     The  expanded 


Fig.  97. — Scheme  to  illistrate  the 
Movements  of  the  Lungs  in  the 
Chest. 

T  is  a  bottle  from  which  the  bottom 
has  been  removed  ;  D,  a  flexible  and 
elastic  membrane  tied  on  the  bottle, 
and  capable  of  being  pulled  out  by 
the  string  S  so  as  to  increase  the 
capacity  of  the  bottle.  L  is  a  thin 
elastic  bag  representing  the  lungs.  It 
communicates  with  the  external  air  by 
a  glass  tube  fitted  airtight  through  a 
cork  in  the  neck  of  the  bottle.  When 
D  is  drawn  down,  the  pressure  oi  the 
external  air  1  auses  I.  to  expand.  When 
the  string  is  let  go,  L  contracts  again, 
in  virtue  of  its  elasticity. 


RESPIRATION  211 

chest  falls  back  to  its  original  limits  ;  the  pressure  in  the  thoracic 
cavity  increases  ;  the  distended  Lungs,  in  virtue  oi  their  elasticity, 
r-ln ink  to  their  former  volume  ;  the  pressure  <>l'  the  air  in  the 
alveoli  rises  above  that  of  the  atmosphere,  and  with  this  reversal 
ot  the  slope  oi  pressure  air  streams  out  of  the  bronchi  and  trachea. 

In  inspiration  the  chest  dilates  in  all  its  diameters.  Its 
vertical  diameter  is  increased  by  the  contraction  of  the 
diaphragm,  which,  composed  of  a  central  tendon,  a  peripheral 
ring  of  muscular  tissue,  and  the  two  muscular  crura,  bulges  up 
into  the  thorax  in  the  form  of  two  flattened  domes,  one  on  each 
side,  and  thus  closes  its  lower  aperture.  When  the  diaphragm 
contracts,  even  in  ordinary  quiet  breathing,  the  central  tendon 
descends  distinctly  (about  half  an  inch)  after  the  manner  of  a 
piston.  The  acute  angle  which  the  muscular  ring  makes  during 
relaxation  with  the  thoracic  wall  opens  out  around  its  whole 
circumference,  so  as  to  form  a  groove  of  triangular  section.  But 
the  most  peripheral  portion  of  the  ring  is  always  kept  in  close 
apposition  to  the  chest-wall  by  the  negative  intrathoracic 
pressure.  The  lungs  follow  the  descending  diaphragm,  their 
lower  borders  keeping  accurately  in  contact  with  it.  The  descent 
of  the  diaphragm  is  not  directly  downwards,  but  downwards 
and  forwards.  For  it  is  compounded  of  two  movements,  the 
spinal  segment  of  the  muscle  (the  crura)  causing  a  vertical 
elongation  of  the  thorax,  while  the  sterno-costal  part  (the 
muscular  ring)  pushes  the  abdominal  viscera  downwards  and 
forwards  (Keith).  Since  the  diaphragm  is  attached  to  the  lower 
ribs,  there  is  a  tendency  during  its  contraction  for  these  to  be 
drawn  inwards  and  upwards  ;  but  this  is  opposed  by  the  pressure 
of  the  abdominal  viscera,  and  by  the  action  of  the  quadratus 
lumborum,  which  fixes  the  twelfth  rib,  and  of  the  serratus  posticus 
inferior,  which  draws  the  lower  four  ribs  backward.  When 
these  and  the  other  inspiratory  muscles  that  act  especially 
upon  the  ribs  are  paralyzed  by  injury  to  the  spinal  cord,  and 
respiration  is  carried  on  by  the  diaphragm  alone,  the  line  of  its 
attachment  to  the  ribs  is  distinctly  marked  during  inspiration 
by  a  shallow  circular  groove. 

The  thorax  is  also  enlarged  by  the  action  of  certain  muscles 
that  act  upon  the  ribs.  Among  the  elevators  of  the  ribs,  as 
their  name  indicates,  are  usually  reckoned,  although  erroneously, 
the  levatores  costarum — twelve  in  number  on  each  side.  Thev 
arise  from  the  transverse  processes  of  the  last  cervical  and  first 
eleven  dorsal  vertebrae,  and  passing  obliquely  downwards  and 
outwards,  are  inserted  between  the  tubercle  and  the  angle  into 
the  first  or  second  rib  below  their  origin.  They  do  not  elevate 
the  ribs,  but  take  part  in  lateral  movements  of  the  spinal  column. 
The  scalene  muscles,  which  may  in  a  lean  person  be  felt  to  be 

14—2 


212  A   MANUAL  OF  PHYSIOLOGY 

tense  during  inspiration,  fix  the  first  and  second  ribs  (scalenus 
anticus  and  medius,  the  first;  scalenus  posticus,  the  second 
rib),  and  so  afford  a  fixed  line  for  the  intercostal  muscles  to  work 
from  on  the  lower  ribs. 

The  most  important  elevators  of  the  ribs  are  the  external 
intercostals.  The  intercartilaginous  portions  of  the  internal 
intercostals  (the  intercartilaginei  muscles,  as  they  are  sometimes 
called)  also  contract  simultaneously  with  the  diaphragm,  and 
may  therefore  be  included  in  the  list  of  inspiratory  muscles  ;  but 
instead  of  elevating  the  ribs  they  depress  the  costal  cartilages, 
and  thus  help  to  widen  the  angles  between  them  and  the  ribs. 
In  addition  to  increasing  the  capacity  of  the  chest,  the  con- 
traction of  the  external  intercostals  and  the  intercartilaginous 
muscles  aids  in  inspiration  by  augmenting  the  rigidity  of  the 
intercostal  spaces,  and  so  preventing  them  from  being  drawn  in  as 
easily  as  would  otherwise  be  the  case  when  the  thorax  is  expanded 
by  the  action  of  the  diaphragm  and  the  other  inspiratory  muscles. 

Leaving  out  of  account  the  floating  ribs,  which  functionally 
form  a  part  of  the  abdominal  wall,  the  ribs  in  relation  to  their 
respiratory  functions  may  be  divided  into  the  following  groups  : 
(i)  The  first  rib,  which,  moving  itself  very  little,  provides  a  fixed 
line  towards  which  the  next  set  of  ribs  may  be  raised. 

(2)  An  upper  costal  series  consisting  of  the  ribs  from  the 
second  to  the  fifth.  These  are  raised  in  inspiration  towards 
the  fixed  first  rib  by  the  contraction  of  the  intercostal  muscles. 
The  movement  of  these  ribs  is,  mainly  at  any  rate,  a  rota- 
tion around  a  transverse  axis,  the  axes  on  which  they  move 
corresponding  to  their  necks.  The  manner  in  which  they  are 
articulated  to  the  vertebne  prevents  any  sensible  rotation 
around  an  antero-posterior  axis  or  '  bucket-handle  '  movement. 
Since  these  ribs  slant  downwards  and  forwards  to  their  sternal 
attachments,  the  sternum  is  raised  when  they  are  elevated  ;  or, 
rather,  since  the  manubrium  is  practically  immovable  in 
ordinary  breathing,  the  body  of  that  bone  is  bent  on  the  manu- 
brium at  the  manubrio-sternal  joint.  This  causes  an  increase 
in  the  antero-posterior  diameter  of  the  thorax.  Further,  since 
the  arches  formed  by  the  ribs  widen  in  regular  progression  from 
above  downwards  in  the  upper  portion  of  the  thoracic  cage,  so 
that  the  second  rib  is  a  segment  of  a  larger  circle  than  the  fust. 
and  the  third  than  the  second,  it  is  clear  that  a  general  elevation 
of  the  chest  will  tend  to  increase  the  transverse  diameter  at  any 
given  level.  Such  an  increase  is  also  favoured  by  the  opening 
out  of  the  angles  between  the  bony  ribs  and  the  costal  cartilages 
under  the  influence  of  the  couple  (or  pair  of  oppositely  directed 
forces)  that  acts  on  them — viz.,  the  upward  pull  of  the  external 
intercostals  exerted  on  the  ribs,  and  the  downward  pull  of  the 


R  INSPIRATION  213 

intercartilaginei  and   the  resistance  of  the  sternum  to  further 
displacement   exerted    on    the  cartilages.     The  whole   arrange 
incut  is  perfectly  adapted  to  permit  the  expansion  of  the  roughly 
conical  upper  lobes  of  the  lungs. 

(3)  The  lower  costal  series,  consisting  of  the  ribs  from  the 
sixth  to  the  tenth.  These  ribs,  with  their  muscles,  form  a 
mechanism  which  normally  acts  along  with  the  diaphragm 
(Keith).  They  are  so  arranged  that  in  inspiration  the  lateral 
and  anterior  part  of  each  moves  outwards  to  a  greater  extent 
than  the  one  above  it.  There  is  not  only  a  rotation  around 
a  transverse  axis,  by  which  the  lower  end  of  the  sternum, 
connected  to  these  ribs  by  the  combined  cartilages  of  the  sixth 
to  the  ninth,  is  elevated,  but  also  a  rotation  around  an  antero- 
posterior axis.  The  movement  of  the  lower  ribs  results,  there- 
fore, in  increasing  both  the  back-to-front  diameter  and  the 
transverse  diameter  of  the  lower  portion  of  the  thorax.  The 
widening  of  the  thorax  from  side  to  side  may  also  be  in  a  slight 
degree  ascribed  to  a  twisting  movement  of  the  ribs,  which  tends 
to  evert  their  lower  borders.  With  the  diaphragm,  these  lower 
ribs  arranged  in  a  vertical  series  of  not  very  different  curvature 
constitute  a  mechanism  for  the  inspiratory  expansion  of  the 
roughly  cylindrical  lower  lobes  of  the  lungs. 

Expiration  in  perfectly  tranquil  breathing  is  brought  about 
with  less  aid  from  active  muscular  contraction.  The  sense  of 
effort  disappears  as  soon  as  the  chest  ceases  to  expand.  The 
diaphragm  and  the  elevators  of  the  ribs  relax.  The  structures 
that  have  been  stretched  or  twisted  recoil  into  their  original 
positions  ;  the  structures  that  have  been  raised  against  the 
force  of  gravity  fall  back  by  their  weight,  and  in  the  measure 
in  which  the  pressure  increases  in  the  thoracic  cavity  the  elasticity 
of  the  lungs  causes  them  to  shrink.  The  pressure  in  the  alveoli, 
which  at  the  end  of  inspiration  was  just  equal  to  that  of  the 
atmosphere,  is  thus  increased,  and  the  air  expelled.  It  is  probable 
that,  even  in  man  and  in  quiet  respiration,  the  interosseous 
portions  of  the  internal  intercostals  help  by  their  contraction  in 
depressing  the  ribs,  and  that  a  slight  contraction  of  the  abdominal 
muscles  hastens  the  return  of  the  diaphragm  to  its  position  of  rest. 
In  reptiles  and  birds,  expiration  is  normally  effected  by  an  active 
muscular  contraction.  This  is  also  true  in  some  mammals — the 
rabbit,  for  instance,  in  which  the  external  oblique  muscles  of  the 
abdominal  wall  take  an  important  share  in  the  expiratory  act. 

Types  of  Respiration. — Differences  exist  also,  not  only  between 
different  groups  of  animals,  but  even  between  women  and  men, 
in  the  relative  importance  in  inspiration  of  the  diaphragm  and 
the  muscles  that  raise  the  lower  ribs  on  the  one  hand,  and  the 
muscles  that  elevate  the  upper  ribs  on  the  other.     When  the 


214  ./   MANUAL  OF  PHYSIOLOGY 

movements  of  the  diaphragm  predominate,  the  respiration  is 
said  tn  be  of  the  abdominal  or  diaphragmatic  type;  when  the 
movements  of  the  upper  ribs  and  sternum  are  most  i  onspicuous, 
<>i  the  costal  or  thoracic  type.  In  abdominal  respiration,  the 
inspiratory  movement  commences  at  the  diaphragm,  and  then 
involves  the  lower  ribs  and  the  tip  of  the  sternum.  In  costal 
respiration,  the  upper  ribs  initiate  the  movement,  and  are 
followed  by  the  abdomen.  In  the  rabbit,  during  quiel  breathing, 
the  respiration  is  purely  diaphragmatic,  the  ribs  remain  motion- 
less ;  and  herbivorous  animals  in  general  conform  more  or  less 
closely  to  this  type.  In  the  carnivora.  on  the  contrary,  the 
costal  type  prevails.  Man  allies  himself  as  regards  his  respira- 
tion with  the  rabbit  and  the  sheep  ;  he  uses  his  diaphragm  more 
than  his  upper  ribs.  Civilized  woman  falls  into  the  class  of  the  wolf 
and  the  tiger  ;  she  uses  her  upper  ribs  more  than  her  diaphragm. 
The  cause  of  the  difference  between  men  and  women  has  been 
much  discussed.  It  is  not  a  primitive  sexual  difference,  for  it  i> 
far  from  being  universal  ;  in  the  uncivilized  and  semi-civilized 
races  that  have  been  investigated,  the  women  breathe  like  the 
men.  It  is  therefore  probable  that  the  predominance  of  the  costal 
type  among  women  of  European  race  is  a  peculiarity  developed 
by  a  mode  of  dressing  which  hampers  the  movements  of  the 
diaphragm  while  permitting  the  elevation  of  the  ribs.  This  con- 
clusion is  strengthened  by  the  fact  that  in  children  no  diffen 
exists  ;  both  boys  and  girls  show  the  abdominal  type  of  respiration. 

All  this  refers  to  ordinary  breathing.  In  forced  respiration, 
when  the  need  for  air  becomes  urgent,  costal  breathing  always 
becomes  prominent  alike  in  men,  in  women,  and  in  animals,  for 
by  elevation  of  the  ribs  the  capacity  of  the  chest  can  be  increased 
to  a  greater  degree  than  by  any  contraction  of  the  diaphragm. 

In  forced  inspiration,  indeed,  all  the  muscles  that  can  elevate 
the  ribs  may  be  thrown  into  contraction,  as  well  as  other  muscles 
which  give  these  fixed  points  to  act  from.  During  a  paroxysm 
of  asthma,  for  example,  the  patient  may  grasp  the  back  of  a 
chair  with  his  hands,  so  as  to  fix  the  arms  and  shoulders  and 
allow  the  pectorals  and  serratus  magnus  to  raise  the  ribs.  Simi- 
larly in  forced  expiration  all  the  muscles  are  used  which  can 
depress  the  ribs,  or  increase  the  intra-abdominal  pressure  and 
push  up  the  diaphragm. 

Artificial  Respiration.— An  efficient  pulmonary  ventilation  can 
be  obtained  by  various  methods  when  the  natural  breathing  is  in 
abeyance.  In  animals  the  method  most  commonly  employed 
for  experimental  purposes  is  the  rhythmical  inflation  of  the  lungs 
by  a  pump  or  bellows,  or  by  a  stream  of  compressed  air  which  is 
regularly  interrupted,  the  chest  being  allowed  t<>  collapse  after 
each  inflation.     When  the  animal  is  to  be  kept  alive  alter  the 


A7  SPIR  1  riON 


215 


experiment  the  inflation  is  produced  through  a  tube  introduced 
through  the  glottis.  It  the  animal  is  not  to  be  kepi  alive,  the 
apparatus  is  generally  connected  with  a  cannula  in  the  trachea. 
In  man  the  exchange  of  air  between  the  atmosphere  and  the 
lungs  may  be  mosl  readily  accomplished  by  strong  rhythmical 
compression  of  the  lower  part  of  the  chest.  This  forces  out  some 
of  the  air  from  the  lungs  ;  on  relaxing  the  pressure  the  chest 
expands  again  and  air  is  drawn  in.  Schafer  has  shown  that 
this  is  the  most  efficient  method  of  respiration  in  resuscitation 
of  the  apparently  drowned.  '  The  patient  is  placed  face  down- 
wards on  the  ground,  with  a  folded  coat  under  the  lower  part  of 
the  chest.  The  operator  puts  himself  athwart  or  at  the  side  of 
the  patient,  lacing  his  head  and  kneeling  upon  one  or  both 
knees  (Fig.  98),  and  places  his  hands  on  each  side  over  the  lower 
part  of  the  back  (lowest  ribs).     He  then  slowly  throws  the  weight 


Fig.  98. — Artificial    Respiration  in   Cases  of  Drowning   (after  Schafer). 

of  his  body  forward  to  bear  upon  his  own  arms,  and  thus  presses 
upon  the  thorax  and  forces  air  out  of  the  lungs.  He  then  gradually 
relaxes  the  pressure  by  bringing  his  own  body  up  again  to  a  more 
erect  position,  but  without  moving  the  hands.'  Air  is  thus 
drawn  into  the  lungs.  The  process  is  repeated  twelve  to  fifteen 
times  a  minute. 

Certain  accessory  phenomena  (movements  and  sounds)  are 
associated  with  the  proper  movements  of  respiration.  The 
larynx  rises  in  expiration,  and  sinks  in  inspiration.  The  glottis 
(and  particularly  its  posterior  portion,  the  glottis  respiratoria) 
is  widened  during  deep  inspiration  and  narrowed  during  deep 
expiration.  The  same  is  the  case  with  the  nostrils,  and,  indeed, 
in  some  persons  the  alae  nasi  move  even  in  ordinary  breathing. 
It  has  long  been  known  that  in  deep  respiration  changes  in  the 
calibre  of  the  bronchi  synchronous  with  the  respiratory  move- 


216  A   MANUAL  OF  PHYSIOLOGY 

merits  may  occur.     Tn  young  persons  it  may  be  directly  obsei 

with  the  bronchoscope,  an  instrument  used  by  laryngolo§ 
for  exploring  the  larger  bronchi,  that  these  dilate  in  inspiration 
and  constrict  in  expiration  (Ingalls).  In  part  at  least  these 
movements  are  passively  produced  by  the  changes  of  intra- 
thoracic pressure,  but  it  has  not  been  definitely  determined 
whether  they  are  not  in  part  caused  by  alternate  contraction 
and  relaxation  of  the  circular  bronchial  muscle?.  To  these  muscles 
has  sometimes  been  attributed  the  function  of  regulating  the  flow 
of  air  into  and  out  of  the  infundibula,  as  the  muscle  of  the 
arterioles  regulates  the  distribution  of  the  blood  in  the  organs. 

As  regards  the  respiratory  sounds,  all  that  is  necessary  to 
be  said  here  is  that  when  we  listen  over  the  greater  portion  of 
the  lungs  with  the  ear.  or.  much  better,  with  a  stethoscope. 
a  soft  breezy  murmur,  that  has  been  compared  to  the  rustling 
of  the  wind  through  distant  trees,  is  heard.  This  has  been 
called  the  vesicular  murmur.  It  is  only  heard  in  health  during 
inspiration  and  the  very  beginning  of  expiration,  and  is  louder 
in  children  than  in  adults.  Around  the  larger  bronchi  and  the 
trachea  a  blowing  sound  is  heard,  which  certainly  originates  at 
the  glottis,  and  is  strengthened  by  the  resonance  of  the  air-tubes. 
In  health  this  is  not  recognised  over  the  greater  portion  of  the 
lung.  But  in  certain  diseases  in  which  the  alveoli  are  filled  up 
with  exudation,  this  bronchial  or  tubular  breathing  may  be  heard 
over  a  large  area,  the  vesicular  sound  being  now  suppressed  and 
the  bronchial  sound  being  better  conducted  through  the  smaller 
bronchi  towards  the  surface  of  the  lungs  when  their  walls  have 
been  rendered  more  rigid  by  the  solidification  of  the  parenchyma, 
in  spite  of  the  fact  that  the  consolidated  tissue  as  such  does  not 
conduct  the  sound  so  well  as  the  air-containing  alveoli. 

It  has  been  much  debated  whether  the  vesicular  murmur  also 
arises  at  the  glottis,  and  is  modified  by  transmission  through  the 
pulmonarv  tissue,  or  whether  it  arises  somewhere  in  the  terminal 
bronchi,  the  infundibula  or  the  alveoli.  Both  views  may  be  sup- 
ported bv  certain  arguments,  and  to  both  some  objections  may 
be  raised.  The  fact  appears  to  be  that  there  are  two  elements 
in  the  inspirator}-  murmur — a  true  vesicular  sound,  produced 
about  the  place  where  the  terminal  bronchioles  give  off  the 
infundibula,  and  a  resonance  sound  set  up  in  the  trachea  and 
bronchi  bv  the  glottic  murmur.  This  resonance  sound  as  heard 
over  portions  of  the  lung  containing  only  small  bronchi  has  a 
different  character  from  that  heard  over  large  bronchi,  inasmuch 
as  the  fundamental  note,  and  to  a  still  greater  extent  the  over- 
tones (p.  280),  are  much  weakened  in  those  small  and  easily- 
distensible  tubes.  The  true  vesicular  element  is  heard  all  over 
the  lungs,  but  the  resonant  laryngeal  element  in  large  animals, 


RESPIRA  TTON 


2l7 


like  the  horse  and  ox,  dies  out  as  an  audible  murmur  before  it 
reaches  the  remotest  lobules,  and  can  only  be  distinguished  over 
,i  portion  of  the  pulmonary  area.  When  the  glottic  sound  is 
eliminated  by  causing  an  animal  to  breathe  through  a  tracheal 
fistula,  the  vesicular  murmur  is  still  heard,  and  in  the  horse  is 
even  somewhat  sharper  than  normal,  although  in  the  dog  it  is 
softer  and  weaker.  The  expiratory  murmur  does  not  seem  to 
contain  a  true  vesicular  element,  but  is  exclusively  due  to  the 
resonance  of  the  expiratory  glottic  sound  (Marek).  It  is  generally 
admitted,  and  this  is  of  great  importance  in  practical  medicine, 
that  when  the  normal  vesicular  sound  is  heard  over  any  portion 
of  the  lung  tissue,  it  may  be  inferred  that  this  portion  is  being 
properly  distended,  and  that  air 
is  freely  entering  its  alveoli. 

Up  to  this  point  we  have 
contented  ourselves  with  a 
purely  qualitative  description 
of  the  mechanical  phenomena 
of  respiration.  We  have  now 
to  consider  their  quantitative 
relations,  and  the  methods  by 
which  these  have  been  studied. 


The  expansion  of  the  lungs  in 
inspiration  may  be  easily  demon- 
strated in  man,  and  even  a  rough 
estimate  of  its  amount  obtained, 
by  the  clinical  method  of  percus- 
sion. For  example,  the  resonant 
note  that  is  elicited  when  a  finger 
laid  on  the  chest  at  a  part  where 
it  overlies  the  right  lung  is 
smartly  struck  can  be  followed 
down  until  it  is  lost  in  the  '  liver 
dulness.'  If  the  lower  limit  of 
the  resonant  area  be  marked  on 
the  chest-wall  first  in  full  in- 
spiration and  then  in  full  ex- 
piration, the  mark  will  be  lower 


Fig.  99- — Scheme  of  Tambour  for 
Recording  Respiratory  Move- 
ments. 

C,  a  metal  capsule  connected  airtight 
with  B,  A,  two  caoutchouc  membranes, 
the  chamber  formed  by  which  can  be 
inflated  by  means  of  the  tube  and  stop- 
cock E.  The  tube  D  connects  the  space 
H  with  a  registering  tambour  provided 
with  a  lever.  The  membrane  A  is  applied 
to  the  chest,  round  which  the  inexten- 
sible  strings  F  are  tied.  At  every  ex- 
pansion of  the  chest  the  pressure  in  H 
is  increased,  and  the  increase  of  pres- 
sure is  transmitted  to  the  registering 
tambour. 


in  the  former  than  in  the  latter, 
and  the  difference  will  represent  the  difference  in  the  vertical  length 
of  the  shrunken  and  distended  lung.  A  similar  enlargement  in  the 
transverse  direction  may  be  demonstrated  in  the  same  way,  the  inner 
borders  of  the  lungs  coming  nearer  to  the  middle  line  in  inspiration, 
and  receding  from  it  in  expiration.  The  examination  of  the  chest  by 
the  Rontgen  rays  has  also  yielded  results  of  importance  in  the  study 
of  normal  respiratory  conditions,  and  still  more  important  results  in 
pulmonary  disease. 

For  most  physiological  purposes,  however,  a  faithful  graphic 
record  of  the  respiratory  movements  is  indispensable.  This  may 
be  obtained — 

(i)  By  registering  the  movements  of  a  single  point,  or  the  varia- 


218  A    MANUAL  OF  PHYSIOLOGY 

tions  in  .1  single  circumference,  oi  the  boundary  oi  the  thoracic 
cavity,  In  man  changes  in  the  circumference  oi  the  thorax  al  any 
level  can  be  recorded  by  means  oi  a  tambour  adjusted  to  the  chest 
(Figs.  <i'i  and  [28),  and  in  communication  with  another,  which  is 
provided  with  a  writing  lever  (Figs.  86  and  [3]       0  stictube, 

with  ;i  spiral  spring  in  its  lumen,  may  be  fastened  around  the  thorax 
or  abdomen  and  connected  with  a  piston-recorder  a  small  cylinder 
in  which  works  a  piston  carrying  a  writing-point)  (Fitz). 

By  recording  the  changes  of  pressure  produced  in  the  air- 
passages  by  the  respiratory  movements.  This  can  1>  ■  done  by  con- 
necting a  cannula  in  the  trachea  of  an  animal  with  a  recording 
tambour  in  the  manner  described  in  the  Practn  al 
The  variations  <>t  pressure  may  b  ■  measured  by  connecting  a  mano- 
meter with  the  trachea,  or  in  man  with  the  nostril. 

(3)   By  writing  off  the  changes  of  pressure  which  occur  in   the 
thoracic  cavity  during  respiration.       For  this  purpos  ir  is 

introduced  through  an  intercostal  spac  i  into  on  oi  the  pleural  sacs, 
without  the  admission  of  air,  or  into  the  pericardium,  and  then  con- 
nected with  a  manometer  or  other  recording  apparatus.  (  >r  a  tub  ■. 
similar  in  construction  to  a  cardiac  sound   (p  ly  be  pushed 


Fig.  100. — Respiratory  Tracing  prom  Man   (Marey). 
Down  stroke,  inspiration  ;  up  stroke,  expiration. 

down  the  oesophagus.  The  variations  in  the  intrathoracic  pressure 
are  transmitted  to  the  air  in  the  elastic  bag.  and  thene  •  to  .t  tambour. 
(4)  In  the  rabbit  the  part  of  the  diaphragm  attached  to  the  ensiform 
cartilage  may  be  isolated  from  the  rest  and  its  <  ontractions  recorded 
by  a  lever  (Head).     For  some  purpos  es  this  is  the  b.>st  method. 

When  the  respiratory  movements  are  studied  in  any  of  these 
ways,  it  is  found  that  there  is  practically  no  pause  between 
the  end  of  inspiration  and  the  beginning  of  expiration.  Nor. 
although  the  chest  collapses  more  gradually  than  it  expands. 
is  there  any  distinct  interval  in  ordinary  breathing  between  the 
end  of  expiration  and  the  beginning  of  the  succeeding  inspira- 
tion. When,  however,  the  respiration  is  unusually  slow,  an  actual 
pause  (expiratory  pause)  may  occur  at  this  point.  Expiration 
takes  somewhat  longer  time  than  inspiration,  the  ratio  varying 
from  7  :  (>  to  3  :  -\  according  to  age.  sex,  and  other  circumstances. 

The  frequency  of  respiration  is  by  no  means  constant  even 
in  health.  All  kinds  of  influences  affec1  it.  It  is  difficult  even 
to  direct  the  attention  to  the  respiratory  act  without  bringing 


RESPIRATION  i\g 

aboul  a  modification   in  its  rhythm.     In   the  adult   15  to  20 

respirations  per  minute  may  be  taken  as  about  the  normal. 
In  young  children  the  frequency  may  be  twice  as  great  (new- 
born child,  50  to  70  ;  child  from  1  to  5  years  old,  20  to  30  per 
minute).  It  is  greater  in  a  female  than  in  a  male  of  the  same 
age.  A  rise  of  temperature  increases  it  ;  150  respirations  per 
minute  have  been  seen  in  a  dog  with  a  high  temperature. 
Sudd<n  cooling  of  the  skin,  exercise,  and  various  emotional 
States,  increase  the  rate,  and  sleep  diminishes  it.  The  will  can 
alter  the  frequency  and  depth  of  respiration  for  a  time,  and 
even  stop  it  altogether,  but  in  less  than  a  minute,  in  ordinary 
individuals,  the  desire  to  breathe  becomes  imperative.  Cato's 
assertion  that  he  could  kill  himself  at  any  time  'merely  by  holding 
his  breath  '  is  only  a  proof  that  he  was  a  better  philosopher  than 
physiologist.  After  a  period  of  forced  respiration  the  breath 
can  be  held  for  a  much  longer  time.  This  is  due  to  the  '  washing 
out  '  of  the  carbon  dioxide,  the  normal  stimulus  to  the  respira- 
tory centre  (p.  231).  After  six  minutes  of  forced  breathing  the 
interval  of  voluntary  inhibition  can  be  extended  beyond  four 
minutes.  A  professional  diver  has  remained  under  water  in  a 
tank  for  about  four  and  three-quarter  minutes.  When  oxygen 
is  inhaled  instead  of  air  during  the  last  few  breaths  of  the  forced 
respiration,  the  interval  during  which  the  breath  can  be  held  may 
be  much  increased  (up  to  nine  or  ten  minutes).  In  animals  the 
rate  of  respiration  can  be  greatly  affected  by  drugs  and  by  the 
section  and  stimulation  of  certain  nerves  ;  but  to  this  we  shall 
return  when  we  come  to  consider  the  nervous  mechanism  of 
respiration. 

It  cannot  fail  to  be  observed  that  to  a  great  extent  the  rate 
of  respiration  is  affected  by  the  same  circumstances  as  the  fre- 
quency of  the  heart  (p.  98),  and  in  the  same  direction.  And, 
indeed,  in  health,  these  two  physiological  quantities,  amid  all 
their  absolute  variations,  maintain  to  each  other  a  fairly  con- 
stant ratio  ( 1  to  4  or  1  to  5  in  man).  Even  in  many  diseases 
this  proportion  remains  tolerably  stable,  although  in  others  it 
is  disturbed. 

The  total  quantity  of  air  expired,  or,  what  comes  to  the 
same  thing,  the  alteration  in  the  capacity  of  the  chest  during 
expiration,  can  be  measured  by  means  of  a  gas-meter  or  of  a 
spirometer  (Fig.  101),  which  consists  of  an  inverted  graduated  glass 
cylinder  dipping  by  its  open  mouth  into  water  and  balanced  by 
weights.  The  vessel  is  sunk  till  it  is  full  of  water,  the  air  being 
allowed  to  escape  by  a  cock.  The  expired  air  is  now  permitted 
to  enter  it  through  a  tube,  and  displaces  some  of  the  water. 
The  spirometer  is  adjusted  so  that  the  level  of  the  water  inside 
and  outside  is  the  same,  and  then  the  volume  of  air  contained 


]   MANUAL  OF  PHYSIOLOGY 


in  it  is  read  off.  This  gives  the  volume  of  the  expired  air  at  atmo- 
spheric  pressure.  Similarly,  by  breathing  air  from  the  spirometer 
the  amount  inspired  can  be  measured  (p.  291). 

From  400  to  500  c.c.  of  air* 
are  taken  in  and  given  out 
at  each  respiration  in  quiet 
breathing.  This  is  called  tidal 
air.  It  amounts  to  35  pounds 
by  weight  in  twenty-four 
hours,  or  enough  to  fill,  at 
atmospheric  pressure,  a  cubical 
box  with  a  side  of  8  feet. 
With  the  deepest  possible  in- 
spiration room  can  be  made 
for  2,000  c.c.  more ;  this  is 
called  complemental  air.  By 
a  forced  expiration  1,500  c.c. 
can  be  expelled  besides  the 
tidal  air  ;  and  to  this  quantity 
the  name  of  supplemental  or 
reserve  air  has  been  given. 
After  the  deepest  expiration 
there  always  remains  1,000 
to  1,200  c.c.  of  air  in  the 
called  the  residual  air.  After  a 
a    normal    inspiration    the   lungs 


Fig.  ioi. — Diagram  of  Spirometer. 
A,  vessel  filled  with  water.     B,  glass 
cylinder  with  scale  C,  swung  on  pulleys 
and   counterpoised  by  weights  W. 
tube  for  breathing  through. 


1), 


lungs    (Durig),    and    this   is 

normal    expiration   following 

still  contain  stationary  air  to  the  amount  of  about  2,500  c.c. 

The  term 
vital  or  res- 
p  i  r  a  to  r  y 
capacity  is 
applied  to 
the  quantity 
of  air  which 
can  be  ex- 
pelled bythe 
deepest  ex- 
piration following  the  deepest  inspiration,  and  amounts  in  an 
adult  of  average  height  to  3,500  or  4,000  c.c.  The  maximum 
quantity  of  air  which  the  lungs  can  contain  is  evidently  equal 
to    vital    capacity  plus   residual    air.      At  one   time   the    vital 

*  The  average  obtained  by  the  writer  for  81  healthy  students,  with  an 
average  body-weight  of  66  kilos,  was  460  c.c,  or  7  c.c.  per  kilo.  In  4  new- 
born children  the  tidal  air  varied  from  20  to  30  c.c,  and  from  y6  to  T$  c.c. 
per  kilo,  which  is  not  very  different  from  the  amount  in  the  adult.  The 
pulmonary  ventilation  must  therefore  be  far  more  rapid  in  the  child,  since 
its  respiratory  frequency  is  so  much  greater. 


(a  m  jili,  11  w  ntal  a  it  ■ 
Tidal   air 
Supplemental  air 
Residual  air 


Fig.  102. — Diagram  to  illustrate  the  Relative  Amouni  oi 

Complemental,  Tidal,  Supplemental,  and  Residual  Air. 


RESPIRATION  221 

icity  was  thought  to  be  capable  of  affording  valuable  informa- 
tion in  the  diagnosis  of  chest  diseases;  but  little  stress  is  now 
[aid  upon  it,  as  it  varies  from  so  many  causes.  Forinstance.it 
can  be  increased  by  practice  with  the  spirometer.  It  is  greater 
in  mountaineers  than  in  the  inhabitants  of  lowland  plains. 

It  is  clear  from  the  figures  we  have  given  that  in  ordinary 
breathing  only  a  small  proportion  of  the  air  in  the  lungs  comes 
in  direct  at  each  inspiration  from  the  atmosphere,  and  only  a 
small  proportion  escapes  into  the  atmosphere  at  each  expira- 
tion. The  greater  part  of  the  air  in  the  lungs  is  simply  moved 
a  little  farther  from  the  upper  respiratory  passages,  or  a  little 
nearer  them  ;  and  fresh  oxygen  reaches  the  alveoli,  as  carbon 
dioxide  leaves  them,  mainly  by  diffusion,  aided  by  convection 
currents  due  to  inequalities  of  temperature,  and  to  the  churning 
which  the  alternate  expansion  and  shrinking  of  the  lungs,  and 
the  pulsations  of  their  arteries,  must  produce.  But  that  some 
of  the  tidal  air  strikes  right  down  to  the  alveoli  is  evident  enough. 
For  the  respiratory  '  dead  space  ' — that  is,  the  capacity  of  the 
upper  air-passages  and  the  bronchial  tree  down  to  the  infundibula 
—is  only  140  c.c,  or  one-third  of  the  amount  of  the  tidal  air 
(Zuntz,  Loewy).  There  is  no  direct  way  of  determining  whether 
any  respiratory  exchange  goes  on  through  the  walls  of  the  upper 
air-passages.  But  by  indirect  methods  it  has  been  estimated 
that  about  30  per  cent,  of  the  volume  of  the  tidal  air  is  pure  air 
(Haldane  and  Priestley).  This,  of  course,  corresponds  to  the 
'  effective  '  dead  space.  Taking  the  average  tidal  air  at  460  c.c. 
(p.  220),  it  is  clear  that  the  effective  corresponds  very  closely  with 
the  anatomical  dead  space — that  is  to  say,  the  respiratory 
function  of  the  air-passages  above  the  point  where  the  infundibula 
are  given  off  is  negligible.  Although  such  calculations  can  only 
be  approximately  correct,  the  agreement  is  of  interest.  The 
immense  extent  of  the  pulmonary  surface,  and  the  extreme  thin- 
ness of  the  layer  of  blood  in  the  capillaries  of  the  lungs,  facilitate 
the  interchange  between  the  gases  of  the  blood  and  the  gases  of 
the  alveoli. 

The  Amount  and  Variations  of  the  Intrathoracic  Pressure. — 
In  the  deepest  expiration  the  lungs  are  never  completely  col- 
lapsed ;  their  elastic  fibres  are  still  stretched  ;  and  the  tension  of 
these  acts  in  the  opposite  direction  to  the  external  atmospheric 
pressure,  and  diminishes  by  its  amount  the  pressure  inside  the 
thoracic  cavity.  In  the  dead  body  Donders  measured  the  value 
of  this  tension,  and  therefore  of  the  negative  pressure  of  the 
thorax,  by  tying  a  manometer  into  the  trachea,  and  then  causing 
the  lungs  to  collapse  by  opening  the  chest.  It  varied  from 
7-5  mm.  of  mercury  in  the  expiratory  position  to  9  mm.  in  the 
inspiratory.     So  far  as  can  be  judged  from  observations  made 


2: -.2  A   MANUAL  OF  PHYSIOLOGY 

on  persons  suffering  from  various  diseases  of  t  he  respiratory 
organs,  the  alterations  during  ordinary  breathing  do  not  amount 
to  more  than  3  or  4  mm.  of  mercury.  But  when  an  attempt  i> 
made  in  the  dead  body  to  imitate  a  deep  inspiration  by  making 
traction  on  the  chest-walls  so  as  to  expand  the  lungs,  the  intra- 
thoracic pressure  may  fall  to  —30  mm.  of  mercury;  and  in  a 
living  rabbit  during  a  deep  natural  inspiration,  a  pressure  of 
—  20  mm.  has  been  seen. 

The  reason  why  the  lungs  collapse  when  the  chest  is  oj 
is  that  the  pressure  is  now  equal  on  the  pleural  and  alveolar 
surfaces,  being  in  both  cases  that  of  the  atmosphere.  There  is 
therefore  nothing  to  oppose  the  elasticity  of  the  lungs,  which 
tends  to  contract  them.  So  long  as  the  chest  is  unopened,  the 
pressure  on  the  pleural  surface  of  the  lungs  is  less  than  that  on 
the  alveolar  surface,  and  the  elastic  tension  can  only  cause  them 
to  shrink  until  it  just  balances  this  difference. 

In  intra-uterine  life,  and  in  stillborn  children  who  have  never 
breathed,  the  lungs  are  completely  collapsed  (atelectatic),  and 
there  is  no  negative  intrathoracic  pressure.  They  are  kept  in 
this  condition  by  adhesion  of  the  walls  of  the  bronchioles  and 
alveoli.  If  the  lungs  have  been  once  inflated,  this  adhesion 
ceases  to  act,  and  they  never  completely  collapse  again. 

Amount  and  Variations  of  the  Respiratory  or  Intrapulmonary 
Pressure. — As  we  have  already  remarked,  the  pressure  in  the 
alveoli  and  air-passages  is  less  than  that  of  the  atmosphere 
while  the  inspiratory  movement  is  going  on,  greater  than  that 
of  the  atmosphere  during  the  expiratory  movement,  and  equal 
to  that  of  the  atmosphere  when  the  chest-walls  are  at  1 
When  the  external  air-passages  are  closed,  e.g.,  by  connecting  a 
manometer  with  the  mouth  and  pinching  the  nostrils,  the  greatest 
possible  variations  of  pressure  are  produced.  In  the  deepest 
inspiration  under  these  conditions  a  negative  pressure  of  about 
75  mm.  of  mercurv  [i.e.,  a  pressure  less  than  that  of  the  atmo- 
sphere by  this  amount)  has  been  found,  and  in  deep  expiration  a 
somewhat  greater  positive  pressure*  (Practical  Exercises,  p.  _ 

But  with  ordinary  breathing,  the  variations  of  pressure  as 
measured  by  this  method  do  not  exceed  5  to  10  mm.  of  mercury 
above  or  below  the  pr<  :  the  atmosph- 

When  the  external  openings  are  not  obstructed.  a>  f<  >r  example, 
when  the  lateral  pressure  is  taken  in  the  trachea  of  an  animal 
by  means  of  a  cannula  with  a  side-tube  connected  with  a  mano- 
meter, still  smaller,  and  doubtless  truer,  values  have  been  found 
(2-3  mm.  of  mercurv,  as  the  positive  expiratory  pressure  and 

*  The  maximum  negative  pressure  in  deepest  inspiration  averaged  for 
49  studerr  am.  (highest  observation    -  137  mm.)  of  mercurv  ;  the 

maximum  positive  pressure  in  deepest  expiration,  +80  mm.  (highest 
observation  +  140  mm.). 


RESPIRATION  223 

1  mm.  as  the  negative  inspiratory  pressure  in  dogs).  Bu1  sin 
the  respiratory  passages  are  abruptly  narrowed  at  the  glottis, 
the  variations  oi  pressure  must  be  greater  below  than  above 
it,  and  in  general  they  must  increase  with  the  distance  from 
that  orifice,  being  greater,  for  instance,  in  'the  alveoli  than  in 
tin-  bronchi. 

Relation  of  Respiration  to  the  Nervous  System. — Unlike 
the  beat  oi  the  heart,  the  respiratory  movements  are  entirely 
dependent  on  the  central  nervous  system.  The  'centre' 
w  huh  presides  over  them  is  situated  in  the  spinal  bulb.  It  is  a 
bilateral  centre— that  is,  it  has  two  functionally  symmetrical 
halves,  one  on  each  side  of  the  middle  line.  Each  of  tl 
hakes  has  to  do  more  particularly  with  the  respiratory  muscles 
of  its  own  side,  for  destruction  of  one-half  of  the  spinal  bulb 
causes  paralysis  of  respiration  only  on  that  side.  Anatomically 
the  respiratory  centre  has  not  been  sharply  localized  ;  but  it 
lies  lower  than  the  vaso- motor  centre,  not  far  from  the  point 
of  the  calamus  scriptorius.  Stimulation  of  this  region  during 
apncea  (p.  231)  is  stated  to  cause  co-ordinated  inspiratory  move- 
ments and  widening  of  the  opening  of  the  glottis  through  abduc- 
tion of  the  vocal  cords.  The  centre  is  brought  into  relation  with 
the  muscles  of  respiration  by  efferent  nerves.  The  phrenic  nerves 
to  the  diaphragm,  and  the  intercostal  nerves  to  the  muscles 
which  elevate  the  ribs,  are  the  most  important  of  those  con- 
cerned in  ordinary  breathing.  The  respiratory  centre  is  further 
related  to  afferent  nerves,  of  which  the  most  influential  is  the 
vagus,  particularly  its  pulmonary  fibres  and  its  superior  laryngeal 
branch.  But  almost  any  afferent  nerve  may  powerfully  affect 
the  centre  ;  and  it  is  also  influenced  by  fibres  passing  to  it  from 
the  higher  parts  of  the  central  nervous  system. 

Section  of  the  spinal  cord  in  animals  above  the  origin  of  the 
phrenic  nerves  causes  complete  paralysis  of  respiration,  and  con- 
sequent death.  The  phrenics  arise  from  the  third  and  fourth 
cervical  nerves,  and  are  joined  b}T  a  branch  from  the  fifth  ;  and 
in  man  fracture  of  any  of  the  four  upper  cervical  vertebrae  is, 
as  a  rule,  instantly  fatal.  But  in  one  case  respiration  was  carried 
on,  and  life  maintained  for  thirty  minutes,  merely  by  the  con- 
traction of  the  muscles  of  the  neck  and  shoulders  in  a  man 
entirely  paralyzed  below  this  level  (Bell).  Section  of  the  cord 
just  below  the  origin  of  the  phrenics  leaves  the  diaphragm 
working,  although  the  other  respiratory  muscles  are  paralyzed. 
A  case  has  been  recorded  of  a  man  in  whom,  from  disease  of  the 
spine  in  the  lower  cervical  region,  all  the  ribs  became  completely 
immovable.  He  was  able  to  lead  an  active  life,  and  to  carry 
on  his  business,  although  he  breathed  entirely  by  his  diaphragm 
and  abdominal  muscles. 


224  A   MANUAL  OF  PHYSIOLOGY 

Section  of  one  phrenic  is  followed  by  paralysis  of  the  corre- 
sponding half  of  the  diaphragm,  section  of  both  phrenics  by 
complete  paralysis  of  that  muscle,  and  although  respiration  still 
goes  on  by  means  of  the  muscles  which  aet  upon  the  ribs,  it  is 
usually  inadequate  to  the  prolonged  maintenance  of  life.  In 
the  horse,  however,  not  only  has  survival  been  seen  after  this 
operation,  but  the  animal,  after  the  first  temporary  increase 
in  the  frequency  of  the  breathing  had  disappeared,  could  be 
driven  in  a  light  vehicle  without  any  marked  dyspnoea.  The* 
phrenic  nuclei  in  the  two  halves  of  the  cord  are  connected 
across  the  middle  line.  For  when  a  semisection  of  the  cord  is 
made  between  this  level  and  the  respiratory  centre  in  the  medulla, 
respiratory  impulses  are  still  able  to  reach  both  phrenic  nerves. 
In  some  animals  both  halves  of  the  diaphragm  go  on  contracting. 
But  when,  as  usually  happens,  this  is  not  the  case,  and  the 
diaphragm  on  the  side  of  the  semisection  has  ceased  to  act,  it 
at  once  begins  to  contract  again  when  the  opposite  phrenic 
nerve  is  cut,  and  the  respiratory  impulse,  descending  from  the 
bulb,  is  blocked  out  from  the  direct,  and  forced  to  follow  the 
crossed  path.  It  has  been  shown  that  the  crossing  takes  place 
at  the  level  of  the  phrenic  nuclei,  and  nowhere  else  (Porter). 

When  one  vagus  is  divided,  there  is  little  or  no  change  in  the 
respiratory  movements.  Half  an  inch  of  one  vagus  nerve  has 
been  excised  in  removing  a  tumour,  and  the  patient  showed  no 
symptoms  whatever.  But  section  of  both  vagi  in  such  animals 
as  the  dog,  cat  and  rabbit  causes  respiration  to  become  much 
deeper  and  slower,  the  one  change  for  a  time  compensating  the 
other,  so  that  the  total  amount  of  air  taken  in  and  given  out, 
the  amount  of  carbon  dioxide  eliminated,  and  the  partial  pres- 
sure of  that  gas  in  the  pulmonary  alveoli  are  not  greatly  altered. 
The  relative  duration  of  the  two  respiratory  phases  is  completely 
changed,  inspiration  being  much  more  prolonged  than  expiration. 
It  has  been  shown  that  the  effect  is  really  due  to  the  loss  of  im- 
pulses that  normally  ascend  the  vagi,  not  to  any  irritation  of  the 
cut  ends.  For  a  nerve  can  be  frozen  without  exciting  it  ;  and 
when  a  portion  of  each  vagus  is  frozen,  the  respiration  is 
affected  in  precisely  the  same  way  as  when  the  nerves  are 
divided. 

After  section  of  both  vagi  certain  fibres  coming  from  the 
brain  above  the  respiratory  centre  appear  to  take  a  share  in  the 
regulation  of  the  respiratory  movements.  The  bloodvessels  sup- 
plying these  fibres,  or  the  centres  from  which  they  come,  can  be 
blocked  by  injection  of  paraffin  wax  into  the  common  or  internal 
carotid,  or  the  bulb  can  be  severed  with  the  knife  above  the  level 
of  the  respiratory  centre,  without  anyjeffect  being  produced  upon 
the  breathing,  except  that  the  rate  is,  as  a  rule,  somewhat  lessened. 


RESPIRATION  225 

Bui  when  both  the  vagi  and  these  upper  paths  are  cut  the  char- 
acter of  1  he  respiration  is  changed,  exceedingly  prolonged  Inspira- 
tory spasms  alternating  with  long  periods  of  complete  relaxation 
of  the  diaphragm  till  the  animal  dies. 

From  these  facts  it  appears  that  the  periodic  automatic  dis- 
charges of  the  respiratory  centre  are  being  continually  controlled 
ami  modified  by  impulses  passing  up  the  vagus,  and  that  in  the 
absence  of  these  impulses  a  certain  degree  of  control  is  exercised 
by  the  higher  paths,  which,  however,  do  not  appear  to  be  nor- 
mally in  action,  at  any  rate  to  the  full  measure  of  their 
capacity.  When  the  vagi  are  severed,  the  control  of  the 
higher  paths  comes  into  play,  and  is  sufficient  still  to  keep  the 
breathing  regular,  although  it  is  slowed.  When  the  higher  paths 
are  cut  off,  the  vagus  of  itself  is  able  to  regulate  the  discharge. 
But  when  both  are  gone,  the  respiratory  centre,  freed  from  con- 
trol, passes  into  a  condition  of  alternate  spasm  and  exhaustion. 
Of  the  central  connections  of  these  upper  paths  but  little  is  surely 
known.  The  corpora  quadrigemina,  however,  seem  to  contain 
centres  which  can  affect  the  respiration.  Certain  areas  on  the 
cerebral  cortex  have  also  been  described,  the  excitation  of  which 
modifies  the  respiratory  movements.  There  is  no  question  that 
the  cortex  is  connected,  and  extensively  connected,  with  the 
respiratory  centre,  since  the  rate  and  depth  of  the  co-ordinated 
respiratory  movements,  which  are  universally  acknowledged  to 
involve  the  activity  of  the  centre,  can  be  altered  not  only  by 
the  will,  but  by  the  most  varied  psychical  events. 

The  rhythmical  excitation  of  the  regulating  vagus  fibres  must 
be  brought  about  either  by  mechanical  stimulation  of  the  nerve- 
endings  in  the  lungs,  due  to  the  alternate  stretching  and  shrink- 
ing, or  by  chemical  stimulation  depending  on  the  changes  that 
occur  with  each  respiration  in  the  content  of  oxygen  and  carbon 
dioxide  in  the  alveolar  air,  and  therefore  in  their  pressure 
(p.  248)  in  the  blood.  Both  views  have  found  advocates,  but 
whatever  influence  the  chemical  changes  in  the  blood  may 
exert,  there  is  no  doubt  that  the  mechanical  factors  are  the 
more  important.  That  the  vagus  is  really  excited  is  shown 
by  the  fact  that  a  negative  variation  (Chap.  XI.)  is  set  up  in 
the  nerve  when  the  lungs  are  inflated.  An  electrical  change, 
although  not  so  pronounced,  is  also  observed  when  air  is  sucked 
out  of  the  lungs  (Alcock  and  Seemann). 

When  the  normal  excitation  of  the  vagus  fibres  by  expansion 
of  the  lungs  is  exaggerated  by  closing  the  trachea  at  the  end  of 
inspiration,  the  diaphragm  immediately  relaxes,  and  a  long 
expiratory  pause  ensues,  broken  at  last  by  a  series  of  inspira- 
tions much  deeper  and  more  prolonged  than  those  which  were 
taking  place  before  occlusion.     When  the  trachea  is  occluded 

15 


226  A  MANUAL  OF  PHYSIOLOGY 

at  the  end  <>1  expiration,  a  scries  of  deep  and  long-drawn  inspira- 
tions occurs,  the  first  of  which  begins  at  the  moment  when  the 
next  normal  inspiration  ought  to  have  taken  place  had  the  wind- 
pipe been  left  free.  The  most  obvious  explanation  of  these 
results  is  that  the  expansion  of  the  lungs  sets  up  impulses  in 
the  vagi  which  cut  short  the  inspiratory  activity  of  the  respira- 
tory centre  (inspiration-inhibiting  fibres),  while  in  collapse  im- 
pulses are  set  up  which  excite  it  to  renewed  inspiratory  discharge 
(inspiration-exciting  fibres).  Since  ordinary  expiration  is  in  the 
main  not  associated  with  active  muscular  contraction,  the 
inspiration-inhibiting  fibres  Mould  be  at  the  same  time  expira- 
tion-exciting. Clearly  this  would  constitute  a  so-called  '  sell- 
steering  '  arrangement,  each  inspiration  leading  inevitably  to  the 
succeeding  expiration,  and  each  expiration  providing  tin   ne< 


Fig.  103. — Respiratory  Tracings:  Dog. 

A,  normal  ;  B,  effect  of  stimulation  of  the  central  end  of  vagus;  C,  effect  of 
section  of  both  vagi.   (Tracing  taken  as  in  Fig.  129,  p.  288.)  Tin*  -tra<  ing,  seconds. 

sary  stimulus  for  the  succeeding  inspiration.  On  this  hypothesis 
section  of  the  vagi  must  necessarily  be  followed  by  slowing  of  the 
respiratory  movements,  and  we  have  seen  that  this  is  the  case. 

A  rival  hypothesis  is  that  the  automatic  activity  of  the  re- 
spiratory centre  leads  normally  to  the  discharge  of  motor  im- 
pulses to  the  inspiratory  muscles,  which  are  cut  short  at  each 
expansion  of  the  lungs  by  the  inhibitory  action  of  the  vagus, 
the  nerve  no1  being  excited  during  pulmonary  collapse,  and 
therefore  carrying  no  inspiratory  impulses  to  the  centre.  On 
this  assumption,  we  may  think  of  the  centre  as  being  '  wound  up  ' 
like  a  clock,  the  periodic  arrival  of  regulating  impulses  acting 
like  an  escapement  movement,  and  allowing  a  certain  amount 
of  discharge.  When  the  vagi  are  cul  the  inspirations  are  greatly 
prolonged  and  deepened,  because  the  check  on  the  discharge  of 
the  centre  has  been  removed. 


/>•/  SPIR  I  l  TON  227 

Attempts  have  been  made  by  experimental  stimulation  of  the 
vagus  trunk  to  determine  whether,  as  a  matter  of  fact,  it  con- 
tains both  inspiratory  and  expiratory  fibres.  But  the  results 
arc  neither  so  dear  nor  so  constanl  thai  we  can  confidently 
appeal  to  them  in  making  a  decision,  and  even  some  of  the  in- 
vestigators who  maintain  the  existence  of  but  one  anatomical 
set  oi  fibres  believe  that  these  are  affected  differently  by  different 
kinds  of  stimulation —momentary  stimuli,  for  example,  setting 
Up  in  them  impulses  which  we  may  call  inspiratory,  and  long- 
lasting  stimuli  impulses  which  we  may  call  expiratory. 

Excitation  of  the  central  end  of  the  cut  vagus  below  the  origin 
of  its  superior  laryngeal  branch,  with  induction  shocks  of  mode- 
rate strength,  certainly  causes  quickening  of  respiration.     If  the 


Fig.  104.  —Effect  of  Stimulation  of  Central  End  of  Vagus  in  a  Cat.     Upper 
Trace,   Respiration  ;  Lower  Trace,   Blood-pressure. 

At  the  top  are  the  time  trace  (seconds),  and  below  it  the  signal  line,  the  depres- 
sion hi  which  indicates  the  duration  of  the  excitation.  Practically  no  effect  was 
produced  on  the  respiration,  but  a  fall  of  blood -pressure  with  slowing  of  the  heart. 

excitation  be  strong,  there  is  arrest  in  the  inspiratory  phase. 
A  brief  mechanical  stimulus,  or  a  series  of  such,  has  a  similar 
effect.  But  chemical  stimulation  (e.g.,  with  a  strong  solution 
of  potassium  chloride)  or  long-continued  mechanical  excitation 
like  that  produced  by  stretching  or  compression  of  the  nerve, 
or  certain  kinds  of  electrical  stimulation — for  instance,  the  very 
weakest  induction  shocks,  or  the  closure  of  an  ascending  voltaic 
current* — cause  slowing  of  the  respiratory  movements  or  ex- 
piratory standstill.  This  is  also  the  usual,  though  not  the 
invariable,  result  of  stimulating  the  superior  laryngeal,  even 
when  weak  induction  shocks  are  employed.  With  stronger 
stimulation  energetic  contractions  of  the  expiratory  muscles 
*  I.e.,  a  current  passing  towards  the  head  in  the  nerve. 

15—2 


;    w  ivi    \L  OF   PHYSIOLOGY 


may  occur.  These  [acts  undoubtedly  suggesl  the  existence  in 
the  vagus  ol  two  kinds  of  afferenl  uerve-fibres  thai  affect  the 
respiratory  centre  in  opposite  ways  inspiratory  fibres,  which 
stimulate  it  to  greater  activity  of  discharge,  and  expiratory 
fibres,  which  inhibit  its  action.  The  lattei  variety  we  may 
suppose  to  be  more  numerous  in  the  superior  laryngeal,  the 
former  in  the  pulmonary  branches  of  the  vagus.  And  there 
is  nothing  forced  in  the  hypothesis  thai  certain  kinds  o\  stimuli 
a<  i  particularly  on  the  one  set  of  fibres,  and  certain  kinds  on 
the  other,  for  we  have  already  seen  an  instance  ol  this  in 
studying  the  differences  between  the  vaso-constrictor  and  the 
vaso-dilator  nerves  (p.  159). 


Fig.   105      I  mm  1  or  Stimulation  of  Central  End  ok  Brachial  Nervi    on 
Respiration    (Upper  Tracing)    \m>   Blood-pressure    (Lower   Tracing) 
in  the  Cat. 
\t  the  top  of  the  figure  are  the  tim<   I  nds)  and  the  signal  line,  showing 

beginning  and  end  ol  stimulation. 

The  most  probable  conclusion,  and  the  one  which  best  recon- 
ciles the  conflicting  hypotheses,  is  thai  two  sets  of  fibres  are 
presenl  :  (1)  Fibres  which  inhibit  inspiration  (and  cause  expira- 
tion), and  are  excited  in  ordinary  inspiration  by  the  expansion 
of  the  lungs.  (2)  Fibres  which  cause  inspiration  (and  inhibit 
expiration),  and  are  excited  in  strong  expiration,  as  in  dyspnoea, 
by  the  collapse  of  the  lungs,  but  are  not  active  in  ordinary 
expiration. 


Rl  SPTRATION  229 

However  this  may  be,  the  facts  we  have  been  discussing  have 
.in  importance  oi  their  own,  apari  from  any  hypothetical  ex- 
planations of  them.  Some  i>i  them  have  been  more  than  once 
unintentionally  illustrated  on  man.  In  one  case  the  Left  vagus 
trunk  was  included  in  a  ligature  with  the  common  carotid.  The 
respiratory  movements  immediately  stopped,  the  pulse  was 
slowed,  and  death  occurred  in  thirty  minutes  (Rouse).  The 
superior  laryngeal  fibres,  unlike  those  of  the  vagus  proper,  are 
not  constantly  in  action,  as  section  of  both  nerves  has  no  effect 
on  respiration.  Any  source  of  irritation  in  the  larynx  may 
stimulate  these  fibres  and  produce  a  cough,  which  may  also  be 
caused  by  irritation  of  the  pulmonary  fibres  of  the  vagus. 

The  cutaneous  nerves,  and  especially  those  of  the  face  (fifth 
nerve),  abdomen  and  chest,  have  a  marked  influence  on  re- 
spiration. They  can  be  easily  excited  in  the  intact  body  by 
thermal  and  mechanical  stimulation.  A  cold  bath,  for  instance, 
usuallv  causes  acceleration  and  deepening  of  the  respiratory 
movements;  and  the  efficacy  of  mechanical  stimulation  of 
sensory  nerves  in  stirring  up  a  sluggish  respiratory  centre  is 
well  known  to  midwives,  who  sometimes  slap  the  buttocks  of 
a  newborn  child  to  start  its  breathing.  The  reflex  expiratory 
standstill  caused  in  rabbits  by  inhalation  of  such  sharp-smelling 
substances  as  ammonia,  acetic  acid,  and  tobacco-smoke  is  due 
to  afferent  impulses  passing  up  the  trigeminus  fibres  from  the 
mucous  membrane  of  the  nose,  and  is  still  obtained  after  section 
of  the  olfactory  nerves. 

Another  set  of  afferent  nerves  which  have  been  supposed  by 
some  to  bear  an  important  relation  to  the  respiratory  centre 
are  those  which  supply  the  muscles.  We  have  already  noticed 
that  the  frequency  of  respiration  is  greatly  augmented  by  mus- 
cular exercise.  The  simplest  explanation  would  seem  to  be  that 
afferent  muscular  nerves  are  stimulated  either  by  mechanical 
compression  of  their  terminal  '  spindles,'  or  by  the  chemical 
action  on  them  of  certain  waste  products  produced  in  contrac- 
tion. It  is  quite  likely  that  this  is  one  way  in  which  the  adjust- 
ment is  achieved.  But  this  is  not  the  only,  and  perhaps  not 
the  most  important,  way.  For  an  increase  in  the  respiratory 
movements  is  caused  by  tetanizing  the  muscles  of  a  limb  whose 
nerves  have  been  completely  severed,  and  which  is  indeed  con- 
nected with  the  rest  of  the  body  by  no  other  structures  than  its 
bloodvessels.  This  can  only  be  due  to  two  things  :  a  direct  action 
on  the  respiratory  centre  by  the  blood  that  has  passed  through, 
and  been  altered  in,  the  contracting  muscles,  or  an  action 
exerted  by  the  blood  indirectly  on  the  centre  through  the  excita- 
tion of  afferent  respiratory  nerves  whose  connection  with  it  is  still 
intact — for   example,    the   other   muscular    nerves   or   the   pul- 


230  A   MANUA1    OF  PHYSIOLOGY 

monary  branches  of  the  vagus.  Thai  the  action  is  direct  is 
shown  by  the  fact  that  after  section  of  the  vagi,  the  sympathetic, 
and  the  spinal  cord  below  the  origin  of  the  phrenics,  an  increase 
in  the  respiratory  movements  is  slill  produced  \<\  tetanizing  a 
limb. 

It  is  generally  acknowledged  thai  the  respiratory  centre  may 
be  excited  both  by  blood  thai  is  rich  in  carbon  dioxide  and  by 
Mood  thai  is  poor  in  oxygen,  the  actual  stimulating  substance 
in  the  latter  case  being,  perhaps,  an  easily  oxidizable  body 
possibly  lactic  acid— which  rapidly  disappears  from  properly 
oxygenated  blood. 

But  it  has  been  the  subject  of  long  -  continued  discussion 
whether  excess  of  carbon  dioxide  or  deficiency  of  oxygen  is  the 
more  potent  stimulus.  The  best  evidence  points  to  the  conclusion 
that  comparatively  small  alterations  in  the  amount  of  carbon 
dioxide  in  the  inspired  air  cause  a  relatively  great  increase  in 
the  respiration,  while  in  the  case  of  the  oxygen  the  departure 
from  the  normal  proportion  must  be  much  more  decided  to 
bring  about  any  notable  effect.  Nor  is  it  at  all  out  of  harmony 
with  this  that,  when  very  large  quantities  of  carbon  dioxide 
(jo  per  cent,  and  upwards  in  rabbits)  are  inhaled,  a  condition 
of  narcosis  comes  on  without  any  previous  respiratory  distress. 
For  many  substances  act  differently  in  large  and  in  small  doses. 
Haldane  has  pointed  out  how  exquisitely  sensitive  the  respiratory 
centre  is  to  even  small  changes  in  the  partial  pressure  of  carbon 
dioxide  in  the  alveolar  air,  and  therefore  in  the  blood  and  the 
centre  itself,  and  has  demonstrated  that  this  is  the  way  in  which 
the  amount  of  the  pulmonary  ventilation  (the  volume  of  air 
breathed  per  unit  of  time)  is  chiefly  regulated  in  ordinary 
breathing. 

For  instance,  an  increase  of  as  little  as  o-2  per  cent,  of  carbon 
dioxide  in  the  alveolar  air,  corresponding  to  an  increase  of  1-4111111. 
of  mercury  in  the  partial  pressure  (p.  248)  of  the  gas,  caused  an 
increase  in  the  pulmonary  ventilation  of  100  per  cent.  The 
alveolar  oxygen, pressure  had  to  be  diminished  to  13  per  cent. 
of  an  atmosphere  before  any  decided  increase  in  the  respiration 
occurred.  During  moderate  muscular  work  the  percentage  of 
carbon  dioxide  in  the  alveolar  air,  and  therefore  in  the  blood, 
increases  slightly,  causing  an  increase  in  the  ventilation,  and  this 
is  one  of  the  ways  in  which  the  hyperpncea  associated  with 
muscular  exercise  is  brought  about.  In  severe  work  lack  ol 
oxygen,  with  accumulation  of  lactic  acid  and  other  metabolic 
products,  which  stimulate  the  respiratory  centre  or  render  it 
excitable  by  smaller  pressures  of  carbon  dioxide,  also  plays  a 
part. 

To  sum   up,  the  regulation  of  normal  breathing  is  twofold — a 


RESPIRATION  231 

chemical  regulation  [through  the  carbon  dioxide)  of  the  amount  of 
air  moved  into  and  out  of  the  lungs  per  unit  of  time  ;  and  a.  nervous 
regulation  [chiefly  through  the  vagi)  of  the  rate  and  depth  of  the 
movements  necessary  to  effect  the  given  amount  of  ventilation. 

When  the  vagi  have  been  divided,  an  increase  in  the  carbon 
dioxide  pressure  within  certain  limits  is  responded  to  by  an 
increase  in  I  he  total  ventilation,  just  as  in  the  normal  animal, 
but  I  he  form  of  t  he  response  is  different.  Whereas  in  the  normal 
animal  both  the  rate  and  the  depth  of  respiration  are  increased, 
in  the  vagotomized  animal  there  is  a  marked  increase  in  depth, 
with  little  or  no  increase  in  rate  (Scott). 

When  the  gaseous  exchange  in  the  lungs  from  any  cause 
becomes  insufficient,  the  respiratory  movements  are  exaggerated, 
and  ultimately  every  muscle  which  can  directly  or  indirectly 
act  upon  the  chest -wall  is  called  into  play  in  the  struggle  to  pass 
more  air  into  and  out  of  the  lungs.  To  a  lesser  and  greater 
degree  of  this  exaggeration  of  breathing  the  terms  Hyperpnaza 
and  Dyspnoea  have  been  respectively  applied.  If  the  gaseous 
interchange  remains  insufficient,  or  is  altogether  prevented, 
asphyxia  sets  in.  Sometimes  in  man  impending  asphyxia  from 
loss  of  function  by  a  part  of  the  lungs  (with  crippling  of  the  lesser 
circulation),  as  in  pneumonia,  may  be  warded  off  by  inhalations  of 
oxygen.  Increase  in  the  temperature  of  the  blood  circulating 
through  the  spinal  bulb,  as  when  the  carotid  arteries  of  a  dog  are 
laid  on  metal  boxes  through  which  hot  water  is  kept  flowing,  also 
causes  dyspncea  (heat-dyspnoea)  (p.  290) .  But  if  the  temperature  be 
too  high,  the  respiratory  movements  may  be  slowed,  perhaps  by 
a  partial  paralysis  or  inhibition  of  the  respiratory  centre.  When 
the  blood  is  cooled  the  respiration  becomes  deeper  and  slower, 
but  if  the  temperature  is  greatly  and  suddenly  lowered,  the 
centre  may  be  stimulated  and  the  breathing  quickened.  In  man 
the  increased  temperature  of  the  blood  in  fever  is  a  cause,  though 
not  the  only  one,  of  the  increase  in  the  rate  of  respiration. 

Apnoea. — The  physiological  opposite  of  dyspncea  is  apnaea. 
This  condition  may  be  produced  in  an  animal  by  rapid  or  pro- 
longed artificial  respiration.  It  is  especially  easy  to  obtain  in  an 
animal  in  which  the  circulation  through  the  brain  and  bulb  is 
interrupted  for  a  time  and  then  restored,  while  artificial  respira- 
tion is  being  kept  up.  Spontaneous  respiration  returns  after  a 
longer  or  shorter  interval,  but  if  the  artificial  respiration  be  still 
maintained,  it  again  ceases.  In  a  successful  experiment  the 
animal  remains  without  breathing  for  many  seconds  after  the 
artificial  respiration  is  stopped.  In  apncea  the  chest  remains  at 
rest  in  the  expiratory  phase  if  the  lungs  have  been  inflated  by 
the  artificial  respiration  and  then  allowed  to  collapse  of  them- 
selves (expiratory  apncea),  but  in  the  inspiratory  phase  if  they 


232  A   MANUA1    OF  PHYSIOLOGY 

have  been  emptied  by  suction  and  then  permitted  ol  themselves 
to  expand  (inspiratory  apncea).  The  apncea  is  not  produced, 
as  some  have  thought,  by  the  accumulation  o\  an  excess  o\  <>xvgen 
in  the  blood,  for  rapid  and  repeated  inflation  of  the  lungs  with 
hydrogen  may  cause  the  condition.  Indeed,  towards  the  end 
of  the  apneeic  period  the  venous  blood  may  be  very  distinctly 
poorer  in  oxygen  than  normal  venous  blood.  Apncea  is 
easily  caused  in  man  by  a  period  of  dec])  and  rapid  breathing 
and  in  other  ways.  The  essential  thing  in  this  chemical  or  true 
apncea  [apncea  vera)  is  the  lowering  of  the  partial  pressure  ol 
carbon  dioxide  in  the  alveolar  air,  and  therefore  in  the  arterial 
blood  and  the  respiratory  centre.  The  carbon  dioxide  is  washed 
out  of  the  body,  so  to  say,  by  the  excessive  pulmonary  ventilation 

In  addition  to  chemical  apncea,  which  is  obtainable  whether 
the  vagi  are  intact  or  not,  a  so-called  mechanical  apncea,  cr 
apncea  vagi,  exists — that  is  to  say,  a  stoppage  of  the  respiration 
due  to  an  inhibitory  effect  produced  through  the  vagi  on  the  re- 
spiratory centre  when  the  vagus  endings  in  the  lungs  are  excited 
mechanically  by  inflation.  Some  observers  state  that  this  vagus 
apncea  does  not  outlast  the  inflation.  Others  believe  that  the 
results  of  successive  inflations  can  be  '  summated  '  in  tin- 
centre,  giving  rise  to  an  apncea  which  persists  after  stoppage 
of  the  artificial  respiration.  That  a  '  memory  '  of  a  prolonged 
rhythmical  inflation  of  the  lung's  can  impress  itself  in  some  way 
on  the  respiratory  centre  is  shown  by  the  curious  phenomenon 
that  in  resuscitation  of  the  bulb  after  a  period  of  anaemia  the 
natural  respiration,  when  it  returns,  may  have  for  a  short  time 
exactly  the  same  rhythm  as  the  artificial  respiration  which  has 
just  been  stopped. 

That  the  blood  when  the  gaseous  exchange  in  the  lungs  is  inter- 
fered with  produces  dyspnoea  by  acting  on  some  portion  of  the 
brain  may  be  shown  in  an  interesting  manner  by  establishing  what 
is  called  a  cross-circulation  in  two  rabbits  or  dogs.  The  vertebral 
arteries  and  one  carotid  are  tied  in  both  animals  ;  the  remaining 
carotids  are  divided  and  connected  ciosswise  by  glass  tubes,  or, 
what  is  better,  as  it  avoids  the  risk  of  clotting,  they  are  crossed 
by  suturing  the  cut  ends,  so  that  the  brain  of  each  is  supplied 
by  blood  from  the  other.  When  the  respiration  is  artificially 
hindered  or  stopped  in  one  of  the  animals,  it  shows  no  dyspnoea  ; 
it  is  in  the  other,  whose  brain  is  being  fed  with  improperly  venti- 
lated blood,  that  the  respiratory  movements  become  exaggerated. 
The  point  of  attack  of  the  'venous'  blood  has  been  further 
localized  in  the  spinal  bulb  by  the  observation  that  when  the 
brain  has  been  cut  away  above  it,  the  cord  severed  below  the 
origin  of  the  phrenics,  and  all  other  nerves  connected  with  the 
region  between  the  two  planes  of  section  divided,  any  interference 


RESPIRATION  233 

with  the  gaseous  exchange  in  the  lungs  is  at  once  followed  by 
dyspnoea.* 

Automaticity  of  the  Respiratory  Centre.— The  question 
has  been  raised  whet  her,  in  the  absence  of  this  'natural' 
stimulation  by  the  blood,  and  of  the  impulses  that  constantly 
reach  the  centre  along  its  afferent  nerves,  it  would  continue 
to  discharge  itself,  or  whether  it  would  sink  into  inaction.  We 
have  already  discussed  a  similar  question  in  regard  to  the  cardiac 
and  vaso-motor  centres,  and  the  subject  must  again  present 
itself  when  we  come  to  examine  the  functions  of  the  central 
nervous  system.  In  the  meantime  it  is  only  necessary  to  say 
that  there  is  evidence  that  it  is  not  the  mere  presence  of  carbon 
dioxide  (or  other  substances)  in  the  blood  circulating  through  the 
respiratory  centre  which  determines  the  constant  excitation  of 
the  centre,  but  rather  the  accumulation  of  carbon  dioxide  in  the 
centre  itself  when  the  partial  pressure  of  that  gas  in  the  blood 
is  raised.  The  idea  that  the  continuous  excitation  of  the  centre 
is  '  autochthonous  ' — in  other  words,  that  it  is  due  to  an  internal 
Stimulating  substance  or  substances  manufactured  in  the  centre 
itself,  as  well  as  carried  to  it  in  the  blood — renders  it  easy  to 
understand  that  the  discharge  of  the  respiratory  centre,  although 
modified  by  the  quality  of  the  blood  which  circulates  in  it,  is 
not  essentially  dependent  on  it.  Indeed,  in  cold-blooded  animals 
whose  blood  has  been  replaced  by  physiological  salt  solution, 
and  (in  frogs)  even  after  the  circulation  has  been  stopped 
altogether  by  excision  of  the  heart,  quiet,  regular  breathing  may 
be  seen  for  a  considerable  time.  Of  course,  blood  is  essential 
for  the  continued  nutrition  of  the  centre  and  its  connections,  and 
it  eventually  breaks  down  and  ceases  to  discharge.  The  respira- 
tory discharge  is  still  less  dependent  for  its  initiation  upon 
the  arrival  of  afferent  impulses.  For  after  section  of  the  bulb 
above  the  centre,  of  the  cord  below  the  origin  of  the  phrenics,  of 
the  vagi  and  of  the  posterior  roots  of  all  the  upper  cervical  nerves, 
the  spasmodic  respiration  which  we  have  already  described  as 
occurring  when  the  vagi  and  the  higher  paths  have  been  severed 
continues  without  essential  modification.  It  has  also  been  ob- 
served that  during  resuscitation  of  the  bulb  and  upper  cervical 
cord  after  a  period  of  anaemia,  stimulation  of  afferent  nerves, 
including  the  vagi,  is  entirely  without  influence  on  the  respiratory 
movements  for  some  time  after  respiration  has  returned,  presum- 
ably because  the  synapses  (p.  749)  on  the  afferent  paths  lying 
within  the  previously  anaemic  area  are  as  yet  unable  to  conduct 
the  nerve  impulses.     Nevertheless,  the  respiratory  centre  con- 

*  The  conclusion  is  doubtless  correct,  but  this  experiment  is  not  decisive. 
For  the  phrenic  nerves  themselves  contain  afferent  fibres,  the  stimulation 
of  which  can  influence  the  respiration  after  section  of  the  vagi. 


2^4  I   MANUAL  OF  PHYSIOLOGY 

tinues  steadily  to  discharge  itself  along  the  efferent  paths,  whose 
synapses  are  situated  beyond  the  anaemic  region.  Section  of 
the  bulb  above  the  level  of  the  respiratory  centre,  and  of  the  cord 
below  the  origin  of  the  phrenic  nerves,  in  addition  to  the  anaemia, 
makes  no  essential  difference  in  the  result.  The  initial  rate  of 
discharge  of  the  centre  thus  isolated  from  afferent  impulses  is 
approximately  constant  in  different  experiments  (about  four  a 
minute  in  cats). 

Action  of  Drugs  on  the  Respiratory  Centre. — The  respira- 
tory centre  is  directly  affected  by  numerous  drugs.  Pituri  and 
nicotine,  for  instance,  cause  in  various  animals  a  quickening  and 
deepening  of  the  respiration,  followed,  if  the  dose  has  been  large. 
by  slowing  and  ultimate  cessation.  The  action  of  the  great 
majority  of  such  substances,  however,  possesses  only  a  pharmaco- 
logical interest,  and  it  would  be  out  of  place  even  to  enumerate 
them  in  a  text-book  of  physiology.  But  there  are  one  or  two 
points  in  the  action  on  the  respiratory  centre  of  chloroform  and 
alcohol — substances  so  greatly  employed  in  practical  medicine 
and  in  physiological  research — which  may  properly  be  touched  on 
here. 

Chloroform. — The  cause  of  the  deaths  from  chloroform  which, 
at  rare  intervals,  startle  the  operating  theatre  of  every  great 
hospital  where  this  anaesthetic  is  used,  has  been,  on  account  of 
its  extreme  practical  interest,  the  subject  of  prolonged  discussion 
and  experiment.  Is  it  the  heart  that  fails  ?  Or  is  it  the  respira- 
tion ?  The  answer  of  what  is  known  as  the  '  Edinburgh  School  ' 
was  that  the  respiration  (in  physiological  terms,  the  respiratory 
centre)  is  always  first  paralyzed.  Their  golden  rule  of  doctrine 
in  chloroform  administration  was,  '  Watch  the  respiration  ; 
the  heart  will  take  care  of  itself' — a  rule  which,  however,  in 
'  Edinburgh  '  practice  did  not  exclude  careful  observation  of 
the  pulse.  This  view,  having  the  merit  of  simplicity,  was 
widely  adopted.  It  was  upheld  by  a  scientific  commission 
appointed  l>v  the  Nizam  of  Hyderabad  to  investigate  the  ques- 
tion witli  the  aid  of  modern  physiological  methods.  But  the 
conclusions  of  the  Hyderabad  Commission  seem  to  have  been 
too  absolutely  drawn.  For  it  has  been  shown  by  a  number  of 
observers  that  chloroform  may  paralyze  the  heart  withoul 
primarily  affecting  the  respiration;  and,  further,  that  paralysis 
of  the  vaso-motor  centre,  and  the  consequent  withdrawal  of 
blood  from  the  heart  and  brain  to  the  dilated  splanchnic  area, 
may  be  an  important  factor  in  bringing  about  a  fatal  result 
(p.  174).  In  normal  chloroform  anaesthesia  in  man  it  is  easy  to 
demonstrate  by  the  sphygmomanometer  a  fall  of  blood-pressure 
in  the  brachial  artery  of  _'o  to  40  mm.  of  mercury  (Hill).  It  would 
seem   that   death  from  chloroform  may  take  place  either  from 


RESPIR  I  HON 


235 


primary  failure  of  the  respiratory  centre  followed  by  failure  of 
the  heart,  or  from  primary  paralysis  of  the  heart  or  of  the  who], 
vascular  mechanism  (including  the  muscular  tissue  of  the  heart 
and  bloodvessels  and  t  he  vaso-motor  centre),  followed  by  paralysis 
of  1  he  respiratory  centre.  Sometimes  the  respiratory  failure  and 
the  vascular  paralysis  may  be  simultaneous;  often  one  may 
follow  so  hard  on  the  heels  of  the  other  that  it  is  difficult  to 
decide  which  is  primary  and  which  secondary.  Much  depends 
upon  the  concentration  of  the  chloroform  vapour.  Where  it 
is  dilute  (at  any  rate,  up  to  5  per  cent,  of  the  inspired  air 
in  cats),  and  is  administered  by  means  of  an  apparatus  which 
insures  a  definite  and  uniform  concentration,  the  respiration 
invariably  stops  before  the  heart.  The  chloroform  is  mainly 
taken  up  by  the  coloured  corpuscles.  The  percentage  of  the  drug 
in  the  blood  increases  very  rapidly  in  the  first  minutes  of  ad- 
ministration, and  then  rapidly  declines,  to  increase  again  to  a 
maximum,  which  is  now  maintained  during  the  remainder  of  the 
anaesthesia.  In  those  first  few  minutes  occurs  a  definite  danger 
point  as  regards  the  respiratory  centre  (Buckmaster).  The 
stronger  the  chloroform  mixture  inhaled  the  greater  is  the 
damage  to  the  vascular  mechanism  relative  to  that  inflicted 
upon  the  respiratory  apparatus,  and  the  more  rapidly  does  it 
become  irreparable.  It  has  been  shown  that  the  concentra- 
tion of  chloroform  necessary  to  produce  serious  effects  upon  the 
isolated  mammalian  heart  when  added  to  the  liquid  used  for 
perfusion  is  practically  identical  with  that  found  in  the  blood  of 
animals  fully  narcotized  with  the  drug  by  inhalation.  In  ether 
narcosis  the  quantity  of  the  anaesthetic  in  the  blood  is  not  suffi- 
cient to  seriously  affect  the  heart,  and  this  is  the  reason  why 
ether  is  so  much  safer  than  chloroform.  The  practical  lesson  is 
that  in  administering  chloroform  both  the  respiration  and  the 
pulse  must  be  watched.  The  drug  should  be  given  by  a  method 
which  allows  exact  control  of  its  concentration  in  the  air.  The 
primitive  drop-bottle  and  towel  method  should  be  abandoned. 
In  addition  to  the  dangers  connected  with  the  direct  action  of 
chloroform  on  bulbar  centres,  the  possibility  of  untoward  reflex 
effects  must  be  borne  in  mind.  At  a  certain  stage  in  chloroform 
anaesthesia,  before  it  has  become  very  deep,  comparatively  trifling 
causes  may  bring  about  great  and  sudden  changes  in  the  pulse- 
rate,  owing  to  the  abnormal  mobility  ol  the  vagus  centre  (Mac- 
William).  It  is  further  of  interest  in  connection  with  the  causa- 
tion of  death  during  the  administration  of  anaesthetics  that  the 
afferent  nerves  of  the  alveoli  can  be  chemically  stimulated  when 
irritant  vapours,  such  as  chloroform,  hydrochloric  acid,  am- 
monia, bromine,  or  formaldehyde  are  inhaled  through  a  tracheal 
cannula,  causing  reflex  arrest  of  the  heart  and  of  the  respiratory 


236  A   M  l\T  II    OF  PHYSIOLOGY 

movements  and  ;i  fall  of  blood-pressure  through  vaso-dilatation 
(Brodie). 

Alcohol  in  small  doses,  when  given  by  the  stomach  or  (in 
animals)  injected  into  the  blood,  causes  stimulation  "I  the 
respiratory  centre  and  [ncrease  in  the  pulmonary  ventilation. 
In  man,  t his  increase  usually  amounts  to  8  to  15  per  cent.,  bul 
is  occasionally  much  greater.  Bui  the  limit  whi<  h  separates  the 
favourable  action  of  the  small  dose  from  the  hurtful  action  of 
the  large,  is  easily  overstepped.  When  this  is  done,  and  the 
dose  is  continually  increased,  the  activity  of  the  respiratory 
centre  is  first  diminished  and  finally  abolished.  In  dogs,  for 
instance,  after  the  injection  of  considerable  quantities  ol  alcohol 
into  the  stomach,  death  takes  place  from  respiratory  failure, 
and  the  breathing  stops  while  the  heart  is  still  unweakened 
(Fig.  73,  ]).  175).  This  is  the  final  outcome  of  a  progressive 
impairment  in  the  activity  of  the  centre,  of  which  the  slow  and 
heavy  breathing  of  the  drunken  man  represents  an  earlier  stage. 

Spinal  Respiratory  Centres. — Although  the  chief  respiratoiv 
centre  lies  in  the  medulla  oblongata,  under  certain  conditions 
impulses  to  the  respiratory  muscles  may  originate  in  the  spinal 
cord.  Thus,  in  young  mammals  (kittens,  puppies),  especially 
when  the  excitability  of  the  cord  has  been  increased  by  strychnine, 
in  birds  and  in  alligators,  movements,  apparently  respiratory, 
have  been  seen  after  destruction  of  the  brain  and  spinal  bulb. 
In  adult  cats,  when  the  functions  of  the  brain,  medulla,  and 
cervical  cord  have  been  abolished  by  occlusion  of  their  vessels, 
similar  movements  of  the  thoracic  and  abdominal  muscles  may 
be  seen,  but  they  are  not  sufficient  for  effective  respiration.  N<> 
proof  has  ever  been  given  that  in  the  intact  organism  the  spinal 
cord  below  the  level  of  the  bulb  takes  any  other  part  in  respira- 
tion than  that  of  a  mere  conductor  of  nerve  impulses  ;  and  it  is 
not  justifiable  to  assume  the  existence  of  automatic  spinal 
respiratory  centres  on  the  strength  of  such  experiments  as  these. 

Death  after  Double  Vagotomy. — Alterations  in  the  rhythm  of 
respiration  are  no1  t  lie  only  effects  that  follow  division  of  both  vagi 
(or  vago-sympathetics)  in  the  neck.  In  certain  animals,  at  least , 
this  operation  is  incompatible  with  life.  In  the  rabbit,  as  a  rule, 
death  takes  place  in  twenty-four  hours.  A  sheep  may  live  three 
days,  and  a  horse  five  or  six.  Dogs  of  ten  live  a  week,  occasionally 
a  month  or  even  two,  and  in  rare  instances  1  heysurvive  indefinitely. 
The  mo>t  prominent  symptoms  (in  the  dog),  in  addition  t<>  the 
marked  and  permanent  slowing  oi  respiration,  quickening  of  the 
pulse  and  contraction  of  the  pupils, are  difficult  deglutition, a<  com- 
panied  by  frequenl  vomiting  and  progressive  emaciation.     The 

appetite  is  sometimes  ravenous,  but  no  sooner  is  t  he  food  swallowed 
than  it  is  rejected  ;  and  t his  is  particularly  tine  of  water  or  liquid 


/.■/  SPIR  I  l  l<>\  237 

food.  Sometimes  the  rejected  food  is  simply  regurgitated  aftei 
having  reached  the  lower  end  <>t'  the  oesophagus,  withoul  enfc 
tlic  stomach.  The  fatal  result  is  usually  caused,  or  at  least  pi- 
rn In  1.  by  changes  oi  a  pneumonic  nature  in  the  lungs.  The  pre- 
cise significance  of  the  pulmonary  lesion  is  obscure.  But  it  would 
seem  that  paralysis  oi  the  laryngeal  and  oesophageal  muscles, 
with  tlu'  consequenl  entrance  of  saliva,  food,  or  foreign  bodies, 
carrying  bacteria  into  the  lungs,  is  responsible  to  a  great  extent. 
And  when  only  a  partial  palsy  of  the  glottis  is  produced,  by  divid- 
ing the  right  vagus  below  the  origin  of  the  recurrent  laryngeal, 
and  the  left  as  usual  in  the  neck,  pneumonia  either  does  not 
occur  or  is  long  delayed.  It  may  be  that  the  tissue  of  the  lungs 
is  rendered  particularly  susceptible  to  such  insults  in  consequence 
of  trophic  or  vascular  changes  induced  by  section  of  the  pul- 
monary and  cardiac  fibres  in  the  vagi.  It  may  be  quite  clearly 
demonstrated,  however,  in  animals  which  live  lor  some  weeks, 
that,  notwithstanding  the  paralysis  of  the  glottis  associated  with 
aphonia,  no  pulmonary  symptoms  may  be  present  till  a  day  or 
two  before  death.  The  picture  presented  in  these  cases  is  that 
of  an  animal  suffering,  above  all,  from  alimentary  disturbances. 
The  respiration  is.  to  be  sure,  very  different  from  the  normal  in 
frequency,  depth,  and  type,  but  there  is  nothing  to  suggest  that 
the  Lungs  are  the  seat  of  any  pathological  process.  Suddenly 
the  picture  changes.  Pulmonary  symptoms  obtrude  themselves. 
The  physical  signs  of  consolidation  of  the  lungs  may  be  detected, 
and  in  a  short  time  the  animal  is  inevitably  dead.  Occasionally 
the  determining  cause  of  the  pulmonary  lesion  seems  to  be  some 
external  circumstance,  as  a  sudden  fall  of  the  air  temperature. 
The  idea  is  exceedingly  apt  to  present  itself  to  the  observer  that 
the  pneumonia  is  an  accident,  an  acute  intercurrent  affection 
breaking  the  course  of  a  chronic  malnutrition,  which  in  any  case 
must  have  ended  in  death.  Of  course,  the  vagotomized  animal  is 
predisposed  to  this  accident,  but  there  is  no  definite  time  after 
section  of  the  nerves  at  which  it  must  take  place.  The  vomiting 
is  certainly  connected  with  the  paralysis  and  consequent  dilatation 
of  the  oesophagus;  and  by  previously  making  an  artificial  opening 
into  the  stomach,  or  by  a  surgical  prophylaxis  still  more  heroic, 
the  establishment  of  a  double  gastric  and  oesophageal  fistula 
(p.  374),  death  may  be  prevented  for  many  months.  Elimination 
of  all  the  pulmonary  fibres  of  the  vagi,  by  extirpation  of  one  lung, 
followed  after  an  interval  by  section  of  the  opposite  vagus  in  the 
neck,  is  not  fatal  in  rabbits.  This  is  also  in  favour  of  the  view- 
that  in  double  vagotomy  the  stress  falls  mainly  on  the  diges- 
tive system. 

Innervation    of    the     Bronchial    Muscles. — Both    constrictor 
and  dilator  fibres  for  the  bronchi  are  contained  in  the  vagus. 


A   MANl    II    "l    PHYSIOLOGY 

They  are  nol  constantly  in  action,  but  can  be  reflexly  i  Kcited, 
most  easily  (in  the  dog  and  cat)  by  stimulating  the  aasal  mucous 
membrane,  and  particular^  a  small  area  well  back  upon  the 
nasal  septum.  Cauterization  oi  the  corresponding  area  in  man 
is  said  to  give  permanenl  relief  in  certain  cases  oi  spasmodic 
asthma,  a  condition  in  which  the  recurrenl  attacks  oi  dyspi 
seem,  according  to  the  most  generally  accepted  view,  to  be 
associated  with  spasm  of  the  bronchial  muscles. 

Special  Modifications  of  the  Respiratory  Movements.  — 
Cheyne-Stokes  Respiration  is  the  name  given  to  a  peculiai  type 
oi  I  Teal  hing,  marked  by  pauses  of  many  seconds  alternating  with 
groups  <>l  respirations.  In  each  group  the  movements  gradually 
increase  to  a  maximum  amplitude,  and  then  become  gradually 
shallower  again,  till  they  cease  for  the  nexl  pause.  The  pheno- 
menon often  occurs  in  certain  diseases  of  the  brain  and  of  the 
circulation,  and  pressure  on  the  spinal  bulb  may  produce  it.  In 
cats  in  which  the  circulation  in  the  brain  and  medulla  oblongata 
has  been  interrupted  for  a  time  and  then  restored  it  is  often 
noticed  at  a  certain  stage  of  resuscitation  of  the  respiratory  centre. 
In  frogs,  Cheyne-Stokes  breathing  has  been  observed  as  the  resull 
of  interference  with  the  circulation  in  the  spinal  bulk,  '  drown- 
ing,' or  ligature  of  the  aorta,  and  also  as  a  consequence  oi  remoA  al 
of  the  brain,  or  parts  of  it  (hemispheres  and  optic  thalami). 
But  it  is  not  peculiar  to  pathological  conditions,  being  also  seen, 
more  or  less  perfectly,  in  normal  sleep,  especially  in  children,  in 
healthy  men  at  high  altitudes,  in  hibernating  animals,  and  in 
morphine  and  chloral  poisoning. 

Well-marked  Cheyne-Stokes  breathing  can  be  obtained  experi- 
mentally in  normal  persons  in  a  variety  of  ways.  II.  for  example, 
the  subject  is  caused  to  breathe  deeply  and  frequently  for  about 
two  minutes,  so  as  to  produce  a  prolonged  apncea,  the  respira- 
tion, when  it  is  resumed  spontaneously,  is  oi  the  Cheyne-Stokes 
type  (Haldane).  The  explanation  given  by  Haldane  is  that  the 
fall  in  the  partial  pressure  of  the  oxygen  in  the  pulmonary  alveoli 
(p.  232)  during  the  primary  apncea,  with  the  consequent  fall 
of  oxygen  pressure  in  the  arterial  blood  and  the  respiratory  centre. 
leads  to  the  production  of  lactic  acid  in  the  respiratory  centre 
and  elsewhere,  which  stimulates  the  centre  in  the  same  way  as 
carbon  dioxide,  and  thus  permits  it  to  be  excited  by  a  smaller 
partial  pressure  of  carbon  dioxide  than  that  normally  necessary, 
As  soon  as  the  pressure  of  carbon  dioxide,  which  is  increasing 
during  the  period  of  apncea.  has  reached  the  exciting  value 
breathing  is  resumed.  The  respirations,  beginning  as  very  feeble 
movements,  rapidly  increase  in  strength  till  the  breathing  be- 
comes quite  deep  pi  a<  tually  dyspneeic.  The  store  oi  oxygen  is 
replenished  by  this  thorough  ventilation  of  the  lungs,  the  changes 


RESPIR  l  I  ION 

in  the  excitability  of  the  respiratory  centre  due  to  Lack  <>t  oxygen 
disappear  (perhaps  by  oxidation  of  the  lactic    acid),  and    the 

centre  relapses  into  a  period  of  repose.  During  this  period 
•  it  apinea  the  oxygen  pressure  sinks  once  more  to  the  point 
at  which  the  change  in  the  excitability  of  the  respiratory  renin 
by  carbon  dioxide  occurs,  and  the  breathing  again  starts.  In 
pathological  cases  the  want  of  oxygen  may  he  associated  either 
with  deficient  circulation  through  the  bulb-centre  or  with  deficient 
intake  by  the  lungs.  The  administration  of  oxygen  through  a 
mask  has  been  shown  in  such  cases  to  abolish  the  periodicity  in 
the  respiration,  and  to  render  it  more  normal. 

Peculiarly  modified,  but  more  or  less  normal,  respiratory  acts 
are  coughing,  sneezing,  yawning,  sighing,  and  hiccup. 

A  cough  is  an  abrupt  expiration  with  open  mouth,  which  forces 
open  the  previously  closed  glottis.  It  may  be  excited  reilcxly 
from  the  mucous  membrane  of  the  respiratory  tract  or  stomach 
through  the  afferent  fibres  of  the  vagus,  from  the  back  of  the 
tongue  or  mouth,  and  (by  cold)  from  the  skin. 

Sneezing  is  a  violent  expiration  in  which  the  air  is  chiefly 
expelled  through  the  nose.  It  is  usually  excited  reflexly  from 
the  nasal  mucous  membrane  through  the  branch  of  the  fifth 
nerve  which  supplies  it.  Pressure  on  the  course  of  the  nasal 
nerve  will  often  stop  a  sneeze.  A  bright  light  sometimes  causes 
a  sneeze,  and  so  in  some  individuals  does  pressure  on  the  supra- 
orbital nerve,  when  the  skin  over  it  is  slightly  inflamed. 

Yawning  is  a  prolonged  and  very  deep  inspiration,  sometimes 
accompanied  with  stretching  of  the  arms  and  the  whole  body. 
It  is  a  sign  of  mental  or  physical  weariness. 

A  sigh  is  a  long-drawn  inspiration,  followed  by  a  deep  expiration. 

Hiccup,  or  hiccough,  is  due  to  a  spasmodic  contraction  of  the 
diaphragm,  which  causes  a  sudden  inspiration.  The  abrupt 
closure  of  the  glottis  cuts  this  short  and  gives  rise  to  the  character- 
istic sound.  The  following  readings  of  the  intervals  between 
successive  spasms  were  obtained  in  one  attack  :  13  sees.,  12  sees., 
15  sees.,  9  sees.,  14  sees.,  etc. — i.e.,  one-fourth  or  one-fifth  of  the 
frequency  of  the  ordinary  respiratory  movements.  The  mere 
fixing  of  the  attention  on  the  observations  soon  stopped  the  hiccup. 

Hiccup  is  generally  considered  to  be  a  reflex  movement,  brought 
about  through  the  respiratory  centre  by  afferent  impulses  origi- 
nating in  the  stomach.  The  irritation  may  be  merely  due  to 
some  slight  digestive  disturbance  set  up  by  overfilling  of  the 
stomach,  perhaps.  This  is  exceedingly  common  in  infants.  But 
persistent  hiccup  may  also  be  a  distressing  symptom  of  very 
formidable  diseases— for  example,  carcinoma  of  the  pylorus. 
Experimentally,  reflex  contractions  of  the  diaphragm  can  some- 
times be  elicited  by  stimulation  of  the  central  end  of  the  vagus  at 


240  ./   .1/  /  \  /    //    OF  PHYSI0L0G  5 

a  time  when  no  spontaneous  respiratory  movements  are  going  on. 
This  h;is  been  observed,  for  instance,  in  cats  during  resuscitation 
of  the  brain  after  a  period  of  anaemia.  In  man  also,  in  a  <  ase  "I 
Cheyne-Stokes  respiration  accompanied  by  hiccup,  it  was  seen 
that  the  hiccup  persisted  during  (lie  periods  <,\  .ipncea.  If  the 
respiratory  centre  is  the  centre  for  the  hiccup  reflex,  it  can  there- 
fore be  excited  l>y  afferent  nervous  impulses  at  a  time  w  hen  it  is  not 
excited  by  the  normal  chemical  stimulus (MacKenzie  and  Cushny). 

Chemistry  of  Respiration. 

Our  knowledge  of  this  subject  has  been  entirely  acquired  in 
the  last  200  years,  and  chiefly  in  the  last  century. 

Boyle  showed  by  means  of  the  air-pump  that  animals  die  in  a 
vacuum,  and  Bernouilli  that  fish  cannot  live  in  water  from  which 
the  air  has  been  driven  out  by  boiling. 

Mayow,  of  Oxford,  seems  to  a  considerable  extent  to  have 
anticipated  Black,  who  in  1757  demonstrated  the  presence  ol 
carbonic  acid  (carbon  dioxide)  in  expired  air  by  the  turbidity 
which  it  causes  in  lime-water. 

A  most  fundamental  step  was  the  discovery  of  oxygen  by 
Priestley  in  1771,  and  his  proof  that  the  venous  blood  could  be 
made  crimson,  like  arterial,  by  being  shaken  up  with  oxygen. 

Lavoisier  discovered  the  composition  of  carbonic  acid,  and 
applied  his  discovery  to  the  explanation  of  the  respiratory  pro- 
cesses in  animals,  the.  heat  of  which  lie  showed  to  be  generated 
like  that  of  a  candle  by  the  union  of  carbon  and  oxygen.  He 
made  many  further  important  experiments  on  respiration,  pub- 
lishing some  of  his  results  in  1789,  when  the  French  Revolution, 
in  which  he  was  to  be  one  of  the  most  distinguished  victims,  was 
breaking  out.  He  made  the  mistake,  however,  of  supposing  that 
the  oxidation  of  the  carbon  takes  place  in  the  blood  as  it  passes 
through  the  lesser  circulation. 

That  some  carbon  dioxide  is  formed  in  the  lungs  there  is  no 
reason  to  doubt,  and  the  quantity  may  even  be  considerable.  But 
that  they  are  not  the  chief  seat  of  oxidation  was  sufficient]  v  |  >m\  <d 
as  soon  as  it  was  known  that  the  blood  which  comes  to  them  from 
the  right  heart  is  rich  in  carbon  dioxide,  while  the  blood  which 
leaves  them  through  the  pulmonary  veins  is  comparatively  poor. 

There  are  two  main  lines  on  which  research  has  gone  in  trying 
to  solve  the  chemical  problems  of  respiration:  (1)  The  analysis 
and  comparison  of  the  inspired  and  expired  air,  or,  in  general, 
the  investigation  of  the  gaseous  exchange  between  the  blood 
and  the  air  in  the  lungs.  (2)  The  analysis  and  comparison  of 
the  gases  of  arterial  and  venous  blood,  of  the  other  liquids,  and 
of  the  solid  tissues  of  the  body,  with  a  view  to  the  determination 


RESPIRA  HON 

oi  the  gaseous  exchange  between  the  tissues  and  t he  blood.     We 
shall  take  these  up  as  far  as  possible  in  their  order. 

The  methods  which  have  been  used  for  comparing  the  com- 
position of  inspired  and  expired  air  are  \  ei  v  \  arious. 

(r)  Breathing  into  one  spirometer  and  out  of  another,  the  inspired 
and  expired  air  being  directed  by  valves.  The  contents  oi  the  spiro- 
meters are  analyzed  at  the  end  of  the  experiment  (Speck).  In  the 
arrangement  of  Zuntz  and  Geppert,  instead  of  the  whole  of  the 
expired  air,  a  sample  is  collected  for  analysis  during  the  entire  dura- 
tion of  the  experiment,  while  the  total  volume  expired  is  measured  by 
a  gas  meter.  This  is  a  very  convenient  method  for  observations  on 
man,  especially  in  disease,  but  each  experiment  can  only  bj  carried 
on  at  most  for  fifteen  to  twenty  minutes. 

(2)  A  small  apparatus,  much  on  the  same  principle,  was  used  for 
rabbits  by  Pfliiger  and  his  pupils.  A  cannula  in  the  trachea  was 
connected  with  a  balanced  and  self-adjusting  spirometer  containing 
oxygen,  and  the  inspired  and  expired  air  separated  by  potassium 
hydroxide  valves,  which  absorbed  the  carbon  dioxide.  The  amount 
of  oxygen  used  could  be  read  off  on  the  spirometer,  and  the  amount 
of  carbon  dioxide  produced  estimated  in  the  liquid  of  the  valves. 

(3)  Elaborate  arrangements,  such  as  Pettenkofer's  great  respira- 
tion apparatus,  and  the  still  larger  and  more  efficient  modifica- 
tions of  it  constructed  since  his  time,  in  which  a  man,  or  even  several 
men,  can  remain  for  an  indefinite  period,  working,  eating,  and 
sleeping.  Air  is  drawn  out  of  the  chamber  by  an  engine,  its  volume 
being  measured  by  a  gas-meter.  But  as  it  would  be  far  too  trouble- 
some to  analyze  the  whole  of  the  air,  a  sample  stream  of  it  is  con- 
stantly drawn  off,  which  also  passes  through  a  gas-meter,  through 
drying-tubes  containing  sulphuric  acid,  and  through  tubes  filled  with 
baryta  water.  The  baryta  solution  is  titrated  to  determine  the 
quantity  of  carbon  dioxide  ;  the  increase  in  weight  of  the  drying 
tubes  gives  the  quantity  of  aqueous  vapour.  A  similar  sample 
stream  of  the  air  before  it  passes  into  the  chamber  is  treated  exactly 
in  the  same  way,  and  from  the  data  thus  got  the  quantity  of  carbon 
dioxide  and  aqueous  vapour  given  off  can  readily  be  ascertained. 
The  oxygen  can  be  calculated,  as  the  difference  between  the  final 
body-weight  and  the  original  body-weight  plus  the  weight  of  the 
carbon  dioxide  and  water  eliminated,  but  may  also  be  directly 
estimated  by  special  methods. 

(4)  Haldane  and  Pembrey  have  elaborated  a  gravimetric  method, 
which  is  very  suitable  for  small  animals.  It  depends  upon  the  ab- 
sorption of  carbon  dioxide  by  soda  lime.  (See  Practical  Exercises, 
p.  2Q3).  In  Atwater's  so-called  respiration  calorimeter,  which  will 
be  referred  to  again  under  '  Animal  Heat,'  and  by  which,  not  only  the 
gaseous  metabolism,  but  the  heat  production  can  be  measured  in 
man,  the  carbon  dioxide  is  estimated  in  the  same  way. 

The  expired  air  is  at  or  near  the  body  temperature,  and  is 
saturated  with  watery  vapour.  In  ordinary  breathing  it  contains 
about  4  per  cent,  of  carbon  dioxide,  while  the  inspired  air  only 
contains  a  trace.  The  expired  air  contains  16  or  17  per  cent,  of 
oxygen,  the  inspired  air  about  21  per  cent.  The  percentage  of 
carbon  dioxide  in  the  alveolar  air  is,  of  course,  greater  than  in  the 
ordinary  expired  air,  since  the  relatively  pure  air  of  the  dead  space 

16 


242  •'   MANUAL  01   PHYSI01  OG  ) 

constitutes  .1  substantia]  fraction  oi  the  tidal  air.     The  carbon 
dioxide  percentage  in  the  alveolar  air  at  the  end  oi  expiration, 
with  the  body  at  rest,  is  remarkably  constanl  in  one  and  the  same 
individual  at  constanl  atmospheric  pressure  (p.  257).     There  arc- 
in  addition  in  expired  air  small  quantities  <>l  hydrogen  an<l  marsh- 
gas  derived  from  the  alimentary  canal,  either  directly  from  eru<  ta 
tion  or  after  absorption  into  the  blood.     Sometimes  a  trace  oi 
ammonia  can  be  detected  in  the  air  of  expiration,  but  this  is  due 
to  decomposition  of  proteins  taking  place  in  the  tnoul  h,  especially 
in  carious  teeth,  or  in  the  air-passages  and  lungs  in  disease  oi  1  hese 
organs.     It  has  indeed  been  shown  that  the  lungs  are  practically 
impermeable  for  ammonia.     Expired  air  is  entirely  free   from 
floating  matter  (dust),  which  is  always  present  in  the  inspired  air. 
The  volume  of  the  expired  air,  owing  to  its  higher  temperature 
and  excess  of  watery  vapour,  is  somewhat  greater  than  thai  oi  the 
inspired  air,  but  if  it  be  measured  at  the  temperature  and  degree 
of  saturation  of  the  latter,  the  volume  is  somewhat  less.     Since 
the  oxygen  of  a  given  quantity  of  carbon  dioxide  would  have 
exactly  the  same  volume  as  the  carbon  dioxide  itself  at  a  given 
temperature  and  pressure,  it  is  clear  that  the  deficiency  is  due  to 
the  fact  that  all  the  oxygen  which  is  taken  up  in  the  lungs  is  not 
given  off  as  carbon  dioxide.  Some  of  it,  going  to  oxidize  hydrogen, 
reappears  as  water.    A  small  amount  of  it  unites  with  the  sulphur 
of  the  proteins  (p.  444).     The  quotient  oi  the  volume  oi  oxygen 
given  out  as  carbon  dioxide  by  the  volume  oi  oxygen  taken  in  is 
the  respiratory  quotient.     It  shows  what  proportion ol  the  oxygen 
is  used  to  oxidize  carbon.     It  ma}-  approach  unity  on  a  carbo- 
hydrate diet,  which  contains  enough  oxygen  to  oxidize  all  its 
own  hydrogen  to  water.     With  a  rich  diet  in  fat  it  is  least  ol  all  ; 
with  a  diet  of  lean  meat  it  is  intermediate   in   amount.     For 
ordinary  fat  contains  no  more  than  one-sixth,  and  proteins  nol 
one-half,  of  the  oxygen  needed  to  oxidize  their  hydrogen.     In  man 
on  a  mixed  diet  the  respiratory  quotient  may  be  taken  as  o-8  or 
0-9.     So  long  as  the  type  of  respiration  is  not  changed,  the  respira- 
tory quotient  may  remain  constant  for  a  wide  range  of  meta- 
bolism.    In    hibernating    animals,     however,     the    respiratory 
quotient  may  become  very  small  during  winter  sleep  (as  low  as 
0-25),  both  the  output  of  carbon  dioxide  and  the  consumption  of 
oxygen    falling   enormously,    but    the    former    in   general    more 
than  the  latter.     This  has  been  explained  on  the  assumption 
that  oxygen  is  stored  away  in  winter  sleep  in  the  form  oi  incom- 
pletely oxidized  substances.     On  the  other  hand,  in  dyspnoea 
accompanying     muscular     exertion    the    respiratory    quotient 
has    been    found   as    high    as    12.      It   must    be   remembered 
that   even  a  voluntary  increase  in  the  respiratory  movements 
causes   an   immediate   temporary   increase   in    the    respiratory 
quotient,    owing    to    the    '  washing     out  '    of    carbon    dioxide 


/.•/  SPIRA  I  TON 


243 


from  the  blood  and  tissues.  This  change  has  no  metabolic 
M^nilicanee.  Indeed,  Hie  determination  of  the  respiratory 
quotient  for  short  periods  has  only  a  limited  value,  and  such 
observations  must  be  interpreted  with  great  care.  In  starvation 
the  respiratory  quotient  diminishes,  the  production  of  carbon 
dioxide  tailing  off  at  a  greater  rate  than  the  consumption  of 
oxygen,  for  the  starving  organism  lives  on  its  own  fat  and  pro- 
teins, and  has  only  a  trifling  carbo-hydrate  stock  to  draw  upon. 
In  a  diabetic  patient,  fed  on  a  diet  of  fat  and  protein  alone,  the 
respiratory  quotient  was  only  o*6to  07,  just  as  in  a  starving  man. 

The  amount  of  oxygen  absorbed  in  a  man  at  rest  has  been 
determined  under  certain  conditions  as  about  o-2q  gramme  per 
hour,  and  the  discharge  of  carbon  dioxide  as  about  0*33  gramme 
per  hour  per  kilogramme  of  body-weight.  In  an  average  man 
weighing  70  kilos  the  mean  production  of  carbon  dioxide  is  about 
800  grammes  (400  litres)  in  twenty-four  hours,  and  the  mean 
consumption  of  oxygen  about  700  grammes  (490  litres).  But 
there  are  very  great  variations  depending  upon  the  state  of  the 
body  as  regards  rest  or  muscular  activity  and  on  other  circum- 
stances. In  hard  work  the  production  of  carbon  dioxide  was 
found  to  rise  to  nearly  1,300  grammes,  and  in  rest  to  sink  to 
less  than  700  grammes,  the  consumption  of  oxygen  in  the  same 
circumstances  increasing  to  nearly  1,100  grammes  and  diminishing 
to  600  grammes.  In  rest,  in  moderate  exertion,  and  in  hard  work, 
the  production  of  carbon  dioxide  was  found  to  be  nearly  pro- 
portionate to  the  numbers  2,  3,  and  6  respectively.  When  un- 
accustomed work  is  performed,  the  increase  in  the  carbon  dioxide 
output  (and  oxygen  intake)  may  be  much  greater.  With  training 
it  diminishes.  In  a  case  of  diabetes  the  consumption  of  oxygen 
was  50  per  cent,  greater  than  in  a  healthy  man,  corresponding  to 
the  higher  heat-equivalent  of  the  food  of  the  diabetic  patient. 

Ventilation. — Taking  400  litres  per  twenty-four  hours,  or 
17  litres  per  hour,  as  the  mean  production  of  carbon  dioxide  by 
an  average  male  adult  at  rest  or  doing  only  light  work,  we  can 
calculate  the  quantity  of  fresh  air  which  must  be  supplied  to  a 
room  in  order  to  keep  it  properly  ventilated. 

It  has  been  found  that  when  the  carbon  dioxide  given  off  in 
respiration  amounts  to  no  more  than  2  parts  in  10,000  in  the  air 
of  an  ordinary  room,  the  air  remains  sweet.  When  the  carbon 
dioxide  given  off  reaches  4  parts  in  10,000,  the  room  feels  dis- 
tinctly, and  at  6  in  10,000  disagreeably,  close,  while  at  9  parts  in 
10,000  it  is  oppressive  and  almost  intolerable.  This  has  been 
supposed  by  some  to  be  due  to  a  volatile  poison  exhaled  from  the 
lungs,  for  pure  carbon  dioxide  added  alone  in  similar  proportions 
to  the  air  of  a  room  has  not  the  same  bad  effect.  Certain  ob- 
servers, indeed,  alleged  that  the  condensed  vapour  of  the  breath, 
when  injected  into  rabbits,  produced  fatal  symptoms.     But  this 

16 — 2 


244  '    ]!  '  vr  "•  OF  PHYSIOLOG  Y 

has  been  shown  to  be  erroneous;  and  the  mosl  careful  exp 
ments  have  tailed  in  detecl  in  the  an  expired  by  healthy  persons 
any  trace  of  such  a  poison.  It  has  therefore  been  suggested  I  ha1 
the  odour  and  other  ill-effects  oi  a  close  room  are  due  to  sub- 
stances given  oil  in  the  sweat  and  the  sebum,  and  allowed  by 
persons  oi  uncleanly  habits  to  accumulate  on  the  skin,  and  also 
to  the  products  of  slow  putrefactive  processes  constantly  going 
on,  under  favourable  conditions,  on  the  walls,  floor,  oi  furni- 
ture, bu1  only  becoming  perceptible  to  the  sense  oi  smell  when 
ventilation  is  insufficient.  In  a  small,  newly-painted  chamber, 
presumably  free  from  such  impurities,  it  was  not  until  the  carbon 
dioxide  reached  3  to  4  per  cent,  that  marked  discomfort,  with 
dyspnoea,  began  to  be  felt.     No  close  odour  could  be  detected 

Nevertheless,  experience  has  shown  thai  it  is  a  good  working 
rule  for  ventilation  to  take  the  limit  of  permissible  respiratory 
impurity  at  2  parts  of  carbon  dioxide  per  10,000  ;  and  the  17  litres 
ol  carbon  dioxide  given  off  in  the  hour  will  require  85,000  litres 
(or  3,000  cubic  feet)  of  air  to  dilute  it  to  this  extent.  This  is  I  he 
average  quantity  required  for  the  male  adult  per  hour.  For 
men  engaged  in  active  labour,  as  in  factories  or  mines,  twice  this 
amount  may  not  be  too  much.  For  women  and  children  less  is 
required  than  for  men.  II  a  room  smells  close,  it  needs  ventila- 
tion, whatever  be  the  proportion  of  carbon  dioxide  in  the  air. 
It  must  l>c  remembered  that  in  permanently-occupied  rooms 
mere  increase  in  the  size  will  not  compensate  lor  incomplete 
renewal  of  the  air,  although  it  may  be  easier  to  ventilate  a  large 
room  than  a  small  one  without  causing  draughts  and  other 
inconveniences.  But  as  few  apartments  are  occupied  dining  the 
whole  twenty-four  hours,  a  large  room  which  can  he  thoroughly 
ventilated  in  the  absence  of  its  inmates  has  a  distinct  advantage 
over  a  small  one  in  its  great  initial  stock  of  fresh  air.  The  cubic 
space  per  head  in  an  ordinary  dwelling-house  should  be  not  less 
than  28  cubic  metres  or  1,000  cubic  feet. 

The  quantity  of  carbon  dioxide  given  off  (and  of  oxygen  con- 
sumed) is  not  only  affected  by  muscular  work,  but  also  by  every- 
thing which  influences  the  general  metabolism.  In  males  it 
is  greater  on  the  average  than  in  females  (in  the  latter  there  is 
a  temporary  increase  during  pregnancy),  but  for  the  same  body- 
weight  and  under  similar  external  conditions  there  is  no  difference 
between  the.  sexes.  The  gaseous  exchange  is  greater  in  pro- 
portion to  the  body-weight  in  the  child  than  in  the  adult.  This 
depends  largely  on  the  fact  that,  other  things  being  equal,  the 
metabolism  is  relatively  to  the  body-weight  more  active  in  a  small 
than  in  a  large  organism,  since  the  surface  (and  therefore  the 
heat  loss)  is  relatively  greater  in  the  former.  Bui  it  has  been 
shown  that  even  in  proportion  to  the  surface  the  metabolism  is 


RESPIRATION 


245 


iter  in  youth  than  in  adult  life,  and  greater  in  the  vigorous 

adult  than  in  the  old  man.  So  that  the  age  of  the  organism  has 
an  influence  apart  from  the  extenl  of  surface.  The  taking  of 
itind  increases  the  gaseous  exchange,  partly  from  the  increased 
mechanical  and  chemical  work  performed  by  the  alimentary 
(anal  and  the  digestive  glands.  But  that  this  is  not  the  sole 
cause  of  the  increase  is  shown  by  the  fact  that  it  varies  with 
different  kinds  of  food  to  a  greater  extent  than  can  be  explained 
by  differences  in  the  ease  with  which  they  are  digested.  For 
instance,  maize  produces  a  much  greater  increase  than  oats 
when  given  in  equal  amount,  and  a  protein  diet  a  greater  increase 
than  a  diet  of  carbo-hydrate  or  fat.  Sleep  diminishes  the  pro- 
duction of  carbon  dioxide  partly  because  the  muscles  are  at  rest, 
but  also  to  some  extent  because  the  external  stimuli  that  in 
waking  life  excite  the  nerves  of  special  sense  are  absent  or 
ineffective.  Even  a  bright  light  is  said  to  cause  an  increase  in 
the  amount  of  carbon  dioxide  produced  and  of  oxygen  con- 
sumed ;  but  probably  only  by  increasing  muscular  movements, 
including  the  movements  of  respiration.  The  external  tempera- 
ture also  has  an  influence.  In  poikilothermal  animals  (such  as  the 
frog),  the  temperature  of  which  varies  with  that  of  the  surround- 
ing medium,  the  production  of  carbon  dioxide,  on  the  whole, 
diminishes  as  the  external  temperature  falls,  and  increases  as  it 
rises.  In  homoiothermal  animals,  that  is,  animals  with  constant 
blood  temperature,  external  cold  increases  the  production  of 
carbon  dioxide  and  the  consumption  of  oxygen.  But  if  the 
connection  of  the  nervous  system  with  the  striated  muscles  has 
been  cut  out  by  curara,  the  warm-blooded  animal  behaves  like  the 
cold-blooded  (Pfiuger  and  his  pupils  in  guinea-pig  and  rabbit). 
These  interesting  facts  will  be  returned  to  under  'Animal  Heat.' 

Cold-blooded  animals  produce  far  less  carbon  dioxide,  and  con- 
sume far  less  oxygen,  per  kilo  of  body-weight  than  warm-blooded. 

The  following  table  shows  the  relation  between  the  body- 
weight  and  the  excretion  of  carbon  dioxide  in  man  : 


Age. 

Weight  in  Kilos. 

CO«  excrete  1  per 
Kilo  per  Hour. 

(58 

44 

Male]  1 5 

16 

I   9-6 

84-6 
76-5 

82 

577 
22 

0*41  gramme 

0-48 

0-51 

0-40 

o*59       „ 

0-92          „ 

(66 

Females  -1 

I19 
UO 

66-9 
5  3 '9 
557 
23 

0-39 

0-54 

o'45 
0-83       „ 

24< 


A   MANUAL  OF  PHYSIOLOGY 


The  next  table  illustrates  the  difference  in  the  intensity  oi 
metabolism  in  different  kinds  of  animals,  a  difference,  however, 
largely  dependent  upon  relative  size  : 


Oxygen  absorbed 

Carbon  Dioxide  given   Respiratory  Quotient 

Animal. 

per  Kilo  ] 

-ter  Hour. 

off  per  Kilo 

per  Hour 

CO, 

— v.. 

in  grm. 

in  r.c. 

in  grin. 

in  1  .<  . 

Greenfinch 

13*000 

1  3' 50O 

6909 

D  -76 

Hen      -     - 

1-058 

740 

[•327 

675 

O  -91 

Dog      -     - 

i-303 

91  ] 

1-325 

674 

0-74 

Rabbit       - 

0-987 

690 

1-244 

632 

O  '91 

Sheep  -      - 

0*490 

343 

0*671 

341 

O  • 

1  Boar     - 

0-391 

273 

0-443 

225 

Ftos.     -     - 

0*105 

73*4 

0-113 

577              0-78 

Crayfish    - 

0*054 

38 

0-064 

32-7              0  ' 

Forced  respiration,  although  it  will  temporarily  increase  the 
quantity  of  carbon  dioxide  given  off  by  the  lungs,  and  thus  raise 
for  a  short  time  the  respiratory  quotient,  does  not  sensibly  affect 
the  production  ;  it  is  only  the  store  of  already  formed  carbon 
dioxide  in  the  body  which  is  drawn  upon.  The  amount  of  oxygen 
taken  up  is  little  altered  by  changes  in  the  movements  of  respira- 
tion. Within  wide  limits  the  oxygen  consumption  of  the 
organism  is  independent  of  the  supply  of  oxygen  offered  to  it. 

How  it  is  that  the  depth  of  the  respiration  may  affect  the 
rate  at  which  carbon  dioxide  is  eliminated,  we  can  only  under- 
stand when  we  have  examined  the  process  by  which  the  gaseous 
interchange  between  the  blood  and  the  air  of  the  alveoli  is 
accomplished  ;  and  before  doing  this  it  is  necessary  to  consider 
the  condition  of  the  oxygen  and  carbon  dioxide  in  the  blood. 


The  Gases  of  the  Blood. 

Physical  Introduction. — Matter  may  be  assumed  to  be  made  up  of 
molecules  beyond  which  it  cannot  be  divided  without  altering  its 
essential  character.  A  molecule  may  consist  of  two  or  more  particles 
of  matter  (atoms)  bound  to  each"  other  by  chemical  links.  The 
kinetic  theory  of  matter  supposes  the  molecules  of  a  substance  to  be 
in  constant  motion,  frequently  colliding  with  each  other,  and  thus 
having  the  direction  of  their  motion  changed. 

In  a  gas  the  mean  free  path,  that  is,  the  average  distance  which  a 
molecule  travels  without  striking  another,  is  comparatively  long,  and 
far  more  time  is  passed  by  any  molecule  without  an  encounter  than 
is  taken  up  with  collisions.  "Although  the  average  velcx  Lty  oi  the 
molecules  is  very  great,  these  collisions  will  produce  all  sorts  of 
differences  in  the  actual  velocity  of  different  molecules  at  any  given 
time.  Some  will  be  moving  at  a  greater,  some  at  a  slower  rate, 
than  the  average  ;  while  some  may  be  for  a  moment  at  rest.  If  the 
gas  is  in  a  closed  vessel,  the  molecules  will  be  constantly  striking  its 


RESPIRATION  -'47 

sides  .uul  rebounding  from  them.  If  a  very  small  opening  is  made 
in  t ho  vossel,  some  molecules  will  occasionally  hit  on  the  opening 
.uul  escape  altogether.  If  the  opening  is  made  larger,  or  the  experi- 
ment continued  for  a  longer  timo  with  the  small  opening,  all  the 
molecules  will  in  course  of  time  have  passed  out  of  the  vessel  into 
the  air.  while  molecules  of  the  oxygen,  nitrogen,  and  argon  of  the  air 
will  have  passed  in.  In  a  gas,  then,  not  enclosed  by  impenetrable 
boundaries,  there  is  no  restriction  on  the  path  which  a  molecule  may 
take,  no  tendency  for  it  to  keep  within  any  limits. 

When  two  chemically  indifferent  gases  are  placed  in  contact  with 
each  other,  diffusion  will  go  on  till  they  are  uniformly  mixed.  The 
diffusion  of  gases  may  be  illustrated  thus.  Suppose  we  have  a 
perfectly  level  and  in  every  way  uniform  field  divided  into  two  equal 
parts  by  a  visible  but  intangible  line,  the  well-known  whitewash 
line,  for  instance.  On  one  side  of  the  line  place  500  blind  men  in 
green,  and  on  the  other  500  blind  men  in  red.  At  a  given  signal  let 
them  begin  to  move  about  in  the  field.  Some  of  the  men  in  green 
will  pass  over  the  line  to  the  '  red  '  side  ;  some  of  the  men  in  red 
will  wander  to  the  '  green  '  side.  Some  of  the  men  may  pass  over 
the  line  and  again  come  back  to  the  side  they  started  from.  But, 
upon  the  whole,  after  a  given  interval  has  elapsed,  as  many  green 
coats  will  be  seen  on  the  red  side  as  red  coats  on  the  green.  And  if 
the  interval  is  long  enough  there  will  be  at  length  about  250  men  in 
red  and  250  in  green  on  each  side  of  the  boundary-line.  When  this 
state  of  equilibrium  has  once  been  reached,  it  will  henceforth  be 
maintained,  for,  upon  the  whole,  as  many  red  uniforms  will  pass 
across  the  line  in  one  direction,  as  will  recross  it  in  the  other. 

In  a  liquid  it  is  very  different  ;  the  molecule  has  no  free  path.  In 
the  depth  of  the  liquid  no  molecule  ever  gets  out  of  the  reach  of 
other  molecules,  although  after  an  encounter  there  is  no  tendency  to 
return  on  the  old  path  rather  than  to  choose  any  other  ;  so  that  any 
molecule  may  wander  through  the  whole  liquid.  Although  the 
average  velocity  of  the  molecules  is  much  less  in  the  liquid  state 
than  it  would  be  for  the  same  substance  in  the  state  of  gas  or  vapour 
(gas  in  presence  of  its  liquid),  some  of  them  may  have  velocities 
much  above  the  average.  If  any  of  these  happen  to  be  moving  near 
the  surface  and  towards  it,  they  may  overcome  the  attraction  of  the 
neighbouring  molecules  and  escape  as  vapour.  But  if  in  their 
further  wanderings  they  strike  the  liquid  again,  they  may  again 
become  bound  down  as  liquid  molecules.  And  so  a  constant  inter- 
change may  take  place  between  a  liquid  and  its  vapour,  or  between 
a  liquid  and  any  other  gas,  until  the  state  of  equilibrium  is  reached, 
in  which  on  the  average  as  many  molecules  leave  the  liquid  to  become 
vapour  as  are  restored  by  the  vapour  to  the  liquid,  or  as  many 
molecules  of  the  dissolved  gas  escape  from  solution  as  enter  into  it. 

For  the  sake  of  a  simple  illustration,  let  us  take  the  case  of  a 
shallow  vessel  of  water  originally  gas-free,  standing  exposed  to  the 
air.  It  will  be  found  after  a  time  that  the  water  contains  the  atmo- 
spheric gases  in  certain  proportions — in  round  numbers,  about  1^  of 
its  volume  of  oxygen  and  ^j  of  its  volume  of  nitrogen  (measured  at 
760  mm.  mercury  and  o°  C). 

Now,  let  a  similar  vessel  of  gas-free  water  be  placed  in  a  large  air- 
tight box  filled  with  air  at  atmospheric  pressure,  and  let  the  oxygen 
be  all  absorbed  before  the  water  is  exposed  to  the  atmosphere  of  the 
box.  The  latter  now  consists  practically  only  of  the  nitrogen  of  the 
air,  and  its  pressure  will  be  only  about  four-fifths  that  of  the  external 


24R  A   MANUAL  OF  PHYSIOLOGY 

atmosphere.  Nevertheless,  the  quantity  of  nitrogen  absorbed  by  the 
water  will  be  exactly  the  same  as  was  absorbed  from  the  air.  If 
the  box  was  completely  exhausted,  and  then  a  quantity  of  oxvgen, 
equal  to  that  in  it  at  first,  introduced  before  the  water  was  exposed 
to  it,  the  pressure  would  be  found  to  be  only  about  one-fifth  that  of 
the  external  atmosphere  ;  but  the  quantity  of  oxygen  taken  up  by 
the  water  would  be  exactly  equal  to  that  taken  up  in  the  first 
experiment. 

Two  well-known  physical  laws  are  illustrated  by  our  supposed 
experiments:  (i)  In  a  mixture  of  gases  which  do  not  act  chemically 
on  each  other  the  pressure  exerted  by  each  gas  (called  the  partial  pressure 
of  the  gas)  is  the  same  as  it  would  exert  if  the  others  were  absent.  (2  )  The 
quantity  (mass)  of  a  gas  absorbed  by  a  liquid  which  does  not  act  chemi- 
cally upon  it  is  proportional  to  the  partial  pressure  of  the  gas.  It  also 
depends  upon  the  nature  of  the  gas  and  of  the  liquid,  and  on  the 
temperature,  increase  of  temperature  in  general  diminishing  the 
quantity  of  gas  absorbed.  It  is  to  be  noted  that  when  the  volume 
of  the  absorbed  gas  is  measured  at  a  pressure  equal  to  the  partial 
pressure  under  which  is  was  absorbed,  the  same  volume  of  gas  is 
taken  up  at  every  pressure. 

Suppose,  now,  that  a  vessel  of  water,  saturated  with  oxygen  and 
nitrogen  for  the  partial  pressures  under  which  these  gases  exist  in  the 
air,  is  placed  in  a  box  filled  with  pure  nitrogen  at  full  atmospheric 
pressure.  As  we  have  seen,  there  is  a  constant  interchange  going  on 
between  a  liquid  which  contains  gas  in  solution  and  the  atmosphere 
to  which  it  is  exposed.  Oxygen  and  nitrogen  molecules  will  there- 
fore continue  to  leave  the  water  ;  but  if  the  box  is  large,  few-  oxvgen 
molecules  will  find  their  way  back  to  the  water,  and  ultimately  little 
oxygen  will  remain  in  it.  In  other  words,  the  quantity  of  oxygen, 
absorbed  by  the  water  will  become  again  proportional  to  the  partial 
pressure  of  oxygen,  which  is  not  now  much  above  zero.  On  the 
other  hand,  molecules  of  nitrogen  will  at  first  enter  the  water  in 
larger  number  than  they  escape  from  it,  for  the  pressure  of  the 
nitrogen  is  now  that  of  the  external  atmosphere,  of  which  its  partial 
pressure  was  formerly  only  four-fifths.  In  unit  volume  of  the  gas 
above  the  water  there  will  be  5  molecules  of  nitrogen  for  every  4 
molecules  in  the  same  volume  of  atmospheric  air.  Therefore,  on  the 
average  5  nitrogen  molecules  will  in  a  given  time  get  entangled  by 
liquid  molecules  for  every  4  which  came  within  their  sphere  of  attrac- 
tion before.  On  the  whole,  then,  the  water  will  lose  oxygen  and  gain 
nitrogen,  while  the  atmosphere  of  the  air-tight  box  will  gain  oxygen 
and  lose  nitrogen. 

If,  now,  the  partial  pressures  of  oxygen  and  nitrogen  under  which 
the  water  had  been  originally  saturated  were  unknown,  it  is  evident 
that  by  exposing  it  to  an  atmosphere  of  known  composition,  and 
afterwards  determining  the  changes  produced  in  the  composition  of 
that  atmosphere  by  loss  to,  or  jjiain  from,  the  gases  of  the  water,  we 
could  find  out  something  about  the  original  partial  pressures.  If. 
for  example,  the  quantity  of  oxygen  in  the  atmosphere  of  the  chamber 
was  increased,  we  could  conclude  that  the  partial  pressure  of  oxygen 
under  which  the  water  had  been  saturated  was  greater  than  that  in 
the  chamber  at  the  beginning  of  the  experiment.  And  if  we  found 
that  with  a  certain  partial  pressure  of  oxygen  in  the  atmosphere  of 
the  chamber  there  was  neither  gain  nor  loss  of  this  gas,  we  might  be 
sure  that  the  partial  pressure  (the  temperature  being  supposed  not 
to  vary)  was  the  same  when  the  water  was  saturated.     We  shall  see 


RESPIRATION 


2  JO 


:  on  how  this  principle  has  been  applied  to  determine  the  parti  il 
pressure  of  oxygen  or  oarbon  dioxide  which  just  suffices  to  prevenl 
blood,  or  any  other  of  the  liquids  "i  the  body,  from  Losing  or  gaining 
these  gases.  This  pressure  is  evidently  equal  to  thai  exerted  by  the 
s  of  the  liquid  at  its  surface,  which  is  sometimes  called  their 
'  tension  '  ;  for  if  it  were  greater,  gas  would,  upon  the  whole,  pass 
into  the  blood:  and  it  it  were 
less,  gas  would  escape  from  the 
blood.  Thus,  ///c  tension  of  a 
gas  in  solution  in  a  liquid  is 
equal  to  the  partial  pressure  of 
that  gas  in  an  atmosphere  to 
which  the  liquid  is  exposed,  which 
is  just  sufficient  to  prevent  gain 
or  loss  of  the  gas  by  the  liquid 
(p.  256). 

The  following  imaginary  ex- 
periment may  further  illustrate 
the  meaning  of  the  term 
'  tension  '  of  a  gas  in  a  liquid 
in  this  connection  : 

Suppose  a  cylinder  filled  with 
a  liquid  containing  a  gas  in  solu- 
tion, and  closed  above  by  apiston 
moving  air-tight  and  without 
friction,  in  contact  with  the 
surface  of  the  liquid  (Fig.  106). 
Let  the  weight  of  the  piston  be 
balanced  by  a  counterpoise. 
The  pressure  at  the  surface  of 
the  liquid  is  evidently  that  of 
the  atmosphere.  Now,  let  the 
whole  be  put  into  the  receiver  of 
an  air-pump,  and  the  air  gradu- 
ally exhausted.  Let  exhaustion 
proceed  until  gas  begins  to 
escape  from  the  liquid  and  lies 
in  a  thin  layer  between  its 
surface  and  the  piston,  the 
quantity  of  gas  which  has  be- 
come free  being  very  small  in 
proportion  to  that  still  in  solu- 
tion. At  this  point  the  piston 
is  acted  upon  by  two  forces 
which  balance  each  other,  the 
pressure  of  the  air  in  the 
receiver  acting  downwards,  and 
the  pressure  of  the  gas  escaping 
from  the  liquid  acting  up- 
wards.    If  the  pressure  in  the 

receiver  is  now  slightly  increased,  the  gas  is  again  absorbed.  The 
pressure  at  which  this  just  happens,  and  against  which  the  piston  is 
still  supported  by  the  impacts  of  gaseous  molecules  flying  out  of  the 
liquid,  while  no  pressure  is  as  yet  exerted  directly  between  the  liquid 
and  the  piston,  is  obviously  equal  to  the  pressure  or  tension  of  the  gas 
in  the  liquid. 


Fig.  106.  — Imaginary  Experiment  to 
illustrate  '  tension  '  of  a  gas  in 
a  Liquid. 

P.  frictionless  piston  ;  L,  liquid  in 
cylinder  ;  G,  gas  beginning  to  escape 
from  liquid.  P  is  exactly  counterpoised. 
In  addition  to  the  manner  described  in 
the  text,  the  experiment  may  be  sup- 
posed to  be  performed  thus  :  Let  the 
weight.  W,  be  determined  which,  when 
the  receiver  is  completely  exhausted, 
suffices  just  to  keep  the  piston  in  con- 
tact with  the  liquid.  The  pressure  of 
the  gas  is  then  just  counterbalanced  by 
W  ;  and  if  S  is  the  area  of  the  cross- 
section    of   the   piston   the   pressure   of 

VV 
the  gas  per  unit  of  area  is  —      Or  if 

the  piston  is  hollow,  and  mercury  is 
poured  into  it  so  as  just  to  keep  it  in 
contact  with  the  liquid,  the  height  of 
the  column  of  mercury  required  is  also 
equal  to  the  pressure  or  tension  of  the 
gas. 


A    M  \NUA1    OF  rilYSWLOGY 


From  the  above  principles  it  follows  that  a  pas  held  in  solution 
may  be  extracted  by  exposure  to  an  a1  mosphere  in  which  the  partial 
pressure  of  the  gas  is  made  as  small  as  possible.  Thus,  oxygen  can 
be  obti i  ined  from  liquids  in  which  it  is  simply  dissolved  by  putting 
them  in  an  atmosphere  of  hydrogen  or  nitrogen,  in  which  the  partial 
pressure  of  oxygen  is  zero,  or  in  the  vacuum  of  an  air-pump,  in  whii  h 
it  is  extremely  small.  Heat  also  aids  the  expulsion  of  dissolved 
gases.     Some  g  ises  held  in  weak  chemical  union,  like  the  loosely- 

A,  the  blood  bulb  ;  B.  the  froth 
i  hamber  ;  C,  the  drying  tube  ; 
1),  fixed  mercury  tube  ;  E,  movable 
mi  ri  ury  bulb  connei  ted  by  a 
flexible  tube  with  D  ;  F,  eudiometer  ; 
G,  a  narrow  delivery  tube  ;  i,  2.  3,  4, 
taps,  (  being  a  three-way  tap.  A  is 
filled  with  blood  by  connecting  the 
tap  1  by  means  of  a  tube  with  a 
bloodvessel.  Taps  1  and  2  are  then 
closed.  The  rest  of  the  apparatus 
from  B  to  D  is  now  exhausted  by 
raising  E,  with  tap  4  turned  so  as 
to  place  D  only  in  communication 
with  G,  till  the  mercury  fills  D.  Tap  4 
is  now  turned  so  as  to  connect  C 
with  I  >,  and  cut  off  G  from  I),  and 
E  is  lowered.  The  mercury  passes 
out  of  D,  and  air  passes  into  it 
from  B  and  C.  Tap  4  is  again 
turned  so  as  to  cut  off  C  from  D 
and  connect  G  and  D.  E  is  raised 
and  the  mercury  passes  into  D  and 
forces  the  air  out  through  G,  the 
end  of  which  has  not  hitherto  been 
placed  under  F.  This  alternate 
raising  and  lowering  of  E  is  con- 
tinued till  a  manometer  connected 
between  C  and  4  indicates  that  the 
pressure  has  been  sufficiently  re- 
duced. The  tap  2  is  now  opened  ; 
the  gases  of  the  blood  bubble  up 
into  the  froth  chamber,  pass  through 
the  drying-tube  C,  which  is  filled 
with  pumice-stone  and  sulphuric 
acid,  and  enter  D.  The  end  of  G 
is  placed  under  the  eudiometer  F, 
and  by  raising  E,  with  tap  1  turned 
so  as  to  cut  off  C,  the  gases  are  forced  out  through  G  and  collected  in  F. 
The  movements  required  for  exhaustion  can  be  repeated  several  times  till  no 
more  gas  comes  off.  The  escape  of  gas  from  the  blood  is  facilitated  by  im- 
mersing the  bull)  A  in  water  at  40°  to  500  C. 

combined  oxygen  of  oxyhemoglobin,  can  be  obtained  by  dissociation 
of  their  compounds  when  the  partial  pressure  is  reduced.  More 
stable  combinations  may  require  to  be  broken  up  by  chemical  agents 
— carbonates,  for  instance,  by  acids. 

Extraction  of  the  Blood-gases. — This  is  best  accomplished  by 
exposing  blood  to  a  nearly  perfect  vacuum.  The  gas-pumps  which 
have  been  most  largely  used  in  blood  analysis  are  constructed  on  the 
principle  of  the  Torricellian  vacuum.      A  diagram  of  a  simple  form  of 


Fig.  iQ7.^Scheme  of  Gas-pump. 


RESPIRATION  251 

Pfluger's gas-pump  is  given  in  Fig.  107.  The  gases  obtained  are  ulti- 
mately dried  and  collected  in  a  eudiometer,  which  is  a  graduated 
t  ube  with  its  mouth  dipping  into  mercury.  The  carbon  dioxidi 
mated  by  introducing  a  lit  1 1'  1  otassium  hydroxide  to  absorb  ii  The 
diminution  in  the  volume  of  the  gas  contained  in  the  eudiometer 
i,rives  the  volume  of  the  carbon  dioxide.  The  oxygen  may  be 
1  *ri  imated  by  putting  into  the  eudiometer  more  than  enough  hydrogen 
to  unite  with  all  the  oxygen  so  as  to  form  water,  and  then, 
reading  off  the  volume,  exploding  the  mixture  by  means  of  an  electric 
spark  passed  through  two  platinum  wires  fused  into  the  glass.  One- 
third  of  the  diminution  of  volume  represents  the  quantity  of  oxygen 
present.  It  can  also  be  estimated  by  absorption  with  a  solution  of 
pyrogallic  acid  and  potassium  hydroxide.*  The  remainder  of  the 
original  mixture  of  blood-gases,  alter  deduction  of  the  carbon  dioxide 
and  oxygen,  is  put  down  as  nitrogen  (with,  no  doubt,  a  small  propor- 
tion of  argon).  For  the  sake  of  easy  comparison,  the  observed 
volume  of  gas  is  always  stated  in  terms  of  its  equivalent  at  a  standard 
pressure  and  temperature  (760  mm.,  or  sometimes  on  the  Continent 
1  metre  of  mercury,  and  o°  C). 

It  is  also  possible  in  various  wavs  to  estimate  the  amount  of  oxygen 
in  blood  without  the  use  of  the  pump.  Thus,  since  a  definite  volume 
of  oxygen  (1*338  c.c.  at  o°  C.  and  760  mm.  pressure)  combines  with 
a  gramme  of  haemoglobin,  we  can  calculate  the  total  volume  of 
oxgyen  present  if  we  know  how  much  of  the  blood-pigment  is  in  the 
form  of  oxyhemoglobin  ;  and  this  can  be  determined  by  means  of 
the  spectrophotometer.  Or  potassium  ferricyanide  may  be  added 
to  the  blood.  This  expels  the  oxygen  from  its  combination  with  the 
haemoglobin,  which  then  unites  with  an  exactly  equal  amount  of 
oxygen  obtained  from  the  ferricyanide  to  form  mcthnsmoglobin 
(Haldane)  (p.  67). 

In  dog's  blood,  which  has  been  up  to  this  time  chiefly  investi- 
gated, there  are  considerable  variations  in  the  quantity  of 
oxygen  and  carbon  dioxide  which  can  be  extracted.  This 
is  particularly  true  of  the  venous  blood,  as  might  naturally  be 
expected,  since  even  to  the  eye  it  varies  greatly  according  to  the 
vein  it  is  obtained  from,  the  rapidity  of  the  circulation,  and  the 
activity  of  the  tissues  which  it  has  just  left.     On  the  average, 

Volumes  of 


O2  CO2         N2 

100  volumes  of  arterial  blood  yield  -         -       20  40        1-2 

,,  ,,  mixed  venous  blood  (from 

right  heart)  yield  -  -  -  -     10-12     45-50      1-2 

(reduced  to  o°  C.  and  760  mm.  of  mercury). 

Average  venous  blood  contains  7  or  8  per  cent,  by  volume 
less  oxygen,  and  7  or  8  per  cent,  more  carbon  dioxide,  than 
arterial  blood.  Thus,  in  the  lungs  the  blood  gains  about  twice 
as  many  volumes  of  oxygen  per  cent,  as  the  air  loses,  and  the  air 
gains  about  half  as  many  volumes  of  carbon  dioxide  per  cent, 
as  the  blood  loses.     It  is  easy  to  see  that  this  must  be  so,  for 

*  Or  an  alkaline  solution  of  sodium  hydrosulphite,  which  is  more  cleanly. 


252  A   MANU  U    01    PHYSIOLOGY 

the  volume  of  the  air  inspiaed  in  a  given  time  is  aboul  twice  as 
great  as  that  of  the  blood  which  passes  through  the  pulmonary 

circulation    (pp.    209,    220,    242).      Even    arterial    I>1 1    is    not 

quite  saturated  with  oxygen  ;  it  can  generally  still  take  up 
one-tenth  to  one-fifteenth  oi  the  quantity  contained  in  it.  Nor 
is  venous  blood  nearly  saturated  with  carbon  dioxide;  when 
shaken  with  the  gas  it  can  take  up  about  150  volumes  per  cent. 

When  the  gases  are  not  removed  from  blood  immediately 
alter  it  is  drawn,  its  colour  becomes  darker,  and  it  yields  more 
carbon  dioxide  and  less  oxygen  than  if  it  is  evacuated  at  once 
(Pfluger).  From  this  it  is  concluded  that  oxidation  goes  on 
in  the  blood  for  some  time  after  it  is  shed.  The  oxidizable 
substances  are,  however,  confined  to  the  corpuscles,  which 
suggests  that  ordinary  metabolism  simply  continues  for  some 
time  in  the  formed  elements  of  the  shed  blood,  and  that  the 
disappearance  of  oxygen  is  not  due  to  the  oxidation  of  substances 
which  have  reached  the  blood  from  the  tissues. 

The  Distribution  of  the  Gases  in  the  Blood.  The  oxygen  is 
nearly  all  contained  in  the  corpuscles.  A  little  oxygen  can  be 
pumped  out  of  serum  (o-i  to  0-2  per  cent,  by  volume),  but  this 
follows  the  Henry-Dalton  law  of  pressures  ;  that  is,  it  comes  off 
in  proportion  to  the  reduction  of  the  partial  pressure  of  the 
oxygen  in  the  pump,  and  is  simply  in  solution. 

When  blood  is  being  pumped  out,  very  little  oxygen  comes 
off  till  the  pressure  has  been  reduced  to  about  half  an  atmo- 
sphere. At  about  a  third  of  an  atmosphere,  if  the  blood  is  nearly 
at  body  temperature,  the  oxygen  begins  to  escape  a  little  more 
freely;  and  when  the  pressure  has  fallen  to  about  one-sixth 
of  an  atmosphere  (corresponding  to  a  partial  pressure  of  oxygen 
of  25  to  30  mm.  of  mercury),  it  is  disengaged  with  a  burst.  This 
shows  that  it  is  not  simply  absorbed,  but  is  united  by  chemical 
bonds  to  some  constituent  of  the  blood.  The  same  thing  is  seen 
when  defibrinated  blood  is  saturated  at  body  temperature  with 
oxygen  at  different  pressures.  The  quantity  taken. up  lessens 
but  slowly  as  the  pressure  is  reduced,  till  at  about  25  to  30  mm. 
of  mercury  an  abrupt  diminution  takes  place.  It  is  found  that 
a  solution  of  pure  haemoglobin  crystals  behaves  towards  oxygen 
somewhat  differently  from  blood  containing  the  same  proportion 
of  blood-pigment  ;  and  although  there  is  no  doubt  that  the  body 
in  blood  with  which  the  oxygen  is  loosely  united  is  intimately 
related  to  the  haemoglobin,  which  can  be  artificially  prepared  from 
it,  there  are  good  reasons  for  believing  that  they  are  not  identical. 
Some  writers  for  this  reason  prefer  to  give  the  special  name 
hamochrome  to  the  native  blood-pigment  as  it  exists  within  the 
unaltered  corpuscles,  reserving  the  term  haemoglobin  for  the  more 
or  less  artificial  though,  perhaps,  only  slightly  altered  product. 


i;l  SPIR  ITION  253 

We  mi. in  Mippi.se  thai  .11  the  ordinary  temperature  and  pri 
some  oxygen  is  continually  escaping  Erom  the  bonds  by  which  LI  Ls 
tied  to  the  haemoglobin  ;  but,  on  the  whole,  an  equal  number  ol 
free  molecules  oi  oxygen,  coming  within  the  range  ol  the  haemoglobin 
molecules,  are  entangled  by  them,  and  thus- equilibrium  is  kept  up. 
II  now  the  atmospheric  pressure,  and  therefore  the  partial  pressure 
"i  oxygen,  is  reduced,  the  tendency  of  the  oxygen  to  break  off 
from  the  haemoglobin  will  be  unchanged,  and  as  many  molecules  on 
the  whole  will  escape  as  before;  but  even  after  a  considerable 
reduction  of  pressure  the  haemoglobin,  such  is  its  avidity  for  oxygen, 
will  still  be  able  to  sei?e  as  many  atoms  as  it  loses.  The  more,  how- 
ever, the  partial  pressure  of  the  oxygen  is  diminished  that  is  to  say, 
the  fewer  oxygen  molecules  there'-  are  in  a  given  space  above  the 
haemoglobin  —the  smaller  will  be  the  chance  of  the  loss  being  made 
up  by  accidental  captures.  At  a  certain  pressure  the  escapes  will 
become  conspicuously  more  numerous  than  the  captures;  and  the 
gas  pump  will  give  evidence  of  this,  although  it  could  give  no  in- 
formation as  to  mere  molecular  interchange,  so  long  as  equilibrium 
was  maintained.  The  higher  the  temperature  of  the  haemoglobin  is, 
the  greater  will  be  the  average  velocity  of  the  molecules,  and  the 
greater  the  chance  of  escape  of  molecules  of  oxygen.  The  '  dissocia- 
tion tension  '  of  oxyhemoglobin,  or  the  partial  pressure  of  oxygen 
at  which  the  oxyhemoglobin  begins  to  lose  more  oxygen  than  it  gains, 
is  increased  by  raising  the  temperature.  Curves  of  dissociation  of 
oxyhemoglobin  and  blood  arc  shown  in  Figs.  108  and  109.  According 
to  Bohr,  Fig.  109  represents  the  curves  for  blood  and  a  haemoglobin 
solution  of  equal  strength.  It  will  be  observed  that  the  two  curves 
are  not  identical,  the  blood-pigment  in  the  corpuscles  not  behaving 
just  as  the  artificially-produced  oxyhemoglobin. 

The  Carbon  Dioxide  of  the  Blood.— Blood  freed  from  gas 
absorbs  carbon  dioxide  partly  in  proportion  to  the  pressure, 
and  in  part  independently  of  it.  Some  of  the  carbon  dioxide 
must  therefore  be  simply  dissolved  ;  some,  and  this  the  greater 
portion,  is  chemically  combined.  The  serum  contains  a  larger 
percentage  of  carbon  dioxide  than  the  clot,  but  this  percentage 
is  not  great  enough  to  allow  us  to  assume  that  the  whole  of  the 
carbon  dioxide  is  confined  to  the  serum.  About  a  third  of  it 
belongs  to  the  corpuscles. 

In  the  serum  the  combined  carbon  dioxide  exists  chiefly  as 
carbonate  and  bicarbonate  of  sodium,  the  relative  amount  of 
each  depending  on  the  quantity  of  carbon  dioxide  and  of  other 
acids,  such  as  phosphoric  acid,  which  dispute  with  it  the  posses- 
sion of  the  bases.  That  its  relations  are  peculiar,  however,  is 
shown  by  the  fact  that  from  defibrinated  blood  the  whole  of  the 
carbon  dioxide  can  in  time  be  pumped  out  without  the  addition 
of  an  acid  to  displace  it  from  the  bases  with  which  it  is  combined. 
It  is  hardly  necessary  to  say  that  this  could  not  be  done  with  a 
solution  oi'  sodium  carbonate.     Yet  when  sodium  carbonate  is 

*  The  partial  pressure  of  oxygen  in  air  at  760  mm.  atmospheric  pressure 

is    — x  760,  or  i;o •(■>  mm. 
100  '         J 


254 


.1   MANUAL  OF  PHYSIOLOGY 


added  to  blood,  even  in  considerable  amount,  all  the  carbon 
dioxide  in  it  can  be  obtained  by  the  pump.     From  serum  a  ^rreat 
deal,  Inn  not  the  whole,  ol  the  carbon  dioxide  can  be  like 
pumped  out.     The  residue  (from  10  to  18  per  cent,  ol  the  whole) 
is  set  free  on  the  addition  of  an  acid,  e.g.,  phosphoric  a<  id. 

The  most  satisfactory  explanation  is  that  in  the  serum  there 
exist  substances  which  can  act  as  weak  acids  in  gradually  driving 
out  the  carbon  dioxide,  when  its  escape  is  rendered  easier  by 
the  vacuum.     The  quantity  of  these,  however,   is  so  small  that  a 


Peroeniaye    o/  Oxyyer) 


0/2 

3     h 

6      7            ?    JO    ]/    11   13    fr   IS    Id  H    18    19  SO  2/ 



*?=A 

r— 



— ' 

— ^~ 



F 

^ 

B 

— 

— 

— 

- 

H 

i 

~i 

a 



— 

. 

an 

i*fl 

iii 

III 
IS 

— 



— 

— 

us 

ssss 

SBSS 

.-- 

: 

•  ^H 

0    7.6    B-2  lit  30.t    38  "tS-b  632  60S  6sS   76  856  01-2  9it  161*    If,  121 1  m  2  USi   ;*j*  r. 

P>cLt~ttCLC  'Pressure  of  Oxyyen  in  millimetres  of  mercury 


Fig.    io8. —  Curve   of   Dissociation    of   Oxyhemoglobin    at    35'    C.    (after 
HCfxer's  Results). 

Alimg  the  horizontal  axis  arc  plotted  the  partial  pressures  (numbers  below  the 
curve)  of  oxygen  in  air.  to  which  .1  solution  oJ  haemoglobin  was  exposed.  The 
corresponding  percent.  1^'-  oi  oxygen  arc  given  above  the  curve.  Along  the 
vertical  axis  is  plotted  the  peri  entage  saturation  of  thi  I  in  with  ox 

Thus,  on  exposure  to  an  atmosphere  in  which  oxygen  existed  to  the  exent  ol 
1  per  cent.,  currespouding  to  a  partial  pressure  of  76  nun.  of  mercury,  the  haemo- 
globin took  up  about  75  per  cent,  of  the  amount  of  oxygen  required  to  saturate 
it.  When  the  ox;  resent  in  the  atmosphere  to  the  amount  of  about  10  per 

cent.,  corresponding  to  a  partial  pressure  of  76  mm.  of  mercury,  the  quantity 
taken  up  by  the  haemoglobin  was  about  96  per  cent,  of  that  required  for  saturation. 

portion  of  the  carbon  dioxide  remains  in  the  scrum.  The  proteins 
of  the  serum,  such  as  serum-globulin,  behave  in  certain  respects  like- 
weak  acids,  and  may  contribute  to  the  driving  out  of  the  carbon 
dioxide.  When  defibrinated  blood  is  pumped  out,  the  whole  of  the 
carbon  dioxide  can  be  removed,  apparently  because  substances  of 
acid  nature  pass  from  the  corpuscles  into  the  serum  and  help  to  break 
up  the  carbonates,  and  because  the  haemoglobin  in  the  corpuscles 
acts  as  a  weak  acid. 

In  the  red  corpuscles  a  portion  of  the  carbon  dioxide  is  in 
combination  with  alkalies.     We  know  that  the  corpuscles  contain 


/.'/  SPIRA  I  Wh 


255 


alkalies,  tor  potassium  has  been  demonstrated  microchemically  in 
frog's  erythrocytes  (Macallum)  (Frontispiece),  and  the  titratable 
alkalinity  o\  '  hiked  '  blood  (pp.  24,  27)  is  greater  than  that  of 
unlaked  blood,  unless  a  long  time  is  allowed  in  the  case  oi  thelattei 

for  the  alkalies  of  the  corpuscles  to  reach  the  acid  used  in  titration. 
Some  observers  believe  that  a  weak  compound  of  carbon  dioxide 
can  be  formed  with  haemoglobin  ;  for  a  solution  of  haemoglobin 
absorbs  more  of  this  gas  than  water,  and  the  quantity  absorbed  is 
not  proportional  to  the  pressure.  The  haemoglobin  oi  the  corpuscles 
may  therefore  hold  a  portion  of  the  carbon  dioxide  in  combination. 

120CC. 


60     70      60     90      100    HO     120    130     140    ISO 


Fig.  ioy. — Curves  of  Dissociation  of  Oxygen  for  Horse's  Blood  (B)  and 

Doc/S    H.EMOGLOBIN    SOLUTION    (H)    AT    38°    C.    (BOHR). 

The  figures  along  the  base-line  and  the  vertical  axis  at  the  left  have  the  same 
signification  as  in  Fig.  108.  The  figures  along  the  vertical  at  the  right  give  the 
actual  number  of  c.c.  of  oxygen  chemically  combined  by  roo  c.c.  of  the  blood 
for  each  pressure  of  oxygen.  Thus,  with  pressure  10  mm.  6  c.c.  of  oxygen  were 
taken  up  by  the  blood-pigment  in  100  c.c.  of  blood.  The  interrupted  line  P 
indicates  the  amount  of  oxygen  dissolved  in  the  plasma  of  the  blood  at  each 
partial  pressure  on  the  assumption  that  the  plasma  is  two-thirds  of  the  volume 
of  the  blood.  Thus,  at  150  mm.  oxygen  pressure  the  plasma  of  100  c.c.  of  blood 
took  up  o-3  c.c.  oxygen. 

When  blood  is  saturated  with  carbon  dioxide  and  then  separated 
into  serum  and  clot,  the  serum  is  found  to  yield  more  gas  than  the 
clot  ;  but  if  the  serum  and  clot  are  separately  saturated,  the  latter 
takes  up  more  carbon  dioxide  than  the  former.  From  this  it  is 
argued  that  a  substance  combined  with  carbon  dioxide  must  in 
blood  saturated  with  the  gas  pass  out  of  the  corpuscles  into  the 
serum.  This  cannot  be  haemoglobin,  for  it  remains  in  the  cor- 
puscles, but  it  may  very  well  be  an  alkali,  combined  with  the  carbon 
dioxide  and  thus  set  free  from  its  connection  with  the  haemoglobin 
And,  as  a  matter  of  fact,  under  the  circumstances  described,  it  has 
been  found  that  alkalies  do  pass  from  the  clot  into  the  serum,  and 
chlorine  from  the  serum  into  the  corpuscles,  which  at  the  same- 
time  gain  water  and  become  larger.  The  molecular  concentration 
(p.  398)  of  the  serum  of  defibrinated  blood,  as  measured  by  the 
lowering  of  the  freezing-point,  increases  when  it  is  saturated  with 
carbon  dioxide.     On  the  other  hand,  when  blood  is  saturated  with 


I   M  INI    II    OF   PHYSIOLOG  ) 

oxygen,  alkalies  pass  mil  oi  the  serum  into  the  corpuscles,  which 
•it  the  same  tunc  lose  water  and  shrink  in  volume,  wnile  tin-  mole- 
culai  concentration  oi  the  serum  is  diminished.  Hamburger  has 
extended  these  observations  to  the  circulating  blood,  and  has  shown 
that  the  plasma  of  venous  bloo<l  has  a  higher  percentagi  ol  alkali, 
protein,  sugar,  and  fat,  than  the  plasma,  of  arterial  blood,  and  that 
the  corpuscles  have  a  greater  volume,  though  not  a  greater  diameter. 
We  may  therefore  suppose  that  in  the  pulmonary  capillaries,  under 
the  influence  ol  oxygen,  water  passes  into  the  plasma  from  th< 
puscles.  In  the  systemic  capillaries  the  blood  becomes  loaded  with 
carbon  dioxide,  and  therefore  the  corpuscles  take  up  water  from 
the  plasma,  which  accordingly  has  a  more  concentrated  supply  oi 
food-substances  to  oiler  to  the  tissues  than  the  plasma  oi  arterial 
blood  itself.  Some  writers  see  in  this  interchange  an  automatic 
arrangement  by  which  oxidation  is  favoured.  Whatever  may  be 
thought  of  this  view — and  objections  to  it  are  not  wanting — the 
current  theory,  that  the  corpuscles  are  simply  passive  carriers  oi 
oxygen,  and  exercise  no  further  influence  on  the  plasma,  breaks 
down  in  face  of  the  facts.  We  must  admit  that  an  active  and 
many-sided  commerce  exists  between  them  and  the  liquid  in  which 
they  float. 

The  nitrogen  of  the  blood  is  simply  absorbed. 

The  Tension  of  the  Blood-gases. — If  the  gases  of  the  blood 
existed  in  simple  solution,  their  tension  or  partial  pressure  could 
be  deduced  from  the  amount  dissolved  and  the  co-efficient  oi 
absorption.  Since  they  are  chemically  combined,  it  is  necessary 
to  determine  it  directly. 

This  has  been  done  by  means  of  an  apparatus  called  the  aerotono- 
meter.  The  blood  is  made  to  pass  directly  from  the  vessel  to  glass 
tubes,  which  it  traverses  at  the  same  time,  the  stream  being  divided 
between  them  ;  it  then  passes  out  again.  The  tubes  are  warmed 
by  means  of  a  water-jacket  to  the  body  temperature.  Some  of  them 
arc  filled  with  gaseous  mixtures  having  a  greater,  and  the  others  with 
mixtures  having  a  smaller,  partial  pressure,  say  of  carbon  dioxide, 
than  is  expected  to  be  found  in  the  blood.  As  the  latter  runs  in  a 
thin  sheet  over  the  walls  of  the  tubes,  it  loses  carbon  dioxide  to  some 
of  them  and  takes  up  carbon  dioxide  from  others.  From  the  altera- 
tion in  the  proportion  of  the  carbon  dioxide  in  the  tubes,  it  is 
easy  to  calculate  the  partial  pressure  of  that  gas  in  the  blood  ;  that 
is,  the  partial  pressure  which  it  would  be  necessary  to  have  in  the 
tubes  in  order  that  the  blood  might  pass  through  them  without 
losing  or  gaining  carbon  dioxide  (p.  248). 

The  pressure  of  oxygen  in  arterial  blood  was  given  by 
Strassburg  as  about  30  mm.  of  mercury  in  the  dog  (corresponding 
to  the  partial  pressure  of  oxygen  in  a  gaseous  mixture  at  atmo- 
spheric pressure  when  4  per  cent,  of  it  is  present),  and  in  venous 
blood  as  something  like  20  mm.  If  we  were  to  accept  the 
experiments  of  Bohr,  made  by  means  of  a  special  form  of  aero- 
tonometer  constructed  and  worked  much  in  the  same  way  as 
Ludwig's  stromuhr  (p.  112),  and  inserted  into  the  course  of  a 
bloodvessel,  it  would  be  necessary  to  treble  or  quadruple  these 
numbers. 


RESPIRATION  257 

The  pressure  oi  carbon  dioxide  in  arterial  blood  we  may  take 
.i!  10  to  40  mm.,  in  venous  blood  at  30  to  50  mm.,  according  to 
the  results  of  different  observers. 

Whenever  the  venous  blood  bas  to  pass  through  a  region  in 
which  the  pressure  of  carbon  dioxide  is  higher  than  its  own, 
carbon  dioxide  will  enter  it.  When  it  enters  a  region  in  which  the 
carbon  dioxide  pressure  is  kept  lower  than  in  itself,  the  carbon 
dioxide  compounds  formed  in  its  passage  through  the  tissues  will  be 
dissociated,  and  it  will  begin  to  lose  carbon  dioxide  by  diffusion. 
If  the  pressure  of  oxygen  in  this  region  is  at  the  same  time  higher 
than  in  the  venous  blood,  some  of  it  will  be  taken  up.  And  to 
bring  about  these  results  no  peculiar  '  vital  '  force  need  be  in- 
voked ;  ordinary  physical  processes  will,  under  the  assumed 
conditions,  be  alone  required. 

Now,  we  know  that  in  the  lungs  carbon  dioxide  is  given  off 
from  the  blood,  and  oxygen  taken  up  by  it.  We  have,  therefore, 
to  inquire  what  the  partial  pressures  of  these  gases  are  in  the 
alveoli,  and  whether  they  are  so  related  to  the  corresponding 
partial  pressures  in  the  blood  that  a  simple  process  of  dissociation 
and  diffusion  will  be  sufficient  to  explain  pulmonary  respiration. 

The  percentage  of  carbon  dioxide  in  expired  air  cannot  tell  us 
the  pressure  of  that  gas  in  the  alveoli,  for  the  air  in  the  upper 
part  of  the  respiratory  tract  is  necessarily  expelled  along  with 
the  alveolar  air,  and  dilutes  the  carbon  dioxide  in  it.  But  the 
mean  of  the  carbon  dioxide  percentages  in  samples  taken  from 
the  last  portions  of  the  air  of  two  deep  expirations,  one  following  an 
ordinary  inspiration  and  the  other  following  an  ordinary  expiration, 
isthemeanpercentageinthe  alveoli.  This  quantity,  while, as  already 
remarked  (p.  242),  very  constant  in  a  given  individual,  varies  in 
different  men  from  4- 6  to  62  (mean  5  -5)  percent,  of  the  dry  alveolar 
air.  In  women  and  in  children  of  both  sexes  it  is  less  than  in 
men.  From  this  we  conclude  that  in  men  the  partial  pressure  of 
carbon  dioxide  in  the  alveoli  may  be  at  least  one-eighteenth  of 
an  atmosphere,  or  42  mm.  of  mercury  (Fitzgerald  and  Haldane). 

In  animals,  samples  of  the  alveolar  air  have  been  drawn  off 
directly  by  means  of  a  pulmonary  catheter.  This  consists  of  two 
tubes,  one  within  the  other.  The  inner  tube,  which  is  a  fine 
elastic  catheter,  projects  free  from  the  other  for  a  little  distance 
at  its  lower  end.  The  outer  tube  terminates  in  an  indiarubber 
ball,  which  can  be  inflated  so  as  to  block  the  bronchus  into  which 
it  is  passed,  and  cut  off  the  corresponding  portion  of  the  lung 
from  communication  with  the  outer  air.  A  sample  of  the  air 
below  the  block  can  be  drawn  off  through  the  inner  tube.  In 
this  way  the  proportion  of  carbon  dioxide  in  the  alveoli  of  the  dog 
was  found  to  be  only  about  38  per  cent.,  corresponding  to  a 
partial  pressure  of  about  29  mm.  of  mercury. 

17 


A  MANUAL  01    PHYSIOLOGl 

In  Bohr's  experiments,  in  some  <>t  which  the  animals  were 
made  to  breathe  air  containing  carbon  dioxide  in  various  pro- 
portions, the  tension  oi  that  gas  in  the  air  of  the  lungs  varied 
from  5*8  to  34*6  mm.  of  mercury,  while  in  arterial  blood,  taken 
at  the  same  time,  it  usually  ranged  from  10  to  38  mm.,  and 
often  less  than  in  the  alveolar  air. 

If  we  accept  these  results,  we  seem  shut  up  to  the  conclusion 
that  carbon  dioxide  does  not  pass  through  the  walls  of  the 
alveoli  solely  by  diffusion.  And  although  Bohr's  experiments 
have  been  severely  criticized,  it  does  not  seem  improbable  in 
itself  that  the  physical  process  of  diffusion,  which  undoubtedly 
plays  a  great  part,  is  aided  by  some  other  process,  which  may 
provisionally  be  termed  secretion.  It  is  possible,  too,  that  when 
the  conditions  are  especially  unfavourable  to  diffusion— when, 
for  instance,  the  partial  pressure  of  carbon  dioxide  is  artificially 
increased  in  the  alveoli—  the  cells  which  line  them  are  stimulated 
to  increased  activity. 

As  to  the  oxygen,  we  are  in  the  same  position.  Its  partial 
pressure  does  not  appear  to  be  always  higher,  even  under 
normal  conditions,  in  the  alveoli  than  in  the  arterial  blood  as  it 
leaves  the  lungs.  Indeed,  Bohr  found  that  in  the  majority  of 
his  observations  on  dogs,  the  oxygen  tension  was  distinctly 
iter  in  the  blood  than  in  the  pulmonary  air.  And  Haldane 
and  Smith,  using  a  new  method.*  have  obtained  a  value  for  the 
oxygen  tension  in  human  blood  (262  per  cent.,  equal  to  200  mm. 
of  mercury)  that  even  exceeds  the  partial  pressure  of  oxygen  in 
the  external  air.  and  is  about  twice  as  great  as  that  of  the  air  of 
the  alveoli.  This  remarkable  result  cannot  be  reconciled  with 
any  purely  physical  explanation  of  the  absorption  of  oxygen. 
But  the  method  by  which  it  was  obtained,  although  correct  in 
principle,  has  not  escaped  criticism  as  to  its  details  (Osborne). 

Additional  evidence  in  favour  of  the  view  that  there  is, 
besides  diffusion,  an  element  of  selective  secretion  in  the  1  \- 
change  of  gases  through  the  pulmonary  membrane  is  afforded 
by  a  study  of  the  gases  of  the  swim-bladder  in  fishes.     These 

*  The  subject  of  the  experiment  breathes  air  containing  a  definitely 
known  very  small  percentage  of  carbon  monoxide  until  the  hamoglobin 
has  united  with  as  much  of  that  gas  as  it  will  take  up  for  the  given  con- 
centration of  it  in  the  air.  Then  the  percentage  amount  to  which  the 
haemoglobin  has  become  saturated  with  carbon  monoxide  is  determined 
in  a  sample  of  blood  taken,  say,  from  the  finger.  Xow,  the  final  saturation 
with  carbon  monoxide  of  a  h.-rmoglobin  solution  brought  into  contact  with 
-  mixture  containing  carbon  monoxide  and  oxygen,  depends  on 
the  relative  tensions  <>t  tin-  two  uases  in  the  liquid.  But  the  tension  of 
carbon  monoxide  in  the  blood  leaving  the  lung^  will  (alter  absorption  ha- 
•  !)  be  tin  same  as  that  in  tin  inspired  air.  Knowing  this  tension  and 
the  d  -aturation  oi    the  hemoglobin  with  carbon   monoxide,  the 

n-inn  in  the  blood  leaving  the  lungs — i.e.,  in  the  arterial  blood — 
iwn. 


RESPJR  I  I  TON 

consist  Hi  oxygen,  nitrogen,  and  usually  a  small  quantity  oi 
carbon  dioxide,  bu1  in  very  differenl  proportions  from  those  in 
which  they  exist  in  the  air  or  the  water.  Thus,  as  much  as  87  pei 
cent.  <>i  oxygen  has  been  found  in  the  bladder  of  fishes  taken  at  a 
considerable  depth,  bul  a  smaller  amounl  in  those  captured  near 
the  surface.  When  the  ,^a>  is  withdrawn  by  puncturing  the 
bladder  with  a  trocar,  the  organ  rapidly  refills,  and  the  percentage 
oi  oxygen  increases.  Further,  this  process  of  gaseous  secretion 
is  under  the  influence  of  nerves,  for  gas  ceases  to  accumulate  in 
the  organ  when  the  branches  of  the  vagi  that  supply  it  are  cut. 
In  the  tortoise  stimulation  of  the  peripheral  end  of  the  vagus 
causes  a  fall  of  gaseous  exchange  in  the  corresponding  lung,  with 
an  accompanying  rise  in  the  other  lung.  That  this  is  not  the 
consequence  of  an  alteration  in  the  pulmonary  circulation  is 
indicated  by  the  fact  that  the  change  is  greater  in  the  intake 
of  oxygen  than  in  the  output  of  carbon  dioxide.  In  the  mammal. 
however,  no  such  effect  has  been  clearly  demonstrated,  and  the 
decisive  proof  that  the  lungs  are  gas-secreting  glands  which  would 
be  afforded  by  the  discovery  of  secretory  nerves  is  still  wanting. 

We  have  now  completed  the  description  of  the  phenomena 
of  external  respiration,  with  the  discussion  of  its  central  fact, 
the  exchange  of  gases  between  the  blood  and  the  air  at  the 
surface  of  the  lungs,  ft  remains  to  trace  the  fate  of  the  absorbed 
oxygen,  and  to  determine  where  and  how  the  carbon  dioxide 
arises. 

Internal  Respiration — Seats  of  Oxidation. — The  suggestion 
which  lies  nearest  at  hand,  and  which,  as  a  matter  of  fact,  was 
first  put  forward,  is  that  the  oxygen  does  not  leave  the  blood 
at  all,  but  that  it  meets  with  oxidizable  substances  in  it,  and 
unites  with  their  carbon  to  form  carbon  dioxide.  While  there  is 
a  certain  amount  of  truth  in  this  view,  oxygen,  as  already 
mentioned,  being  to  some  extent  taken  up  by  freshly-shed  blood, 
and  also  by  blood  under  other  conditions,  to  oxidize  bodies, 
other  than  haemoglobin,  either  naturally  contained  in  it  or  arti- 
ficially added,  there  is  no  doubt  that  the  cells  of  the  body  are  the 
busiest  seats  of  oxidation.  This  is  shown  by  the  presence  of 
carbon  dioxide  in  large  amount  in  lymph  and  other  liquids 
which  are,  or  have  been,  in  intimate  relation  with  tissue  elements  ; 
by  its  presence,  also  in  considerable  amount,  in  the  tissues  them- 
selves— in  muscle,  for  instance  ;  by  its  continued  and  scarcely 
lessened  production  not  only  in  a  frog  whose  blood  has  been 
replaced  by  physiological  salt  solution,  and  which  continues  to  live 
in  an.  atmosphere  of  pure  oxygen,  but  in  excised  muscles  ;  and  by 
the  remarkable  connection  between  the  amount  of  this  production 
and  the  functional  state  of  those  tissues.  In  insects  the  finest  twigs 
of  the  tracheae,  through  which  oxygen  passes  to  the  tissues,  actually 

17 — 2 


A   MANUAL  OF  PHYSIOLOGl 

end  in  the  cells;  and  in  luminous  insects,  like  the  glow-worm, 
it  has  been  noticed  that  the  phosphorescence,  which  is  certainly 

dependent  on  oxidation,  begins  and  is  most  brilliant  in  t  hose  parts 
of  the  cells  of  the  light-producing  organ  that  surround  the  ends 
of  the  tracheae.  Microscopic  evidence  has  been  obtained  that  the 
nucleus  plays  a  predominant  part  in  intracellular  oxidation  ;  e.g.,  in 
the  indophenol  (p.  265)  and  similar  reactions  the  coloured  oxida- 
tion products  are  deposited  chieflyin  and  around  the  nuclei  of  such 
cells  as  liver  and  kidney  cells  and  frog's  red  corpuscles  (Libit). 

yrhe  fact  observed  by  Bohr  that  an  increase  in  the  carbon 
dioxide  tension  of  blood  diminishes  its  combining  power  for 
oxygen,  and  therefore  favours  the  giving  up  of  oxygen  to  the 
lymph  and  tissues,  may  have  an  important  influence  on  internal 
respiration.  The  effect  is  much  more  marked  where  the  oxygen- 
tension  is  low  than  where  it  is  high,  so  that  in  the  lungs  t  he  taking 
up  of  oxygen  is  scarcely  interfered  with  even  by  a  high  carbon 
dioxide  tension.  Lymph,  bile,  urine,  and  the  serous  fluids  con- 
tain very  little  oxygen,  but  so  much  carbon  dioxide  thai  the 
pressure  of  that  gas  in  all  of  them  is  greater  than  in  arterial 
blood,  while  in  lymph  alone  (taken  from  the  large  thoracic  duct) 
has  it  been  found  less  than  that  of  venous  blood.  And  it  is 
probable  that  lymph  gathered  nearer  the  primary  seats  of  its 
production  (the  spaces  of  areolar  tissue)  would  show  a  higher  pro- 
portion of  carbon  dioxide.  Strassburg  found  that  with  a  pressure 
of  carbon  dioxide  in  the  arterial  blood  of  21  mm.  of  mercury,  the 
pressure  in  bile  was  50  mm.,  in  peritoneal  fluid  58  mm.,  in  urine 
68  mm.,  in  the  surface  of  the  empty  intestine  58  mm.  Saliva, 
pancreatic  juice,  and  milk,  also  contain  much  carbon  dioxide,  and 
only  a  little,  if  any,  oxygen.  From  muscle  (to  facilitate  pumping, 
the  muscle  is  minced  and  warmed)  no  free  oxygen  at  all  can  be 
pumped  out,  but  as  much  as  15  volumes  per  100  of  carbon  dioxide, 
some  of  which  is  free,  that  is,  is  given  up  to  the  vacuum  alone,  while 
some  of  it  is  fixed,  and  only  comes  off  after  the  addition  of  an  acid. 

Muscle  may  be  safely  taken  as  a  type  of  the  other  tissues  in 
regard  to  the  problems  of  internal  respiration.  It  is  instructive, 
therefore,  to  observe  that  the  great  scarcity  of  oxygen  in  the 
parenchymatous  liquids  which  bathe  the  tissues,  here  in  the 
tissues  themselves  deepens  into  actual  famine.  The  inference 
is  plain.  The  active  tissues  are  greedy  of  oxygen  ;  as  soon  as 
it  enters  the  muscle  it  is  seized  and  '  fixed  '  in  some  way  or  other. 
The  traces  of  oxygen  in  the  lymph  cannot  therefore  be  journeying 
away  from  the  tissue  elements  ;  they  must  have  come  from  another 
source,  and  this  can  only  be  the  blood.  Could  we  gather  tissue 
lymph  for  analysis  directly  from  the  thin  sheets  that  lie  between 
the  blood  capillaries  and  the  tissues,  we  might  find  more  oxygen 
present  as  well  as  more  carbon  dioxide.     But  if  we  did  find  more 


h'FSPTR.-ITTON 


2f>l 


oxygen,  it  would  still  be  oxygen  in  transil  from  the  capillaries 
low. nils  places  where  the  partial  pressure  of  oxygen  is  less.  In 
the  lymph,  the  pressure  is  kept  low  by  the  avidity  of  (lit-  tissues 
with  which  it  is  in  contact,  and  possibly  by  the  existence  in  it 
ol  oxidizable  substances  which  have  come  from  the  tissues.  In 
the  tissues  there  is  no  partial  pressure  at  all,  because  the  oxygen 
that  reaches  them  is  at  once  stowed  away  in  some  compound  in 
which  it  has  lost  the  properties  of  free  oxygen. 

Assuming,  then,  that  at  least  a  great  part  of  the  oxidation 
and  consequent  production  of  carbon  dioxide  goes  on  in  the 
tissues,  let  us  follow  the  steps  of  the  process,  as  far  as  we  can, 
in  the  light  of  our  knowledge  of  the  respiration  of  muscle. 

Respiration  of  Muscle. — It  is  a  remarkable  fact  that  an  ex- 
cised  frog's  muscle   is   capable   of  going   on   producing   carbon 


Fig.   i io. — Fatigue  of  a  Pair  of  Sartorius  Muscles  (Fletcher). 
A,  in  an  atmosphere  of  oxygen  ;  B,  in  an  atmosphere  of  nitrogen.     A  is  partially 
restored  by  a  rest  of  five  minutes. 

dioxide  for  a  long  time,  in  the  entire  absence  of  oxygen,  in  a 
chamber,  for  instance,  filled  with  nitrogen  or  other  indifferent 
gas.  Not  only  so,  but  it  can  be  made  to  contract  many  times 
in  this  oxygen-free  atmosphere,  although  it  loses  its  power  of 
contraction  sooner  than  in  oxygen,  and  does  not  show  the  same 
capacity  for  recuperation  during  an  interval  of  rest.  In  mam- 
mals the  muscles  can  also  be  made  to  contract  repeatedly  when 
the  dissociable  oxygen  has,  as  far  as  possible,  been  got  rid  of 
from  the  blood  by  asphyxiating  the  animal,  and  to  produce 
a  correspondingly  large  quantity  of  carbon  dioxide,  although' 
they  lose  their  contractility  much  more  rapidly  than  the  muscles 
of  the  frog.  This  leads  us  to  the  important  conclusion  that  the 
carbon  dioxide  does  not  arise,  so  to  speak,  on  the  spot,  from 
the  immediate  union  of  carbon  and  oxygen.  Oxygen  is  essential 
to  muscular  life  and  action.     But  a  stock  of  it  is  apparently 


262 


A    MANV  U    OF  PHYSIOLOGY 


taken  up  by  the  muscle,  and  stored  in  some  compound  or  com- 
pounds, probably  essential  constituents  of  the  living  muscular 
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and  more  slowl\-  during  rest,  carbon  dioxide  in  both  cases  being 
one  of  the  end  products.  It  is  possible  that  there  is  an  ascending 
series  of  bodies  through  which  oxygen  passes  up,  and  a  descend- 


RESPIRATION 

ing  scries  through  which  it  passes  down,  before  the  final 
reached     In   a   normal   muscle   with   intact   circulation,    while 
carbon  dioxide  is  given  off,  certain  of  the  other  decomposition 
products  appear,  in  conjunction  with  oxygen  and  somesubstan*  e 

i  icli  in  carbon,  like  sugar,  to  he  regenerated  into  the  material 
which  breaks  down  in  contraction.  When  oxygen  is  not  avail- 
able, as  in  an  atmosphere  of  nitrogen,  carbon  dioxide  is  still 
given  off,  but  the  other  decomposition  products  are  not  re- 
generated to  contractile  substance,  but  accumulate  in  the  muscle, 
producing  the  phenomena  of  fatigue,  and  eventually  of  rigor. 

When  muscle  goes  into  rigor  (Chap.  IX.) — and  this  is  most 
strikingly  seen  when  the  rigor  is  caused  by  raising  the  tempera- 
ture of  frog's  muscle  to  about  400  or  410  C. — there  is  a  sudden 
increase  in  the  quantity  of  carbon  dioxide  given  off.  Moreover, 
in  an  isolated  muscle  the  total  quantity  of  carbon  dioxide  obtain- 
able during  rigor  is  markedly  less  if  the  muscle  has  been  pre- 
viously tetanized.  From  this  it  has  been  argued  that  the 
hypothetical  substance,  the  decomposition  of  which  yields 
carbon  dioxide  in  contraction,  is  also  the  substance  which  de- 
composes so  rapidly  in  rigor ;  that  a  given  amount  of  it  exists 
in  the  muscle  at  the  time  it  is  removed  from  the  influence  of 
the  blood  ;  and  that  this  can  all  explode  either  in  contraction 
or  in  rigor,  or  partly  in  the  one  and  partly  in  the  other.  Accord- 
ing to  Fletcher,  there  is  no  increase  in  the  amount  of  carbon 
dioxide  given  off  during  tetanus  by  an  excised  frog's  muscle  unless 
the  stimulation  is  so  severe  and  prolonged  as  to  hasten  the 
onset  of  rigor.  He  therefore  supposes  that  in  the  contraction 
the  decomposition  does  not  proceed  quite  to  the  formation  of 
carbon  dioxide,  which  in  the  intact  body  is  afterwards  liberated 
from  some  more  complex  carbon-containing  waste-product. 

The  respiration  of  muscles  in  situ  can  be  studied  by  collecting 
samples  of  the  blood  coming  to  and  leaving  them  and  analyzing 
the  gases.  The  mere  difference  of  colour  between  the  venous 
and  arterial  blood  of  a  muscle,  or  other  active  organ,  is 
sufficient  to  show  that  oxygen  is  taken  up  and  carbon  dioxide 
given  out  by  it  to  the  blood.  This  is  the  case  in  muscles  at 
rest,  and  even  in  muscles  with  artificial  circulation  after  they 
have  become  inexcitable.  In  active  muscles  more  oxygen  is  used 
up  and  more  carbon  dioxide  produced  than  in  the  resting  state. 
Chauveau  and  Kaufmann,  in  their  experiments  on  the  levator 
labii  superioris  muscle  of  the  horse  in  feeding,  found  that  the 
consumption  of  oxygen  and  the  production  of  carbon  dioxide 
might  be  many  times  as  great  in  activity  as  in  rest. 

Thus  in  one  experiment  the  amount  of  oxygen  taken  in,  ex- 
pressed in  c.c.  per  gramme  of  muscle  per  minute,  was  0*0079 
during  rest,  and  0-14  during  work  ;  the  corresponding  quantities 


264  A   MANUAL  OF  PHYSIOLOGY 

for  the  carbon  dioxide  given  off  were  00058  and  o-i8.  The 
respiratory  quotient  rose  to  1*3  in  two  experiments,  and  even 
to  17  in  a  third,  showing  that  the  increase  in  the  production  of 
carbon  dioxide  was  relatively  greater  than  the  increase  in  tin- 
intake  of  oxygen.  These  experiments  were  performed  under 
conditions  so  normal  that  the  animal  continued  to  eat  its  hay 
with  seeming  unconcern  throughout  the  observations,  although 
these  involved  the  exposure  of  the  main  bloodvessels  of  the 
muscle,  and  the  collection  of  samples  of  blood  from  them. 

In  the  heart  of  a  small  dog  through  which  blood  was  pumped 
by  a  larger  dog  the  oxygen  intake  when  the  heart  was  beating 
feebly  was,  on  the  average,  about  001  c.c.  per  gramme  of  heart- 
muscle  per  minute.  When  the  heart  was  caused  to  beat  very 
strongly  under  the  influence  of  adrenalin,  the  oxygen  intake 
rose  in  one  case  to  o-o8,  and  in  two  others  to  0-04.  In  the 
resting  pancreas  the  oxygen  intake  has  been  found  to  be  0-03 
to  005  c.c.  per  gramme  per  minute  ;  in  the  active  pancreas, 
01  c.c.  The  corresponding  number  for  the  submaxillary  gland 
at  rest  is  0-03,  and  in  activity  009  ;  for  the  kidney,  003  at  rest  or 
during  scanty  secretion,  and  0-07  during  active  secretion  (Barcroft) . 

Nature  of  the  Oxidative  Process.— When  we  have  recognised 
the  cells  as  the  seat  of  oxidation,  the  question  immediately 
presents  itself,  How  do  they  accomplish  the  feat  of  burning  such 
masses  of  food  substances  as  can  only  be  rapidly  oxidized  in  the 
laboratory  at  the  temperature  of  the  body  by  the  most  energetic 
chemical  reagents  ?  The  researches  of  late  years  have  furnished 
a  key  to  the  solution  of  this  long-standing  puzzle  by  demonstrat- 
ing the  existence  in  the  tissues  of  oxidizing  ferments  or  oxy- 
dases. Of  these,  one  of  the  most  widely  distributed  is  a  ferment 
which  splits  off  oxygen  from  hydrogen  peroxide.  Since  any 
oxidation  produced  is  only  secondary  to  this  decomposition, 
ferments  which  decompose  hydrogen  peroxide  are  often  spoken 
of  as  catalases,  to  distinguish  them  from  the  oxydases  proper.  A 
catalase  is  found  in  practically  all  the  tissues  of  the  bod} 
well  as  in  vegetable  cells,  and  we  have  already  mentioned  in- 
stances of  its  action  in  connection  with  the  oxidation  of  the 
guaiaconic  acid  in  tincture  of  guaiacum  in  the  presence  of  the 
peroxide  (p.  69).  As  regards  the  activity  of  this  ferment,  blood 
comes  first  ;  then  follow  spleen,  liver,  pancreas,  thymus,  brain, 
muscle,  and  ovary.  It  is  present  in  the  blood-free  organs  as 
well  as  in  the  blood.  Some  tissues,  both  animal  and  vegetable. 
contain  a  ferment,  an  oxydase,  which  causes  the  oxidation  of 
guaiaconic  acid  in  the  presence  of  atmospheric  oxygen,  and 
these  do  not  need  peroxide  of  hydrogen  in  order  to  render  guaia- 
cum blue.  An  allied  ferment  which  also  induces  the  blue  colour 
in  tincture  of  guaiacum  is  the  so-called  laccase  found  in  the  most 


RESPIR  ITION  265 

active  form  in  the  latex  of  the  tree  from  which  Japanese  lacquer 
is  obtained,  but  also  in  many  other  plants.  Many  fungi  contain 
a  ferment,  tyrosinase,  which  oxidizes  tyrosin,  and  in  certain 
animals  tyrosinases  have  also  been  demonstrated.  Another 
well-known  oxidizing  ferment  in  fresh  animal  tissues  is  charac- 
terized by  the  property  of  forming  indophenol  by  oxidation  in 
an  alkaline  solution  of  paraplienylenediamin  and  a-naphthol, 
and  may  therefore  be  termed  indophenyloxydase.  The  colour- 
less solution  becomes  reddish  or  violet.  This  ferment  is  con- 
tained in  pancreas,  salivary  glands,  spleen,  thymus,  and  bone- 
marrow,  but  has  not  been  detected  in  muscle,  lungs,  brain, 
kidneys,  and  other  organs.  Finally,  we  may  mention  a  ferment 
which  favours  the  oxidation  of  aldehydes  to  the  corresponding 
acids,  and  is  appropriately  named  aldehydase.  Evidence  of  its 
presence  in  most  organs  has  been  obtained,  but  it  seems  to  be 
absent  from  muscle,  pancreas,  bone-marrow,  and  mammary 
glands.  It  is  to  be  expected  that  other  oxydases  capable  of 
favouring  oxidation  of  specific  kinds  of  food  substances  or  their 
decomposition  products  will  be  discovered,  but  it  would  be  rash 
to  conclude  that  this  is  the  only  way  in  which  living  protoplasm 
can  bring  about  the  rapid  oxidation  which  is  so  characteristic  a 
feature  of  its  activity. 

The  Influence  of  Respiration  on  the  Blood-pressure. — We 
have  already  stated,  in  treating  of  arterial  blood-pressure  (p.  104), 
that  a  normal  tracing  shows  a  series  of  waves  corresponding  with 
the  respiratory  movements. 

The  relationship  between  the  respiratory  phases  and  the  rise 
and  fall  of  the  blood-pressure  is  not  by  any  means  a  simple  and 
invariable  one.  It  depends  upon  a  number  of  factors,  which 
need  not  be  equally  influential  under  different  conditions  or  in 
different  animals  (Lewis).  Something  depends  upon  the  rate, 
something  upon  the  relative  preponderance  of  costal  and  ab- 
dominal respiration,  and  something  probably  upon  the  size  of  the 
animal.  For  instance,  an  inspiratory  rise  of  blood-pressure  occurs 
in  man  with  pure  diaphragmatic,  and  a  fall  with  pure  thoracic, 
breathing  (Fig.  112).  In  cats  with  fairly  fast  and  not  very  deep 
respiration  the  blood-pressure  rises  in  expiration  and  sinks  in 
inspiration.  With  deep  and  slow  respiration  the  opposite  effect 
may,  upon  the  whole,  be  seen.  In  dogs,  according  to  Einbrodt, 
although  the  mean  blood-pressure  is  falling  for  a  short  time  at 
the  beginning  of  inspiration,  it  soon  reaches  its  minimum,  then 
begins  to  rise,  and  continues  rising  during  the  rest  of  this  period. 
At  the  commencement  of  expiration  it  is  still  mounting,  but  soon 
reaches  its  maximum,  begins  to  fall,  and  continues  falling  through 
the  remainder  of  the  expiratory  phase. 

A  partial  explanation  is  afforded  by  a  consideration  of  the 


iGG 


A   MA  vr  //    OF  PHYSIOLOG  \ 


mechanical  changes  produced  in  the  thorax  by  the  respiratory 
movements.  Of  these,  the  influence  of  variations  in  the  intra- 
thoracic pressure  on  the  filling  oi  the  heart  is  of  special  importance. 
With  deep  abdominal  breathing  the  changes  of  intra-abdominal 


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Fig.    112. — Respiratory    Waves    in    the    Blood-pressure  :    Simultaneous 
Tracings  of  Movi  ments  of  Respiration  and  of  Radial  Pulse  in  Human 
Subject  (Lewis). 
In  A  tlic  respiration  was  diaphragmatic;  in  B,  costal.      In  A  the  respiratory 

tracing  was  taken  from  the  abdominal  wall  ;  in  1!.  from  the  chest. 

pressure  also  affed  the  filling  of  the  heart,  an  increase  of  pressure 
(in  inspiration)  tending  to  cause  more  Mood  to  be  squeezed  from 
the  abdominal  veins  towards  the  chesl .  The  changes  of  vascular 
resistance  in  the  lungs,  due  to  the  alteration  in  the  calibre  of 
the  pulmonary  vessels,  also  contribute,  but,  for  such  variations 

of  intrathoracic  pressure  as 
normally  occur,  only  in  a 
minor  degree.  The  changes 
in  the  vascular  capacity  of 
the  lungs  that  is,  in  the 
amount  of  blood  contained 
in  the  pulmonary  vessels — 
are  of  importance  especially 
in  delaying  or  accelerating 
the  alterations  of  blood-pres- 
sure in  the  systemic  arteries 
due  to  the  other  factors. 

The  intrathoracic  pressure, 
which,  as  we  have  seen,  is 
always  less  than  that  of  the 
atmosphere,  unless  during  a  forced  expiration  when  the  free 
escape  of  air  from  the  lungs  is  obstructed,  diminishes  in 
inspiration  ami  increases  in  expiration.  The  great  veins  outside 
the  chest,  the  jugular  veins  in  the  neck,  for  example,  are  under 


Fig.  113. 
The  upper  tracing  shows  the  respiratory 
movements  in  a  rabbit  with  rattier  deep 
and  slow  diaphragmatic  breathing  :  the 
Lower  tracing  is  the  blood-pressure  curve ; 
I,  inspiration  :  E,  expiration,  including  1  he 
pause. 


RESPIR  ITION 

the  atmospheric  pressure,  which  is  readily  transmitted  through 
their  thin  walls,  while  the  hear!  and  thoracic  veins  are  under 
a  smaller  pressure.  The  venous  blood  both  in  inspiration 
and  expiration  will,  accordingly,  tend  lobe  drawn  into  the  right 
auricle.  In  inspiration  the  venous  How  will  be  increased,  since 
the  pressure  in  the  thorax,  and  therefore  in  the  pericardial 
cavity,  is  diminished  ;  and  upon  the  whole  more  venous  blood 
will  pass  into  the  right  heart  during  inspiration  than  during 
expiration.  Now,  the  righl  ventricle  is  not  in  general  working 
as  hard  as  it  can  work.  I  fence,  the  excess  of  blood  which 
reaches  it  during  an  inspiration  is  at  once  sent  into  the  lungs, 
although  not  even  the  first  of  it  can  have  passed  through  to  the 
left  side  of  the  heart  at  the  end  of  the  inspiration,  since  the 
pulmonary  circulation-time  (four  to  live  seconds  in  a  small  dog, 
two  to  three  seconds  in  a  rabbit)  is  longer  than  the  time  of  a 
complete  inspiration  at  any  ordinary  rate.  The  increase  in  the 
quantity  of  blood  pumped  into  the  pulmonary  artery  will,  if  not 
counteracted  by  other  circumstances,  tend  to  raise  the  blood- 
pressure  in  the  artery  and  its  branches,  and  therefore  at  once  to 
accelerate  the  outflow  through  the  pulmonary  veins.  This  will 
be  aided  if  at  the  same  time  the  vascular  resistance  in  the  lungs 
is  reduced,  as  is  known  to  be  the  case.  The  left  ventricle,  like 
the  right,  is  capable  oi  discharging  more  blood  than  it  ordinarily 
receives.  The  excess  of  blood  coming  to  it  is  easily  and  promptly 
ejected.  The  systemic  arteries  are  better  filled  and  the  arterial 
pressure  rises. 

In  expiration  the  contrary  will  happen.  The  return  of  blood 
to  the  thorax  will  be  checked.  This  is  well  shown  by  the  swelling 
of  the  veins  at  the  root  of  the  neck  in  expiration,  their  shrinking 
in  inspiration,  the  so-called  respiratory  venous  pulse.  Less 
blood  being  drawn  into  the  right  heart,  less  will  be  pumped  into 
the  pulmonary  artery,  in  which  the  pressure  will,  of  course,  fall. 
The  outflow  into  the  left  auricle  will  thus  be  diminished — all 
the  more  as  in  the  expiratory  phase  the  vascular  resistance  in 
the  lungs  is  increased — and  the  systemic  arterial  pressure  will 
be  lowered.  In  both  cases,  however,  the  change  seen  in  the 
blood-pressure  curve  will  be  belated,  and  will  not  coincide 
exactly  with  the  commencement  of  the  inspiration  or  the  expira- 
tion. If  it  is  delayed  for  a  period  about  equal  to  the  length  of 
an  inspiration  or  an  expiration,  the  blood-pressure  will  be  seen 
to  sink  in  inspiration  and  to  rise  in  expiration.  If  the  period  of 
delay  is  less  than  this,  the  pressure  will  be  mounting  during  a 
part  of  each  respiratory  phase  and  falling  during  the  rest.  As 
to  the  explanation  of  the  delay,  several  factors  may  be  concerned. 

The  negative  pressure  of  the  thorax  acts  on  the  aorta,  as  well 
as  on  the  thoracic  veins,  although,  on  account  of  the  greater 


268  A   MANUAl    OF  PHYSIOLOGY 

thickness  of  its  walls,  to  a  smaller  extent  than  on  the  veins. 
The  diminution  of  pressure  in  inspiration  tends  to  expand  the 
thoracic  aorta,  and  to  draw  Mood  hack  out  of  the  systemic 
arteries,  while  expiration  has  the  opposite  effect.  And  although 
the  hindrance  caused  in  this  way  to  the  (low  of  blood  into  the 
arteries  during  inspiration,  and  the  acceleration  of  the  flow  during 
expiration  may  not  be  great,  they  will,  of  course,  he  better 
marked  in  small  animals  with  comparatively  yielding  arteries 
than  in  large  animals.  Yet.  whether  great  or  small,  the  tendency 
will  be  to  diminish  the  pressure  in  the  one  phase  and  increase  it 
in  the  other.  As  soon  as  the  changes  of  pressure  produced  by 
alterations  in  the  flow  of  venous  blood  into  the  chest  and  through 
the  lungs  are  thoroughly  established,  the  arterial  effect  will  be 
overborne  ;  but  before  this  happens,  that  is,  at  the  beginning 
of  inspiration  and  expiration,  it  will  be  in  evidence,  and  will 
help  to  delay  the  main  change. 

Another  factor  in  this  delay  is  found  in  the  changes  of  vascular 
capacity  which  take  place  in  the  lungs  when  they  pass  from 
the  expanded  to  the  collapsed  condition.  The  expansion  of 
the  lungs  in  natural  respiration  causes  a  widening  of  the  pul- 
monary capillaries,  with  a  consequent  increase  of  their  capacity 
and  diminution  of  their  resistance.  When  the  vessels  at  the 
base  of  the  heart  are  ligatured  either  at  the  height  of  inspiration 
or  the  end  of  expiration,  so  as  to  obtain  the  whole  of  the  blood 
in  the  lungs,  it  is  found  that  they  invariably  contain  more  blood 
in  inspiration  than  in  expiration.  During  inspiration,  as  we 
have  seen,  the  right  ventricle  is  sending  an  increased  supply  of 
blood  into  the  pulmonary  artery  ;  but  before  any  increase  in 
the  outflow  through  the  pulmonary  veins  can  take  place,  the 
vessels  of  the  lung  must  be  filled  to  their  new  capacity.  The 
first  effect,  then,  of  the  lessened  vascular  resistance  of  the  lungs 
in  inspiration  is  a  temporary  falling  off  in  the  outflow  through  the 
aorta,  and  therefore  a  fall  of  arterial  pressure.  As  soon  as  a 
more  copious  stream  begins  to  flow  through  the  lungs,  this  is 
succeeded  by  a  rise.  In  like  manner  the  first  effect  of  expiration. 
which  increases  the  resistance  and  diminishes  the  capacity  ol 
the  pulmonary  vessels,  is  to  force  out  of  the  lungs  into  the  hit 
auricle  the  blood  for  which  there  is  no  room.  This  causes  a 
rise  of  arterial  blood-pressure,  succeeded  by  a  fall  as  soon  as 
the  lessened  blood-flow  through  the  lungs  is  established. 

The  changes  in  the  diastolic  capacity  of  the  chambers  of  the 
heart  itself,  with  the  changes  of  pericardial  pr  ssure.  must  also 
act  in  the  same  direction.  It  is  obvious,  then,  how  greatly  the 
rate  and  depth  of  respiration  in  relation  to  the  size  of  the  animal 
and  the  other  circumstances  already  mentioned  may  influence 
the  time  relations  of  the  respiratory  oscillations  in  the  arterial 


Rl  SPIR  /  /  TON  269 

pressure  curve,  so  thai  we  oughl  n<»t  to  expect  them  to  be  abso- 
lutely constanl . 

In  artifu  i.il  respiration  oscillations  of  blood-pressure,  synchronous 
with  the  movements  oi  the  Lungs,  arc  al.su  seen.  During  inflation 
(inspiration)  the  arterial  pr<  ssure  rises  ;  during  deflation  (expiration) 
it  falls.  The  waves  are  qo1  entirely  abolished  even  when  the  thorax 
is  opened.  In  the  latter  case  there  are,  of  course,  no  variations  of 
intrathoracic  pressure,  and  the  oscillations  must  be  connected  with 
the  changes  in  the  pulmonary  circulation,  the  inflation  squeezing 
blood  from  the  lungs  into  the  left  side  of  the  heart,  while  deflation 
permits  the  pulmonary  vessels  to  become  filled  to  their  new  capacity 
at  the  expense  of  the  stream  flowing  into  the  left  auricle.  When 
artificial  respiration  is  stopped  at  the  height  of  inflation  (Fig.  114), 
the  arterial  blood-pressure  falls  rapidly,  and  continues  low  until  the 
rise  of  asphyxia  begins.  The  fall  of  pressure  when  the  chest  has 
been  previously  opened  is  due  to  the  increased  vascular  resistance 


Fig.  114. — Effect  on  Blood-pressure  of  Inflation  of  the  Lungs  :  Rabbit. 

Artificial  respiration  stopped  in  inflation  at  1.  Interval  between  2  and  3  (not 
reproduced)  51  seconds,  during  which  the  curve  was  almost  a  straight  line.  Time 
tracing  shows  seconds. 

in  the  lungs,  due  to  the  narrowing  of  the  capillaries  by  the  increased 
alveolar  pressure.  With  intact  chest  the  increased  intrathoracic 
pressure  due  to  the  inflation  is  also  an  important  factor.  When 
the  respiration  is  stopped  in  collapse,  instead  of  a  fall  a  steady  rise 
of  pressure  occurs  (as  in  Fig.  72,  p.  172).  This  ultimately  merges 
in  the  elevation  due  to  asphyxia,  which  shows  itself  sooner  than  in 
inflation.  When  the  tracheal  cannula  is  closed  in  natural  respira- 
tion, no  initial  fall  of  pressure  takes  place  (Fig.  115). 

Besides  the  mechanical  effects  of  the  respiratory  movements 
on  the  circulation,  it  may  be  influenced  by  changes  in  the  cardio- 
inhibitory  and  vaso-motor  centres  synchronous  with  the  rhythm 
of  the  respiratory  centre.  In  many  animals  (the  dog,  for  instance) 
and  in  man,  it  can  be  very  easily  made  out  that  the  rate  of  the 
heart  is  greater  during  inspiration,  especially  towards  its  end, 
than  in  expiration.      The  phenomenon  is  especially  distinct  in 


•V" 


I    W  I  xi    ]  i    OF  I'll  YSIOl  OG  \ 


deep  and  slew  respiration.  1 1  is  caused  l>v  a  rhythmi*  al  rise  and 
I. ill  in  the  activity  of  the  cardio-inhibitory  centre,  synchronous 
with  the  respiratory  movements,  for  the  difference  disappears 
after  division  <>!  both  vagi.  The  normal  respiratory  oscillations 
of  blood-pressure  arc  not  due  in  any  greal  degree  to  such  changes 
in  the  rate  of  the  heart,  foi  iIha  persisl  aftei  section  of  the  \ 
and  they  arc  seen  in  animals  like  the  rabbit,  in  which  in  ordinal  v 
breathing  little  or  no  variation  in  the  rate  oi  the  hearl  is  i 
nected  with  the  phases  of  respiration.  The  mosl  probable  ex- 
planation of  the  respiratory  variations  in  the  pulse  rate  is  that 
the  respiratory  centre,  when  it  is  discharging  itself  in  inspiration, 
sends  out  impulses  as  a  sort  of  overflow  along  fibres  connecting 
it  with  the  cardio-inhibitory  centre.  These  increase  the  tone  of 
that  centre,  but,  owing  to  the  longulatent  period  <>!  the  cardio- 
inhibitory  apparatus,  the  inhibition  does  not  reveal  itself  till  the 


Fig.  115. — Blood-pressure  Tracing:  Rabbit,  i  nder  Chloral, 
Natural  respiration  stopped  at  I  in  inspiration,  at  E  in  expiration.     The  mean 
blood-pressure  is  scarcely  altered  j  but  the  respiratory  waves  become  much  larger 
owing  to  the  abortive  efforts  at  breathing.     Time  tracing  shows  seconds. 

succeeding  expiration.  It  may  be,  however,  that  the  impulses 
discharged  from  the  respiratory  centre  in  inspiration  diminish 
the  tone  of  the  cardio-inhibitory  centre,  and  thus  lead  to  accelera- 
tion of  the  heart  towards  the  end  of  the  inspiratory  phase 
In  certain  pathological  conditions  the  influence  of  the  respira- 
tion on  the  pulse-rate  is  exaggerated  (so-called  respiratory 
arhythmia). 

Traube-Hering  Curves. — Rhythmical  changes  in  the  activity 
of  the  vaso-motor  centre,  also  associated  with  periodic  discharges 
from  the  respiratory  centre,  may  be  observed  under  certain  con- 
ditions— e.g.,  when  in  an  animal  paralyzed  by  curara,  and 
therefore  unable  to  breathe  spontaneously,  the  artificial  respira- 
tion is  stopped  for  a  time.  If  such  a  dose  of  curara  be  given  as 
will  still  permit  slight  spontaneous  respiration  to  go  on,  and 
both  vagi  be  cut,  it  can  be  seen  on  stopping  the  artificial  respira- 
tion that  the  \\a\c-  on  the  blood-pressure  curve  are  exactly 
synchronous    with     the    slow     respiratory    movements. 


/,'/  SPIR  ITION 


27' 


[Yaube  Hering  waves   sink   in    inspiration   and   rise   in  expira 

t  ion. 

["he  i. Hi  thai  they  have  invariably  a  longer  period  than  the 
natural  respiratory  movements  indicates  that  they  are  not  con- 
cerned in  the  production  oi  the  normal  respiratory  oscillations 
i>i  arterial  pressure.  Probably  the  reason  why  the  Traube  waves 
appear  after  section  of  the  vagi  is  the  increased  vigour  oi  the 
slow  respiratory  discharges,  coupled  with  a  hyperexcitability  oi 
the  vaso-motor  centre,  due  to  the  Long  pauses  in  the  aeration  oi 
the  blood.  In  the  asphyxia!  rise  of  pressure  in  a  i  urarized  dog  they 
art'  constantly  seen,  and  are  often  observed  when  the  circulation 
in  the  medulla  oblongata  is  in  any  way  interfered  with  (Fig.  116). 
In  addition  to  the  true  Traube-Hering  waves,  other  and  much  longer 
periodic  variations  in  the  blood-pressure  are  sometimes  noticed. 


hh|h| 


Fig.  i  i 6. 


-Traube-Hering  Waves  as  the  Blood-pressure  is  falling  during 
Occlusion  of  the  Cerebral  Arteries  in  a  Cat. 


If  spontaneous  respiration  is  going  on  their  long  sweeping  curves 
then  show  the  'ordinary  respiratory  waves  superposed  on  them. 

The  normal  respiratory  oscillations  in  the  veins,  as  might  be 
expected,  run  precisely  in  the  opposite  direction  to  those  in  the 
arteries,  and  so  do  the  Traube-Hering  curves.  The  increased 
flow  from  the  veins  to  the  thorax  during  inspiration  lowers  the 
pressure  in  the  jugular  vein,  while  it  increases  the  pressure  in 
the  carotid.  The  constriction  of  the  small  bloodvessels  to  which 
the  Traube-Hering  curves  are  due  increases  the  blood-pressure  in 
the  arteries,  because  it  increases  the  peripheral  resistance  to  the 
blood-flow  ;  in  the  veins  it  lowers  the  pressure,  because  less  blood 
gets  through  to  them.  Accordingly,  when  the  Traube-Hering 
curve  is  ascending  in  the  carotid,  it  is  descending  in  the  jugulai. 

The  respiratory  variations  in  the  volume  of  the  brain, 
which  are  so  striking  a  phenomenon  when  a  trephine  hole  is 
made  in  the  skull,  but  which  can  also  take  place,  thanks  to  the 


272  ./    MANl  AL  OF  PHYSIOLOG  J 

displacemenl  oJ  cerebro-spinaJ  fluid  (p.  i6o),  when  the  cranium 

is  intact,  have  by  some  been  attributed  to  interference  with  the 
venous  outflow  from  the  cranial  cavity  during  expiration,  and 
by  others  to  those  changes  in  the  arterial  pressure  whose  causes 
we  have  just  been  discussing.  The  truth  is  that  neither  factor 
is  exclusively  concerned.  The  question  turns  largely  upon  the 
time-relations  of  the  movements.  The  swelling  of  the  brain  is 
sometimes  synchronous  with  expiration,  and  the  shrinking  with 
inspiration.  Here  the  damming  back  of  the  blood  in  the  sinuses 
when  the  outflow  is  checked  by  the  expiratory  rise  of  pressure 
in  the  thoracic  veins  either  conspires  with  an  expiratory  rise  of 
arterial  pressure  or  is  more  than  enough  to  counterbalance  an 
expiratory  fall  of  pressure  in  the  cerebral  arteries  if  the  respiratory 
conditions  are  such  as  to  lead  to  an  expiratory  fall.  But  some- 
times the  dura  mater  bulges  into  the  trephine  hole  in  inspiration 
and  sinks  down  in  expiration.  Here  the  increase  in  the  volume 
of  the  brain  produced  by  the  increased  pressure  in  the  arteries 
and  capillaries  in  inspiration  is  more  than  sufficient  to  counter- 
balance the  quickened  escape  of  blood  from  the  cerebral  veins. 

The  effects  of  breathing  condensed  and  rarefied  air  are — 
(i)  mechanical,  shown  chiefly  by  changes  in  the  circulation,  in 
the  blood-pressure,  for  instance  ;  (2)  chemical. 

The  mechanical  effects  differ  according  to  whether  the  whole 
body,  or  only  the  respiratory  tract,  is  exposed  to  the  altered 
pressure.  When  the  trachea  of  an  animal  is  connected  with  a 
chamber  in  which  the  pressure  can  be  raised  or  lowered,  it  is 
found  that  at  first  the  arterial  blood-pressure  rises  as  the  pressure 
of  the  air  of  respiration  is  increased  above  that  of  the  atmo- 
sphere. But  a  maximum  is  soon  reached  ;  and  when  respira- 
tion begins  to  be  impeded,  the  pressure  falls  in  the  arteries  and 
increases  in  the  veins.  When  the  pressure  of  the  air  in  the 
chamber  is  diminished  a  little  below  that  of  the  atmosphere, 
there  is  a  slight  sinking  of  the  arterial  blood-pressure,  which 
rises  if  the  air-pressure  is  further  diminished. 

It  is  clear  that  any  change  of  the  air-pressnre  which  tends  to 
diminish  the  intrathoracic  pressure  will  favour  the  venous  return 
to  the  heart,  and  therefore,  if  the  exit  of  blood  from  the  thorax  is 
not  proportionally  impeded,  the  filling  of  the  arteries.  An  increase 
in  the  intra-alveolar  pressure  must  tend  on  the  whole  to  increase, 
and  a  diminution  in  it  to  lessen,  the  pressure  inside  the  thorax, 
which  always  remains  equal  to  the  intra-alveolar  pressure,  mums 
the  elastic  tension  of  the  lungs.  Breathing  compressed  air  should, 
therefore,  under  the  conditions  described,  be  upon  the  whole  un- 
favourable to  the  venous  return  to  the  heart  and  to  the  filling  of 
the  arteries,  and  the  arterial  pressure  should  fall  ;  while  breathing 
rarefied  air  should  have  the  opposite  effect.  But  a  very  great 
diminution  of  the  intrathoracic  pressure  is  not  necessarily  favourable 
to  the  circulation,  since  the  auricles  are  then  unable  to  contract 
perfectly. 


RESPIRATION 


273 


Fir,. 


117. — Pulse  Tracing  in  Valsalva's 
Experiment  (Rollett). 


Certain  chesl  diseases  have  been  treated  by  the  use  of  apparatus 
by  which  the  patient  is  made  to  breathe  either  compressed  or  rarefied 
,m  ;  or  to  inspire  air  at  one  pressure  and  to  expire  into  air  at  another 
pressure.  And  it  has,  upon  the  whole,  been  found,  in  agreement  with 
theory,  that  condensed  air  cannot  help  the  circulation  however  it  is 
applied,  but  always  hinders  it  ;  while  rarefied  air  aids  the  circulation 
both  in  inspiration  and  in  expiration.  But  the  increased  work  of 
the  inspiratory  muscles  may  counterbalance  the  advantage. 

Valsalva's  experiment,  which  is  performed  by  closing  the  mouth 
and  nostrils  after  a  pre- 
vious inspiration,  and 
then  forcibly  trying  to 
expire,  is  an  imitation 
of  breathing  into  com- 
pressed air.  The  intra- 
thoracic pressure  is  raised, 
it  may  be,  to  considerably 
more  than  that  of  the 
atmosphere  ;  the  venous 
return  to  the  heart  is 
impeded,  and  may  be  stopped  ;  and  the  pulse  curve  is  altered  in  such 
a  way  as  to  indicate  first  an  increase  and  then  a  decrease  of  the 
arterial  blood-pressure  (Fig.  117). 

Midler's  experiment,  which  should  be  bracketed  with  Valsalva's, 
consists  in  making,  after  a  previous  expiration,  a  strong  inspiratory 
effort  with  mouth  and  nostrils  closed.  Here  the  intrathoracic 
pressure  is  greatly  diminished,  more  blood  is  drawn  into  the  chest, 
and  upon  the  whole  effects  opposite  to  those  of  Valsalva's  experiment 

are  produced  (Fig.  118).  Neither         

experiment  is  quite  free  from 
danger.  In  both  the  dicrotism 
of  the  pulse  becomes  more 
marked. 

When    the   whole    body   is 
subjected  to  the  changed  pres-    p-  "*£££2^£*1— "■ 

sure,  as  in  a  balloon  or  on  a 

mountain,  in  a  diving-bell  or  a  caisson  used  in  building  the 
piers  of  a  bridge,  the  conditions  are  very  different.  For  the 
blood-pressure,  the  intrathoracic  pressure,  and  the  intra-alveolar 
pressure,  all  fall  together  when  the  pressure  of  the  atmosphere 
is  diminished,  and  all  rise  together  when  it  is  increased.  It  is 
possible  not  only  to  live,  but  to  do  hard  manual  labour,  at 
very  different  atmospheric  pressures. 

As  regards  the  chemical  effects  of  condensed  and  rarefied 
air,  Loewy  found  that  the  quantity  of  oxygen  absorbed  by  a 
man  breathing  air  in  the  pneumatic  cabinet  remained  constant 
at  all  pressures  between  about  two  atmospheres  and  half  an 
atmosphere.  At  440  mm.  of  mercury  dyspnoea  became  evident ; 
but  if  the  person  was  now  made  to  work,  the  dyspnoea  passed 
away,  and  did  not  again  manifest  itself  till  the  pressure  was 
reduced  to  410  mm.     There  are  towns  on  the  high  tablelands 

18 


274  A   MANUAL  OF  PHYSIOLOGY 

of  the  Andes,  and  in  the  Himalayas,  where  the  barometric  pres- 
sure is  not  more  than  16  to  20  inches,  yet  the  inhabitants  feel 
no  ill  effects.  And  in  the  caissons  of  the  Forth  Bridge  the  work- 
men were  engaged  in  severe  toil  under  a  maximum  pressure  of 
over  three  atmospheres,  while  in  the  caissons  of  the  St.  Louis 
Bridge  in  America  a  maximum  pressure  of  over  four  atmospheres 
(i.e.,  more  than  three  atmospheres  in  addition  to  the  ordinary 
air-pressure)  was  reached. 

Inside  the  caissons  the  men  sometimes  suffer  from  pain  and  noise 
in  the  ears,  due  to  excessive  pressure  on  the  external  surface  of  the 
tympanic  membrane.  If  the  pressure  in  the  tympanum  is  raised  by 
a  swallowing  movement,  which  opens  the  Eustachian  tube  and  per- 
mits air  to  enter  it,  the  symptoms  generally  disappear.  The  sudden- 
ness of  the  change  of  pressure  has  much  to  do  with  its  effects,  and  it 
is  found  that  the  men  are  most  liable  to  dangerous  symptoms  while 
passing  through  the  air-lock  from  the  caissons  to  the  external  air. 
It  may  be  concluded  from  experiments  on  animals,  that  some  of  the 
most  serious  of  these — the  localized  paralysis  usually  affecting  the 
legs  (paraplegia)  and  the  circulatory  disturbances — are  due  to  the 
formation  of  gaseous  emboli,  by  the  liberation  of  nitrogen  in  the 
blood  and  other  body-fluids  when  the  pressure  is  abruptly  reduced. 
And,  indeed,  it  is  found  that  the  symptoms  can  often  be  caused  to 
disappear,  both  in  animals  and  men.  by  promptly  subjecting  them 
again  to  compressed  air.  To  avoid  gas  embolism  on  decompression, 
the  shift  should  be  so  short  that  the  body-fluids  do  not  become  fully 
saturated  with  nitrogen,  and  the  decompression  should  be  slow. 
Even  with  a  rate  of  decompression  of  twenty  minutes  for  each  atmo- 
sphere of  excess  pressure  the  equilibrium  between  the  dissolved  and 
the  atmospheric  nitrogen  is  not  entirely  established  fifteen  minutes 
after  decompression. 

But  that  the  action  of  air  under  a  high  pressure  is  not  merely 
mechanical  follows  from  the  singular  fact  that  in  pure  oxygen 
at  a  pressure  of  4  to  5  atmospheres,  which  corresponds  to  air 
at  20  to  25  atmospheres,  convulsions  arc  often  produced  in  verte- 
brate animals,  while  exposure  to  6  to  25  atmospheres  of  oxygen 
causes  dyspnoea  and  coma,  usually  without  convulsions.  All 
animals,  so  far  as  investigated,  are  instantly  convulsed  and  killed 
under  a  pressure  of  50  atmospheres  of  oxygen  (Hill  and  Macleod). 
Even  seeds  and  vegetable  organisms  in  general  are  killed  in  a  short 
time  in  oxygen  at  3  to  5  atmospheres  ;  and  an  atmosphere  of  pure 
oxygen,  equal  to  five  atmospheres  of  air,  hinders  the  develop- 
ment of  eggs.  Lorrain  Smith  has  shown  that  in  small  birds  and 
mice  exposure  for  many  hours  to  a  pressure  of  between  1  and  2 
atmospheres  of  pure  oxygen  causes  pneumonia.  He  confirms  Bert's 
observations  on  the  acute  toxic  effects  produced  by  higher  pressures, 
and  supposes  that  in  the  production  of  caisson  disease  the  special 
action  of  the  oxygen  at  high  pressure  may  play  a  part  as  well  as 
the  rapid  decompression. 

When  the  air-pressure  is  diminished  below  a  certain  limit,  death 
takes  place  from  asphyxia,  more  or  less  gradual  according  to  the 
rate  at  which  the  pressure  is  reduced.  The  haemoglobin  cannot 
get  or  retain  enough  oxygen  to  enable  it  to  perform  its  respira- 


RESPIRATION  275 

torv  function;  its  dissocial  ion  tension  is  no  longer  balanced  by  an 
equal  or  greater  partial  pressure  of  oxygen  in  the  air.     The  ten 
sionof  carbon  dioxide  in  the  blood  is  also  lessened,  owing  to  the 
dyspnoea  and  the  consequent  increase  of  pulmonary  ventilation. 

To  such  changes,  as  well  as  to  the  cold,  some  of  the  deaths  in 
high   balloon   ascents   must   be   attributed.      Messrs.    Glaisher   and 
Coxuvll  supposed  that  they  reached  the  height  of  37,000  feet  ;  the 
former  became  unconscious   at    29,000  feet  (8,800  metres),  at  which 
height  the  amount  of  oxygen  in  the  arterial  blood  would  probably 
not  exceed  10  volumes  per  cent.,  but  recovered  during  the  descent. 
The  symptoms  of  the    '  mountain  sickness  '   so  familiar  to  Alpine 
climbers    (nausea,    headache,    and    marked    depression),    the    undue 
hyperpncea  produced  by  muscular  exertion,  and  the  sleep  disturbed 
by  irregular  breathing,  are  also  mainly  due  to  deficiency  of  oxygen 
in  the  blood.     The  most  rational  prophylaxis  is  to  leave  the  high 
peaks  severely  alone.     But  for  the  enthusiasts  who  cannot  do  this 
a    portable   apparatus   for    generating    oxygen    has   been   devised. 
Experiments   in   the    pneumatic    cabinet    indicate    that  the  hyper- 
pncea is  due  to  the    indirect    action    of    want   of   oxygen   already 
referred  to  in  discussing  the  normal  regulation  of  respiration  (p.  230) 
— that   is,    to    the   formation,    in    consequence    of    the   insufficient 
oxygen  supply,  of  lactic  acid  or  other  substances  which  have  the 
same  influence  as  carbon  dioxide  on  the  respiratory  centre — -so  that 
less  carbon  dioxide  is  required  to  excite  the  centre.      Although  the 
hyperpncea  leads  to  a  diminution  in  the  partial  pressure  of  carbon 
dioxide  in  the  pulmonary  alveoli,  there  is  no  evidence  that  lack  of 
carbon  dioxide  ('  acapnia  ')  is  the  primary  cause  of  mountain  sick- 
ness (Haldane).     It  must  be  remembered,  however,  that    here  the 
influence  of  the  low  barometric  pressure  is  complicated  by  other  con- 
ditions.    For  example,  while  in  the  pneumatic  cabinet,  as  already 
stated,  diminution  of  the  pressure  does  not  affect  the  oxygen  con- 
sumption, it  is  relatively  much  greater  on  the  high  mountain  levels 
both  during  rest  and  during  work  than  on  the  plains.     This  is  not 
the  case  in  balloon  ascents.     And  evidence  has  been  brought  for- 
ward that  changes  in  the  mechanics  as  well  as  in  the  chemistry  of 
respiration  are  concerned  (the  breathing,  for  instance,  taking  on  a 
periodic  character,  with  some  approach  to  the  Cheyne-Stokes  type 
[p.  238]),  and  that  there  is  something  not  connected  with  the  want 
of  oxygen  which  diminishes  the  capacity  for  muscular  work.     This 
'  something  '  is  perhaps  a  peculiar  excitation  of  the  nervous  system 
in  the  fierce  light  of  those  high  levels,  which  acts  not  only  on  the 
retina,  but  on  the  skin,  and  may  even  affect  the  distribution  of  the 
blood.     It  is  said  that  a  so-called  light  bath,  as  used  in  the  treat- 
ment  of  certain  diseases,   may  increase  the  quantity  of  blood  in 
rabbits  by  25  per  cent,  in  four  hours.    The  shorter  wave-lengths  which 
are  relatively  more  intense  in  the  mountain  light  are  most  effective. 
Cutaneous  Respiration. — It  has  already  been  remarked  that  a  frog 
survives  the  loss  of  its  lungs  for  some  time,  respiration  going  on 
through  the  skin.     Indeed,  it  has  been  calculated  that  in  the  intact 
frog,  under  ordinary  conditions,  as  much  as  three-quarters  of  the 
total  gaseous  exchange  may  be  cutaneous.     Two  frogs  were  seen 
to  live  thirty-three  days,  and  one  even  forty  days,  after  excision 
of  the  lungs.     The  effect  of  exclusion  of  the  pulmonary  respiration 
on  the  gaseous  exchange  depends  on  the  previous  intensity  of  the 
metabolism.     If  this  is  high  the  gaseous  exchange  sinks  markedly  ; 
if  it  is  low  there  is  scarcely  any  alteration.       At  their  maximum 

18—2 


876  A   MANUAL  OF  PHYSIOLOGY 

efficiency  the  frog's  lungs  are  capable  of  sustaining  a  much  greater 
exchange  than  the  skin.  Besides  this  quantitative,  there  is  a 
qualitative  difference,  the  carbon  dioxide  passing  more  easily  through 
the  skin  than  I  tie  0x5  gen,  so  that  the  respiratory  quotient  is  increased 
by  elimination  of  the  lungs.  In  mammals  the  structure  of  the  skin 
is  different,  and  respiration  can  only  go  on  through  it  to  a  very 
slight  extent.  The  amount  of  carbon  dioxide  excreted  in  man, 
although  only  about  4  grin,  or  2  litres  in  twenty-four  hours,  is  much 
greater  Hum  corresponds  to  the  quantity  of  oxygen  absorbed  through 
the  skin.  It  has  been  asserted,  and  no  doubt  with  justice,  that 
some  at  least  of  the  carbon  dioxide  given  off  is  due  to  putrefactive 
processes  taking  place  on  the  surface  of  the  body.  Such  procc 
as  has  already  been  pointed  out,  seem  also  responsible  in  part  for 
the  heavy  odour  of  a  '  close  '  room.  For  no  harmful  products 
appear  to  be  exhaled  from  the  skin  when  it  is  properly  cleansed. 
In  spite  of  the  romantic  statements  to  the  contrary  in  ancient  and 
modern  books  (for  instance,  the  story  of  the  child  that  was  gilded 
to  play  the  part  of  an  angel  at  the  coronation  of  a  medieval  pope, 
but  died  before  the  cercmonv  began),  the  whole  of  the  human  skin 
may  be  coated  with  an  impermeable  varnish  without  any  ill  effects. 
The  entire  surface  of  the  body  of  a  patient  with  cutaneous  disease 
was  covered  with  tar,  and  kept  covered  for  ten  days.  There  was 
not  the  least  disturbance  of  any  normal  function.  The  serious  effects 
of  varnishing  the  skin  in  animals  are  due,  not  to  retention  of  poisonous 
substances,  but  to  increased  heat  loss.  Varnishing  is  not  so  rapidly 
harmful  in  large  animals  like  dogs  as  in  rabbits,  which  have  a 
relatively  great  surface  and  a  delicate  skin.  The  danger  of  wide- 
spread superficial  burns  is  well  known.  But  it  is  not  due  to 
diminished  excretion  by  the  skin,  for  death  occurs  when  large 
cutaneous  areas  remain  uninjured.  The  patient  nearly  always  dies 
when  a  quarter  of  the  whole  skin  is  burnt  ;  yet  the  remaining  three- 
quarters  may  surely  be  considered  capable,  from  all  analogy,  of 
making  up  the  loss  by  increased  activity.  One  kidney  is  enough  to 
eliminate  the  products  of  the  nitrogenous  metabolism  of  the  whole 
body.  It  is  difficult  to  see  why  the  excretion  of  the  trifling  amount 
of  solid  matter  in  the  perspiration  should  be  interfered  with  by  the 
loss  of  25  per  cent,  of  the  sweat-glands.  The  real  explanation  of 
the  serious  effects  of  extensive  superficial  burns  is  perhaps  the  ex- 
cessive irritation  of  the  sensory  nerves,  which  may  lead  to  changes 
in  the  nervous  centres,  or  reflexly  in  other  organs,  or  the  chemical 
changes  in  the  damaged  tissue,  for  example,  in  the  blood-corpuscles, 
or  the  transudation  of  lymph  at  the  injured  part,  and  consequent 
increase  in  the  concentration  of  the  blood. 

Voice  and  Speech. 

Voice. — Sounds  of  various  kinds  are  frequently  produced  by 
the  movements  of  animals  as  a  whole,  or  of  individual  organs. 
The  muscular  sound,  the  sounds  of  the  heart  and  of  respiration, 
we  have  already  had  to  speak  of.  Such  sounds  may  be  considei  ed 
as  purely  accidental  as  the  footfall  of  a  man  or  the  buzzing  of  a 
fly.  The  wings  of  an  insect  beat  the  air,  not  to  cause  sound,  but 
to  produce  motion  ;  the  respiratory  murmur  is  a  mere  indication 
that  air  is  finding  its  way  into  the  lungs,  it  is  in  no  way  related 


RESPIRATION  277 

to  the  oxidation  of  the  blood  in  the  pulmonary  capillaries.  Bui 
in  many  of  the  highei  animals  mechanisms  exist  which  are 
specially  devoted  to  the  utterance  of  sounds  as  their  prime  and 
proper  end.  In  man  the  voice-producing  mechanism  consists  of 
a  triple  series  of  tubes  and  chambers  :  (1)  The  trachea,  through 
which  a  blast  of  air  is  blown  ;  (2)  the  larynx,  with  the  vocal 
cords,  by  the  vibrations  of  which  sound-waves  are  set  up  ;  and 
(3)  the  upper  resonance  chambers,  the  pharynx,  mouth,  and  nasal 
cavities,  in  which  the  sounds  produced  in  the  larynx  are  modified 
and  intensified,  and  in  which  independent  notes  and  noises  arise. 

The  larynx  is  a  cartilaginous  box,  across  which  are  stretched, 
from  front  to  back,  two  thin  and  sharp-edged  membranes,  the 
(tine)  vocal  cords.  In  front  the  cords  are  attached  to  the 
thvroid  cartilage,  one  a  little  to  each  side  of  the  middle  line  ; 
behind  they  are  connected  to  the  vocal  or  anterior  processes  of 
the  pyramidal  arytenoid  cartilages.  The  thyroid  and  the  two 
arytenoids  are  mounted  upon  a  cartilaginous  ring,  the  cricoid. 
The  arytenoids  can  rotate  on  the  cricoid  about  a  vertical  axis, 
while  the  cricoid  can  rotate  on  the  thyroid  cartilage  around  a 
transverse  horizontal  axis.  The  cricoid  can  thus  be  raised  by 
the  contraction  of  the  crico-thyroid  muscle,  and  the  vocal  cords 
stretched.  By  the  pull  of  the  posterior  crico-arytenoid  muscles, 
attached  to  the  external  or  muscular  processes  of  the  arytenoid 
cartilages,  the  vocal  processes  are  rotated  outwards,  the  cords 
separated  from  each  other  or  abducted,  and  the  chink  between 
them,  the  rima  glottidis,  widened.  When  the  vocal  processes 
are  approximated  by  contraction  of  the  lateral  crico-arytenoid 
muscles  and  the  consequent  forward  movement  of  the  muscular 
processes,  the  vocal  cords  are  brought  closer  together,  or  adducted, 
and  the  rima  is  narrowed.  The  transverse  or  posterior  arytenoid 
muscle,  which  connects  the  two  arytenoid  cartilages  behind,  also 
helps,  by  its  contraction,  to  narrow  the  glottis  by  shifting  the 
cartilages  on  their  articular  surfaces  somewhat  nearer  the  middle 
line.  Running  in  each  vocal  cord,  and,  in  fact,  incorporated  with 
its  elastic  tissue,  is  a  muscle,  the  thyro-arytenoid,  the  external 
portion  of  which  may  to  some  extent  cause  inward  rotation  of 
the  vocal  processes  and.  adduction  of  the  cords  ;  but  the  main 
function,  at  least  of  its  inner  part,  is  to  alter  the  tension  of  the 
cords.  The  diagrams  in  Figs.  119  and  120  illustrate  the  action 
of  the  abductors  and  adductors  of  the  vocal  cords. 

The  crico-thyroid  muscle  and  the  deflectors  of  the  epiglottis 
are  supplied  by  the  superior  laryngeal  branch  of  the  vagus, 
which  also  contains  the  sensory  fibres  for  the  mucous  membrane 
of  the  larynx  above  the  vocal  cords.  In  the  dog  and  rabbit 
motor  fibres  also  reach  the  crico-thyroid  by  the  so-called  middle 
laryngeal  nerve  which  arises  from  the  superior  pharyngeal  Dranch 


278 


A    1/  INI    1/    OF   PHYSIOLOG  V 


"I  the  vagus.  All  the  other  intrinsic  muscles  arc  supplied  by  the 
recurrent  Laryngeal  branch  of  the  vagus.  It  receives  these  motor 
fibres  from  the  spinal  accessory,  and  supplies  sensorj  fibres  to 
the  mucous  membrane  of  the  larynx  below  the  vocal  cords  and 
to  the  trachea. 

The  voice  is  produced,  like  the  sounds  of  a  reed  instrument, 
by  the  rhythmical  interruption  of  an  expiratory  blast  of  air  by 
the  vibrating  vocal  cords.  When  a  bell  is  struck,  vibrations  are 
up  in  tlic  metal,  which  are  communicated  to  the  air.  It 
is  not  the  same  with  the  vibrations  of  the  vocal  cords  ;  it  they 
were  plucked  or  struck,  they  would  only  produce  a  treble  note. 
The  air  in  the  month,   pharynx,  larynx,  trachea,  and  lungs  is 


Fig.   hq. — Diagrammatic  Fig.  120. — Direction  of  Pull 

Horizontal       Section       of  of     the      Lateral     Crico- 

Larynx    to    show    the    I'i-  arytenoids,  which    adduct 

rection     of     Pull    of    the  the  Vocal  Cords. 

Posterior  Crico-arytenoid  Dotted   lines  show   position  in 

MrsCI.ES,         WHICH         ABDUCT  adduction. 

the  Vocal  Cords. 

Dotted    lines   show    position    in 
abduction. 

the  real  sounding  body  ;  a  pulse  of  alternate  rarefaction  and  con- 
densation is  set  up  in  it  by  the  interference,  at  regular  intervals, 
of  the  vocal  cords  with  the  expiratory  blast.  Forced  abruptly 
from  their  position  of  equilibrium  as  the  blast  begins,  they  almost 
immediately  regain  and  pass  below  it,  in  virtue  of  their  elasticity, 
and  continue  to  vibrate  as  long  as  the  stream  of  air  continues  to 
issue  in  sufficient  strength.  Not  only  do  they  vibrate  up  and 
down,  but  also  towards  and  away  from  the  middle  line,  so  that, 
at  least  in  the  chest  voice,  they  come  into  contact  with  each  other 
at  each  swing.  The  sound-waves  thus  set  up  spread  out  on 
every  side,  impinge  on  the  tympanic  membrane,  set  it  quivering 
in  response,  and  give  rise  to  the  sensation  of  sound. 

We  may  say,  in  a  word,  that  the  whole  exquisite  mechanism 
of  cartilages.  Ligaments,  and  muscles,  has  for  its  object  the  pro- 
duction of  a  sufficient  pressure  in  the  blast  of  air  driven  through 
the  windpipe  by  an  expiratory  act,  and  of  a  suitable  tension  in 


RESPIRATION  270 

the  vibrating  cords.  An  approximation  oi  the  cords,  a  narrowing 
oi  the  glottis,  is  essentia]  to  the  production  of  voice  ;  with  a 
widely-opened  glottis  the  air  escapes  too  easily,  and  the  necessary 
pressure  cannot  be  attained.    The  pressure  in  the  windpipe  was 

found  in  a  woman  with  a  tracheal  fistula  to  be  about  12  mm.  of 
mercury  for  a  note  of  medium  height,  about  15  mm.  for  a  high 
note,  and  about  72  mm.  for  the  highest  possible  note.  The 
period  of  vibration  of  structures  like  the  vocal  cords  depends  on 
their  length,  thickness,  density  and  tension  ;  the  shorter,  thinner, 
more  tense  and  less  dense  a  stretched  string  is,  the  greater  is 
the  vibration  frequency,  the  higher  the  note.  In  the  child 
the  cords  are  short  (6  to  8  mm.),  in  woman  longer  (10  to  12  mm. 
when  slack,  13  to  15  mm.  when  stretched),  in  man  longest  of 
all  (14  to  18  mm.  in  the  relaxed,  and  18  to  22  mm.  in  the  stretched 
position)  ;  and  the  lower  limit  of  the  voice  is  fixed  by  the 
maximum  length  of  the  relaxed  cords.  A  boy  or  a  woman 
cannot  utter  a  deep  bass  note,  because  their  vocal  cords  are 
relatively  short,  and  do  not  vibrate  with  sufficient  slowness. 
It  is  true  that  by  the  action  of  the  crico-thyroid  muscle  the 
cords  can  be  lengthened,  and  that  the  maximum  length  in  a 
woman  approaches  or  exceeds  the  minimum  length  in  a  man. 
But  the  lengthening  of  the  vocal  cords  in  one  and  the  same 
individual  is  always  accompanied  by  other  changes — increase 
of  tension,  decrease  of  breadth  and  thickness — which  tell  upon 
the  vibration  frequency  in  the  opposite  way,  and  more  than 
compensate  the  effect  of  the  increase  of  length,  so  that  for  high 
notes  the  cords  are  longer  than  for  low.  The  contraction  of  the 
thyro-arytenoid  muscle  is  a  more  influential  factor  in  altering  the 
tension  of  the  cords  than  the  contraction  of  the  crico-thyroid. 
It  is  probable  that  when  the  highest  notes  are  uttered,  only  the 
anterior  portions  of  the  cords  are  free  to  vibrate,  their  posterior 
portions  being  damped  by  the  approximation  of  the  vocal  pro- 
cesses of  the  arytenoid  cartilages  by  the  contraction  of  the  lateral 
crico-arytenoid  and  transverse  arytenoid  muscles.  The  range 
of  an  ordinary  voice  is  2  octaves  ;  by  training  2\  octaves  can  be 
reached  ;  but  in  exceptional  cases  a  range  of  3,  and  even  3 \, 
octaves  (as  in  the  celebrated  singer  Catalani)  has  been  known. 

The  development  of  the  voice  in  children  is  of  great  interest.  At 
the  age  of  six  years  the  boy's  voice  has  a  rather  narrower  range  than 
the  girl's  in  both  directions.  The  boy's  voice  reaches  its  full  height 
in  the  twelfth  and  its  full  depth  in  the  thirteenth  year,  when  the 
range  is  almost  3  octaves,  its  upper  limit  being  a  semitone  higher 
than  the  girl's,  but  its  lower  limit  a  whole  tone  deeper.  When  the 
voice  '  breaks  '  in  boys  at  the  age  of  puberty  it  falls  about  an  octave. 
The  control  of  the  vocal  organs  becomes  so  incomplete  that  only  in 
one-fourth  of  the  cases  can  notes  of  sufficient  steadiness  to  be  used 
in  music  be  produced.  The  vocal  CDrds,  as  may  be  seen  with  the 
laryngoscope,  are  frequently,  though  not  always,  congested. 


28o  A   MANUAL  OF  PHYSIOLOGY 

I  he  pitch  of  a  note,  while  it  depends  chiefly,  as  has  bi  en  said, 
on  the  tension  of  the  vocal  cords,  rises  and  falls  somewhat  with 
the  strength  of  the  expiratory  blast  ;  the  highest  notes  are  only 
reached  with  a  strong  expiratory  effort.  The  uitoisity  of  all 
vocal  sounds  is  determined  by  the  strength  of  the  blast,  for  the 
amplitude  of  vibration  of  the  cords  is  proportional  to  this. 
Besides  pitch  and  intensity,  the  ear  can  still  distinguish  the 
quality  or  iimhre  of  sounds  ;  and  the  explanation  is  as  follows  : 
Two  simple  tones  of  the  same  pitch  and  intensity,  that  is,  the 
sounds  caused  by  two  series  of  air-waves  of  the  same  period 
and  amplitude — of  the  same  frequency  and  height,  to  use  less 
technical  terms— would  appear  absolutely  identical  to  the  sense 
of  hearing  ;  just  as  the  aerial  disturbances  on  which  they  depend 
would  be  absolutely  alike  to  any  physical  test  that  could  be 
appl  ud.  But  no  musical  instrument  ever  produces  sound-waves  of 
one  definite  period,  and  one  only  ;  and  the  same  is  true  of  the 
voice.  When  a  stretched  string  is  displaced  in  any  way  from 
its  position  of  rest,  it  is  set  into  vibration  ;  and  not  only  does 
the  string  vibrate  as  a  whole,  but  portions  of  it  vibrate  inde- 
pendently and  give  out  separate  tones.  The  tone  corresponding 
to  the  vibration  period  of  the  whole  string  is  the  lowest  of  all. 
It  is  also  the  loudest,  for  it  is  more  difficult  to  set  up  quick  than 
slow  vibrations.  The  ear  therefore  picks  it  out  from  all  the 
rest  ;  and  the  pitch  of  the  compound  note  is  taken  to  be  the  pitch 
of  this,  its  fundamental  tone.  The  others  are  called  partial  or 
overtones,  or  harmonics  of  the  fundamental  tone,  their  vibration 
frequency  being  twice,  three  times,  four  times,  etc.,  that  of  the 
latter.  Now,  the  fundamental  tone  of  a  compound  note  or 
clang  produced  by  two  musical  instruments  may  be  the  same, 
while  the  number,  period,  and  intensity  of  the  harmonics  are 
different  ;  and  this  difference  the  ear  recognises  as  a  difference 
of  timbre  or  quality.  The  timbre  of  the  voice  depends  for  tin 
most  part  on  partial  tones  produced  or  intensified  in  the  upper 
resonance  chambers. 

A  great  deal  of  our  knowledge  as  to  the  mode  and  mechanism 
.  >t  the  production  of  voice  has  been  acquired  by  means  of  the 
laryngoscope  (Fig.  121).  This  consists  of  a  small  plane  mirror 
mounted  on  a  handle,  which  is  held  at  the  back  of  the  mouth  in 
such  a  position  that  a  beam  of  light,  reflected  from  a  larger 
concave  mirror  fastened  on  the  forehead  of  the  observer,  is 
thrown  into  the  larynx  of  the  patient.  The  observer  looks 
through  a  hole  in  the  centre  of  the  large  mirror  :  and  an  image 
of  the  interior  of  the  larynx  is  seen  in  the  small  mirror,  in  which 
the  parts  that  are  anterior  appear  as  posterior,  the  arytenoid 
cartilages  in  front,  the  thyroid  behind,  and  the  vocal  cords 
stretching    between.     The   small   mirror    is    warmed    to    body- 


h'i:s/'l  RATION 


•st 


temperature  before  being  introduced,  so  as  to  prevent  the 
condensation  of  moist  me  on  it.  The  tendency  to  retch  which 
is  caused  by  contact  of  the  instrument  with  the  soft  palate  may  be 
removed  or  lessened  by  the  application  of  a  solution  of  cocaine. 
Examined  with  the  laryngoscope  during  quiet  respiration, 
the  glottis  is  seen  to  be  moderately,  though  not  widely,  open, 
and  the  vocal  cords  almost  motionless.  Although  the  portion 
between  the  arytenoid  cartilages  has  received  the  name  of  glottis 
respiratoria,  in  contradistinction  to  the  glottis  vocalis  between 
the  vocal  cords,  the  rima  in  its  whole  extent  from  front  to  back 
is  really  concerned  in  the  respiratory  act.  In  dee]-)  expiration 
the  vocal  cords  come  nearer  to  the  middle  line,  and  the  glottis 


Fie.  121. — Diagram  of  Laryngoscope. 


is  narrowed  ;  in  deep  inspiration  they  are  widely  separated,  and 
the  rings  of  the  trachea,  and  even  its  bifurcation,  may  be  dis- 
closed to  view.  When  a  sound  is  produced — a  note  sung,  for 
example — the  cords  are  approximated  (Figs.  122  and  123)  ;  and 
with  a  high  note  more  than  with  a  low. 

The  essential  difference  between  the  production  of  notes  in  the 
lower  register,  or  chest  voice,  and  in  the  higher  register,  or  falsetto, 
has  been  much  debated.  The  lowest  notes  which  can  be  uttered  by 
any  grven  voice  are  chest  notes,  the  highest  are  falsetto  notes  :  but 
there  is  a  debatable  land  common  to  both  registers,  and  medium 
notes  can  be  sung  either  from  the  chest  or  from  the  head.  Chest 
notes  impart  a  vibration  or  fremitus  to  the  thoracic  walls,  from  the 
resonance  of  the  lower  air-chambers,  the  trachea  and  bronchi  ;  and 
this  can  be  distinctly  felt  by  the  hand.  In  head  notes  or  falsetto 
the  resonance  is  chieflv  in  the  upper  cavities,  the  pharynx,  mouth. 


282 


A    MANI'AI    OF   I'JIYSIOIOCY 


.mkI  nose.     As  to  the  me<  hani<  al  i  onditions  in  the  larynx,  there  is  a 
pretty  general  agreement  thai  during  the  produi  tion  oJ  falsetto  n< 
the  vocal  ( ords  are  less  closely  approximated  tha  i  in  the  sounding  <>i 
chest  notes.     The  escape  of  air  is  consequently  more  rapid  in  the 

head  voice,  and  a  falsetto  note  cannot  be  maintained  so  long  as  a 
note  sung  from  the  chest.  But  it  is  only  the  anterior  part  of  the 
rim. i  glottidis  that  is  wider  in  the  falsetto  voice;  the  whole  of  the 
glottis  respiratoria,  and  even  the  posterior  portion  of  the  glottis 
voi. >lis.  are  closed  during  the  emission  of  falsetto  notes. 

( )ertel  has  stated,  and  the  statement  has  been  confirmed  by  others, 
that  the  free  edge  of  the  vocal  cord  alone  vibrates  in  the  falsetto 
voice,  one  or  more  nodes  or  motionless  lines  parallel  to  the  edge 
being  formed  by  the  contraction  of  the  internal  part  of  the  thyro- 
arytenoid muscle,  which  thus  acts  like  a  stop  upon  the  <  ord. 

Approximation  of  the  vocal  cords  may  take  place  in  certain 
acts  unconnected  with  the  production  of  voice.     Thus,  a  cough, 


Fig.  122. — Position  of  the 
Glottis  preliminary  to  the 
Utterance  of  Sound. 

rs,  false  vocal  cord  ;  ri,  true 
vocal  cord  ;  ar,  arytenoid  carti- 
lage ;  b,  pad  of  the  epiglottis. 


Fig.  123. —  Position  of  Open  Glottis. 

/.  tongue  ;  e,  epiglottis  ;  ae,  ary- 
epiglottidean  fold ;  c,  cartilage  of 
Wrisberg ;  ar,  arytenoid  cartilage ; 
0,  glottis  ;  v,  ventricle  of  Morgagni  ; 
ti,  true  vocal  cord  ;  ts,  false  vocal  cord. 


as  has  already  been  mentioned,  is  initiated  by  closure  of  the 
glottis.  During  a  strong  muscular  effort,  too,  the  chink  of  the 
glottis  is  obliterated,  and  respiration  and  phonation  both 
arrested.  The  object  of  this  is  to  fix  the  thorax,  and  so  afford 
points  of  support  for  the  action  of  the  muscles  of  the  limbs  and 
abdomen.  But  considerable  efforts  can  be  made  even  by 
persons  with  a  tracheal  fistula. 

Speech. — Ordinary  speech  is  articulated  voice — voice  shaped 
and  fashioned  by  the  resonance  of  the  upper  air-cavities,  and 
jointed  together  by  the  sounds  or  noises  to  which  the  varying 
form  of  these  cavities  gives  rise.  Here  we  come  upon  the 
fundamental  distinction  between  vowels  and  consonants.  Vowels 
are  musical  sounds  ;  consonants  are  not  musical  sounds,  but 
noises — that  is  to  say,  they  are  due  to  irregular  vibrations,  not 
to  regularly  recurring  waves,  the  frequency  oi  which  the  ear  can 


RESP1RA  I  ION 

appreciate  as  a  definite  pitch.  This  difference  of  character 
coi  responds  to  a  difference  oi  origin  :  the  vowels  are  produ<  ed  by 
the  vibrations  of  the  vocal  cords  ;  the  consonants  are  due  to  the 
rushing  of  the  expiratory  blast  through  certain  constricted 
port  ions  of  the  buccal  chamber,  where  a  kind  of  temporary 
glottis  is  established  by  the  approximation  of  its  walls.  One  of 
these  '  positions  of  articulation  '  is  the  orifice  of  the  lips;  the 
consonants  formed  there,  such  as  />  and  b,  are  called  labials. 
A  second  articulation  position  is  between  the  anterior  part  of 
the  tongue  and  the  teeth  and  hard  palate.  Here  are  formed 
the  dentals,  /,  </,  etc.  The  ordinary  English  r,  and  the  r  of  the 
Berwickshire  and  East  Prussian  '  burr,'  also  arise  in  this  position 
through  a  vibratory  motion  of  the  point  of  the  tongue.  The 
third  position  of  articulation  is  the  narrow  strait  formed  between 
the  posterior  portion  of  the  arched  tongue  and  the  soft  palate. 
To  the  consonants  arising  here  the  name  of  gutturals  has  been 
given.  They  include  k.  g,  the  Scottish  ch,  and  the  uvular  German 
r.  The  latter  is  produced  by  a  vibration  of  the  uvula.  The 
aspirated  //  is  a  noise  set  up  by  the  air  rushing  through  a  moder- 
ately wide  glottis,  and  some  have  therefore  included  the  glottis 
as  a  fourth  articulation  position  for  consonants.  Certain  sounds 
like  n,  m,  and  ng,  when  final  (as  in  pen,  dam,  ring),  although 
produced  at  the  glottis,  are  intensified  by  the  resonance  of  the 
air  in  the  nose  and  pharynx,  and  are  sometimes  spoken  of  as 
nasal  consonants. 

As  we  have  said,  the  vowels  are  produced  by  vibrations  of  the 
vocal  cords,  but  to  what  they  owe  their  special  timbre  or  quality 
has  been  much  discussed.  According  to  the  view  with  which 
Helmholtz's  name  is  particularly  connected  this  is  due  to  the 
reinforcement  of  certain  overtones  by  the  resonating  cavities,  the 
shape  and  fundamental  tone  of  which  are  different  for  each  vowel. 

When  a  vowel  is  whispered,  the  mouth  assumes  a  characteristic 
shape,  and  emits  the  fundamental  tone  proper  to  the  form  and  size 
of  the  particular  '  vowel-cavity,'  not  as  a  reinforcement  of  a  tone 
set  up  by  the  vibrations  of  the  vocal  cords,  but  in  response  to  the 
rush  of  air  through  the  cavity  ;  just  as  a  bottle  of  given  shape  and 
size  gives  out  a  definite  note  when  the  air  which  it  contains  is  set 
in  vibration,  by  blowing  across  its  mouth.  A  whisper,  in  fact,  is 
speech  without  voice  ;  the  larynx  takes  scarcely  any  part  in  the 
production  of  the  sound  ;  the  vocal  cords  remain  apart  and  com- 
paratively slack  ;  and  the  expiratory  blast  rushes  through  without 
setting  them  in  vibration. 

The  fundamental  tone  of  the  '  vowel-cavity  '  may  be  found  for 
each  vowel  by  placing  the  mouth  in  the  position  necessary  for 
uttering  it,  then  bringing  tuning-forks  of  different  period  in  front 
of  it,  and  noting  which  of  them  sets  up  svmpathetic  resonance  in 
the  air  of  the  mouth,  and  so  causes  its  sound  to  be  intensified. 
The  fundamental  tone  is  lowest  for  u  (as  in  lute).      Next  comes  o  ; 


-M 


A   MANUAL  or  PHYSIOLOGY 


then  a  (as  in  path)  :  then  a  (as  in  fane)  ;  then  * :  while  e  is  higbesl 
11.  A  simple  illustration  of  this  may  !><■  found  in  the  fact  that 
when  the  vowels  are  whispered  in  the  order  given,  the  pitch  rises. 
When  u  or  o  is  sounded,  the  buccal  cavitv  has  the  form  of  a  wide- 
bellied  flask,  with  a  shorl  and  narrow  neck  for  it.  a  still  shorter  but 
wider  neck  for  o.  For  e  the  tongue  is  raised  and  almost  in  contact 
with  the  palate,  and  the  cavity  of  the  mouth  is  shaped  like  i  fl  isk 
with  a  long  narrow  neck  and  a  very  short  belly.  For  i  the  shape  is 
similar,  but  the  neck  is  not  so  narrow.  For  a  (as  in  path)  the  vowel- 
cavity  is  intermediate  in  form  between  that  of  u  and  e,  being  roughly 
funnel-shaped,  and  the  mouth  is  rati  er  widely  opened.  For  u 
the  resonating  cavity  is  made  as  long  as  possible,  the  larynx  being 
depressed  and  the  lips  protruded  ;  for  e  the  resonating  cavitv  is  at  its 
shortest,  the  larynx  being  raised  as  much  as  possible  and  the  lips 
retracted  (Figs.   124  to  126). 

.V  (  ording  to  Helmholtz,  all  that  the  resonating  cavity  does  is  to 
strengthen  certain  of  the  partials  or  overtones  of  the  laryngeal  note. 
If  this  is  true,  the  partials  which  give  a  vowel-sound  the  timbre  by 


Fig.   124. 


Fig.  125. 


Fig.  126. 


which  we  recognise  it  as  different  from  other  vowel-sounds  cannot 
preserve  the  same  numerical  relation  to  the  fundament. d  tone  when 
the  pitch  of  the  latter  is  altered.  Suppose,  for  example,  that  a 
given  vowel  is  sounded  with  a  pitch  corresponding  to  100  vibra- 
tions a  second,  and  that  the  partial  which  is  particularly  strengthened 
by  the  resonance  of  the  mouth  cavity  is  the  fifth  overtone,  corre- 
sponding to  600  vibrations.  Then  when  the  same  vowel  is  sounded 
with  a  pitch  of  20c)  vibrations  the  reinforced  partial  which  will  now 
give  the  quality  to  the  sound  will  still  correspond  to  600  vibrations 
a  second,  since  this  is  the  rate  which  most  easily  elicits  the  resonance, 
but  it  will  not  now  be  the  fifth  but  the  second  overtone. 

Universally  accepted  tor  a  time,  the  Helmholtz  theory  has  been  in 
recent  years  assailed,  especially  by  Hermann,  who  bases  his  criticism 
on  microscopic  examination  of  curves  obtained  by  the  Edison  phono- 
graph, and  on  reproductions  of  such  records  obtained  by  photo- 
graphing on  a  moving  drum  covered  with  sensitive  paper  a  beam 
of  light  reflected  from  a  small  mirror  attached  to  a  system  of  levers 
whose  movements  fellow  the  curves  faithfully  and  greatly  magnify 
them.      Hermann  has  come  to  the  conclusion  that  the  mouth  does 


RESPIRATION  285 

not  act  as  a  mere  resonator,  but  that  for  each  vowel,  in  addition  to 
the  fundamental  note  due  to  the  vibration  of  the  vocal  coil 
pitch  ot  which  is,  of  course,  variable,  one  or,  it  may  lie,  two  0 
notes  (formants,  as  he  calls  them),  not  neccssarilv  hirmonics  of  the 
1  iryngeal  note,  but  separated  from  it  by  a  constant  or  nearly  con- 
stant musical  interval,  are  directly  produced  by  the  passage  of  the 
regularly  interrupted  expiratory  blast  through  the  mouth,  the  air 
contained  in  that  cavity  being  for  an  instant  set  into  vibration  at 
each  interruption.  On  this  view  it  is  the  musical  effect  produced 
by  the  oscillation  or  continual  recurrence,  in  short  series,  of  thesi 
vibrations  which  uives  the  vowels  their  quality.  The  fact  that  it 
is  by  no  means  difficult  to  sing  (with  the  larynx)  and  whistle  (with 
the  mouth)  at  the  same  time,  shows  the  possibility  of  Hermann's 
view,  that  a  fixed  tone  can  be  generated  in  the  mouth  by  the  inter 
mittent  stream  of  air  issuing  from  between  the  vibrating  vocal  cords, 
just  as  a  tone  is  generated  in  a  pipe  bv  blowing  into  or  over  it,  and 
his  records  do  show  continually  recurring  groups  of  vibrations  as 
his  theory  requires.  McKendrick  takes  up  a  middle  position, 
believing  that  both  theories  are  partially  true,  and  this  seems  to 
be  the  best  conclusion  which  can  at  present  be  arrived  at.  It 
seems  clear,  at  any  rate,  that  more  than  one  factor  is  concerned  in 
the  timbre  of  the  vowel  sounds. 

When  the  vowels  are  being  uttered,  the  soft  palate  closes  the 
entrance  to  the  nasal  chambers  completely,  as  may  be  shown 
by  holding  a  candle  in  front  of  the  nose,  or  trying  to  inject  water 
through  the  nares.  If  the  cavities  of  the  nose  are  not  completely 
blocked  off,  the  voice  assumes  a  nasal  character  in  pronouncing 
certain  of  the  vowels  ;  and  in  some  languages  this  is  the  ordinary 
and  correct  pronunciation. 

Many  animals  have  the  power  of  emitting  articulated  sounds  ; 
a  few  have  risen,  like  man,  to  the  dignity  of  sentences,  but  these 
only  by  imitation  of  the  human  voice.  Both  vowels  and  con- 
sonants can  be  distinguished  in  the  notes  of  birds,  the  vocal 
powers  of  which  are  in  general  higher  than  those  of  mammalian 
animals.  The  latter,  as  a  rule,  produce  only  vowels,  though 
some  are  able  to  form  consonants  too. 

The  nervous  mechanism  of  voice  and  speech  will  have  to 
be  again  considered  when  we  come  to  study  the  physiology  of 
the  brain  and  spinal  cord.  But  the  curious  physiological  anti- 
thesis between  the  functions  of  abduction  and  of  adduction  of 
the  vocal  cords  may  be  mentioned  here.  The  abductor  muscles 
are  not  employed  in  the  production  of  voice  ;  they  are  associated 
with  the  less  specialized,  the  less  skilled  and  purposive  function 
of  respiration.  The  adductor  muscles  are  not  brought  into 
action  in  respiration  ;  they  are  associated  with  the  highly- 
specialized  function  of  speech.  Corresponding  to  this  difference 
ot  function,  we  find  that  adduction  is  preponderatingly  re- 
presented in  the  cortex  of  the  brain,  abduction  in  the  medulla 
oblongata.     Stimulation  of  an  area  in  the  lower  part  of  the 


>sr, 


!    \i  I  \  i    li    01    PHYSIOLOGY 


ascending  frontal  convolution,  near  the  fissure  of  Rolando,  in 
the  macaque  monkey,  causes  adduction  of  the  vocal  cords,  never 
abduction.  In  the  cat,  however,  abduction  <>i  the  cords  may 
also  be  obtained  by  stimulation  of  the  cortex.  The  same  is  true 
of  the  dog,  but  only  when  the  peripheral  adductor  nerves  have 
been  divided.  Stimulation  of  the  medulla  oblongata  (accessory 
nucleus)  causes  abduction,  never  adduction.  The  skilled 
adductor  function  is,  therefore,  placed  under  control  oi  the 
cortex.  The  vitally  important,  but  more  mechanical,  abductor 
function  is  governed  by  the  medulla.  The  abductor  movements 
are  more  likely  to  be  affected  by  organic  disease,  the  adductor 
movements  by  functional  changes.  Bui  the  distinction  between 
the  two  groups  of  muscles  is  not  entirely  due  to  a  difference  ol 
central  connections,  since  by  altering  the  strength  of  the  stimulus 
and  the  external  conditions  the  one  or  the  other  may  be  separately 


Fig.  127. — Diagram  of  Vocal  Cords  in  Paralyses  of  the  Larynx. 

a.  Paralysis  of  both  inferior  laryngeal  nerves.  The  vocal  cords  have  taken  up 
the  '  mean  '  position,  b.  Paralysis  of  right  inferior  laryngeal  nerve.  An  attempt 
is  being  made  to  narrow  the  glottis  for  the  utterance  of  sound.  The  right  cord 
remains  in  its  'mean'  position,  c.  Paralysis  of  the  abductor  muscles  only,  on 
both  sides.  The  cords  are  approximated  beyond  the  '  mean  '  position  by  the 
action  of  the  adductors. 


excited  through  the  inferior  laryngeal  nerve.  Thus,  strong 
stimulation  of  the  inferior  laryngeal  causes  closure  of  the  glottis, 
for  although  it  supplies  both  abductors  and  adductors,  the  latter, 
as  the  stronger  muscles,  prevail.  With  weak  stimulation,  and 
in  young  animals,  the  abductors,  owing  to  the  greater  excitability 
of  the  neuro-muscular  apparatus,  carry  off  the  victory,  and  the 
glottis  is  opened  (Russell). 

When  the  nerve  is  cooled  the  abductors  give  way  before  the 
adductors.  The  same  is  true  when  it  is  allowed  to  become  dry. 
And  after  death  in  a  cholera  patient  it  was  observed  that  the 
posterior  crico-arytenoid,  an  abductor  muscle,  was  the  first  of 
the  intrinsic  laryngeal  muscles  to  lose  its  excitability.  Lesions 
of  the  medulla  oblongata  are  often  accompanied  by  marked 
changes  in  the  character  of  the  voice  and  the  power  of  articulation. 

Section  or  paralysis  of  the  superior  laryngeal  nerve  causes  the 


RFSPTRATKhW 


287 


voice  to  become  hoarse,  and  renders  the  sounding  of  high  notes 
an  impossibility,  owing  to  the  want  of  power  to  make  the  vocal 
cords  tense.  Stimulation  of  the  vagus  within  the  skull  causes 
contraction  of  the  crico  thyroid  muscle  and  increased  tension  of 
the  cords.  Section  or  paralysis  of  the  inferior  laryngeal  nerves 
leads  to  loss  ol  voice  or  aphonia,  and  dyspnoea  (Fig.  127).  Both 
adductor  and  abductor  muscles  are  paralyzed  ;  the  vocal  cords 
assume  their  mean  position  the  position  they  have  in  the  dead 
body — and  the  glottis  can  neither  be  narrowed  to  allow  of  the 
production  of  a  note,  nor  widened  during  inspiration.  It  is  said, 
however,  that  young  animals,  in  which  the  structures  around 
the  glottis  are  more  yielding  than  in  adults,  can  still  utter  shrill 
cries  after  section  of  the  inferior  laryngeals,  the  contraction  of 
the  crico-thyroid  muscle  alone  being  able,  while  increasing  the 
tension  of  the  cords,  to  draw  them  together. 

Interference  with  the  connections  on  one  side  between  the 
higher  cerebral  centres  and  the  medulla  oblongata,  as  by  rupture 
of  an  artery  and  effusion  of  blood  into  the  posterior  portion  of 
the  internal  capsule  (giving  rise  to  hemiplegia,  or  paralysis  of 
the  opposite  side  of  the  body),  is  not  followed  by  loss  of  voice  ; 
the  laryngeal  muscles  on  both  sides  are  still  able  to  act. 


PRACTICAL  EXERCISES  ON  CHAPTER  III. 

1.  Tracing  of  the  Respiratory  Movements  in  Man. — Pass  a  tape 
through   the  rings  B   of   the   stethograph  shown  in    Fig.   128,   and 
then  around  the  neck  or  over  the  shoulders,  so  as  to  support  the 
instrument  on 
the    chest    at 
a    convenient 
height.  Fasten 
tapes    to    the 
hooks    and 
tie    them    by 
a     slip  -  knot 
round     the 
chest.        The 
tube  E  is  con- 
nected to  a  re- 
cording   tam- 
bour,   writing 
on     a     drum. 
Or     use      the 
belt  stetho- 
graph or  spiro- 
graph of  Fitz 
(p.  2 1 8),  fasten- 
ing the  elastic  tube  round  the  chest  with  the  chain,  and  connecting 
it    with   a   tambour  or   the   bellows   recorder    shown    in    Fig.    131. 
Compare  the  extent  of  the   excursion  when  the  tube  is  adjusted  at 
different  levels  over  the  thorax  and.  abdomen. 


Fig.  128. — Stethograph. 


288 


./   MANUAL  OF  PHYSIOLOGY 


2*  Production  of  Apnoea  and  Periodic  Breathing  in  Man.  -Arrange 
for  taking  tracings  oi  the  respiratory  movements  from  a  Mlow- 
studenl  as  in  i.  Let  the  subje<  t  oi  the  experimenl  rei  Line  in  a  per- 
fectly easy  position  in  an  armchair.  Let  him  then  breathe  <  l<:uply 
and  frequently  for  about  two  minutes,  so  as  to  produce  a  prolonged 
apnoea  of  about  two  minutes'  duration  Whenever  any  desire  to 
breathe  returns,  the  breathing  is  to  be  allowed  to  lake  its  own  course. 
It  maybe  expected  at  first  to  be  oJ  the  periodic  (<  heyne-Stokes)  type. 

■;.   Tracing   of   the   Respiratory   Movements   in   Animals. 
up  the  arrangement  shown  in   Fig.   129,  and  b  ther  it  is  air- 


Trach 


Fig.   129. — Arrangement  for  Respiratory  Tracing. 

Two  glass  tubes  are  inserted  through  a  cork  in  the  mouth  of  the  large  bottle. 
One  of  them  has  a  small  piece  of  indiarubber  tubing  on  it,  which  is  closed  or 
opened,  as  m.iv  be  required,  by  a  screw-clamp.  The  other  is  connected  by  a 
rubber  tube  with  a  recording  tambour.  The  tubulure  at  the  bottom  of  the  bottle 
is  closed  by  a  cork,  through  which  passes  a  glass  tube,  connected  by  a  rubber 
tube  with  the  tracheal  cannula.  If  no  bottle  with  tubulure  is  available,  it  is  only 
necessary  to  pass  through  the  cork,  down  to  the  bottom  of  the  bottle,  a  third 
glass  tube,  which  is  connected  with  the  tracheal  cannula.  While  a  tracing  is  being 
taken  the  animal  breathes  the  air  contained  in  the  bottle.  When  this  becomes 
vitiated  the  respiratory  movements  are  exaggerated  and  a  normal  tracing  is  no 
longer  obtained.  For  this  reason  the  tracheal  cannula  must  be  connected  with  the 
bottle  only  at  the  moment  when  a  tracing  is  to  be  taken.  The  arrangement  is 
most  suitable  11  animal. 

tight.  Have  also  in  readiness  an  induction  machine  and  electrodes 
arranged  for  an  interrupted  current.  Anaesthetize  a  rabbit  with 
chloral  or  ether  (p.  204),  or  a  small  dogf  with  morphine  and  ether, 

*  This  experiment  is  only  to  be  attempted  under  the  direct  supervision 
of  the  demonstrator. 

f  If  a  large  dog  is  used  the  bottle  should  be  omitted,  the  tracheal  cannula 
being  connected  with  the  stem  of  a  T-tube.  One  end  of  the  horizontal  limb 
of  the  T-tube  is  connected  with  the  tambour;  the  other  is  provided  with  a 
rubber  tube,  which  can  be  partially  closed  by  a  screw-clamp  to  regulate  the 
excursion.  Ether  may  be  given  when  required  by  connecting  the  horizontal 
limb  of  the  T-tube  with  a  bottle  with  two  glass  tubes  in  the  cork  (p.  186). 


PR  ICTTC  \L   I  KERCISES 

at  \  C.E.  mixture.  Insert  a  cannula  into  the  trachea  (p.  186),  and 
connect  it  with  the  large  bottle  l>v  a  tube.  Connect  the  bottle 
with  a  recording  tambour  adjusted  to  write  on  a  drum,  and  regulate 
the  amount  of  the  excursion  of  the  lever  by  slackening  or  tightening 
the  screw-clamp.  Set  the  drum  off  at  slow  speed,  and  take  a 
tracing. 

(b)  Then  disconnect  the  cannula  from  its  tube.  Dissect  out  the 
vagus  in  the  lower  part  of  the  neck,  pass  a  ligature  under  it.  hut  do 
not  tii-  it.  Connect  the  cannula  again  with  the  bottle,  and  while  a 
tracing  is  being  taken  ligature  the  vagus.  Cut  below  the  ligature 
and  stimulate  its  central  end  with  weak  shocks,  marking  the  time 
of  stimulation  on  the  drum.  Repeat  the  stimulation  with  strong 
shocks,  and  observe  the  results. 

Apply  a  strong  solution  of  potassium  chloride  with  a  camel's- 
hair  brush  to  the  central  end  of  the  vagus  while  a  tracing  is  being 
taken,  and  observe  the  effect. 

(</)  Isolate  the  sciatic  nerve  (p.  198),  ligature  it.  and  cut  below  the 
ligature.  Stimulate  its  central  end  while  a  tracing  is  being  taken. 
The  respiratory  movements  will  be  increased. 

(e)  Disconnect  the  cannula,  and  isolate  the  vagus  on  the  other 
side.  While  a  tracing  is  being  taken,  divide  it.  The  respiratory 
movements  will  probably  at  once  become  deeper  and  less  frequent. 

(/)  Again  disconnect  the  cannula. 
Isolate  the  superior  laryngeal  branch 
of  the  vagus.  This  will  be  found 
entering  the  larynx  at  the  point 
where  the  laryngeal  horn  of  the 
hyoid  bone  is  connected  with  the 
thvroid  cartilage.  If  the  finger  is 
passed  back  along  the  upper  border 
of  the  thyroid  cartilage,  this  point 
will  easily  be  felt.  Ligature  the 
nerve,  and  divide  it  between  the  Fig.  130. — Stethograph  (Crile). 
larynx  and  the  ligature.  Recon- 
nect the  cannula.  Take  a  tracing  first  with  weak,  and  then  with 
strong  stimulation  of  the  central  end  of  the  superior  laryngeal. 

(g)  Make  an  incision  through  the  abdominal  wall  in  the  linea  alba, 
and  study  the  movements  of  the  diaphragm.  Find  the  nerves  from 
which  the  phrenics  take  origin  in  the  neck.  In  the  dog  they  arise 
from  the  fifth,  sixth,  and  seventh  cervical  nerves.  Divide  the 
phrenic  fibres  on  one  side,  and  observe  that  the  diaphragm  on  the 
corresponding  side  is  now  paralyzed. 

(h)  Insert  a  cannula  into  the  carotid  artery.  While  a  respiratory 
tracing  is  being  taken,  allow  blood  to  flow  from  the  artery.  Dyspnoea 
and  exaggeration  of  the  respiratory  movements  will  be  seen  when  a 
considerable  quantity  of  blood  has  been  lost.  Mark  and  varnish  the 
tracings. 

In  the  whole  of  this  experiment  the  tracheal  cannula  is  to  be  dis- 
connected, except  when  the  lever  is  actually  writing  on  the  drum,  in 
order  that  the  period  during  which  the  animal  must  breathe  into  the 
confined  space  of  the  bottle  may  be  diminished  as  much  as  possible. 
Instead  of  the  method  described,  the  stethograph  shown  in  Fig.  130 
may  be  used  to  obtain  respiratory  tracings  from  animals,  a  broad 
canvas  band  being  put  round  the  animal's  chest.  To  each  end  of 
this  band  is  clamped  with  sufficient  tension  a  strong  thread  (F), 
fastened  to  a  small  metal  disc  on  the  inside  of  the  rubber  dam  closing 

19 


2QO 


I   M.i.xr  1/    <>/■  Flivsioi  in,  y 


the  obliquely-cut  ends  of  the  metal  cylinder  D.      The  i  ube  <  '<  is  con- 
nected with  a  tambour  or  with  a  bellows  recorder  (Fig,    i  ;i  i. 

|.  The  Effect  of  Temperature   on  the  Respiratory   Centre     Heat 

Dyspnoea.  Set  up  ;m  arrangemenl 
for  taking  a  respiratory  tracing 
in  _>  (footnote,  p.  288)  Anaesthetize 
a  dog,  and  fasten  it.  bat  k 
downward,  mi  a  holder. 
Make  an  incision  in  the 
middle  line  i>t  the  neck, 
commencing  a  little  below  the  (  11 
coid  cartilage,  and  extending  down 
for  4  or  5  inches.  Insert  a  cannula 
into  the  trachea.  Isolate  both  caro- 
tid arteries  for  as  great  a  distance  as 
possible,  and  arrange  them  on  the 
brass  tubes  shown  in  Fig,  132.  Con- 
nect two  adjacent  ends  of  the  tubes 
by  a  short  rubber  tube.  Connect  one 
of  the  remaining  ends  to  a  funnel, 
supported  on  a  stand,  and  the  other 
to  a  rubber  tube  hanging  over  the 
table  above  a  large  jar.  Slip  two  or 
three  folds  of  paper  between  the 
tubes  and  the  vagus  nerves.  Heat 
two  or  three  litres  of  water  to  about 
6 50  C.  (a)  Now  connect  the  tracheal 
cannula  with  the  tambour.  As  soon 
as  the  tracing  is  under  way,  let  the 
hot  water  run  through  the  funnel 
and  tubes  into  the  jar.  Mark  on 
the  tracing  the  point  at  which  the  flow  of  the  hot  water  was 
begun,  and  go  on  passing  it  until  it  has  produced  an  effect.  Then 
stop  the  drum,  and  circulate  water    at  the  ordinary  temperature 

till  the  breathing  is  again 
normal.  Then,  while  a 
tracing  is  being  taken, 
pass  ice-cold  water 
through  the  tubes,  and 
again  notice  the  effect. 

(b)  Expose  the  sciatic. 
Pass  ice-water  through 
the  tubes,  and  while  a 
respiratory  tracing  is 
being  taken  stimulate 
its  central  end  with  in- 
duction shocks  so  weak 
as  just  to  cause  an  effect. 
Pass  water  at  air  tem- 
perature through  the 
tubes,  and  repeat  the 
stimulation  with  the 
coils  at  the  same  dis- 
tance. Do  the  same 
while  hot  water  is  being 


Fig.  131.— Bellows  Recorder 
(Crile). 

B,  a  lead  tube  connected  with  the 
small  bellows  A,  which  consists  of  a 
light  wooden  base  and  top,  to  which 
is  cemented  very  flexible  (organ  key) 
leather,  properly  creased  for  expan- 
se hi  and  contraction ;  C,  writing  lever. 


Fig.  132. —Arrangement  for  Heating  or  Cool- 
ing the  Blood  in  the  Carotid  Arteries. 
A,  cylindrical  portion  of  tube  :  B,  flattened 
portion  in  the  groove  between  which  and  A.  the 
artery,  li'-s  ;  C,  cross-section,  showing  the  lumen 
extending  into  B  :  I>,  rubber  tube  attached  t<>  1 
brass  tube  soldered  into  A.  The  other  end  of  A 
has  a  similar  brass  tube  soldered  into  it  (not 
shown  in  the  figure).  This  is  connected  by  a 
rubber  tube  with  a  similar  apparatus,  on  which 
the  other  carotid  lies.  D  is  connected  with  a 
funnel  containing  hot  or  cold  water  or  with  the 
outflow  tube,  as  the  case  may  lie. 


passed  through  the  tubes,  and  compare  the  results.    Always  allow 
the  water  to  pass  for  a  time  before  making  an  observation. 


PRACTK    \L  EXERCISES  291 

5.  Measurement  of  Volume  of  Air  inspired  or  expired  —  Vital 
Capacity. — A  spirometer  (Fig.  101,  p.  220)  of  sufficient  accuracy  for 
this  experiment  can  be  made  by  removing  the  bottom  of  a  la 
bottle  with  a  capacity  of  not  less  than  4  litres.  A  good  cork,  through 
which  passes  a  glass  tube  connected  with  a  rubber  tube,  is  fitted 
into  the  neck.  The  bottle  is  fixed  vertically,  mouth  downwards. 
the  glass  tube  being  closed  for  the  time,  and  graduated,  by  pouring  in 
measured  quantities  of  water,  say  100  c.c.  at  a  time,  and  marking  the 
level,  The  divisions  are  then  etched  in.  If  the  cork  does  not  fit 
air-tight,  it  is  covered  with  wax.  The  bottle  is  swung  on  two  pulleys, 
counterpoised  and  immersed,  bottom  down,  in  a  large  glass  jar  or  a 
small  cask  nearly  full  of  water.  A  smaller  bottle  may  be  used  for 
the  determination  of  the  tidal  air,  so  as  to  reduce  the  error  of  reading. 

(1)  Submerge  the  bottle  to  the  stopper,  after  opening  the  pinchcock 
on  the  rubber  tube.  Breathe  into  the  bottle,  close  the  cock,  adjust 
the  bottle  so  that  the  level  of  the  water  is  the  same  inside  and  outside, 
and  then  read  off  the  level.     Determine  the  volume  of  air  expired  in  : 

(a)  A  normal  expiration  after  a  normal  inspiration  (tidal  air)  ; 

(b)  The  greatest  possible  expiration  after  a  normal  inspiration 
(supplemental  air  plus  tidal  air)  ; 

(c)  The  greatest  possible  expiration  after  the  greatest  possible 
inspiration  (vital  capacity). 

(2)  Open  the  cock  and  raise  the  bottle  till  it  is  nearly  full  of  air. 
Determine  the  volume  of  air  inspired  in  : 

(a)  A  normal  inspiration  after  a  normal  expiration  (tidal  air)  ; 

(b)  The  greatest  possible  inspiration  after  a  normal  expiration 
(complemental  air  plus  tidal  air)  ; 

(c)  The  greatest  possible  inspiration  after  the  greatest  possible 
expiration  (vital  capacity). 

Make  several  observations  of  each  quantity,  and  take  the  mean. 

(3)  Count  the  rate  of  respiration  for  three  minutes,  keeping  the 
breathing  as  nearly  normal  as  possible  ;  repeat  the  observation  ;  and 
from  the  mean  result  and  the  amount  of  the  tidal  air  calculate  the 
quantity  of  air  taken  into  the  lungs  in  twenty-four  hours  (pulmonary 
ventilation). 

6.  Cardio-Pneumatic  Movements. — Fill  a  U-tube  with  tobacco- 
smoke.  One  end  of  the  tube  is  placed  in  the  nostril  of  a  fellow- 
student,  and  made  tight  with  a  little  cotton-wool.  The  other  nostril 
and  mouth  are  closed,  and  respiration  suspended.  The  column  of 
smoke  moves  in  and  out  at  each  beat  of  the  heart.  By  feeling  the 
apex-beat,  try  to  verify  the  fact  that  during  systole  the  cardio- 
pneumatic  movement  is  inspiratory,  and  in  diastole  expiratory. 

7.  Auscultation  of  the  Lungs. — Make  the  following  observations 
on  a  fellow-student,  who  should  strip  to  the  waist,  and  should  be 
seated  on  a  stool,  so  that  the  back  can  be  easily  examined  as  well 
as  the  front  of  the  chest  : 

(a)  Vesicular  Breathing. — Place  the  stethoscope  2  or  3  inches 
below  the  axilla.  The  rustling  vesicular  sound  will  be  heard.  It  is 
more  intense  in  inspiration  than  in  expiration,  and  much  more 
prolonged,  being  heard  during  the  whole  of  the  inspiratory  act,  but 
in  health  only  at  the  beginning  of  expiration.  Another  position  in 
which  to  listen  for  the  typical  vesicular  sound  is  below  the  angle  of 
the  scapula.  Study  the  sound  in  deep  and  in  ordinary  breathing. 
Now  go  over  the  whole  chest  systematically,  noting  the  positions 
where  the  typical  vesicular  sound  can  be  clearly  heard  and  the 
positions  where  itjis  not  heard  or  is  obscured  by — 

19 — 2 


292  A   MANUAL  OF  PHYSIOLOGY 

(b)  Bronchial  Breathing. — Place  the  stethoscope  over  the  trachea, 
where  the  breath-sounds  are  of  the  bronchial  type,  although  louder 
than  the  bronchial  breathing  heard  over  a  consolidated  area  of  lung 
in  pneumonia.  The  expiratory  sound  is  generally  louder  than  tlv- 
inspiratory,  and  at  least  as  long  as  the  inspiratory  sound,  extending 
throughout  the  greater  part  of  expiration.  Both  sounds  are  higher 
in  pitch  than  the  vesicular  murmur,  and  have  a  blowing  chara 
Go  over  the  chest,  and  note  the  points  at  which  bronchial  breathing 
can  be  heard. 

Repeat  {a)  and  (b).  using  the  ear  applied  to  a  towel  laid  • 
the  various  regions  of  the  chest  instead  of  the  stethoscope. 

(d)  Perform  the  following  experiment  on  a  dog  used  for  some 
other  purpose  :  Open  the  trachea  as  described  on  p.  186.  I: 
into  it  the  cross-piece  of  a  glass  T-tube  of  as  large  a  bore  as  possible, 
tving  the  trachea  over  it  on  each  side  of  the  stem.  The  stem  pro- 
jecting from  the  wound  is  armed  with  a  short  piece  of  rubber  tubing, 
which  can  be  closed  at  will  with  a  clip.  When  the  tube  is  thus  ci 
the  animal  breathes  through  the  glottis  in  the  ordinary  way.  When 
the  tube  is  open,  and  the  mouth  and  nose  covered  tightly  with  a 
cloth,  no  air  goes  through  the  glottis.  The  tube  being  closed,  listen 
with  the  stethoscope  or  the  ear  alone  over  a  part  of  the  chest  where 
the  vesicular  murmur  is  well  heard.  If  the  rubbing  of  the  hairs 
below  the  stethoscope  causes  disturbing  sounds,  shave  a  portion  of 
the  skin.  Continue  listening  while  an  assistant  closes  the  tube  and 
covers  up  the  animal's  muzzle.  Determine  whether  any  change 
takes  place  in  the  vesicular  sound. 

(e)  Repeat  (dt  while  listening  over  the  lower  part  of  the  trachea, 
and  determine  whether  any  change  takes  place  in  the  bronchial 
breathing  sound. 

8.  Respiratory  Pressure. — Connect  a  strong  rubber  tube  with  a 
glass  bulb,  and  the  bulb  with  a  mercurial  manometer  provided  with  a 
scale,  (i)  Fasten  the  tube  with  a  little  cotton-wool  in  one  nostril, 
breathe  through  the  other  with  closed  mouth,  and  observe  the 
amount  by  which  the  level  of  the  mercury  is  altered  in  ordinary 
inspiration  and  expiration. 

(2)  Repeat  the  observation  with  forced  breathing,  pinching  the 
tube  at  the  height  of  inspiration  and  expiration,  and  reading  off  the 
maximum  inspirator},*  and  expiratory  pressure. 

Repeat     i    with  the  tube  connected  to  the  mouth  by  a  glass 
tube  held  between  the  lips,  and  the  nostrils  open. 

Kepeat  (2)  with  the  tube  in  the  mouth  and  the  nostrils  closed. 

9-  Determination  of  Carbon  Dioxide  and  Oxygen  in  inspired  and 
expired  Air  l  Estimation  of  Carbon  Dioxide.  —  Fill  a  burette  with 
water,  and  close  the  pinchcock  on  the  rubber  tube.  Immerse  the 
wide  end  of  the  burette  in  a  large  vessel  of  water,  and  fill  it  with 
carbon  dioxide  bv  putting  into  it  below  the  water  a  tube  connected 
with  a  bottle  in  which  carbon  dioxide  is  being  evolved  by  the  action 
of  hydrochloric  acid  on  marble  chips.  See  that  gas  has  been  coming 
off  freely  from  the  bottle  for  a  little  time  before  the  tube  is  put  under 
the  burette.  Do  not  fill  the  burette  with  gas  beyond  the  graduated 
part.  To  prevent  warming  the  burette  by  the  hand,  hold  it, 
means  of  a  clamp  or  test-tube  holder,  in  the  vertical  position,  its 
mouth  being  still  immersed.  Make  the  level  of  the  water  the  same 
inside  and  outside,  and  read  off  the  meniscus.  Then  introduce  a 
piece  of  stick  sodium  hydroxide,  close  the  burette  with  a  finger  or  the 
palm  of  the  hand,  lift  it  out  of  the  water,  and  by  a  sort  of  see-saw 


PRACTIi    II    I  XI  R(  ISES 

movement  shake  the  sodium  hydrate  repeatedly  from  end  to  end  <>i 
it.     Again  immerse  the  burette,  and  read  the  Level  of  the  menis 

M,>-,t   of  thf  gas   will   be  absorbed.     Repeat  the  shaking.     If  the 
reading  is  still  the  same,  absorption  is  now  complete. 

Estimation  of  Oxygen  (Analysis  of  inspired  Ain.  I  ill  the 
burette  with  the  air  of  the  laboratory.  Open  the  pinchcoek,  and 
immerse  the  wide  end  of  the  burette  till  the  water  reaches  the  gradua- 
tion. Then  close  the  cock,  and  read  off  the  meniscus.  Introduce  a 
puce  of  sodium  hydroxide,  and  proceed  as  in  (i).  Notice  that  there 
apprei  iable  absorption.  (This  method  is  not  suitable  for  the 
measurement  ol  the  small  quantity  of  carbon  dioxide  in  ordinary 
air.)  Now  introduce,  under  water,  some  pyrogallic  acid.  This  can  be 
done  conveniently  by  wrapping  up  some  of  the  crystals  in  thin  paper 
-  to  form  a  kind  of  small  cigarette,  which  is  pushed  up  into  the 
burette.  A  little  more  sodium  hydroxide  may  also  be  added,  if  the 
piece  first  introduced  is  entirely  dissolved.     Shake  as  described  in  (i), 


Fig.  135. — Haldane's  Apparatus  for  Measuring  the  Quantity  of  CO.,  and 
Aqueous  Vapour  given  oef  by  an  Animal. 

A,  chamber  into  which  the  animal  is  put  ;  1  and  4,  WoulrT's  bottles  filled  with 
soda-lime  to  absorb  carbon  dioxide  ;  2,  3,  and  5,  Woulffs  bottles  filled  with 
pumice-stone  soaked  in  sulphuric  acid  to  absorb  watery  vapour  ;  B,  glass  bell-jar 
suspended  in  water,  by  means  of  which  the  negative  pressure  is  known  ;  P,  water- 
pump  which  sucks  air  through  the  apparatus  ;  1  and  2  are  simply  for  absorbing 
the  carbon  dioxide  and  water  of  the  ingoing  air. 

till  no  more  absorption  takes  place.  Then  read  off  the  meniscus  again 
(always  making  the  level  the  same  inside  and  outside  the  burette). 
The  difference  in  the  two  readings  gives  the  amount  of  oxygen 
present.  What  remains  in  the  burette  is  nitrogen  (and  a  little  argon) . 
Its  amount  is,  of  course,  equal  to  the  reading  of  the  burette,  plus  the 
capacity  of  the  ungraduated  part  at  the  narrow  end  of  the  burette, 
which  must  be  determined  once  for  all  by  a  separate  measurement. 

(3)  Analysis  of  expired  Air. — (a)  Fill  the  spirometer  with  water. 
Breathe  into  it  several  times  in  your  ordinary  way,  but  be  careful  not 
to  inspire  any  air  from  the  spirometer  ;  then  fill  the  burette  with  the 
expired  air  from  it.  Or  simply  expire  several  times  through  the 
burette,  seeing  that  none  of  the  inspired  air  comes  through  it. 
Determine,  as  in  (1)  and  (2),  the  percentage  amount  of  carbon 
dioxide,  oxygen,  and  nitrogen,  (b)  Repeat  (a)  with  air  expired 
after  the  lungs  have  been  thoroughly  ventilated  by  taking  a  number 
of  deep  breaths  in  succession,  and  determine  whether  there  is  any 
difference  in  the  percentage  amounts. 

10.  Estimation  of  the  Quantity  of  Water  and  of  Carbon  Dioxide 


294 


A   MANUAL  OF  PHYSIOLOGY 


given  off  by  an  Animal  (Haldane's  Method). — (i)  Connect  the 
apparatus  shown  in  Fig.  133  with  the  water-pump.  Allow  a  negative 
pressure  of  5  or  6  inches  of  water  to  be  established  in  it,  as  shown 
by  the  rise  of  water  in  the  bell- jar  B.  Then  close  the  open  tube  of 
carbon  dioxide  bottle  1 ,  and  clamp  the  tube  between  the  water-pump 
and  the  bell-jar.  If  the  negative  pressure  is  maintained,  the  arrange- 
ment is  air-tight.  Now  weigh  bottle  3  and  bottles  4  and  5,  the  last 
two  together.  Place  a  cat  in  the  respiratory  chamber  A,  connect  the 
chamber  directly  with  the  water-pump,  and  test  whether  it  is  tight. 
Then  take  the  stopper  out  of  bottle  1,  and  adjust  the  rate  at  which 
air  is  drawn  through  the  apparatus.  Let  the  ventilation  go  on  for  a 
few  minutes,  then  insert  bottles  3,  4,  and  5  again.      Note  the  time 

exactly  at  tins  point,  and 
after  an  hour  disconnect  3, 
1  and  5 .  and  again  weigh. 
The  difference  of  the  two 
weighings  of  3  shows  the 
quantity  <>t  water  given  off 
by  the  animal  in  an  hour; 
the  difference  in  the  com- 
bined weight  of  4  and  5,  the 
quantity  of  carbon  dioxide. 
Weigh  the  cat.  and  calculate 
the  amount  of  water  and  of 
carbon  dioxide  given  off 
per  kilo  per  hour. 

(2)  For  the  student  it  is 
more  convenient  to  use 
smaller  animals.  The  mouse 
may  be  taken  as  an  ex- 
ample of  a  warm-blooded 
animal,  and  the  frog  of  a 
cold-blooded.  Instead  of 
the  Woulff's  bottles  use 
wide  test-tubes  connected 
as  in  Fig.  134,  and  for  the 
animal  chamber  a  small 
beaker,  closed  with  a  very 
carefully-fitted  cork  which 
has  been  boiled  in  paraffin.  The  inlet  and  outlet  tubes  of  the 
chamber  are  to  be  introduced  through  this  cork.  The  holes  for 
these  are  to  be  bored  with  the  greatest  care,  and  the  tubes  to  be 
put  in  while  the  cork  is  still  hot  from  boiling  in  paraffin.  Also  insert 
a  thermometer  about  6  inches  long  registering  from  o°  C.  to  45 °  C. 
Modeller's  wax  is  to  be  used  finally  to  render  all  the  junctions  air-tight. 
Add  to  the  series  of  tubes  described  in  the  apparatus  a  single  tube 
containing  baryta-water.  This  is  placed  to  the  left  of  tube  5,  and 
so  arranged  that  the  air-current  bubbles  through  the  water.  As  long 
as  the  absorption  of  carbon  dioxide  is  complete,  the  baryta-water 
remains  clear.  Beyond  this  a  water-bottle  should  be  placed  to  act 
as  a  valve  and  to  indicate  the  negative  pressure  in  the  apparatus. 
It  can  be  most  simply  constructed  by  using  a  cvlinder  of  stout  glass 
tubing  in  a  wide-mouthed  bottle  containing  some  water,  the  inlet  and 
outlet  tubes  passing  through  a  paraffined  cork  which  seals  the  upper 
end  of  the  cylinder. 

Before  making  an  observation,  test  whether  the  apparatus  is  air- 
tight,  as  explained   above,   after  introducing  the  animal  into  the 


Fig.  134. — Absorption  Tubes  for  CO.,  and 
Moisture. 

A,  soda-lime  tube  ;  B,  sulphuric  acid  tube  : 
C,  wooden  frame,  in  which  A  and  B  are  sup- 
ported by  wires  d  ;  b..  wire  hook,  which  grips 
the  glass  tube  firmly,  and  by  means  of  which 
the  tubes  are  lifted  out  of  the  frame  in  order 
to  be  weighed  ;  a.  short  piece  of  glass  tubing, 
by  taking  out  which  the  absorption  tubes  are 
disconnected  from  the  rest  of  the  apparatus  ; 
e,  glass  tube  going  off  to  animal  chamber. 


PRACTICAL  EXERCISES 

chamber,  sealing  the  latter  with  wax,  and  connecting  it  with  the 
irption-tubes.     Hut  a  m  gative  pressure  of  2  or  3  inches  of  water 
is  a  sufficient  test  for  the  small  apparatus. 

To  make  an  observation,  set  the  air-current  going  at  the  desired 
rate.  Allow  it  to  run  for  .1  few  minutes  till  the  carbon  dioxide,  which 
bas  accumulated  during  the  testing,  has  been  swept  out.  At  a  time 
which  has  been  decided  on  and  noted,  stop  the  current  by  discon- 
ne  ting  the  water-pump.  Disconnect  and  stopper  up  the  animal 
1  li  nil  ler,  and  weigh  it  as  quickly  as  possible.  Connect  up  again, 
using  only  recently-weighed  absorption-tubes,  and  finally  connect 
with  the  water-pump  and  allow  the  current  to  pass  for  a  definite 
period,  s:iv  an  hour. 

The  soda-lime  should  not  be  too  dry.  or  absorption  is  not  suffi- 
1  iently  rapid.     The  following  facts  are  made  out  in  the  observation  : 

(a)  The  loss  of  weight  by  the  animal  chamber  (chieflv  loss  by  the 
animal),  (b)  The  gain  of  the  sulphuric  acid  tube  in  water,  (c)  The 
of  the  soda-lime  tubes  in  carbon  dioxide. 

If  we  compare  total  loss  and  total  gain,  we  find  that  they  do  not 
correspond,  the  gain  being  always  greater  than  the  loss.  The  surplus 
can  only  be  oxygen  which  has  been  absorbed  by  the  animal  and  added 
to  the  hydrogen  and  carbon  of  its  substance  to  form  water  and  carbon 
dioxide.     Calculate  the  respiratory  quotient  (p.  242). 

11.  Muscular  Contraction  in  the  absence  of  Free  Oxygen  (see 
p.  261). — (1)  Pith  a  frog  (brain  and  cord).  Cut  off  one  hind-leg 
at  the  middle  of  the  thigh,  and  strip  the  skin  from  it.  Pass  a 
thread  under  the  tendo  Achillis.  tic  it,  and  divide  the  tendon  below 
it.  Free  the  tendon  and  the  gastrocnemius  muscle  from  the  loose 
connective  tissue  lying  between  them  and  the  bones  of  the  leg,  and 
divide  the  latter  just  btlow  the  knee.  Remove  superfluous  thigh 
muscles,  and  fasten  the  gastrocnemius  in  a  moist  chamber  by  means 
of  the  femur.  Attach  the  thread  on  the  tendon  to  a  lever.  Connect 
the  poles  of  the  secondary  coil  of  an  induction  machine  by  fine  copper 
wires  to  the  femur  and  the  tendon.  Put  a  battery  and  simple  key  in 
the  primary,  and  arrange  it  for  single  shocks.  Stimulate  the  muscle 
and  observe  the  height  of  the  contraction.  Now  pass  into  the  chamber 
a  current  of  washed  hydrogen  gas  from  a  bottle  containing  granulated 
zinc,  upon  which  a  little  dilute  sulphuric  acid  is  poured  from  time  to 
time.  The  air  in  the  moist  chamber  will  soon  be  entirely  displaced 
by  the  hydrogen.  Nevertheless,  the  muscle  will  contract  on  being 
stimulated  as  before,  and  the  stimulation  can  be  repeated  many  times. 

12.  Oxidising  Ferments. — Wash  out  the  bloodvessels  of  a  dog  or 
rabbit  (Practical  Exercises,  p.  57).  Chop  up  finely  portions  of 
pancreas,  spleen,  muscle,  lungs,  and  kidney,  keeping  each  separate, 
and  avoiding  any  contamination  of  one  by  another.  Grind  up  half 
of  each  portion  with  sand  in  a  small  mortar,  and  extract  with  a  small 
quantity  of  water,  keeping  all  the  extracts  separate.  Into  each  of 
eleven  test-tubes  put  10  c.c.  of  a  colourless  dilute  alkaline  solution  of 
paraphenvlenediamin  and  a-naphthol  (freshly  made  by  mixing  solu- 
tions of  the  two  substances  in  equimolecular  proportions*  and  adding 
a  little  sodium  carbonate).  To  five  of  the  tubes  add  the  chopped 
organs,  to  five  the  watery  extracts  of  the  organs,  and  enough  water 
to  make  the  volume  equal  in  all  the  tubes.  To  the  remaining  tube 
add  the  same  amount  of  water.  Observe  in  which  tube  a  change  of 
colour  takes  place  (p.  265), 

*  I.e.,  the  weight  of  ench  of  the  two  substances  in  the  mixture  shou'd  be 
propcrtioial  to  its  mole:'jlar  weight. 


CHAPTER    IV 

DIGESTION 

In  the  last  chapter  we  have  described  the  manner  in  which  Hie 
interchange  of  gases  between  the  tissues  and  the  air  is  carried 
out.  We  have  now  to  consider  the  digestion  and  absorption  of 
the  solid  and  liquid  food,  its  further  fate  in  relation  to  the 
chemical  changes  or  metabolism  of  the  tissues,  and  finally  the 
excretion  of  the  waste  products  by  other  channels  than  the 
lungs. 

Logically,  we  ought  to  take  metabolism  after  absorption  and 
before  excretion,  tracing  the  food  through  all  its  vicissitudes 
from  the  moment  when  it  enters  the  blood  or  lymph  till  it  is 
cast  out  as  useless  matter  by  the  various  excretory  organs. 
Unfortunately,  however,  the  steps  of  the  process  are  as  yet 
almost  entirely  hidden  from  us  ;  we  know  only  the  beginning 
and  the  end.  We  can  follow  the  food  from  the  time  it  enters 
the  alimentary  canal  till  it  is  taken  up  by  the  tissues  of  absorp- 
tion ;  and  we  have  really  a  fair  knowledge  of  this  part  of  its 
course.  We  can  collect  the  end  products  as  they  escape  in  the 
urine,  or  in  the  breath,  or  in  the  sweat  ;  and  our  knowledge  of 
them  and  of  the  manner  in  which  they  are  excreted  is  consider- 
able. But  of  the  wonderful  pathway  by  which  the  dead  mole- 
cules of  the  food  mount  up  into  life,  and  then  descend  again  into 
death,  we  catch  only  a  glimpse  here  and  there.  Only  the  intro- 
duction and  the  conclusion  of  the  story  of  metabolism  are  at 
present  in  our  possession  in  fairly  continuous  and  legible  form. 
We  will  read  these  before  we  try  to  decipher  the  handful  of  torn 
leaves  which  represents  the  rest. 

Comparative. — In  the  lowest  kinds  of  animals,  such  as  the  Amoeba, 
there  is  neither  mouth,  nor  alimentary  canal,  nor  anus  :  the  food, 
wrapped  round  by  pseudopodia,  is  taken  in  at  any  part  of  the  animal 
with  which  it  happens  to  come  in  contact.  A  vacuole  is  formed 
around  it.  Acid  is  secreted  into  the  vacuole,  the  food  is  digested 
within  the  cell-substance,  and  the  part  of  it  which  i.s  useless  for  nutri- 
tion is  cast  out  again  at  any  part  of  the  surface. 

Coming  a  little  higher,  we  find  in  the  Coclenteratcs  a  mouth  and 


DIGESTION 

alimentary  tube,  which  opens  into  the  body  cavity,  where  i  certain 
•  mount  ot  digesl  urn  seems  to  take  pla<  e,  and  from  which  the  food  is 
absorbed  either  through  the  cells  01  t  1k>  endoderm,  or,  as  in  Medusa, 
In-  means  of  fine  canals,  which  radiate  from  the  body-cavity  into  its 
walls,  and  form  part  of  the  so-called  gastro-vascular  system.  In  the 
Echinodermata  we  have  a  further  development,  a  complete  alimen- 
tary canal  with  mouth  and  anus,  and  entirely  shut  oil  from  the  body- 
cavity.  In  many  Arthropods  it  is  possible,  already  to  distinguish 
parts  corresponding  to  the  stomach,  and  the  small  and  large  intes- 
tines of  higher  forms,  the  digestive  glands  being  represented  by 
organs  which  in  some  groups  seem  to  be  homologous  with  the  liver, 
and  in  others  with  the  salivary  glands  of  the  higher  Vertebrates.  A 
few  Molluscs  seem  in  addition  to  possess  a  pancreas. 

Among  Vertebrates  fishes  have  the  simplest,  and  birds  and 
mammals  the  most  complicated,  alimentary  system.  In  the  lowest 
fishes  the  stomach  is  only  indicated  by  a  slight  widening  of  the 
anterior  part  of  the  digestive  tube.  In  water-living  Vertebrates  there 
are  no  salivary  glands.  In  birds  the  oesophagus  is  generally  dilated 
to  form  a  crop,  from  which  the  food  passes  into  a  stomach  consisting 
of  two  parts,  one  pre-eminently  glandular  (proventriculus),  the  other 
pre-eminently  muscular  (ventriculus).  Among  mammals  a  twofold 
division  of  the  stomach  is  distinctly  indicated  in  rodents  and  cetaceae, 
but  this  organ  reaches  its  greatest  complexity  in  ruminants,  which 
possess  no  fewer  than  four  gastric  poucnes.  The  differentiation  of 
the  intestine  into  small  and  large  intestine  and  rectum  is  more 
distinct,  both  anatomically  and  functionally,  in  mammals  than  in 
lower  forms  ;  but  there  are  marked  differences  between  the  various 
mammalian  goups  both  in  the  relative  size  of  the  several  parts  of 
the  digestive  tube,  and  in  the  proportion  between  the  total  length  of 
the  alimentary  canal  and  the  length  of  the  body.  In  general,  the 
canal  is  longest  in  herbivora,  shortest  in  carnivora.  Thus,  the  ratio 
between  length  of  body  and  length  of  intestine  is  in  the  cat  i  :  4. 
dog  1  :  6,  man  1  :  5  or  6,  horse  1:12,  cow  1  :  20,  sheep  1  :  27.  The 
relative  capacity  of  the  stomach,  small  intestine,  and  large  intestine, 
is  in  the  dog  6:2:  1*5,  in  the  horse  1  :  3*5  :  7,  in  the  cow  7:2:1 
The  area  of  the  mucous  surface  of  the  alimentarv  canal  is  very  con- 
siderable, in  the  dog  more  than  half  that  of  the  skin,  the  surface  ol 
the  small  intestine  being  three  times  that  of  the  stomach  and  four 
times  that  of  the  large  intestine.  In  the  horse  the  mucous  surface 
has  twice  the  a,rea  of  the  skin. 

Anatomy  of  the  Alimentary  Canal  in  Man. — The  alimentary  canal 
is  a  muscular  tube,  which,  beginning  at  the  mouth,  runs  under  the 
various  names  of  pharynx,  oesophagus,  stomach,  small  intestine,  large 
intestine,  and  rectum,  till  it  ends  at  the  anus.  Its  walls  are  largelv 
composed  of  muscular  fibres  ;  its  lumen  is  clad  with  epithelium,  and 
into  it  open  the  ducts  of  glands,  which,  morphologicallv  speaking, 
are  involutions  or  diverticula  formed  in  its  course.  In  virtue  of  its 
muscular  fibres  it  is  a  contractile  tube  ;  in  virtue  of  its  epithelial 
lining  and  its  special  glands  it  is  a  secreting  tube  ;  in  virtue  of  both 
it  is  fitted  to  perform  those  mechanical  and  chemical  actions  upon 
the  food  which  are  necessary  for  digestion.  Its  inner  surface  is  in 
most  parts  richly  supplied  with  bloodvessels,  and  in  special  regions 
beset  with  peculiarly-arranged  lymphatics ;  by  both  of  these  channels 
the  alimentary  tube  performs  its  function  of  absorption.  From  the 
beginning  of  the  oesophagus  to  the  end  of  the  rectum  the  muscular 
:vall  consists,  broadly  speaking,  of  an  outer   coat  of  longitudinally- 


./   MANUAL  OF  PHYSIOLOGY 

arranged  fibres,  and  a  thicker  inner  coat  of  fibres  running  circularly 
or  transversely  around  the  tube.  Between  the  layers  lies  a  plexus 
of  non-medullated  nerves  and  nerve-cells  (Aucrbach's  plexus).  In  the 
stomach  the  longitudinal  fibres  are  found  only  on  the  two  curvatures, 
and  a  third  incomplete  coat  of  oblique  fibres  makes  its  appearance 
internal  to  the  circular  layer.  In  the  large  intestine,  again,  the 
longitudinal  fibres  are  chiefly  collected  into  three  isolated  strand-. 
In  the  pharynx  the  typical  arrangement  is  departed  from,  inasmuch 
as  there  is  no  regular  longitudinal  layer  ;  but  the  three  constrictor 
muscles  represent  to  a  certain  extent  the  great  circular  coat.  The 
muscles  of  the  mouth  and  of  the  pharynx  are  of  the  striped  variety. 
So  is  the  muscle  of  the  upper  half  of  the  oesophagus  in  man  and  the 
cat.  and  of  the  whole  oesophagus  in  the  dog  and  the  rabbit.  In  the 
rest  of  the  alimentary  canal  the  muscle  is  smooth,  except  at  the  very 
end.  .'.here  the  external  sphincter  of  the  anus  is  striped.  In 
certain  situations  the  circular  coat  is  developed  into  a  regular  ana- 
tomical sphincter,  a  definite  muscular  ring,  whose  function  it  is  to 
shut  one  part  of  the  tube  off  from  another  (sphincter  pylori,  ileo- 
colic sphincter),  or  to  help  to  close  the  external  opening  of  the  tube 
(internal  sphincter  of  anus).  Elsewhere  a  tonic  contraction  of  a 
portion  of  the  circular  coat,  not  anatomically  developed  beyond  the 
rest,  creates  a  functional  sphincter  (cardiac  sphincter  of  stomach). 

Throughout  the  greater  part  of  the  digestive  tract  the  peritoneum 
forms  a  thin  serous  layer,  external  to  the  muscular  coat.  Internally 
the  muscular  coat  is  separated  from  the  mucous  membrane,  the  lining 
of  the  canal,  by  some  loose  areolar  tissue  containing  blood  ve-- 
lymphatics,  and  nerves  (Meissner's  plexus),  and  called  the  submucous 
coat.  Between  the  mucous  and  submucous  layers,  but  belonging  to 
the  former,  in  the  whole  canal  below  the  beginning  of  the  oesophagus, 
is  a  thin  coat  of  smooth  muscular  fibres,  the  muscularis  mucosa?,  con- 
sisting in  some  parts,  e.g.,  in  the  stomach,  of  two,  or  even  three, 
layers.  Between  this  and  the  lumen  of  the  canal  lie  the  ducts  and 
alveoli  of  glands,  surrounded  by  bloodvessels  and  embedded  in 
adenoid  or  lvmphoid  tissue,  which  in  particular  regions  is  collected 
into  well-defined  masses  (solitary  follicles,  Peyer's  patches,  tonsils), 
extending,  it  may  be,  into  the  submucous  tissue.  In  the  mouth, 
pharynx,  and  oesophagus,  the  glands  lie  in  the  submucosa,  as  do  the 
glands  of  Brunner  in  the  duodenum  ;  everywhere  else  they  are  con- 
fined to  the  mucous  membrane  proper.  Between  the  openings  of 
the  glands  the  mucous  membrane  is  lined  with  a  single  layer  of 
columnar  epithelial  cells,  sometimes  (in  the  small  intestine i  arranged 
along  the  sides  of  tiny  projections  or  villi.  At  the  ends  of  the  alimen- 
tary canal,  viz.,  in  the  mouth,  pharynx,  and  osopluigus,  and  at  the 
anus,  the  epithelium  is  stratified  squamous,  and  not  columnar. 

Lli'-  purpose  of  food  is  to  supply  the  waste  of  the  tissues,  to 
replenish  the  stores  of  material  from  the  oxidation  of  which  the 
energy  required  for  the  running  of  the  bodily  machine  is  derived, 
and  thus  to  maintain  the  normal  composition  of  the  body.  In 
the  body  we  find  a  multitude  of  substances  marked  off  from  i 
other,  some  by  the  sharpest  chemical  differences,  others  by  char- 
acters much  less  distinct,  but  falling  upon  the  whole  into  the 
few  fairly  definite  groups  already  described  (p,  i).  Thus, 
there  are  bodies  like  serum-albumin,  serum-globulin,  mvosinogen, 
and  so  on.  which  are  so  much  alike  that  they  can  all  be  placed 


DIGESTION  299 

111  one  great  class,  the  proteins.  Then  we  have  substances  like 
glycogen  and  dextrose,  vastly  simpler  in  their  composition,  and 
belonging  to  the  group  of  carbo-hydrates.  Then,  again,  fats  of 
various  kinds  are  widely  distributed  in  normal  animal  bodies; 
and  inorganic  materials  (water  and  salts)  are  never  absent. 

Now,  although  it  is  by  no  means  necessary  that  a  substance 
111  the  body  belonging  to  one  of  these  great  groups  should  be 
derived  from  a  substance  of  the  same  group  in  the  food,  it  has 
been  found  that  no  diet  is  sufficient  for  man  unless  it  contains 
representatives  of  all  ;  a  proper  diet  must  include  proteins,  carbo- 
hydrates, fats,  inorganic  salts,  and  water.  These  proximate 
principles  have  to  be  obtained  from  the  raw  material  of  the  food- 
stuffs— that  is,  as  regards  the  first  three  groups,  which  can  alone 
yield  energy  in  the  body,  from  the  tissues  and  juices  of  other 
living  things,  plants  or  animals  ;  it  is  the  business  of  digestion  to 
sift  them  out  and  to  prepare  them  for  absorption.  This  pre- 
paration is  partly  mechanical,  partly  chemical. 

The  water  and  salts  and  some  carbo-hydrates,  such  as  dextrose, 
are  ready  for  absorption  without  change.  Fats  are  split  into 
glycerin  and  fatty  acids  before  absorption.  Indiffusible  col- 
loidal carbo-hydrates,  like  starch  and  dextrin,  are  changed  into 
diffusible  and  readily  soluble  sugars,  and  the  natural  proteins 
into  diffusible  peptones,  and  eventually — in  great  part,  at  least— 
into  much  simpler  decomposition  products.  These  changes  are 
obviously  favourable  to  absorption.  But  this  is  not  their  whole 
significance.  For  disaccharides,  such  as  cane-sugar,  maltose, 
or  lactose,  although  easily  soluble  in  the  contents  of  the  gut,  and 
in  themselves  perfectly  capable  of  being  absorbed  without  change, 
are,  unless  present  in  unusually  large  amount,  all  converted  into 
monosaccharides,  such  as  dextrose,  levulose,  or  galactose,  either 
in  the  lumen  or  in  the  wall  of  the  alimentary  tube.  The  reason 
is  that  the  disaccharides  are  unsuitable  as  pabulum  for  the  cells. 
Digestion  is  not  only  a  preparation  of  the  food  for  absorption 
by  the  gut,  but  for  assimilation  by  the  tissues  after  absorption. 
An  equally  important  instance  of  this  double  function  is  seen 
in  the  digestion  of  proteins.  The  complete  shattering  of  the 
protein  molecule  into  amino-acids  and  the  other  groups  yielded 
by  its  decomposition  (p.  332)  is  required,  in  the  case  of  that 
portion  of  the  protein  which  goes  to  build  up  the  tissues,  because 
of  the  high  degree  of  specificity  of  the  tissue  proteins.  The 
myosinogen  of  beef  cannot  be  cobbled  into  the  myosinogen  of 
human  muscle,  still  less  we  may  suppose  into  the  serum  albumin 
of  human  blood.  It  is  necessary  that  the  food  protein  should  be 
completely  '  wrecked  '  in  digestion  so  that  protein  which  is  to  take 
its  place  in  protoplasm  may  be  built  exactly  to  order  from  the 
bricks.      A  satisfactory  '  fit '  cannot  be  obtained  with  ready- 


300  A   M.t\  ill    OF   PHYSIOLOG  ) 

made  protein.  Mechanical  division  <>l  the  food  is  an  important 
aid  to  the  chemical  action  of  the  digestive  juices.  We  shall  see 
that  this  mechanical  division  forms  a  greal  pari  ol  the  work 
of  the  stomach,  but  it  is  normally  begun  in  the  mouth,  and  n  is 
"i  consequence  that  this  preliminary  stage  should  be  properly 
pei  formed. 


I.   The   Mechanical  Phenomena  of  Digestion. 

Mastication.^  It  is  among  the  mammalia  thai  regulai  masti 

cation  of  the  food  first  makes  its  appearance  as  an  important 
aid  to  digestion.  The  amphibian  bolts  its  fly,  the  bird  its  grain, 
.ind  the  fish  its  brother,  without  the  ceremony  of  (hewing.  In 
ruminating  mammals  we  see  mastication  carried  to  it-  highest 
point;  the  teeth  work  all  day  long,  and  mosl  of  them  are 
specially  adapted  for  grinding  the  loud.  The  carnivora  spend 
hut  a  short  time  in  mastication  ;  their  teeth  are  in  general  adapted 
rather  for  tearing  and  cutting  than  for  grinding.  Where  the  diet 
is  partly  animal  and  partly  vegetable,  as  in  man,  the  teeth  are 
fitted  for  all  kinds  of  work  ;  and  the  process  oi  mastication  is  in 
general  neither  so  long  as  in  the  purely  vegetable  feeders,  nor  -<> 
short  as  in  the  carnivora. 

In  man  there  are  two  sets  of  teeth  :  the  temporary  or  milk 
teeth,  and  the  permanent  teeth.  The  milk  teeth  are  twenty 
in  number,  and  consist  on  each  side  of  four  incisors  or  cutting- 
teeth,  two  canines  or  tearing-teeth,  and  four  molars  or  grinding- 
teeth.  The  central  incisors  emerge  at  the  seventh  month  from 
birth,  the  other  incisors  at  the  ninth  month,  the  canines  at  the 
eighteenth,  and  the  molars  at  the  twelfth  and  twenty-fourth 
month  respectively.  Each  tooth  in  the  lower  jaw  appears  a 
little  before  the  corresponding  one  in  the  upper  jaw.  Each  of 
the  milk-teeth  is  in  course  of  time  replaced  by  a  permanent 
tooth,  and  in  addition  the  vacant  portion  of  the  gums  behind 
the  milk  set  is  now  tilled  up  by  twelve  teeth,  six  on  each  side, 
three  above  and  three  below.  These  twelve  are  the  permanent 
molars  ;  they  raise  the  number  of  the  permanent  teeth  to  thirty- 
two.  The  permanent  teeth  which  occupy  the  position  of  the 
milk  molars  now  receive  the  name  of  premolars.  The  lust  tooth 
of  the  permanent  set  (the  first  true  molar)  appears  at  the  age 
of  6£  years  ;  the  last  molar,  or  wisdom  tooth,  does  not  emerge 
tiJl  the  seventeenth  to  the  twenty-fifth  year. 

In  mastication  the  lower  jaw  is  moved  up  and  down,  so  as  to 
alternately  separate  and  approximate  the  two  n>w>  of  teeth.  It 
has  also  a  certain  amount  of  movement  from  side  to  side,  and 
from  front  to  back.  The  masseter.  temporal  and  internal  ptery- 
goid muscles  raise,  and  the  digastric,  with  the  assistance  of  the 


DIGESTION  301 

mylo-  .ind  genio-hyoid,  depresses,  the  Lower  jaw,  bul  its  down- 
ward movement  is  mainly  ;i  passive  one.  The  external  ptery- 
goids pull  it  forward  when  both  contract,  forward  and  to  one  side 
when  only  one  contracts.  The  lower  fibres  of  the  temporal  muscle 
retract  the  jaw.  The  buccinator  and  orbicularis  oris  muscles 
prevent  the  food  from  passing  between  the  teeth  and  the  cheeks 
and  lips.  The  tonglie  keeps  the  food  in  motion,  works  it  up  with 
the  saliva,  and  finally  gathers  it  into  a  bolus  ready  for  deglutition. 

Deglutition. — This  act  consists  of  a  voluntary  and  an  involun- 
tary stage.  Just  before  the  beginning  of  the  voluntary  stage 
mastication  is  suspended,  and  a  slight  contraction  of  the  dia- 
phragm generally  takes  place.  The  anterior  part  of  the  tongue 
is  suddenly  elevated  and  pressed  against  the  hard  palate,  and  the 
ele\  ation  travels  back  from  the  tip  towards  the  root,  as  the  mylo- 
hyoid muscles  in  the  floor  of  the  mouth  contract  sharply,  so  as 
to  thrust  the  bolus  through  the  isthmus  of  the  fauces.  As  soon  as 
this  has  happened  and  the  food  has  reached  the  posterior  portion 
of  the  tongue,  it  has  passed  beyond  the  control  of  the  will,  and 
the  second  or  involuntary  stage  of  the  process  begins. 

This  stage  may  be  divided  into  two  parts  :  (1)  Pharyngeal, 
(2)  oesophageal — both  being  reflex  acts.  During  the  first  the 
food  has  to  pass  through  the  pharynx,  the  upper  portion  of  which 
forms  a  part  of  the  respiratory  tract,  and  is  in  free  communication 
with  the  larynx  during  ordinary  breathing.  It  is  therefore 
necessary  that  respiration  should  be  interrupted  and  the  larynx 
closed  while  the  food  is  being  moved  through  the  pharynx.  But 
that  the  interruption  may  be  short,  the  food  must  be  rapidly 
passed  over  this  perilous  portion  of  its  descent.  The  main  pro- 
pelling force  under  which  the  bolus  is  shot  through  the  back  of 
the  pharynx  is  derived  from  the  contraction  of  the  mylo-hyoid 
muscles  already  mentioned,  assisted  to  some  extent  by  the  stylo- 
and  palato-glossi  ;  and  that  none  of  the  purchase  may  be  lost, 
the  pharyngeal  cavity  is  cut  off  from  the  nose  and  mouth  as  soon 
as  the  bolus  has  entered  it.  The  soft  palate  is  raised  by  the 
levator  palati  and  palato-pharyngei  muscles  ;  at  the  same  time 
the  upper  part  of  the  pharynx,  narrowed  by  the  contraction  of  the 
superior  constrictor,  comes  forward  to  meet  the  soft  palate, 
closes  in  upon  it,  and  so  prevents  the  food  from  passing  into  the 
nasal  cavities.  The  pharynx  is  cut  off  from  the  mouth  by  the 
closure  of  the  fauces  through  the  contraction  of  the  palato- 
pharyngeal muscles  which  lie  in  their  posterior  pillars.  The 
upper  free  end  of  the  epiglottis  (the  so-called  pharyngeal  part) 
aids  the  back  of  the  tongue  in  completing  a  movable  partition 
across  the  pharynx,  which  keeps  close  to  the  bolus  as  it  passes 
down  between  the  posterior  surface  of  the  epiglottis  and  the 
posterior  wall  of  the  pharynx.     Almost  immediately  after  the 


302  A    MANUAL  OF  PHYSIOLOGY 

contraction  of  the  mylo-hyoids  the  larynx  is  pulled  upwards  and 
forwards  l>v  the  contraction  of  the  thyro-hyoid  muscle,  and  the 
elevation  of  the  hyoid  hone  by  the  muscles  which  connect  it  to  the 
lower  jaw.  The  base  of  the  tongue  is  simultaneously  drawn  back- 
wards by  the  stylo-  and  palato-glossus.  The  lower  or  laryngeal 
portion  of  the  epiglottis  is  thus  caused  to  come  into  contact 
with  the  upper  orifice  of  the  larynx,  occluding  it  completely,  but 
the  pharyngeal  portion  projects  beyond  the  larynx,  and  takes  no 
share  in  its  closure  (Eykman).  The  glottis  is  closed  by  the  ap- 
proximation of  the  vocal  cords  and  the  arytenoid  cartilages. 
The  epiglottis,  however,  is  not  absolutely  indispensable  for 
closing  the  larynx,  since  swallowing  proceeds  in  the  ordinary  way 
when  it  is  absent.  The  morsel  of  food,  grasped  by  the  middle  and 
lower  constrictors  as  it  leaves  the  back  of  the  tongue,  passes 
rapidlv  and  safely  over  the  closed  larynx,  the  process  being  accele- 
rated by  the  pulling  up  of  the  lower  portion  of  the  pharynx  i 
the  bolus  by  the  action  of  the  palato-  and  stylo-pharyngei. 

The  second  or  oesophageal  portion  of  the  involuntary  stage  is 
a  more  leisurelv  performance.  The  bolus  is  carried  along  by  a 
peculiar  '  peristaltic  '  contraction  of  the  muscular  wall  of  the 
'hagus,  which  travels  down  as  a  wave,  constricting  the  tube 
and  pushing  the  food  before  it.  In  front  of  the  constricting  wave 
moves  a  wave  of  inhibition,  so  that  the  part  of  the  oesophagus 
into  which  the  bolus  is  about  to  pass  is  always  relaxed,  while  the 
part  behind  it  is  contracted.  This  exact  co-ordination  of  inhibi- 
tion and  contraction  is  the  essential  thing  in  peristalsis.  When 
the  food  reaches  the  lower  end  of  the  gullet  the  tonic  contraction 
of  that  part  of  the  tube  is  for  a  moment  relaxed  by  reflex  inhibi- 
tion, and  the  morsel  passes  into  the  stomach.  Beaumont  saw.  in 
the  case  of  St.  Martin,  that  the  oesophageal  orifice  of  the  stomach 
contracted  firmlv  after  each  morsel  was  swallowed,  and  so  did 
the  gastric  walls  in  the  neighbourhood  of  the  fistula  when  food 
was  introduced  by  this  opening.  In  the  dog  the  whole  process 
of  swallowing  from  mouth  to  stomach  has  been  shown  to  occupy 
four  to  five  seconds,  but  the  time  is  by  no  means  constant.  In 
man  the  peristaltic  wave  requires  about  five  to  six  seconds  to 
travel  from  the  level  of  the  glottis  to  the  cardiac  orifice.  The 
rate  of  movement  is  greater  in  the  upper  than  in  the  lower  portion 
of  the  oesophagus. 

Such  is  the  mechanism  of  deglutition  when  the  bolus  is  of  such 
consistence  and  size  that  it  actually  distends  the  oesophagus. 
But  it  has  been  shown  that  liquid  food  is  swallowed  in  a  different 
way.  The  food  lying  on  the  dorsum  of  the  tongue,  suddenly  put 
under  pressure  by  the  sharp  contraction  of  the  mylo-hyoid 
muscles,  is  shot  rapidly  down  to  the  lower  part  of  the  lax  oeso- 
phagus, or,  occasionally,  some  of  it  even  into  the  stomach.     So 


DIG1  STIOh  303 

far  the  process  has  only  occupied  one-tenth  of  a  second.  After 
several  seconds,  the  food,  or  the  portion  which  still  remains  in 
the  oesophagus,  is  forced  through  the  cardiac  sphincter  into  the 
stomach  by  the  arrival  of  the  tardy  peristaltic  contraction  ol 
the  oesophageal  wall  (Kronecker  and  Meltzer).  Two  sounds  may 
be  heard  in  man  on  listening  in  the  region  of  the  stomach  or 
oesophagus  during  deglutition  of  liquids,  especially  when,  as 
crucially  happens,  they  are  mixed  with  air.  The  first  sound 
occurs  at  once,  and  is  due  to  the  sudden  squirt  of  the  liquid  along 
the  gullet  ;  the  second,  which  is  heard  after  a  distinct  interval 
(about  six  seconds),  is  caused  by  the  forcing  of  the  fluid  through 
the  cardiac  orifice  of  the  stomach  by  the  contraction  of  the  oeso- 
phagus. 

There  are  certain  peculiarities  which  distinguish  this  peri- 
staltic movement  of  the  oesophagus  from  that  of  other  parts  of 
the  alimentary  canal.  It  is  far  more  closely  related  to  the  central 
nervous  system,  and,  unlike  the  peristaltic  contraction  of  the 
intestine,  can  pass  over  any  muscular  block  caused  by  ligature, 
section,  or  crushing,  so  long  as  the  nervous  connections  are  intact. 
But  division  of  the  oesophageal  nerves  causes,  as  a  rule,  stoppage 
of  oesophageal  movements  ;  although  an  excised  portion  of  the 
tube  retains  its  vitality  for  a  long  time,  and  may,  under  certain 
circumstances,  go  on  contracting  in  the  characteristic  way  after 
removal  from  the  bdoy.  Stimulation  of  the  mucous  membrane 
of  the  pharynx  will  cause  reflex  movements  of  the  oesophagus, 
while  stimulation  of  its  own  mucous  membrane  is  ineffective. 
From  these  facts  we  learn  that  although  the  oesophageal  wall 
may  possess  a  feeble  power  of  spontaneous  peristaltic  contraction, 
yet  this  is  usually  in  abeyance,  or  at  least  overmastered  by  central 
nervous  control  ;  so  that  impulses  discharged  as  a  '  fusillade  ' 
from  successive  portions  of  the  vagus  centre,  and  travelling  down 
the  oesophageal  nerves,  excite  the  muscular  fibres  in  regular 
order  from  the  upper  to  the  lower  end  of  the  tube. 

Nervous  Mechanism  of  Deglutition. — The  centre  for  the 
whole  involuntary  stage  (both  pharyngeal  and  oesophageal)  lies 
in  the  upper  part  of  the  medulla  oblongata.  When  the  brain  is 
sliced  away  above  the  medulla,  deglutition  is  not  affected  ;  but 
it  the  upper  part  of  the  medulla  is  removed,  the  power  of 
swallowing  is  abolished.  In  man,  disease  of  the  spinal  bulb 
interferes  far  more  with  deglutition  than  disease  of  the  brain 
proper. 

Normally,  the  afferent  impulses  to  the  centre  are  set  up  by  the 
contact  of  food  or  saliva  with  the  mucous  membrane  of  the  pos- 
terior part  of  the  tongue,  the  soft  palate  and  the  fauces,  the 
nerve-channels  being  the  superior  laryngeal,  the  pharyngeal 
branches  of  the  vagus,  and  the  palatal  branches  of  the  fifth 


304  A    MANUAL  OF  PHYSTOLOCY 

nerve.*     A  feather  has  sometimes  been  swallowed  involuntarily 
by  a  reflex  movement  of  deglutition  set  up  while  the  soft  palate 
or  pharynx  was  being  tickled  to  produce  vomiting.      Artificial 
stimulation   of  the   central   end   of   the  superior  laryngeal   will 
cause  the  movements  of  deglutition  independently  of  the  presence 
of  food  or  liquid  ;  but  if  the  central  end  of  the  glossopharyngeal 
nerve  be  stimulated  at  the  same  time,  the  movements  do  nut 
occur.     The  glossopharyngeal  is  therefore  able  to  inhibit   the 
deglutition  centre,  and  it  is  owing  to  the  action  of  this  nerve 
that  in  a  series  of  efforts  at  swallowing,  repeated  within  less  than 
a  certain  short  interval  (about  a  second),  only  the  last  is  sua 
fill.     It   is  also  through   the  glosso-pharyngeal  nerve  that  the 
respiratory  movements  are  inhibited  during  deglutition.     When 
the  central  end  of  this  nerve  is  stimulated,  respiration  is  stopped 
for  four  or  five  seconds,  and  this  cessation  is  distinguished  from 
that  produced  by  any  other  afferent  nerve  by  the  circumstance 
that   it  occurs  not  in  expiration  exclusively  or  in   inspiration 
exclusively,  but  with  the  respiratory  muscles  in  the  precise  degree 
of  contraction  in  which  they  happened  to  be  at  the  moment  of 
stimulation.     The  efferent  nerves  of  the  reflex  act  of  deglutition 
are  the  hypoglossal  to  the  tongue  and  the  thyro-hyoid  and  other 
muscles  concerned  in  raising  the  larynx  ;  the  glosso-pharyngeal, 
vagus,  facial  and  fifth  to  the  muscles  of  the  palate,  fauces,  and 
pharynx  ;  the  fifth  to  the  mylo-hyoid  ;  and  the  vagus  to  the 
larynx  and  oesophagus.     Section  of  the  vagus  interferes  with 
the  passage  of  food  along  the  oesophagus  ;   stimulation   of  its 
peripheral  end  causes  oesophageal  movements. 

Movements  of  the  Stomach  and  Intestines. — The  whole  of 
the  stomach  does  not  take  part  equally  in  the  movements  associ- 
ated with  digestion.  We  may  divide  the  organ,  both  anatomically 
and  functionally,  into  two  portions — a  pyloric  portion,  or  antrum 
pylori,  comprising  about  a  fifth  of  the  stomach,  and  a  larger 
cardiac  portion,  or  fundus.^  At  the  junction  of  the  antrum 
and  the  fundus  the  circular  muscular  coat  is  slightly  thickened 
into  a  ring  called  the  '  transverse  band,'  or  '  sphincter  of  the 
antrum.'     In  the  living  stomach  the  region  of  the  transverse 

*  It  appears  that  the  most  influential  reflex  paths  may  differ  in  different 
animals.  In  the  rabbit,  e.g.,  the  reflex  is  set  up  by  excitation  of  the 
trigeminal  fibres  which  supply  the  mucous  membrane  anterior  to  the 
tonsils,  in  the  dog  and  cat  by  excitation  of  the  glosso-pharyngeal  fibres 
in  the  posterior  wall  of  the  pharynx,  and  in  monkeys  by  excitation  of 
the  trigeminal  branches  distributed  to  the  mucous  membrane  over  the 
tonsils  (Kahn). 

f  Here  '  fundus  '  is  used  in  the  sense  in  which  it  is  generally  employed 
in  speaking  of  the  stomach  of  the  dog  or  cat  as  signifying  the  whole  of  the 
organ  with  the  exception  of  the  antrum  pylori.  By  the  fundus  of  the 
human  stomach  most  writers  mean  only  the  Cul-de-sac  at  the  cardiac  end  ; 
the  portion  intervening  between  it  and  the  antrum  pylori  js  often  termed 
the  body  of  the  stomach. 


DIGESTIOh 

band  is  usually  contracted  so  strongly  ;ni<l  continuously  thai  .1 
distinct  groove  is  seen  to  separate  the  tubular  antrum  from  the 

like  cardiac  end.  The  suggestion  of  a  massive  constricting 
1  mi;  of  muscle  is  belied  by  an  examination  of  the  dead  viscus. 
I  he  transverse  band  is  really  little  more  than  a  physiological 
sphincter.  The  empty  stomach  is  contracted  and  at  rest.  A 
few  minutes  after  food  is  taken  contractions  begin  in  the  antrum, 
and  run  on  in  constricting  undulations  (in  the  cat  at  the  rate  of 
six  in  the  minute)  towards  the  pyloric  sphincter.  Each  wave 
takes  about  twenty  seconds  (in  the  cat)  to  pass  from  the  middle 
of  the  stomach  to  the  pylorus.  Feeble  at  first,  they  become 
stronger  and  stronger  as  digestion  proceeds,  and  gradually  come 
to  involve  the  portion  of  the  fundus  next  the  sphincter  of  the 
antrum,  but  their  direction  is  always  towards  the  pylorus, 
never,  in  normal  digestion,  away  from  it.  The  food  is  thus  sub- 
jected to  energetic  churning  movements  in  the  pyloric  end  of 
the  stomach,  and  worked  up  thoroughly  with  the  gastric  juice. 
Kept  in  constant  circulation,  it  gradually  becomes  reduced  to 
a  semi-liquid  mass,  the  chyme,  which  is  at  intervals  driven 
against  the  pylorus  by  strong  and  regular  peristaltic  contrac- 
tions of  the  lower  end  of  the  stomach,  the  sphincter  relaxing 
from  time  to  time  by  a  reflex  inhibition  to  admit  the  better- 
digested  portions  into  the  duodenum,  but  tightening  more 
stubbornly  at  the  impact  of  a  hard  and  undigested  morsel.  The 
nature,  as  well  as  the  consistence  of  the  food,  influences  the 
length  of  its  sojourn  in  the  stomach.  Carbo-hydrate  food  passes 
more  rapidly  through  the  pylorus  than  fatty  food,  and  fat  more 
rapidly  than  protein.  The  reason  is  that  the  acidity  of  the 
gastric  juice  varies  with  the  different  kinds  of  food,  hydrochloric 
acid  being  secreted  in  abundance  in  the  presence  of  proteins,  and 
to  a  much  smaller  extent  in  the  presence  of  fats  and  carbo- 
hydrates. Now,  dilute  hydrochloric  acid  when  introduced  into 
the  stomach  remains  there  for  a  much  longer  time  than  water. 
This  depends  upon  the  fact  that  such  portions  of  the  acid  as  get 
into  the  duodenum  stimulate  afferent  fibres  in  its  mucous 
membrane,  and  so  cause  reflex  spasm  of  the  pyloric  sphincter. 
When  the  acid  chyme  becomes  neutralized  to  a  certain  point  by 
the  bile  and  pancreatic  juice,  inhibitory  impulses  pass  up  from 
the  duodenum  and  cause  the  sphincter  to  relax.  The  cardiac 
division  of  the  stomach,  with  the  exception  of  the  portion  that 
borders  the  transverse  band,  takes  no  share  in  the  peristaltic 
movements.  And,  indeed,  it  is  far  more  difficult  to  cause  such 
contractions  by  artificial  stimulation  in  the  fundus  than  in  the 
pylorus.  The  two  portions  of  the  stomach  are  partially,  or  in 
certain  animals  from  time  to  time  completely,  cut  off  from  each 
other  by  the  contraction  of  the  sphincter  of  the  antrum.     The 

20 


3o6 


A    M.l.\  I    II    OF    I'HY>I<>I.<><,  Y 


II  AM 


fundus,  so  t.ii  as  its  mechanical  functions  are  concerned,  acta 
chiefly  as  .1  resei  voir  for  the  loud,  which,  like  a  hopper,  it  gradually 
passes  into  the  pyloric  mill  as  digestion  goes  011  by  a  tonic 
contraction  of  its  walls.  The  existence  ol  this  reservou  enables 
larger  quantities  of  food  to  be  taken  at  one  meal,  which  can  then 

be  digested  gradually.  Tin—  fai  ts 
have  been  mainly  ascertained  by  ob- 
servations on  animals.  Mich  a>  the 
dog  and  the  cat,  either  by  direct  in- 
spection after  opining  the  abdomen 
(Rossbach),  or  in  the  intact  body, 
under  absolutely  physiological  condi- 
tions, by  means  of  the  Rontgen  rays 
(Cannon).  In  the  latter  method  the 
food  is  mixed  with  subnitrate  of 
bismuth,  which  is  opaque  to  these 
rays,  so  that  when  the  animal  is  looked 
at  through  a  fluorescent  screen  the 
stomach  appears  as  a  dark  shadow 
in  the  field  (Fig.  135).  Even  in  the 
excised  stomach,  kept  in  salt  solution 
at  the  body-temperature,  the  typical 
movements  can  be  observed  proceed- 
ing for  some  time. 

In  the  small  intestine  two  kinds  of 
movements  are  to  be  seen  :  (1)  Gentle, 
swaying.  '  pendulum  '  movements, 
sometimes  irregular,  but  often  recur- 
ring rhythmically  at  the  rate  (in  the 
dog)  of  10  or  12  in  the  minute.  Both 
the  longitudinal  and  the  circular  mus- 
cular coats  contract,  causing  slight 
waves  of  constriction,  which  may 
originate  at  any  part  of  the  gut.  hut. 
under  normal  circumstances,  nearly 
The  outlines  ol  the  stomach  always  travel  from  above  downwards, 
containing  food  mixed  with  bis-    with  a  velocity  of  2   to   5  centimetres 

per  second.  These  movements  cause 
the  coils  of  the  intestine  to  sway 
gently  from  side  to  side.  Under 
abnormal  conditions,  as  in  the  exposed  '  surviving  '  intes- 
tines of  the  rabbit,  contractions,  probably  similar  to  the 
pendulum  movements,  hut  running  indifferently  in  both  direc- 
tions, can  be  set  up  by  local  stimulation.  The  function 
of  these  pendulum  movements  seems  to  be  the  thorough 
mixing  of  the  food  with  the  digestive  juices  in  the  intestine. 


Fig.  135. — Cat's  Stomach  seen 
m  Rontgen  Rays  (Cannon). 


ninth   subnitrate    were 
at    intervals  from   11   a. in 
4.30  p.m. 


drawn 
to 


DIGESTION  507 

When  .in  animal  is  fed  with  food  containing  bismuth  subnitrate 
.iii.l  observed  with  the  Rontgen  rays,  it  is  seen  thai  the  food 
in  a  coil  is  often  divided  into  small  segments,  which  then  join 
together  to  form  longer  masses,  these  being  in  turn  again  divided. 
This  segmentation  is  rhythmically  repeated  (in  the  cat  at  the 
rate  .>!  thirty  times  a  minute).  Although  of  itself  it  insures  only 
the  mixing  of  the  contents  of  the  gut,  and  not  their  onward 
progress,  it  is  usually  accompanied  by  peristalsis,  so  that  while 
the  food  is  undergoing  segmentation,  it  is  also  slowly  passing 
down  the  intestine.  Often,  however,  a  column  of  food  remains 
for  a  considerable  time,  dividing,  uniting,  and  dividing  again, 
without  sensibly  shifting  its  position.  In  addition  to  the  rela- 
tively rapid  pendulum  movements,  much  slower  periodic  varia- 
tions of  tone  of  the  whole  musculature  may  be  normally  observed. 
(2)  True  peristaltic  movements,  in  which  a  ring  of  constriction, 
obliterating  the  lumen,  moves  slowly  down  the  tube,  with  a  speed, 
it  may  be,  no  greater  than  i  mm.  per  second.  The  portion  of 
the  intestine  immediately  below  the  advancing  constriction  is 
relaxed  and  motionless,  so  that  we  may  say  that  a  wave  of 
inhibition  precedes  the  wave  of  contraction.  The  peristaltic 
movements  of  the  small  intestine,  the  most  typical  of  their  kind, 
are  most  easily  excited  by  mechanical  stimulation  of  the  mucous 
membrane,  as  by  the  contact  of  a  morsel  of  food  or  an  artificial 
bolus  of  cotton-wool.  Travelling,  under  normal  conditions, 
always  downwards,  the  constriction  squeezes  the  contents  of  the 
tube  before  it,  and  the  wave  usually  ends  at  the  ileo-caecal  valve, 
which  separates  the  small  intestine  from  the  large.  The  cause 
of  the  definite  direction  of  the  peristaltic  wave  is  grounded  in 
the  anatomical  relations  of  the  intestinal  waU.  For  when  a 
portion  of  the  intestine  is  resected,  turned  round  in  its  place 
and  sutured,  so  that  what  was  before  its  upper  is  now  its  lower 
end,  the  contraction  wave  is  unable  to  pass,  and  the  obstruction 
to  the  onward  flow  of  the  intestinal  contents  causes  marked 
dilatation  of  the  gut,  and  sometimes  serious  disturbance  of 
nutrition.  The  most  probable  explanation  is  that  the  peristalsis 
is  governed  by  a  local  reflex  nervous  mechanism  (Auerbach's 
plexus),  the  stimulation  of  which  by  the  contact  of  the  food 
with  the  mucous  membrane  or  by  the  distension  of  the  gut 
causes  excitation  of  the  circular  muscular  fibres  above  the 
point  of  stimulation  and  inhibition  of  them  below  it.  The 
automatic  pendulum  movements  and  also  the  slow,  rhythmical 
variations  of  tone,  have  a  different  relation  to  the  local  nervous 
mechanism,  for  they  behave  differently  to  poisons  like  cocaine 
and  nicotine,  which  act  on  that  mechanism.  The  pendulum 
movements  are,  if  anything,  increased  in  intensity  and  made 
more  regular.     But  the  peristaltic   waves,   although   they  can 

20 — 2 


$08  A    M  INI    U    OF  PHYSIOLOG  \ 

be  Locally  excited  by  direct  stimulation  of  the  muscular  fibred, 
are  no  longer  propagated,  and  a  bolus  introduced  into  the  intes- 
tine remains  a1  rest  where  it  is  placed.  Some  have  interpreted 
these  facts  as  indicating  that  the  pendulum  movements  are 
myogenic  in  origin.  But  evidence  has  lately  been  obtained  that, 
although  they  are  not  reflex  movements  elicited  by  afferenl 
impulses  from  the  mucous  membrane,  since  they  continue  in 
unaltered  intensity,  in  isolated  loops  of  intestine  immersed  in 
Locke's  solution  (p.  139)  after  removal  of  both  mucosa  and  mi1>- 
mucosa,  they  are  nevertheless  dependent  upon  Auerbach's 
plexus.  For  when  the  circular  muscular  coat  is  separated  from 
this  plexus,  the  automatic  movements  of  this  coat  are  abolished, 
although  the  excitability  of  the  musculature  to  direct  stimulation 
is  not  affected.  The  longitudinal  coat,  which  is  still  in  connection 
with  Auerbach's  plexus,  goes  on  contracting  spontaneously 
(Magnus).  Under  certain  conditions  a  movement  of  food  or 
secretions  in  the  reverse  of  the  normal  direction  can  be  set  up 
in  the  small  intestine  in  the  intact  body, e.g.,  in  the  case  of  obstruc- 
tion of  the  intestine  leading  to  vomiting  of  its  contents.  But 
this  does  not  necessarily  indicate  a  reversal  of  the  normal  direc- 
tion of  the  peristalsis.  Such  a  reversal,  if  it  occurs  at  all,  is  not 
easy  to  realize  by  artificial  stimulation,  and  even  when  an  anti- 
peristaltic wave  is  apparently  started  it  travels  up  the  intestine 
only  for  a  short  distance  and  then  dies  out.  A  third  variety  of 
intestinal  movement  has  sometimes  been  described,  the  so- 
called  '  peristaltic  rush  '  (Meltzer,  etc.).  It  consists  of  a  rapidly 
moving  peristaltic  contraction,  preceded  by  relaxation  of  a  long 
portion  of  the  tube.  Such  a  contraction  may  even  sweep  down 
without  pause  from  the  duodenum  to  the  end  of  the  ileum. 

The  movements  of  the  large  intestine  differ  from  those  of 
the  small  mainly  in  the  great  frequency  of  antiperistalsis.  This. 
indeed,  seems  to  be  the  usual  movement  of  the  transverse  and 
ascending  colon.  The  antiperistalsis  recurs  in  periods  about 
every  fifteen  minutes,  and  each  period  generally  lasts  about  five 
minutes.  The  constrictions,  running  towards  the  caecum, 
thoroughly  churn  and  mix  the  remnants  of  the  food,  a  con- 
siderable absorption  of  which  may  take  place  in  the  upper  part 
of  the  large  intestine.  Regurgitation  into  the  ileum  in  man  is 
pi  evented  partly  by  the  oblique  entry  of  the  ileum  through  the 
wall  of  the  colon  (so-called  ileo-cascal  valve),  but  essentially  by 
the  tonic  contraction  of  the  ileo-colic  sphincter.  The  sphincter 
usually  permits  the  passage  of  material  only  in  the  direction 
from  smaD  to  large  intestine.  But  as  an  occasional  phenomenon, 
a  reverse  movement  may  occur.  Thus  food  may  actually  pass 
back  through  the  ileo-colic  sphincter  into  the  small  intestine 
under  the  action  of  a  long-continued  and  vigorous  antiperistalsis, 
and   a  this  way  a  considerable  portion  of  a  bulky  enema  may  be 


DIGES7  TON 

eventually  disposed  of  (Cannon).  This  so-called  antiperistalsis 
is  not  precisely  the  same  kind  oi  movemenl .  except  for  its  di 
t ion.  as  the  peristalsis  already  described  in  the  small  intestine, 
since  it  is  not  preceded  by  a  wave  of  inhibition.  True  peristaltic 
contractions  preceded  by  relaxation  of  the  gut  may  also  be 
observed  to  starl  in  the  caecum,  and  to  travel  down  the  large 
intestine.  They  are  not  very  frequent  in  comparison  with  those 
of  the  small  intestine,  and  they  die  away  hefore  reaching  the 
end  of  the  colon,  allowing  the  food  to  he  driven  hack  again 
towards  the  caecum  hy  the  antiperistalsis.  A  true  downward 
peristalsis  is  more  commonly  seen  in  the  descending  colon,  and 
is  here  associated  with  the  propulsion  and  collection  of  the 
faeces,  which  are  mainly  stored  in  the  sigmoid  flexure.  These 
peristaltic  contractions  do  not  normally  reach  the  rectum, 
which,  except  during  defalcation,  remains  at  rest. 

Influence  of  the  Central  Nervous  System  on  the  Gastro- 
intestinal Movements. — As  we  have  already  said,  these  move- 
ments are  much  less  closely  dependent  on  the  central  nervous 
system  than  are  those  of  the  oesophagus.  They  can  not  only  go 
on,  hut  are  in  general  hetter  marked  when  the  extrinsic  nervous 
connections  are  cut  ;  they  cannot  spread  when  the  continuity  of 
the  tube  is  destroyed,  and  the  mere  presence  of  food  will  excite 
them  when  other  than  local  reflex  action  has  been  excluded  by 
section  of  the  nerves.  Nevertheless,  the  central  nervous  system 
does  exercise  some  influence  in  the  way  of  regulation  and  control, 
if  not  in  the  way  of  direct  initiation  of  the  movements,  and  the 
swallowing  or  even  the  smell  of  food  has  been  observed  to 
strengthen  the  contractions  of  a  loop  of  intestine  severed  from 
the  rest,  but  with  its  nerves  still  intact.  The  vagus  is  the  efferent 
channel  of  this  reflex  action  :  stimulation  of  its  peripheral  end 
may  cause  movements  of  all  parts  of  the  alimentary  canal  from 
(esophagus  to  large  intestine,  and  may  strengthen  movements 
already  going  on  ;  but  section  of  it  does  not  stop  them,  nor  hinder 
the  food  from  causing  peristalsis  wherever  it  comes.  The  vagus 
also  contains  inhibitory  fibres  for  the  lower  end  of  the  oesophagus 
and  the  whole  of  the  stomach.  Stimulation  of  it  is  followed  first 
by  inhibition,  and  then,  after  an  interval,  by  an  increase  of  tone 
and  augmentation  of  the  contraction  of  the  whole  stomach, 
including  the  cardiac  and  pyloric  sphincters.  The  splanchnic 
nerves  contain  fibres  by  which  the  intestinal  movements  can  be 
inhibited,  and  they  appear  to  be  always  in  action,  for  after 
section  of  these  nerves  the  movements  are  strengthened.  On  the 
other  hand,  stimulation  of  the  peripheral  end  of  the  cut  splanchnic 
causes  arrest  of  the  movements.  Occasionally,  however,  it  has 
the  opposite  effect.  Contractions  of  the  small  intestine  are  more 
easily  caused  by  excitation  of  the  vagus  after  the  inhibitory 
splanchnic  nerves  have  been  cut.     The  splanchnics  also  contain 


310  A   MANUAL  OF  PHYSIOLOGY 

inhibitory  fibres  for  the  stomach,  and  it  is  only  when  these  are 
intact  that  complete  reflex  inhibition  of  the  organ  can  be 
obtained  in  the  rabbit  (Auer).  The  gastric  movements  are  not 
permanently  affected  hy  section  of  these  nerves  alone,  or  even  by 
simultaneous  section  of  the  splanchnics  and  the  gastric  branches 
of  the  vagi.  But  if  the  vagi  are  cut  while  the  splanchnics  remain 
intact,  the  peristalsis  of  the  stomach  is  weakened,  its  onset 
delayed,  and  the  proper  emptying  of  the  viscus  through  the 
pylorus  interfered  with.  In  all  probability  these  results  are  due 
to  the  uncontrolled  action  of  the  inhibitory  fibres.  The  splanch- 
nics have  a  special  relation  to  the  ileo-colic  sphincter,  which 
closes  when  they  are  stimulated,  and  becomes  insufficient  when 
they  are  cut.     The  vagus  does  not  affect  it. 

The  lower  part  of  the  large  intestine  is  influenced  by  the  sacral 
nerves  (second,  third,  and  fourth  sacral  in  the  rabbit),  and  by  certain 
lumbar  nerves,  in  the  same  way  as  the  higher  parts  of  the  alimentary 
canal,  and  particularly  the  small  intestine,  arc  influenced  by  the 
vagus  and  the  splanchnics.  Stimulation  of  these  sacral  nerves 
within  the  spinal  canal,  or  of  the  pelvic  nerves  (nervi  erigentes)  into 
which  they  pass,  causes  contraction  of  the  parts  of  the  large  intes- 
tine concerned  in  defalcation — that  is,  in  the  dog,  of  the  whole  colon, 
with  the  exception  of  the  caecum  ;  in  the  cat,  of  the  distal  two-thirds 
of  the  colon.  The  colon  first  undergoes  rapid  shortening  due  to 
the  contraction  of  the  longitudinal  fibres  and  the  recto-coccygeus 
muscle.  After  a  few  seconds  this  is  followed  by  contraction  of  tin- 
circular  fibres,  beginning  at  the  lower  limit  of  the  region  in  which 
antiperistalsis  can  occur,  and  spreading  downwards,  so  as  to  empty 
the  portion  of  the  bowel  involved  in  the  contraction.  This  is  a  very 
close  imitation  of  what  occurs  in  natural  defalcation.  In  man  the 
parts  involved  in  these  movements  are  probably  the  sigmoid  flexure 
and  rectum.  In  addition  to  these  characteristic  motor  effects  on  the 
lower  part  of  the  large  intestine,  stimulation  of  the  pelvic  nerves 
causes  an  increase  in  the  antiperistalsis  of  its  upper  portions.  Stimu- 
lation of  the  lumbar  nerves  or  of  the  portions  of  the  sympathetic 
into  which  their  visceral  fibres  pass  (lumbar  sympathetic  chain  from 
second  to  sixth  ganglia,  or  the  rami  from  it  to  the  inferior  mesenteric 
ganglia)  causes  inhibition  of  the  movements  of  the  caecum  and  the 
whole  colon,  including  the  antiperistaltic  movements. 

Excitation  of  the  sacral  nerves  initiates  or  increases  the  contraction 
of  both  coats  of  the  portions  of  the  large  intestine  on  which  they  act, 
excitation  of  the  lumbar  nerves  inhibits  both.  And  in  the  small 
intestine  the  same  law  holds  good  ;  the  two  coats  arc  contracted 
together  by  the  action  of  the  vagus  or  inhibited  together  by  that  of 
the  splanchnics.  With  the  establishment  of  these  facts,  the  theory 
that  the  same  nerve  which  causes  contraction  of  the  circular  coat  in 
all  tubes  whose  walls  are  made  up  of  two  layers  of  muscle  also  con- 
tains fibres  that  bring  about  inhibition  of  the  longitudinal  coat,  and 
vice  versa,  falls  to  the  ground.  It  was  suggested  that  in  this  way 
antagonism  between  the  two  coats  was  prevented. 

Defaecation  is  partly  a  voluntary  and  partly  a  reflex  act. 
But  in  the  infant  the  voluntary  control  has  not  yet  been  de- 
veloped ;  in  the  adult  it  may  be  lost  by  disease  ;  in  an  animal 


DIGESTION  jii 

it  may  be  abolished  by  operation,  and  in  each  case  the  action 
becomes  wholly  reflex.  In  the  normal  course  of  events,  the  pres- 
sure of  the  faeces  accumulating  in  the  sigmoid  flexure  at  last  begins 
to  elicit  the  discharge  of  that  reflex  contraction  of  the  lower 
portion  of  the  bowel  already  described  (p.  310),  of  which  the  pelvic 
nerves  constitute  the  efferent  path.  At  the  same  time,  the  sensa- 
tions  set  up  by  the  presence  of  faeces  in  the  rectum,  the  lower 
part  of  which,  at  any  rate,  is  empty  and  quiescent  in  the  intervals 
of  defecation,  give  rise  to  the  characteristic  desire  to  empty  the 
bowels.  This  desire  may  for  a  time  be  resisted  by  the  will,  or  it 
may  be  yielded  to.  In  the  latter  case  the  abdominal  muscles 
are  forcibly  contracted,  and  the  glottis  being  closed,  the  whole 
effect  of  their  contraction  is  expended  in  raising  the  pressure 
within  the  abdomen  and  pelvis,  and  so  aiding  the  muscular  wall 
of  the  bowel  itself  in  driving  the  feces  from  the  sigmoid  flexure  to 
the  rectum.  The  two  sphincters  which  close  the  anus — the  internal 
sphincter  of  smooth  muscle,  and  the  external  of  striated — are 
now  relaxed  by  the  inhibition  of  a  centre  in  the  lumbar  portion  of 
the  spinal  cord,  through  the  activity  of  which  the  tonic  contrac- 
tion of  the  sphincters  is  normally  maintained.  This  relaxation 
is  partly  voluntary,  the  impulses  that  come  from  the  brain  acting 
probably  through  the  medium  of  the  lumbar  centre.  But  in  the 
clog,  after  section  of  the  cord  in  the  dorsal  region,  the  whole  act 
of  defecation,  including  contraction  of  the  abdominal  muscles  and 
relaxation  of  the  sphincters,  still  takes  place,  and  here  the  process 
must  be  purely  reflex.  Even  after  complete  destruction  of  the 
lumbar  and  sacral  portions  of  the  spinal  cord  the  tone  of  the 
sphincters  returns  after  a  time,  and  defecation  is  carried  on  as  in 
a  normal  animal,  the  control  of  the  sphincters  being  due  either 
to  a  property  of  the  muscular  tissue  itself  or  to  local  ganglia. 
The  contraction  of  the  levatores  ani  helps  to  resist  overdistension 
of  the  pelvic  floor  and  to  pull  the  anus  up  over  the  feces  as  they 
escape.  The  nervi  erigentes  carry  efferent  constrictor  fibres,  and 
the  hypogastrics,  as  a  rule,  efferent  dilator  fibres,  to  the  sphincters. 
While  the  internal  sphincter  is  by  itself  capable  of  maintaining  a 
tonus  of  considerable  strength,  the  external  sphincter  contributes 
an  important  share  (30  to  60  per  cent.)  to  the  closure  of  the 
rectum. 

The  time  of  passage  of  substances  through  the  alimentary 
canal  has  been  studied  by  administering  collodion  capsules 
filled  with  subnitrate  of  bismuth  to  human  beings,  and  observing 
their  progress  by  taking  shadow  pictures  of  them  at  intervals 
with  the  Rontgen  rays.  During  the  first  twenty  minutes  two 
such  capsules  swallowed  at  the  same  time  by  a  healthy  young 
man  were  clearly  seen  in  the  greater  curvature  of  the  stomach, 
but  in  the  interval  between  the  first  half-hour  and  the  seventh  or 


}I2  I   M  l  \r  //    OF  PHYSIOLOGY 

cightli  houi  ii"  further  trace  of  them  was  detected.  Aboul  the 
eighth  hour  they  reappeared  in  the  caecum,  where  they  remained 
with  little  or  no  onward  movement  till  the  fourteenth  hum. 
From  the  fourteenth  to  the  sixteenth  houi  they  travelled  along 

the  ascending  colon,  and  tarried  a  long  time  at  the  left  angle  of 
the  colon.  From  the  nineteenth  to  the  twenty  second  oi  twenty- 
fourth  hour  they  slowly  passed  downward  in  the  descending  colon 
and  stopped  at  the  sigmoid  flexure,  till  their  expulsion  in  defal- 
cation. In  some  subjects  the  entire  passage  oi  the  capsules  was 
complete  in  sixteen  hours,  in  others  not  until  after  thirty  hours. 

Vomiting. — We  have  seen  that  under  normal  conditions  th< 
movements  of  the  alimentary  canal  always  tend  to  carry  the  food 
in  one  definite  direction,  along  the  tube  from  the  month  to  the 
rectum.  The  peristaltic  waves  generally  run  only  in  this  direc- 
tion, and,  further,  regurgitation  is  prevented  at  three  points  by 
the  cardiac  and  pyloric  sphincters  of  the  stomach  and  the  ileo- 
colic sphincter  and  valve.  But  in  certain  circumstances  the 
peristalsis  may  be  reversed,  one  or  more  of  the  guarded  orifices 
forced,  and  the  onward  stream  of  the  intestinal  contents  turned 
back.  In  obstruction  of  the  bowel,  the  faecal  contents  of  the 
large  intestine  may  pass  up  beyond  the  ileo-caecal  valve,  and. 
reaching  the  stomach,  be  driven  by  an  act  of  vomiting  through 
the  cardiac  orifice  ;  in  what  is  called  a  '  bilious  attack,'  the  con- 
tents of  the  duodenum  may  pass  back  through  the  pylorus  and 
be  ejected  in  a  similar  way  ;  or,  what  is  by  far  the  most  common 
case,  the  contents  of  the  stomach  alone  may  be  expelled. 

Vomiting  is  usually  preceded  by  a  feeling  of  nausea  and  a  rapid 
secretion  of  saliva,  which  perhaps  serves,  by  means  of  the  air 
carried  down  with  it  when  swallowed,  to  dilate  the  cardiac  orifice 
of  the  stomach,  but  may  be  a  mere  by-play  of  the  reflex  stimula- 
tion bringing  about  the  act.  The  diaphragm  is  now  forced  down 
upon  the  abdominal  viscera,  first  with  open  and  then  with  closed 
glottis.  The  thoracic  portion  of  the  (esophagus  is  thus  placed 
under  diminished  pressure,  and  therefore  widened,  while  saliva 
and  air  are  aspirated  into  it  out  of  the  mouth.  The  abdominal 
muscles  strongly  contract.  At  the  same  time  the  stomach  itself, 
and  particularly  the  antrum  pylori,  contracts,  the  cardiac  orifice 
relaxes,  and  the  gastric  contents  are  shot  uj>  into  the  lax  (eso- 
phagus, and  through  it  into  the  pharynx,  and  issue  by  the  mouth 
or  nose.  The  movements  of  the  stomach  during  vomiting  induced 
by  apomorphine  have  been  studied  in  the  cat  by  the  Rontgen  ray 
method.  There  is  first  observed  extreme  relaxation  of  the  cardiac 
end  ;  then  a  deep  constriction  appears  a  little  below  the  cardiac 
orifice,  and  runs  towards  the  pylorus,  increasing  in  depth  as  it 
goes.  When  the  transverse  band  is  reached,  this  contracts 
firmly  and  remains  contracted,  and  the  constriction  passes  on 


DIGESTION 

ovei  the  antrum  pylori.  Ten  oi  twelve  similai  waves  follow,  a1 
the  end  of  which  time  the  constriction  in  the  region  of  the  trans- 
verse band  divides  the  stomach  into  the  firmly-contracted 
antrum  and  the  relaxed  fundus.  Now  follows  a  sudden  contrac- 
tion of  the  diaphragm  and  abdominal  muscles  accompanied  by 
the  opening  of  the  cardiac  orifice.  Either  the  diaphragm  and 
abdominal  muscles  alone,  without  the  stomach,  or  the  diaphragm 
and  stomach  together,  without  the  abdominal  muscles,  can  carry 
out  the  act  of  vomiting.  For  an  animal  whose  stomach  has  heen 
replaced  by  a  bladder  filled  with  water  can  be  made  to  vomit  by 
the  administration  of  an  emetic  (Magendie)  ;  and  Hilton  saw  that 
a  man  who  lived  fourteen  years  after  an  injury  to  the  spinal  cord 
at  the  height  of  the  sixth  cervical  nerve,  which  caused  complete 
paralysis  below  that  level,  could  vomit,  though  with  great  diffi- 
culty.  In  a  young  child  in  which  very  slight  causes  will  induce 
vomiting,  the  stomach  alone  contracts  during  the  act.  But  in 
the  adult  such  a  contraction  is  ineffectual,  and  the  same  is  the 
case  in  animals,  for  a  dog  under  the  influence  of  a  moderate  dose 
of  curara,  which  paralyzes  the  voluntary  muscles  but  not  the 
stomach,  cannot  vomit. 

The  nerve-centre  is  in  the  medulla  oblongata.  It  may  be 
excited  by  many  afferent  channels  :  the  sensory  nerves  of  the 
fauces  or  pharynx,  of  the  stomach  or  intestines  (as  in  strangulated 
hernia),  of  the  liver  or  kidney  (as  in  cases  of  gall-stone  or  renal 
calculi),  of  the  uterus  or  ovary,  and  of  the  brain  (as  in  cerebral 
tumour),  are  all  capable,  when  irritated,  of  causing  vomiting  by 
impulses  passing  along  them  to  the  vomiting  centre. 

The  vagus  nerve  in  man  certainly  contains  afferent  fibres  by 
the  stimulation  of  which  this  centre  can  be  excited,  for  it  has  been 
noticed  that  when  the  vagus  was  exposed  in  the  neck  in  the  course 
of  an  operation,  the  patient  vomited  whenever  the  nerve  was 
touched  (Boinet,  quoted  by  Gowers).  In  meningitis,  vomiting 
is  often  a  prominent  symptom,  and  is  sometimes  due  to  irritation 
of  the  vagus  nerve  by  the  inflammatory  process. 

Some  drugs  act  as  emetics  by  irritating  surfaces  in  which 
efficient  afferent  impulses  may  be  set  up,  the  gastric  mucous 
membrane,  for  example  ;  sulphate  of  zinc  and  sulphate  of  copper 
act  mainly  in  this  way.  Apomorphine,  on  the  other  hand,  stimu- 
lates the  centre  directly,  and  this  is  also  the  mode  in  which  vomit- 
ing is  produced  in  certain  diseases  of  the  medulla  oblongata. 
The  efferent  nerves  for  the  diaphragm  are  the  phrenics,  for  the 
abdominal  muscles  the  intercostals.  The  impulses  which  cause 
contraction  of  the  stomach  pass  along  the  vagi.  Dilatation  of 
the  cardiac  orifice  is  brought  about  by  the  inhibitory  fibres  in 
the  vagus  already  mentioned. 


314  '    MANUAl    OF  PHYSIOLOGY 

II.  The  Chemical  Phenomena  of  Digestion. 

Ferments. — The  chemical  changes  wrought  in  the  food  as  it 
passes  along  the  alimentary  canal  are  due  to  the  secretions  of 
various  glands  which  line  its  cavities  or  pour  their  juices  into  it 
through  special  ducts.  These  secretions  owe  their  power  for  the 
most  part  to  substances  present  in  them  in  very  small  amount. 
but  which,  nevertheless,  act  with  extraordinary  energy  upon  tin 
various  constituents  of  the  food,  causing  profound  changes  with- 
out, upon  the  whole,  being  themselves  used  up,  or  their  digestive 
power  affected.  The  active  agents  are  the  enzymes,  sometimes 
spoken  of  as  unformed  or  unorganized  ferments— unorganized 
because  their  action  does  not  depend  upon  the  growth  of  living 
cells,  which  was  long  supposed  to  be  the  case  for  some  other 
ferments,  such  as  yeast.  Since  it  has  been  shown  that  specific 
enzymes  can  be  separated  from  cells  which  were  formerly  believed 
to  act  by  their  mere  growth,  the  distinction  between  formed  and 
unformed  ferments  has  lost  its  significance,  and  has  to  a  great 
extent  been  superseded  by  the  distinction  between  intra-  and 
extra-cellular  enzymes — i.e.,  between  ferments  which  normally 
act  in  the  interior  of  the  cells  where  they  are  produced  and 
ferments  which  act  outside  of  the  cells  that  secrete  them.  From 
yeast  cultures,  for  instance,  by  crushing  the  cells,  a  substance 
can  be  obtained  which  in  the  complete  absence  of  living  yeast- 
cells,  and,  indeed,  of  any  living  micro-organism,  forms  alcohol 
and  carbon  dioxide  from  sugar,  just  as  living  yeast  does.  There  is 
every  reason  to  believe  that  it  is  by  the  intracellular  action  of  this 
endoenzyme  that  the  yeast-cell  normally  causes  alcoholic  fermen- 
tation. The  digestive  ferments  are  typical  extracellular  enzymes. 
Their  chemical  nature  has  not  been  exactly  made  out  ;  some  of 
them  at  least  do  not  appear  to  be  proteins,  or  to  contain  a  protein 
group.  Some  of  them  apparently  exist  in  the  colloidal  condition, 
although  this  has  not  been  shown  for  all.  In  certain  cases  the 
more  or  less  stable  union  of  a  definite  inorganic  substance  with  the 
ferment,  or  its  actual  inclusion  in  the  ferment  molecule,  seems  to 
be  a  condition  of  its  action.  Thus  there  is  reason  to  believe  that 
in  gastric  digestion  hydrochloric  acid  is  loosely  combined  with 
the  pepsin.  In  the  plant  oxydase,  laccase  (p.  264),  manganese 
is  present.  And  the  fact  that  manganese  salts  oxidize  certain 
substances  as  laccase  does  suggests  that  it  is  the  manganese  in 
combination  with  some  protein  or  other  organic  compound  in 
the  ferment  molecule  which  confers  upon  laccase  its  oxidizing 
power.  A  similar  relation  between  iron  and  some  animal  oxydases 
is  possible,  though  not  definitely  proved.  But  none  of  the 
ferments  of  the  digestive  juices  has  as  yet  been  satisfactorily 
isolated,  and  at  present  it  is  only  l>v  their  effects  that  we  recognise 


DIGEST  JOh  315 

them.     Some  of  them  acl  besl  in  an  alkaline,  some  in  an  acid 
medium.     They  all  agree  in  having  an  '  optimum  '  temperature, 

which  is  more  favourable  to  their  action  than  any  other  ;  a  low 
temperature  suspends  their  activity,  and  boiling  abolishes  it  for 
ever.  The  optimum  temperatures  of  the  majority  of  enzymes 
lie  between  370  and  530  C.  ;  the  '  killing  '  temperatures  between 
6o°  and  750  C.  when  they  are  heated  in  solutions,  but  considerably 
higher  when  they  are  heated  dry.  The  action  of  all  of  them  is 
hydrolytic — i.e.,  it  is  accompanied  with  the  taking  up  of  the 
elements  of  water  by  the  substance  acted  upon.  The  accumula- 
tion of  the  products  of  the  action  first  checks  and  then  arrests  it. 
It  has  been  demonstrated  in  the  case  of  some  enzymes  that 
this  is  due  to  their  action  being  reversible.  For  example,  lipase 
p.  334)  not  only  decomposes  ethyl  butyrate  or  glycerin  butyrate, 
but  also  builds  them  up  again  from  the  decomposition  products — 
e.g.,  glycerin  butyrate  from  glycerin  and  butyric  acid  (Hanriot, 
Kastle  and  Loevenhart).  Sometimes  the  action  is  not  strictly 
reversible  in  the  sense  that  precisely  the  original  material  is 
reconstructed,  but  from  the  products  of  the  hydrolysis  substances 
are  synthesized  or  condensed,  which  are  then  incapable  of  being 
split  by  the  ferment.  When  a  concentrated  solution  of  dextrose 
is  acted  on  for  a  long  time  by  yeast  maltase,  a  ferment  obtained 
from  yeast  which  changes  maltose  into  dextrose,  some  of  the 
dextrose  is  reconverted  into  isomaltose  and  dextrin-like  bodies. 
Isomaltose  is  not  again  hydrolysed  by  maltase.  The  ferment 
emulsin  contained  in  almonds  behaves  in  the  converse  way. 
It  hydrolyses  isomaltose  so  as  to  form  dextrose,  and  then  con- 
denses dextrose  to  maltose  (Armstrong). 

Many  of  the  ordinary  substances  of  the  laboratory  will  accelerate 
a  reaction  which  goes  on  slowly  in  their  absence.  These  are  called 
catalysers.  Some  writers  also  speak  of  catalysers  which  retard 
a  reaction  progressing  quickly  in  their  absence.  The  process  by 
which  the  reaction  is  accelerated  (or  retarded)  is  termed  catalysis. 
A  typical  catalyser  can  exert  its  action  when  it  is  present  in 
exceedingly  small  amount  in  comparison  with  the  substance 
acted  upon.  However  it  may  enter  into  the  reaction,  it  does 
not  take  part  in  the  formation  of  the  final  products  nor  contribute 
to  the  energy  changes,  and  for  this  reason  is  often  apparently  un- 
altered at  the  end  of  the  process.  A  classical  instance  of  catalysis 
is  the  inversion  of  cane-sugar  by  weak  acids,  i.e.,  the  change  of 
the  cane-sugar  into  a  mixture  of  equal  quantities  of  dextrose  and 
levulose — a  reaction  which  may  be  represented  by  the  equation  : 
C12H,,On  +  H20  =  C6H12Oe+  CbHjjA,. 

Cane-sugar.      Water.       Dextrose.         Levulose. 

This  is  a  reaction  which  occurs  also  when  the  sugar  is  simply 
dissolved  in  water,  but  with  extreme  slowness  at  the  ordinary 


316  A   MANUAL    OF  PHYSIOLOGY 

temperature,  although  more  rapidly  at  too  C.  I  he  efifed  of  the 
acid  is  to  catalyse  the  rea<  tion,  to  markedly  accelerate  it.  The 
hydrogen  ions  of  the  free  acid  appear  to  be  responsible  foi  tin- 
catalysis.  The  same  action  upon  cane-sugar  is  exerted  by  an 
enzyme,  invertase,  found  in  intestinal  juice,  although  the  laws 
governing  the  reaction  are  somewhat  different.  And  it  is 
probable  that  there  is  no  fundamental  difference  between  the 
action  of  the  digestive  enzymes  and  that  of  the  inorganic 
catalyse  rs. 

Not  even  the  markedly  specific  action  of  the  digestive  ferments  can 
be  considered  an  essential  distinction.  It  is  true  that  invertase  will 
act  upon  dextrose,  and  not  at  all  upon  maltose  or  lactase.  But  there 
arc  other  sugars,  e.g.,  ramnose,  a  trisaccharidc  with  the  formula 
C,J1 .,.,< )li;.  obtained  from  beet-sugar  residues,  which  it  will  hydrolysc. 
Ramnose  is  made  up  of  one  molecule  each  of  dextrose,  levulose,  and 
galactose.  On  heating  with  dilute  acids,  it  is  decomposed  into 
these  substances.  Invertase,  however,  only  splits  off  the  levulose 
molecule,  leaving  a  disaccharide  isomeric,  but  not  identical  with 
lactose.  Similarly  lactase,  which  is  without  action  upon  cane-sugar 
or  maltose,  will  hydrolyse  the  /3-galactosides,  and  maltase,  inert  as 
regards  cane-sugar  or  lactose,  will  hydrolyse  the  a-glucosides.  '  >n 
the  other  hand,  emulsin  decomposes  the  p-glucosides,  to  which 
group  most  of  the  natural  glucosidcs  belong,  as  well  as  the  £-galacto- 
sides  and  lactose.  From  ramnose  emulsin  splits  off  galactose, 
leaving  cane-sugar.  Since  the  a  and  /3  compounds  are  isomeric,  and 
differ  not  in  their  composition  but  in  their  structure,  it  has  been 
concluded  that  the  structure  of  the  molecule  of  a  substance  must  be 
related  to  the  structure  of  the  enzyme  which  can  act  on  it,  in  some 
such  way  as  a  lock  is  related  to  its  proper  key.  Thus  the  key  lactase 
fits  in  the  lock  lactose,  but  not  in  the  lock  dextrose  or  the  lock  mal- 
tose. 

As  to  the  manner  in  which  an  enzyme  increases  the  velocity  of  its 
appropriate  reaction,  it  is  not  easy  to  make  any  very  positive  state- 
ment. Several  possibilities  are  recognised,  of  which  two  have  been 
especially  discussed,  (i)  The  existence  of  the  enzyme  in  colloidal 
solution  may  be  important.  It  is  characteristic  of  colloidal  solutions, 
in  which  the  dissolved  substance  is  present  in  the  form  of  extremely 
fine  particles,  that  the  total  surface  of  the  particles  is  very  gn  .it 
in  proportion  to  the  mass  of  the  substance  in  solution.  Thus,  a 
sphere  of  about  the  same  volume  as  the  eyeball,  with  a  diameter  of, 
say,  2  centimetres,  would  have  a  surface  of  12  5  square  centimetres. 
If  this  material  were  subdivided  into  spheres  of  about  the  same 
volume  as  a  leucocyte,  with  a  diameter  of,  say,  10  m,  it  would  form 
eight  thousand  million  of  these  spheres,  with  a  total  surface  of  over 
_'.',  square  metres.  If  the  small  spheres  were  further  subdivided  into 
spherical  particles,  with  a  diameter  only  the  thousandth  part  of  that 

of  a  leucocyte,  sav        ,  each  would  form  a  thousand  million  of  these 

J  J  100 

particles,  and  the  total  surface  of  all  the  particles  would  be  about 
2,500  square  metres. 

Now.  it  is  known  that  the  intensity  of  action  of  some  of  the  in- 
organic catalysers  is  proportional  to  the  surface  exposed.  For 
example,  hydrogen  peroxide,  if  left  to  itself,  is  slowly  decomposed  into 
water  and  oxygen.     The  addition  of  finely  divided  platinum,  in  the 


DIGESTIOh  317 

form  "f  platinum  black,  greatly  hastens  the  decomposition,  and  the 

oxygen  bubbles  off.  A  colloidal  solution  of  platinum,  prepared  by 
passing  electric  sparks  between  two  platinum  electrodes  immersed 
in  distilled  water,  and  containing  the  metal  in  the  form  of  ultra- 
microscopic  particles,  is  still  more  effective.  The  precise  nature  of 
the  surface  effect  is  not  entirely  clear.  One  factor  appears  to  be 
an  increase  in  the  concentration  of  dissolved  substances  at  the  sur- 
Lur.  and  the  better  opportunity  for  mutual  action  thus  afforded  to 
the  ferment  and  the  substrate,  as  the  substance  acted  on  by  the 
ferment  is  termed.  The  greaf  extension  of  the  surface  cannot  be 
i he  only  factor  in  the  catalysis;  otherwise  any  fine  powder  or  sus- 
pension would  have  a  catalytic  action.  But  kaolin,  or  fine  sand,  or 
colloidal  solutions  of  ordinary  proteins  or  gelatin,  have  little,  if 
any,  effect  on  the  decomposition  of  hydrogen  peroxide. 

(2)  Enzymes  may  produce  their  effects  by  contributing  to  the 
formation  of  bodies  intermediate  between  the  substrate  and  the  end- 
products.  If  the  time  required  for  the  formation  of  a  given  quantity 
of  the  intermediate  compound  and  the  time  required  for  the  decom- 
position of  this  compound  into  the  final  products  of  the  ferment 
action  are  in  sum  less  than  the  time  required  for  the  direct  change 
of  the  substrate  into  the  end-products,  the  enzyme  will  clearly  act 
as  a  catalyser  of  the  reaction.  It  has  been  shown  that  in  the  case 
of  certain  inorganic  catalysers  this  does  occur.  There  is  some  evi- 
dence that  the  ferment  actually  combines  with  the  substrate,  the 
combination  then  breaking  up  to  form  the  end-products. 

The  Quantitative  Estimation  of  Ferment  Action. — Since  we  have  as 
yet  no  certain  method  of  freeing  the  digestive  ferments  from  im- 
purities, our  only  quantitative  test  is  their  digestive  activity.  And 
since  a  very  small  quantity  of  ferment  can  act  upon  an  indefinite 
amount  of  material  if  allowed  sufficient  time,  we  can  only  make  com- 
parisons when  the  time  of  digestion  and  all  other  conditions  are  the 
same.  If  we  find  that  a  given  quantity  of  one  gastric  extract,  acting 
on  a  given  weight  of  fibrin,  dissolves  it  in  half  the  time  required  by 
an  equal  amount  of  another  gastric  extract,  or  dissolves  twice  as 
much  of  it  in  a  given  time,  we  conclude  that  the  digestive  activity  of 
the  pepsin  is  twice  as  great  in  the  first  extract  as  in  the  second.  But 
this  does  not  permit  us  to  say  that  the  one  contains  twice  as  much 
pepsin  as  the  other.  For  it  has  been  found  that  the  amount  of  diges- 
tion in  a  given  time  is  not  directly  proportional  to  the  quantity  of 
ferment  present,  but  to  the  square  root  of  the  quantity  of  ferment 
(Schutz's  law).  This  law  was  deduced  by  Schiitz  for  pepsin,  but  is 
said  to  hold  also  for  trypsin,  steapsin,  and  ptyalin  (Pawlow,  Vernon). 
To  determine  the  amount  of  proteolysis  the  nitrogen  of  the  protein 
which  has  gone  into  solution  may  be  estimated  (p.  482).  The 
following  table  shows  the  results  of  one  experiment  : 


Pepsin  Solution 
in  c.c. 

used 

Digested  Nitrogen  in 

Grammes. 

Found. 

Calculated. 

I 

4 

9 

16 

0-0230 
0-0427 
OO686 
0-0889 

00223 
0-0446 
O0669 

0-0892 

I    MA  \  I    //    OF   PHYSIOLOG ) 

Or  .t  piece  oi  a  glass  capillary-tube  filled  with  beat-coagulated  egg- 
white  may  be  cut  ofl  and  placed  in  the  digestive  mixture  (Mctt's 
tubes).     At   the  end  of  the  period  oi  digestion  tin-  length  ol  the 

piece  of  tube  and  that  <>f  the  undigested  remnant  "I  the  column  ot 
coagulated  protein  are  measured  with  a  millimetre  scale  under  a 
low-power    microscope.     The    difference    gives   the    Length    oi    the 

column  digested.  If  i  c.C.  of  gastric  juice  caused  in  a  given  time 
digestion  of  2  mm.  of  the  egg-white.  4  c.c.  of  the  same  juice  would 
digest  in  the  same  time  and  under  identical  conditions  about  4  mm., 
and  9  c.c.  about  6  mm. 

Besides  the  ferments  of  the  digestive  juices  which  act  extra- 
cellularly  in  the  lumen  of  the  alimentary  canal,  and  those  which 
do  their  work  intracellularly  in  its  walls,  micro-organi-in-  are 
present  in  the  gut,  and  even  in  normal  digestion  contribute  to 
the  changes  brought  about  in  the  food  ;  while  under  abnormal  con- 
ditions they  may  awaken  into  troublesome,  and  even  dangerous, 
activity.  It  is  now  known  that  many  of  these  act  by  pro- 
ducing intracellular  enzymes. 

It  may  be  noted  here,  although  the  subject  must  be  again 
referred  to  (p.  361),  that  specific  substances  capable  of  inhibiting 
the  action  of  ferments  exist.  Some  of  these  antiferments  are 
normally  present  in  the  body — an  antitrypsin,  for  instance,  in 
normal  blood-serum.  Xumerous  antiferments  may  be  artificially 
obtained  by  immunising  animals  with  the  original  ferments. 
Thus  an  antilipase  is  found  in  the  serum  of  rabbits  after  injection 
of  pancreatic  lipase,  and  an  antiemulsin  after  injection  of 
emulsin.  Injection  of  rennin  causes  the  formation  of  anti- 
rennin,  which  can  be  demonstrated  in  the  blood-serum  and  milk 
of  the  immunized  animal. 

It  is  now  necessary  to  consider  in  detail  the  nature  of  the 
various  juices  yielded  by  the  digestive  glands,  and  the  mechanism 
of  their  secretion.  Since  it  is  along  the  digestive  tract  that 
glandular  action  is  seen  on  the  greatest  scale,  this  discussion 
will  practically  embrace  the  nature  of  secretion  in  general. 
And  here  it  may  be  well  to  say  that,  although  in  describing 
digestion  it  is  necessary  to  break  it  up  into  sections,  a  true 
view  is  only  got  when  we  look  upon  it  as  a  single,  though  com- 
plex, process,  one  part  of  which  fits  into  the  other  from  beginning 
to  end.  It  is,  indeed,  the  business  of  the  physiologist,  wherever 
it  is  possible  to  insert  a  cannula  into  a  duct  and  to  drain  off  an 
unmixed  secretion,  to  investigate  the  properties  of  each  juice 
upon  its  own  basis  ;  but  it  must  not  be  forgotten  that  in  the 
body  digestion  is  the  joint  result  of  the  chemical  work  of  rive  or 
six  secretions,  the  greater  number  of  which  are  actually  mixed 
together  in  the  alimentary  canal,  and  of  the  mechanical  work  of 
the  gastro-intestinal  walls. 


DIGESTION  319 

The  Chemistry  of  the  Digestive  Juices. 

Saliva. — The  saliva  of  the  mouth  is  a  mixture  of  the  secre- 
tions of  three  large  glands  on  each  side,  and  of  many  small  ones. 
The  large  glands  arc  the  parotid,  which  opens  by  Stenson's 
duct  opposite  the  second  upper  molar  tooth  ;  the  submaxillary, 
which  opens  by  Wharton's  duct  under  the  tongue  ;  and  the  sub- 
lingual, opening  by  a  number  of  ducts  near  and  into  Wharton's. 
The  small  glands  are  scattered  over  the  sides,  floor,  and  roof  of 
the  mouth,  and  over  the  tongue. 

Two  types  of  salivary  glands,  the  serous  or  albuminous  and  the 
mucous,  are  distinguished  by  structural  characters  and  by  the 
nature  of  their  secretion  ;  and  the  distinction  has  been  extended 
to  other  glands.  The  parotid  of  many,  if  not  all,  mammals  is 
a  purely  serous  gland  ;  it  secretes  a  watery  juice  with  a  general 
resemblance  in  composition  to  dilute  blood-serum.  The  sub- 
maxillary of  the  dog  and  cat  is  a  typical  mucous  gland  ;  its 
secretion  is  viscid,  and  contains  mucin.  The  submaxillary 
gland  of  man  is  a  mixed  gland  ;  mucous  and  serous  alveoli, 
and  even  mucous  and  serous  cells,  are  intermingled  in  it. 
The  submaxillary  of  the  rabbit  is  purely  serous.  The  sublingual 
is,  in  general,  a  mixed  gland,  but  with  far  more  mucous  than 
serous  alveoli.  Some  of  the  small  glands  are  serous,  others 
mucous  in  type. 

The  mixed  saliva  of  man  is  a  somewhat  viscous,  colourless 
liquid  of  low  specific  gravity  (1002  to  1008,  average  about  1005), 
alkaline  to  litmus,  acid  to  phenolphthalein,  but  when  tested  by 
the  electrical  method  (p.  23)  almost  neutral.  Besides  water  and 
salts,  it  contains  mucin  (entirely  from  the  submaxillary,  the 
sublingual  and  the  small  mucous  glands  of  the  mouth),  to  which 
its  viscidity  is  due,  traces  of  serum-albumin  and  serum-globulin 
(chiefly  from  the  parotid),  and  a  ferment  called  ptyalin,  which 
hydrolyses  starch,  and  therefore  belongs  to  the  group  of  amylases 
or  diastases.  An  oxydase  or  oxidizing  ferment  is  also  present. 
The  salts  are  calcium  carbonate  and  phosphate  (often  deposited 
as  '  tartar  '  around  the  teeth,  occasionally  as  salivary  calculi 
in  the  glands  and  ducts),  sodium  bicarbonate,  sodium  and  potas- 
sium chloride,  and  almost  always  a  trace  of  sulphocyanide  of 
potassium,  detected  by  the  red  colour  which  it  strikes  with  ferric 
chloride.*  The  total  solids  amount  only  to  five  or  six  parts  in 
the  thousand.  A  great  deal  of  carbon  dioxide  can  be  pumped 
out  from  saliva,  as  much  as  60  to  70  c.c.  from  100  c.c.  of  the 

*  In  100  students  investigated  by  the  writer  the  saliva  only  once  failed 
to  give  the  reaction,  and  in  this  individual  a  trace  of  sulphocyanide  was 
present  3  days  later.  It  is  absent  from  the  saliva  of  many  animals.  In 
25  dogs  submaxillary  saliva  obtained  by  stimulation  of  the  chorda  tym- 
pani  only  once  gave  the  ferric  chloride  reaction,  and  then  faintly. 


320  /   MANUAL  OF  PHYSI01  0G  5 

secretion —  i.e. ,  more  than  can  be  obtained  from  venous  blood. 
Only  a  small  proportion  of  this  is  in  solution,  the  resl  existing  as 
carbonates.     Oxygen  i^  also  present  even  in  saliva  which  has 

not  come  into  contact  with  the  air,  and,  indeed,  in  somewhat 
greater  quantity  than  in  serum  (about  o*6  volume  per  cent. 
in  dog's  saliva).     Under  the  microscope  epithelial  scales,  dead 

and  swollen  leucocytes  (the  so-called  salivary  corpuscles), 
bacteria,  and  portions  of  food,  may  be  found.  All  these  things 
are  as  accidental  as  the  last — they  are  mere  flotsam  and  jetsam, 
washed  by  the  saliva  from  the  inside  of  the  mouth.  But  greatei 
significance  attaches  to  certain  peculiar  bodies,  either  spherical 
or  of  irregular  shape,  that  are  seen  in  the  viscid  submaxillary 
saliva  of  the  dog  or  cat.  They  appear  to  be  masses  of  secreted 
material.  The  quantity  of  saliva  secreted  in  the  twenty-four 
hours  varies  a  good  deal.  On  an  average  it  is  from  i  to  2  litres 
(Practical  Exercises,  p.  422). 

Besides  its  functions  of  dissolving  sapid  substances,  and  so 
allowing  them  to  excite  sensations  of  taste,  of  moistening  the 
food  for  deglutition  and  the  mouth  for  speech,  and  of  cleansing 
the  teeth  after  a  meal,  saliva,  in  virtue  of  its  ferment,  ptyalin, 
has  the  power  of  digesting  starch  and  converting  it  into  maltose, 
a  reducing  sugar.  In  man  the  secretion  of  any  of  the  three 
great  salivary  glands  has  this  power,  although  that  of  the  parotid 
is  most  active.  In  the  dog,  on  the  other  hand,  parotid  saliva 
has  little  action  on  starch,  and  submaxillary  none  at  all  ;  while 
in  animals  like  the  rat  and  the  rabbit  the  parotid  secretion  is 
highly  active.  In  the  horse,  sheep,  and  ox,  the  saliva  secreted 
by  all  the  glands  seems  equally  inert. 

When  starch  is  boiled,  the  granules  are  ruptured,  and  the 
starch  passes  into  imperfect  solution,  yielding  an  opalescent 
liquid.  If  a  little  saliva  be  added  to  some  boiled  starch  solution 
which  is  free  from  sugar,  and  the  mixture  be  set  to  digest  at  a 
suitable  temperature  (say  400  C),  the  solution  in  a  very  short 
time  loses  its  opalescence  and  becomes  clear.  It  still,  however, 
gives  the  blue  reaction  with  iodine  ;  and  Trommer's  test  (p.  10) 
shows  that  no  sugar  has  as  yet  been  formed.  The  change  is 
so  far  purely  a  physical  one  ;  the  substance  in  solution  is  soluble 
starch.  Later  on  the  iodine  reaction  passes  gradually  through 
violet  into  red  ;  and  finally  iodine  causes  no  colour  change  at 
all,  while  maltose  is  found  in  large  amount,  along  with  some 
isomaltose,  a  sugar  having  the  same  formula  as  maltose,  but 
differing  from  it  in  the  melting-point  of  the  crystalline  com- 
pound formed  by  it  with  phenyl-hydrazine  (p.  4<SN).  Traces  of 
dextrose,  a  sugar  which  rotates  the  plane  of  polarization  less 
than  maltose,  but  has  greater  reducing  power,  may  be  found 
among  the  end-products  when    the  digestion   is  conducted   in 


DIGESTlQH  jzt 

vitro.  It  is  possible  thar  this  is  produced  from  the  maltose  l>y 
maltase,  which  some  writers  assert  to  be  present  in  small  amount 
in  saliva.  Hut  the  observation  has  also  been  made  that  the  saliva 
itself  (in  the  cat)  may  contain  a  trace  of  dextrose  (Carlson). 

The  red  colour  indicates  the  presence  of  a  kind  of  dextrin 
called  erythrodextrin  ;  the  violet  colour  shows  that  at  first  this 
is  still  mixed  with  some  unchanged  starch.  Soon  the  erythro- 
dextrin disappears,  and  is  succeeded  by  another  dextrin,  which 
gives  no  colour  with  iodine,  and  is  therefore  called  achroodextrin. 
This  is  partly,  but  in  artificial  digestion  never  completely,  con- 
verted into  maltose,  and  can  always  at  the  end  be  precipitated 
in  greater  or  less  amount  by  the  addition  of  alcohol  to  the  liquid. 
It  is  probable  that  a  whole  series  of  dextrins  is  formed  during  the 
digestion  of  starch.  Some  of  these  may  appear  as  forerunners  of 
the  sugar,  others  merely  as  concomitants  of  its  production.  The 
latter  may  never  pass  into  sugar  ;  and  it  is  certain  that  sugar 
may  appear  before  all  the  starch  has  been  converted  into  achroo- 
dextrin. When  the  sugar  is  removed  as  it  is  formed,  as  is 
approximately  the  case  when  the  digestion  is  performed  in  a 
dialyser,  the  residue  of  unchanged  dextrin  is  less  than  when  the 
sugar  is  allowed  to  accumulate  (Lea).  In  ordinary  artificial 
digestion,  for  instance,  under  the  most  favourable  circumstances 
at  least  12  to  15  per  cent,  of  the  starch  is  left  as  dextrin  ;  in 
dialyser  digestions  the  residue  of  dextrin  may  be  little  more  than 
4  per  cent.  This  goes  far  to  explain  the  complete  digestion  of 
starch  which  takes  place  in  the  alimentary  canal,  a  digestion  so 
exhaustive  that,  although  soluble  starch  and  dextrin  may  be 
iound  in  the  stomach  after  a  starchy  meal,  they  do  not  occur  in 
the  intestine,  or  only  in  minute  traces.  Here  the  amylolytic 
ferment  of  the  pancreatic  juice,  which  is  essentially  the  same  in 
its  action  as  ptyalin,  only  more  powerful,  must  effect  a  very 
complete  conversion  of  the  starch  molecules  accessible  to  its 
attack.  It  is  not  inconsistent  with  this,  that  unchanged  starch 
granules  may  sometimes  be  excreted  in  the  faeces,  especially  when 
imbedded  in  raw  vegetable  structures. 

It  is  a  notable  fact  that  amylolytic  or  starch-splitting  ferments, 
also  called  diastases  or  amylases,  are  not  confined  to  the  animal 
body,  but  are  widely  distributed  in  plants.  A  diastase,  which 
is  present  in  all  sprouting  seeds,  and  may  be  readily  extracted 
by  water  from  malt,  forms  dextrin  and  maltose  from  starch. 
The  optimum  temperature  of  malt  diastase,  however,  is  about 
55°  C,  while  that  of  pytalin  is  about  400  C. 

While  a  neutral  or  weakly  alkaline  reaction  is  not  unfavourable 
to  salivary  digestion,  it  goes  on  best  in  a  slightly  acid  medium. 
It  has  been  shown  that  the  activity  of  ptyalin  on  starch,  both 
having  been  previously  dialysed  to  get  rid  as  far  as  possible 

21 


322  A   M.l\  UAL  OB   I'll  YSI01  OC  Y 

of  salts,  is  increased  by  the  addition  of  very  small  amounts  of 
acids  and  of  the  neutral  salts  of  strong  monobasic  acids.     The 

action  is  decreased  by  larger  amounts  of  acid  (00007  to  OOOI2 
per  cent,  of  hydrochloric  acid)  and  by  neutral  salts  ot  weak  acids. 
An  acidity  equal  to  that  of  a  01  per  cent,  solution  <>l  hydrochloric 
acid  stops  salivary  digestion  completely,  although  the  ferment  is 
still  for  a  time  able  to  act  when  the  acidity  is  sufficiently  reduced. 
Strong  acids  or  alkalies  permanently  destroy  it.  These  facts  in- 
dicate that  in  the  mouth,  where  the  reaction  is  weakly  alkaline, 
the  conditions  are  comparatively  favourable  to  the  action  ol  the 
ptyalin.  They  are  still  more  favourable  in  the  stomach  for  sonic 
time  after  the  beginning  of  a  meal,  while  the  reaction  is  \«t 
weakly  acid.  It  has  been  ohserved  that  (in  cats)  salivary  digestion 
may  go  on  for  an  hour  or  more  in  the  cardiac  end  of  the  stomach, 
since  free  hydrochloric  acid  does  not  appear  here  before  thai  time. 
Since  the  contents  of  the  cardiac  end  arc  not  freely  intermixed 
with  those  of  the  pyloric  end,  a  greater  proportion  of  sugar  is 
found  in  the  former,  and  the  difference  is  more  marked  with  solid 
than  with  liquid  food  (Cannon  and  Day).  But  during  the  greater 
part  of  gastric  digestion  the  degree  of  acidity  is  such  that  the 
ptyalin  must  be  hindered.  Although  the  food  stays  but  a  short 
time  in  the  mouth,  there  is  no  doubt  that,  in  man  at  least,  some 
of  the  starch  is  there  changed  into  sugar  (p.  424).  But  this 
is  not  the  case  in  all  animals.  Something  depends  on  the 
amylolytic  activity  of  the  saliva,  and  something  upon  the  form 
in  which  the  starchy  food  is  taken,  whether  it  is  cooked  or  raw, 
enclosed  in  vegetable  fibres  or  exposed  to  free  admixture  with 
the  secretions  of  the  mouth. 

The  fact  already  mentioned  that  hydrolytic  changes  of  the 
same  nature  as  those  produced  by  enzymes  can  be  brought  about 
in  other  ways  holds  good  for  ptyalin.  If  starch  is  heated  for  a  time 
with  dilute  hydrochloric  or  sulphuric  acid,  it  is  changed  first  into 
dextrin,  and  then  into  a  form  of  reducing  sugar,  which,  however, 
is  not  maltose,  but  dextrose.  If  maltose  is  treated  with  acid  in 
the  same  way,  it  is  also  changed  into  dextrose.  When  glycogen 
(p.  1)  is  boiled  with  dilute  oxalic  acid  at  a  pressure  of  three 
atmospheres,  isomaltose  and  dextrose  are  formed  (Cremer). 
Facts  will  be  cited  later  on  which  show  that  the  action  of  the 
other  digestive  ferments,  as  already  mentioned,  can  also  be 
imitated  by  purely  artificial  means.  Indeed,  we  may  say  that 
the  ferments  accomplish  at  a  comparatively  low  temperature 
what  can  be  done  in  the  laboratory  at  a  higher  temperature, 
and  by  the  aid  of  what  may  be  called  more  violent  methods. 

Gastric  Juice. — The  Abbe  Spallanzani,  although  not,  perhaps, 
the  first  to  recognise,  was  the  first  to  study  systematically,  the 
chemical  powers  of  the  gastric  juice,  but  it  was  by  the  careful 


DIGESTION  323 

and  convincing  experiments  of  Beaumont  that  the  foundation 
of  "iir  exact  knowledge  of  its  composition  and  action  was  laid. 

It  is  difficult  to  speak  without  enthusiasm  of  the  work  of  Beaumont, 

il  we  consider  the  difficulties  under  which  it  was  carried  on.  An 
anny  surgeon  stationed  in  a  lonely  post  in  the  wilderness  that  was 
then  called  the  territory  of  Michigan,  a  thousand  miles  from  a 
University,  and  lour  thousand  from  anything  like  a  physiological 
laboratory,  he  was  accidentally  called  upon  to  treat  a  gun-shot 
wound  of  the  stomach  in  a  Canadian  voyagcur,  Alexis  St.  Martin. 
When  the  wound  healed  a  permanent  fistulous  opening  was  left,  by 
means  of  which  food  could  be  introduced  into  the  stomach  and 
gastric  juice  obtained  from  it.  Beaumont  at  once  perceived  the 
possibilities  of  such  a  case  for  physiological  research,  and  began  a 
series  of  experiments  on  digestion.  After  a  while,  St.  Martin,  with 
the  wandering  spirit  of  the  voyageur,  returned  to  Canada  without 
Dr.  Beaumont's  consent  and  in  his  absence.  Beaumont  traced  him, 
with  great  difficulty,  by  the  help  of  the  agents  of  a  fur-trading 
company,  induced  him  to  come  back,  provided  for  his  family  as  well 
as  for  himself,  and  proceeded  with  his  investigations.  A  second 
time  St.  Martin  went  back  to  his  native  country,  and  a  second  time 
the  zealous  investigator  of  the  gastric  juice,  at  heavy  expense,  secured 
his  return.  And  although  his  experiments  were  necessarily  less 
exact  than  would  be  permissible  in  a  modern  research,  the  modest 
book  in  which  he  published  his  results  is  still  counted  among  the 
classics  of  physiology.  The  production  of  artificial  fistulae  in  animals, 
a  method  that  has  since  proved  so  fruitful,  was  first  suggested  by 
his  work. 

Gastric  juice  when  obtained  pure,  as  it  can  be  from  an  acci- 
dental fistula  in  man,  or,  better,  by  giving  a  dog  with  an  oeso- 
phageal as  well  as  a  gastric  fistula  a  '  sham-meal  '  (p.  374),  is  a 
clear,  thin,  colourless  liquid  of  low  specific  gravity  (in  the  dog 
1003  to  1006)  and  distinctly  acid  reaction.  The  total  solids 
average  about  5  parts  per  thousand,  of  which  the  ash  (chiefly 
sodium  and  potassium  chloride,  with  small  quantities  of  calcium 
and  magnesium  phosphate)  represents  about  a  fourth,  and  heat- 
coagulable  substances  (proteins,  nucleoprotein)  about  a  third. 
None  of  these  has  any  special  importance  in  digestion.  Of 
quite  a  different  significance  are  the  three  ferments  present  : 
pepsin,  which  changes  proteins  into  peptones  ;  rennin,  which 
curdles  milk  (but  see  p.  327)  ;  and  a  fat-splitting  ferment  which, 
under  certain  conditions  at  least,  splits  up  emulsified  neutral 
fats — e.g.,  the  fat  of  milk  —  into  glycerin  and  fatty  acids,  but 
has  no  action  upon  non-emulsified  fat.  The  acidity  is  due  to 
free  hydrochloric  acid,  the  other  important  constituent  of  the 
juice.  In  the  dog  the  proportion  of  this  acid  varies  from  0-46  to 
058  per  cent.  In  such  analyses  as  have  been  made  of  approxi- 
mately pure  human  gastric  juice  a  smaller  percentage  of  hydro- 
chloric, acid  has  usually  been  obtained  (at  most  0-35  to  04  per 
cent.).  But  there  is  some  reason  to  believe  that  if  the  human 
juice  could  be  collected  in  a  faultless  manner,  and  especially  free 

21 — 2 


524  \  MANUAL  OF  PHYSIOLOGY 

from  any  admixture  with  saliva  or  with  a  pathological  secretion 
of  mucus,  it  would  show  as  high  a  percentage  of  acid  as  the  dog's 
juice. 

In  cases  of  cancer,  whether  the  growth  is  situated  in  the 
stomach  or  not,  the  free  hydrochloric  acid  of  the  gastric  juice 
is  usually  much  reduced,  and  often  absent,  ruder  such  con- 
ditions some  lactic  acid  may  be  present  in  the  stomach,  being 
produced  from  the  carbo-hydrates  by  the  action  of  bacteria 
(Bacillus  acidi  lactici),  which  are  normally  held  in  check  l>y  the 
hydrochloric  acid,  although  not  rendered  incapable  of  growth 
when  they  have  passed  on  into  the  intestine.  Even  in  the 
strength  of  0-07  to  0-08  per  cent,  hydrochloric  acid  prevents  the 
formation  of  lactic  acid  from  dextrose.  Indeed,  when  all  the 
hydrochloric  acid  of  the  gastric  juice  is  combined  with  proteins, 
the  protein-acid  compound  still  inhibits  the  growth  of  bacteria 
in  the  stomach,  although  not  so  efficiently  as  the  same  amount 
of  free  acid.  That  in  normal  gastric  juice  the  acidity  is  not  due 
to  lactic  acid  can  be  shown  by  shaking  the  juice  with  ether, 
which  takes  up  lactic  acid,  and  then  applying  Uffelmann's  test 
to  the  ethereal  extract  (Practical  Exercises,  p.  428). 

More  than  this,  it  is  not  due  to  an  organic,  but  to  an  inorganic 
acid,  for  healthy  gastric  juice  causes  such  an  alteration  in  the 
colour  of  aniline  dyes  like  congo-red  and  methyl  violet  as  would 
be  produced  by  dilute  mineral  acids,  and  not  by  organic  acids, 
even  when  present  in  much  greater  strength.*  Finally,  when  the 
bases  and  acid  radicles  of  the  juice  are  quantitatively  compared, 
it  is  found  that  there  is  more  chlorine  than  is  required  to  combine 
with  the  bases  ;  the  excess  must  be  present  as  free  hydrochloric 
acid.  In  the  pure  gastric  juice  of  fishes  like  the  dogfish  and  skate, 
however,  the  acid  is  said  not  to  be  hydrochloric  but  an  organic 
acid.  The  quantity  of  gastric  juice  secreted  depends  upon  the 
nature  and  amount  of  the  food.  It  has  been  estimated  at  as  much 
as  5  litres  in  twenty-four  hours,  or  several  times  the  quantity  of 
saliva  secreted  in  the  same  time.  With  sham  feeding  a  dog  may 
yield  200-300  c.c.  in  an  hour. 

The  great  action  of  gastric  juice  is  upon  proteins.  In  this  two 
of  its  constituents  have  a  share,  the  pepsin  and  the  free  acid. 
One  member  of  this  chemical  copartnery  cannot  act  without  the 
other  ;  peptic  digestion  requires  the  presence  both  of  pepsin 
and  of  acid  ;  and,  indeed,  an  active  artificial  juice  can  be  obtained 
by  digesting  the  gastric  mucous  membrane  with  dilute  (02  to 
0-4  per  cent.)  hydrochloric  acid.     A  glycerin  extract  of  a  stomach 

*  A  dilute  solution  of  congo-red  is  turned  violet  by  organic  and  blue  by 
inorganic  acids  ;  the  gastric  juice  turns  it  blue.  Methyl  violet  is  rendered 
blue  by  an  inorganic  acid  like  hydrochloric  acid,  and  green  if  more  of  the 
acid  be  added.  It  is  not  altered  by  organic  acids.  Gastric  juice  turns  it 
blue. 


DIGESTION 

which  is  not  too  fresh  also  possesses  peptic  powers  ;  but  it 
requires  the  addition  of  a  sufficient  quantity  of  acid  to  render 
them  available. 

Well-washed  fibrin  obtained  from  blood  is  a  convenient  protein 
for  use  in  experiments  on  digestion.  Since  the  blood  contains 
traces  of  pepsin,  the  fibrin  should  be  boiled  to  destroy  any  which 
may  be  present  (see  also  p.  422). 

If  we  place  a  little  fibrin  in  a  beaker,  cover  it  with  gastric  juice 
obtained  from  a  dog  or  with  04  per  cent,  hydrochloric  acid,  to 
which  a  small  quantity  of  pepsin  or  of  a  gastric  extract  has  been 
added,  and  put  the  beaker  in  a  water-bath  at  400  C,  the  fibrin  soon 
swells  up  and  becomes  translucent,  then  begins  to  be  dissolved,  and 
in  a  short  time  has  disappeared  (see  Practical  Exercises,  p.  426).  If 
we  examine  the  liquid  before  digestion  has  proceeded  very  far,  we 
shall  find  chiefly  acid-albumin  in  solution  ;  later  on,  chiefly  albu- 
moses  ;  and  of  these  the  primary  albumoses  (proto-albumose  and 
hetero-albumose)  are  the  first  to  appear  in  quantity,  followed  by 
secondary  or  deutero-albumose  (p.  10).  Still  later,  peptones  in  large 
and  always  relatively  increasing  amounts  will  be  present  along  with 
the  albumoses.  From  this  we  conclude  that  acid-albumin  is  a  stage 
in  the  conversion  of  fibrin  into  albumose,  and  albumose  a  half-way 
house  between  acid-albumin  and  peptone.  It  must  not  be  supposed, 
however,  that  all  the  protein  is  first  changed  into  acid-albumin  before 
any  of  the  acid-albumin  is  changed  into  albumose,  or  that  all  the 
protein  has  already  reached  the  albumose  stage  before  peptone 
begins  to  appear.  On  the  contrary,  a  certain  amount  of  albumoses 
and  of  peptones  are  present  very  early  in  peptic  digestion,  while  the 
greater  part  of  the  original  protein  is  still  unaltered.  Similar,  but 
not  identical,  intermediate  substances  occur  in  the  digestion  of  the 
other  proteins,  including  that  of  bodies  like  gelatin,  which  are  not 
ordinary  proteins,  but  which  pepsin  can  digest.  The  generic  name 
of  proteose  properly  includes  all  bodies  of  the  albumose  type,  the 
term  '  albumose  '  itself  being  sometimes  reserved  for  such  inter- 
mediate products  of  the  digestion  of  albumin  ;  while  those  of  fibrin 
are  called  fibrinoses  ;  of  globulin,  globuloses  ;  of  casein,  caseoses  ; 
and  so  on.  The  peptones  produced  from  different  proteins  are  also 
not  absolutely  identical.  If  the  digestion  is  prolonged,  the  peptones 
are  in  turn  further  hydrolysed,  so  that  eventually  a  considerable 
proportion  of  the  original  protein  is  converted  into  amino-acids  and 
other  substances  (p.  332). 

In  the  stomach,  however,  during  the  four  or  five  hours  for 
which  gastric  digestion  ordinarily  lasts,  little,  if  any,  of  the 
protein  passes  beyond  the  stage  of  proteose  and  peptone,  and  it 
is  in  these  forms  that  the  bulk,  at  any  rate,  of  the  protein  food 
enters  the  duodenum.  The  pancreatic  juice,  as  we  shall  see 
later  on,  not  only  effects  a  more  complete  conversion  into 
peptone,  but  can  split  up  the  whole  or  a  very  large  proportion 
of  the  peptone  itself  into  substances  which  are  no  longer 
protein.  Since  the  subject  of  protein  digestion  must  come  up 
again,  it  will  be  well  to  postpone  any  closer  discussion  of  the 
process  till  we  can  view  it  as  a  wrhole.     In  the  meantime  it  is 


326  A   MANUAl    OF  PHYSIOLOGY 

only  necessary  1<>  repeat  that  pepsin  alone  cannot digesl  proteins 
at  all.  Its  action  requires  the  presence  of  an  acid  ;  in  a 
neutral  or  alkaline  medium  peptic  digestion  stops.  As  in  the 
case  of  other  ferments,  there  is  a  certain  temperature  at  which 
pepsin  acts  best,  an  'optimum'  temperature  (350  to  400  C,  or 
about  that  of  the  body).  At  o"  C.  it  is  inactive,  excepl  in  cold- 
blooded animals  (frog).     Boiling  destroys  it. 

Dilute  acid  alone  does  not  dissolve  coagulated  proteins  like 
boiled  fibrin,  or  does  so  only  with  extreme  slowness.  I'ncoagu- 
lated  proteins,  however,  are  readily  changed  by  it  into  acid- 
alhumin  ;  and  by  the  prolonged  action  of  acids,  especially  a1  a 
high  temperature,  further  changes  of  much  the  same  nature 
as  those  produced  in  peptic  digestion  may  be  caused  in  all 
proteins.  But  under  the  ordinary  conditions  of  natural  gastric 
digestion,  it  may  be  said  that  the  acid  alone  does  little  until  it 
is  aided  by  the  ferment,  just  as  the  ferment  alone  does  nothing 
without  the  aid  of  the  acid.  The  acid  enters  into  a  temporary 
combination  with  the  protein,  the  more  highly  hydrolysed  pro- 
teins, such  as  peptone,  combining  with  a  greater  proportion 
of  acid  than  such  proteins  as  fibrin  or  albumin.  These  com- 
pounds so  easily  undergo  hydrolytic  dissociation  that,  in  spite 
of  its  union  with  the  proteins,  the  hydrochloric  acid  is  able  to 
act.  along  with  the  pepsin,  so  that  peptic  digestion  goes  on  even 
when  enough  protein  is  present  to  combine  with  all  the  acid. 
There  is  evidence  that  in  the  gastric  juice  the  pepsin  exists  in 
the  form  of  an  unstable  compound  with  hydrochloric  acid,  and 
it  is  probably  this  pepsin-hydrochloric  acid  compound  which  is 
actual  catalytic  agent  in  peptic  digestion.  Although  hydro- 
chloric acid  acts  most  powerfully,  other  acids,  such  as  nitric, 
phosphoric,  sulphuric,  or  lactic  (arranged  in  the  order  of  their 
efficacy),  can  replace  it. 

The  milk-curdling  ferment,  roniiii.  or  chymosin,  is  contained  in 
large  amount  in  an  extract  of  the  fourth  stomach  of  the  calf, 
which,  as  rennet,  has  long  been  used  in  the  manufacture  of 
cheese.  It  exists  in  the  healthy  gastric  juice  of  man.  but  dis- 
appears in  cancer  of  the  stomach  and  in  chronic  gastric  catarrh. 
It  is  doubtful  whether  the  properties  of  rennin  are  ever  found  in 
gastric  juice  or  any  preparation  obtained  from  it  or  from  the 
gastric  mucous  membrane  unless  pepsin  is  present.  This  has 
suggested  that  there  is  no  separate  milk-curdling  ferment,  but 
that  the  clotting  of  caseinogen  is  merely  an  associated  action  of 
the  pepsin.  Proteolytic  ferments  of  the  most  varied  origin  will 
curdle  milk.  Pawlow  has  recently  shown  that  it  is  highly  prob- 
able that  the  milk-curdling  property  not  only  of  the  gastric 
juice,  but  also  of  the  pancreatic  juice  and  of  the  secretion  of 
Brunner's  glands,  is  associated  with  the  proteolytic  ferment. 


DIGESTWh  327 

He  states  thai  when  the  comparison  is  instituted  under  proper 
conditions  there  is  an  exacl  parallelism  between  the  proteolytic 
.iiul  the  milk-curdling  power  of  these  secretions,  no  matter 
what  the  circumstances  may  be  in  which  they  are  collected, 
or  the  influences  to  which  they  are  exposed  after  collection. 
He  has  found  it  impossible  to  separate  from  any  one  of  them 
a  fraction  which  has  milk-curdling  power  without  proteolytic 
1  h  >wer. 
The  curdling  of  milk  by  the  gastric  ferment  includes  two  pro- 

ses  :  (1)  An  action  on  caseinogen  in  the  course  of  which  a  sub- 
stance, whey-protein,  not  previously  present  in  the  milk,  is  pro- 
duced. This  substance  is  not  capable  of  being  converted  into 
casein,  and  remains  in  solution  in  the  whey.  (2)  The  altered 
caseinogen  is  precipitated  in  the  presence  of  calcium  salts,  but 
not  otherwise,  as  casein,  which  is  insoluble,  and  forms  the  curd. 
Dilute  acid  will  of  itself  precipitate  caseinogen,  and  the  presence 
of  acid,  and  particularly  hydrochloric  acid,  in  the  gastric  juice 
helps  its  milk-curdling  action.  But  that  a  ferment  is  really 
concerned  is  indicated  by  the  fact  that  the  juice,  after  being  made 
neutral  or  alkaline,  still  curdles  milk,  and  that  this  power  is 
destroyed  by  boiling.  The  optimum  temperature  is  the  same 
as  that  of  the  other  ferments  of  the  digestive  tract,  about  400  C. 

(P-  315)- 

As  to  the  exact  function  of  the  milk-curdling  ferment  of 
the  gastric  juice  in  digestion,  we  have  no  precise  knowledge. 
It  seems  superfluous  if  we  suppose  that  the  free  acid  is  able 
of  itself  to  do  all  that  the  ferment  does  along  with  it.  But 
there  is  evidence  that  the  curd  produced  by  the  ferment  is  more 
profoundly  changed  than  the  precipitate  caused  by  dilute  acids  ; 
for  the  latter  may  be  redissolved,  and  then  again  curdled  by 
rennin  in  the  presence  of  calcium  salts,  while  this  cannot  be  done 
with  the  former.  We  may  suppose,  then,  that  the  ferment  is 
capable  of  effecting  changes  more  favourable  to  the  subsequent 
action  of  the  pepsin  upon  the  casein  than  those  which  the  acid 
alone  would  effect.  Or  it  may  be  that  the  ferment  acts  in  the 
early  stages  of  digestion  before  much  acid  has  been  secreted. 
We  do  not  know  whether  the  curdling  of  milk  renders  it  easier 
for  the  watery  portion  to  be  absorbed  by  the  walls  of  the  stomach, 
or  insures  that  it  shall  be  more  rapidly  passed  on  into  the  duo- 
denum. If  this  were  the  case,  it  would  be  a  raison  d'etre  for  early 
curdling,  since  milk  is  a  very  dilute  food,  and  the  immense  pro- 
portion of  water  in  it  might  weaken  the  gastric  juice  too  much  for 
rapid  digestion  of  the  proteins.  But  caution  should  be  exercised 
in  giving  a  physiological  value  to  all  the  details  of  the  milk- 
curdling  action  of  the  gastric  juice.  Milk-curdling  ferments,  or, 
at  any  rate,  ferments  with  a  milk-curdling  influence,  have  an 


328  A   MANUAL  OF  PHYSIOLOGY 

extremely  wide  distribution,  both  in  secretions  which  in  norma) 
circumstances  i  an  never  come  into  contacl  with  milk,  and  in  the 
tissues  of  animals  and  plants.  Many  bacteria  produce  them. 
And  it  appears  that  in  the  suckling,  where  it  might  be  expected, 
if  anywhere,  to  have  a  definite  and  important  office,  the  rennet 
a<  imn  of  the  gastric  juice  is  distinctly-  Less  than  in  the  adult. 
It  is  worthy  of  note  that  the  curd  formed  by  rennet  from 
human  milk  is  more  finely  divided  than  that  formed  from  cow's 
milk,  and  therefore  is  more  easily  digested.  The  addition  ol 
lime-water  or  barley-water  to  cow's  milk  keeps  the  curd  from 
adhering  in  large  masses,  and  thus  aids  its  digestion  a  fact 
which  is  sometimes  usefully  applied  in  the  artificial  feeding 
infants. 

On  fats  gastric  juice  has  usually  heen  supposed  to  have  no 
action,  although  everybody  admits  that  it  will  dissolve  the 
protein  constituents  of  fat-cells  and  the  protein  substances 
which  keep  the  fat-globules  of  milk  apart  from  each  other.  It 
has.  however,  been  recently  shown  that  both  in  the  stomach 
and  in  vitro  (with  glycerin  extracts  of  the  gastric  mucous 
membrane)  a  considerable  amount  of  well-emulsified  fat  may  In- 
split  up.  Gastric  juice  splits  up  fat.  both  in  neutral  and  in 
weakly  acid  solutions.  The  slightest  excess  of  alkali  checks 
the  action.  The  glycerin  extract  is  much  more  resistant  to 
alkali,  while  very  sensitive  to  hydrochloric  acid.  This  indicates 
that  the  fat-splitting  ferment  exists  in  the  mucous  membrane 
in  a  different  form  from  that  in  which  it  exists  in  the  juice — 
namelv.  as  a  z.vmogen  or  mother-substance.  As  regards  the 
carbo-hydrates  the  swallowed  saliva  will  continue  to  act  on  starch 
in  the  stomach,  so  long  as  the  acidity  is  not  too  great  ;  while  the 
hydrochloric  acid  of  the  gastric  juice  is  able  to  invert  cane-sugar, 
changing  it  into  a  mixture  of  dextrose  and  levulose,*  and  also, 
doubtless,  to  hydrolyse  to  dextrose  a  portion  of  the  maltose 
formed  by  the  saliva.  Altogether,  there  is  no  doubt  that  the 
proportion  of  the  carbo-hvdrates  of  the  food  digested  in  the 
stomach  is  far  from  insignificant. 

The  Antiseptic  Function  of  the  Gastric  Juice. — The 
stomach,  with  its  acid  contents,  forms  during  the  greater  part 
of  gastric  digestion  a  valve  or  trap  to  cut  off  the  upper  end  of 

*  These  are  both  reducing  sugars,  but,  as  their  names  indicate,  they 
rotate  the  plane  of  polarization  in  opposite  directions.  The  specific 
rotatory  power  of  levulose  is  greater  than  that  of  dextrose,  so  that  when 
cane-sugar  is  completely  inverted,  although  equal  quantities  ol  dextrose 
and  levulose  are  produced,  the  plane  of  polarization  i>  rotated  to  the  left. 
Cane-sugar  itself  rotates  it  to  the  ri.sdit.  The  term  '  inversion  '  has  been 
extended  to  include  the  similar  hydrolysis  of  other  sugars  ot  the  disacchar- 
ride  group — e.g.,  maltose  to  dextrose,  and  lactose  to  a  mixture  of  dextrose 
and  galacto>e.  even  although  the  products  are  not  levo-rotatory. 


DIGESTION 

the  intestine  from  the  bacteria  infested  regions  of  the  month 
and  pharynx,  and  to  destroy  oi  inhibit  the  micro-organisms 
swallowed  with  the  food  and  saliva.  The  occasional  presence 
m  vomited  matter  of  sarcinae  or  regularly  arranged  groups  of 
micrococci,  generally  four  to  a  group,  shows  that  under  abnormal 
conditions  the  gastric  contents  are  not  perfectly  aseptic;  and 
even  from  a  normal  stomach  active  micro-organisms  of  various 
kinds  can  be  obtained.  But  upon  the  whole  there  is  no  doubt 
that  the  acidity  of  the  gastric  juice  is  an  important  check  on 
bacterial  activity  during  the  first  part  of  digestion,  and  in  the 
upper  portion  of  the  alimentary  canal.  Koch  has  shown  that 
the  acidity  of  the  gastric  juice  of  a  guinea-pig  is  sufficient  to 
kill  the  comma  bacillus  of  cholera.  Normal  guinea-pigs  fed 
with  cholera  bacilli  were  unaffected.  But  if  the  gastric  juice 
was  neutralized  by  an  alkali  before  the  administration  of  the 
bacilli  the  guinea-pigs  died.  Charrin  found,  too,  that  digestion 
with  pepsin  and  hydrochloric  acid  causes  an  appreciable  destruc- 
tion or  attenuation  of  diphtheria  toxin.  Bacteria,  like  the 
lactic  acid  bacillus,  which  form  acid  products,  may  be  less  pro- 
foundly affected  by  the  acid  gastric  juice  than  the  putrefactive 
bacteria,  which,  on  the  whole,  form  alkalies,  and  are  therefore 
accustomed  to  an  alkaline  medium.  Yet  we  have  seen  that  the 
growth  of  even  the  lactic  acid  bacillus  is  very  strictly  controlled 
when  the  gastric  juice  contains  the  normal  amount  of  hydro- 
chloric acid. 

It  has  been  supposed  by  some  that  this  bactericidal  action 
is  the  chief  function  of  the  stomach,  and  the  question  has  been 
asked  why  we  should  attribute  any  digestive  importance  to  the 
secretion  of  that  viscus,  since  the  pancreatic  juice  can  do  all 
that  the  gastric  juice  does,  and  some  things  which  it  cannot 
do.  Further,  it  has  been  shown  that  a  dog  may  live  five  years 
after  complete  excision  of  the  stomach,  comport  himself  in  all 
respects  like  a  normal  dog,  and  when  killed  for  autopsy  show 
every  organ  in  perfect  health  (Czerny).  In  man,  too,  the  stomach 
has  been  excised  with  a  successful  result.  But  if  this  is  to  be 
admitted  as  evidence  against  the  digestive  function  of  the 
stomach,  it  is  just  as  good  evidence  against  the  bactericidal 
function,  particularly  as  it  has  in  addition  been  shown  that 
even  putrid  flesh  has  no  harmful  effect  on  a  dog  after  excision 
of  the  stomach,  any  more  than  on  a  normal  dog.  And,  indeed, 
the  reasoning  is  fallacious  which  assumes  that  what  may  happen 
under  abnormal  conditions  must  happen  when  the  conditions 
are  normal.  For  nothing  is  impressed  more  often  on  the  physio- 
logical observer  than  the  extraordinary  power  of  adaptation,  of 
making   the   best   of  everything,   which    the   animal   organism 


.^o  I    u  I  \  i    //    OF  PHYSIOLOGY 

possesses.  Doubtless,  a  dog  without  a  stomach  will  us.-  to  the 
besl  advantage  the  digestive  fluids  that  remain  to  him  ;  and  the 
pancreatic  juice,  with  the  aid  of  the  bile  and  the  succus  entericus, 
may  be  adequate  to  the  complete  task  of  digestion.  So.  too,  a 
man  from  whom  the  surgeon  has  removed  a  kidney,  01  a  testicle, 
or  a  lobe  of  the  thyroid  gland,  may  be  in  no  respect  worse  off 
than  the  man  who  possesses  a  pair  of  these  organs.  Bui  what 
do  we  deduce  from  this  ?  Not,  surely,  that  the  excised  thyroid, 
or  testicle,  or  kidney  was  useless,  or  the  gastric  juice  inactive, 
hnt  that  the  organism  lias  been  able  to  compensate  itself  for 
their  loss.  Further,  it  would  seem  that  the  fate  of  the  protein 
or  of  part  of  the  protein  digested  and  absorbed  l>v  tin-  stomach 
is  different  from  that  digested  and  absorbed  by  tin-  intestine 
For  after  the  operation  of  gastroenterostomy  (the  establish- 
ment of  an  artificial  opening  hetween  the  stoma*  h  and  the  small 
intestine  through  which  the  food  passes  rapidly  without  having 
to  submit  to  the  challenge  of  the  pyloric  sphincter),  the  ingested 
nitrogen  is  more  quickly  eliminated  than  when  the  protein  is 
first  suhjected  to  full  gastric  digestion.  So  that  when  the 
quantity  of  protein  in  the  food  is  increased  above  that  neces- 
sary for  nitrogen  equilibrium  (p.  529)  none  of  the  excess  is 
assimilated  and  stored  up,  as  is  the  case  in  a  normal  animal 
I  Levin,  etc.). 

Pancreatic  Juice. — Pancreatic  juice,  bile,  and  intestinal  juice 
are  all  mingled  together  in  the  small  intestine,  and  act  upon  the 
food,  not  in  succession,  hut  simultaneously.  But  by  artificial 
fistuhc  in  animals  they  can  be  obtained  separately  ;  and  occa- 
sionally some  of  them  can  be  procured  through  accidental  fistulae 
in  man.  It  is  said  that  under  certain  conditions,  especially 
when  fat  or  oil  is  introduced  into  the  stomach,  the  pylorus  may 
remain  open  long  enough  to  permit  the  passage  of  pancreatic 
juice  or  bile  from  the  duodenum  into  the  stomach,  and  this  has 
been  recommended  as  a  practical  method  of  obtaining  these 
secretions  in  man. 

Human  pancreatic  juice,  as  obtained  from  a  fistula,  is  a  clear. 
only  slightly  viscid  liquid  of  distinctly  alkaline  reaction  to 
litmus.  Its  specific  gravity  is  aboul  1007  to  mm.  The  total 
solids  constitute  about  1  "5  or  2  per  cent.,  of  which  a  little  less 
than  1  pei  cent,  is  made  up  of  inorganic  salts,  chiefly  sodium 
carbonate,  with  small  quantities  of  chlorides.  The  balance  of 
the  solids  consists  mainly  of  proteins.  The  alkaline  reaction 
is  due  to  the  sodium  carbonate,  and  it  is  worthy  of  remark,  as 
showing  the  important  part  la  ken  by  this  secret  ion  in  the  neutrali- 
zation of  the  chyme,  that  when  titrated  against  standard  acid 
the  alkalinity  of  the  pancreatic  juice  is  not  much  less  than  the 


DIGESTION  $31 

acidity  of  the  gastric  juice  when  titrated  againsl  standard 
alkali.  The  quantity  oi  pancreatic  juice  secreted  during  the 
Iwenty-four  hours  in  an  average  man  has  been  estimated  at 
to  800  c.c.  from  observations  on  cases  of  fistula.  Probably 
under  perfectly  normal  conditions  it  is  greater.  A  so-called 
artificial  pancreatic  juice  can  be  made  by  extracting  the  pancreas 
with  water  or  glycerin.  Since  better  methods  of  obtaining  the 
natural  juice  have  been  developed,  these  extracts  have  lost  some 
of  their  importance. 

Fresh  pancreatic  juice  contains  four  ferments  :  (i)  The  mother- 
substance,  trypsinogen,  of  a  proteolytic  or  protein-digesting 
ferment,  trypsin  ;  (2)  an  amylolytic  ferment,  amylopsin  ;  (3)  a 
fat-splitting  or  lipolytic  ferment,  steapsin  ;  (4)  a  milk-curdling 
ferment.  It  is  doubtful  whether  the  last  is  a  different  body 
from  the  trypsin  (see  p.  326).  In  any  case,  it  cannot  be  con- 
sidered as  taking  any  practical  share  in  digestion,  since  it  can 
hardly  ever  happen  that  milk  passes  through  the  stomach  with- 
out being  curdled. 

Trypsinogen  has  no  action  upon  proteins,  but  in  normal 
digestion  it  is  changed  into  active  trypsin  by  the  enterokinase 
of  the  intestinal  juice  (p.  343).  Pancreatic  juice  collected  with- 
out contact  with  intestinal  contents  or  with  the  mucous  mem- 
brane of  the  intestine  does  not  digest  proteins.  The  same  is 
true  of  extracts  of  perfectly  fresh  pancreas,  but  if  the  pancreas  is 
allowed  to  stand  for  a  time,  the  extracts  contain  active  trypsin, 
perhaps  because  some  decomposition  product  has  activated 
the  trypsinogen.  Some  writers,  however,  state  that  when  con- 
tamination of  the  gland  with  intestinal  contents  or  contact  with 
the  mucosa  has  been  avoided  in  its  removal  from  the  body,  such 
extracts  will  remain  inactive  for  months,  although  the  trypsin- 
ogen can  at  once  be  activated  to  trypsin  by  the  addition  of 
enterokinase. 

Trypsin,  to  a  certain  extent,  corresponds  with  pepsin  in  its 
action  on  proteins.  But  it  acts  energetically  in  an  alkaline  as 
well  as  in  a  not  too  acid  medium  (a  very  slight  amount  of  diges- 
tion may  go  on  in  distilled  water)  ;  and  its  action,  unlike  that 
of  pepsin — at  least  in  digestions  of  moderate  duration — does  not 
stop  mainly  at  the  peptone  stage,  but  goes  on  rapidly  to  the 
production  of  the  amino -acids,  the  basic  substances  arginin. 
lysin,  and  histidin,  known  as  the  hexone  bases,  and  most  of 
the  other  decomposition  products  obtained  by  boiling  proteins 
with  dilute  acids.  The  most  important  of  these  products,  so  far 
as  thev  have  been  isolated  and  identified,  are  enumerated  in 
the  following  table  (see  also  pp.  1-3)  : 


A   MANUAL  or  PHYSIOLOG  \ 


i  mi  i     Di  i  «  >MP<  »S1  I  [ON    PRODU<   I  -   "I     PR<  H  I 

Mono imino  ^cids  ind  i hi  n 

'Glyt  in  or  L'lvi  ex  "ll  (amii  HoCOOH. 

\ l.i urn  (aminopropionii  acid),  <  II  I  HNH  '  OOn 
Serin  or  oxyalanin  (oxyaminqprqpionic  acid) 

(  ll  nil  .  <  H\lf     i  OOH 
<  II 

•  II 


Ammovalerianic  acid. 


(  ll'   HMI  «  OOH 


I  If 


Leucin*(a-aminoisobutylaceticacid)^      '  II'  II  '  II  Ml'  OOH 


_  j  S    |  \   ;,  irtic  or  aminosuccinii 
—  ~  Z  \  Glutamic  or  glutaminic  acid. 


£  •'-  >    (Tyrosin*   (p  enylaminopropionic  acid 

g  g'-g  J  C6H4Of[.  '  II.  .(  H\ll..<  OOH. 

=  5  >    |  Phenylalanin  (phenylaminopropionic  acid). 


- 


(plienylaminopropk 

I     II  (  11/  HNH.J  OOH 


~2  -■  ;   fProlin  (pyrrolidin  carboxylic  acid). 

"3-g  "  {  Oxyprolin  (oxypyrrolidin  carboxylic  acid). 

P  _i  —    I  I  tryptophane  hndol-aminopropionic  acid). 


DlAMINO-ACIDS    AND    THEIR     I  OS. 

Xysin  (a-f-diaminocaproic  acid),  C6HMN,0,,  or 

(  H.MI    I  H  ,    i  ll\H  /  OOH. 
nn  (guanidinaminovahrianic  acid),  (  ,11,  A'/)...,  or 
i  r  v     r      NHn 

1IN  \IK  If  ..<  II,,  i  ||\H.<  OOH. 

Histidin  (/3-imidazol-a-aminopropionic  acid),  CBH.,N  /> 


tin,  CgHigNgSgQi  (derived  from  a  complex  amino-acid.  amino- 
thiolactic  acid,  containing  the  greater  part  of  the  sulphur 
of  the  protein  molecule). 
Ammonia  (representing  the  so  called  'amide  nitrogen, '  and  liber- 
ated from  the  products  of  acid  hydrolysis  <>t  proteins  by 
heating  the  mixture  after  addition  of  alkali). 

After  the  most  prolonged  artificial  digestion  with  trypsin,  a 
residue  of  the  protein  remains  unconverted  into  these  relatively 
simple  substances.  But  even  this  small  portion  <>f  the  original 
protein  Pas  undergone  a  great  change,  for  it  no  longer  gives  the 
biuret  reaction.  It  can  be  split  into  amino-acids,  etc.,  by  heating 
with  acid.  When  trypsin  acts  upon  protein  already  digested 
by  pepsin,  this  partially  hydrolysed  residue  is  smaller  than  when 
the  trypsin  acts  alone,  no  matter  for  how  long  a  time.  This 
illustrates   the  co-operative   relation   of  these   two   ferments — a 

*  Leucin  is  formed  from  a-isobutyl  acetic  acid  by  the  replacement  of 
one  H  by  N'H,,.  Tyrosin  is  related  to  propionic  acid  I  ll,/'  ).  If  one 
H  in  propionic  acid  is  replaced  by  N'H.,  we  get  aminopropionic  acid, 
C.H.iMI".  if  another  H  is  replaced  by  oxyphenyl  (CjH4OH),  an 
aromatic  radicle,  we  gel  tyrosin. 


nir, I  STIOh 

relation  still  more  clearly  implied  in  the  fact  that,  although  trypsin 
readily  forms  albumoses  and  peptones  from  native  protein  when 
-.luh  is  offered  to  it.  yet  in  natural  digestion  the  great  albumose 
and  peptone-forming  fermenl   is  pepsin.     In  the  lumen  of  the 

intestine  the  trypsin  is  confronted  mainly  with  protein  already 
hydrolysed  to  the  albumose  and  peptone  stage  in  the  stomach. 

There  is  no  reason  to  believe  that  there  is  any  fundamental 
difference  between  the  action  of  trypsin  and  pepsin  on  the  protein 
molecule     at  any  rate,  up  to  the  point  of  peptone  formation. 

The  order  in  which  they  appear  and  their  relative  amount  at 
different  stages  of  the  digestion  show  that  the  alkali-albumin 
ami  the  albumoses  produced  when  trypsin  acts  in  an  alkaline 
medium,  such  as  a  i  per  cent,  solution  of  sodium  carbonate, 
are,  like  the  acid-albumin  and  albumoses  of  peptic  digestion, 
mainly,  at  any  rate,  intermediate  substances  through  which 
protein  passes  on  its  way  to  peptone.  In  both  cases  the  action 
consists  in  a  splitting  up  of  the  complex  protein  with  assumption 
of  water,  so  that  each  successive  product  is  further  hydrated 
than  the  last.  Nor  is  it  possible  to  point  out  any  radical  differ- 
ence between  the  peptone  of  gastric  and  the  peptone  of  pan- 
creatic digestion.  The  further  rapid  hydrolysis  of  the  peptone 
by  trypsin  into  decomposition  products  of  low  molecular  weight 
is  a  distinction  merely  of  degree.  For  pepsin  can  also,  as  we 
have  seen,  produce  a  certain  amount  of  these  after  prolonged 
digestion.  Trypsin  is  a  more  powerful  ferment  than  pepsin, 
and  naturally  carries  the  decomposition  farther,  and  accom- 
plishes it  with  greater  ease. 

In  all  that  we  have  hitherto  said  regarding  tryptic  digestion 
we  have  supposed  that  putrefaction  has  been  entirely  prevented. 
If  no  antiseptic  is  added  to  a  tryptic  digest,  it  rapidly  becomes 
tilled  with  micro-organisms,  and  emits  a  very  disagreeable  faecal 
odour  ;  and  now  various  bodies  which  are  not  found  in  the 
absence  of  putrefaction  make  their  appearance,  such  as  indol, 
skatol,  and  other  substances,  to  which  the  faecal  odour  is  due. 
They  are  not  true  products  of  tryptic  digestion,  but  are  formed 
by  the  putrefactive  micro-organisms,  which  can  themselves 
split  oft  from  proteins  numerous  decomposition  products, 
including  tyrosin,  and  change  tyrosin  into  indol. 

Amylopsin,  or  pancreatic  ptyalin,  the  diastatic  or  sugar- 
forming  ferment  of  pancreatic  juice,  changes  starch  into  dextrin 
and  maltose,  just  as  the  ptyalin  of  saliva  does.  The  two  ferments 
are  possibly  identical,  but  under  the  conditions  of  action  of  the 
pancreatic  juice  its  diastatic  power  is  greater  than  that  of  saliva, 
and  it  readily  acts  on  raw  starch  as  well  as  boiled.  Amylopsin 
is  mainly,  perhaps  entirely,  present  in  the  juice  in  the  form  of 
active  ferment.      If   a  zymogen   stage  exists,  the  mother-sub- 


534  '    MAh  i    II    OB   PHYSIOLOGY 

stance  is  less  stable  or  Less  easily  extracted  from  the  gland  than 
is  trypsinogen.  In  this  respect  amylopsin also  resembles  ptyalin. 
A  small  amount   "l    tnaltase  is  contained    in   pancreatic   juice, 

and    further  hydrolyses   to  dextrose  a  portion  of  the  maltose 

formed  by  the  amylopsin. 

Steapsin  splits  up  neutral  fats  into  glycerin  and  the  corre- 
sponding fatty  acids.  The  latter  unite  with  the  alkalies  of  the 
pancreatic  juice  and  the  bile  to  form  soaps.  In  this  important 
process  bile  acts  as  the  helpmate  of  pancreatic  juice  ;  together 
they  effect  much  more  than  either  or  both  can  accomplish  by 
separate  action.  Many  tissues  contain  fat-splitting  ferments  or 
lipases,  which  are  probably  not  identical  with  steapsin.  Steapsin 
exists  as  active  ferment  in  the  pancreatic  juice,  but  there  is 
some  reason  to  believe  that  a  portion  of  it  may  be  present  as  .1 
mother-substance,  steapsinogen,  in  the  gland,  and  probably  in 
the  secretion  as  well.  Active  steapsin  can  also  be  extracted 
from  the  pancreas  by  glycerin  or  water.  It  is  to  be  noted  that 
it  is  only  the  proteolytic  enzyme  which  is  totally  inactive  till  it 
reaches  the  intestine.  The  significance  of  this  will  be  discussed 
later  on. 

Bile. — Bile  is  a  liquid  the  colour  of  which  varies  in  different 
groups  of  animals,  and  even  in  the  same  species  is  not  constant, 
depend  ng  on  the  length  of  time  the  fluid  has  remained  in  the 
gall-bladder  and  other  circumstances.  When  it  is  recognised 
that  the  colour  is  due  to  a  series  of  pigments,  which  are  by 
no  means  stable,  and  of  which  one  can  be  caused  to  pass  into 
another  by  oxidation  or  reduction,  this  want  of  uniformity  will 
be  easily  intelligible.  The  fresh  bile  of  carnivora  is  golden- 
red.  The  bile  of  herbivorous  animals  is  in  general  of  a  green 
tint,  but,  when  it  has  been  retained  long  in  the  gall-bladder,  may 
incline  to  reddish-brown.  Fresh  human  bile,  as  it  flows  from  a 
fistula  just  established,  is  of  a  reddish-brown,  golden-yellow 
or  yellow  colour.  Beaumont  speaks  of  the  yellowish  bile  which 
he  could  press  into  the  stomach  of  St.  Martin  by  manipulating 
the  abdomen.  In  a  case  observed  by  the  writer,  it  was  seen  that 
when  the  bile  flowing  from  a  fistula  was  allowed  to  spread  out 
in  a  dressing,  it  became  greenish,  because  of  oxidation  of  a  part 
of  the  bilirubin  to  biliverdin,  although  as  it  actually  escaped 
from  the  fistula  it  was  yellow.  The  bile  of  a  monkey  taken  from 
the  gall-bladder  immediately  after  death  is  dark  green,  but  if 
left  a  few  hours  in  the  gall-bladder  it  is  brown,  the  green  pigment 
having  been  reduced.  It  should  be  remembered  that  human 
bile  from  the  post-mortem  room  may  alter  its  colour  in  the 
interval  which  must  elapse  before  it  can  usually  be  procured 
after  death.  Bile,  as  obtained  from  fistuke  in  otherwise  healthy 
persons,  has  a  specific  gravity  of  about  1008  to  1010.     In  the 


DIGESTIOh  J35 

gall  bladder  water  is  absorbed  Imm  the  bile  and  mucin  added  to 
it,  so  th.it  the  specific  gravity  oi  bladder  bile  is  as  high  as  1030 

to  n'4<>.     The  reaction  is  feebly  alkaline  to  Litmus. 

I  lie  composition  of  two  specimens  of    human  bile — one  from  a 
fistula,  the  other  from    the  gi ill-bladder — is  shown  in  the  following 

table  : 


Bladder  Bile. 

Fistula  Bile. 

977'4 

226 

^'3 

IOI 

8"5 

005 
056 

Water 

Solids 

.Mucin  and  other  substances  in- 
soluble in  alcohol 

Sodium  taurocholate  and  sodium 
glycocholate 

Inorganic  salts     .  . 

Kit          .. 

Lecithin 

Cholesterin 

898-1 
1019 

M"5 

56-5 
63 

1 

3°"9 
1 

The  substance  which  renders  bladder  bile  viscid,  but  which  is 
present  in  much  smaller  amount  in  bile  from  a  fistula,  and  is  probably 
entirely  absent  from  the  fluid  as  it  is  secreted  by  the  liver-cells,  is 
commonly  termed  '  mucin.'  It  has  been  shown,  however,  that  in 
many  animals — for  example,  the  ox,  dog,  sheep,  etc. — the  substance 
is  not  a  true  mucin.  It  does  not  yield,  like  mucin,  reducing  sub- 
stances on  boiling  with  dilute  acid,  or  only  very  small  amounts  of 
these.  It  is  relatively  rich  in  phosphorus,  and  consists — mainly,  at 
any  rate — of  a  phospho-protein  (p.  2).  The  mucilaginous  substance 
of  human  bile  consists  largely  of  true  mucin. 

Mucin  is  scarcely  to  be  looked  upon  as  an  essential  constituent  of 
bile  ;  it  is  not  formed  by  the  actual  bile-secreting  cells,  but  by 
mucous  glands  in  the  walls  and  goblet-cells  in  the  epithelial  lining 
of  the  larger  bile-ducts,  and  especially  of  the  gall-bladder. 

Bile-pigments. — It  has  been  said  that  these  form  a  series,  but 
only  two  of  the  pigments  of  that  series  are  present  in  normal  bile, 
bilirubin,  and  biliverdin.  In  human  bile,  the  former,  in  herbivorous 
bile  and  that  of  some  cold-blooded  animals,  such  as  the  frog,  the 
latter  is  the  chief  pigment.  But  bilirubin  can  be  extracted  in  large 
amount  from  the  gall-stones  of  cattle  ;  while  the  placenta  of  the  bitch 
contains  biliverdin  in  quantity,  although,  as  in  all  carnivora,  it  is 
either  absent  from  the  bile  or  exists  in  it  in  comparatively  small 
amount.  These  facts  show  that  the  two  pigments  are  readily  inter- 
changeable. 

Bilirubin  is  best  prepared  from  powdered  red  gall-stones  by  dis- 
solving the  chalk  with  hydrochloric  acid,  and  extracting  the  residue 
with  chloroform,  which  takes  up  the  pigment.  From  this  solution, 
on  evaporation,  beautiful  rhombic  tables  or  prisms  of  bilirubin 
separate  out  ;  and  the  crystals  are  finer  when  the  solution  also  con- 
tains cholesterin  than  when  it  is  pure. 

Biliverdin  can  be  obtained  from  the  placenta  of  the  bitch  by 
extraction  with  alcohol.  It  is  insoluble  in  chloroform,  and  by  means 
of  this  property  it  may  be  separated  from  bilirubin  when  the  two 
happen  to  be  present  together  in  bile.     Biliverdin  can  also  be  formed 


53  i  I   M A \  i    //    OF   PHYSIOLOGY 

from  bilirubin  by  oxidation.  By  the  aid  of  active  oxidizing  agents* 
such  as  yellow  nitric  acid  (which  contains  some  nitrous  acid),  a 
whole  series  of  oxidation  products  of  bilirubin  is  obtained,  beginning 
with  bilivenlin.  and  passing  through  bilicyanin,  a  blue  pigment, 
to  bili-purpurin,  which  is  purple,  and  finally  to  choletelin,  a  yellow 
substance.  It  is  possible  that  there  are  other  intermediate  bodies. 
This  is  the  foundation  of  Gmelin's  test  for  bile-pignuiits  (see  Practical 
I'm  rcises,  p.  431)-  The  same  substances  are  produced,  and  in  the 
same  order,  when  a  solution  of  bilirubin  in  chloroform  is  treated 
with  a  dilute  alcoholic  solution  of  iodine. 

The  positive  pole  of  a  galvanic  current  causes  the  same  oxidative 
changes,  the  same  play  of  colours,  while  the  reducing  action  of  the 
negative  pole  reverses  the  effect,  if  the  action  of  the  positive  electrode 
has  not  gone  too  far.  Starting  from  biliverdin,  the  negative  pole 
causes  the  green  to  pass  through  yellowish-green  into  golden-yellow, 
and  ultimately  into  pale  yellow,  indicating  a  series  of  bodies  formed 
by  reduction  of  the  biliverdin.  These  reactions  can  also  be  used  for 
the  detection  of  bile-pigments. 

By  the  reducing  action  of  sodium  amalgam,  or  of  tin  and  hydro- 
chloric acid,  on  bilirubin,  hydrobilirubin  is  obtained.  This  is  simUar 
to  but  not  identical  with  the  urobilin  of  urine,  or  with  the  urobilin 
(stcrcobilin)  found  in  the  faeces  (partly  in  the  form  of  its  mother- 
substance  or  chromogen,  urobilinogen)  from  birth  onwards,  although 
not  in  the  meconium  (p.  396) .  Urobilin  is  derived  from  the  normal  bile- 
pigment  by  reduction  in  the  intestine  itself,  where  reducing  sub- 
stances due  to  the  action  of  micro-organisms  are  never  absent  in 
extra-uterine  life.  The  changes  occurring  in  oxidation  and  reduc- 
tion of  the  bile-pigment  may  be  partially  represented  as  follows  : 

(C32H30N  4O0)  +  02  =  (C32H36N40.) ,  +  202  =  (C32H:J(.,X4Ol2) 

Bilirubin.  Biliverdin.  Choletelin. 

2  (C^H^N.Oe)  -  02  +  4H20  =  2  (C^HUN^) . 

Bilirubin.  Hydrobilirubin. 

The  bile  of  most  animals  shows  no  characteristic  absorption 
spectrum.  But  the  fresh  bile  of  certain  animals,  the  ox,  for  instance, 
does  show  bands — a  strong  one  over  C,  and  two  weaker  bands,  one 
of  which  is  just  to  the  left  of  D,  and  the  other  to  the  right  of  it.  but 
nearer  D  than  E.  The  two  last  bands  grow  stronger  when  the  bile 
is  allowed  to  stand  for  twenty-four  hours,  and  in  about  three  days, 
in  warm  weather,  a  fourth  sharp  band  may  appear  between  C  and  B. 
But  none  of  these  bands  is  due  to  the  normal  bile-pigment,  and 
they  are  not  essentially  changed  when  this  is  oxidized  or  reduced  by 
electrolysis.  MacMunn  attributes  the  spectrum  of  the  bile  of  the 
ox  and  sheep  to  a  body  which  he  calls  cholohsematin,  and  which 
does  not  belong  to  the  bile-pigments  proper.  Of  the  derivatives 
of  the  bilirubin  set,  only  the  lowest  and  the  highest  members, 
hydrobilirubin  and  choletelin,  are  described  as  giving  absorption 
spectra. 

The  Bile-salts. — These  arc  the  sodium  salts  of  two  acids,  glyco- 
cholic  and  taurocholic.  In  the  bile  of  omnivora,  including  man, 
both  arc  in  general  present,  and  in  various  proportions  ;  in  human 
bile  there  is  more  glycocholic  than  taurocholic  acid  ;  sometimes 
taurocholic  acid  is  entirely  absent.  In  the  bile  of  many  carnivora — 
e.g.,  the  dog  and  cat — only  taurocholic  acid  is  found  ;  in  that  of  the 
carnivora  generally  it  is  by  far  the  more  important  of  the  two  acids. 
In  the  bile  of  most  herbivora  there  is  much  more  glycocholic  than 
taurocholic  acid. 


DIGESTION  337 

Both  .uiils  arc  made  up  of  a.  non-nitrogenous  body,  cholic  or 
cholalic  acid,  and  .1  nitrogenous  body,  glycin  or  glycocol]  in  glyco- 
(  holic,  and  taurin  in  taurocholic  a<  id 

The  decomposition  of  the  bile-acids  into  these  substances  is 
effected  by  boiling  them  with  dilute  acid  or  alkali,  a  molecule  of 
water  bring  taken  up  ;  thus — 

C,,l  1 1:;.\( ),.  +  H2C>  =C2H,NO,  +  C2lTIlllO,  ; 
Glycocholic  acid.  Glycin.  I  nolicacid. 

C.,,l  l,,\'S<  )7  V  H20  =C,H7NSO,  +  C24H,0O,. 

Taurocholic  acid,  Taurin.  Cholic  acid. 

Taurocholic  acid  is  much  more  easily  split  up  than  glycocholic  ; 
even  boiling  with  water  is  sufficient. 

Cdycin,  as  already  stated,  is  amino-acetic  acid,  taurin  is  amino- 
ethyl-sulphonic  acid,  an  atom  of  hydrogen  being  in  each  case 
replaced  by  NH2.  A  notable  difference  between  glycocholic  and 
taurocholic  acid  is  that  the  latter  contains  sulphur.  The  whole  of 
this  belongs  to  the  taurin.  Both  glycin  and  taurin  are  derived  from 
the  disintegration  of  proteins,  and  the  sulphur  of  the  taurin  repre- 
sents a  portion  of  the  sulphur  of  the  proteins.  We  have  already 
seen  that  among  the  products  of  protein  hydrolysis  a  sulphur- 
containing  body,  cystin,  is  found,  and  there  is  good  evidence  that 
taurin  is  derived  from  cystin. 

Traces  of  cholic  acid,  formed  by  hydrolysis  from  the  bile-acids  by 
the  action  of  putrefactive  bacteria,  are  found  in  the  intestines, 
especially  in  the  lower  portion. 

Pettenkofer's  test  for  bile-acids  (Practical  Exercises,  p.  430),  acci- 
dentally discovered  in  examining  the  action  of  bile  upon  sugar, 
depends  upon  three  facts  :  (1)  That  cholic  acid  and  furfuraldehyde 
give  a  purple  colour  when  brought  together  ;  (2)  that  the  bile-salts 
yield  cholic  acid  when  acted  upon  by  sulphuric  acid  ;  (3)  that  when 
cane-sugar  is  decomposed  by  strong  sulphuric  acid,  furfuraldehyde 
is  formed. 

Since  a  similar  colour  is  given  when  the  same  reagents  are  added 
to  a  solution  containing  albumin,  it  is  necessary  to  remove  this,  if 
present,  from  any  liquid  which  is  to  be  tested  for  bile-acids. 

Lecithin  and  cholesterin  are  by  no  means  peculiar  to  bile  (p.  4). 
They  are  very  widely  distributed  in  the  body.  Lecithin  belongs  to 
the  group  of  phosphatides,  fat-like  phosphorus-containing  substances 
present  in  all  cells.  It  is  a  compound  of  glycerin  with  two  molecules 
of  fatty  acid  and  one  of  phosphoric  acid.  The  phosphoric  acid  is 
at  the  same  time  united  with  a  base  cholin.  The  fatty  acid  (stearic, 
palmitic,  oleic,  etc.)  varies  in  different  varieties  of  lecithin.  Heated 
with  baryta-water,  lecithin  yields  the  corresponding  fatty  acid  in 
the  form  of  a  soap,  along  with  cholin  and  glycero-phosphoric  acid, 

Cholesterin  is  an  alcohol  with  the  empirical  formula  C2-H40O.  It  is 
best  obtained  from  white  gall-stones,  of  which  it  is  the  chief,  and  some- 
times almost  the  sole  constituent  (see  Practical  Exercises,  p.  431). 

The  chief  inorganic  salts  of  bile  are  sodium  chloride,  sodium  car- 
bonate, and  alkaline  sodium  phosphate.  The  phosphoric  acid  of  the 
ash  comes  partly  from  the  phosphorus  of  organic  compounds  (leci- 
thin and  bile-mucin),  the  sulphuric  acid  from  the  sulphur  of  tauro- 
cholic acid,  the  sodium  largely  from  the  bile-salts.  Iron  is  a  notable 
inorganic  constituent  of  bile,  although  it  exists  only  in  traces,  in  the 
form  of  phosphate  of  iron.  Manganese  is  also  present  in  minute 
amount.  100  c.c.  of  fresh  bile  yields  50  to  100  c.c.  of  carbon  dioxide, 
part  of  which  is  in  solution  and  part  combined  with  alkalies. 

22 


3.i8  A   MANUAL  OF  PHYSIOLOGY 

The  quantity  of  bile  secreted  in  twenty-four  hours  in  an  average 
man  is  probably  from  750  c.c.  to  a  litre.  In  nine  cases  of  fistula 
of  the  gall-bladder  in  patients  operated  on  for  gall-stones  or 
echinococcus  the  daily  quantity  varied  from  500  to  1,100  c.c. 
(Brand). 

The  great  action  of  the  bile  in  digestion  is  undoubtedly  the 
preparation  of  the  fats  for  absorption.  In  this  preparation  four 
processes  are  important  :  two  chemical  actions,  hydrolysis  of 
neutral  fats  to  glycerin  and  fatty  acids,  and  saponification,  or 
the  formation  of  soaps  by  the  union  of  fatty  acids  with  liases. 
especially  sodium  ;  and  two  physical  processes,  emulsification, 
or  the  formation  of  a  mechanical  suspension  of  such  fine  globules 
of  unaltered  neutral  fat  as  exist  in  milk,  and  solution  of  soaps  and 
fatty  acids.  While  there  has  been  much  discussion  as  to  the 
relative  share  taken  by  these  processes,  and  especially  by 
saponification  and  emulsification  in  the  absorption  of  fat  (p.  412). 
there  is  no  doubt  that  they  are  all  concerned  in  the  digestion  of 
fat  or  the  preparation  of  it  for  absorption.  In  this,  indeed,  the 
processes  are  complementary  to  each  other,  for  an  essential  pre- 
liminary to  emulsification  in  the  intestine  seems  to  be  the  for- 
mation of  a  certain  amount  of  soaps,  soluble  in  the  intestinal 
contents,  while  the  formation  of  an  emulsion  at  least  increases 
the  surface  of  contact  between  the  unaltered  fat  and  the  digestive 
juices,  and  so  favours  more  rapid  saponification  and  solution.  In 
the  whole  series  of  changes  the  bile  plays  a  part,  though  not  an 
independent  one  ;  it  acts  always  in  conjunction  with  the  pan- 
creatic juice. 

While  no  complete  explanation  has  been  given  of  the  precise 
nature  of  this  partnership,  it  is  certain  that  the  fat-splitting 
ferment  of  the  pancreatic  juice,  on  the  one  hand,  and  the  bile- 
salts  on  the  other,  contribute  largely  to  the  total  action.  An 
alkaline  solution,  a  solution  of  sodium  carbonate,  e.g.,  is  unable 
of  itself  to  emulsify  a  perfectly  neutral  oil  ;  but  if  some  free  fatty 
acid  be  added,  emulsification  is  rapid  and  complete  (p.  12).  Now. 
there  is  no  doubt  that  here  a  soap  is  formed  by  the  action  of  the 
alkali  on  the  fatty  acid,  and  there  is  equally  little  doubt  that  the 
formation  of  the  soap  is  an  essential  part  of  the  emulsification. 
But  it  is  not  clear  in  what  manner  the  soap  acts,  whether  In- 
forming a  coating  round  the  oil-globules,  or  by  so  altering  the 
surface-tension,  or  other  physical  properties  of  the  solution  in 
which  it  is  dissolved,  that  they  no  longer  tend  to  run  together. 
However  this  may  be,  in  pancreatic  juice  we  have  the  two  factors 
present  which  this  simple  experiment  shows  to  be  necessary  and 
sufficient  for  emulsification  ;  we  have  a  ferment  which  can  split 
up  neutral  fats  and  set  free  fatty  acids,  and  an  alkali  which  can 
combine  with  those  acids  to  form  soaps.     Accordingly,  pancreatic 


DIGESTION  339 

juice  is  able  <>f  itself  to  form  emulsions  with  perfectly  neutral  oils. 
It  is  possible  that  the  protein  constituents  of  pancreatic  juice 
may  have  a  share  in  emulsification,  since  the  addition  of  protein 
— e.g.,  egg-white — to  a  soap  solution  increases  the  stability  of 
the  emulsions  formed  by  the  soap.  In  bile,  on  the  contrary, 
.ilt hough  the  alkali  is  present,  there  is  no  fat-splitting  ferment, 
and  according  to  the  best  experiments,  bile  alone  has  no  emulsify- 
ing power  on  perfectly  neutral  fat.  But.  we  now  come  to  a  re- 
markable fact  :  this  inert  bile  when  added  to  pancreatic  juice 
greatly  intensities  its  emulsifying  action,  and  a  solution  of  bile- 
salts  has  much  the  same  effect  as  bile  itself.  The  fact  is  un- 
doubted, but  the  explanation  is  obscure.  What  it  is  that  the 
bile  or  bile-salts  can  add  to  the  pancreatic  juice  which  so  increases 
its  power  of  emulsification,  we  do  not  know.  It  has  been  sur- 
mised that  a  characteristic  physical  property  of  bile,  the  diminu- 
tion of  the  surface-tension  of  watery  liquids  to  which  it  is  added, 
may  play  an  important  part,  perhaps,  in  enabling  the  fat- 
splitting  ferments  or  the  emulsifying  soaps  to  get  into  closer 
contact  with  the  unaltered  fat.  It  is  also  true  that  bile  by  itself, 
presumably  in  virtue  of  the  chemical  action  of  its  alkaline  salts, 
can,  in  presence  of  a  free  fatty  acid,  rapidly  form  an  emulsion. 
But  the  pancreatic  juice  itself  contains  so  considerable  a  quantity 
of  sodium  carbonate  that  it  would  scarcely  seem  to  require  the 
relatively  feeble  reinforcement  of  the  alkaline  salts  of  the  bile. 

A  part  of  the  effect  of  the  bile  is  certainly  due  to  its  favouring 
the  fat-splitting  action  of  the  pancreatic  juice.  By  the  addition 
of  bile,  the  quantity  of  fat  split  up  by  a  definite  amount  of 
dog's  pancreatic  juice  may  be  increased  two  to  threefold.  It 
has  been  shown  that  this  is  an  action  of  the  bile-salts.  The 
sodium  salts  of  synthetically-obtained  glycocholic  and  tauro- 
cholic  acids  produce  the  same  effect.  The  capacity  of  dissolving 
soaps,  which  is  a  property  of  the  bile-salts,  is  also  of  great  im- 
portance in  supplementing  the  solvent  power  of  the  intestinal 
liquids  for  the  products  formed  by  the  pancreatic  juice.  The 
solution  of  soaps  in  the  bile-salts  has  the  power  in  its  turn  of 
dissolving  free  fatty  acids.  The  significance  of  this  in  fat  absorp- 
tion will  be  referred  to  again.  Although  our  knowledge  of  the 
mutual  action  of  the  two  juices  on  the  digestion  of  fats  is  still 
incomplete,  there  is  no  doubt  that  they  are  equally  necessary. 
For  in  some  diseases  of  the  pancreas  fat  or  fatty  acid  often  appears 
in  the  stools,  and  this  token  of  imperfect  digestion  of  the  fatty 
food  may  be  confirmed  by  the  wasting  of  the  patient.  The  same 
may  occur  when  the  bile  is  prevented  by  obstruction  of  the  duct 
or  by  a  biliary  fistula  from  entering  the  intestine.  Yet  in  some 
cases  of  fistula,  where  there  is  every  reason  to  believe  that  all 
the  bile  is  escaping  externally,  the  nutrition  of  the  patient-  at 

22 — 2 


340  A   MANUA1    OF  PHYSIOLOGY 

any  rate,  on  a  die!  not  abnormally  rich  in  fat-  is  unaffected.  The 
mere  deficiency  of  bile  in  the  intestine  is,  of  course,  complicated 
in  obstructive  jaundice  by  the  harmful  effects  "I  the  biliary 
constituents  circulating  in  the  blood. 

The  white  stools  of  jaundice  owe  their  colour,  not  merely  to  the 
absence  of  bile-pigment,  but  also  to  the  presence  oi  fat.  Their 
highly  offensive  odour  used  to  be  adduced  as  evidence  thai  I >il<-  is 
the  '  natural  antiseptic  '  of  the  intestine.  It  seems  rather  to  be  due 
to  the  coating  of  the  particles  of  food  with  undigested  fat,  which 
shields  the  proteins  from  the  action  of  the  digestive  juices  while 
permitting  the  putrefactive  bacteria  to  revel  in  them  unchecked. 
As  a  matter  of  fact,  the  bile  itself  has  little,  if  any,  power  of  hindering 
the  growth  of  micro-organisms,  although  the  free  bile-acids  are 
tolerably  active  antiseptics.  In  suckling  children  it  is  not  un- 
common to  see  the  faeces  white  with  fat.  This  is  a  less  serious 
symptom  than  in  adults,  and  perhaps  betokens  merely  that  the 
milk  in  the  feeding-bottle  is  undiluted  cow's  milk,  which  is  richer 
in  fat  than  human  milk,  and  ought  to  be  mixed  with  water. 

Bidder  and  Schmidt  found  that  the  chyle  in  the  thoracic  duct 
of  a  normal  dog  contained  3-2  per  cent,  of  fat.  In  a  dog  with 
the  bile-duct  ligatured  the  proportion  fell  to  02  per  cent.  It  is 
an  instance  of  the  extraordinarily  exact  adaptation  of  the  diges- 
tive juices  to  the  nature  of  the  food,  the  mechanism  of  which  will 
present  itself  for  discussion  later  on,  that  the  reinforcing  action  of 
the  bile  upon  the  fat-splitting  ferment  of  the  pancreatic  juice  is 
said  to  be  greater  when  the  food  is  rich  in  fat  (p.  381). 

Bile  has  been  credited  with  a  physical  power  of  aiding  the 
passage  of  fat  through  membranes  moistened  with  it  by  diminish- 
ing the  surface  tension,  and  it  has  been  inferred  that  this  has  an 
important  bearing  on  the  absorption  of  fat  from  the  intestine. 
But  the  inference  does  not  follow  from  the  statement,  and  the 
statement  has  been  itself  denied.  There  is  at  present  no  evidence 
that  the  digestive  function  of  the  bile  extends  beyond  the  pre- 
paration of  the  food  for  absorption  to  the  preparation  of  the 
mucosa  for  absorbing  it. 

On  proteins  bile  has  either  no  digestive  action,  or  only  a  feeble 
one.  Fibrin  is  slightly  digested  by  the  bile  of  the  dog  and  of 
man.  But  the  addition  of  it  to  fresh  pancreatic  juice  consider- 
ably increases  the  proteolytic  power  of  that  secretion  (Rach- 
ford),  although  not  so  decidedly  as  in  the  case  of  the  fat-splitting 
action.  The  amylolytic  action  of  the  pancreatic  juice  is  also 
favoured  by  the  bile,  and  in  about  the  same  degree  as  its  proteo- 
lytic effect.  Although  bile  sometimes  exerts  by  itself  a  feebly 
amylolytic  action,  this  is  not  to  be  included  among  its  specific 
powers,  for  a  diastatic  ferment  in  small  quantities  is  widely 
diffused  in  the  body. 

The  addition  of  bile  or  bile-salts  to  a  gastric  digest  causes  the 


DIGESTIOh  Hi 

precipitation  of  any  unaltered  native  protein,  acid  albumin, 
albumose,  and  pepsin.  The  precipitate  which  is  a  salt  like 
compound  of  protein  with  taurocholic  acid,  is  redissolved  when  the 
liquid  is  rendered  alkaline,  and  therefore  in  excess  of  bile,  or  of 
a  solution  of  bile-salts,  but  the  pepsin  has  no  longer  any  power 
of  digesting  proteins.  Pari  of  the  bile-acids  and  bile-mucin  is 
also  thrown  down  by  the  acid  of  the  digest.  It  has  been  sug- 
gested  that  by  thus  precipitating  the  constituents  of  the  chyme 
which  have  not  been  carried  to  the  peptone  stage  bile  prepares 
them  for  the  action  of  the  pancreatic  juice.  But  it  is  difficult  to 
see  how  the  precipitation  of  a  suhstance  can  prepare  the  way  for 
its  digestion,  and  it  is  more  probable  that  if  any  physiological 
value  is  to  he  given  to  this  reaction,  it  has  the  function  of  pre- 
venting the  absorption  of  proteins  which  have  not  been  suffi- 
ciently split  up.  There  is  little  doubt,  however,  that  the  ren- 
dering of  the  pepsin  inactive  has  physiological  significance,  for 
pepsin  exerts  an  injurious  influence  upon  the  ferments  of  the 
pancreatic  juice.  In  digestion,  then,  the  bile  has  a  twofold  func- 
tion, favouring  greatly  the  activity  of  the  pancreatic  ferments, 
especially  the  fat-splitting  ferment,  and  aiding  in  establishing  the 
conditions  necessary  for  the  transition  of  gastric  into  intestinal 
digestion. 

Succus  entericus. — This  is  the  name  given  to  the  special 
secretion  of  the  small  intestine,  which  is  supposed  to  be  a  product 
of  the  Lieberkuhn's  crypts.  In  order  to  obtain  it  pure,  it  is 
of  course  necessary  to  prevent  admixture  with  the  bile,  the  pan- 
creatic juice,  and  the  food.  This  can  be  done  by  dividing  a  loop 
of  intestine  from  the  rest  by  two  transverse  cuts,  the  abdomen 
having  been  opened  in  the  linea  alba.  The  continuity  of  the 
digestive  tube  is  restored  by  stitching  the  portion  below  the 
isolated  loop  to  the  part  above  it.  One  end  of  the  loop  is  sewed 
into  the  lips  of  the  wound  in  the  linea  alba,  and  the  other  being 
closed  by  sutures,  the  whole  forms  a  sort  of  test-tube  opening  ex- 
ternally (Thiry's  fistula).  Or  both  ends  are  made  to  open  through 
the  abdominal  wound  (Vella's  fistula).  Another  method  is  to  make 
a  single  opening  in  the  intestine,  and  by  means  of  two  indiarubher 
halls,  one  of  which  is  pushed  down,  and  the  other  up  through  the 
opening,  and  which  are  afterwards  inflated,  to  block  off  a  piece 
of  gut  from  communication  with  the  rest.  Or  several  openings 
may  he  made  at  different  levels  in  the  intestine,  each  being  allowed 
to  heal  into  a  wound  in  the  abdominal  wall.  When  pure  juice 
is  required  it  is  collected  from  the  lower  fistulas,  while  the  upper 
fistulae  are  opened  to  permit  the  escape  of  the  secretions  which 
enter  the  higher  portions  of  the  alimentary  canal  (gastric  juice, 
pancreatic  juice,  and  bile).  The  intestinal  juice  so  obtained  is  a 
thin  yellowish  liquid  of  alkaline  reaction,  generally  somewhat 


342  /    MANUAL  OF  PHYSIOLOGY 

turbid  from  the  presence  of  a  certain  number  «»f  leucocytes  and 
epithelial  cells.  Its  specific  gravity  is  about  ioio,  the  total 
solids  about  15  per  cent.  It  contains  a  small  amount  of  pro- 
teins, including  serum  albumin  and  serum  globulin,  and  about 
the  same  proportion  of  inorganic  salts  as  most  of  the  liquids  and 
solids  of  the  body,  namely,  07  or  08  per  cent.,  chiefly  sodium 
carbonate  and  sodium  chloride;  but,  like  the  other  digestive 
liquids,  it  is  adapted  to  the  nature  of  the  food,  and  therefore 
its  composition  is  not  quite  constant.  Like  bile,  intestinal  juice 
acts  but  feebly  on  the  food  substances  by  itself,  and  if  we  con- 
tented ourselves  with  examining  the  pure  and  isolated  secretion, 
we  should  greatly  underestimate  its  importance.  The  sodium 
carbonate,  in  which  it  is  relatively  rich,  will,  to  be  sure,  form 
soaps  with  fatty  acids  produced  by  the  action  of  the  pancreatic 
juice  or  of  the  fat-splitting  bacteria  in  which  the  intestine 
abounds,  and  thus  aid  in  the  digestion  of  fats.  A  lipase,  feebler 
than  that  of  the  pancreatic  juice,  or  present  in  smaller  concen- 
tration, is  also  a  constituent  of  the  succus  entericus.  That  a  great 
deal  of  fat  may  be  split  up  in  the  alimentary  canal  in  the  absence 
both  of  bile  and  pancreatic  juice  is  well  ascertained.  The  alkali  of 
the  succus  entericus  must  at  the  same  time  aid  in  neutralizing  the 
original  acidity  of  the  chyme,  and  in  preserving  the  proper  reaction 
of  the  intestinal  contents.  A  ferment  called  invertase,  or  sucrase 
— which  is  not  introduced  with  the  food  or  formed  by  bacterial 
action  as  has  been  suggested,  since  it  occurs  in  the  aseptic 
intestine  of  the  new-born  child — will  invert  cane-sugar.  The 
ferments  maltase  and  lactase  will  cause  a  corresponding  change 
in  maltose  and  lactose  (see  footnote,  p.  328).  It  is  worthy 
of  remark  that  these  inverting  enzymes  are  present  in  the 
intestinal  mucosa  as  well  as  in  the  intestinal  juice,  and  extracts 
of  the  mucosa  are  usually  distinctly  more  active  than  the  juice 
itself.  So  that  there  is  reason  to  believe  that  hydrolysis  of  the 
disaccharides  may  take  place  both  in  the  lumen  of  the  gut 
before  absorption  and  in  the  wall  of  the  gut  during  absorption. 
Inverting  enzymes  appear  in  the  intestine  early  in  embryonic 
life.  Maltase  is  the  most  generally  distributed  of  all  these 
enzymes,  and  it  is  found  along  with  lactase  in  the  intestine  of  the 
embryo  pig,  while  invertase  is  missing  till  after  birth  (Mendel). 
On  native  proteins  and  starch  the  isolated  succus  entericus  has 
little  or  no  action.  But  it  contains  a  ferment,  crcptm.  which, 
although  it  does  not  affect  native  proteins  like  serum-  and  egg- 
albumin  (fibrin  and  caseinogen  maybe  slightly  digested),  exerts 
a  powerful  action  on  the  first  products  of  protein  hydrolysis, 
albumoses,  and  peptones,  breaking  them  up  into  bodies  which 
no  longer  give  the  biuret  reaction  (ammonia,  mono-amino  acids. 
hexone   bases,  etc.).      It  destroys  the  diphtheria  toxin,  which 


DIG1  STION 


343 


is  also  rendered  innocuous  by  trypsin.  Erepsin,  however,  is 
not  specific  to  the  secreted  intestinal  juice,  for  it  occurs  also,  not. 
only  in  the  mucous  membrane  of  the  intestine,  which,  indeed. 
contains  a  greater  quantity  of  it  than  the  succus  entericus, 
hut  in  all  animal  tissues  hitherto  investigated.  The  kidney  in 
mammals  is  even  richer  in  erepsin  than  the  intestinal  mucous 
membrane.  Next  to  these  come  the  pancreas,  spleen,  and  liver, 
then  at  a  long  interval  the  heart  muscle,  while  skeletal  muscle 
and  brain-tissue  are  poorest  of  all  in  the  ferment.  The  intestinal 
mucosa  varies  in  its  erepsin  content  at  different  levels  and  on 
different  diets.  In  cats  on  a  meat  or  a  mixed  diet  the  duo- 
denum is  ahout  five  times  richer  in  the  ferment  than  the  stomach. 
The  ileum  is  about  half  as  rich  as  the  duodenum,  and  the  jejunum 
occupies  an  intermediate  position  between  the  duodenum  and 
ileum  (Vernon).  The  secretion  of  Bmnner's  glands  in  the  duo- 
denum, which  resemble  in  structure  the  pyloric  glands  of  the 
stomach,  digests  coagulated  albumin,  although  its  proteolytic 
powers  are  feebler  than  those  of  the  pancreatic  juice. 

The  most  characteristic  constituent  of  succus  entericus  is  a 
ferment,  enterokinase,  which  differs  from  all  the  ferments  we 
have  hitherto  described  in  acting  not  directly  upon  the  food- 
stuffs, but  upon  the  trypsinogen  of  the  pancreatic  juice,  changing 
it  into  the  active  enzyme  trypsin.  It  may  therefore  be  spoken 
of  as  a  ferment  of  ferments.  It  has  been  previously  stated  that 
freshly  secreted  pancreatic  juice  is  without  action  upon  proteins. 
The  addition  of  succus  entericus  immediately  confers  upon  it  a 
high  degree  of  proteolytic  power.  In  one  experiment  pancreatic 
juice,  obtained  by  a  temporary  fistula,  required  four  to  six  hours 
to  dissolve  fibrin,  and  did  not  attack  coagulated  albumin  even  in 
ten  hours.  On  addition  of  succus  entericus,  the  same  pancreatic 
juice  dissolved  fibrin  in  three  to  seven  minutes,  and  rapidly 
digested  coagulated  albumin  (Pawlow).  In  like  manner  a 
glycerin  extract  of  a  fresh  pancreas  has  hardly  any  effect  on 
proteins  ;  a  similar  extract  of  a  stale  pancreas  is  active.  The 
fresh  pancreas  contains  trypsinogen,  which  is  soluble  in  glycerin, 
for  the  inert  extract  becomes  active  when  it  is  treated  with  dilute 
acetic  acid,  or  even  when  it  is  diluted  with  water  and  kept  at 
the  body-temperature.  If  the  fresh  pancreas  be  first  treated  with 
dilute  acetic  acid,  and  then  with  glycerin,  the  extract  is  at  once 
active.  The  trypsinogen  can  therefore  be  activated  within  the 
pancreatic  cells,  gradually  when  the  pancreas  is  simply  allowed  to 
stand  after  excision,  more  rapidly  in  presence  of  the  dilute  acid. 
The  ordinary  tests  for  ferment  action  (destruction  by  boiling, 
activity  in  very  small  amounts,  etc.)  have  shown  that  this  pro- 
perty of  the  intestinal  juice  is  due  to  a  ferment,  although  it 
differs  in  certain  respects  from  most  ferments — for  instance,  in 


344  A    MAh  UAL  OF  PHYSIOLOC  J 

requiring  a  relatively  high  temperature  to  inactivate  it.  The 
smallest  trace  of  enterokinase  will  convert  a  large  quantity  of 

trypsinogen  into  trypsin  if  time  be  given.  At  the  same  time, 
although  to  a  much  smaller  extent,  the  fat-splitting  and  starch- 
digesting  activity  of  the  pancreatic  juice  is  increased.  The 
secretion  of  the  duodenum  causes  a  greater  increase  in  the  proteo- 
lytic power  than  that  of  the  other  portions  of  the  small  intestine, 
while  no  such  difference  has  been  made  out  in  the  case  "I  the 
amylolytic  and  lipolytic  functions.  It  is  probable  that  the 
enterokinase,  which  is  secreted  mainly  in  the  upper  part  of  the 
small  intestine,  and  solely  by  the  intestinal  epithelium,  acts  only 
on  the  trypsinogen,  and  that  the  amylopsin  and  steapsin  are 
aided  in  some  other  way.  Enterokinase  is  only  found  in  the 
intestinal  juice  when  pancreatic  juice  is  present  in  the  gut.  It 
is  therefore  secreted  in  response  to  the  presence  of  trypsinogen 
or  of  some  other  constituent  of  the  pancreatic  juice. 

Dele/enne  has  attempted  to  explain  the  interaction  of  entero- 
kinase and  trypsinogen  as  an  adaptive  phenomenon  of  the  same 
kind  as  the  formation  of  antitoxins  and  hemolysins  (p.  27).  Ac- 
cording to  him,  enterokinase  acts  like  a  complement  in  haemolysis, 
while  trypsinogen  plays  the  part  of  an  intermediary  body  or  ambo- 
ceptor which  enables  the  enterokinase  to  attack  the  protein  mole- 
cule. He  asserts  that  enterokinase,  or  a  substance  which  produces 
a  similar  effect  on  trypsinogen,  is  contained  not  only  in  the  mucous 
membrane  of  the  intestine,  but  also  in  leucocytes,  in  fibrin  (one  of 
whose  properties  it  is  to  pick  out  ferments  from  liquids  containing 
them),  in  lymph-glands,  in  snake  venom,  and  even  in  certain  anae- 
robic bacteria.  On  this  view  trypsin  would  not  be  a  definite  sub- 
stance produced  by  the  interaction  of  enterokinase  and  trypsinogen, 
but  only  an  expression  for  these  two  bodies  acting  together.  Strong 
evidence  against  this  view,  and  in  favour  of  the  independent  existence 
of  trypsin,  has  been  brought  forward  by  Bayliss  and  Starling,  and 
it  does  not  seem  to  merit  further  consideration. 

According  to  Pawlow,  the  reason  why  the  trypsin  is  not  secreted 
in  the  active  form  is  that  active  trypsin  readily  destroys  the 
amylolytic  and  lipolytic  ferments.  In  the  intestine,  where  trypsin 
is  rendered  active  by  enterokinase,  these  ferments  are  protected 
from  its  attack  by  the  proteins  of  the  food  and  by  the  bile. 

Having  now  finished  our  review  of  the  chemistry  of  the  diges- 
tive juices,  our  next  task  is  to  describe  what  is  known  as  to  their 
secretion — the  nature  of  the  cells  by  which  it  is  effected  and  their 
histological  appearance  in  activity  and  repose,  and  the  manner  in 
which  it  is  called  forth  and  controlled. 

III.  The  Secretion  of  the  Digestive  Juices. 

The  digestive  glands  are  formed  originally  from  involutions  of  the 
mucous  membrane  of  the  alimentary  canal,  the  salivary  glands 
from  the  ectoderm,  the  others  from  the  endoderm  (Chap.  XIV.). 
Some  are  simple  unbranched  tubes,  in  which  there  is  either  no  dis- 


DIGESTION 

tun  tnm  into  body  and  duct,  as  in  Lieberkuhn's  crypts  in  the  in 
tines,  or  in  which  one  or  more  of  the  tubes  open  into  .1  du<  t,  .is  in 
the  glands  of  the  fundus  of  the  stomach.  Some  are  branched  tub<  . 
several  ol  which  may  end  in  a  common  duel  ;  such  arc  the  glands  of 
the  pyloric  end  of  the  stomach,  and  the  Brunner's  glands  in  the 
duodenum.  In  others  the  main  duct  ramifies  into  a  more  or  less 
i  omplex  system  of  small  channels,  into  each  of  the  ultimate  branches 
oi  which  one  or  more  (usually  several)  of  the  secreting  tubules  or 
alveoli  open.  The  salivary  glands  and  the  pancreas  belong  to  this 
elass  of  compound  tubular  or  racemose  glands,  and  so  does  the  liver 
of  such  animals  as  the  frog.  But  in  the  latter  organ  the  typical 
arrangement  is  obscured  in  the  higher  vertebrates  by  the  predomi- 
nance of  the  portal  bloodvessels  over  the  system  of  bile-channels  as 
a  groundwork  for  the  grouping  of  the  cells. 

In  every  secreting  gland  there  is  a  vascular  plexus  outside  the 
cells  of  the  gland-tubes,  and  a  system  of  collecting  channels  on 
their  inner  surface  ;  and  in  a  certain  sense  the  cells  of  every  gland 
are  arranged  with  reference  to  the  bloodvessels  on  the  one  hand,  and 
the  ducts  on  the  other.  But  in  the  ordinary  racemose  gland  the 
blood-supply  is  mainly  required  to  feed  the  secretion  ;  the  cells  of 
the  alveoli  have  either  no  other  function  than  to  secrete,  or  if  they 
have  other  functions,  they  are  not  such  as  to  entail  a  great  dispro- 
portion between  the  size  of  the  cells  and  the  lumen  of  the  channels 
into  which  they  pour  their  products.  For  both  reasons  the  relation 
of  the  grouping  of  the  cells  to  the  duct-system  is  very  obvious,  to 
the  blood-system  very  obscure.  In  the  liver  the  conditions  are 
precisely  reversed.  We  cannot  suppose  that  the  manufacture  of  a 
quantity  of  bile  less  in  volume  than  the  secretion  of  the  salivary 
glands,  though  doubtless  containing  far  more  solids,  requires  an 
immense  organ  like  the  liver,  and  a  tide  of  blood  like  that  which 
passes  through  the  portal  vein.  And,  as  we  shall  see,  the  liver  has 
other  functions,  some  of  them  certainly  of  at  least  equal  importance 
with  the  secretion  of  bile,  and  one  of  them  evidently  requiring  from 
its  very  nature  a  bulky  organ.  Accordingly,  both  the  richness  of  the 
blood-supply  and  the  size  of  the  secreting  cells  are  out  of  proportion 
to  the  calibre  of  the  ultimate  channels  that  carry  the  secretion  away. 
The  so-called  bile-capillaries,  which  represent  the  lumen  of  the 
secreting  tubules,  are  mere  grooves  in  the  surface  of  adjoining  cells  ; 
and  the  architectural  lines  on  which  the  liver  lobule  is  built  are  : 
(1)  the  interlobular  veins  which  carry  blood  to  it  ;  (2)  the  rich  capil- 
lary network  which  separates  its  cells  and  feeds  them  ;  and  (3)  the 
central  intra-lobular  vein  which  drains  it.  Thus  a  network  of  cells 
lying  in  the  meshes  of  a  network  of  blood-capillaries  takes  the  place 
of  a  regular  dendritic  arrangement  of  ducts  and  tubules  ;  and  in 
accordance  with  this  the  bile-capillaries,  instead  of  opening  sepa- 
rately into  the  ducts,  form  a  plexus  with  each  other  within  the 
hepatic  lobule  (see  also  footnote,  p.  14). 

The  ducts  and  secreting  tubules  of  all  glands  are  lined  by  cells  of 
columnar  epithelial  type,  but  the  type  is  most  closely  preserved  in 
the  ducts.  In  none  of  the  digestive  glands  is  there  more  than  a 
single  complete  layer  of  secreting  cells.  But  the  alveoli  of  the 
mucous  salivary  glands  show  here  and  there  a  crescent-shaped 
group  of  small  deeply-staining  cells  (crescents  of  Gianuzzi)  outside 
the  columnar  layer  (Fig.  141,  A",  B"),  and  between  it  and  the  basement 
membrane,  while  the  gland-tubes  of  the  fundus  of  the  stomach  have 
in  the  same  situation   a  discontinuous  layer  of  large   ovoid   cells. 


H  I   .1/  l.vr  //    OF  PHYSIOLOC  Y 

termed  parietal  from  their  position,  oxyntic  (or  acid  secreting)  from 
their,  supposed  Function  (Figs.  i  jN-i-40).  Access  to  the  Lumen  of  the 
glands  is  provided  for  these  deeply-placed  parietal  cells  and  for  the 
cells  of  the  crescents  by  fine  branching  channels  which  enter  and  sur- 
round the  cells.  The  serous  salivary  glands,  the  pyloric  glands  of  the 
stomach,  and  the  Lieberkuhn's  crypts,  have  but  a  single  layer  of 
epithelium  ;  and  since  there  is  no  hepatic  cell  winch  is  not  in  cont.n  t 
with  at  least  one  bile-capillary,  the  liver  may  be  regarded  as  having 
no  more.  The  same  is  true  of  the  pancreatic  alveoli,  except  thai 
m  the  centre  of  many  of  the  acini  a  few  spindle-shaped  cells  (centro- 
acinar  cells),  apparently  continued  from  the  lining  of  the  smallest 
ducts,  may  be  seen.  Remarkable  histological  changes,  evidently 
connected  with  changes  in  functional  activity,  have  been  noticed 
in  most  of  the  digestive  glands.  In  discussing  these,  it  will  be 
best  to  omit  for  the  present  any  detailed  reference  to  the  liver,  since, 
although  there  are  histological  marks  of  secretive  activity  in  this 
gland  as  well  as  in  others,  and  of  the  same  general  character,  they 
are  accompanied,  and  to  some  extent  overlaid,  by  the  microscopic 


A  B 

Fig.   136. — Pancreas  in  '  Loaded  '  and  '  Discharged  '  State. 

A,  alveolus  of  rabbit's  pancreas,  '  loaded'  (resting)  ;  B,  '  discharged'  (active), 
observed  in  the  living  animal  (Kiihne  and  Lea). 

evidences  of  other  functions  (p.  311).  The  serous  salivary  glands 
and  the  pancreas  can  be  taken  together  ;  so  can  the  glands  of  the 
various  regions  of  the  stomach  ;  the  mucous  salivary  glands  must 
be  considered  separately. 

Changes  in  the  Pancreas  and  Parotid  during  Secretion.— 
The  cells  of  the  alveoli  of  the  pancreas  or  parotid  timing  rest,  as 
can  be  seen  by  examining  thin  lobules  of  the  former  between  the 
folds  of  the  mesentery  in  the  living  rabbit,  or  fresh  teased  pre- 
parations of  the  latter,  are  filled  with  fine  granules  to  such  an 
extent  as  to  obscure  the  nucleus.  In  the  parotid  the  whole  cell 
is  granular,  in  the  pancreas  there  is  still  a  narrow  clear  zone  at 
the  outer  edge  of  the  cell  which  contains  few  granules  or  none  ; 
in  both,  the  divisions  between  the  cells  are  very  indistinct,  and 
the  lumen  of  the  alveolus  cannot  be  made  out.  During  activity 
the  granules  seem  to  be  carried  from  the  outer  portion  of  the  cell 
towards  the  lumen,  and  there  discharged  ;  the  clear  outer  /one 


DJG1  STION 


347 


of  the  pancreatic  eel]  grows  broader  and  broader  at  theexpt 
of  the  inner  granular  zone,  until  at  last  the  granular  zone  may  in 
its  turn  be  reduced  to  a  narrow  contour  line  around  the  lumen 
i  36).  In  the  uniformly  clouded  parotid  cell  a  similar  change 
takes  place  ;  a  transparent  outer  zone  arises  ;  and,  after  prolonged 
secretion,  only  a  thin  edging  of  granules  may  remain  at  the  inner 
portion  of  the  cell  (Fig.  i.lj).  In  both  glands  the  outlines  of  the 
cells  become  more  clearly  indicated,  and  a  distinct  lumen  can  now 
he  recognised.     The  cells  are  smaller  than  they  are  during  rest. 

The  disappearance  of  granules  from  without  inwards  during 
activity  suggests  that  these  are  manufactured  products  eliminated 
in  the  secretion. 

In  one  respect  the  changes  in  the  pancreas  differ  remarkably 
from  those  in  the  salivary  glands.  The  '  islets  of  Langerhans,' 
those  characteristic  groups  of  small  polygonal  cells,  richly  sup- 
plied with  bloodvessels,  but  not  arranged  in  the  form  of  alveoli 


Fig.  137. — Alveoli  of  Parotid  Gland  :  A,  at  Rest  ;  B,  after  a  Short  Period 
of  Activity  ;  C,  after  a  Prolonged  Period  of  Activity  (Fresh  Pre- 
parations) (Langley). 

In  A  and  B  the  nuclei  are  obscured  by  the  granules  of  zymogen. 


and  unprovided  with  ducts,  which  are  scattered  here  and  there 
among  the  alveoli,  are  markedly  increased  in  size  and,  it  is  said, 
in  number  when  the  pancreas  is  caused  to  secrete  actively  by 
repeated  injections  of  secretin,  and  also  in  starvation.  Some 
observers  consider  that  they  are  derived  from  the  ordinary 
secreting  cells,  which  when  exhausted  undergo  rearrangement, 
and  that  they  can.  in  turn,  give  rise  to  new  alveoli  by  a  process 
of  proliferation.  Others  look  upon  them  as  independent  struc- 
tures, with  a  different  function  from  the  pancreatic  alveoli 
(P-  554b  The  discussion  of  this  question  is  assuredly  not  yet 
closed. 

Changes  in  the  Glands  of  the  Stomach  during  Secretion. — The 
mucous  membrane  of  the  stomach  is  covered  with  a  single  layer  of 
columnar  epithelium,  largely  consisting  of  mucigenous  goblet-cells. 
It  is  studded  with  minute  pits,  into  which  open  the  ducts  of  the 
peptic  and  pyloric  glands,  the  ducts  being  lined  with  cells  just  like 
those  of  the  general  gastric  surface.     Three  varieties  of  gastric 


34§ 


A    MANX    II    OB    PHYSIOLOGY 


glands  have  been  distinguished  :  (i)  The  glands  of  the  cardia.  In 
man  these  occupy  a  small  portion  of  the  mucous  membrane  at 
the  cardial  end,  neai  the  orifice  oi  the  oesophagus.  Some  of  the 
glands  are  single  tubules,  but  others  have  two  or  more  tubules 
opening  into  .1  common  duct.  Both  are  lined  by  a  single  layei 
"l  short  columnar  epithelium  j  which  contains  granules.  12)  The 
glands  oi  the  pyloric  canal  or  antrum.     These  consist  of  short, 


Fie  138.  A  I- 1  ndus  Gland  oi  Simple 
1  orm  1  rom  1111  Bat's  Stomach  ((  >smi< 
\mh  Preparation)  (Langley). 

<,  t  olumnar  epithelium  "I  tin'  surfai  1  ; 
n,  aeck  nt  the  gland  with  chief  or  centra! 
and  parietal  cells ;  >.  base,  occupied  only  by 
chief  cells,  which  show  the  granules  ai  i  u- 
mulattil  towards  the  lumen  of  tin-  gland. 


]'ir,.      139. — A     Fundus     Gland 

111   PARI   I'      HV     GOLGl'S     Ml    1  Him. 

showing     i  in      Modi     "i     (  <>m- 

MUNII    \  1  ION       OF      Till         PARI!   I  AI 
(Ills    w  I  1  II      I  III      (  rLAND  ■   I 
(SciIAFER,    AFTER     E.     Mi   I.LER). 


branclied  tubules,  which  open  by  twos  and  threes  into  long  ducts. 
(3)  The  glands  of  the  fundus  or  oxyntic  glands,  occupying  the 
intermediate  and  greater  portion  of  the  organ.  The  gland 
tubules  are  long  ami  seldom  branched,  and  the  ducts,  into  each 
of  which  open  from  one  to  three  tubules,  are  relatively  short. 
The  secreting  parts  <»l  both  kinds  of  glands  are  lined  by  short 
columnar  granular  cells  ;  and  in   the  pyloric    tubules  no  others 


DIGESTION  140 

present.  But,  as  we  have  said,  in  the  glands  of  the  fundus 
there  are  besides  large  ovoid  cells  scattered  at  intervals  like 
heads  between  the  basemenl  membrane  and  the  lining  or  chiei 
cells.  The  cells  oi  the  pyloric  glands  have  a  general  resemblance 
to  the  chief  cells  of  the  fund  us  glands,  I  ml  they  are  no1  quite  the 
same.  For  example,  the  granules  are  less  distind  in  the 
pyloric  glands.  In  the  human  stomach  it  is  only  quite  near 
the  pylorus  thai  the  parietal  cells  disappear  altogether.  The 
parietal  cells  also  contain  granules,  but  they  are  smaller  and  less 
numerous  than  those  of  the  chief  cells,  so  that  the  deeper  por- 
tions of  the  fundus  glands  are  much  darker  in  appearance  than 
the  more  superficial  portions,  since  the  oxyntic  cells  are  more 
numerous  in  the  neighbourhood  of  the  ducts  (Bensley). 

The  histological  changes  connected  with  gastric  secretion  do  not 
differ  essentially  from  those  described  in  the  pancreas  and  the 
p, not  id.  hut  there  is  much  greater  difficulty  in  making  observa- 
tions on  the  living,  or  at  least  but  slightly  altered,  cells.  For 
the  mammal  the  best  method  is  to  use  animals  with  a  permanent 
gastric  fistula,  and  to  remove  from  time  to  time  small  portions 
of  the  mucous  membrane  for  examination  in  the  fresh  condition. 
During  digestion  the  granules  disappear  from  the  outer  part  of 
the  chief  cells  of  the  fundus  glands,  leaving  a  clear  zone,  the 
lumen  heing  bordered  by  a  granular  layer.  Or,  more  rarely, 
there  may  be  a  uniform  decrease  in  the  number  of  granules 
throughout  the  cell.  The  total  volume  of  the  cell  is  less  than  in 
the  fasting  condition.  The  ovoid  cells,  which  are  small  in  the 
fasting  animal,  swell  up,  so  as  to  bulge  out  the  membrana  propria. 
They  reach  their  maximum  size  (in  the  dog)  very  late  indigestion 
(the  thirteenth  to  the  fifteenth  hour).  No  such  definite  changes 
in  their  contents  as  those  observed  in  the  other  cells  have  been 
made  out.  The  granules  in  the  ovoid  cells  during  and  after 
activity  seem  to  be  as  large  and  as  numerous  as  in  the  resting 
cell,  or  even  larger.  After  sham  feeding  in  dogs  the  histological 
changes  in  the  gastric  glands  are  very  slight,  even  when  con- 
siderable amounts  of  gastric  juice  have  been  secreted  (Noll  and 
Sokoloff). 

The  chief  cells  of  the  oxyntic,  and  the  similar  if  not  identical 
cells  of  the  pyloric  glands,  are  believed  to  manufacture  the  pepsin- 
forming  substance.  The  ovoid  cells  of  the  former  are  supposed 
to  secrete  the  hydrochloric  acid.  The  evidence  on  which  this 
belief  is  based  is  as  follows  : 

The  glands  of  the  antrum  pylori  in  the  dog,  in  which  in  most 
situations  no  ovoid  cells  are  to  be  seen, secrete  pepsin,  but  no  acid. 
The  pyloric  end  of  the  stomach  or  a  portion  of  it  has  been  isolated, 
the  continuity  of  the  alimentary  canal  restored  by  sutures,  and 
the  secretion  of  the  pyloric  pocket  collected.     It  was  found  to  be 


350 


A    1/  \\r  //    OF  PHYSIOLOGY 


alkaline,  and  contained  pepsin.  The  glands  of  the  frog's  o 
phagns,  which  contain  only  chief  cells,  secrete  pepsin,  but  no  a<  id. 
Ii  seems  fair  to  conclude  thai  the  chief  cells  of  the  fundus  glands 
in  the  mammal  secrete  none  of  Hie  free  hydrochloric  acid,  but 
certainly  some  of  pepsin.  But  it  does  not  follow  that  all  the  pep- 
sin is  formed  by  these  cells,  although  it  would  seem  that  all  the 
hydrochloric  acid  must  be  secreted  by  the  only  other  glandular 


Fig.   140. — The  Gastric  Glands  (Ebstein). 
On  the  left,  oxyntic  ;  right,  pyloric. 


elements  present,  the  ovoid  or  '  border  '  cells.  And,  indeed,  the 
glands  in  the  fundus  of  the  frog's  stomach,  which  are  composed 
only  of  ovoid  cells,  whilst  secreting  much  acid,  also  form  some 
pepsin,  although  far  less  than  the  oesophageal  glands.  During 
winter  sleep  (in  the  marmot)  the  production  of  hydrochloric 
acid  in  the  parietal  cells  stops  altogether,  while  the  chief  cells 
continue  to  accumulate  granules  of  pepsinogen. 


DIGESTION  351 

That  some  pepsin  is  secreted  by  the  pyloric  end  of  the  stomach 
is  not  difficult  to  prove.  The  secretion  collected  from  the  isolated 
pyloric  portion  is,  indeed,  like  the  secretion  of  the  Brunner's 
glands  in  the  duodenum,  quite  unable  to  digest  protein  until 
dilute  hydrochloric  acid  is  added.  But  this  is  because  in  both  cases 
the  juice  as  it  (lows  from  the  glands  is  slightly  alkaline,  and,  as  we 
have  already  seen,  pepsin  only  acts  in  the  presence  of  an  acid. 
The  milk-curdling  action  of  these  two  juices  also  unfolds  itself 
only  when  the  secretions  are  first  acidulated,  and  later  on  again 
neutralized  ;  in  other  words,  the  ferments  must  be  activated  by 
the  addition  of  an  acid.  In  normal  digestion  the  pepsin  of  the 
(in  itself)  alkaline  secretion  of  the  pyloric  end  of  the  stomach 
heroines  a  constituent  of  the  acid  gastric  juice  ;  and  it  may. 
perhaps,  be  considered  a  morphological  accident,  so  to  speak, 
that  the  oxyntic  cells  of  the  fundus  should  mingle  their  acid 
products  with  the  (presumedly)  alkaline  secretion  of  the  chief 
cells  in  the  lumen  of  each  gland-tube,  instead  of  being  massed 
as  a  separate  organ  with  a  special  duct. 

We  are  not  without  other  examples  of  digestive  juices  fitted  or 
destined  to  act  in  a  medium  with  an  opposite  reaction  to  their 
own.  The  '  saliva  '  of  the  cephalopod  Octopus  macropus,  strongly 
acid  though  it  is,  contains  a  proteolytic  ferment  which  in  vitro 
acts,  like  trypsin,  better  in  an  alkaline  than  in  an  acid  solution. 
And  trypsin,  whose  precursor  is  a  constituent  of  the  alkaline 
pancreatic  juice  and  the  enterokinase  which  activates  it,  a  con- 
stituent of  the  alkaline  succus  entericus,  performs  a  part  at  least 
of  its  work  in  an  acid  medium. 

Attempts  made  to  demonstrate  an  acid  reaction  in  the  border  cells 
have  hitherto  failed,  perhaps  because  the  acid  is  poured  into  the 
ducts  as  fast  as  it  is  formed.  But  it  may  be  mentioned,  although 
only  as  a  matter  of  historical  interest,  that  some  observers  have 
denied  that  the  acid  is  secreted  in  the  depths  of  any  cell  from  the 
chlorides  of  the  blood,  and  have  asserted  that  it  is  formed  at  the 
surface  of  contact  of  the  stomach-wall  with  the  gastric  contents  from 
the  sodium  chloride  of  the  food  by  an  exchange  of  sodium  ions 
(p.  400)  for  hydrogen  ions  from  the  blood  or  lymph.  It  was  pointed 
out  in  favour  of  this  view  that  when,  instead  of  sodium  chloride, 
sodium  bromide  is  given  in  the  food,  the  hydrochloric  acid  in  the 
stomach  is  to  a  large  extent  replaced  by  hydrobromic  acid.  And 
it  was  argued  that  this  cannot  be  due  to  the  decomposition  of  the 
bromide  by  hydrochloric  acid,  since  it  occurs  in  animals  deprived 
for  a  considerable  time  of  salts,  and  in  '  salt-hunger  '  the  stomach 
contains  no  acid  (Koeppe).  It  may  be,  however,  that  even  in  '  salt- 
hunger  '  the  presence  of  sodium  bromide  in  the  stomach  stimulates 
the  secretion  of  hydrochloric  acid,  which  then  decomposes  the 
bromide,  with  the  formation  of  hydrobromic  acid.  The  sodium 
chloride  formed  in  the  double  decomposition  might  be  re-absorbed, 
and  the  stock  of  chlorides  in  the  blood  remain  undiminished.  It 
is  in  any  case  a  decisive  objection  to  this  now  defunct  theory  that 
a  copious  secretion  of  gastric  juice,  containing  hydrochloric  acid  in 


352 


A    MAXrU.   OF  PHYSIOLOGY 


abundance,  can  bo  obtained,  without  the  introduction  of  any  food 
into  the  stomach,  either  l>v  the  process  of  sham  feeding  (p,  -17})  or 
by  psychical  stimulation  of  the  gastric  glands  when  food  is  shown 

to  an  animal. 

Changes  in  Mucous  Glands  during  Secretion.  -  In  the  mucous 
salivary  and  other  mucous  glands  similar,  bul  apparently  more 
complex,  changes  occur.  During  rest  the  cells  which  line  the 
lumen  may  be  seen  in  fresh,  teased  preparations  to  be  filled  with 
granules  or  '  spherules.'  After  active  secretion  there  is  a  great 
diminution  in  the  number  of  the  granules.  Those  that  remain 
are  chiefly  collected  around  the  lumen,  although  some  may  also 
be  seen  in  the  peripheral  portion  of  the  cell  ;  and  there  is  no  vei  v 
distinct  differentiation  into  two  zones.  That  a  discharge  of 
material  takes  place  from  these  cells  is  shown  by  their  smaller 
size  in  the  active  gland.     That  the  material  tints  discharged  is  no1 


Fig.   141. — Mucous  Cells  (from  Submaxillary  of  Dog)  in   Rest 
and  Activity  (Langley). 

A,  B,  fresh  ;  A',  B',  after  treatment  with  dilute  acetic  acid  ;  A",  B",  alveoli 
hardened  in  alcohol  and  stained  with  carmine.  A,  A',  and  A"  represent  the 
loaded  ;  B,  B',  and  B",  the  discharged  condition. 

protoplasmic  is  indicated  by  the  behaviour  of  the  cells  to  proto- 
plasmic stains  such  as  carmine.  The  resting  cells  around  the 
lumen  stain  but  feebly,  in  contrast  to  the  deep  stain  of  the 
demilunes,  while  the  discharged  cells  take  on  the  carmine  stain 
much  more  readily.  Further,  when  a  resting  gland  is  treated 
with  various  reagents  (water,  dilute  acids,  or  alkalies),  the 
granules  swell  up  into  a  transparent  substance  identical  with 
mucin,  which  fills  the  meshes  of  a  fine  protoplasmic  network. 

In  ordinary  alcohol-carmine  preparations  only  the  network  and 
nucleus  are  stained  ;  the  nucleus,  small  and  shrivelled,  is  situated 
close  to  the  outer  border  of  the  cell.  When  a  discharged  gland  is 
treated  in  the  same  way  there  is  proportionally  more  '  proto- 
plasm '  (or  '  bioplasm  ')  and  less  of  the  clear  material,  what 
remains  of  the  latter  being  chiefly  in  the  inner  portion  of  the 
cell,  while  the  nucleus  is  now  large  and  spherical,  and  not  so 
near  the  basement 'membrane  (Fig.  141). 


Plate    II 


Srrniijt  nht.obi 


Ivtoht.*. 


Crescents  of  Gianuzzi 


Duct 


Supporting  connective  tissue 


1.  Section  of  submaxillary  gland  showing  both  mucous  and  serous  alveoli,   x  250. 
{Stained  loith  hematoxylin.) 


, 


Before  secretion  (resting)  After  secrttion  (active) 

2.  Section  of  serous  gland,  x  300.     (Stained  with  borax  carmine. ) 


Crescents  of 

>i:zi 
(very  large) 


Mucous  cells 


3 


Connective  tissue 


Intermediate  duct 

leading  from  acini  of  gland 

to  intralobular  duct 


^  I 


Blood^wtmd 


Duct  (intralobular) 


3.  Section  of  mucous  gland  (after  secretion),   x  300.     (Stained  with  picrocarmine.) 


Geo  Virtratoa*  Sol 


DIGESTION  353 

Everything,  therefore,  points  to  the  granules  in  what  we  may 
now  tall  the  mucin-ibrming  cells  as  being  in  some  way  or  other 
precursors  of  the  fully-formed  mucin  ;  manufactured  during 
'  rest  '  by  the  protoplasm  and  partly  at  its  expense,  moved 
towards  the  Lumen  in  activity,  discharged  as  mucin  in  the  secre- 
tion. It  has  been  asserted  that  not  only  is  the  protoplasm 
lessened  in  the  loaded  cell  and  renewed  after  activity,  but  that 
many  of  the  mucigenous  cells  may  be  altogether  broken  down 
and  discharged,  their  place  being  supplied  by  proliferation  of 
the  small  cells  of  the  demilunes.  This  conclusion,  however,  is 
not  supported  by  sufficient  evidence.  The  cells  of  the  crescents 
contain  fine  granules,  but  none  which  can  be  changed  into  mucin. 
They  are  of  serous  and  not  of  mucous  type.  But  the  fact  on 
which  we  would  specially  insist  is  that  the  granules  of  the  resting 
mucigenous  cell  may  be  looked  upon  as  a  mother-substance  from 
which  the  mucin  of  the  secretion  is  derived  ;  they  are  not  actual, 
but  potential,  mucin. 

So  in  the  pancreas,  the  serous  or  albuminous  salivary  glands, 
and  the  glands  of  the  stomach,  there  is  every  reason  to  believe 
that  the  granules  which  appear  in  the  intervals  of  rest,  and  are 
moved  towards  the  lumen  and  discharged  during  activity,  are 
the  precursors,  the  mother-substances,  of  important  constituents 
of  the  secretion.  These  granules  are  sharply  marked  off  from  the 
protoplasm  in  which  they  lie  and  by  which  they  are  built  up. 
By  every  mark,  by  their  reaction  to  stains,  for  instance,  they  are 
non-living  substance,  formed  in  the  bosom  of  the  living  cell  from 
the  raw  material  which  it  culls  from  the  blood,  or,  what  is  more 
likely,  formed  from  its  own  protoplasm,  then  shed  out  in  granular 
form  and  secluded  from  further  change.  The  granules  in  the 
ferment-forming  glands  are  not  in  general  composed  of  the  actual 
ferments,  and,  indeed,  in  several  instances  it  has  been  shown  that 
the  actual  ferments  are  not  present  in  the  secreting  cells  at  all. 

We  have  already  seen  that  the  pancreas  and  even  the  fresh 
pancreatic  juice  are  devoid  of  active  trypsin.  Similarly,  a 
glycerin  extract  of  a  fresh  gastric  mucous  membrane  is  inert  as 
regards  proteins,  or  nearly  so.  But  if  the  mucous  membrane  has 
been  previously  treated  with  dilute  hydrochloric  acid,  the 
glycerin  extract  is  active,  as  is  an  extract  made  with  acidulated 
glycerin.  Here  we  must  assume  the  existence  in  the  gastric 
glands  of  a  mother-substance,  pepsinogen,  from  which  pepsin  is 
formed.  The  rennin  of  the  gastric  juice,  which  is  formed  in  the 
chief  cells,  also  has  a  precursor,  which,  if  the  ferment  is  identical 
with  pepsin  (p.  326),  must  be  pepsinogen.  The  proteolytic  power 
of  an  extract  of  the  pancreas,  when  the  trypsinogen  has  been 
activated  into  trypsin,  or  of  the  gastric  mucous  membrane,  when 
the  pepsinogen  has  been  changed  into  pepsin,  seems  to  be,  roughly 


354  A    M.l\  i    II-   OF    PHYSIOLOG  Y 

speaking,  in  proportion  to  the  quantity  oi  granules  presenl  in 
tlif  colls.  Therefore  it  is  concluded  that  the  granules  represent 
mother-substances  of  the  ferments  or  zymogens.  Some  observers 
believe  they  have  obtained  evidence  of  stages  in  the  elaboration 
of  the  ferments  still  further  back  than  the  mother-substances, 
grandmother-substances  so  to  speak,  or  prozymogens.  Bensley, 
e.g.,  concludes  that  the  nuclei  of  the  chief  cells  in  the  fundus 
glands  of  the  stomach  take  part  in  the  formation  of  a  prozymo- 
gen,  the  precursor  of  the  zymogen  or  pepsinogen,  as  pepsin- 
is  the  precursor  of  the  enzyme  pepsin. 

A  glycerin  or  watery  extract  of  the  salivary  glands  always 
contains  active  anxiolytic  ferment,  if  the  natural  secretion 
is  active.  So  that  if  ptyalin  is  preceded  by  a  zymogen  in  the 
cells,  it  must  be  very  easily  changed  into  the  actual  ferment. 

But  we  should  greatly  deceive  ourselves  if  we  supposed  that 
granules  of  this  nature  in  gland-cells  are  necessarily  related  to 
the  production  of  ferments.  The  mucigenous  granules  have  no 
such  significance.  Most  digestive  secretions  contain  protein 
constituents,  with  which  the  granules  may  have  to  do,  as  well  as 
with  ferments.  And  bile,  a  secretion  which  contains  no  mucin, 
no  proteins,  and  either  no  ferments  or  mere  traces,  as  essential 
and  original  constituents,  is  formed  in  cells  with  granules  so  dis- 
posed and  so  affected  by  the  activity  of  the  gland  as  to  suggest 
some  relation  between  them  and  the  pro<  ess  of  secretion.  In  the 
liver-cells  of  the  frog,  in  addition  to  glycogen,  and  oil-globule>. 
small  granules  may  be  seen,  especially  near  the  lumen  of  the 
gland  tubules ;  they  diminish  in  number  during  digestion,  when  the 
secretion  of  bile  is  active,  and  increase  when  food  is  withheld  and 
secretion  slow.  And  in  fasting  dogs  the  secreting  cells  of  Brunner's 
glands,  the  pyloric  glands  and  the  pancreas,  as  well  as  the  lining 
epithelium  of  the  bile-ducts,  have  been  found  to  contain  many 
fatty  granules.  Possibly  some  of  these  represent  the  fat  which 
is  known  to  be  excreted  into  the  alimentary  canal  (pp.  415,  416). 
The  Nature  of  the  Process  by  which  the  Digestive  Secretions 
are  Formed.— -We  have  spoken  more  than  once  of  the  gland-cells 
as  manufacturing  their  secretions.  It  is  an  idea  that  rises 
naturally  in  the  mind  as  we  follow  with  the  microscope  the 
traces  of  their  functional  activity.  And  when  we  compare  the 
composition  of  the  digestive  juices  with  that  of  the  blood-plasma 
and  lymph,  the  suggestion  that  the  glands  which  produce  them 
are  not  merely  passive  filters,  but  living  laboratories,  acquires 
additional  strength.  It  is  evident  that  everything  in  the  secre- 
tion must,  in  some  form  or  other,  exist  in  the  blood  which  comes 
to  the  gland,  and  in  the  lymph  which  bathes  its  cells.  No 
glandular  cell,  it  we  except  the  leucocytes,  which  in  some  respects 
are  to  be  considered  as  unicellular  glands,  dips  directly  into  the 


DIGESTION  355 

Mood;  everything  .1  gland-cell  receives  must  pass  through  the 
walls  of  tlu>  bloodvessels.  (But  see  footnote  on  p.  14.)  So  that 
anything  which  we  find  in  the  secretion  and  do  not  find  in  the 
blood  must  have  been  elaborated  by  the  gland  epithelium  (or 

by  the  capillary  endothelium)  from  raw  material  brought  to  it 
by  the  blood. 

Take,  for  example,  the  saliva  or  gastric  juice.  These  liquids 
both  contain  certain  things  that  also  exist  in  the  blood,  but  in 
addition  they  contain  certain  things  specific  to  themselves  : 
mucin  in  saliva,  hydrochloric  acid  in  gastric  juice,  ferments  in 
both.  It  is  true  that  a  trace  of  pepsin  and  a  trace  of  a  diastatic 
ferment  may  be  discovered  in  blood  ;  but  there  is  no  reason 
whatever  to  believe  that  this  is  the  source  of  the  pepsin  of  the 
gastric  juice,  or  the  ptyalin  of  the  salivary  glands,  except, 
perhaps,  in  animals  like  the  cat,  whose  saliva  contains  a  diastase 
in  still  smaller  concentration  than  the  serum  (Carlson).  On  the 
contrary,  it  is  possible  that  the  ferments  of  the  blood  may  be  in 
part  absorbed  from  the  digestive  glands,  the  rest  being  formed 
by  the  leucocytes  and  liberated  when  they  break  down.  The 
liver  affords  an  even  better  example  of  this  '  manufacturing  ' 
activity  of  gland-cells,  and  many  facts  may  be  brought  forward 
to  prove  that  the  characteristic  constituents  of  the  bile,  the  bile- 
pigments  and  bile-acids,  are  formed  in  the  liver,  and  not  merely 
separated  from  the  blood.  Bile-pigment  has  indeed  been  recog- 
nized in  the  normal  serum  of  the  horse,  and  bile-acids  in  the  chyle 
of  the  dog,  but  only  in  such  minute  traces  as  are  easily  accounted 
for  by  absorption  from  the  intestine.  Frogs  live  for  some  time 
after  excision  of  the  liver,  but  no  bile-acids  are  found  in  the 
blood  or  tissues.  But  if  the  bile-duct  be  ligatured,  bile-acids  and 
pigments  accumulate  in  the  body,  being  absorbed  by  the 
lymphatics  of  the  liver  (Ludwig  and  Fleischl).  If  the  thoracic 
duct  and  the  bile-duct  are  both  ligatured  in  the  dog,  no  bile- 
acids  or  pigments  appear  in  the  blood  or  tissues.  Wertheimer 
and  Lepage  state  that  bile  or  bilirubin  injected  into  a  bile-duct 
appears  sooner  in  the  urine  than  in  the  lymph  of  the  thoracic 
duct,  and  therefore  conclude  that  the  bloodvessels  are  the  most 
important  channel  of  absorption.  This  conclusion,  however, 
cannot  be  accepted  until  it  is  shown  that  in  these  experiments 
the  injection  did  not  cause  rupture  of  some  of  the  hepatic 
capillaries  and  direct  entrance  of  the  bile-pigment  into  the  blood. 
It  is  not  improbable  that  the  pressure  attained  by  the  bile  in 
the  bile-capillaries  is  a  factor  in  determining  the  path  by  which 
it  is  absorbed,  and  that  when  the  pressure  rises  beyond  a  certain 
limit  it  may  pass  both  into  the  bloodvessels  and  into  the 
lymphatics.  In  mammals  life  cannot  be  maintained  for  any 
length  of  time  after  ligature  of  the  portal  vein,  since  this  throws 

23—2 


556  I    MANUAL  OF  PHYSIOLOGY 

the  whole  intestinal  tract  out  of  gear.  But  after  an  artificial  com- 
munication has  been  made  between  the  portal  and  the  left  renal 
vein  or  the  inferior  cava,  the  portal  may  be  tied  and  the 
animal  live  for  months  (Eck).  The  liver  can  now  be  completely 
removed,  but  death  follows  in  a  few  hours.  A  good  method  of 
establishing  an  Eck's  fistula  is  to  make  a  longitudinal  incision 
in  the  inferior  vena  cava  and  the  portal  or  superior  mesenteric 
vein,  and  to  suture  the  edges  of  the  two  openings  together  with  a 
very  fine  sewing-needle  and  thread  (Carrel  and  Guthrie).*  In 
birds  there  exists  a  communicating  branch  between  the  portal 
vein  and  a  vein  (the  renal-portal)  which  passes  from  the  posterior 
portion  of  the  body  to  the  kidney,  and  there  breaks  up  into 
capillaries  ;  and  not  only  may  the  portal  be  tied,  but  the  liver 
may  be  completely  destroyed  without  immediately  killing  the 
animal.  In  the  hours  of  life  that  still  remain  to  it  no  accumula- 
tion of  biliary  substances  takes  place  in  the  blood  or  tissues.  A 
further  indication  that  bile-pigment  is  produced  in  the  liver  is  the 
fact  that  the  liver  contains  iron  in  relative 
abundance  in  its  cells  (p.  21),  and  eliminates 
small  quantities  of  iron  in  its  secretion. 
Now.  bile-pigment,  which  contains  no  iron,  is 
certainly  formed  from  blood -pigment,  which 
is  rich  in  iron,  for  haematoidin  (Fig.  142),  a 
crystalline  derivative  of  haemoglobin  found 
in  old  extravasations  of  blood,  especially  in 
the  brain  and  in  the  corpus  luteum,  is  identi- 
ig.  142.—   .*  ••  caj  w-t^  Di]jmDm      The  seat  of  formation  of 

bile-pigment  must  therefore  be  an  organ  peculiarly  rich  in  iron. 
The  existence  of  haematoidin,  however,  shows  that  bile-pigment 
may,  under  certain  conditions,  be  formed  outside  of  the  hepatic 
cells.  The  occurrence  of  biliverdin  in  the  placenta  of  the  bitch 
points  in  the  same  direction.  But  the  pathological  evidence  in 
favour  of  the  pre-formation  of  the  biliary  constituents  tends 
rather  to  shrink  than  to  increase.  For  many  cases  of  what  used 
to  be  considered  '  idiopathic  '  or  '  hematogenic  '  jaundice, 
i.e.,  an  accumulation  of  bile-pigments  and  bile-acids  in  the 
tissues,  due  to  defective  elimination  by  the  liver,  are  now  known 
to  be  caused  by  obstruction  of  the  bile-ducts  and  consequent  re- 
absorption  of  bile  ('  obstructive  '  or  '  hepatogenic  '  jaundice). 

But  if  substances  such  as  the  ferments,  mucin,  hydrochloric 
acid,  the  bile-salts  and  bile-pigments,  are  undoubtedly  manu- 
factured in  the  gland-cells,  it  is  different  with  the  water  and 
inorganic  salts  which  form  so  large  a  part  of  every  secretion. 

*  By  means  of  a  small  clamp,  the  jaws  of  which  arc  shaped  so  as  to 
isolate' a  longitudinal  strip  at  one  side  of  a  bloodvessel  while  the  circulation 
goes  on  through  the  rest  of  the  lumen,  the  veins  may  be  opened  and 
sutured  without  interrupting  the  circulation. 


PTGESTTON 


357 


No  (issue  lacks  them  ;  no  physiological  process  goes  on  without 
them  ;  they  are  not  high  and  special  products.  As  we  breathe 
nitrogen  which  we  do  not  need  because  it  is  mixed  with  the 
0x3  gen  we  require,  the  secreting  cell  passes  through  its  substance 
water  and  salts  as  a  sort  of  by-play  or  adjunct  to  its  specific 
work.  But  this  is  not  the  whole  truth.  The  gland-cell  is  not  a 
mere  filter  through  which  water  and  salts  pass  in  the  same 
proportions  in  which  they  exist  in  the  liquids  that  the  cell  draws 
them  from.  When,  e.g.,  the  salivary  glands  secrete  against  the 
resistance  of  an  abnormally  high  pressure  in  the  ducts,  the  per- 
centage of  salts  in  the  saliva  increases.  The  secretions  of 
different  glands  differ  in  the  nature,  and  especially  in  the  relative 
proportions,  of  their  inorganic  constituents.  They  differ  also 
in  their  osmotic  pressure  and  electrical  conductivity,  which 
depend  so  largely  upon  those  constituents,  notwithstanding  the 
fact  that  the  osmotic  pressure  and  conductivity  of  the  blood- 
serum  (p.  25)  vary  only  within  narrow  limits.  Even  the  secre- 
tion of  one  and  the  same  gland  is  by  no  means  constant  in  this 
respect,  as  we  shall  have  to  note  more  especially  when  we  come 
to  deal  with  the  influence  of  the  nervous  system  on  secretion 
(p.  367).     The  following  tables  illustrate  this  point  : 


Dog. 

Blood-serum." 

Filtrate  of  Gastric  Contents. 

I. 

II. 

III. 

At 

KJ  (^C.)xio*. 

A 

K*(5"Oxio*. 

0-643° 
0-628° 

0-602° 

92-0 

876 

87-7 

0-5850 
0-5350 
0-642° 

3125 
I79-4 

35I-7 
84-7 

Vomit  of  man  with  complete  intes- 
tinal obstruction 

0-4330 

Pancreatic  Juice  of  Dog  (Pincussohn) . 


Diet. 

A 

Milk 

Cauliflower 
Horseflesh 

o- 57°— 0-63° 
0-58°— 0-63° 
0-62°— 0630 

*  The  blood  and  gastric  contents  were  obtained  from  the  animals  in  the 
writer's  laboratory  twenty-four  hours  after  the  last  meal. 

f  The  depression  of  the  freezing-point  below  that  of  distilled  water. 

%  K  is  the  specific  conductivity  of  a  cube  of  the  liquid  of  1  centimetre 
side,  the  conductivity  of  a  similar  cube  of  mercury  being  taken  as  unity. 
The  number  in  brackets  is  the  temperature  at  which  the  measurement  was 
made.     To  obtain  expressions  for  K  in  whole  numbers,  it  is  multiplied  by  io4. 


358 


A   MANUA1    OF  PHYSIOLOGY 


Gastric  Juice  from   Miniature  Stomach  in  a  Dog  in  Different 
Experiments  (Bickel). 


Mill:  Diet. 

Meal 

A 

052° 
0-65° 
064° 
069° 

o-8i° 

K(25°C.)xio\ 

A 

o-6o° 
0710 

1-21° 

0-79° 

0-70° 

K  (95   C.)xi<*». 

3IO-3 
473' 5 

l\V3 
5<4  ' 

5M'i 

195"  9 

4026 
4365 
4°4'2 
4365 

A  of  Blood  and  Saliva  Compared  (Jappelli). 


A  of  Wood. 

A  of  Submaxillary  Saliva  of  Dog. 

0-570° 

0410° 

06 10° 

0350° 

o-  6oo° 

04300 

o-  590° 

0410° 

0580° 

04500 

0-605° 

O4250 

0-650° 

0380° 

0610° 

0-475° 

A  of  Human  Fistula  Bile. 

A  of  Human  Bladder  Bile. 

O560 

0-547° 
0615° 
060° 
0-545° 

0650 
0865° 
O780 
092° 

A  of  Dog's  Submaxillar?  Saliva. 


Chorda  stimulated  : 
I. (ii  submaxillary 
Both  glands 

Spontaneous  secretion  : 
Right  submaxillary 
A  of  dog's  serum 


0-408° 

0195 

0-590° 


The  protein  substances,  such  as  serum-albumin  and  globulin, 
common  to  blood  and  to  some  of  the  digestive  secretions,  take 
a  middle  place  between  the  constituents  that  are  undoubted ly 


DIG1  STION 

manufactured  in  the  cell  and  those  which  seem  by  a  less  special 
and  laborious,  though  .1  selective,  process  to  be  passed  through 
it  from  the  blood.  Their  practical  absence  from  bile,  and,  as 
shall  see,  from  urine,  their  relative  abundance  in  pancreatic  and 
scantiness  in  gastric  juice,  point  to  a  1  loser  dependence  upon 
the  special  activity  of  the  gland-cell  than  we  can  suppose  m 
sai  v  m  the  case  of  the  salts. 

Although  it  is  in  the  cells  of  the  digestive  glands  that  the  power 
of  forming  ferments  is  most  conspicuous,  it  is  by  no  means  confined 
to  them.  It  seems  to  be  a  primitive,  a  native  power  of  protoplasm. 
Lowly  animals,  like  the  amoeba,  lowly  plants,  like  bacteria,  form 
ferments  within  the  single  cell  which  serves  for  all  the  purposes 
of  their  life.  The  ferment-secreting  gland-cells  of  higher  forms  are 
perhaps  only  lop-sided  amoeba?,  not  so  much  endowed  with  new- 
properties  as  disproportionately  developed  in  one  direction.  The 
contractility  has  been  lost  or  lessened,  the  digestive  power  has  been 
retained  or  increased  ;  just  as  in  muscle  the  power  of  contraction 
has  been  developed,  and  that  of  digestion  has  fallen  behind.  The 
muscle-cell  and  the  cartilage-cell  are  parasites,  if  we  look  to  the 
function  of  digestion  alone.  They  live  on  food  already  more  or 
less  prepared  by  the  labours  of  other  cells  ;  and  it  is  a  universal 
law  that  in  the  measure  in  which  a  power  becomes  useless  it  dis- 
appears. But  the  presence  of  pepsin  in  the  white  blood-corpuscles, 
the  parasites  as  well  as  the  scavengers  of  the  blood,  and  of  amylo- 
lvtic.  proteolytic  and  lipolytic  ferments  in  many  tissues,  should  warn 
us  not  to  conclude  that  the  power  of  forming  ferments  belongs  ex- 
clusively to  any  class  of  cells.  There  is  good  and  growing  evidence 
that  food-substances  absorbed  from  the  blood  are  further  decomposed 
and,  in  turn,  elaborated  by  ferment  action  within  the  tissues 
themselves  ;  while  many  facts  show  that  the  power  of  contraction  is 
widely  diffused  among  structures  whose  special  function  is  very 
different,  and  a  few  point  to  its  possession  in  some  degree  even  by 
glandular  epithelium.  On  the  other  hand,  it  must  be  remembered 
that  none  of  the  digestive  glands  absorb  food  directly  from  the  ali- 
mentary canal  to  be  then  digested  within  their  own  cell-substance  ; 
the  ferments  which  they  form  do  their  work  outside  of  them  ;  their 
cells  feed  also  upon  the  blood. 

Why  are  the  Tissues  of  Digestion  not  affected  by  the  Digestive 
Ferments  ? — This  is  the  place  to  mention  a  point  which  has  been 
very  much  debated.  Why  is  it  that  the  stomach  or  the  small 
intestine  does  not  digest  itself  ?  This  is  really  a  part  of  a  wider 
question  :  Why  is  it  that  living  tissues  resist  all  kinds  of  influences, 
which  attack  dead  tissties  with  success  ?  And  we  have  to  inquire 
whether  the  immunity  of  the  alimentary  canal  to  the  digestive 
juices  is  an  example  of  a  general  resistance  of  all  living  tissues  to 
destructive  agencies,  or  a  specific  resistance  of  certain  tissties  to 
certain  influences. 

That  all  living  tissues  cannot  withstand  the  action  of  the  gastric 
juice  has  been  shown  by  putting  the  leg  of  a  living  frog  inside 
the  stomach  of  a  dog  ;  the  leg  is  gradually  eaten  away  (Bernard). 


360  A   MANUAL  OF  PHYSIOLOGY 

It  is  true  thai  it  has  firsl  been  killed  and  then  digested,  but 

the  question  is,  why  the  stomach-wall  is  no1  fust  killed  and  then 
digested  ?  When  the  wall  has  been  injured  by  caustics  01  by 
an  embolus,  the  ,^.isi  1  ic  juice  acts  on  it.  But  the  living  epithelium 
that  covers  it  is  able  to  resist  the  action  of  the  acid  and  pepsin, 
winch  destroys  the  tissues  ol  the  frog's  leg.  The  explanation  is 
not  to  he  found  in  the  alkalinity  of  the  blood,  for  the  frog's  blood 
is  also  alkaline,  and  the  cells  that  line  the  intestine  are  preserved 

from  the  pancreatic  juice,  which  is  intensely  active  in  an  alkaline 
medium,  while  the  living  frog's  leg  is  not  harmed  by  a  weakly 
alkaline  pancreatic  extract,  which  does  not  digest  the  epithelium 
because  it  cannot  kill  it.  A  certain  amount  of  protection  may 
he  afforded  to  the  walls  of  the  stomach  by  the  thin  layer  ol 
mucus  which  covers  the  whole  cavity,  for  mucin  is  not  affected 
by  peptic  digestion.  And  a  mucous  secretion  seems  in  some 
other  cases  to  act  as  a  protective  covering  to  the  walls  of  hollow 
viscera,  whose  contents  are  such  as  would  certainly  be  harmful 
to  more  delicate  membranes,  e.g.,  in  the  urinary  bladder,  large 
intestine,  and  gall-bladder.  Still,  however  important  such  a 
mechanical  protection  may  be,  it  does  not  explain  the  whole 
matter,  and  it  is  necessary  to  suppose  that  the  gastric  epithelium 
has  some  special  power  of  resisting  the  gastric  juice,  either  In- 
turning  any  of  the  ferment  which  may  invade  it  into  an  inert 
substance  and  neutralizing  any  intrusive  acid,  or  by  opposing 
their  entrance  as  the  epithelium  of  the  bladder  opposes  the 
absorption  of  urea.  There  is  reason  to  believe  that,  as  a  matter 
of  fact,  free  hydrochloric  acid  cannot  penetrate  the  living  cells, 
and  it  is  to  be  noted  that  both  active  pepsin  and  free  acid  must 
be  present  at  the  same  point  within  the  cells  before  digestion  of 
them  can  take  place.  In  the  gland-cells  of  the  pancreas  the 
protoplasm  is,  no  doubt,  shielded  from  digestion  by  the  existence 
of  the  ferment  in  an  inert  form  as  zymogen  ;  and  it  is  possible 
that  this  is  one  of  the  reasons  for  the  existence  of  the  mother- 
substance.  But  no  such  explanation  is,  of  course,  available  for 
the  intestinal  epithelium.  Trypsin  when  injected  below  the  skin 
causes  the  tissue  to  break  down  and  ulcerate.  And  while  an 
active  solution  of  trypsin  can  he  allowed  to  remain  a  long  time 
in  an  isolated  loop  of  small  intestine  without  producing  any  ill 
effect,  damage  is  soon  caused  not  only  to  the  intestinal  wall. 
but  also  to  the  liver,  when  the  mucous  membrane  of  the  loop 
has  been  injured  before  the  introduction  of  the  trypsin.  We 
must  suppose,  then,  that  the  normal  mucous  membrane  of  the 
intestine  prevents  the  absorption  of  trypsin,  or,  if  it  absorbs  any 
of  it,  renders  it  harmless  Indeed,  it  is  impossible  to  escape 
the  conclusion  that  each  membrane  becomes  accustomed,  and. 
so  to  speak,  '  immune,'  to  the  secretion  normally  in  contacl  with 


DIGESTION  361 

it,  although  qoI   necessarily  to  othei   secretions.     It   is  easy  to 
multiply  illustral  ions  of  this  pi  inciple. 

Few  tissues  hut  the  lining  of  the  urinary  trad  or  of  the  large 
intestine  could  bear  the  constant  contact  of  mine  or  fae< 
When  urine  is  extravasated  under  the  skin,  or  the  contents  oi 
the  alimentary  canal  hurst  into  the  peritoneal  cavity,  they  come 
into  contact  with  tissues  which,  although  alive,  are  much  less 
fitted  to  resist  them  than  the  surfaces  by  which  they  are  noi  mally 
enclosed  ;  and  the  consequences  are  often  disastrous.  Leucocytes 
thrive  in  the  blood,  but  perish  in  urine.  Blood  does  not  harm 
the  endothelial  cells  of  the  vessels,  but  kills  a  muscle  whose  cross- 
section  is  dipped  into  it.  The  defensive,  or  in  some  cases,  offen- 
sive liquids  secreted  by  many  animals  are  harmless  to  the  tissues 
which  produce  and  enclose  them.  A  caterpillar  investigated 
by  Poulton  secretes  a  liquid  so  rich  in  formic  acid  that  the  mere 
contact  of  it  would  kill  most  cells.  The  so-called  saliva  of 
Octopus  macropus  contains  a  substance  fatal  to  the  crabs  and 
other  animals  on  which  it  preys.  The  blood  of  the  viper  contains 
an  active  principle  similar  to  that  secreted  by  its  poison-glands, 
but  its  tissues  are  not  affected  by  this  substance,  so  deadly  to 
other  animals. 

A  step  in  the  solution  of  our  problem  has  lately  been  taken 
by  Weinland.  Starting  with  the  idea  that  if  special  protective 
mechanisms  against  the  digestive  juices  were  anywhere  to  be 
found  it  would  he  in  the  intestinal  parasites  whose  whole  exist- 
ence is  passed  among  them,  he  has  made  the  important  discovery 
that  in  these  parasitic  worms  specific  antiferments  exist — i.e., 
substances  which  inhibit  the  action  either  of  pepsin  or  of  trypsin 
or  of  both.  These  substances  can  be  precipitated  from  the 
expressed  juice  of  the  worms  by  alcohol,  without  completely 
losing  their  activity.  Fibrin  can  be  impregnated  with  them, 
and  it  is  then,  just  like  the  '  living  tissue,'  rendered  for  a  longer 
or  shorter  time  unassailable  by  the  proteolytic  ferments.  While 
the  supposed  proof  that  similar  antiferments  are  contained  in  the 
cells  of  the  mucous  membrane  of  the  stomach  and  intestines  of 
the  higher  animals  appears  to  have  broken  down,  these  facts  are 
full  of  suggestion  for  future  work.  As  already  mentioned,  it  is 
known  that  an  antitrypsin  exists  in  the  blood,  with  the  same 
properties  as  the  antitrypsin  in  the  intestinal  worms  (Hamill). 
This  explains  the  resistance  of  blood-serum  to  the  digestive 
action  of  trypsin.  In  addition  to  this  body,  which  hinders  the 
action  of  fully-formed  trypsin,  and  has  .  o  effect  upon  entero- 
kinase,  the  blood  of  some  animals  contains  an  antikinase — i.e.,  a 
substance  which  hinders  the  action  not  of  trypsin,  but  of 
enterokinase,  preventing  it  from  activating  the  trypsinogen  into 
trypsin. 


362 


/    W  I  \r  \i    OF  PHYSIOLOGY 


The  Influence  of  the  Nervous  System  on  the  Digestive 
Glands. 

(1)  The  Influence  of  Nerves  on  the  Salivary  Glands.  —  All 
the  salivary  glands  have  a  double  nerve-supply,  from  the 
medulla    oblongata    through   some  of   the  cranial   nerves,   and 

from  the  spinal  cord 
through  the  cervical 
sympathetic  'Fig. 
1  1  ;). 

In  the  dop;  the 
c  li  or  da  1  y  m  p  an  i 
branch  of  the  facial 
nerve  carries  the 
cranial  supply  of  the 
sublingual  and  sub- 
maxillary glands.  It 
joins  the  lingual 
branch  of  the  fifth 
nerve,  runs  in  com- 
pany with  it  for  a 
Little  way,  and  then. 
breaking  off,  after 
giving  some  fibres  to 
the  lingual,  passes,  as 
the  chorda  tympani 
proper,  along  Whar- 
ton's duct  to  the  sub- 
maxillary gland.  In 
the  hilus  of  this  gland 
most  of  its  fibres  break 
up  into  fibrils  around 
nerve  -  cells    situated 


Fig.   143. — Nerves  of  the  Salivary  Glands. 


SM  and   SL.   submaxillary  and  sublingual  glands  ; 

1'.  parotid;  V.  fifth  nerve:  VII.  facial:  GP,  glosso-  there    and    lose    their 

pharyngeal;   L,   lingual;  CT,   chorda  tympani;  CL.  medulla  in  doing   so. 

chordo-lingual  j   I  >.   submaxillary  (Wharton's)  duct:  A  few  fibres  terminate 

C,   ganglion   cell   of  so-called  submaxillary  ganglion  in    a   similar    manner 

in     the    chordo-lingual    triangle,    connected    with    a  before      entering     the 

aerve  fibre  going  to  sublingual  gland:  C",  ganglion  hilus,     and     a     few 

cell    in    hilus    of    submaxillary    gland  ;    SSP,    small  deeper    in    the   gland. 

superficial   petrosal   branch   of  the   facial;   <><i.    otic  |]u.    nervous   oath  is 

anglion;   IM,    inferior   maxillary   division  of   fifth  continuedbytneaxis- 

erve ;    AI.    auriculo-temporal    branch   of   fifth  ;    IN,  ,.       ,            J 

,       ,                   <•*            1-           ,,                    ■  cvlmder  processes 

acobson  S    nerve:    (   .     ganglion    cells    in    superior  -\,           ___J  ,      .  ,. 


ncrv 

Jacobson's    nerve  :    C,    ganglion    cells    in    supen 
cervical  ganglion   (SG)  connected  with  sympathetic 
fibres  going  to  parotid,  submaxillary  and  sublingual 
glands.     The  figure  is  schematic. 


(Chap.  XII.)  of  these 
nerve  -  cells,  which, 
passing  in  as  non- 
111  cdu  Hated  tih  res. 
end  in  a  plexus  on  the  basement  membrane  of  the  alveoli.  From 
the  plexus  fibrils  run  in  among  the  gland-cells,  but  do  not  seem 
to  penetrate  them.  The  lingual,  the  chorda  tympani  proper,  and 
Wharton's  duct  form  the  sides  of  what  is  called  the  chordo- 
lingual  triangle.  Within  this  triangle  are  situated  many  ganglion 
cells,  a  special  accumulation  of  which  has  received  the  name  of  the 
submaxillary  ganglion.     This,  however,  should  rather  be  called  the 


DIGESTION 

Bllblingual  ganglion,  since  its  cells,  as  well  as  the  others  in  the 
chordo  -  lingual  triangle,  are  the  cells  of  origin  of  axons 
which  proceed  as  non-medullated  fibres  to  the  sublingual  gland. 
I  he  sublingual  gland  receives  its  cerebral  fibres  partly  from 
branches  given  off  from  the  lingual  in  the  chordo-lingual  triangle 
after  the  chorda  tympani  proper  has  separated  from  it,  and  ending 
around  the  nerve-cells  within  that  triangle,  partly  from  the  chorda 
itself  in  the  terminal  portion  of  its  course.  These  statements  rest  on 
anatomical  and  physiological  evidence.     The  latter  we  shall  return  to. 

The  cerebral  fibres  for  the  parotid  (in  the  dog)  pass  from  the 
tympanic  branch  of  the  glosso-pharyngeal  ( Jacobson's  nerve)  through 
connecting  filaments  to  the  small  superficial  petrosal  branch  of  the 
facial,  with  this  nerve  to  the  otic  ganglion,  and  thence  by  the 
auriculo-temporal  branch  of  the  fifth  to  the  gland. 

The  sympathetic  fibres  for  all  the  salivary  glands  appear  to  arise 
from  nerve-cells  in  the  upper  dorsal  portion  of  the  spinal  cord. 
Issuing  from  the  cord  in  the  anterior  roots  of  the  upper  thoracic 
nerves  (first  to  fifth,  but  mainly  second  thoracic  for  the  submaxillary), 
they  enter  the  sympathetic  chain,  in  which  they  run  up  to  the 
superior  cervical  ganglion.  Here  they  break  up  into  terminal 
twigs,  and  thus  come  into  relation  with  ganglion  cells,  whose 
axons  pass  out  as  non-medullated  fibres,  and,  surrounding  the 
external  carotid,  reach  the  salivary  glands  along  its  branches. 
Langley  has  shown,  by  means  of  nicotine  (p.  165),  that  the  sym- 
pathetic fibres  for  the  submaxillary  and  sublingual,  and,  indeed,  for 
the  head  in  general  in  the  dog  and  cat,  are  connected  with  nerve- 
cells  in  this  ganglion,  but  not  between  it  and  their  termination,  or 
between  it  and  their  origin  from  the  spinal  cord. 

Stimulation  of  the  Cranial  Fibres. — When  in  a  dog  a  cannula 
is  placed  in  Wharton's  duct,  and  the  saliva  collected  (p.  424), 
it  is  found  that  stimulation  of  the  peripheral  end  of  the  divided 
chorda  causes  a  brisk  flow  of  watery  saliva,  and  at  the  same 
time  a  dilatation  of  the  vessels  of  the  gland,  which  we  have 
already  described  in  dealing  with  vaso-motor  nerves  (p.  163). 
Notwithstanding  the  vaso-dilatation,  the  volume  of  the  gland  is 
in  general  diminished,  owing  to  the  rapid  passage  of  water  into 
the  duct  (Bunch).  The  blood  has  been  shown  to  lose  water  in 
making  the  circuit  of  the  submaxillary  gland  during  excitation  of 
the  chorda,  but  doubtless  some  of  the  water  of  the  saliva  comes 
directly  from  the  cells  or  from  the  lymph.  That  the  increased 
secretion  is  not  due  merely  to  the  greater  blood-supply,  and  the 
consequent  increase  of  capillary  pressure,  is  shown  by  the 
injection  of  atropine,  after  which  stimulation  of  the  nerve, 
although  it  still  causes  dilatation  of  the  vessels,  is  not  followed  by 
a  flow  of  saliva.  Mere  increase  of  pressure  could  not  in  any  case 
of  itself  account  for  the  secretion,  since  it  has  been  found  that 
the  maximum  pressure  in  the  salivary  duct  when  the  outflow  of 
saliva  from  the  duct  is  prevented  may,  during  stimulation  of  the 
chorda,  much  exceed  the  arterial  blood-pressure  (Ludwig).  In 
one  experiment,  for  example,  the  pressure  in  the  carotid  of  a  dog 
was  125  mm.,  in  Wharton's  duct  195  mm.  of  mercury. 


564  A   M  I  \r  \l    OF  PHYSIOLOGY 

Even  in  the  head  "l  a  decapitated  animal  a  certain  amount  ol 
saliva  may  be  caused  to  flow  by  stimulation  of  the  chorda,  but 
too  much  may  easily  ho  made  of  this.  And  since  the  blood  is  the 
ultimate  source  of  the  secretion,  we  could  not  expect  a  permanent 
or  copious  How  in  the  absence  of  the  circulation,  even  if  the  gland- 
cells  could  continue  to  live.  In  fact,  when  the  circulation  is 
almost  stopped  by  strong  stimulation  of  the  sympathetic,  the 
How  of  saliva  caused  by  excitation  of  the  chorda  is  at  the  same 
time  greatly  lessened  or  arrested,  even  though  the  sympathetic 
itself  possesses  secretory  fibres.  So  that,  while  there  is  no  doubt 
that  the  chorda  tympani  contains  fibres  whose  function  is  to 
increase  the  activity  of  the  gland-cells,  its  vaso-dilator  action  is, 
under  normal  conditions,  closely  connected  with,  and,  indeed. 
auxiliary  to,  its  secretory  action,  although  the  dilation  of  the 
vessels  does  not  directly  produce  the  secretion.  This  is  onlv  a 
particular  case  of  a  physiological  law  of  wide  application,  that  an 
organ  in  action  in  general  receives  more  blood  than  the  same  organ 
in  repose,  or,  in  other  words,  that  the  tissues  are  fed  according  to 
their  needs.  The  contracting  muscle,  the  secreting  gland,  is  flushed 
with  blood,  not  because  an  increased  blood-flow  can  of  itself  cause 
contraction  or  secretion,  but  because  these  high  efforts  require 
for  their  continuance  a  rich  supply  of  what  blood  brings  to  an 
organ,  and  a  ready  removal  of  what  it  takes  away. 

The  quantity  of  blood  passing  through  the  parotid  of  a  horse 
when  it  is  actively  secreting  during  mastication  may  be  quad- 
rupled (Chauveau).  The  parallel  between  the  muscle  and  the 
gland  is  drawn  closer  when  it  is  stated  that  electrical  changes 
accompany  secretion  (p.  734),  and  that  the  rate  of  production  of 
carbon  dioxide  and  consumption  of  oxygen  (in  the  submaxillary 
gland)  is  three  or  four  times  greater  during  activity  than  during 
rest.  The  temperature  of  the  saliva  flowing  from  the  dog's 
submaxillary  during  stimulation  of  the  chorda  has  been  found  to 
be  as  much  as  1-5°  C.  above  that  of  the  blood  of  the  carotid. 
although  with  the  gland  at  rest  no  constant  difference  could 
be  detected  between  the  arterial  blood  and  the  interior  of 
Wharton's  duct.  But  such  measurements  are  open  to  many 
fallacies  ;  and  while  there  is  no  doubt  that  more  heat  is  produced 
in  the  active  than  in  the  passive  gland,  it  will  not  be  surprising, 
when  the  vastly-increased  blood-flow  is  remembered,  that  no 
difference  of  temperature  between  the  incoming  and  outgoing 
blood  has  been  satisfactorilv  demonstrated. 

It  has  already  been  mentioned  that  most  of  the  fibres  of  the  chorda 
tympani  proper  become  connected  with  ganglion-cells,  and  lose  their 
medulla  inside  the  submaxillary  gland,  only  .1  few  having  already  lost 
it  by  a  similar  connection  with  ganglion-cells  in  the  chordo-lingual 
triangle.     These  facts  have  been  made  ou1  l>v  means  of  the  nicotine 


DIGESTION 

method  previously  described  (p.  165).  Tims,  it  is  found  bhat,  aft<  1 
the  injection  <>i  nicotine  (5  i<>  i<>  mg.  in  ;i  rabbil  or  cat,  40  or  50  mg. 
in  .t  dog),  stiiuiil.it  ion  of  the  1  horda  I  ympani  proper  or  of  t  he  chordo- 
LinguaJ  nerve  causes  no  secretion  from  the  submaxillary  gland  ;  but 
stimulation  of  the  hilus  of  the  gland  is  followed  by  a  copious  secret  ion 
— as  much,  if  the  stimulation  is  fairly  strong,  ;is  was  caused  by 
excitation  of  the  nerve  before  injection  of  nicotine  That  this  is 
due  neither  to  any  direct  action  on  the  gland-cells,  nor  to  stimulation 
til  the  sympathetic  plexus  on  the  submaxillary  artery,  but  to  stimula- 
tion of  chorda  fibres  beyoml  the  hilus,  is  shown  by  the  fact  that 
alter  atropine  has  been  injected  in  sufficient  amount  to  paralyze  the 
nerve  endings  of  the  chorda,  but  not  of  the  sympathetic,  stimulation 
of  the  hilus  causes  little  or  no  flow  of  saliva.  The  application  of 
nicotine  solution  to  the  chordo-lingual  triangle  does  not  affect  the 
submaxillary  secretion  caused  by  stimulation  of  the  chordo-lingual 
nerve,  even  in  cases  where  a  few  secretory  fibres  for  the  submaxillary 
do  not  leave  the  chordo-lingual  nerve  in  the  chorda  tympani  proper, 
but  arc  given  off  to  the  chordo-lingual  triangle.  This  shows  that 
none  of  the  ganglion-cells  in  the  triangle  arc  connected  with  the 
secretory  fibres  of  the  submaxillary  gland.  By  observations  of 
the  same  kind  they  are  known  to  be  connected  with  fibres  going 
to  the  sublingual.  In  a  similar  way,  by  observing  the  effects  of 
stimulation  of  the  chorda  on  the  bloodvessels  before  and  after  the 
application  of  nicotine,  it  has  been  found  that  the  vaso-dilator  fibres 
are  connected  with  ganglion-cells  in  the  same  positions  as  the 
secretory  fibres  (Langley). 

Stimulation  of  the  Sympathetic  Fibres. — The  sympathetic, 
as  has  been  already  indicated,  contains  both  vaso-constrictor 
and  secretory  fibres  for  the  salivary  glands.  If  the  cervical 
sympathetic  in  the  dog  is  divided,  and  the  cephalic  end  mode- 
rately stimulated,  a  few  drops  of  a  thick,  viscid  and  scanty  saliva 
flow  from  the  submaxillary  and  sublingual  ducts,  while  the 
current  of  blood  through  the  glands  is  diminished.  As  a  rule,  no 
visible  secretion  escapes  from  the  parotid,  but  microscopic  exam- 
ination shows  that  many  of  the  ductules  are  filled  with  fluid, 
which  is  apparently  so  thick  as  to  plug  them  up  (Langley)  ; 
while  the  cells  show  signs  of  '  activity  '  (p.  347). 

Simultaneous  Stimulation  of  Cranial  and  Sympathetic  Fibres. — 
When  the  chorda  and  sympathetic  are  stimulated  together, 
the  former  prevails  so  far,  with  moderate  stimulation  of  the 
latter,  that  the  submaxillary  saliva  is  secreted  in  considerable 
quantity,  and  is  not  particularly  viscid.  It  is,  however,  richer 
in  organic  matter  than  is  the  chorda  saliva  itself.  When  the 
chorda  is  weakly,  and  the  sympathetic  strongly,  excited,  the 
scanty  secretion  (if  there  is  any)  is  of  sympathetic  type,  thick 
and  rich  in  organic  matter.  With  strong  stimulation  of  both 
nerves,  the  secretion,  at  first  plentiful  and  watery,  soon  dimin- 
ishes, even  below  the  amount  obtained  by  stimulation  of  the 
chorda  alone,  because  of  the  diminution  in  the  blood-flow,  and 
therefore  in  the  oxygen  supply,  produced  by  the  vaso-constrictors 


366  A   MANUAL  OF  PHYSIOLOGY 

of  the  sympathetic  (Heidenbain).  \\ritli  stimulation  just  strong 
enough  to  cause  secretion  when  applied  separately  to  either 
nerve,  there  is  no  secretion  when  it  is  applied  simultaneously  to 
both. 

All  tins  refers  to  the  dog.  In  this  animal,  then,  there  seems 
to  be  a  certain  amount  of  physiological  antagonism  between  the 
secretory  action  of  the  two  nerves.  But  it  differs  in  one  respect 
from  the  antagonism  between  their  vaso-motor  fibres  ;  for  with 
strong  stimulation  the  constrictors  of  the  sympathetic  always 
swamp  the  dilators  of  the  chorda,  while  the  secretory  fibres  of  the 
chorda  appear  upon  the  whole  to  prevail  over  those  of  the  sympa- 
thetic. And  in  all  probability  this  apparent  secretory  antagonism 
is  very  superficial,  and  is  due  largely  to  the  difference  in  the 
vasomotor  effects  of  the  two  nerves.  For  it  has  been  shown 
that  when  the  blood-flow  through  the  submaxillary  gland  is 
artificially  diminished  by  graduated  compression  of  its  artery, 
stimulation  of  the  chorda  gives  rise  to  a  thick  viscid  and  scanty 
saliva,  relatively  rich  in  organic  solids  (Heidenhain).  When  the 
amount  of  blood  passing  through  the  gland  is  made  approximately 
the  same  as  during  stimulation  of  the  sympathetic,  the  chorda 
saliva  becomes  practically  identical  in  composition  with  the 
sympathetic  saliva.  This  is  one  reason,  perhaps  the  chief  one,  why 
the  sympathetic,  when  both  nerves  are  stimulated  together,  with- 
out artificial  interference  with  the  blood-supply,  always  appears  to 
add  something  to  the  common  secretion  when  there  is  a  secretion 
at  all,  this  something  being  represented  by  an  increase  in  the 
percentage  of  organic  matter.  The  observation  that  the  sympa- 
thetic effect  persists  after  stimulation  has  been  stopped,  and 
that  excitation  of  the  chorda  after  previous  stimulation  of  the 
sympathetic  causes  a  flow  of  saliva  richer  in  organic  matter 
than  would  have  been  the  case  if  the  sympathetic  had  not  been 
stimulated,  has  long  been  considered  a  proof  that  the  secretory 
fibres  of  the  two  nerves  are  widely  different  in  function.  To 
explain  this  result,  Heidenhain  assumed  the  existence  in  the 
sympathetic  of  a  preponderance  of  fibres  concerned  in  the 
building  up  in  the  cells  of  the  organic  constituents  of  the  saliva 
(so-called  "  trophic,"  or,  better,  since  the  word  trophic  is  usually 
associated  with  the  building  up  of  the  bioplasm  itself.  "  trophic- 
secretory  "  fibres).  It  would  seem,  however,  that  the  increase 
in  organic  constituents  is  only  realized  when  a  sufficient  time 
has  not  been  allowed,  after  stimulation  of  the  sympathetic,  for 
the  normal  circulation  to  become  re-established  in  the  gland. 
The  saliva  obtained  by  stimulation  of  the  chorda  immediately 
after  a  period  of  artificially  diminished  blood-flow,  without  any 
previous  excitation  of  the  sympathetic,  also  contains  a  surplus 
of  organic  matter  (Carlson). 


DIGES1  K>\ 

Indeed,  the  distinction  between  chorda  and  sympathetic 
saliva,  which,  by  taking  account  of  the  parotid  as  well  as  the  sub- 
maxillary .md  sublingual  glands,  has  been  generalized  into  a  dis- 
tinction between  cerebral  and  sympathetic  saliva,  and  which, 
when  the  vasomoiO]  conditions  are  left  ou1  of  account,  appears 
to  hold  good  in  the  dog  and  the  rabbit,  breaks  down  before  a 
wider  induction.  For  in  the  cat  the  sympathetic  saliva  of  the 
submaxillary  gland,  although  much  more  scanty,  is  more  watery 
than  the  chorda  saliva  (Langley),  which,  however  is  by  no  means 
viscid  ;  and  the  two  secretions  differ  far  less  than  in  the  dog. 
The  discovery  of  Carlson  that  the  cat's  cervical  sympathetic 
contains  so  many  vaso-dilator  fibres  for  the  submaxillary  gland 
that  the  usual  effect  of  its  stimulation  with  a  weak  interrupted 
current  is  a  marked  augmentation  in  the  blood-flow  affords  an 
explanation.  In  accordance  with  this  functional  similarity, 
there  is  a  much  smaller  difference  in  the  action  of  atropine  on 
the  two  sets  of  fibres  in  the  cat  than  in  the  dog,  although  even 
in  the  cat  the  sympathetic  is  less  readily  paralyzed  than  the 
chorda. 

In  their  secretory  action  there  is  not  even  an  apparent  anta- 
gonism in  the  cat,  with  minimal  stimulation  of  both  nerves,  which 
causes  as  much  secretion  as  would  be  produced  if  both  were 
separately  excited.  Further,  even  in  the  dog,  after  prolonged 
stimulation  of  the  sympathetic,  the  submaxillary  saliva  is  no 
longer  viscid,  but  watery,  the  proportion  of  solids,  and  especially 
of  organic  solids,  being  much  lessened,  as  it  is  also  in  chorda 
saliva  after  long  excitation.  When  the  cerebral  nerve  of 
the  resting  gland  is  strongly  excited,  it  is  found  that  up  to  a 
certain  limit  the  percentage  of  organic  matter  in  a  small  sample 
of  saliva  subsequently  collected  during  a  brief  weak  excitation 
increases  with  the  strength  of  the  previous  stimulation  ;  this  is 
also  true  of  the  inorganic  solids.  But  there  is  a  striking  difference 
when  the  experiment  is  made  on  a  gland  after  a  long  period  of 
activity  ;  here  increase  of  stimulation  causes  no  increase  in  the 
percentage  of  organic  material,  while  the  inorganic  solids  are  still 
increased.  In  both  cases  the  absolute  quantity  of  water,  and 
therefore  the  rate  of  flow  of  the  secretion,  is  augmented. 

All  this  points  to  the  same  conclusion  as  the  microscopic 
appearances  in  the  gland-cells,  that  the  cells  during  rest  manufac- 
ture the  organic  constituents  of  the  secretion,  or  some  of  them, 
and  store  them  up,  to  be  discharged  during  activity.  The  water 
and  the  inorganic  salts,  on  the  other  hand,  seem  rather  to  be 
secreted  on  the  spur  of  the  moment,  so  to  speak,  and  not  to  require 
such  elaborate  preparation.  And  it  has  been  stated  that  when 
the  chorda  tympani  is  stimulated  with  currents  of  varying 
strength,  the  quantity  of  organic  substances  in  small  samples  ot 


/    MA  \  V  \L  OF  PHYSI01  OGY 

saliva  collected  from  a  fresh  gland  is  more  nearly  proportional 
in  the  rate  ol  secretion  than  i>  the  quantity  oi  watet  and  salts, 
which  varies  also  with  the  blood-supply. 

I  est  the  apparently  insignificant  result  of  artificial  stimulation 
oi  the  sympathetic  in  such  animals  as  the  dog  should  cause  its 
tory  action  to  be  appraised  at  too  low  a  value,  it  should 
be  remembered  that  in  the  intact  body  the  sympathetic  s<  i  retory 
fibres,  when  they  are  excited,  arc  it  may  be  assumed,  excited 
independently  of  the  vaso-constrictors,  and  even  in  conjunction 
with  the  vaso-dilators  of  the  salivary  glands. 

It  is  conceivable  that  such  differences  between  chorda  and 
sympathetic  saliva  as  arc  not  accounted  for  by  the  differences  in 
the  blood-flow  during  their  stimulation  are  due,  not  to  the 
nerve  fibres,  but  to  the  end  organs  with  which  they  are  con- 
nected :  that  is,  the  two  nerves  may  supply,  not  the  same,  but 
different  gland-cells.  And  it  is  well  known  that  even  after 
prolonged  stimulation  of  the  chorda  or  chordo-lingual  alone, 
some  alveoli  of  the  dog's  submaxillary  gland  remain  in  the 
'  resting  '  stair  ;  alter  stimulation  of  the  sympathetic  alone,  the 
number  of  unaffected  alveoli  is  much  greater  ;  while  after 
stimulation  of  both  nerves,  few  alveoli  seem  to  have  escaped 
change.  If  there  is  no  essential  difference  between  the  cranial 
and  sympathetic  secretory  fibres,  if  is  easy  to  understand  that 
they  will  be  distributed  to  different  secreting  elements.  The 
supposed  proof  that  there  must  be  seme  overlapping  in  the 
nerve-supply — i.e.,  that  some  cells  must  be  supplied  from  both 
sources,  since  excitation  of  the  sympathetic  influences  the 
amount  of  organic  material  in  the  saliva  obtained  by  subsequent 
stimulation  of  the  chorda — -is,  as  we  have  just  seen,  byno  means 
so  cogent  as  has  been  assumed.  And.  indeed,  we  know  nothing 
of  a  division  of  labour  between  the  cells  of  a  gland,  except  when 
there  are  obvious  anatomical  distinctions.  Thus,  the  sub- 
maxillary gland  in  man  contains  both  serous  and  mucous  acini, 
and  mucin-making  cells  are  scattered  over  the  ducts  of  most 
glands,  and,  indeed,  on  nearly  every  surface  which  is  clad  with 
columnar  epithelium.  In  these  cases  we  cannot  doubt  that  one 
constituent — mucin — of  the  entire  secretion  is  manufactured  by 
a  portion  only  of  the  cells.  In  the  cardiac  glands  of  the  stomach, 
too,  the  ovoid  cells,  in  all  probability,  yield  the  whole  of  the 
acid  of  the  gastric  juice.  But,  so  far  as  we  know,  every  hepatic 
cell  is  a  liver  in  little.  Every  cell  secretes  fully-formed  bile  ; 
every  cell  stores  up,  or  may  store  up,  glycogen.  So  it  is  with 
the  secretory  alveoli  of  the  pancreas,  if  we  consider  the  islands 
of  Langerhans  as  having  no  connection  with  the  alveoli  ;  one 
cell  is  just  like  another  ;  all  apparently  perform  the  same  work  ; 
each  is.a  unicellular  pancreas.    (But  see  p.  554 


DIGESTION  j6g 

Paralytic  Secretion.  -When  the  chorda  tympani  Is  divided,  a  slow 
'  paralytic  '  secretion  Erom  the  submaxillary  gland  begins  in  a  few 
hours,  and  continues  for  a  long  time  accompanied  by  atrophy  >>i 
the  gland.  There  is  also  a  secretion  of  the  same  kind  from  the 
Submaxillary  on  the  opposite  side,  but  it  is  less  copious.  This  is 
called  the  '  antilytic  '  secretion,  which  is  most  pronounced  in  the  first 
few  days  after  the  operation,  and  seems  to  be  a  transient  pheno- 
menon. It  can  be  at  once  abolished  l>v  section  both  of  the  chorda 
and  the  sympathetic  on  the  corresponding  side,  and  is  therefore  due 
to  impulses  arising  in  the  central  nervous  system.  The  caus  i  of  the 
paralytic  secretion  lias  not  been  fully  made  out.  If  within  two  or 
three  days  of  division  of  the  chorda  the  sympathetic  on  the  same 
side  is  cut,  the  secretion  is  greatly  diminished  or  stop-;  altogether; 
and  it  is  concluded  that  up  to  this  time  it  is  maintained  by  impulses 
passing  along  the  sympathetic  to  the  gland  from  the  salivary  centre, 
the  excitability  of  which  has  been  in  some  way  increased  by  division 
of  the  chorda,  possibly  by  some  such  degenerative  process  in  the 
cells  as  the  changes  seen  in  cerebro-spinal  motor  cells  whose 
axons  have  been  divided  (p.  750).  This  may  also  account  for  the 
antilytic  secretion.  But  if  section  of  the  sympathetic  is  not  per- 
formed for  several  days,  it  has  no  effect  on  the  paralytic  secretion, 
which  at  this  stage  seems  to  depend  on  local  changes  in  or  near  the 
gland  itself,  leading  to  a  mild  continuous  excitation  of  those  nerve- 
cells  on  the  course  of  the  fibres  of  the  chorda  to  which  reference  has 
already  been  made.  Section  of  the  sympathetic  alone  causes  neither 
secretion  nor  atrophy,  nor  does  removal  of  the  superior  cervical 
ganglion.  The  histological  characters  of  the  gland-cells  during 
paralytic  secretion  are  those  of  '  rest.' 

Reflex  Secretion  of  Saliva. — The  reflex  mechanism  of  salivary 
secretion  is  very  mobile,  and  easily  set  in  action  by  physical  and 
mental  influences.  It  is  excited  normally  by  impulses  which 
arise  in  the  mouth,  especially  by  the  contact  of  food  with  the 
buccal  mucous  membrane  and  the  gustatory  nerve-endings. 
The  mere  mechanical  movement  of  the  jaws,  even  when  there  is 
nothing  between  the  teeth,  or  only  a  bit  of  a  non-sapid  sub- 
stance like  indiarubber,  causes  some  secretion.  The  vapour  of 
ether  gives  rise  to  a  rush  of  saliva,  as  does  gargling  the  mouth 
with  distilled  water.  The  smell,  sight,  or  thought  of  food,  and 
even  the  thought  of  saliva  itself,  may  act  on  the  salivary  centre 
through  its  connections  with  the  cerebrum,  and  make  '  the  teeth 
water.'  A  copious  flow  of  saliva,  reflexly  excited  through  the 
gastric  branches  of  the  vagus,  is  a  common  precursor  of  vomit- 
ing. The  introduction  of  food  into  the  stomach  also  excites 
salivary  secretion. 

The  researches  of  Pawlow  and  his  pupils  have  shown  that  the 
salivary  glands  are  not  excited  indifferently  by  everything  which 
comes  into  contact  with  the  buccal  mucous  membrane.  A 
remarkable  adaptation  exists  between  the  properties  of  food  or 
foreign  bodies  introduced  into  the  mouth  and  their  effects  upon 
the  secretion  of  saliva.  When  solid  dry  food  is  given  to  a  dog 
saliva  is  copiously  poured  out  ;  much  less  is  secreted  when  the 

24 


370  A    MAX  UAL  OF  PHYSIOLOGY 

food  is  moist.  Acids  or  salts  induce  an  abundant  flow,  in  order 
that  they  may  be  neutralized,  diluted  or  washed  oul  of  the 
mouth.  In  this  case  a  watery  liquid,  poor  in  mucin.  Hows  from 
the  mucous  glands.  Mucin  is  a  lubricant  to  facilitate  the  swal- 
lowing of  solid  food,  and  here  it  could  be  of  no  use.  When  clean 
pebbles  are  put  in  the  dog's  mouth  the  animal  may  try  to  chew 
them,  but  eventually  ejects  them.  Either  no  saliva  oi  very 
little  is  secreted,  since  it  could  not  aid  in  their  expulsion.  If. 
however,  the  very  same  stones  are  reduced  to  sand  and  again 
introduced  into  the  animal's  mouth,  saliva  is  plentifully  secreted 
to  wash  it  out. 

The  serous  and  mucous  salivary  glands  are  not  necessarily 
excited  by  the  same  food  materials,  and  here  again  we  can  trace 
an  astonishingly  exact  adaptation.  A  permanent  parotid  or  sub- 
maxillary fistula  can  easily  be  made  in  a  dog  by  fleeing  Stenson's 
or  Wharton's  duct  from  the  surrounding  mucous  membrane 
for  a  little  distance,  bringing  the  natural  orifice  of  the  duct  out 
through  a  small  wound  in  the  cheek,  and  stitching  it  in  position 
there.  When  it  is  desired  to  collect  saliva,  the  wide  end  of  a 
funnel-shaped  tube,  whose  stem  is  bent  so  as  to  hang  vertically, 
can  be  attached  by  a  little  shellac  of  low  melting-point  to  the 
skin  around  the  orifice  of  the  duct  and  at  some  distance  from  it, 
and  on  the  narrow  end  can  be  hung  a  small  graduated  tube,  into 
which  the  saliva  drops.  When  fresh  meat  is  given  to  the  animal 
little  or  no  parotid  saliva  is  secreted,  while  a  copious  (low  takes 
place  from  the  submaxillary  gland,  mucin  being  required  to 
lubricate  it  for  deglutition,  while  water  is  not  specially  needed. 
But  if  the  meat  is  in  the  form  of  a  dry  powder  the  parotid  pours 
out  a  plentiful  secretion,  while  the  submaxillary  also  secretes  a 
fluid  relatively  rich  in  mucin.  The  same  difference  is  seen 
between  fresh  moist  bread  and  dry  bread.  The  afferent  nerve- 
endings  from  which  impulses  are  carried  to  the  reflex  centres  (or 
the  portions  of  the  salivary  centre)  which  preside  over  the  various 
salivary  glands  must  possess  the  power  of  very  delicate  selection 
as  regards  the  kinds  of  stimulation  by  which  they  are  affected. 
The  mere  relish  of  the  animal  for  the  different  kinds  of  food 
plays  but  a  small  part.  Most  dogs  display  a  much  livelier 
interest  in  a  piece  of  meat  than  in  a  piece  of  dry  biscuit,  yet 
it  is  the  biscuit  which  excites  the  parotid  to  activity. 

The  sight  of  dry  food  causes  an  abundant  flow  of  watery  saliva 
from  the  parotid,  and  a  flow  of  fluid  rich  in  mucin  from  the  sub- 
maxillary. Various  uneatable  substances,  including  substances 
which  in  contact  with  the  mucous  membrane  of  the  mouth 
produce  strong  and  disagreeable  stimulation  of  it,  and  excite  dis- 
gust, cause  also,  when  viewed  from  a  distance,  secretion  by  all 
the  salivary  glands  ;  but  the  submaxillary  saliva,  as  ought  to  be 


DIGESTION  371 

the  case  for  substances  unfit  for  food,  and  therefore  not  destined 
tn  be  swallowed,  is  poor  in  mucin.  When  the  animal  is  shown 
pebbles  and  sand  the  phenomena  are  qualitatively  the  same 
as  when  they  are  put  into  its  mouth — the  glands  remaining 
inactive  in  presence  of  the  pebbles,  but  secreting  plentifully  at 
sight  of  the  sand.  In  short,  the  same  adaptation  is  observed  in 
the  case  of  the  so-called  psychical  secretion  as  when  the  stimu- 
lating substances  act  directly  upon  the  endings  of  the  afferent 
salivary  nerves  in  the  buccal  mucous  membrane.  It  is  further 
worthy  of  note  that  when  the  animal  is  hungry  the  psychical 
secretion  is  most  copious  and  most  easily  obtained.  After  a 
full  meal  it  eannot  be  elicited  at  all.  When  food  (or  other 
exciting  substance)  is  repeatedly  shown  to  a  fasting  animal  the 
reaction  becomes  each  time  weaker,  and  finally  the  glands 
cease  to  respond.  All  that  is  then  necessary  to  restore  the  re- 
action is  to  put  into  the  animal's  mouth  a  little  of  the  food  (or 
other  object).  When  it  is  now  shown  it  at  a  distance  the  ordinary 
effect  follows  promptly.  This  indicates  that  the  condition  of  the 
salivary  centre  exercises  an  important  influence  upon  the  psychical 
secretion,  its  excitability  to  the  weaker  stimulus  set  up  by  the 
sight  of  the  object  being  increased  by  the  stronger  reflex  stimula- 
tion coming  directly  from  the  mouth.  In  the  condition  of 
satiety  the  inexcitability  of  the  centre  may  be  due  to  the  action 
of  food-products  in  the  blood. 

In  most  animals  and  in  man  the  activity  of  the  large  salivary 
glands  is  strictly  intermittent.  But  the  smaller  glands  that  stud 
the  mucous  membrane  of  the  mouth  never  entirely  cease  to  secrete, 
and  the  same  is  the  case  with  the  parotid  in  ruminant  animals. 

The  centre  is  situated  in  the  medulla  oblongata,  stimulation 
of  which  causes  a  flow  of  saliva.  The  chief  afferent  paths  to  the 
salivary  centre  are  the  lingual  branch  of  the  fifth  and  the  glosso- 
pharyngeal ;  but  stimulation  of  many  other  nerves  may  cause 
reflex  secretion  of  saliva.  In  experimental  reflex  stimulation,  the 
sole  efferent  channel  seems  to  be  the  cerebral  nerve-supply  of  the 
glands.  After  section  of  the  chorda,  no  reflex  secretion  by  the 
submaxillary  gland  can  be  caused,  although  the  sympathetic 
remains  intact. 

It  was  alleged  by  Bernard  that,  after  division  of  the  chordo- 
lingual,  a  reflex  secretion  could  be  obtained  from  the  submaxillary 
gland  by  stimulating  the  central  end  of  the  cut  lingual  nerve 
between  the  so-called  submaxillary  ganglion  and  the  tongue,  the 
ganglion  being  supposed  to  act  as  '  centre.'  It  has  been  shown, 
however,  that  this  is  not  a  true  reflex  effect,  but  is  due  to  the 
excitation  of  certain  (recurrent)  secretory  fibres  of  the  chorda 
that  run  for  some  distance  in  the  lingual,  then  bend  back  on 
their  course  and  pass  to  the  gland.     It  may  be  in  part  a  pseudo- 

24 — 2 


375 


A   MANUAL  OF  PHYSIOI.(u;y 


ophagus 

us  gastricus 
terior  vagi 


or  axon-reflex  (p.  809),  elicited  by  excitation  of  efferent  fibres, 
which  send  brain  Iks  to  some  of  the  ganglion  cells. 

The  salivary  centre  can  also  be  inhibited,  especially  by  emol  inns 
of  a  painful  kind  for  instance,  the  nervousness  which  often 
dries  up  the  saliva,  as  well  as  the  eloquence,  of  a  beginner  in 
public  speaking,  and  the  Tear  which  sometimes  made  the  medie^  a] 
ordeal  of  the  consecrated  bread  pick  out  the  guilty. 

In  rare  cases  the  reflex  nervous  mechanism  that  governs  the 
salivary  glands  appears  to  completely  break  down  ;  and  then 
two  opposite  conditions  may  be  seen — xerostomia,  or  '  dry 
mouth,1  in  which  no  saliva  at  all  is  secreted,  and  chronic  ptyalism, 
or  hydrostomia,  where,  in  the  absence  of  any  discoverable  cause, 
the  amount  of  secretion  is  permanently  increased.  Both  conditii  ins 

are  said  to  be 
more  common 
in  women  than 
in  men. 

The  Influ- 
ence of  Nerves 
on  the  Gastric 
Glands. — Like 
saliva,  gastric 
juice  is  not 
secreted  con- 
tinuously, ex- 
cept in  ani- 
mals such  as 
the  rabbit, 
whose  stom- 
achs are  never 
empty.  The 
normal  and 
most   efficient 

stimulus  is  the  eating  of  food  and  its  presence  in  the  stomach. 
Mechanical  stimulation  of  the  gastric  mucous  membrane  with 
a  non-digestible  substance,  such  as  a  feather  or  a  glass  rod, 
causes  secretion  of  mucus,  but  not  of  gastric  juice.  But  the 
observations  mentioned  above  on  the  difference  of  response 
of  the  salivary  glands  to  different  substances  suggest  that 
the  local  mechanical  stimulation  of  the  food  on  the  gastric 
glands  may  be  more  effective.  There  is  also  at  first  thought 
much  to  indicate  that  the  gastric  glands  are  stimulated  chemi- 
cally in  a  more  direct  manner  than  the  salivary  glands  by  the 
local  action  of  food  substances  reaching  the  cells  by  a  short- 
cut from  the  cavity  of  the  stomach,  or  in  a  more  roundabout  way 
by  the  blood.     And  it  might  be  very  plausibly  argued  that  the 


Fig.   144. — Pawlow's  Stomach  Pouch. 

AB,  line  of  incision  ;  C,  flap  for  forming  the  stomach  pouch. 
At  the  base  of  the  flap  the  serous  and  muscular  coats  are 
preserved,  and  only  the  mucous  membrane  divided,  so  that 
the  branches  of  the  vagus  going  to  the  punch  are  not  severed. 


DIGESTION 


373 


Muscularis 


gastric  glands  are  favourably  situated  for  direct  stimulation,  while 
the  large  salivary  glands  arc  not  ;  and  that  the  great  function  oi 
saliva  being  to  aid  deglutition,  an  almost  momentary,  and  at 
the  same  time  a  perilous  act,  it  is  necessary  to  provide  by  a 
nervous  mechanism  for  an  immediate  rush  of  secretion  at  any 
instant,  while  it  is  not  important  whether  the  gastric  juice  is 
poured  out  a  little  sooner  or  a  little  later,  and  therefore  it  is  left 
to  be  called  forth  by  the  more  tardy  and  haphazard  method  of 
local  action.  Nevertheless,  on  looking  a  little  closer,  we  find 
that  this  does  not  exhaust  the  subject,  and  that  the  gastric 
secretion  can 
be  influenced 
by  events 
taking  place 
in  distant 
parts  of  the 
body,  just  as 
the  salivary 
secretion 
can.  In  a  boy 
whose  oeso- 
phagus was 
completely 
closed  by  a 
cicatrix,  the 
result  of 
swallowing  a 
strong  alkali, 
and  who  had 
to  be  fed  by 
a  gastric  fis- 
tula, it  was 
found  that 
the  presence 
of  food  in  the 
mouth,    and 

even    the   sight  or  smell  of   food,    caused   secretion  of    gastric 
juice  (Richet). 

Here  there  must  have  been  some  nervous  mechanism  at  work. 
The  secretion  cannot  have  been  excited  by  the  direct  action  of 
absorbed  food-products  circulating  in  the  blood— an  explanation 
which  might  be  given,  though  an  insufficient  one,  of  the  secretion 
seen  in  an  isolated  portion  of  the  cardiac  end  of  the  stomach 
during  the  digestion  of  food  in  the  rest.  The  efferent  nervous 
channels  through  which  these  effects  are  produced  have  been 
defined   by    Pawlow's   experiments   on   dogs.       He    first    made 


Fig.   145. — Pawlow's  Stomach  Pouch. 
S,  the  completed  pouch  ;  V,  cavity  of  stomach. 


374  A   MANX)  \L  OF  PHYSIOLOGY 

a  gastric  fistula,  then  a  few  days  afterwards  divided  the 
oesophagus  through  a  wound  in  the  neck,  and  stitched  the  two 
cut  ends  to  the  edges  of  the  wound.  After  the  animals  had 
recovered,  it  was  observed  that  when  meat  was  given  to  them 
by  the  mouth,  a  copious  secretion  of  gastric  juice  followed  in 
five  or  six  minutes,  notwithstanding  the  fact  that  in  this  '  sham 
feeding'  the  food  immediately  escaped  from  the  opening  in  the 
upper  portion  of  the  divided  oesophagus.  Much  the  same 
result  was  seen  when  the  food  was  simply  shown  to  the  animal. 
Indeed,  when  a  hungry  animal  is  tempted  with  the  sighl  ol 
meat,  the  flow  of  gastric  juice,  always  occurring  alter  a  kit  en t 
period  of  five  or  six  minutes,  may  be  even  greater  than  with 
sham  feeding.  Division  of  the  splanchnic  nerves  had  no  effect 
on  this  reflex  secretion,  while  it  could  not  be  obtained  after 
division  of  both  vagi  below  the  origin  of  their  cardiac  and 
pulmonary  branches,  by  which  disturbance  of  the  heart  and 
respiration  are  avoided.  Further,  stimulation  of  the  peripheral 
end  of  the  vagus  in  the  neck*  caused  secretion.  These  experi- 
ments show  that  secretory  fibres  for  the  gastric  glands  run  in  the 
vagi.  It  is  probable  that  the  vagi  also  contain  efferent  fibres 
which  inhibit  the  gastric  secretion.  The  excitation  ol  the 
secretory  fibres  is  not  produced  reflexly  by  the  processes  of 
mastication  and  deglutition  as  such.  Dilute  acid  is  the  most 
powerful  chemical  stimulus  for  the  buccal  mucous  membrane, 
and  when  it  is  introduced  into  the  mouth  of  a  dog  with  a  doubl< 
oesophageal  and  gastric  fistula,  an  abundant  secretion  of  saliva  at 
once  ensues.  But  no  matter  how  long  the  animal  continues  to 
swallow  the  mixture  of  saliva  and  acid,  no  gastric  juice  is  formed. 
The  same  is  the  case  in  sham  feeding  with  salt,  pepper,  mustard, 
smooth  stones,  and  even  extract  of  meat.  It  is  the  desire  for 
food — the  appetite,  as  we  call  it — and  the  feeling  of  satisfaction 
associated  with  eating  food  that  the  animal  relishes,  which  is 
the.  efficient  cause  of  the  gastric  secretion  in  sham  feeding.  The 
more  eagerly  the  dog  eats,  the  greater  is  the  flow  of  gastric  juice. 
Paw  low  also  performed  the  converse  experiment.  In  dogs 
in  which  a  pouch  had  been  isolated  from  the  stomach  and 
made  to  open  to  the  exterior  by  the  surgical  procedure 
illustrated  in  Figs.  144  and  145,  he  introduced  into  the  large 
stomach,  without  the  animal's  knowledge,  food  of  various 
kinds.  This  is  best  done  in  a  sleeping  dog.  The  secretion  of 
gastric  juice,  both  in  the  main  stomach  and  in  the  pouch  01 
miniature  stomach,  which  is  known  in  a  great  variety  of  condi- 
tions to  present  an  exact  picture  of  the  process  of  secretion  in 

*  The  nerve  was  not  stimulated  till  a  few  days  after  the  section,  so  as  to 
allow  the  cardio-inhibitory  fibres  to  degenerate.  Otherwise  the  heart 
would  have  been  stopped  by  the  stimulation. 


DIGESTION  375 

the  large,  is  markedly  delayed  and  scanty  when  it  does  appear, 
I'.ivad  and  coagulated  egg-white  did  not  yield  a  single  drop 
during  the  first  hour  or  more.  Raw  flesh  excited  a  secretion, 
Imt  alter  an  interval  of  fifteen  to  forty-five  minutes,  instead  of 
five  or  six  to  ten,  as  in  sham  feeding.  It  was  very  scanty  during 
the  first  hour  (only  one-third  the  normal  amount),  and  possessed 
a  very  low  digestive  power.  The  importance  of  the  psychical 
element  is  shown  by  the  fact  that  in  one  dog,  which,  after  a 
weighed  amount  of  meat  had  been  introduced  into  its  stomach 
(without  its  knowledge)  received  a  sham  meal  of  meat,  the 
amount  of  protein  digested  after  one  and  a  half  hours  was  five 
times  greater  than  in  another  animal  treated  exactly  in  the  same 
way,  except  that  the  sham  meal  was  omitted.  But  even  after 
division  of  the  vagi,  gastric  secretion  is  still  caused  by  the  intro- 
duction of  various  substances  into  the  stomach,  especially  water 
and  meat  extract.  The  active  substances  in  the  meat  extract 
are,  for  the  most  part,  insoluble  in  alcohol.  Kreatin  is  inactive. 
It  is  in  virtue  of  these  substances  that  raw  meat  placed  directly  in 
the  stomach  causes  some  secretion  after  a  time.  Milk  and  gelatin 
solution  are  also  direct  excitants  of  gastric  secretion  apart  from 
the  water  in  them.  Starch,  fat,  and  egg-white  are  totally 
inert.  After  section  of  both  vagi  in  dogs,  no  marked  quali- 
tative or  quantitative  changes  have  been  observed  in  the  gastric 
juice.  The  secretion  caused  by  the  presence  of  food  in  the 
stomach  is  still  obtained  when,  in  addition  to  the  vagi,  all  other 
nerves  which  can  possibly  connect  the  central  nervous  system 
with  the  organ  have  been  severed  and  the  sympathetic  abdo- 
minal plexuses  have  been  destroyed  (Popielski).  We  must 
therefore  suppose  that  the  gastric  glands,  while  normally  under 
the  control  of  a  nervous  mechanism  in  the  upper  portion  of  the 
cerebro-spinal  axis  whose  efferent  fibres  run  in  the  vagi,  are  also 
capable  of  being  locally  stimulated  through  the  peripheral 
ganglia  in  the  stomach  walls  or  the  chemical  action  of  the  products 
of  digestion  absorbed  into  the  blood.  Edkins  showed  that  the 
injection  of  food  substances  or  the  products  of  their  digestion 
(broth,  dextrin,  peptone)  or  of  acid  into  the  blood  caused  no 
secretion  of  gastric  juice,  while  the  injection  of  an  extract  of 
the  pyloric  mucous  membrane,  made  by  boiling  it  with  water, 
acid,  or  peptone,  excited  a  certain  amount  of  secretion.  He 
therefore  concluded  that  the  secondary  secretion  of  gastric 
juice  is  determined,  not  by  local  stimulation  of  a  reflex  mechanism 
in  the  gastric  wall,  but  by  the  production  in  the  mucous  membrane 
of  the  pyloric  end  of  a  chemical  substance,  the  gastric  secretin  or 
gastric  hormone,*  which  is  absorbed  by  the  blood,  and  acts  as 

*   '  Hormone  '    (from  opixau,  I  arouse  or  excite)  is  the  name  given  to  a 
substance  which,  carried  by  the  blood  from  the   place  where  it  is  formed 


376  A    MA  \  I    ll    OF   PHySIOLOG  Y 

an  excitanl  to  all  the  gastric  glands.  The  cardiac  mucosa  was 
found  incapable  oi  forming  this  substance. 

It  is  not  to  be  imagined  that  the  '  psychical  '  secretion  and  the 
secretion  called  forth  by  the  direct  action  oi  the  food  or  food- 
products  in  the  stomach  perform  independent  offices.  They  can, 
in  various  instances,  be  shown  to  supplement  each  other.  For 
example,  not  more  than  one-half  or  one-third  of  the  gastiie 
juice  secreted  during  the  digestion  of  bread  or  boiled  egg-albumin 
can  be  ascribed  to  the  psychic  effect.  Yet  these  substances,  when 
introduced  directly  into  the  stomach,  cause  practically  no  secre- 
tion. We  must  suppose  that  during  the  digestion  oi  the  bread 
■Mid  albumin  by  the  psychically  secreted  juice  certain  products 
analogous  to  those  in  the  meat  extract  are  formed,  which  act  as 
chemical  excitants  of  the  local  secretory  apparatus.  The  psychic 
juice  is  indispensable  in  this  case  to  start  the  process,  '  to  set  the 
stove  ablaze,'  as  Pawlow  puts  it.  In  the  case  of  meat  it  is  not 
indispensable,  since  the  meat  can  chemically  excite  the  gastric 
glands  ;  but  it  greatly  hastens  the  process  of  digestion.  These 
facts  emphasize  the  importance  of  appetite  in  digestion,  a  truism 
in  treatment  which  thus  receives  for  the  first  time  a  rational 
explanation.  The  influence  of  good-humour  upon  nutrition,  which 
experience  has  crystallized  into  the  proverb  '  Laugh  and  grow 
fat,'  has  also  been  shown  to  depend — in  great  part,  at  least — upon 
a  beneficial  action  on  the  digestive  functions,  both  motor  and 
chemical.  The  movements  of  the  cat's  stomach  and  intestines 
have  been  observed  to  cease  when  the  animal  became  angry 
or  excited  by  unpleasant  emotions  ;  and  in  a  dog  whose  gastric 
glands  were  pouring  out  a  copious  psychical  secretion  in  response 
to  a  sham  meal,  secretion  stopped  abruptly  when  the  animal's 
wrath  was  awakened  by  what  is  probably  to  the  normal  dog 
the  most  specifically  '  adequate  '  stimulus  for  the  emotion  of 
anger — the  sight  of  a  cat  which  he  was  restrained  from  chasing. 

By  means  of  experiments  with  the  miniature  stomach  it  has 
been  further  shown  that  each  kind  of  food  has  its  own  charac- 
teristic curve  of  gastric  secretion.  With  flesh  diet  the  maximum 
rate  of  secretion  occurs  during  the  first  or  second  hour,  and  in 
each  of  the  lust  two  hours  the  quantity  of  juice  furnished  is 
approximately  the  same.  With  bread  diet  we  have  always  a 
sharply-indicated  maximum  in  the  first  hour,  and  with  milk  a 
similar  one  during  the  second  or  the  third  houi  (Fig.  14')). 
The  juice  secreted  on  different  diets  also  differs  in  digestive 
power  -  i.e.,  in  the  amount  of  protein  which  a  given  quantity  oi 

acts  as  a  chemical  messenger  in  exciting  the  activity  <>l  some  more  or  less 
distant  organ.      The-  classical   example  is  tin-  pancreati<    secretin  which, 
manufactured   in  the  intestinal  mucosa,   exciter  the  secretion  ot   the  pan 
■  reatic  juice. 


DIGESTION 


7  7 


: 

n 

fi 

j 

8 

4 

? 

0 

J 

Flesh,  200  | 


Bread,  200  grm. 


Milk,  600  c.c. 


Fig. 


146. — Rate    of   Secretion    of    Gastric    Juice    with 
Diets  of  Meat,  Bread,  and  Milk  (Pawlow). 


ii  will  digesl  in  a  given  time.     '  Bread  juice  '  is  much  strongei 

111  Iriiiu'iit  than  '  meal  juice, '  and  '  meal  juice  '  somewhat 
stronger  than  '  milk  juice  '  (Fig.  147).  But  '  meat  juice  '  has 
.1  higher  acidity  than  '  bread  juice,'  '  milk  juice  '  being  inter- 
mediate. These  differences  do  not  necessarily  indicate  that  the 
gastric  mu- 
cous     mem-    Hou"    123    45678    I     23456    7  8  9  10   1    23456 

brane    re- 
sponds in  a 

specific  way 
to  each  kind  u 
of  food  sub-  ^ 
stance,      as   i 
suggested   5 
by  Pawlow.    "* 
They     may 
depend     on 
several    cir- 
cumstances, 
and  particu- 
larly on  this 

— that  the  quantity,  though  not  the  quality,  of  the  psychical 
or  '  appetite '  juice  is  related  to  the  relish  with  which  the 
animal  eats  the  food.  The  products  formed  in  the  digestion  of 
the  different  foods  by  the  psychical  juice  may  therefore  be 
different  in  nature  and  amount,  and  thus  the  quantity  of  the 
gastric  hor- 
mone which 
determines 
the  second- 
ary secre- 
tion may 
vary  with 
the  food. 

The young 
mammal, 
like  the 
adult,  se- 
cretes gas- 
tric juice  be- 
fore the  food 
reaches  the 
s  t  om  ach. 

In  puppies  from  one  to  eighteen  days  old  sham  feeding  (sucking 
the  teats  of  the  mother  after  an  oesophageal  fistula  has  been 
made   in   the   younger  animals  and  a   double  oesophageal  and 


Hours   I 
10.0 


2345678234     5678923456 


a.o 


■£•2 

5 


6,0 


40 


2.0 


z^z 


Fi 


Flesh,  200  grm.  Bread,  200  grm.  Milk,  600  c.c. 

147. — Digestive    Power  of   Gastric   Juice   (Pawlow). 

The  digestive  power  of  the  juice,  as  measured  by  the  length 
of  the  protein  column  digested  in  Mett's  tubes,  is  represented 
hour  by  hour,  with  diets  of  flesh,  bread,  and  milk. 


378 


.1   MANU  \1.  <>/■    I'llYSlOLOCV 


gastric  fistula  in  the  older)  causes  a  liquid  with  the  properties  of 
gastric  juice  to  gather  in  the  stomach.  This  power,  then,  is  a 
congenital  one.  The  individual  does  not  gain  it  by  experience; 
it  comes  into  the  world  with  him  (Cohnheim). 

The  Influence  of  Nerves  on  the  Pancreas. — Like  the  stomach, 
the  pancreas  receives  secretory  fibres  through  the  vagus.  These 
are  probably  connected  with  a  reflex  centre  in  the  medulla 
oblongata.  It  has  long  been  known  that  when  tin:  medulla 
is  stimulated  a  flow  of  pancreatic  juice  is  occasionally  set   up, 

or  is  increased  il 
already  going  on. 
The  same  is  true 
when  the  vagus 
is  stimulated  in 
the  ordinary  wax- 
in  the  neck.  But 
the  experiment 
often  tailed,  for 
the  pancreas  is 
peculiarly  sus- 
cepl  ible  to  circu- 
latory disturb- 
ances, and  stimu- 
lation of  the  bulb 
or  the  vagus  may 
interfere  with 
the  blood -tlou 
through  thegland 
by  exciting  its 
vaso  -  constrictor 
fibres  or  causing 
inhibition  of  the 
heart.  These  dis- 
turbing i  nflu- 
ences  may  be 
avoided,  as  Paw- 
low  has  shown,  by  stimulating  the  vagus,  three  or  four  days  after 
dividing  it.  with  slowly-recurring  stimuli  (induction  shocks  or 
light  blows  from  a  small  hammer  worked  by  an  electro-magnet 
a1  the  rate  of  about  one  in  the  second).  The  secretory  fibres  are 
still  susceptible  of  excitation,  while  the  cardio-inhibitorv  fibres, 
which  degenerate  more  rapidly,  are  almost  or  altogether  inex- 
citable,  and  the  vaso-constrictors  are  but  little  affected  by  these 
slow  rhythmical  stimuli,  which  excite  the  secretory  nerves 
(p.  159).  A  pancreatic  fistula  has  previously  been  established 
by  excising  a  small  portion  of  the  duodenal  wall  containing  the 


Secretion  of  Pepsin. 


C  shows  tin-  quantity  of  pepsin(ogen)  in  the  mucous 
membrane  "t  the  cardiac  end  of  the  stomach  at  different 
times  during  digestion  ;  I',  the  quantity  of  pepsinogen  )  in 
tli<'  mucous  membrane  of  the  pyloric  end  :  S,  the  quantity 
oi  pepsin  in  the  secretion  of  the  cardiac  glands.  The 
numbers  marked  along  the  horizontal  axis  are  hours  since 
1  lie  last  meal.  About  five  hours  after  the  meal.  S  reaches 
its  maximum.  From  the  very  beginning  of  the  meal  (  falls 
steadil)  down  to  the  tenth  hour,  and  then  begins  to  rise 
— i.e.,  the  gland-cells  oi  the  cardial  end  of  the  stomach 
become  poorer  in  pepsin(ogen)  as  secretion  proceeds. 


DIGESTION  379 

opening  of  the  pancreatic  duct,  closing  the  intestine  by  sutureSj 
.iii.l  stitching  the  orifice  "I  the  duct  into  the  abdominal  wound. 
On  stimulation  of  the  vagus  the  juice  will  begin  in  two  to  three 

minutes  to  drop  from  a  cannula  in  the  duct,  and  will  continue  to 
flow  for  several  minutes  after  cessation  of  the  stimulus.  The 
sympathetic  also  contains  secretory  fibres  for  the  pancreas. 
Efferent  fibres  which  inhibit  the  secretion  have  also  been  dis- 
covered in  the  vagus.  Their  presence  may  be  most  clearly  demon- 
strated when  that  nerve  is  stimulated  during  the  flow  of  pan- 
creatic juice  excited  by  the  introduction  of  dilute  acid  into  the 
duodenum.  Stimulation  of  the  central  end  of  the  vagus  and  ot 
the  other  nerves  is  capable  of  reflexly  inhibiting  the  pancreatic 
secretion.  Painful  impressions  have  a  strong  inhibitory  influ- 
ence. This  is  one  of  the  reasons  why  many  observers  failed  to 
detect  the  secretory  nerves.  The  inhibition  caused  by  vomiting 
is  probably  due  to  impulses  ascending  the  vagus.  It  is  possible 
that  through  these  nervous  channels  the  pancreatic  secretion  is 
affect-d  by  the  psychical  conditions  connected  with  eating  and 
the  desire  for  food,  just  as  in  the  case  of  the  gastric  secretion  ; 
but  our  information  on  this  subject  is  scantier  and  less  precise. 
A  flow  of  juice  may  undoubtedly  take  place  within  three  or  four 
minutes  after  food  is  taken,  but  it  is  not  quite  certain  whether 
this  is  not  determined  by  the  passage  of  some  of  the  acid  gastric 
contents  into  the  duodenum. 

Secretin. — We  have  already  referred  to  the  fact  that  pancreatic 
secretion  is  excited  by  the  presence  of  acid  in  the  duodenum. 
The  mechanism  of  this  action  is  of  great  interest.  Two  or  three 
minutes  after  the  introduction  of  0*4  per  cent,  hydrochloric  acid 
into  the  duodenum  pancreatic  juice  begins  to  flow.  A  similar 
effect  is  seen  when  the  acid  is  placed  in  the  jejunum,  but  not  when 
it  is  injected  into  the  lower  part  of  the  ileum.  It  is  obtained  as 
strongly  and  as  promptly  from  an  isolated  loop  of  intestine  when 
all  the  nerves  passing  to  it  have  been  cut,  and  the  solar  plexus 
extirpated,  and  also  after  the  administration  of  atropine,  which 
paralyzes  the  endings  of  secretory  nerves  elsewhere.  The  secre- 
tion accordingly  does  not  depend  upon  a  local  reflex  mechanism 
with  its  afferent  endings  in  the  intestinal  mucous  membrane, 
but  upon  some  substance  which  is  carried  to  the  pancreas  by 
the  blood,  and  acts  directly  upon  its  cells.  This  substance  is 
not  the  acid,  for  the  injection  of  0-4  per  cent,  hydrochloric  acid 
into  the  blood  produces  no  effect  upon  the  pancreas.  It  has  been 
shown  by  Bayliss  and  Starling  that  the  exciting  substance  is  a 
diffusible  body  of  low  molecular  weight,  probably  of  organic 
nature,  but  not  a  protein,  which  they  call  secretin.  It  is  soluble 
in  alcohol  or  alcohol  and  ether,  and  is  not  destroyed  by  boiling. 
It  is  produced  in  the  mucous  membrane  of  the  jejunum  or  duo- 


38o 


/    MA  Mil    OF  rHYSIOI.(>(,\ 


secretin  is  split  off  from  it. 


denum  or  exposure  to  dilute  hydrochloric  acid.  Extracts  of 
i nun  his  membrane  so  treated  cause  a  copious  pancreatic  secretion, 

and  a  smaller  secretion  of  bile,  when  injected  in  small  quantities 
into  the  blood  of  animals  in  which  no  such  secretion  is  taking 
place,  but  have  no  influence  on  any  other  gland.  At  the  same 
time  the  arterial  blood-pressure  falls  somewhat.  The  sub- 
stance which  product's  the  fall  of  blood-pressure  is  different  from 
xrni in.  since  acid  extracts  of  the  lower  end  of  the  ileum, 
which  have  no  effect  on  the  flow  of  pancreatic  juice,  diminish 
tlu'  blood-pressure.  A  precursor  of  secretin,  called  prosecretin, 
exists  in  the  intestinal  mucous  membrane,  and  can  be  extracted 
from  it  by  physiological  salt  solution.  It  does  nol  affect  the 
pancreatic   secretion.     By    boiling    or    by    the    action    oi    acid 

Pro-secretin  is  most  abundant  in  the 
duodenum,  and  diminishes  as  we 
pass  down  the  intestine. 

Secretin  is  very  widespread  in 
the  animal  kingdom.  In  the 
monkey,  dog,  cat,  rabbit,  man, 
ox,  sheep,  pig,  squirrel,  goose, 
tortoise,  salmon,  dog-fish,  and 
skate  evidence  of  its  presence 
f  has  been  obtained.  The  secretin 
of  one  animal  will  excite  a  flow 
of  pancreatic  juice  in  an  animal 
of  a  different  kind  as  well  as  in 
one  of  the  same  kind.  In  normal 
be  seen  that  the  maxima  of  s  fall  digestion  secretin  is  formed  under 

at  the  same   time   as   the  maxima  of     ,1  a  £   j.u  -j      i 

P.  The  numbers  along  the  horizontal  the  influence  of  the  acid  chyme, 
axis  are  hours  since  the  last  meal.  not    in    the  stomach,    but    after  it 

has  passed  into  the  duodenum. 
The  passage  of  the  chyme  through  the  pylorus,  as  previously 
mentioned  (p.  305),  is  regulated  by  the  reaction  of  the  duodenal 
contents,  as  well  as  by  the  consistence  of  the  gastric  contents. 
So  long  as  the  liquid  in  the  duodenum  is  acid,  the  pylorus  re- 
mains closed.  As  soon  as  the  first  small  portion  of  acid  chyme 
ejected  from  the  stomach  has  been  neutralized  by  the  increased 
secretion  of  the  pancreatic  juice  and  the  outpouring  of  bile  from 
the  gall-bladder  in  response  to  the  stimulus  of  the  acid,  the 
pylorus  opens  again. 

According  to  Pawlow,  certain  food  substances,  notably  fat.  and 
water  stimulate  the  pancreatic  secretion,  and  with  great  prompt- 
ness, even  before  any  acid  has  been  produced  in  the  stomach, 
and  therefore  before  any  can  have  passed  into  the  duodenum. 
Possibly  this  effect  is  elicited  through  the  long  reflex  paths 
already  described  as  running  in  the  vagi  or  through  a  local  ner- 


Fig.  149. — Kate    of   Secretion    of 
Pancreatic  Juice. 

S  shows  ilii-  \  ariation  in  the  rate  of 
secretion  of  the  pancreatic  juice  in  a 
dog;    I',   thr    variation    in    the    per- 

i  I'lit.i-i-  nt  sulids  in  tin'  juice.       It  w  ill 


nicrsTWN 


38' 


I    II   III  IV  V     |U  HI  IV    V  VI  VII  VIII  1    II  III  IV   V    VI 


■  ■■■■■■■I 

■■  HUB 

■■■■■!■■■■■ 


vous  mechanism,  which,  although  it  does  not  take  part  in  the 
excitation  of  the  pancreatic  secretion  by  acid,  may  yet  exisl 
for  the  performance  of  oilier  offices.  It  is  more  probable,  how- 
ever, that  it  is  due  to  the  passage  of  some  of  the  gastric  contents 
through  the  pylorus  ;  for  when  oil  is  introduced  into  the  small  in- 
testine, it  causes  the  production  of  secretin,  although,  unlike  dilute 
acid,  it  is  quite  ineffective  in  forming  secretin  when  rubbed  up 
with  the  scraped- 
oli  mucous  mem- 
brane. 

The  pancrea- 
tic, like  the  gas- 
tric, juice  is  said 
to  vary  as  regards 
its  digestive  pro- 
perties with  the 
nature  of  the 
food.  On  a  diet 
of  bread  the  juice  . 
is  very  poor  in  " 
fat-splitting  fer- "« 
ment,  while  on  a  |3 
diet  of  flesh  it  is 
richer,  and  on  a 
diet  of  milk  rich- 
est of  all.  With 
bread  the  juice  is 
relatively  rich  in 
amylolytic  fer- 
ment. When  we 
take  the  quan- 
tity of  the  juice 
as    well    as    its 


0 


(■■■■■una     ■■■■■■ 

■■■" 


BBBBIIBIIB    BBBBBBflfl 
BBflllllllfl 

(rain  unflfl 
IB  lllflllBBB 
IB  IllflllBflflflBfl 
IB  IBBIII  MM 

1 


BBMBBI     BBBBfl 

SISBBkUBM 

nun  BBi 

BUI  ififl      1KB 

bbbbbi  BfiBfl  mm 

BBBBBBBBBBBBBIBBBBB 


Flesh,  100  grm. 

Fig.  150 


Bread,  250  grm. 


Milk,  600  grm. 


— Secretion  of  Pancreatic  Juice  with 
Different  Diets  (Pawlow). 

The  hours  are  in  roman  numerals. 


strength  in  fer- 
ments into  con- 
sideration, it  is 
stated  that  bread 
occasions  the  se- 
cretion of  a  juice  with  a  greater  quantity  of  proteolytic  ferment 
than  either  milk  or  meat,  although  it  is  relatively  dilute  (Fig.  150). 
The  vegetable  proteins  require  more  ferment  to  digest  them 
than  proteins  of  animal  origin.  There  is  no  more  evidence  that 
the  adaptation  of  the  pancreatic  juice  to  the  nature  of  the  food 
is  due  to  a  specific  sensibility  of  the  duodenal  mucosa  to  the 
various  food-stuffs  than  there  is  in  the  case  of  the  adaptation  of 
the  gastric  juice.     If  the  volume  of  the  chyme  and  its  acidity 


382  A   MANUAL  OF  PHYSIOLOGY 

are  related  to  the  nature  of  the  food,  then  the  amount  of  secretin 
formed,  and  therefore  the  intensity  of  secretion  in  the  pancreas, 
will  he  similarly  related.  The  one  apparently  proved  example 
of  specific  adaptation  of  the  pancreatic  juice  lias  not  stood 
the  test  of  a  critical  examination.  It  was  asserted  that  in 
dogs  ted  for  some  days  with  food  containing  lactose  (milk)  the 
ferment,  lactase,  is  present  in  that  secretion,  while  tin-  pancreati 
juice  of  dogs  whose  food  is  free  from  lactose  does  not  contain 
lactase.  The  adaptation  of  the  pancreas  to  lactose  was  sup- 
posed to  be  achieved  through  some  substance  produced  by  tin- 
action  of  lactose  on  the  intestinal  mucous  membrane,  which 
plays  the  part  of  a  specific  chemical  stimulus  to  the  pain  reatic 
cells  or  their  secretory  nervous  mechanism,  causing  them  to  form 
lactase.  But  it  has  been  conclusively  shown  that  when  dogs  are 
fed  with  lactose  lor  weeks  no  lactase  appears  in  the  pancreatic 
juice  (Plimmer). 

The  natural  secretion  of  pancreatic  juice  is  by  no  means  so 
intermittent  as  that  of  saliva.  In  the  rabbit  the  pancreatic,  like 
the  gastric,  juice  flows  continuously.  In  the  dog  it  begins  almosl 
as  soon  as  food  is  taken,  rises  in  two  or  three  hours  to  a  maximum, 
then  falls  till  the  fifth  or  sixth  hour,  after  which  it  may  mount 
again  somewhat,  and  then,  gradually  diminishing,  ultimately 
stops  (Figs.  149,  150).  During  normal  activity  the  blood- 
vessels of  the  gland  are  dilated.  But  under  experimental  condi- 
tions the  increased  secretion  caused  by  secretin  is  accompanied 
sometimes  by  an  increase  and  sometimes  by  a  diminution  in  the 
blood-flow,  and  secretion  may  continue  for  some  time  after  com- 
plete cessation  of  the  circulation,  while  the  increased  consumption 
of  oxygen  which  goes  hand  in  hand  with  the  increased  secretion  is 
also  independent  of  the  blood-supply  (May,  Barcroft  and  Starling). 
This  shows  how  far  the  secretory  process  is  from  a  mere  mechanical 
filtration,  although  it  does  not  follow  that,  under  normal  condi- 
tions, a  decreased  blood-flow  ever  does  accompany  an  increased 
secretion.  There  is  one  difference  between  the  normal  secretion 
of  pancreatic  juice  and  of  saliva  which  may  still  be  mentioned : 
the  pressure  of  the  latter  in  the  submaxillary  duct  may,  as  we 
have  seen,  greatly  exceed  the  arterial  blood-pressure,  without 
reabsorption  and  consequent  cedema  of  the  gland  occurring  ; 
but  the  secretory  pressure  of  the  pancreatic  cells  is  very  low,  in >t 
more  than  a  tenth  of  that  of  the  salivary  gands.  (Edema  begins 
before  a  manometer  in  the  duct  shows  a  pressure  of  20  mm.  of  mer 
cury,  the  secreted  fluid  passing  very  easily  into  the  lymph  spaces. 

The  mutual  relations  of  the  spleen  and  pancreas  have  formed 
the  subject  of  numerous  inquiries.  Some  authors  maintain 
that  tin'  spleen  plays  an  important  idle  in  the  elaboration 
of    the    proteolytic   ferment    of    the    pancreas,    forming   a    sub- 


h/CISTWN 


383 


stance  which  we  may  call  pro- tripsinogen,  since  it  is  supposed  to 
be  carried  in  the  blood  to  the  pancreatic  cells,  and  changed  by 
them  into  trypsinogen.  There  is  some  evidence  that  extracts 
of  the  spleen  prepared  from  it  when  congested  (hiring  digestion 
exerl   a   favourable  influence  on   the  proteolytic  power  of  the 

pancreas  (Mendel).  And  there  is  no  doubt  that  the  spleen,  like 
other  organs,  contains  an  intracellular  enzyme  which  can  aid 
in  the  digestion  of  protein.  The  products  of  the  action  in  an 
acid  medium  of  this  enzyme  are  the  same  as  those  formed  by 
trypsin  in  an  alkaline  medium 
(Leathes).  But  this  is  not  enough 
to  prove  that  the  spleen  has  any 
special  relation  to  pancreatic  diges- 
tion. 

The  Influence  of  Nerves  on  the 
Secretion  of  Bile. — Although  bile  is 
secreted  constantly,  it  only  passes  at 
intervals  into  the  intestine.  For  the 
liver  in  many  animals,  unlike  every 
other  gland  except  the  kidney,  has 
in  connection  with  it  a  reservoir, 
the  gall-bladder,  in  which  its  secre- 
tion accumulates,  and  from  which 
it  is  only  expelled  occasionally.  We 
have  therefore  to  distinguish  the 
bile-secreting  from  the  bile-expelling 
mechanism,  To  study  the  rate  of 
secretion  of  bile  (Fig.  151),  a  fistula 
of  the  gall-bladder  can  be  established. 
But  to  learn  the  function  of  bile  in 
digestion  it  is  more  important  to 
know  when  and  at  what  rate  it  enters 
the  intestine.  For  this  purpose  a 
fistula  is  made  by  cutting  the  natural 
orifice  of  the  common  bile-duct  with 

a  piece  of  the  surrounding  mucous  membrane  out  of  the  intestine 
and  transplanting  it  upon  the  serous  coat,  where  it  is  sutured.  The 
loop  of  intestine,  with  the  orifice  of  the  duct  facing  outwards,  is 
then  stitched  into  the  abdominal  wound,  where  it  is  allowed  to 
heal.  Of  course,  since  a  circulation  of  the  bile-acids  takes  place 
— i.e.,  an  absorption  from  and  re-excretion  into  the  intestine — 
the  formation  of  that  juice  cannot  proceed  upon  absolutely 
normal  lines  when  the  bile  no  longer  enters  the  duodenum. 
The  only  condition  under  which  fistula  bile  could  have  the  same 
composition  as  normal  bile  would  be  that  in  which  as  great  an 
amount  of  bile-acids  is  introduced  into  the  gut  as  escapes  through 


Fig.    151. — Rate  of  Secretion 
of  Bile. 

S  shows  how  the  rate  of  secre- 
tion of  bile  falls  in  a  dog  when  a 
biliary  fistula  is  first  made,  and 
the  bile  thus  prevented  from 
entering  the  intestine  ;  P  shows 
the  fall  of  the  percentage  of 
solids.  The  numbers  along  the 
horizontal  axis  are  quarters  of 
an  hour  since  bile  began  to  escape 
through  the  fistula.  The  num- 
bers along  the  vertical  axis  refer 
only  to  curve  S,  and  represent 
the  rate  of  secretion  in  arbitrary 
units. 


384  !  MANX    ll    OF  PHYSIOLOGY 

the  fistula.  A  circulation  of  a  smaller  proportion  of  the  bile- 
pigments  is  also  probable,  Imt  there  is  no  circulation  <»!'  thebiliai  v 
cholesterin  (Stadelmann). 

Of  tin-  direct  influence  of  nerves,  either  on  the  secretion  of  bile  or 
on  its  expulsion,  we  have  scarcely  any  knowledge,  scarcely  even  any 
guess  which  is  worth  mentioning  here.  It  is  true  the  secretion  of 
bile  may  be  distinctly  affected  by  the  section  and  stimulation  of 
nerves  which  control  the  blood-supply  of  the  stomach,  intestines, 
.iikI  spleen,  for  the  quantity  of  blood  passing  by  the  portal  vein  to 
the  liver  depends  upon  the  quantity  passing  through  these  organs, 
and  the  rate  of  secretion  is  diminished  when  the  blood-supply  is 
greatly  lessened.  In  this  way  stimulation  of  the  medulla  oblongata, 
the  spinal  cord,  or  the  splanchnic  nerves  stops  or  slows  the  secre- 
tion of  bile  by  constricting  the  abdominal  vessels  ;  and  the  same 
effect  can  be  rcflexly  produced  by  the  excitation  of  afferent  nerves. 

The  right  splanchnic  nerve  contains  inhibitory  with  some  motor 
fibres,  and  the  vagi  (especially  the  left)  contain  motor  fibres  for 
the  gall-bladder.  Probably  its  contraction  takes  place  naturally 
in  response  to  reflex  impulses  from  the  mucous  membrane  of  the 
duodenum,  for  the  application  of  dilute  acid  to  the  mouth  of  the 
bile-duct  causes  a  sudden  flow  of  bile,*  and  the  acid  contents  of  the 
stomach,  when  projected  through  the  pylorus  into  the  intestine. 
have  a  similar  effect.  But,  in  addition,  as  we  have  seen,  the 
secretin  formed  will  cause  an  increase  in  the  rate  of  secretion  of  the 
bile.  In  studying  the  effect  of  secretin  it  is  necessary  to  obtain 
it  free  from  bile-salts,  since  these  cause  of  themselves  an  increased 
secretion  of  bile.  When  this  is  done  by  dissolving  out  with 
alcohol  any  bile-salts  which  may  be  present  in  the  extract  of 
intestinal  mucous  membrane,  a  solution  of  the  residue  containing 
the  secretin  still  evokes  a  rapid  secretion  of  bile.  The  fact  that 
the  same  hormone  excites  the  formation  both  of  pancreatic 
juice  and  bile  is  obviously  related  to  that  common  action  of 
the  two  juices  in  digestion  on  which  we  have  already  dwelt. 

When  food  passes  into  the  stomach,  there  is  at  once  a  sharp 
rise  in  the  rate  of  secretion  of  bile.  A  maximum  is  reached 
from  the  fourth  to  the  eighth  hour — that  is,  while  the  food  is 
in  the  intestine.  There  is  then  a  fall,  succeeded  by  a  second 
smaller  rise  about  the  fifteenth  or  sixteenth  hour,  from  which 
the  secretion  gradually  declines  to  its  minimum.  Upon  the  whole, 
the  curves  of  secretion  of  pancreatic  juice  and  bile  show  a  fairly 
close  correspondence,  except  that  the  latter  is  more  nearly  con- 
tinuous. But  when  we  compare  the  curves  representing  the  rate 
at  which  the  bile  actually  enters  the  intestine  with  the  curve  of 
pancreatic  secretion  (Fig.  152),  we  are  struck  by  their  almost 
absolute  parallelism.     This  lends  additional  support  to  the  con- 

*  This  result  seems  to  be  difficult  to  realise  experimentally.  Bain- 
bridge  and  Dale  could  not  elicit  reflex  contraction  of  the  gall-bladder  (in 
anaesthetized  animals)  in  this  way. 


DIGESTION 


385 


elusion  tied  need   from  their  chemical  and  physical  properties, 
that  in  digestion  thej  are  partners  in  a  common  work. 

While  the  rate  at  which  bile  passes  into  the  intestine  seems  to 
be  influenced  by  digestion  much  in  the  same  way  as  the  rate 
nl  pancreatic  secretion,  the  details  are  as  yet  less  exactly  known. 
In  the  fasting  animal  no  bile  enters  the  gut.  When  food  is  taken 
the  flow  begins  alter  a  definite  interval,  which  varies  for  the 
different  kinds  of  food.  As  long  as  digestion  lasts  bile  continues 
to  escape,  but  both  the  quantity  and  quality  depend  upon  the 
nature  of  the  food.  Water,  raw  egg-white,  and  starch  paste, 
whether  given  by  the  mouth  or  introduced  directly  into  the 
stomach  of  a  dog, 
cause  no  flow  of 
bile.  But  fat,  the 
exl  r actives  of 
meat,  and  the  pro- 
ducts of  digestion 
of  egg-white  pro- 
duce a  copious  dis- 
charge. This  dis- 
charge may  be  de- 
termined by  the 
relatively  large 
amount  of  acid 
chyme  passed 
through  the  py- 
lorus when  pro- 
teins are  digested 
in  the  stomach 
and  the  stimulus 
to  the  formation 
of  secretin  occa- 
sioned by  the 
presence    of     this 

chyme  or  of  fatty  material  in  the  duodenum.  In  the  case  of 
fat  a  further  favourable  influence  on  the  secretion  of  bile  is 
the  absorption  of  bile-salts  which  accompanies  the  absorption 
of  the  fatty  acids  and  soaps  produced  in  fat  digestion.  Bile- 
salts  stimulate  the  secretion  of  bile,  including  bile-salts  them- 
selves. An  increased  flow  of  bile-salts  into  the  intestine  acceler- 
ates the  splitting  of  fats  by  the  pancreatic  juice,  and  therefore 
the  absorption  of  bile-salts  acting  as  solvents  for,  or  chemically 
united  to,  the  fatty  acids  and  soaps.  A  circle  analogous  to  the 
'  vicious  circle  '  of  the  logicians,  but  constituting  a  physiological 
adaptation  of  most  potent  virtue  in  the  digestion  of  fats,  is  thus 
established.     Not  only  is  the  quantity  of  bile  poured  into  the 

25 


Fig.    152. — Pancreatic    Juice   and    Bile    (Pawlow). 

The  upper  curves  represent  the  hourly  rate  of  pan- 
creatic secretion,  and  the  lower  the  rate  at  which  the 
bile  enters  the  intestine  ;  a,  a',  milk  diet  ;  b,  b',  meat ; 
c,  c',  bread.  Only  the  general  form  of  the  curves  is  to 
be  compared.  The  scale  of  the  ordinates  of  the  various 
curves  was  not  the  same. 


j86  A   MANUAL  OF  PHYSIOLOGY 

intestine  increased  on  a  did  rich  in  fat,  but  it  is  said  thai  a  given 
amount  oi  it  aids  the  fat-splitting  action  "I  the  pancreatic  juice 
more  powerfullj  than  it  the  did  were  |)<><t  in  fat.  This  may 
depend  upon  an  increase  in  the  concentration  oi  the  bile-salts  in 
bile  secreted  when  a  large  amount  oi  fat  is  ingested.  But  it  is 
well  to  recognise  that  we  do  not  at  present  know  with  any  great 
exactness  the  mechanism  by  which  the  rate  oi  secretion  and 
expulsion  of  bile  and  the  properties  oi  thai  juice  are  influenced 
l>v  digestion.  It  has  been  conjectured  thai  the  firsl  abrupt  rise 
may  be  started  by  reflex  nervous  action,  and  thai  later  on 
tin  and,  in  the  case  of  fat  digestion,  bile-salts  may  directly 

excite  the  hepatic  cells. 

Tlie  pressure  under  which  the  bile  is  secreted  is  higher  than 
the  pressure  of  the  portal  blond,  and  therefore  the  liver  ranges 
itself  with  the  high-pressure  salivary  glands  rather  than  with 
the  low-pressure  pancreas.  But  although  the  biliary  pressure 
is  high  relatively  to  that  of  the  blood  with  which  the  secreting 
cells  are  supplied,  it  is  absolutely  low,  the  maximum  being  no 
more  than  25  mm.  of  mercury.*  This  is  a  point  of  practical 
importance,  for  a  comparatively  slight  obstruction  to  the  out- 
flow, even  such  as  is  offered  by  a  congested  or  inflamed  condition 
of  the  duodenal  wall  about  the  mouth  of  the  duct,  may  be  suffi- 
cient to  cause  reabsorption  of  the  bile  through  the  lymphatics, 
and  consequent  jaundice.  Of  course,  complete  plugging  of  the 
duel  by  a  biliary  calculus  is  a  much  more  formidable  hairier,  and 
inevitably  leads  to  jaundice,  just  as  ligature  of  a  salivary  duct, 
in  spite  of  the  great  secretory  pressure,  inevitably  <  auses  oedema 
of  the  gland. 

The  Influence  of  Nerves  on  the  Secretion  of  Intestinal  Juice. — 
As  to  the  influence  of  nerves  on  the  secretion  of  the  succus 
entericus,  our  knowledge  is  almost  limited  to  a  single  experi- 
ment, and  that  an  inconclusive  one.  Moreau  placed  four 
ligatures  on  a  portion  of  the  small  intestine,  so  as  to  form  three 
compartments  separated  from  each  other  and  from  the  resl  oi 
the  gut.  The  mesenteric  nerves  going  to  the  middle  loop  wen 
divided,  and  the  intestine  returned  to  the  abdomen.  After  some 
time  a  watery  secretion  was  found  in  the  middle  compartment. 
little  or  none  in  the  others.  This  i>  a  hue  '  paralytic  '  secretion, 
and  not  a  mere  transudation  depending  simply  on  the  vascular 
dilatation  caused  by  section  of  the  vaso-constrictor  nerves,  for 
it  has  the  same  composition  and  digestive  action  as  normal 
succus  entericus  obtained  from  a  fistula.  The  secretion  begins 
about  four  hours  after  section  of  the  nerves,  goes  on  increasing 

*  In  the  dog,  cat,  and  monkey  the  average  maximum  pressure  at  which 
as  much  bile  is  secreted  as  is  taken  up  from  the  bile-paths  by  the  portal 
lymphatics  is  aboul  300  mm.  ol  bile,  the  highest  pressure  recorded  was 
373  11 1  in.  oi  bile  in  a  ca1  (Herring  and  Simpson). 


DIGESTION  387 

for  about  twelve  hours,  and  then  rapidly  diminishes,  so  thai 
after  about  two  days  the  middle  loop,  as  well  as  the  other  two, 
will  be  found  empty.  The  interpretation  usually  put  upon  the 
experiment  is  that  nerves  which  normally  inhibit  the  local 
secretory  mechanism  have  been  divided.  But  there  is  no  real 
proof  of  the  existence  of  such  nerves. 

The  same  adaptation  is  seen  in  the  secretion  of  the  succus 
entericus  as  in  the  secretion  of  the  other  digestive  juices,  and  the 
adaptation  is  naturally  most  striking  in  regard  to  those  points 
in  which  the  intestinal  juice  is  peculiar.  While  mechanical 
stimulation  of  the  stomach  is  ineffective  as  regards  the  secretion 
of  gastric  juice,  mechanical  stimulation  of  the  intestine,  as  by  the 
contact  of  a  cannula,  produces  a  free  flow  of  succus  entericus. 
The  reaction  is  a  localized  one,  the  secretion  only  taking  place 
from  the  portion  of  the  mucous  membrane  stimulated.  This  fact 
acquires  significance  when  we  reflect  that  the  food  moves  very 
slowly  in  the  intestine,  and  a  secretion  could  be  of  use  only  at 
the  points  where  the  food  happened  to  be.  The  juice  secreted 
in  response  to  mechanical  stimulation  is  poor  in  enterokinase. 
But  if  a  little  pancreatic  juice  be  put  into  the  intestine,  and  left 
there  for  some  time,  the  juice  afterwards  secreted  is  rich  in 
enterokinase. 

Effect  of  Certain  Drugs  on  the  Digestive  Secretions. — A  small  dose 
of  atropine,  as  has  been  said,  abolishes  the  secretory  action  of  the 
chorda  tympani.  This  it  does  by  paralyzing  the  nerve-endings  or 
'  receptive  '  substances  in  the  gland-cells  through  which  the  nerve- 
impulses  excite  secretion.  The  gland-cells  are  not  completely 
paralyzed,  for  the  sympathetic  can  still  cause  secretion.  The 
nerve-fibres  are  not  paralyzed,  because  the  direct  application  of 
atropine  does  not  affect  them  ;  nor  is  the  seat  of  the  paralysis  the 
ganglion-cells  on  the  course  of  the  fibres,  for  stimulation  between 
those  cells  and  the  gland-cells  is  ineffective.  Pilocarpine  is  the 
physiological  antagonist  of  atropine,  and  restores  the  secretion  which 
atropine  has  abolished.  In  small  doses  it  causes  a  rapid  flow  of 
saliva,  its  action  being  certainly  a  peripheral  action,  and  probably 
an  action  on  the  nerve-endings  (or  receptive  substances),  for  it 
persists  after  all  the  nerves  going  to  the  salivary  glands  have  been 
divided,  and  after  the  ganglion-cells  have  been  paralyzed  by  nico- 
tine. Atropine  and  pilocarpine  act  similarly  on  some  of  the  other 
digestive  glands,  atropine  paralyzing  the  pancreatic  secretion  elicited 
by  stimulation  of  the  vagus,  although  not  that  obtained  by  the 
introduction  of  acid  into  the  intestine.  Pilocarpine  seems  only  to 
cause  a  secretion  of  pancreatic  juice  when  other  stimuli  are  already 
acting,  especially  the  stimulus  determined  by  the  presence  of  acid 
in  the  duodenum.  Pilocarpine  increases  the  secretion  of  gastric, 
and  probably  of  intestinal  juice,  but  atropine  does  not  stop  the 
secretion  caused  by  division  of  the  intestinal  nerves.  Physostigmine 
and  muscarine  act  on  the  whole  like  pilocarpine,  but  physostigmine 
in  small  doses  gives  rise  to  an  abundant  flow  of  pancreatic  juice,  even 
when  the  intestine  is  empty,  probably  by  stimulating  the  endings 
of  the  secretory  fibres  in  the  vagus. 

25—2 


VSS  A    MANUAL  OP  PHYSIOLOGY 

The  action  of  alcohol  on  the  secretion  of  gastric  juice  has  been 
studied  in  a  dog  with  a  double  gastric  and  oesophageal  fistula. 
Before  or  during  a  sham  meal  of  meat,  alcohol  diluted  with  water 
was  given  as  an  enema.  After  the  enema  the  quantity  of  hydro- 
chloric acid  secreted  increased  in  about  the  same  proportion  as  the 
quantity  of  juice,  but  the  pepsin  was  diminished,  reaching  a  mini- 
mum after  three-quarters  to  one  and  a  quarter  hours.  The  increase 
in  the  total  quantity  of  the  juice  and  in  the  acid  over-compensated 
the  moderate  diminution  in  the  digestive  power,  so  that  the  net 
result  was  beneficial  (Pekelharing).  But  it  must  be  remembered 
that  strong  alcoholic  beverages,  when  mixed  with  the  gastric  juice, 
and  therefore  when  taken  by  the  mouth,  retard  the  proteolytic 
action,  so  that  any  favourable  effect  on  the  secretion  of  the  juice  may 
easily  be  lost  in  the  subsequent  digestion,  unless  the  alcohol  is  dilute 
(Chittenden  and  Mendel).  The  action  of  alcohol  introduced  into  the 
rectum  on  the  gastric  secretion  is  both  reflex  and  direct. 

Cholagogues. — The  action  of  a  host  of  drugs  on  the  secretion  of  bile 
has  been  investigated  by  various  observers,  but  till  something  like 
unanimity  has  been  reached  it  would  not  be  profitable  to  go  into 
details  here.  The  only  real  cholagogues  at  present  positively  known 
appear  to  be  the  salts  of  the  bile-acids,  which,  given  by  themselves 
or  in  the  bile,  cause  not  only  an  increase  in  the  volume  of  the  biliary 
secretion,  but  also  an  increase  in  its  solids.  Certain  compounds  of 
salicylic  acid,  as  salol  (phenyl  salicylate)  and  sodium  salicylate,  also 
appear  to  slightly  increase  the  flow,  while  usually  diminishing  the 
concentration  of  the  bile.  The  injection  of  haemoglobin  into  the 
blood-stream,  or  its  liberation  there  by  substances,  such  as  toluylene- 
diamin  and  arseniuretted  hydrogen,  which  cause  destruction  of  the 
corpuscles,  leads  to  an  increased  secretion  of  bile-pigment  as  well  as 
a  more  rapid  flow  of  bile. 

Summary. — Here  let  us  sum  up  the  most  important  points 
relating  to  the  secretion  of  the  digestive  juices.  They  are  all 
formed  by  the  activity  of  gland-cells  originally  derived  from  the 
epithelial  lining  of  the  alimentary  canal.  The  organic  constituents 
or  their  precursors  {including  the  mother-substances  of  the  ferments) 
are  prepared  in  the  intervals  of  rest- — absolute  in  some  glands, 
relative  in  others — and  stored  up  in  the  form  of  granules,  which 
during  activity  are  moved  towards  the  lumen  of  the  gland  tubules, 
and  there  discharged. 

The  nerves  of  the  salivary  glands  are,  as  regards  their  origin, 
(a)  cerebral,  (b)  sympathetic  /  the  former  group  is  vaso-dilator,  the 
latter  (usually)  vaso-constrictor ;  both  are  secretory.  Secretion  of 
saliva  depends  strictly  on  the  nervous  system.  That  nerves  influence 
the  gastric  and  pancreatic  secretions  is  also  made  out.  The  psychical 
secretion  is  of  greater  importance  for  the  saliva  and  gastric  juice 
than  for  the  pancreatic  juice.  The  direct  action  of  secretin  {pro- 
duced in  the  intestinal  mucous  membrane  by  the  influence  of  the 
chyme)  is  the  most  characteristic  factor  in  pancreatic  secretion. 
As  regards  the  intestinal  glands  and  the  liver,  it  has  not  been 
proved  that  their  secretive  activity  is  under  the  control  of  the  nervous 
system,  except  in  so  far  as  the  latter  may  indirectly  govern  it  through 


DIGESTION  389 

the  blood-supply,  although  various  circumstances  suggest  the 
probability  of  a  more  direct  action.  All  the  digestive  juices  show 
a  certain  adaptation  to  the  nature  of  the  food,  although  it  has  not  been 
demonstrated  that  this  is  due  to  a  specific  sensibility  of  the  mucous 
membranes  for  each  kind  of  food-stuff.  The  action  of  one  juice 
on  the  secretion  of  another  is  also  of  great  significance.  Thus, 
the  water  of  the  saliva  directly  excites  a  flow  of  gastric  juice  when 
it  reaches  the  stomach  ;  the  acid  of  the  gastric  juice  excites  a  flow 
of  pancreatic  juice  when  it  reaches  the  duodenum  ;  and  the  pan- 
creatic juice  excites  the  intestinal  mucous  membrane  to  the  pro- 
duction of  enterokinase,  the  most  characteristic  constituent  of  the 
succus  entericus.  In  all  the  glands  the  blood-flow  is  increased 
during  activity ;  in  some  (salivary  glands)  this  is  known  to  be 
caused  through  vaso-motor  nerves.  In  the  salivary  glands  electro- 
motive changes  accompany  the  active  state,  and  more  heat  is  pro- 
duced. Both  in  the  salivary  glands  and  the  pancreas  it  has  been 
shown  thai  much  more  carbon  dioxide  is  given  off,  and  much  more 
oxygen  used  up,  during  secretion  than  during  rest.  In  the  other 
glands  we  may  assume  that  the  same  occurs.  This  is  one  proof 
that  work  is  done  in  the  separation  or  manufacture  of  the  con- 
stituents of  the  various  secretions. 

IV.  Digestion  as  a  Whole. 

Having  discussed  in  detail  the  separate  action  of  the  digestive 
secretions,  it  is  now  time  to  consider  the  act  of  digestion  as  a 
whole,  the  various  stages  in  which  are  co-ordinated  for  a  common 
end.  The  solid  food  is  more  or  less  broken  up  in  the  mouth 
and  mixed  with  the  saliva,  which  its  presence  causes  to  be 
secreted  in  considerable  quantity.  Liquids  and  small  solid 
morsels  are  shot  down  the  open  gullet  without  contraction 
of  the  constrictors  of  the  pharynx,  and  reach  the  lower  portion 
of  the  oesophagus  in  a  comparatively  short  time  (TV  second)  ; 
while  a  good-sized  bolus  is  grasped  by  the  constrictors,  then  by 
the  oesophageal  walls,  and  passed  along  by  a  more  deliberate 
peristaltic  contraction. 

Chemical  digestion  in  man  begins  already  in  the  mouth,  a 
part  of  the  starch  being  there  converted  into  dextrins  and  sugar 
(maltose),  as  has  been  shown  by  examining  a  mass  of  food  con- 
taining starch  just  as  it  is  ready  for  swallowing  (p.  424).  This 
process  is  no  doubt  continued  during  the  passage  of  the  food 
along  the  oesophagus. 

The  first  morsels  of  a  meal  which  reach  the  stomach  find  it 
free  from  gastric  juice,  or  nearly  so.  They  are  alkaline  from  the 
admixture  of  saliva  ;  and  the  juice  which  is  now  beginning 
to  be  secreted,  in  response  to  the  psychical  excitement,  and 


ioo  ./   .1/  I  \  r  \i    OF  PHYSlOl  X)GY 

reflexly  through  the  presence  "I  the  food  and  the  water  of  the 
saliva  in  the  stomach,  is  for  a  time  neutralized,  and  amylolytic 
digestion  still  permitted  to  go  on.  For  20  to  40  minutes  after 
digestion  has  begun  there  is  no  free  hydrochloric  acid  in  the 
stomach,  although  some  is  combined  with  proteins,  and  during 
this  period  the  ptyalin  of  the  swallowed  saliva  will  be  abl  to 
act  even  better  than  in  the  mouth,  being  favoured  by  a  weakly 
acid  reaction.  Indeed,  for  a  time,  as  the  meal  goes  on,  the 
successive  portions  of  food  which  arrive  in  the  stomach  will 
find  the  conditions  more  and  more  favourable  for  amylolytic 
digestion.  But  as  the  acidity  continues  to  increase,  the  activity 
of  the  ptyalin  will  first  be  lessened,  and  ultimately  abolished; 
and,  upon  the  whole,  a  considerable  proportion  of  the  starches 
must  usually  escape  complete  conversion  into  sugar  until  they 
are  acted  upon  by  the  pancreatic  juice.  This  is  particularly 
the  case  with  unboiled  starch,  as  contained  in  vegetables  which 
are  eaten  raw  ;  and,  indeed,  we  know  that  sometimes  a  certain 
amount  of  starch  may  escape  even  pancreatic  digestion,  and 
appear  in  the  faeces.  Meanwhile,  pepsin  and  hydrochloric  acid 
are  being  poured  forth  ;  the  latter  is  entering  into  combination 
with  the  proteins  of  the  food  ;  and  before  the  end  of  an  ordinary 
meal  peptic  digestion  is  in  full  swing.  The  movements  of  the 
pyloric  end  of  the  stomach  increase,  and  eddies  are  set  up  in  its 
contents,  which  carry  the  morsels  of  food  with  them,  and  throw 
them  against  its  walls.  In  this  way  not  only  are  the  contents 
thoroughly  mixed,  and  fresh  portions  of  food  constantly  brought 
into  contact  with  the  gastric  juice  secreted  mainly  in  the  more 
passive  cardiac  end,  but  a  certain  amount  of  mechanical  disinte- 
gration is  brought  about.  This  is  aided  by  the  digestion  of 
the  gelatin-yielding  connective  tissue  which  holds  together  the 
fibres  of  muscle  and  the  cells  of  fat,  and  the  digestible  structures 
in  vegetable  tissue  which  enclose  starch  granules.  II  milk  has 
formed  a  portion  of  the  meal,  the  caseinogen  will  have  been 
curdled  soon  after  its  entrance  into  the  stomach,  by  the  action 
of  the  rennet  ferment  alone  (see  p.  326)  when  the  milk  has 
been  taken  at  the  beginning  of  digestion  before  the  gastric 
contents  have  become  distinctly  acid,  by  the  acid  and  ferment 
together  when  it  has  been  taken  later.  The  caseinogen  and  other 
proteins  of  milk,  like  the  myosinogen  and  other  proteins  of 
meat,  and  the  globulins,  albumins,  and  other  proteins  of  bread  and 
of  vegetable  food  in  general,  are  acted  upon  by  the  pepsin  and 
hydrochloric  acid,  yielding  ultimately  peptones  ;  while  variable 
quantities  of  these  proteins  and  of  the  acid-albumin  and  pro- 
teoses derived  from  them  may  escape  this  final  change,  and  pass 
on  as  such  into  the  duodenum.  In  the  dog,  indeed,  a  very  large 
proportion  of  a  meal  of  flesh  has  been  found  to  be  digested  to  the 


Did  STION 

peptone  stage  while  still  in  the  stomach,  Leaving  for  the  juices 
thai  acl  "!i  it  in  the  intestine  only  its  further  hydrolysis  to 
amino-acids,  etc.  Bui  we  may  safely  assume  that,  in  the  case  "I 
a  man  living  on  an  ordinary  mixed  diet,  a  good  deal  of  the  food 
proteins  passes  through  the  pylorus  chemically  unchanged,  or 
having  undergone  only  the  first  steps  of  hydration.  For,  even  a 
few  minutes  after  food  has  been  swallowed,  especially  liquid  food 
or  water,  the  pyloric  sphincter  may  relax  and  allow  the  stomach 
to  propel  a  portion  of  its  contents  into  the  intestine  ;  and  such 
relaxations  occur  at  intervals  as  digestion  goes  on,  although  it  is 
not  for  several  hours  (three  to  five)  that  the  greater  portion  of 
the  food  reaches  the  duodenum.  During  this  period  the  acidity 
has  at  first  been  constantly  increasing,  although  for  a  time  the 
hydrochloric  acid  has  combined,  as  it  is  formed,  with  the  proteins 
of  the  food.  Then  comes  a  stage  where  the  hydrochloric  acid 
has  so  much  increased  that,  after  combining  with  all  the  proteins, 
some  of  it  remains  over  as  free  acid.  After  a  time  the  total  acidity 
begins  to  fall,  the  partially  digested  proteins  continually  passing 
on  through  the  pylorus,  while  a  considerable  proportion  is  so 
fully  digested  as  to  be  absorbed  by  the  gastric  mucous  membrane 
itself.  Thus,  in  one  experiment  on  the  digestion  of  meat  in  a 
dog.  it  was  found  that  30  per  cent,  was  absorbed  in  the  stomach, 
while  40  per  cent,  passed  through  the  pylorus  as  peptone,  over 
20  per  cent,  as  undissolved  or  soluble  protein  (acid-albumin), 
and  a  little  more  than  8  per  cent,  as  proteose  (Tobler).  The 
large  proportion  of  peptone  is  noteworthy,  as  indicating  some 
kind  of  selective  passage  of  the  different  digestive  products 
from  the  stomach  into  the  duodenum.  For  the  gastric  contents 
contain  plenty  of  proteose,  although  only  traces  of  peptone. 
The  total  '  titratable  acidity  '  goes  on  diminishing  till  the  third 
or  fourth  hour,  the  proportion  of  free  to  combined  acid  con- 
tinuing, nevertheless,  to  rise,  since  nearly  all  that  is  now  secreted 
remains  free.  In  addition  to  a  certain  amount  of  protein,  small 
quantities  of  soluble  and  easily  diffusible  substances,  like  sugars 
and  some  of  the  organic  crystalline  constituents  of  meat — e.g., 
kreatin — may  also  be  absorbed  into  the  blood  by  the  gastric 
mucous  membrane. 

The  substances  which  reach  the  duodenum  are  :  (1)  The 
greater  part  of  the  fats.  The  partial  digestion  in  the  stomach 
of  the  envelopes  and  protoplasm  of  the  cells  of  adipose  tissue, 
and  of  the  protein  which  keeps  the  fat  of  milk  in  emulsion, 
prepares  the  fats  which  are  not  split  up  by  the  gastric  juice  for 
what  is  to  follow  in  the  intestine.  (2)  All  the  proteins  which 
have  not  been  carried  to  the  stage  of  peptone,  and  much  peptone. 
(3)  All  the  starch  and  dextrins — and  glycogen,  if  any  be  present — 
which  have   not   been   converted  into  sugars,   and  probably  a 


392  .1   MAS  I    II    OF   PHYSIOLOGY 

porti >i  iIh  sugars.     (4)  Elastin,  nucleins,  cellulose,  and  other 

substances  nol  digestible,  or  digestible  only  with  difficulty,  in 
gastric  juice  (5)  The  constituents  <>|  the  gastric  juice  itself, 
including  pepsin.  The  ptyalin  o\  the  saliva  has  been  already 
destroyed, 

It  must  lie  remembered  that  all  this  time,  even  from  the 
beginning  of  digestion,  a  certain  amount  oi  pancreatic  juice  has 
been  finding  its  way  into  the  duodenum  in  response  m  s1  perhaps  to 
the  psychical  excitation,  and  later  to  that  action  of  the  acid  chyme 
on  the  intestinal  mucous  membrane  which  has  been  described. 
In  the  duodenum  its  trypsinogen  is  becoming  activated  to 
trypsin  by  the  enterokinase  of  the  intestinal  juice.  The  s< 
tion  of  bile,  too,  has  quickened  its  pace,  the  gall-bladder  is 
getting  more  and  more  full  as  the  meal  proceeds  and  gastric 
digestion  begins,  and  some  of  the  bile  may  very  soon  escape  into 
the  intestine.  The  pylorus  opens  occasionally  for  a  moment 
whenever  the  small  portions  of  chyme  which  at  this  stage  are 
beginning  to  pass  through  have  been  sufficiently  neutralized  by 
the  pancreatic  juice  and  bile,  although  it  is  not  necessary  that 
the  reaction  should  become  actually  neutral.  When  the  acid 
chyme,  a  greyish  liquid,  turbid  with  the  debris  of  animal  and 
vegetable  tissues — with  muscular  fibres,  fat  globules,  starch 
granules,  and  dotted  ducts — gushes  through  the  pylorus  and 
strikes  the  duodenal  wall,  the  muscular  fibres  of  the  gall-bladder 
contract,  and  sudden  rushes  of  bile  take  place  from  the  common 
duct.  By-and-by,  as  bile  and  pancreatic  juice  continue  to  be 
poured  out,  the  reaction  in  the  duodenum,  as  tested  by  litmus, 
becomes  less  acid  and  even  weakly  alkaline  for  a  time.  But  it 
soon  becomes  acid  again,  and  the  acidity  at  first  increases  as  the 
food  passes  down  the  gut.  In  the  lower  portion  of  the  small 
intestine  the  acidity  diminishes,  and  the  contents  may  be 
neutral  or  actually  alkaline  for  some  distance  above  the  ileo- 
cecal valve.  To  phenolphthalein  the  reaction  is  acid  through- 
out the  whole  intestine.  But  methyl  orange  shows  an  alkaline 
reaction,  all  the  way  from  the  lower  end  of  the  duodenum  to  tin- 
caecum  (Moore  and  Rockwood).  In  the  upper  pari  oJ  the 
duodenum  the  reaction  with  this  indicator  is  sometimes  found 
acid,  but  sometimes  neutral  or  alkaline.  All  this  refers  to  the 
conditions  during  full  digestion  (3  or  4  to  8  or  9  hours  after  the 
taking  of  food).  When  digestion  is  over  (20  to  24  hours  alter  a 
meal)  the  reaction  becomes  acid  to  methyl  orange,  litmus,  and 
phenolphthalein  throughout  the  whole  intestine.*  But  it  must 
be  remembered  that  the  differences  in  true  reaction  at  different 

*  In  r8  dogs  fed  with  meat  20  to  -'4  hours  before  death  this  was  found 
to  be  tin-  case.  In  4  of  the  dogs  the  gastric  contents  were  almost  neutral 
to  litmus  and  methyl  orange,  bu1  slightly  alkaline  to  phenolphthalein  ;  in 

the  re>t  acid  to  all  three  indicators. 


DIG1  STION 

stages  "l  intestinal  digestion  and  at  differenl  levels  oi  the  gul 
are  always  slight.  There  Is  nevera  greal  preponderance  eithei 
oi  hydroxy!  or  of  hydrogen  ions  between  the  point  at  which 
the  pancreatic  juice  and  bile  are  mingled  with  the  gastric  chyme 
.iml  the  lower  part  oi  the  ileum. 

Reaction  of  Intestinal  Contents.  -A  consideration  oi  the  properties 
of  the  indicators  mentioned  enables  us  to  interpret  in  some  measure 
t  hese  results,  which  at  first  sight  appear  so  confusing.    Methyl  orange, 
the  most  stable  of  the  series,  is  not  affected  by  weak  organic  acids,  but 
reacts  acid  to  inorganic,  and  the  stronger  organic  acids  like  lactic, 
acetic  and  butyric  acids,  and  alkaline  to  salts  of  the  weaker  acids, 
Midi  as  sodium  carbonate  and  bicarbonate.      Phenolphthalein  is  very 
sensitive  to  acids,  even  to  weak  organic  acids  such  as  the  fatty  acids 
derived  from  the  fat  of  meat,  and  to  carbonic  acid.      Litmus  is  inter- 
mediate between  methyl  orange  and  phenolphthalein.     The  chyme, 
as  it   passes  through  tie  pylorus,  contains  free  hydrochloric  acid. 
It  mingles  immediately  with  the  alkaline  contents  of  the  duodenum. 
If  these  contain  a  sufficient  quantity  of  bases  to  combine  with  the 
whole  of  the  acids  which  would  affect  methyl  orange,  that  indicator 
will  show  a  neutral  or  alkaline  reaction.     Phenolphthalein  may  at 
the  same  time  react  acid  on  account  of  the  presence  of  weaker  acids, 
including  carbonic  acid,  either  originally  dissolved  in  the  intestinal 
thud  or  liberated  by  the  action  of  the  acids  of  the  chyme  on  the 
carbonates.     If  there  is  not  enough  alkali  to  combine  with  the  whole 
of  the  stronger  acids,  the  reaction  will  be  at  first  acid  to  all  the 
indicators,  but  may  soon  become  alkaline  to  methyl  orange  or  even 
to  litmus,  as  pancreatic  juice  and  bile  continue  to  enter  the  duo- 
denum.    As  the  food  progresses  along  the  intestine  a  certain  amount 
of  lactic  acid  is  produced  by  the  action  of  micro-organisms  on  the 
carbo-hydrates.     The  alkalies  of  the  intestinal  secretions  are  being 
continually  used  up,  both  to  neutralize  this  acid,  and  to  form  soaps 
with  the  fatty  acids  set  free  from  the  fats  by  the  steapsin  and  the 
fat-splitting  bacteria.     The  point  may  easily  be  reached,  and  as  a 
rule  is  reached,  at  which  enough  of  the  weak  acids  or  of  acid  salts 
is  present  to  give  an  acid  reaction  with  phenolphthalein  or  litmus, 
while  the  reaction  is  still  alkaline  to  methyl  orange.     By  the  time 
the  food  has  arrived  at  the  lower  end  of  the  small  intestine  the 
greater  part  of  the  fat-splitting  may  be  supposed  to  be  over,  and  the 
greater  part  of  the  fatty  acids  absorbed.     The  acids  that  remain  may 
be  easily  neutralized  by  the  alkaline  succus  entericus,  reinforced  by 
the  alkalies,  especially  ammonia,  produced  by  the  ordinary  putrefac- 
tive bacteria  from  proteins  ;  and  the  reaction,  previously  alkaline  to 
methyl  orange  only,  may  thus  become  alkaline  to  litmus  as  well. 
Dissolved  carbonic  acid  will  still  account  for  the  acid  reaction  to 
phenolphthalein.     Towards  the  end  of  intestinal  digestion  the  dis- 
charge of  pancreatic  juice,  bile  and  succus  entericus  having  almost  or 
entirely  ceased,  the  acid-forming  bacteria  appear  again  to  get  the 
upper  hand  ;  and  since  the  reaction  is  acid  to  methyl  orange  as  well 
as  to  the  other  indicators,  we  must  assume  that  strong  organic  acids, 
like  lactic  acid,  are  present.     Very  early  in  the  meal  the  inflow  of 
alkaline  pancreatic  juice,  and  perhaps  of  succus  entericus,  into  the 
intestine  begins  ;  and  for  a  considerable  time  this  is  not  counteracted 
bv  the  escape  of  any  large  quantity  of   acid  chyme  through  the 
pylorus.     We  must  accordingly  suppose  that  the  conditions  for  the 
establishment  of  an  alkaline  reaction  of  the  intestinal  contents  are 


194  A    1/  IA  /    \l    OF  PHYSIOLOGY 

unfavourable  .it   the  end  ol  intestinal  digestion,  and  favourable  at 
the  beginning  oi  gasl  ric  digestion. 

rrypsin,  like  pepsin,  performs  its  work  in  pari  in  an  acid 
medium  ;  and  although  the  cause  of  the  acidity  and  the  char- 
actei  "i  the  medium  arc  far  from  being  tin-  same  as  in  tin-  gastric 
juice,  it  is  obviously  an  advantage  thai  the  chiel  proteolytic 
fermenl  should  be  able  to  act  upon  the  proteins  in  all  part-  oi 
the  intestine  and  at  every  stage  oi  intestinal  digestion  whether 
the  reaction  is  acid  or  alkaline.  The  proteins  oi  the  chyme  ar< 
all  carried  by  the  trypsin  to  the  stage  of  peptone,  and  the  peptone, 
or  a  great  part  of  it,  even  in  perfectly  normal  digestion,  is  further 
split  up  into  amino-  and  diamino-acids  by  the  ti  ypsin  and  by  the 
erepsin  of  the  succus  entericus. 

In  the  lower  portions  of  the  small  intestine  bacteria  ol  \  ai  10US 
kinds  are  present  and  active  ;  and  it  is  not  unlikely  thai  even 
throughout  its  whole  length  a  certain  range  o1  action  is  per- 
mitted to  them,  checked  by  the  acidity  of  the  chyme,  though 
scarcely  by  the  feeble  antiseptic  properties  of  the  bile. 

The  lower  end  of  the  small  intestine  is  not  cut  oil  by  any 
bacteria-proof  barrier  from  tin;  large  intestine,  in  which  putre- 
faction is  constantly  going  on.  It  has  been  actually  shown  thai 
small  particles,  such  as  lycopodium  spores,  suspended  in  water, 
soon  reach  the  stomach  when  injected  into  the  rectum.  So 
that  micro-organisms,  aided  by  the  antiperistalsis  of  the  colon, 
may  be  able  to  work  their  way  above  the  ileocolic  sphincter 
and  valve,  even  against  the  downward  peristaltic  movement  of 
the  small  intestine.  But  even  if  this  were  not  the  case,  a  few- 
bacteria  or  their  spores,  passing  through  the  stomach  with  the 
food,  would  be  enough  to  set  up  extensive  changes  as  soon  as  they 
reached  a  part  of  the  alimentary  canal  where  the  conditions  wen 
favourable  to  their  development.  Indeed,  from  the  time  when 
the  first  micro-organism  enters  the  digestive  tube  soon  after  birth, 
it  is  never  tree  from  bacteria  ;  and  their  multiplication  in  one  pari 
of  it  lather  than  another  depends  not  so  much  on  the  number 
01  iginally  present  to  start  the  process,  as  on  the  conditions  which 
encourage  or  restrain  their  increase. 

A  certain  amount  ol  already  emulsified  fats  is  broken  up  into 
then  fatty  acids  and  glycerin  in  the  stomach,  unemulsilied  tats 
entirely  by  the  fat-splitting  fermenl  oi  the  pancreatic  puce.  The 
acids  will  form  soaps  with  alkalies  wherever  they  meet  them  in 
the  intestinal  contents,  or  even  in  the  mucous  membrane.  A 
portion  of  those  soluble  soaps  may  be  immediatelj  absorbed  :  the 
resl  will  aid  in  the  emulsification  of  the  tats  nol  vet  chemically 
decomposed,  and  thus  greatly  hasten  llie  lat -splitting  action  of 
the  pancreatic  juice.  The  starch  and  dextrin  which  have  escaped 
the  action  of  the  saliva  are  changed  into  maltose  by  the  amylopsin. 


DIGESTION  $95 

[Tie  succus  entericus,  in  addition  to  its  importanl  functions 
already  mentioned,  aids  as  an  alkaline  liquid  in  lessening  the 
acidit}  ol  the  chyme  and  establishing  the  reaction  favourable  to 
intestinal  digestion,  h  will  invert  any  cane-sugar,  maltose,  or 
lactose,  which  may  reach  the  intestine  ;  bul  it  cannol  be  doubted 
ih.it  some  cane-sugar  may  be  absorbed  by  the  stomach,  after 
being  inverted  by  the  hydrochloric  acid  of  the  gastric  juice  or  by 
inverting  ferments  taken  in  with  the  food,  or  on  its  way  through 
the  gastric  walls. 

Upon  the  whole  no  greal  amount  of  water  is  absorbed  in  the 
small  intestine,  or  at  least  the  loss  is  balanced  by  the  gain,  for 
the  intestinal  contents  are  as  concentrated  in  the  duodenum  as 
in  the  ileum.  But  as  soon  as  they  pass  beyond  the  ileo-caecal 
valve  water  is  rapidly  absorbed,  and  the  contents  thicken  into 
normal  faeces,  to  which  the  chief  contribution  of  the  large  intestine 
is  mucin,  secreted  by  the  vast  number  of  goblet  cells  in  its 
Lieberkuhn's  crypts. 

Bacterial  Digestion. — So  far  we  have  paid  no  special  atten- 
tion to  other  than  the  soluble  ferments  of  the  digestive  tract, 
although  we  have  incidentally  mentioned  the  action  of  the  lactic 
acid  bacilli  on  carbo-hydrates  and  of  the  fat-splitting  bacteria 
'  on  fats.  It  is  now  necessary  to  recognise  that  the  presence  of 
bacteria  is  an  absolutely  constant  feature  of  digestion  ;  and 
although  their  action  must  in  part  be  looked  upon  as  a  necessary- 
evil  which  the  organism  has  to  endure,  and  against  the  conse- 
quences of  which  it  has  to  struggle,  it  is  not  unlikely  that  in 
part  it  may  be  ancillary  to  the  processes  of  aseptic  digestion. 
But  bacteria  are  not  essential  (in  mammals,  at  any  rate,  living 
on  milk),  as  some  have  supposed.  For  it  has  been  shown 
that  a  young  guinea-pig,  taken  by  Cesarean  section  from  its 
mother'^  uterus  with  elaborate  aseptic  precautions,  and  fed  in  an 
aseptic  space  on  sterile  milk,  grew  apparently  as  fast  as  one  of 
its  sisters  brought  up  in  the  orthodox  microbic  way.  The 
alimentary  canal  remained  free  from  bacteria  (Nuttall  and 
Thierfelder).  On  the  other  hand,  chickens  hatched  from  sterile 
eggs  and  kept  in  a  sterile  enclosure  lived,  indeed,  for  a  time, 
but  did  not  thrive  in  comparison  with  the  control  animals,  and 
died  at  latest  after  eighteen  days  (Schottelius).  It  is  probable 
that  the  difference  in  the  results  is  to  be  attributed  to  the 
difference  in  the  food,  purely  vegetable  food  requiring  the  aid  of 
bacteria  for  its  proper  digestion,  while  an  easily-digestible  food 
like  milk  does  not. 

Among  the  more  important  actions  of  bacteria  on  the  protein 
food-products  in  the  intestines  may  be  mentioned  the  formation 
of  indol,  phenol,  and  skatol,  the  first  having  tyrosin  for  its  pre- 
cursor,  and  being  itself  after  absorption  the  precursor  of  the 


196  .'   MANU  //.  OF  PHYSI01  OG  1 

'  indican  '  in  the  urine  ;  the  second  being  t<>  a  small  extent 
thrown  out  with  the  laces,  hut  chiefly  absorbed  and  eliminated 
by  the  kidneys  as  an  aromatic  compound  of  sulphuric  acid  ;  the 
third  passing  out  mainly  in  the  faeces. 

The  large  intestine  is  the  chosen  haunt  of  the  bai  teria  of  the 
alimentary  canal  ;  they  swarm  in  the  faeces,  and  by  their  influ- 
ence, especially  in  the  aecum  of  herbivora,  but  also  to  a  small 
extent  in  man,  even  cellulose  is  broken  up,  the  final  products 
being  carbon  dioxide  and  marsh  gas.  A  cellulose-dissolving 
enzyme  of  great  activity  is  present  in  the  hepatic  '-•net ion  of 
the  snail,  which  rapidly  produces  sugar  from  cellulose.  Bu1 
in  herbivorous  mammals  no  such  ferment  has  been  found  ;  and 
although  cellulose  can  be  split  up  by  bacteria  in  their  intestines, 
sugar  is  not  among  the  products.  In  this  case  the  cellulose 
makes  only  an  insignificant  contribution  to  the  metabolism  of 
the  animal.  The  contents  of  the  large  bowel  are  generally  acid 
from  the  products  of  bacterial  action,  although  the  wall  itself  is 
alkaline. 

Faeces. — In  addition  to  mucin,  secreted  mainly  by  the  large 
intestine,  the  faeces  consist  of  indigestible  remnants  of  the  food, 
such  as  elastic  fibres,  spiral  vessels  of  plants,  and  in  general  all 
vegetable  structures  chiefly  composed  of  cellulose.  They  are 
coloured  with  a  pigment,  stercobilin,  derived  from  the  bile-pig- 
ments. Stercobilin  is  identical  with  urobilin,  which  forms  a 
common,  though  not  an  invariable,  constituent  of  bile  itself.  A 
portion  of  it  is  absorbed  by  the  intestine  and  then  excreted  in 
the  urine,  the  urobilin  in  which  is  often  much  increased  in  fe\  ei 
('  febrile  '  urobilin).  No  bilirubin  or  biliverdin  occurs  in  normal 
faeces,  although  pathologically  they  may  be  present.  The  dark 
colour  of  the  faeces  with  a  meat  diet  is  due  to  haematin  and  sulphide 
of  iron,  the  latter  being  formed  by  the  action  of  the  sulphuretted 
hydrogen  which  is  constantly  present  in  the  large  intestine  on  the 
organic  compounds  of  iron  contained  in  the  food  or  in  the  secre- 
tions of  the  alimentary  canal.  A  small  amount  of  altered  bile- 
acids  and  their  products  is  also  found  ;  and  in  respect  to  these, 
and  to  the  altered  pigments,  bile  is  an  excretion.  And  although 
its  entrance  into  the  upper  instead  of  the  lower  end  of  the  in- 
testine, the  ascertained  importance  of  its  function  in  digestion, 
and  the  fact  that  the  greater  part  of  the  bile-salts  is  reabsorbed, 
show  that  in  the  adult  it  is  very  far  from  being  solely  a  waste 
product,  the  equally  cogent  fact,  that  the  intestine  of  the  new- 
born child  is  filled  with  what  is  practically  concentrated  bile 
(meconium),  proves  that  it  is  just  as  far  from  being  purely  a 
digestive  juice.  Skatol  and  other  bodies,  formed  by  putrefactive 
changes  in  the  proteins  of  the  food,  are  also  present  in  the  taeces, 
and  are  responsible  for  the  faecal  odour.     Masses  of  bacteria  are 


DIGESTION 


397 


invariably  present,  and  often  make  up  a  very  considerable  pro- 
portion of  the  total  faecal  solids.  Of  the  inorganic  substances  in 
faeces  the  numerous  crystals  of  triple  phosphate  are  the  most 
characteristic.  When  the  diet  is  too  large,  or  contains  too  much 
of  a  particular  kind  of  food,  a  considerable  quantity  of  digestible 
material  may  be  found  in  the  faeces — e.g.,  muscular  fibres  and 
fat.  But  it  should  be  remembered  that  under  all  circumstances 
the  composition  of  the  faeces  differs  from  that  of  the  food.  The 
intestinal  contribution  is  always  an  important  one,  although 
relatively  more  important  with  a  flesh  than  with  a  vegetable 
diet.  The  xanthin  or  purin  bases  normally  found  in  human 
faeces  come  both  from  the  food  directly  and  from  the  metabolism 
ni  the  tissues.  They  are  increased  in  amount  on  a  diet  rich  in 
purin  bodies  (such  as  meat  extract  or  thymus),  but  are  also 
formed  on  a  diet  like  milk,  from  which  xanthin  bases  cannot  be 
obtained. 


CHAPTER  V 
ABSORPTION 

Physical  Introduction. — Imbibition,  or  molecular  imbibition,  is  the 
term  applied  to  the  entrance  of  liquid  into  a  colloid,  without  the  loss 
of  its  properties  as  a  solid,  when  no  preformed  capillary  spaces  are 
present.  The  entrance  of  water  into  a  piece  of  gelatin,  or  an  epi- 
dermic scale,  is  an  example  of  molecular  imbibition.  Most  animal 
and  vegetable  tissues  possess  this  property,  which  is  believed  to  be 
of  importance  in  such  physiological  processes  as  absorption,  secretion, 
and  the  excretion  of  water  from  the  lungs  and  skin.  The  process  by 
which  liquid  passes  into  a  solid  with  preformed  capillary  spaces — 
e.g.,  a  sponge — is  sometimes  spoken  of  as  capillary  imbibition. 

Diffusion.  -When  a  solution  of  a  substance  is  placed  in  a  vessel, 
and  a  layer  of  water  carefully  run  in  on  the  top  of  it,  it  is  found 
after  a  time  that  the  dissolved  substance  has  spread  itself  through 
the  water,  and  that  the  composition  of  the  mixture  is  uniform 
throughout.  The  result  is  the  same  when  two  solutions  containing 
different  proportions  of  the  same  substance,  or  containing  different 
substances,  are  placed  in  contact.  The  phenomenon  is  called 
diffusion.  The  time  required  for  complete  diffusion  is  comp 
tively  short  in  the  case  of  a  substance  like  hydrochloric  acid  or 
sodium  chloride,  exceedingly  long  in  the  case  of  albumin  or  gum.  In 
both  it  is  more  rapid  at  a  high  temperature  than  at  a  low. 

Osmosis. — If  the  solution  be  separated  from  water  by  a  membrane 
absolutely  or  relatively  impermeable  to  the  dissolved  substance,  but 
permeable  to  water,  water  passes  through  the  membrane  into  the 
solution.  This  phenomenon  is  called  osmosis.  E.g.,  a  membrane  of 
ferrocyanide  of  copper,  nearly  impermeable  to  cane-sugar,  can  be 
formed  in  the  pores  of  an  unglazed  porcelain  pot  by  allowing  potas- 
sium ferrocyanide  and  cupric  sulphate  to  come  in  contact  there.  If 
the  pot  is  filled  with,  say,  a  i  per  cent,  solution  of  cane-sugar,  closed 
by  a  suitable  stopper,  connected  to  a  manometer,  and  then  placed  in 
a  vessel  of  water,  water  passes  into  it  till  the  pressure  indicated 
by  the  manometer  rises  to  a  certain  height.  With  a  2  per  cent, 
solution  it  reaches  twice  this  height,  and  in  general  the  osmotic 
pressure,  as  it  is  called,  is  in  any  solution  proportional  to  the  mole- 
cular concentration*  of  the  solution,  or,  in  other  words,  to  the 
number  of  molecules  of  the  dissolved  substance  in  a  given  volume  of  the 
solution.    If  in  this  sentence  we  substitute  '  gaseous  pressure '  for  '  os- 

*  The  molecular  concentration  is  strictly  defined  as  the  number  of 
grammes  of  the  dissolved  substance  in  a  litre  of  the  solution  divided  by 
the  gramme-molecular  weight.  The  gramme-molecular  weight,  or 
gramme-molecule,  is  the  number  of  grammes  corresponding  to  the  mole- 
cular weight.  Thus,  the  gramme-molecular  weight  of  sodium  chloride 
(Nad)  is  58*36  grammes,  ami  of  cane-sugar  (Cj-.H.^Oj,),  342  grammes. 

398 


IBS0RP7  TON 


399 


D 


in.  >ti.  pressure,'  and  '  gas  'for'solution,'  we  have  a  statement  of  Boyle' 
law,  win*  li  asserts  thai  the  pressure  of  a  ^1S  's  proportional  to  its  den- 
sity. Indeed,  it  lias  been  shown  thai  the  osmotii  pressure  oi  the 
dissolved  substance  is  the  same  as  the  pressure  thai  would  be  exerted  by 
.1  gas,  say  hydrogen,  if  all  the  water  were  removed,  and  a  molei  ule  "! 
hydrogen  substituted  Eoi  each  molecule  of  the  substance,  or  as  would  be 
exerted  by  the  substance  itseb  ii,  after  removal  of  the  solvent,  ii  eon  Id 
be  left  as  a  gas  filling  the  same  volume.  And  the  osmol  u 
pressured  a  solution  of  one  substance  is  the  same  as 
that  of  a  solution  of  any  other  substance  which  con- 
tains in  a  given  volume  the  same  number  of  mole- 
cules of  the  dissolved  substance.  In  other  words,  the 
osmotic  pressure  is  not  dependent  on  the  nature,  but 
on  the  molecular  concentration,  of  the  substance.  The 
analogy  of  the  laws  of  osmotic  to  those  of  gaseous  pres- 
sure becomes  still  more  obvious  when  it  is  added  that 
the  osmotic  pressure  of  a  substance  with  any  given 
molecular  concentration  is  proportional  to  the  absolute 
temperature;  and  that  when  a  solution  contains  more 
than  one  dissolved  substance  the  total  osmot  ic  pressure 
is  the  sum  of  the  partial  osmotic  pressures 
which  each  substance  would  exert  if  it  were 
present  alone  in  the  same  volume  of  the  solution. 

The  osmotic  pressure  of  a  solution  may  reach 
an  enormous  amount.  Thus,  a  i  per  cent,  solu- 
tion of  cane-sugar  has  a  pressure  at  o°  C.  of 
493  mm.  of  mercury.  A  io  per  cent,  solution 
of  cane-sugar  would  have  an  osmotic  pressure  of 
more  than  six  atmospheres,  and  a  17  per  cent, 
solution  of  ammonia  a  pressure  of  no  less  than 
224  atmospheres.  The  manner  in  which  the 
phenomenon  known  as  osmotic  pressure  is  de- 
veloped is  not  definitely  known.  One  theory 
attributes  it  to  the  attraction  between  the 
dissolved  molecules  and  the  molecules  of  the 
solvent  on  the  other  side  of  the  membrane. 
The  most  commonly  accepted  view  is  that  the 
osmotic  pressure  is  due  to  the  kinetic  energy 
of  the  moving  molecules.  Where  the  mole- 
cules are  hindered  from  passing  a  bounding 
membrane,  the  pressure  exerted  by  their  im- 
pacts on  the  boundary  is  greater  than  where 
the  membrane  is  easily  permeable,  because  in 
the  latter  case  many  of  the  molecules  pass 
through,  carrving  with  them  their  kinetic 
energy.  The  pressure  must  be  still  less  when 
a  dissolved  substance  diffuses  freely  into 
water  ;  but  however  small  it  may  become,  it  is  in  the  same  force  which 
gives  rise  to  the  osmotic  pressure  of  the  molecules  of  the  dissolved  sub- 
stance that  the  cause  of  diffusion  must  be  sought.  Recently  interest 
in  the  nature  of  the  membrane  itself  as  an  important  factor  in  osmosis 
has  been  revived  (Kahlenberg,  Armstrong,  etc.).  There  are  many  facts 
which  indicate  that  in  physiological  processes  the  affinity  of  the  dissolved 
substances  for,  or  their  solubility  in,  the  cell  envelopes  or  the  cytoplasm 
plays  an  important  role. 

It  is  as  yet  impossible  to  directly  measure  the  osmotic  pressure  with 
accuracy  by  means  of  a  semi-permeable  membrane  like  ferrocyanide  of 


Fig.  153. — Beckmann's 
Apparatus. 

For  description,  see 
p.  492. 


400  A   MANUAL  OF  PHYSIOLOGY 

copper.  Recourse  is  therefore  had  to  indirect  methods,  especially  one 
which  depends  on  the  fact  that  the  freezing-point  of  a  solution  is  lower 
than  that  of  the  solvent,  salt  water,  e.g.,  freezing  at  a  lower  temperature 
than  fresh  water.  The  amount  by  which  the  freezing-point  is  lowered 
depends  on  the  molecular  concentration  of  the  dissolved  substance,  to 
which,  as  we  have  seen,  the  osmotic  pressure  is  also  proportional.  When 
a  gramme-molecule  of  a  substance  is  dissolved  in  water,  and  the  volume 
made  up  to  a  litre,  the  freezing-point  is  lowered  by  1860  C. ;  the  osmotic 
pressure  is  22-35  atmospheres  (16,986  mm.  of  mercury).  It  is  therefore 
easy  to  calculate  the  osmotic  pressure  of  any  solution  if  we  know  the 
amount  by  which  its  freezing-point  is  lowered.  A  1  per  cent,  solution  of 
cane-sugar,  for  example,  would  freeze  at  about  -  0-054°  C.     ^ts  osmotic 

pressure  =  -  iff  x  16,986  =  493  mm.  of  mercury. 

A  convenient  apparatus  for  making  freezing-point  measurements 
is  shown  in  Fig.  153.  The  details  of  the  method  are  given  in  the 
Practical  Exercises,  p.  492. 

The  osmotic  pressure  of  different  solutions  may  also  be  compared 
by  observing  the  effect  produced  on  certain  vegetable  and  animal 
cells.  When  a  solution  with  a  greater  osmotic  pressure  than  the 
cell-sap  (a  hyperisotonic  solution)  is  left  for  a  time  in  contact  with 
certain  cells  in  the  leaf  of  Tradescantia  discolor,  plasmolysis  occurs — 
that  is,  the  protoplasm  loses  water  and  shrinks  away  from  the  cell- 
wall.  If  the  osmotic  pressure  of  the  solution  is  lower  than  that  of 
the  coloured  cell-sap  (hypoisotonic  solution),  no  shrinking  of  the 
protoplasm  takes  place.  By  using  a  number  of  solutions  of  the  same 
substance  but  of  different  strength,  two  can  be  found,  the  stronger  of 
which  causes  plasmolysis,  and  the  weaker  not.  Between  these  lies 
the  solution  which  is  isotonic  with  the  cell-sap — that  is,  has  the  same 
molecular  concentration  and  osmotic  pressure.  The  strengtn  of  an 
isotonic  solution  of  some  other  substance  can  then  be  determined  in 
the  same  way  with  sections  from  the  same  leaf. 

Animal  cells  (red  blood-corpuscles)  may  also  be  employed,  the 
liberation  of  haemoglobin  or  the  swelling  of  the  corpuscles,  as 
measured  by  the  hasmatocrite  (p.  59),  being  taken  as  evidence  that 
the  solution  in  contact  with  them  is  hypoisotonic  to  the  contents  of 
the  corpuscles.  Here  we  may  suppose  that  the  impacts  of  the 
molecules  of  the  salts  of  the  corpuscle  on  the  inside  of  its  envelope, 
not  being  balanced  by  similar  impacts  on  the  outside,  tend  to 
distend  it,  and  thus  to  create  a  potential  vacuum  for  the  surrounding 
water,  which  accordingly  enters.  If  the  corpuscles  shrink,  the  solution 
is  hyperisotonic  to  their  contents.  But  since  the  cells  are  much  more 
permeable  to  certain  substances  than  to  others,  this  method  does  not 
always  yield  trustworthy  results. 

Electrolytes. — We  have  said  that  the  osmotic  pressure  is  propor- 
tional to  the  concentration  of  the  solution,  but  this  statement  must 
now  be  qualified.  For  certain  compounds,  including  all  inorganic 
salts  and  many  organic  substances,  the  osmotic  pressure  decreases 
less  rapidly  than  the  theoretical  molecular  concentration  as  the 
solution  is  diluted.  The  explanation  is  that  in  solution  some  of 
the  molecules  of  these  bodies  are  broken  up  into  simpler  groups 
or  single  atoms,  called  ions.  Each  ion  exerts  the  same  osmotic 
pressure  as  the  molecule  did  before.  The  proportion  between  the 
average  number  of  these  dissociated  molecules  and  of  ordinary 
molecules  is  constant  for  a  given  concentration  of  the  solution  and  a 
given  temperature.     But  as  the  solution  is  diluted,  the  proportion  of 


ABSORPTION  4oi 

k  Lated  molecules  becomes  greater.  The  bodies  which  behavi  in 
this  way  arc  electrolytes  thai  is,  their  solutions  conduct  a  current  of 
electricity  ;  bodies  which  do  not  exhibit  this  behaviour  do  not  con- 
du<  t  in  solution.  And  there  are  many  reasons  for  believing  that  the 
dissociation  of  the  electrolytes  is  the  essential  thing  in  electrolytic 
conduction.  We  may  suppose  that  in  a  solution  of  an  electrolyte — 
sodium  chloride,  for  instance — a  certain  number  of  the  molecules 
fall  asunder  into  a  kation  (Na),*  carrying  a  charge  of  positive  elec- 
tricity, and  an  anion  (CI),  carrving  an  equal  negative  charge.  These 
electrical  charges,  it  must  be  remembered,  are  not  created  by  the 
passage  of  a  current  through  the  solution.  We  do  not  know  how 
they  arise,  but  the  ions  must  be  supposed  to  be  electrically  charged 
at  the  moment  when  the  molecule  is  broken  up.  And  the  ions  of 
different  substances  must  each  be  supposed  to  carry  the  same 
quantity  of  electricity.  But  since  they  are  all  wandering  freely  in 
t  he  solution,  no  excess  of  negative  or  of  positive  electricity  can 
accumulate  at  any  part  of  it — in  other  words,  no  difference  of  poten- 
tial can  exist.  When  electrodes  connected  with  a  voltaic  battery 
are  dipped  into  a  solution  of  an  electrolyte,  a  difference  of  potential, 
an  electrical  slope,  is  established  in  the  liquid,  and  the  positively 
charged  kations  are  compelled  to  wander  towards  the  negative  pole, 
the  negativelv  charged  anions  towards  the  positive  pole.  In  this 
way  that  movement  of  electricity  which  is  called  a  current  is  main- 
tained in  the  solution.  It  is  clear  that  the  greater  the  number  of 
ions,  and  the  faster  they  move  in  the  solution,  the  greater  will  be 
the  quantity  of  electricity  carried  to  the  electrodes  in  a  given  time, 
when  the  difference  of  potential  between  the  electrodes,  or  the 
steepness  of  the  electric  slope,  remains  constant.  In  other  words, 
the  specific  conductivity  of  a  solution  of  an  electrolyte  varies  as  the 
number  of  dissociated  molecules  in  a  given  volume  and  the  speed  of 
the  ions.  It  increases  up  to  a  certain  point  with  the  concentration, 
because  the  absolute  number  of  dissociated  molecules  in  a  given 
volume  increases.  The  molecular  conductivity — that  is,  the  conduc- 
tivity per  molecule,  or,  strictly,  the  ratio  of  the  specific  conductivity 
to  the  molecular  concentration,  increases  with  the  dilution,  because 
the  relative  number  of  dissociated  molecules,  as  compared  with  un- 
dissociated,  increases.  At  a  certain  degree  of  dilution  the  molecular 
conductivity  reaches  its  maximum,  for  all  the  molecules  are  dissoci- 
ated. The  ratio  of  the  molecular  conductivity  of  any  given  solution 
to  this  maximum  or  limiting  value  is  therefore  a  measure  of  the  pro- 
portion between  the  number  of  dissociated,  and  the  total  number 
of  molecules.  The  molecular  conductivity  of  the  salts  dissolved  in 
the  liquids  of  the  animal  body,  for  the  degree  of  dilution  in  which  they 
exist  there,  is  such  that  we  must  assume  them  to  be  for  the  most  part 
dissociated. 

Absorption  of  the  Food. — In  the  preceding  chapter  we  have 
traced  the  food  in  its  progress  along  the  alimentary  canal,  and 
sketched  the  changes  wrought  in  it  by  digestion.  We  have 
next  to  consider  the  manner  in  which  it  is  absorbed.  Then,  for 
a  reason  which  has  already  been  explained,  instead  of  following 
its  fate  within  the  tissues,  until  it  is  once  more  cast  out  of  the 

*  J.  J.  Thomson  has  shown  that  the  chemical  atoms  must  be 
assumed  to  consist  of  smaller  corpuscles  or  particles  of  electricity 
called  electrons. 

26 


4'  '-' 


A    M  KM   .11.   OF   PHYSIOLOGY 


body  in  the  form  of  waste  products,  it  will  be  best  to  drop  the 
logical  order  and  pick  up  the  other  end  of  the  clue — in  other 
words,  to  pass  from  absorption  to  excretion,  from  the  first  step 
in  metabolism  to  the  closing  act,  and  afterwards  to  return  and 
fill  in  the  interval  as  best  we  can. 

Comparative. — And  here,  first  of  all,  it  should  be  remembered  that 
the  epithelial  surfaces,  through  which  the  substances  needed  by  the 
organism  enter  it,  and  waste  products  leave  it,  are,  physiologically  con- 
sidered, outside  the  body.  The  mucous  membranes  of  the  alimentary, 
respiratory,  and  urinary  tracts  are  in  a  sense  as  much  external  as  the 
fourth  great  division  of  the  physiological  surface,  the  skin.  The  two 
latter  surfaces  are  in  the  mammal  purely  excretory.  Absorption  is 
the  dominant  function  of  the  alimentary  mucous  membrane,  but  a 
certain  amount  of  excretion  also  goes  on  through  it.  The  pulmonary 
surface  both  excretes  and  absorbs,  and  that  in  an  equal  measure. 
But  it  is  by  no  means  necessary  that  the  surface  through  which 

oxgyen  is  taken  in  and  gaseous 
waste  products  given  off  should  be 
buried  deep  in  the  body,  and  com- 
municate onlv  bv  a  narrow  channel 
with  the  exterior.  In  the  frog  the 
skin  is  largely  an  absorbing  as  well 
as  an  excreting  surface ;  oxygen 
passes  freely  in  through  it,  just  as 
carbon  dioxide  passes  freely  out 
In  most  fishes,  and  many  other  gill- 
bearing  animals,  the  whole  gaseous 
interchange  takes  place  through 
surfaces  immersed  in  the  surround- 
ing water,  and  therefore  distinctly 
external.  In  certain  forms  it  has 
even  been  shown  that  the  aliment- 
tary  canal  may  serve  conspicuously 
for  absorption  and  excretion  of 
gaseous,  as  well  as  liquid  and  solid 
substances.  Still  lower  down  in 
the  animal  scale,  the  surface  of  a 
single  tube  may  perform  all  the 
functions  of  digestion,  absorption 
and  excretion.  Lower  still,  and 
even  this  tube  is  wanting,  and 
everything  passes  in  and  out 
through  an  external  surface  pierced  by  no  permanent  openings. 

Indeed,  even  in  man  the  functions  of  the  various  anatomical 
divisions  of  the  physiological  surface  are  not  quite  sharply  marked  off 
from  each  other.  Though  gaseous  interchange  goes  on  far  more 
readily  through  the  pulmonary  membrane  than  anywhere  else, 
swallowed  oxygen  is  easily  enough  absorbed  from  the  alimentary 
canal  and  carbon  dioxide  given  off  into  it  ;  and  to  a  small  extent 
these  gases  can  also  pass  through  the  skin.  Though  water  is  excr< 
chieflv  by  the  skin,  the  pulmonary  and  the  urinary  surfaces,  and  on 
the  whole  absorbed  chieflv  from  the  digestive  tract,  there  is  no  surface 
which  in  the  twenty-four  hours  pours  out  so  mu:h  water  as  the 
mucous  membrane  of  the  stomach.  Under  normal  conditions,  it 
is  true,  by  far  the  greater  part  of  this  is  reabsorbed  in  the  intestine, 


Fig.     ij|. — Diagram    of    Absorp- 
tion and  Excretion-. 

Carbon  c,  nitrogen  n,  hydrogen  h, 
and  oxygen  o.  L  represents  the  pul- 
monary surface  ;  K,  the  surface  of 
the  renal  epithelium  ;  A,  the  ali- 
mentary canal  ;  S,  the  skin. 


ABSORPTION  403 

j  1  1  in  diarrhoea,  whethei  nal  ural  or  caused  by  purgatives,  the  intes- 
tines  themselves  may,  instead  of  absorbing,  contribute  largely  to  the 
1  11011  ol  water.  Again,  although  the  solids  of  the  excreta  arc 
normally  given  oil  in  far  the  greatest  quantity  in  the  urine  and  fae<  1 
(only  part  of  the  latter  is  truly  an  excretion,  since  much  of  the  faxes 
,.t  .1  mixed  diet  has  never  been  physiologically  inside  the  body  at  all), 
yet  salts  and  traces  ol  urea  are  constantly  found  in  the  sweat,  and 
salts  and  mucin  in  the  excretions  of  the  respiratory  tract.  Further, 
although  the  solids  and  liquids  of  the  food  are  usually  taken  in  by 
the  alimentary  mucous  surface,  it  is  possible  to  cause  substances  of 
both  kinds  to  pass  in  through  the  skin  ;  and  a  certain  amount  of 
absorption  may  also  take  place  through  the  urinary  bladder.  So 
that  really  it  may  be  considered,  from  a  physiological  point  of  view, 
as  more  or  less  an  accident  that  a  man  should  absorb  his  food  by 
dipping  the  villi  of  his  intestine  into  a  digested  mass,  rather  than 
by  dipping  his  fingers  into  properly  prepared  solutions,  as  a  plant 
dips  its  roots  among  the  liquids  and  solids  of  the  soil  ;  or  that  he 
should  draw  air  into  organs  lying  well  in  the  interior  of  his  thorax, 
instead  of  letting  it  play  over  special  thin  and  highly  vascular 
portions  of  his  skin  ;  or  that  the  surface  by  which  he  excretes  urea 
should  be  buried  in  his  loins,  instead  of  lying  free  upon  his  back. 

It  has  been  already  explained  that,  although  digestion  is  a 
necessary  preliminary  to  the  absorption  of  most  of  the  solids  of 
the  food,  we  are  not  to  suppose  that  all  the  food  must  be  digested 
before  any  of  it  begins  to  be  absorbed.  On  the  contrary,  the 
two  processes  go  on  together.  As  soon  as  any  peptone,  or,  at 
least,  any  amino-acids,  have  been  formed  from  the  proteins,  or 
any  dextrose  from  the  starch,  they  begin  to  pass  out  of  the 
alimentary  canal  ;  and  by  the  time  digestion  is  over,  absorption 
is  well  advanced. 

Even  in  the  mouth  it  has  already  begun,  although  the  amount 
of  absorption  here  is  quite  insignificant,  and  it  is  continued  with 
greater  rapidity  in  the  stomach.  Here  a  not  inconsiderable 
part  of  the  proteins — at  least,  in  the  easily  digested  form  of 
animal  food — a  certain  amount  of  the  sugar  representing  the 
carbo-hydrates  and  diffusible  substances  like  alcohol,  and  the 
extractives  of  meat,  which  form  an  important  part  of  most  thin 
soups  and  of  beef-tea,  are  undoubtedly  absorbed.  Water  is 
very  sparingly  taken  up  by  the  stomach.  It  is  in  the  small 
intestine  that  absorption  reaches  its  height.  The  mucous  mem- 
brane of  this  tube  offers  an  immense  surface,  multiplied  as  it  is 
by  the  valvulae  conniventes,  and  studded  with  innumerable 
villi.  Here  the  whole  of  the  fat,  much  sugar,  proteose  and 
peptone,  or  rather  the  products  of  the  further  action  of  the 
ferments  of  the  intestine  on  these  derivatives  of  the  native 
proteins,  and  certain  constituents  of  the  bile  are  taken  in. 
In  the  large  intestine,  as  has  been  already  said,  water  and 
soluble  salts  are  chiefly  absorbed. 

What  now  is  the  mechanism  by  which  these  various  products 

26 — 2 


> 


404  A    MAh  i    II    OF    PHYSIOLOG  Y 


are  taken  up  from  the  digestive  tube,  and  what  paths  do  they 
follow  on  their  way  to  the  tissues  ? 

Theories  of  Absorption. — Not  so  very  long  ago  it  was  supposed  by 
many  that  the  processes  of  diffusion,  osmosis  and  filtration  offen 

tolerably  complete  explanation  of  physiological  absorption.  At  thai 
time  the  dominant  note  of  physiology  was  an  eager  appeal  to 
chemistry  and  physics  to  '  come  over  and  help  it  ';  and  as  new  I 
were  discovered  in  these  sciences  they  were  applied,  with  .1  1  onfidence 
t  hat  was  almost  naive,  to  the  problems  of  the  animal  organism.  The 
phenomena  of  the  passage  of  liquids  and  dissolved  solids  through 
animal  membranes,  upon  which  the  work  of  Graham  had  cast  so 
much  light,  seemed  to  find  their  parallel  in  the  absorptive  processes 
of  the  alimentary  canal.  And  when  digestion  was  more  deeply 
studied,  facts  appeared  which  seemed  to  show  that  its  whole  drill 
was  to  increase  the  solubility  and  diff usability  of  the  constituents  of 
the  food.  But  as  time  went  on,  and  more  was  learnt  of  the  pheno- 
mena of  absorption  and  the  powers  of  cells,  these  crude  physical 
theories  broke  down,  and  discarded  '  vitalistic  '  hypotheses  began 
once  more  to  arouse  attention.  Then  came  the  investigations 
of  De  Vries,  Van  'T  Hoff,  and  others  in  the  domain  of  molecular 
physics,  which  gave  to  our  notions  of  osmosis  the  precision  that  was 
wanted  before  its  relation  to  many  physiological  processes  could  be 
profitably  discussed.  At  the  present  time  it  must  be  admitted  that 
we  possess  no  explanation  of  absorption  which  is  more  than  a  con- 
fession of  ignorance,  and  does  not  itself  need  to  be  explained.  Some 
physiologists,  impressed  with  the  vast  progress  of  physics  and 
chemistry,  believe  that  it  will  eventually  become  possible  to  explain 
on  mechanical  and  chemical  principles  all  the  peculiar  phenomena 
which  we  observe  in  the  passage  of  substances  through  the  walls  of 
the  alimentary  canal.  Others,  taking  account  of  the  number  and 
nature  of  these  peculiarities,  oppressed  with  the  perennial  paradox 
of  vital  action,  incline  to  the  less  sanguine  view,  that  after  all 
physical  explanations  have  been  exhausted,  the  real  secret  of  the 
cell  will  still  lurk  in  some  ultimate  '  vital  '  property  of  structure  or 
of  function,  and  still  elude  our  search.  Both  the  optimist  and  the 
pessimist,  the  adherent  of  the  physical  and  the  adherent  of  the 
vitalistic  hypothesis,  admit  that  the  phenomena  of  absorption  are 
essentially  connected  with  the  cells  that  line  the  alimentary  canal. 
But  the  one  must  confess  what  the  other  proclaims,  that  while  the 
processes  carried  on  in  these  cells  are  definite,  well  ordered,  and 
evidently  guided  by  laws,  these  laws  have  as  yet  denied  themselves 
to  the  modern  physiologist,  with  chemistry  in  one  hand  and  physics 
in  the  other,  as  they  denied  themselves  to  his  predecessor,  equipped 
only  with  his  scalpel,  his  sharp  eyes,  and  his  mother-wit.  So  that 
in  the  present  state  of  our  knowledge  all  we  can  really  say  is  that. 
while  absorption  is  certainly  aided  by  physical  processes,  like-  osmosis 
and  diffusion,  possibly  by  physical  processes  like  imbibition,  it  is  at 
bottom  the  work  of  cells  with  a  selective  power  which  we  do  not 
understand.  Thus,  dissolved  substances  pass  with  equal  ease  in 
either  direction  through  an  ordinary  diffusion  membrane,  but  in 
general  they  pass,  with  the  water  in  which  they  are  dissolved,  more 
readily  out  of  the  intestine  than  into  it.  This  normal  direction  of 
the  stream  is  still  maintained  for  a  considerable  time  after  stoppage 
of  the  circulation,  provided  that  the  intestine  is  kepi  in  good  con- 
dition  by   being  suspended   in    well-.oxygenated   blood.     Water   or 


IBSORPTION  405 

solutions  of  sodium  chloride  or  sugar  disappear  from  the  Lumen. 
\  1 1 . 1  this  is  not  due  to  mere  imbibition  by  the  intestinal  wall,  but 
1  lie  liquid  is  actually  transported  across  it.  The  theory  that  liquids 
might  betaken  up  from  the  gu1  l>v  imbibition,  and  the  water  then 
mechanically  removed  by  the  blood  flowing  on  the  other  side  of  the 
imbibing  cells,  is  incompatible  with  this  experiment  (Cohnheim). 
When  the  cells  thai  line  the  intestine  are  injured  or  destroyed,  or 
subjected  to  the  action  of  certain  poisons,  absorption  from  it  is 
diminished  or  abolished.  And  in  their  normal  state  they  do  not  take 
up  indiscriminately  all  kinds  of  diffusible  substances,  or  absorb 
those  which  they  do  take  up  in  the  direct  ratio  of  their  diffusibility. 
Nor  do  they  reject  everything  which  does  not  diffuse.  Albumin,  for 
example,  which  does  not  pass  through  dead  animal  membranes,  is  to 
a  certain  extent  taken  up  from  a  loop  of  intestine  without  change. 
Cane-sugar  (after  inversion)  and  dextrose  are  absorbed  more  rapidly 
than  their  velocity  of  diffusion  would  indicate,  when  compared  with 
inorganic  salts.  Glauber's  salt  diffuses  in  water  fifteen  times  as 
fast  as  cane-sugar,  but  cane-sugar  is  absorbed  from  the  intestines 
ten  times  faster  than  Glauber's  salt.  The  velocity  of  absorption  is 
different  even  for  simple  stereoisomer^  sugars — i.e.,  sugars  whose 
molecule,  with  the  same  number  of  atoms  combined  in  the  same 
way,  has  a  different  form  (Nagano).  Nor  is  there  any  clear  relation 
between  the  rate  of  absorption  of  the  various  sugars  and  their 
osmotic  pressure.  Dextrose  and  cane-sugar  are  always  absorbed  in 
greater  amount  than  lactose  from  solutions  of  the  same  osmotic 
pressure.  Indeed,  as  we  shall  see,  lactose  is  practically  not  taken  up 
at  all  as  such  (p.  416),  and  in  concentrated  solutions  may  even  cause 
a  reversal  of  the  normal  movement  of  water,  and  act  as  a  purgative. 
Even  the  water,  organic  and  inorganic  solids  of  the  serum  of  an 
animal,  are  absorbed  from  a  loop  of  its  intestine  when  the  blood- 
pressure  in  the  capillaries  of  the  intestinal  wall  is  considerably 
greater  than  the  pressure  in  the  cavity  of  the  gut.  Since  the  serum 
in  the  intestine  and  the  plasma  in  the  capillaries  must  be  isotonic, 
and  practically  identical  in  chemical  composition,  the  absorption 
cannot  be  due  to  ordinary  osmosis  or  diffusion.  Nor  can  it  be  due 
to  filtration,  since  the  slope  of  pressure  is  from  the  capillaries  to  the 
lumen  of  the  gut  (Reid).  It  is  therefore  extremely  difficult  to  re- 
concile this  experiment  with  any  purely  physical  theory  of  absorp- 
tion. The  same  investigator,  summing  up  the  result  of  careful 
experiments  on  the  absorption  of  weak  solutions  of  glucose,  con- 
cludes that  '  with  the  intestinal  membrane  as  normal  as  the  experi- 
mental procedure  will  permit,  phenomena  present  themselves  which 
are  as  distinctly  opposed  to  a  simple  physical  explanation  as  those 
previously  studied  in  the  absorption  of  serum.' 

But  if  it  be  true  that  the  action  of  the  columnar  epithelium  of  the 
intestinal  mucous  membrane  is  secretory  and  selective,  making  use 
of  purely  physical  processes,  but  not  mastered  by  them,  the  possi- 
bility must  be  admitted  that  in  the  cells  of  endothelial  type  which 
line  the  serous  cavities,  the  lymphatics,  the  bloodvessels,  the  alveoli 
of  the  lungs,  and  the  Bowman's  capsules  of  the  kidney  (p.  452),  the 
element  of  secretion  may  be  less  marked,  and  more  overshadowed 
by  the  physical  factors.  And  it  may  very  plausibly  be  urged  that 
changes  of  considerable  physiological  complexity  can  only  be 
wrought  on  substances  that  have  to  pass  through  a  cell  of  con- 
siderable depth,  while  a  mere  film  of  protoplasm  suffices  for,  and 
indeed  favours,  mechanical  filtration  and  diffusion.  We  have 
already  seen  (p.  258),  in  the  case  of  the  lungs,  that  whatever   the 


4or,  I   M  iv/'  !/.  or  PHYSIOLOGY 

complete  explanation  may  be  of  the  gaseous  exchange  which  takes 
place  through  the  alveolar  membrane,  physical  diffusion  undoubtedly 
plays  an  important  part.  We  shall  see,  too  (p.  466),  that  in  the 
rase  of  the  kidney  the  endothelium  of  the  Bowman's  capsule, 
although  by  no  means  devoid  of  selective  power,  does  seem  to  have 
allotted  to  if  a  simpler  task  than  falls  to  the  share  of  the  '  rodded  ' 
epithelium. 

Absorption  from  the  Peritoneal  Cavity.  -Further,  it  has  been  stated 
that  interchange  between  blood-serum,  circulated  artificially  in  the 
Is  of  dogs  and  rabbits  which  have  been  dead  for  hours,  and 
liquids  introduced  into  the  peritoneal  cavity,  is  essentially  the  same 
as  in  the  living  animal,  and  can  be  explained  on  purely  physical 
principles  (Hamburger).  But  there  is  one  experiment,  at  any  rate, 
which  is  certainly  difficult  so  to  explain — viz.,  the  absorption  from  the 
peritoneal  cavity  of  sodium  chloride  solution  isotonic  with  the  blood- 
serum,  an  absorption  which  goes  on  with  considerable  rapidity. 
Starling  has  supposed  that  this  is  due  to  the  circumstance  that  the 
proteins  of  the  serum  exert  osmotic  pressure,  the  peritoneal  membrane 
being  almost  or  altogether  impermeable  for  them  in  comparison  to 
its  permeability  for  the  salt  solutions.  In  consequence,  water  passes 
into  the  bloodvessels  from  the  peritoneal  cavity.  The  solution  thus 
becomes  more  concentrated  as  regards  sodium  chloride,  some  of 
which  accordingly  enters  the  blood  by  diffusion,  and  so  on.  But 
even  isotonic  serum  is  absorbed  from  the  peritoneal  cavity,  and  it 
seems  to  savour  of  special  pleading  to  suggest,  as  has  been  done, 
that  this  takes  place  through  the  lymphatics,  and  not  at  all  through 
the  bloodvessels. 

Up  to  a  certain  point  an  increase  in  the  intraperitoneal  pressure 
favours  absorption,  but  beyond  this  it  hinders  it  by  interfering  with 
the  circulation.  The  removal  of  a  portion  of  the  fluid  in  this  con- 
dition facilitates  the  absorption  of  the  rest — a  fact  which  has  long 
been  applied  in  the  operation  of  tapping.  Ligation  of  the  thoracic 
duct  has  little  effect  on  the  fate  of  liquids  injected  into  serous  cavities, 
since  the  bloodvessels  play  the  chief  part  in  their  absorption,  just  as 
strychnine,  when  injected  under  the  skin — i.e.,  into  the  lymph  spaces 
of  areolar  tissue— is  taken  up  by  the  blood  and  does  not  appear  in 
the  lymph. 

But  even  if  we  admit  that  substances  can  pass,  by  physical  pro- 
cesses alone,  from  serous  cavities  into  the  blood,  and  from  the  blood 
into  serous  cavities,  this  has  little  bearing  upon  the  question  of 
intestinal  absorption.  For  we  can  hardly  put  anything  into  the 
peritoneal  cavity  which  is  not  foreign  to  it.  It  was  never  intended 
to  come  into  contact  with  the  hundred  and  one  solutions,  extracts, 
suspensions,  and  what  not,  which  the  industrious  experimenter  has 
offered  to  its  unsophisticated  endothelium.  It  cannot  possibly  have 
developed  any  high  degree  of  '  selective  '  power.  In  the  intestine 
everything  is  different.  The  mucosa  is  adapted  to  come  into 
contact  with  an  immense  variety  of  materials,  all  kinds  of  food- 
substances  mingled  with  many  kinds  of  refuse,  the  products  of 
the  action  of  numerous  digestive  ferments,  and  of  a  vigorous  and 
varied  bacterial  flora.  All  these  it  has  to  sift  and  try.  It  cannot 
fail  to  have  properties  which  suggest  a  severe  and  searching 
selection. 

Formation  of  Lymph. — Closely  connected  with  the  question  of 
absorption  from  and  secretion  (or  transudation)  into  the  serous 


IBSORPTJON  407 

cavities  is  the  question  of  the  factors  concerned  in  the  formation  of 
the  lymph,  even  although  recent  researches  throw  grave  doubl  on 
the  common  view  thai  these  sacs  are  merely  expanded  lymph 
spaces,  and  indicate  that  t ho  liquid  found  in  them  has  a  different 
origin  from  lymph.  Weought  to  distinguish  the  lymph  as  we  col- 
led it  from  the  great  lymphatic  trunks,  not  only  from  the  liquids 
of  the  serous  cavities,  but  still  more  sharply  from  the  liquid  which 
tills  the  multitudinous  clefts  and  spaces  of  the  tissues.  It  is  now 
pretty  definitely  est  al dished  that  the  tissue  spaces  do  not  com- 
municate by  actual  passages  with  the  lymphatic  vessels,  but  that 
the  latter  form  everywhere  a  closed  system  like  the  blood-vascular 
system,  the  lymph  capillaries  merely  lying  in  the  tissue  spaces 
(\Y.  ( i.  McCallum,  etc.).  This  conception  entails  a  radical  change 
in  the  current  views  of  lymph  production.  If  the  lymphatics  form 
a  closed  system,  the  lymph  cannot  be  actual  tissue  fluid,  but  only 
tissue  fluid  modified  by  its  passage  through  the  walls  of  the 
lymph  capillaries,  just  as  tissue  fluid  is  not  actual  blood-serum, 
but  serum  modified  by  its  passage  through  the  walls  of  the 
blood  capillaries. 

Although  it  is  customary  to  speak  of  the  lymph  obtained  from 
the  lymphatic  vessels  as  if  it  were  perfectly  homogeneous,rthere 
is  no  experimental  ground  for  supposing  that  the  lymphrfrom 
different  tracts,  or  the  tissue  liquid  in  contact  with  the^cells 
of  different  organs,  or  even  the  tissue  liquid  in  contact  with  one 
and  the  same  cell  at  different  parts  of  its  periphery,  has  a  uniform 
composition,  or  even  a  uniform  molecular  concentration.  There 
are  indeed  certain  general  considerations  which  show  that  this 
cannot  be  so. 

The  teaching  of  Ludwig,  that  lymph  is  formed  by  the  filtration, 
and  in  a  minor  degree,  diffusion,  of  the  constituents  of  blood- 
plasma  through  the  walls  of  the  capillaries  into  the  tissue  spaces, 
was  based  on  such  facts  as  the  increase  in  the  tissue  liquid  of  a 
limb  or  organ  which  occurs  when  the  exit  of  blood  from  it  by  the 
veins  is  hindered,  or  when  the  quantity  of  the  circulating  liquid 
is  increased  by  the  injection  of  blood  or  salt  solution.  It  was 
first  seriously  called  in  question  by  Heidenhain,  who  advanced 
the  theory  that  lymph  is  secreted  by  the  endothelium  of  the  blood 
capillaries.  One  of  Heidenhain's  strongest  arguments  in  favour  of 
his  secretion  theory  was  the  existence  of  substances  which,  when 
injected  into  the  blood,  increased  the  flow  of  lymph  from  the 
thoracic  duct  of  the  dog  without  affecting  appreciably  the 
arterial  pressure.  He  divided  these  so-called  lymphagogues  into 
two  classes:  (i)  substances  like  peptone,  extracts  of  the  head 
and  liver  of  the  leech,  extract  of  crayfish  muscle,  egg-albumin, 
etc.,  which  cause  not  only  an  increase  in  the  rate  of  flow,  but  an 
increase  in  the  specific  gravity  and  total  solids  of  the  lymph ; 


■1' '8 


A    m  I  \  r  1/    OF  PHYSIOLOGY 


(2)  crystalloid  substances,  like  sugar,  salt,  etc.,  which  cause  an 
increased  flow  of  Lymph  more  watery  than  normal. 

Starling  has  shown  that  although  the  lymphagogues  oi  the 
second  class  do  no1  raise  the  arterial  pressure,  they  do,  by  atti  a<  1 
ing  water  from  the  tissues  and  thus  causing  hydraemic  plethora 
(an  excess  of  blood  of  low  specific  gravity),  bring  about  a  marked 
rise  of  venous,  and  therefore,  what  is  the  important  thing  for 
Lymph  lilt  rat  ion,  of  capillary  pressure.  But  it  can  be  demon- 
strated that  vaso-dilatation  with  increase  of  capillary  pressure 
is  not  in  itself  sufficient  to  increase  the  formation  of  lymph. 
We  have  seen,  e.g.  (p.  163),  that  when  the  chorda  tympani  nerve 
is  stimulated  in  the  dog  the  arterioles  of  the  submaxillary  gland 

are  dilated,  and  no  doubt  the 
pressure  in  the  capillaries  is  in- 
creased. No  increased  flow  of 
lymph,  however,  takes  place  from 
the  submaxillary  lymphatics  dur- 
ing even  prolonged  excitation  of 
the  chorda,  nor  do  the  lymph 
spaces  of  the  gland  become  dis- 
tended (Heidenhain).  In  the  horse 
also  the  spontaneous  flow  of  lymph 
from  the  quiescent  parotid  is  not 
appreciably  altered  by  excitation 
of  the  secretory  nerves  of  the 
gland  or  by  pilocarpine  (Carlson). 
There  is  every  reason  to  believe 
that  during  active  secretion  of 
saliva  tissue  liquid  is  really 
formed  from  the  blood  in  in- 
creased amount,  and  that  it  is 
from  the  tissue  spaces  that  the 
gland-cells  directly  obtain  the  in- 
creased supply  of  water  and  other 
substances  necessary  to  sustain  the  increased  secretion.  But  a 
balance  is  maintained  between  the  production  of  tissue  liquid 
and  its  removal  by  the  gland-cells.  When  the  gland  is  quiescent . 
the  small  amount  of  tissue  liquid  normally  formed  from  the 
blood  capillaries  for  the  nutrition  of  the  cells  is  balanced  by. 
upon  the  whole,  an  equal  amount  of  lymph  secreted  from  the 
tissue  spaces  into  the  lymph  capillaries. 

We  may  say,  indeed,  that  the  closed  lymphatic  system  has 
for  its  great  function  the  regulation  of  the  quantity  and  quality 
of  the  tissue  liquid.  In  glands  with  an  external  secretion 
increased  irrigation  of  the  tissue  spaces  from  the  blood  does  not, 
as  a  rule,  lead  to  increased  flow  of  lymph,  because  the  surplus 


Fig.  155. — Vertical  Section  of  a 
Villus  :  Cat.      X  300. 

a,  layer  of  columnar  epithelium 
covering  the  villus — the  outer  edge 
of  the  cells  is  striated  ;  b.  central 
lacteal  of  villus  ;  c,  unstriped  mus- 
cular fibres  ;  </.  mucin  -  forming 
goblet-cell. 


\BSORPTIOK 

fluid  is  required  to  form  the  secretion,  [n  other  organs,  howevei . 
such  as  the  muscles  and  the  ductless  glands,  it  is  probable  thai 
the  augmented  irrigation  rendered  necessary  by  functional 
activity  is  always  associated  with  an  accelerated  flovi  oi  lymph, 
which  carries  ofl  the  surplus  liquid,  including  a  portion  of  the 
waste  products.  It  is  possible  that  an  important  factor  in  the 
production  of  oedema  may  be  the  derangemenl  oi  the  mechanism, 
whatever  it  is,  through  which  the  adjustment  of  the  rate 
"i  formation  of  tissue  liquid  to  that  of  lymphatic  hrnph  is 
achieved.  Bui  it  must  be  remembered  that  in  all  the  organs 
the  blood  capillaries  not  only  supply  materials  to  the  tissue  spaces, 
but  take  up  materials  from  them.  So  that,  while  the  lymphatics 
constitute  an  important  drainage  system,  the  bloodvessels 
irrigate  the  tissues  and  drain  them  as  well. 

A  mere  increase  in  the  capillary  blood-pressure  does  not  of  itself 
accelerate  the  formation  of  tissue  liquid  from  the  blood  any  more 
than  that  of  lymph  from  the  tissue  liquid,  as  is  shown  by  the 
fact  that,  when  the  chorda  tjmipani  is  stimulated  after  injection 
of  a  dose  of  atropine  sufficient  to  prevent  all  salivary  secretion, 
there  is  neither  oedema  of  the  gland  nor  increase  in  the  flow  of 
lymph  from  it,  although  the  arterioles  are  as  widely  dilated  as 
before.  Further,  after  division  or  embolism  of  the  medulla 
oblongata,  and  consequent  paralysis  of  the  vaso-motor  centre 
and  general  vascular  dilatation,  it  is  stated  that  the  injection  of 
sodium  chloride  produces  an  increase  in  the  lymph-flow  as  great 
and  as  durable  as  in  the  normal  animal,  and  which  can  con- 
tinue even  after  death  (Pugliese).  The  action  of  the  first  class 
of  lymphagogues,  which  cannot  be  explained  as  the  conse- 
quence of  an  increase  of  capillary  pressure,  because  the  pressure 
in  the  capillaries  is  not  consistently  increased,  and  may  even  in 
the  case  of  some  of  these  lymphagogues  be  diminished.  Starling 
attributes  to  an  injurious  effect  on  the  capillary  endothelium 
(and  especially  on  the  endothelium  of  the  capillaries  of  the  liver, 
since  nearly  the  whole  of  the  increased  lymph-flow  comes  from 
chat  organ),  which  increases  its  permeability.  But  it  is  not  easy 
to  distinguish  an  increase  of  permeabilitv  produced  by  lympha- 
gogues from  an  increase  of  secretory  activity  of  the  endothelial  cells. 

Hamburger,  too,  has  brought  forward  results  which  it  is 
difficult  to  reconcile  with  a  theory  of  filtration  even  for  the 
second  class  of  lymphagogues.  Further,  Heidenhain  has  shown 
that  some  time  after  injection  of  a  crystalloid  substance,  like 
sugar,  into  the  blood,  a  greater  percentage  of  the  substance  may 
be  found  in  the  lymph  than  in  the  blood.  Now,  when  a  mixture 
of  crystalloids  and  colloids  is  filtered  through  a  thin  membrane, 
the  percentage  of  crystalloids  in  the  filtrate  is  never,  at  most, 
greater  than   in  the  original  liquid.     And  although   Cohnstein 


4io  I    MANUAL  OF  PHYSIOLOGY 

states  that  if  time  enough  be  allowed,  the  maximum  concentra- 
tion of  sodium  chloride  in  the  lymph,  after  intravenous  injection, 
becomes  approximately  the  same  as  the  maximum  in  the  blood, 
this  fact  loses  its  weight  as  an  argument  in  favour  of  the  filtra- 
tion hvpothesis  when  we  remember  that,  according  to  Asher, 
all  the  solids  of  the  lymph  are  markedly  increased  when  even 
small  quantities  of  crystalloids  are  injected  into  the  veins.  Nor 
is  it  at  all  easier  to  explain  lymph  formation  as  a  matter  of 
osmosis  or  diffusion  combined  with  filtration.  Lazarus-Barlow 
found,  for  example,  that  in  the  great  majority  of  his  experiments 
the  injection  of  a  concentrated  solution  of  sodium  chloride, 
dextrose  or  urea  into  a  vein  was  followed,  not  by  an  initial  diminu- 
tion in  the  outflow  of  lymph  (as  might  have  been  expected  if 
the  exchange  of  water  between  the  blood  and  the  tissue  spaces, 
and  between  the  tissue  spaces  and  the  lymph  capillaries,  was 
regulated  solelv  by  differences  in  osmotic  pressure),  but  by  an 
immediate  increase.  And  Carlson  has  shown  that  the  osmotic 
pressure  of  lymph  coming  from  the  active  salivary  glands,  as 
measured  bv  the  freezing-point  method,  may,  under  chloroform 
or  ether  anaesthesia,  be  distinctly  less  than  that  of  the  blood- 
serum.  Water  must  therefore  be  passing  from  a  liquid  of  higher 
to  one  of  lower  osmotic  concentration. 

So  far  we  have  considered  the  passage  of  the  lymph  con- 
stituents, on  the  one  hand  through  the  endothelium  of  the  blood 
capillaries  into  the  tissue  spaces  ;  on  the  other,  from  the  tissue- 
spaces  through  the  endothelium  of  the  lymph  capillaries.  But 
it  is  not  to  be  supposed  that  the  liquid  lying  in  clefts,  partly 
bounded  by  blood  capillaries,  partly  by  lymph  capillaries,  partly 
by  tissue-cells,  should  be  affected  solely  by  the  first  two.  The 
third  anatomical  element  must  contribute  something  to,  or  with- 
draw something  from,  the  tissue  liquid,  and  may  thus  play  a 
part  in  the  formation  of  lymph  from  the  latter.  The  recent 
researches  of  Asher  and  his  pupils  have  raised  the  question  of 
the  relation  between  the  physiological  activity  of  the  organs, 
and  especiallv  of  the  glands,  and  the  formation  of  the  lymph. 
Thev  conclude  that  the  common  doctrine  that  lymph  is  simply 
a  diluted  blood-plasma  is  erroneous.  Lymph,  they  say,  far  from 
being  a  mere  filtrate  or  even  a  secretion  from  the  blood,  is  formed 
by  the  activity  of  the  organs,  and  may  actually  be  absorbed  by 
the  blood  from  the  tissue  spaces.  In  fact,  according  to  their 
view,  the  intravenous  injection  of  lymphagogues,  both  crys- 
talloid and  colloid,  only  causes  an  increased  flow  of  lymph  in  so 
far  as  it  leads  to  increased  glandular  secretion.  But  this  generali- 
zation has  had  only  a  short-lived  vogue,  and  one  by  one  the 
results  which  seemed  to  support  it  have  been  disproved.  For 
example,  it  was  stated  that  secretin  causes  a  flow  of  lymph  from 


IBSORPTION  41  r 

the  lymphatics  of  the  pancreas,  as  well  as  a  flow  of  pancreatic 
juice.  Hut  it  has  been  shown  thai  the  increased  production  of 
Lymph  is  not  due  to  the  secretin  at  all,  but  to  lymphagogue 
>iihstances,  including  albumose,  extracted  with  the  secretin 
from  the  intestinal  mucous  membrane.  A  solution  of  secretin 
can  be  prepared  which  causes  a  considerable  increase  in  the 
secretion  of  pancreatic  juice  and  bile,  but  no  augmentation  what- 
ever in  the  flow  of  lymph  from  the  thoracic  duct.  Again,  it  was 
asserted  that  peptone,  a  noted  lymphagogue,  produces  a  great 
increase  in  the  biliary  secretion,  ft  has  been  demonstrated, 
however,  that  the  action  of  the  peptone  is  merely  to  cause 
expulsion  of  the  contents  of  the  gall-bladder  by  the  mechanical 
effect  of  the  swelling  of  the  liver,  and  not  at  all  to  stimulate 
the  liver-cells  to  form  more  bile.  For  it  produces  no  effect 
on  the  flow  of  bile  if  the  gall-bladder  be  emptied  or  the  cystic 
duct  tied  before  the  injection  (Ellinger).  That  active  salivary 
secretion  is  not  accompanied  by  increased  lymph-flow  from 
the  lymphatics  of  the  salivary  glands  has  been  mentioned  above. 
Nevertheless,  we  may  safely  assume  that  the  activity  of  the 
organs  does  make  a  contribution  to  the  lymph — to  its  solids, 
if  not  in  any  important  degree  to  its  water-content,  although 
to  say  that  they  alone  are  concerned  in  its  formation,  to 
the  exclusion  of  the  capillaries,  is  altogether  an  over-state- 
ment. The  waste-products  of  the  tissues  pass  into  the  lymph, 
and  possibly,  as  Koranyi  suggests,  may,  by  increasing  its  mole- 
cular concentration,  cause  the  passage  of  some  water  into  it  from 
the  blood.  Or  the  decomposition  of  the  large  protein  molecules, 
which  in  tissue  metabolism  are  breaking  down  into  numerous 
smaller  molecules,  may  entail  an  increase  of  osmotic  pressure  in 
the  cells  themselves,  which  in  turn  may  lead  to  withdrawal  of 
water  by  the  cells  from  the  tissue  liquid.  The  osmotic  pressure 
of  the  liquid  may  thus  rise,  and  water  may  pass  into  the  tissue 
spaces  from  the  blood.  The  molecular  concentration  of  lymph 
(except  in  anaesthetized  animals  as  mentioned  above)  is  in 
general  somewhat  greater  than  that  of  blood-serum — e.g., 
in  one  observation  A  of  serum  was  0'6o5°  C,  and  of  lymph 
06100  C.  For  the  solid  tissues,  the  freezing-point  of  which, 
however,  cannot  be  as  satisfactorily  determined  as  that  of 
liquids,  the  following  values  of  A  were  obtained  :  Brain,  0650  ; 
muscle,  o-68°  ;  kidney,  0-94°  ;  liver,  0*97°  ;  while  for  blood  it  was 
°'57°  (Sabbatani). 

To  sum  up,  we  may  say  that  while  the  physical  processes  of 
filtration,  osmosis  and  diffusion  may  play  a  part  in  the  passage  of 
water  and  solids  through  the  walls  of  the  blood  capillaries,  as  well 
as  from  the  tissue-cells  into  the  tissue  spaces,  and  from  these  spaces 
into  the  lymph  capillaries,  there  is  much  which  they  leave  unex- 


4i2  I    MANUAL  OF  PHYSIOLOGY 

plained,  and  which  at  present,  for  the  want  <>f  a  mere  precise  term 
we  must  attribute  to  secretory  activity. 

Although  no  definite  lvmph-secretory  nerve-fibres  have  as 
ye1  been  discovered,  it  is  possible  that  they  exist  (Sihler).  As 
already  pointed  out,  the  same  volume  of  liquid  as  escapes  into 
the  ducts  "i  the  active  submaxillary  gland  must,  upon  the  whole. 
pass  out  of  the  blood  capillaries.  On  what  principle  shall  we 
distinguish  one  only  of  these  processes  as  physiological  se<  retion  ? 
Thev  begin  together  when  the  chorda  tympani  is  stimulated. 
A  drug  which  paralyzes  secretory  nerve-endings  abolishes  both 
'Meets.  The  simplest  explanation  is  that  the  chorda  contains 
secretory  fibres  which  influence  the  formation  both  of  saliva  and 
of  the  tissue  liquid  from  which  it  is  recruited  ;  and,  so  far  as  this 
consideration  goes,  it  is  just  as  logical  to  consider  the  increase 
in  the  supply  of  tissue  liquid  as  the  cause  of  the  increase  in  the 
flow  of  saliva  as  to  consider  the  increased  salivary  secretion  as 
the  cause  of  the  increased  flow  of  liquid  into  the  tissue  spaces. 
The  increased  flow  of  liquid  may  be  brought  about  either  by  an 
action  of  the  nerve  on  the  gland-cells,  causing  them  to  produce 
a  hormone,  winch-  then  affects  the  blood  capillaries  (Carlson),  or 
by  a.  direct  action  on  the  capillary  endothelium.  The  advant 
to  cells  engaged  in  the  active  secretion  of  saliva  of  being  immersed 
in  an  abundant  bath  of  tissue  liquid  is  obvious.  The  post- 
mortem flow  of  lymph,  which  may  continue  in  some  cases  long 
after  complete  cessation  of  the  circulation — for  an  hour  after 
injection  of  dextrose  to  produce  hydraemic  plethora  ;  for  as 
much  as  four  hours  after  injection  of  extract  of  the  strawberry, 
which  is  a  lymphagogue  of  Heidenhain's  first  group  (Mendel 
and  Hooker) — is  a  phenomenon  whose  relation  to  normal  lymph 
formation  has  not  been  definitely  settled. 

It  ought  to  be  remembered  in  this  whole  discussion  that  the 
epithelium  of  ordinary  glands  derives  its  supplies  of  material 
from  the  tissue  lymph.  The  vicissitudes  of  blood-pressure  atleet 
it  only  in  a  secondary  and  indirect  manner.  On  the  other  hand, 
the  endothelial  cells  of  the  capillaries  are  in  direct  contact  with 
the  blood.  And  it  is  interesting  to  observe  that  in  this  resped 
the  glomeruli  of  the  kidney  and  the  alveoli  of  the  lungs  (if  the 
endothelial  lining  of  Bowman's  capsule  and  the  alveolar  mem- 
brane are  assumed  to  be  complete)  take  a  middle  place  between 
the  glands  proper  and  the  quasi-glandular  capillaries. 

Absorption  of  Fat.  -It  has  been  already  mentioned  that  fat 
is  split  up  in  the  intestine  into  glvcerin  and  fatty  acids.  bu1  it 
has  been  a  subject  of  discussion  whether  it  all  undergoes  this 
change  or  only  a  portion  of  it.  The  common  view  has  long  been 
that  the  greater  part  of  the  fat  escapes  decomposition,  and, 
after  emulsihcation  by  the  soaps  formed  from  the  liberated  fatty 


IBSORPTIOIi 


I'  I 


acids,  i^  absorbed  as  neutral  tat  by  the  epithelial  cells  covering 
the  villi.  If  an  animal  is  killed  during  digestion  of  a  fatty 
meal,  these  cells  are  found  to  contain  globules  ol  differenl  siz<  - 
which  stain  black  with  osmic  acid,  are  -lissolved  out  by  ether, 
leaving  vacuoles  in  the  cell  substance,  and  are  therefore  fat 
(Fig.  156).  It  has  always  been  difficult  to  explain  how  droplets 
of  emulsified  fat  could  get  into  the  interior  of  the  epithelial  cells, 
although,  perhaps,  no  more  difficult  than  to  explain  the  passage 
of  living  tubercle  bacilli  from  the  contents  of  the  intestine  into 
the  chyle  of  the  thoracic  duct — a  fact  which  has  been  clearly 
demonstrated  (Ravenel).  The  fat  certainly  passes  into  the  cells, 
and  not  between  them.  When  fat  is  found  in  the  cement  substance 
between  the  cells,  it  has  been  mechanically  squeezed  out  of 
them  by  the  shrinking  of  the  villi  in  preparation.  This  difficulty 
is  obviated  if  we  suppose  that  the 
whole  of  the  fat  is  split  up  in  the 
intestine,  the  products  being  ab- 
sorbed in  solution,  the  glycerin 
as  such,  and  the  fatty  acids  either 
as  soaps  or  in  the  free  state,  or 
partly  free  and  partly  saponified. 
If  this  is  the  true  theory — and 
the  evidence  of  its  truth  has  of 
late  years  been  continually  grow- 
ing —  neutral  fat  must  again  be 
built  up  in  the  epithelial  cells  from 
the  absorbed  glycerin  and  the 
fatty  acids  or  soaps.     Now,  it  has 

been  shown  that  when  an  animal  border 7c7iymph  cOTpusclesTriac 
is  fed  with   fatty  acids  they  are  teal. 
not  only  absorbed,  but  appear  as 

neutral  fats  in  the  chyle  of  the  thoracic  duct,  having  combined 
with  glycerin  in  the  intestinal  wall  ;  and  the  epithelial  cells 
contain  globules  of  fat,  just  as  they  do  when  the  animal  is  fed 
with  neutral  fat.  Further,  it  is  known  that  fat-splitting  goes 
on  in  the  alimentary  canal  to  a  much  greater  extent  than  would 
be  necessary  merely  for  the  formation  of  a  quantity  ot  soap 
sufficient  to  emulsify  the  whole  of  the  fat  in  the  food.  Indeed, 
at  certain  stages  of  digestion  most  of  the  fatty  material,  both 
in  the  small  and  large  intestine,  has  been  found  to  consist  of 
fatty  acids.  To  clinch  the  matter,  it  has  been  proved  that  when 
mixtures  of  paraffin  and  fat,  which  can  be  emulsified  in  a  watery 
solution  of  sodium  carbonate,  are  eaten,  the  paraffin  is  com- 
pletely excreted  with  the  faeces,  while  the  greater  part  of  the  fat 
is  absorbed.  And  fatty  substances  which  are  not  easily  split 
up  and  saponified  (for  example,  lanolin,  the  fat  of  sheep's  wool, 


Fig.  156. — Mucous  Membrane  of 
Frog's  Intestine  during  Ab- 
sorption of  Fat  (Schafer). 

ep,    epithelial    cells  ;    str,    striated 


4M  A   MANUAL  OF  PHYSIOLOGY 

a  mixture  oi  i  ompounds  of  [atty  acids  with  cholesterin  and  allied 
bodies)  are  not  absorbed  even  when  they  are  easily  emulsified. 
Even  fats  with  a  melting-point  far  above  the  temperature  of  the 
body  can  he  absorbed  alter  being  split  up.  The  palmitate  of 
cetyl  alcohol,  the  chief  constituent  of  spermaceti,  melting  at 
53°  C,  was  absorbed  to  the  extent  of  15  per  cent.,  85  per  cent, 
being  excreted  in  the  laces.  It  appeared  as  palmitin  in  the  chyle 
of  a  human  being  flowing  from  a  fistula,  the  palmitic  acid  having 
been  absorbed  as  such,  or  as  a  sodium  soap,  and  having  then 
united  with  glycerin  to  form  the  neutral  fat,  palmitin. 

Some  observers  have  endeavoured  to  show  that  the  fat  is 
absorbed  without  change  by  introducing  into  the  intestine  fat 
stained  with  dyes,  such  as  alkanna  red  or  Sudan  III.,  which  are 
insoluble  in  water.  The  stained  fat  was  found  in  the  epithelial  cells 
of  the  villi,  in  the  lacteals,  and,  in  the  case  of  a  patient  suffering 
from  chyluria,  in  the  urine.  But  this  evidence  is  not  conclusive, 
for  it  has  been  shown  that  the  pigments  might  easily  have  been 
absorbed  after  decomposition  of  the  fat,  since,  although  insoluble 
in  water,  they  are  soluble  in  fatty  acids,  and  therefore  to  some 
extent  in  the  intestinal  contents,  and  readily  pass  into  the  lymph. 
As  already  pointed  out,  the  bile  plays  an  important  part  in 
the  solution  of  the  fatty  acids,  which  may  form  loose  compounds 
with  the  amide  group  of  the  bile-acids.  In  these  loose  combina- 
tions, soluble  in  water,  the  fatty  acids  can  be  absorbed  from  the 
intestinal  contents  (Plluger). 

Leucocytes  have  been  asserted  to  be  the  active  agents  in  the 
absorption  of  fat.  They  have  been  described  as  pushing  their 
way  between  the  epithelial  cells,  fishing,  as  it  were,  for  fatty 
particles  in  the  juices  of  the  intestine,  and  then  travelling  back 
to  discharge  their  cargo  into  the  lymph.  This  view,  however, 
is  erroneous.  But,  although  the  leucocytes  do  not  aid  in  the 
absorption  of  fat  from  the  intestine,  they  appear  to  take  it  up 
from  the  epithelial  cells,  conveying  it  through  the  spaces  of  the 
network  of  adenoid  tissue  that  occupies  the  interior  of  the  villus, 
to  discharge  it  into  the  central  lacteal,  where  it  mingles  with  the 
lymph  and  forms  the  so-called  molecular  basis  of  the  chyle.  A 
part  of  the  fat  reaches  the  lacteal  in  another  way.  The  con- 
traction of  the  smooth  muscular  fibres  of  the  villus  and  the 
peristaltic  movements  of  the  intestinal  walls  alter  the  capacity 
oi  the  lacteal  chamber,  and  so  alternately  fill  it  from  the  lymph 
of  the  adenoid  reticulum,  and  empty  it  into  the  lymphatic 
vessel  with  which  it  is  connected.  By  this  kind  of  pumping 
action  the  passage  of  fat  and  other  substances  into  the  lym- 
phatics is  aided.  In  the  dog  most  of  the  fat  goes  into  the  lacteals, 
and  thence  by  the  general  lymph-stream  through  the  thoracic 
duct  into  the  blood.     And  in  man  the  chyle  collected  from  a 


IB  SORPTION  415 

lymphatic  fistula  contained  a  huge  proportion  of  the  fat  given 
in  the  food  (Munk).  But  this  bare  statement  would  be  mis- 
leading il  we  did  not  add  that  the  fat  taken  in  can  never  be 
entirely  recovered  in  the  chyle  collected  from  the  thoracic  duct. 
A  small  fraction  of  the  deficit  might  be  accounted  for  as  fat 
directly  used  up  for  the  nutrition  of  the  intestinal  wall  itself.  But 
even  after  ligation  of  the  thoracic  and  right  lymphatic  ducts  a 
large  proportion  of  a  meal  of  fat  (32  to  48  per  cent.)  is  absorbed 
from  the  intestine,  obviously  by  the  channel  of  the  bloodvessels, 
since  the  fat-content  of  the  blood  increases  up  to,  it  may  be,  six 
times  the  highest  amount  present  in  the  blood  of  fasting  animals. 
The  statement  that  only  fatty  acids  can  be  absorbed  under  these 
conditions  is  erroneous  (Munk  and  Friedenthal) . 

A  dog  normally  absorbs  9 — 21  per  cent,  of  the  fat  in  a  meal 
in  three  to  four  hours  ;  21 — 46  per  cent,  in  seven  hours  ;  and 
86  per  cent,  in  eighteen  hours  (Harley).  After  excision  of  the 
pancreas  the  absorption  of  fat  is  hindered,  though  not  abolished. 
More  fat,  indeed,  can  be  recovered  from  the  intestine  than  is  given 
in  the  food.  This  at  first  sight  paradoxical  result  is  explained 
by  the  well-established  fact  that  a  certain  amount  of  fat  is 
normally  excreted  into  the  intestine. 

As  to  the  manner  in  which  the  synthesis  of  the  fat  in  the 
intestinal  epithelium  is  accomplished,  the  most  fascinating 
theory  is  that  which  attributes  it  to  the  reversed  action  of  a  fat- 
splitting  ferment  or  lipase,  possibly  the  very  same  steapsin  as 
originally  split  it  up  in  the  intestine.  The  reversibility  of  the 
action  of  various  enzymes  under  changed  conditions  has  been 
well  made  out,  and  it  has  been  stated  that  even  outside  of  the 
body  the  pancreas,  intestinal  mucous  membrane,  lymph  glands, 
etc.,  and  even  cell-free  extracts  of  these  organs  have  the  power  of 
synthesizing  the  ester,  ethyl  butyrate  from  butyric  acid,  and 
ethyl  alcohol  (p.  315).  Moore,  however,  finds  that  in  the  case  of 
ordinary  fats  the  synthesis  takes  place  in  the  intestinal  wall 
only  in  situ  and  while  the  circulation  is  going  on.  In  the  in- 
testinal mucosa  the  greater  part  of  the  fatty  acid  is  already 
combined  with  glycerin  as  neutral  fat,  although  considerable 
quantities  of  free  fatty  acid  are  also  present.  In  the  lymph 
coming  directly  from  the  mesenteric  glands  practically  the  whole 
of  the  fatty  acids  are  in  the  form  of  neutral  fat. 

An  additional,  and  in  some  respects  even  more  remarkable, 
illustration  of  the  synthesizing  powers  of  the  intestinal  wall  is  the 
discovery  of  Munk,  already  referred  to  (p.  413),  that  fatty  acids 
given  by  the  mouth  appear  in  the  lymph  of  the  thoracic  duct  as 
neutral  fats,  having  somewhere  or  other,  in  all  probability  on 
their  way  through  the  epithelium  of  the  gut,  been  combined  with 
glycerin. 


416  A    l/./A  UA1    OF  PHYSIOLOGY 

Since,  however,  the  amount  of  neutral  I. it  recovered  from  the 
thoracic  duel  is  nol  equivalent  to  more  than  one-third  of  the 
fatty  acids  given,  it  has  been  suggested  that  tins  synthesis  ol 
fat  is  only  apparent,  and  that  the  whole  of  the  fat  which  appears 
in  the  chyle  after  a  meal  of  fatty  acids  comes  from  the  fat 
excreted  into  the  intestine  (Frank),  which  is  increased  when  fatty 
acid-  are  given  by  the  mouth.  But  the  suggestion  is  more  in- 
genious than  the  evidence  advanced  in  its  support  is  convincing. 
And,  as  we  have  seen  (p.  415),  a  part  of  the  deficit  may  be 
accounted  for  by  absorption  directly  into  the  bloodvessels. 

Absorption  of  Carbo-hydrates.  —  Carbo-hydrates  are  normally 
absorbed  from  the  alimentary  canal  only  in  the  form  of  mono- 
saccharides, such  as  dextrose,  levulose,  and  galactose,  but 
especially  dextrose.  These  monosaccharides  are  readily  formed 
from  polysaccharides  like  starch  and  dextrin,  and  the  disaccharide 
maltose,  which  they  yield,  as  well  as  from  disaccharides  like 
cane-sugar  and  lactose,  by  the  ferments  already-  studied.  That, 
as  a  matter  of  fact,  the  hydrolysis  in  the  intestine  must  convert 
practically  all  the  carbo-hydrate  into  monosaccharides  before 
absorption  can  be  shown  in  various  ways.  The  ferment  lactase, 
while  present  in  the  small  intestine  of  all  young  mammals,  is 
regularly  absent  in  some  mammalian  groups  in  the  adult.  In 
other  species,  including  man,  it  is  found  in  some  adults,  but  not 
in  all.  In  birds  and  other  animals  below  the  mammals,  it  has  not 
hitherto  been  found  at  any  age.  It  has  been  surmised  that  these 
differences  depend  upon  the  presence  or  absence  of  lactose  (milk) 
as  a  regular  constituent  of  the  food.  (But  see  p.  382.)  If,  now, 
lactose  is  introduced  into  a  loop  of  intestine  in  an  animal  which 
does  not  possess  lactase — e.g.,  an  adult  rabbit — it  is  not  absorbed, 
but  remains  in  the  lumen  till  it  is  at  last  decomposed  by  bacterial 
action.  In  animals  in  which  lactase  is  present  the  lactose  is 
rapidly  absorbed.  Maltose  is  easily  taken  up  from  the  intestine 
because  of  the  action  of  the  ferment  maltase,  which  is  the  most 
widely  spread  of  all  the  inverting  ferments.  The  dextrose 
formed  by  the  maltase  is  so  rapidly  absorbed  that  none,  or  only 
traces,  of  it  can  be  detected  in  the  contents  of  the  intestinal 
loop.  But  it  absorption  be  interfered  with  by  injuring  the 
intestine,  maltose  disappears,  and  dextrose  accumulates  in  the 
lumen.  The  reason  for  the  discrimination  exercised  by  the  in- 
testinal mucosa  in  favour  of  the  monosaccharides  becomes 
apparent  when  an  attempt  is  made  to  circumvent  it  by  injecting 
the  sugars  subcutaneously.  Cane-sugar  and  lactose  so  intro- 
duced are  ex<  reted  unchanged  in  the  urine.  Dextrose,  levulose, 
and  galactose  are  used  up  in  the  bod)*,  and  maltose  likewise, 
thanks  to  the  presence  of  lactase  in  the  blood  and  tissues.  The 
cells  of  the  body  in  general  will  burn  only  monosaccharides,  and 


ABSORPTION  417 

not  di-  or  poly-saccharides.  Therefore  the  intestine  admits  the 
simple,  but  rejects  the  more  complex  sugars.  It  is  only  in  the 
presence  of  abnormally  great  quantities  or  abnormally  great 
.  "iicentrations  of  the  sugars  which  are  not  directly  utilizable 
that  they  are  to  a  certain  extent  taken  up  unaltered,  to  be 
quickly  excreted  as  such  (p.  516).  The  sugar  absorbed  from  the 
intestine  passes  normally  into  the  rootlets  of  the  portal  vein,  not 
into  the  chyle,  for  no  increase  in  the  quantity  of  that  substance 
in  the  contents  of  the  thoracic  duct  takes  place  during  digestion, 
while  the  sugar  in  the  portal  blood  is  increased  after  a  starchy 
meal.  The  blood  of  the  portal  vein  of  a  dog  in  the  fasting  con- 
dition contained  02  per  cent,  of  dextrose.  During  absorption 
of  a  meal  rich  in  carbo-hydrates  it  contained  as  much  as  o-4  per 
cent.  In  the  lymph  issuing  from  the  thoracic  duct  the  amount 
was  the  same  in  both  conditions — viz.,  o-i6  per  cent.  In  a  case 
<>t  lymph  (chyle)  fistula  in  a  human  being,  where  almost  all  the 
lymph  from  the  digestive  tract  escaped  through  the  fistula,  out 
of  100  grammes  of  carbo-hydrate  taken  (50  grammes  starch  and 
50  grammes  sugar),  only  |  gramme,  or  not  1  per  cent,  of  the  sugar 
corresponding  to  the  carbo-hydrates  of  the  food,  could  be  re- 
covered in  the  chyle.  But  when  a  large  amount  of  a  dilute 
solution  of  sugar  is  introduced  into  the  intestine,  some  of  it  is 
taken  up  by  the  lacteals. 

Absorption  of  Water  and  Salts. — -The  main  channel  for  absorp- 
tion of  these  is  the  bloodvessels  of  the  intestine.  As  much  as 
3  to  5  litres  of  water  can  be  absorbed  in  a  day  in  the  intestine  of 
a  healthy  man,  exceptionally  even  6  to  10  litres,  without  the 
faeces  altering  their  normal  consistence.  Absorption  of  the  water 
and  dissolved  salts  may  theoretically  take  place  either  through 
the  epithelial  cells  (intra-epithelial  absorption),  or  between  the 
cells  (interepithelial  absorption).  According  to  Hober,  most 
metallic  salts  (silver,  mercury,  lead,  bismuth,  copper,  manganese, 
etc.)  are  absorbed  interepithelially,  while  iron  salts  form  an 
exception,  and  pass  into  the  epithelial  cells.  The  distinction 
between  interepithelial  and  intra-epithelial  absorption  does  not 
rest  upon  an  absolutely  sure  foundation.  Yet  it  is  probable  that 
everything  which  is  useful  in  the  nutrition  of  the  body  is  taken 
up  by  the  cells,  while  such  substances  as  metallic  salts  which 
are  foreign  to  the  organism,  and  are  denied  entrance  into  the 
cells,  may  pass  in  small  amount  between  them,  their  passage 
being  perhaps  associated  with  more  or  less  injury  to  the  inter- 
stitial substance.  The  vigilant  selection  exercised  by  the 
mucosa  is  well  illustrated  by  the  facts  that,  although  manganese 
and  iron  are  chemically  so  closely  related,  iron,  which  is  necessary 
for  the  formation  of  the  blood-pigment,  is  absorbed  in  immensely 
greater  amount  than  manganese ;  and  that  chlorides,  especially 

27 


418  I  MANUAL  OF    ri/YSIOLOGY 

sodium  chloride,  are  readily  taken  up,  sulphates  with  difficulty. 
Iron  is  absorbed  by  the  bloodvessels,  but  also  to  some  extent  by 
the  Luteals.  From  the  blood  it  is  carried  to  various  organs, 
especially  the  spleen  and  liver.  There  is  reason  to  believe  thai 
the  eosinophil  leucocytes  take  some  share  in  its  transportation. 

It  wa-  supposed  by  Bunge  that  only  organic  compounds  oi 
iron  could  be  absorbed,  and  that  the  undoubted  benefil  derived 
from  the  administration  of  inorganic  iron  compounds,  such  as 
it  i  ric  chloride,  in  chlorosis,  was  due  not  to  then  direct  absorption, 
but  to  their  shielding  the  organic  compounds  from  the  attack 
of  the  sulphuretted  hydrogen  in  the  intestine  (p.  396).  But  this 
theory  has  been  shown  to  be  inconsistent  with  the  facts.  For 
instance,  after  the  administration  of  salts  of  iron,  the  iron  in 
the  blood,  liver,  spleen,  and  other  organs  increases,  but  there  is 
no  accumulation  of  iron  in  the  liver  of  an  animal  to  which  salts 
of  manganese  have  been  given,  although  these  are  equally 
decomposed  by  sulphuretted  hydrogen. 

Absorption  of  Proteins. — The  proteins  of  the  food  or  their 
digested  products  also  pass  directly  into  the  blood-capillaries 
which  feed  the  portal  system.  For  it  has  been  shown  that  after 
ligature  of  the  thoracic  duct  protein  substances  are  still  absorbed 
from  the  intestine,  and  the  urea  corresponding  to  their  nitrogen 
appears  in  the  urine.  And  the  total  nitrogen  in  the  chyle 
flowing  from  a  fistula  of  the  thoracic  duct  in  a  man  was  not  found 
to  be  increased  during  the  digestion  of  protein  food.  The 
quantity  of  chyle  escaping  in  a  given  time  was  also  unaffected, 
whereas  during  the  digestion  of  fats  it  was  greatly  augmented 
(Munk). 

Although  a  certain  amount  oi  egg-albumin,  serum-albumin, 
alkali-albumin,  and  other  native  or  slightly  altered  protein 
substances  can  be  absorbed  as  such  by  the  small,  and  even  by 
the  large,  intestine,  there  is  no  evidence  that,  under  ordinary 
conditions,  this  mode  of  absorption  is  of  any  practical  importance. 
For  when  native  proteins,  with  the  possible  exception  of  the  serum 
proteins  from  an  animal  of  the  same  species,  are  introduced 
'  parenterally  ' — that  is,  injected  directly  into  the  blood,  the  peri- 
toneal cavity,  or  the  muscles,  or  under  the  skin,  so  that  theydo  not 
reach  the  tissues  by  way  of  the  alimentary  canal-  they  behav< 
in  a  very  differenl  manner  from  the  same  proteins  when  given 
by  the  mouth.  One  notable  difference  is  that  the  parenterally 
administered  proteins  give  rise  in  general  to  the  formation  of 
specific  precipitins  (p.  30).  This  is  not  the  case  when  they 
are  administered  per  os,  unless,  like  raw  egg-white,  which,  as 
already  mentioned  (p.  ,175),  evokes  no  secretion  of  gastric  juice, 
they  remain  long  undigested  in  the  alimentary  canal,  when  an 
amount  sufficient  to  canst'  the  production    of    precipitins  may 


IBSORPTJON 


419 


eventually  be  absorbed  unaltered.  Secondly,  thej  are  not,  as  ;i 
rule,  utilized  in  the  metabolism  of  the  body,  or  are  utilized  very 
incompletely.  Egg-albumin,  for  instance,  when  injected  into 
the  blood,  is  excreted  in  the  urine.  It  has  been  previously 
pointed  out  tli.it  the  various  proteins  differ  remarkably  in  the 
kind  and  quantity  ot  the  amino-  and  diamino-acids  which  can 
be  obtained  from  them  (p.  2).  This  is  unquestionably  one 
important  reason  why  the  food  proteins  are — for  the  most  part, 
at  any  rate — so  thoroughly  hydrolysed  before  absorption. 
Another  may  be  that  it  is  easier  for  the  intestine  to  take  up  the 
small  molecules  of  the  decomposition  products  than  the  large 
colloid  aggregates  of  the  original  protein  solutions. 

So  far  as  the  first  reason  is  concerned,  the  degree  of  decom- 
position need  not  be  the  same  for  all  the  food  proteins.  A 
new  house  has  to  be  built  from  the  materials  of  an  old  one. 
How  far  the  work  of  demolition  must  be  carried  will  depend 
upon  the  difference  between  the  plans  of  the  two  houses. 
Sometimes  the  main  part  of  the  old  building  may  be  saved, 
and  only  the  wings  require  reconstruction.  In  like  manner  it 
is  conceivable  that  the  central  group  or  nucleus  of  the  molecule  of 
a  given  food  protein  may  be  identical  with  that  of  a  given  body 
protein,  and  that  only  the  side  chains  may  be  so  different  that 
they  must  be  broken  up  and  reconstructed.  Or,  again,  the  whole 
architectural  plan  of  the  new  house  may  be  so  distinct  from  that 
of  the  old  that  the  only  feasible  method  is  to  completely  demolish 
the  latter,  and  then  to  use  the  individual  bricks  in  the  new  con- 
struction ;  just  as  a  protein  in  the  food  may  differ  so  radically 
from  a  tissue  protein  into  which  it  is  to  be  transformed  that  it 
must  be  decomposed  into  the  simplest  products  of  proteolysis 
before  the  reconstruction  of  the  molecule  can  begin.  It  is  not 
known  what  the  minimum  degree  of  hydrolysis  is  which  will 
permit  of  effective  absorption  and  utilization.  There  can  be  no 
doubt  that  by  far  the  greater  part  of  the  proteins  of  the  food  is 
first  changed  into  proteoses  and  peptones.  But  proteose  and 
peptone  are  absent  from  the  blood,  and,  indeed,  when  injected 
into  the  blood,  they  are  excreted  in  the  urine.  When  injected 
in  larger  amount,  they  pass  also  into  the  lymph,  from  which  they 
gradually  reach  the  blood  again,  and  are  eventually,  as  before, 
eliminated  by  the  kidneys.  The  clear  inference  is  that  if  they 
are  absorbed  as  such  from  the  alimentary  canal,  they  must  be 
changed  in  their  passage  through  its  walls.  The  fact  that  a 
portion  of  the  peptone  and  albumose  is  decomposed  into  amino- 
acids,  etc.,  in  the  lumen  of  the  intestine  has  been  already  alluded 
to.  It  would  seem  that  a  further  portion  of  the  remaining 
peptone  and  albumose — probably  the  whole — is  similarly  de- 
composed by  the  action  of  erepsin  in  the  intestinal  wall.     It 

27 — 2 


420  A   MAS  i    II    OF   PHYSIOLOGY 

has  actually  been  shown  that  during  the  digestion  of  a  protein 
meal  the  mucosa  of  the  stomach  and  intestine  contains  proteose 
and  peptone,  while  none  is  present  in  the  muscular  coat  or  in 
any  other  organ.  They  rapidly  disappear  from  a  portion  of 
the  mucous  membrane  kept  at  a  temperature  of  about  400  C. 
outside  of  the  body,  and  their  disappearance  is  due  nol  to  their 
regeneration  into  serum  proteins,  as  was  once  supposed,  bu1  to 
their  decomposition  by  the  erepsin.  We  must  suppose  thai  the 
serum  and  organ  proteins  are  built  up  from  the  products  of  this 
decomposition.  But  whether  the  mucosa  of  the  alimentary  tract 
is  especially  a  seat  of  the  synthesis  is  unknown  (p.  497).  It  is 
at  least  equally  probable  that  it  occurs  in  all  the  cells  of  the 
body,  each  one  building  up  for  itself  the  particular  kind  of  protein 
which  it  needs.  The  direct  way  of  testing  the  question  would 
be  to  examine  the  blood  coming  from  the  intestine  during  the  ab- 
sorption of  proteins,  and  to  determine  quantitatively  any  changes 
which  might  have  occurred  in  the  nitrogenous  constituents. 
But  the  flow  of  blood  through  the  intestine  is  so  great,  the  absorp- 
tion of  the  digestive  products  so  gradual,  and  their  removal  from 
the  blood  by  the  tissues,  in  all  probability,  so  rapid,  that  there 
is  no  reason  for  surprise  that  hitherto  the  results  of  such  de- 
terminations have  been  ambiguous.  It  has,  however,  been 
shown  that  when  peptone,  albumose,  or  the  final  product.-  oi 
tryptic  digestion  are  introduced  into  a  ligated  segment  of  a  dog's 
small  intestine,  there  is  always,  when  absorption  occurs,  an 
increase  in  the  nitrogenous  substances  in  the  blood,  in  the  form 
of  compounds  which  are  not  precipitated  by  tannic  acid,  and 
therefore  are  neither  native  proteins  nor  proteose.  Urea 
accounts  for  about  one-half  of  the  increase  ;  the  rest  probably 
represents  amino-acids  and  similar  substances  (Leathes).  A 
much  more  conclusive  experiment  has  been  made  on  the  in- 
testines of  certain  octopods,  which,  when  excised  and  suspended 
in  the  oxygenated  blood,  will  live  for  many  hours.  A  solution 
of  peptone  was  introduced  into  the  isolated  intestine,  and  after 
twenty  hours  the  crystalline  products,  leucin.  ty rosin,  lysin,  and 
arginin,  were  found  in  the  blood.  In  the  intact  animal  none 
of  these  bodies  could  be  detected  in  the  blood  (Cohnheim).  The 
inference  is  that  protein  in  these  animals  is  absorbed  in  the 
form  of  amino-acids,  etc.,  which  are  then  carried  to  the  tissues 
and  utilized  there.  It  may  be  that  some  of  the  proteose  and 
peptone  are  regenerated  by  a  shorter  process,  and  without  having 
been  further  split  up,  but  of  this,  too,  there  is  no  definite  proof. 
The  regeneration,  wherever  it  occurs,  must  presumably  take 
place  in  cells,  and  the  only  available  cells  in  the  digestive  mucous 
membrane  are  those  which  line  the  tube,  or  the  leucocytes  which 
wander  between  them.     Accordingly,  both  have  been  credited 


IBSORPTION  421 

with  the  power  of  absorbing  (and  perhaps  transforming)  these 
substances,  bu1  the  balance  of  evidence  is  in  favour  of  the 
epithelial  cells.  We  cannot,  however,  as  in  the  case  of  the  Eat, 
single  out  any  particular  tract  of  epithelium  as  alone  engaged  in 
the  absorption  (and  possibly  in  the  resynthesis)  of  the  products 
of  thi"  digestion  of  the  proteins.  In  all  likelihood  the  cells  covering 
the  villi  are  actively  concerned,  but  there  is  no  valid  reason  for 
denying  a  share  to  the  general  lining  of  the  stomach  and  small 
intestine,  even  including  the  Lieberkuhn's  crypts,  which  morpho- 
logically form  a  kind  of  inverted  villi.  It  is,  indeed,  true  that 
the  crypts  do  not  take  part  in  the  absorption  of  fat,  for  no 
granules  blackened  by  osmic  acid  occur  in  them  during  digestion 
of  a  fatty  meal.  But  this  is  a  ground  for  attributing  to  them 
other  absorptive  functions  rather  than  for  altogether  denying 
to  them  a  share  in  absorption,  unless,  indeed,  we  assume  that 
the  secretion  of  the  succus  entericus  engrosses  the  whole  activity 
of  this  extensive  sheet  of  cells. 

The  extraordinary  efficiency  of  the  small  intestine  in  digestion 
and  absorption  is  shown  by  the  fact  that  after  removal  of  even 
70  to  83  per  cent,  of  the  combined  jejunum  and  ileum  in  dogs, 
the  metabolism  is  not  necessarily  much  affected.  On  a  diet 
poor  in  fat  the  animals  absorb  as  much  of  the  fat  as  a  normal 
dog,  although  a  smaller  proportion  when  the  diet  is  rich  in  fat. 
It  has  been  generally  stated  that  it  is  never  permissible  to 
remove  more  than  one-third  of  the  small  intestine  in  man.  But 
in  one  case  2§  metres  was  resected,  or  quite  one-half,  and  the 
patient  recovered.  Even  the  large  intestine,  which  possesses 
Lieberkuhn's  crypts,  but  no  villi,  is  able  to  absorb  not  only 
peptones  and  sugar,  especially  monosaccharides  like  dextrose, 
but  also  fats  and  undigested  native  proteins.  And,  although 
these  are  power's  which  can  be  rarely  exercised  to  any  great 
extent  in  normal  digestion,  they  form  the  physiological  basis 
of  the  important  method  of  treatment  by  nutrient  enemata. 
The  observation  already  mentioned  (p.  309),  that  considerable 
quantities  of  food  administered  by  the  rectum  can  pass  through 
the  ileo-colic  sphincter  and  valve  into  the  lower  part  of  the 
ileum,  thanks  to  the  antiperistaltic  movements  of  the  large 
intestine,  indicates  that  an  important  part  of  the  preliminary 
digestion  and  of  the  absorption  of  enemata  may  occur  in  the 
small  intestine.  But  remnants  of  the  proteolytic,  amylolytic, 
fat-splitting,  and  inverting  ferments  which  have  done  their  work 
in  the  small  intestine  are  passed  on  into  the  large,  and  may  be 
demonstrated  in  its  contents.  Doubtless  these  are  able  to 
act  upon  food  substances  which  may  have  escaped  complete 
digestion  and  absorption  in  the  higher  parts  of  the  alimentary 
canal,  as  well  as  upon  food  substances  injected  into  the  rectum. 


422  A   M  J  vr  U    OF  PHYSIOLOGY 


I'KACTICAL  EXERCISES  ON  CHAPTERS    [V.   AND  V. 

Quantitative  Estimation  of  Ferment  Action.  For  pepsin  an  easy 
method,  although  not  a  very  accurate  one,  ol  estimating  the  rate  at 
which  the  fibrin  disappears  is  to  use  fibrin  stained  with  carmine.  \s 
solution  goes  on.  the  dye  colours  the  liquid  more  and  more  < l<<-] >l \'. 
and  by  comparing  the  depth  of  colour  at  any  time  with  standard 
solutions  of  carmine,  we  get  the  quantity  of  dye  sel  free,  and  th 
fore  of  fibrin  digested.  This  method  cannot  be  used  for  trypsin.  A 
much  better  method  is  that  of  Mett  (p.  318).  Mind  egg-white  is 
sucked  up  into  fine  glass  tubes  (of  1  to  2  mm.  bore  The  tubes  are 
then  heated  in  a  bath  at  950  C.  For  use  short  pieces  (1  or  2  cm. 
long)  are  cut  off  and  placed  in  1  or  2  c.c.  of  the  liquid  to  be  tested. 
the  whole  being  kept  at  380  to  400  C.  At  the  end  of  a  certain  time 
the  length  of  the  column  of  undissolved  protein  is  measured  with  a 
scale  and  low-power  microscope.  Deducting  this  from  the  length  of 
the  tube,  we  get  the  length  of  the  column  digested.  As  a  test  of  the 
activity  of  a  diastatic  ferment,  we  take  the  amount  of  sugar  formed 
in  a  given  time  in  a  given  quantity  of  a  standard  starch  solution. 
Where  rapid  work  is  required,  glass  tubes  filled  with  tinted  starch 
paste  may  be  used  in  the  same  way  as  the  Mett's  tubes.  A  more 
accurate  method,  and  yet  a  rapid  and  convenient  one,  is  based  upon 
the  time  which  is  necessary  in  order  that  the  iodine  reaction  with 
starch  may  just  disappear  when  a  standard  starch  solution  is  digested 
with  a  dilution  of  the  ferment  solution  at  400  C.  To  determine 
the  activity  of  pancreatic  juice  as  regards  fat-splitting  ferment, 
the  acidity  of  the  emulsion  formed  by  the  juice  and  fat  after  standing 
for  a  definite  time  at  a  given  temperature  (with  occasional  shaking) 
can  be  estimated  by  titration  with  baryta  solution. 

1.  Saliva. — Collection  and  Microscopic  Examination  of  Saliva. — 
Chew  a  piece  of  paraffin-wax,  or  inhale  ether  or  the  vapour  of  strong 
acetic  acid.  The  flow  of  saliva  is  increased.  Collect  it  in  a  porcelain 
capsule.  Examine  a  drop  under  the  microscope.  It  may  contain  a 
few  flat  epithelial  scales  from  the  mouth  and  a  few  round  granular 
bodies,  the  salivary  corpuscles,  the  granules  in  which  often  show  a 
lively,  dancing  movement  (Brownian  motion).  Filter  the  saliva  to 
free  it  from  air-bubbles,  and  perform  the  following  experiments  : 

(a)  Test  the  reaction  with  litmus  paper.  It  is  usually  alkaline. 
An  acid  reaction  may  indicate  that  bacterial  processes  arc  abnormally 
active  in  the  mouth. 

(b)  Add  dilute  acetic  acid.  A  precipitate  indicates  the  presence 
of  mucin  (p.  319).     Filter. 

(c)  Add  a  drop  or  two  of  silver  nitrate  solution  to  the  filtrate  from 
(b).  A  precipitate  insoluble  in  nitric  acid,  soluble  in  ammonia. 
proves  that  chlorides  are  present. 

(d)  Add  to  another  portion  a  few  drops  .>!  dilute  ferric  chloride 
slightly  acidulated  with  dilute  hydrochloric  acid,  and  the  same 
quantity  to  as  much  distilled  water  in  a  control  test-tube.  A 
reddish  coloration  is  obtained,  due  to  the  presence  of  sulphocyanic 
acid,  which  is  combined  with  potassium  and  other  bases  in  the  saliva. 
The  colour  is  discharged  by  mercuric  chloride.  I  )r,  a  drop  of  saliva 
may  be  allowed  to  fall  from  the  mouth  on  .1  test-paper  (prepared  ln- 
soaking  filter-paper  with  a  dilute  starch  solution,  containing  a  little 
iodic  acid,  and  allowing  it  to  dry  in  the  air).       The  paper  is  coloured 


PR  ICTIC  II    EXERCISES  423 

blue  1>\-  tin-  union  oi  ill*-  starch  with  iodine  sel  tree  Erona  the  iodic 
acid  l>v  the  act  ion  of  the  sulphocyanic  acid. 

bake  some  boiled  starch  mucilage,  and  test  it  for  reducing 
sugar  l>\-  Trommer's  tesl  (p.  eo).  It"  no  sugar  is  found,  take  three 
tesl  tubes,  label  them  \.  B,  C,  and  nearly  half  till  each  with  the 
boiled  starch.  To  A  add  a  little  saliva,*  to  B  some  saliva  which  has 
been  boiled,  to  C  a  little  saliva  which  has  been  neutralized,  and  as 
much  o- 1  per  rent,  hydrochloric  acid  as  has  been  taken  of  the 
mucilage,  so  as  to  make  the  strength  of  the  acid  in  the  mixture  02  per 
cenl  .  a  proportion  well  below  that  of  the  gastric  juice.  Put  the  test- 
t  ubes  into  a  water-bath  at  400  C.  In  a  few  minutes  test  the  contents 
for  reducing  sugar.  Abundance  will  be  found  in  A,  none  in  B  or  C. 
In  B  the  ferment  ptyalin  has  been  destroyed  by  boiling  ;  in  C  its 
art  ion  has  been  inhibited  by  the  acid.  If  the  test-tubes  have  been 
left  long  enough  in  the  bath,  no  blue  colour  will  be  given  by  A  on 
the  addition  of  iodine,  but  a  strong  blue  colour  by  B  and  C — i.e.,  the 
starch  will  have  completely  disappeared  from  A. 

(/)  Put  some  starch  in  a  test-tube,  add  a  little  saliva,  and  hold  in 
the  hand  or  place  in  a  bath  at  400  C.  On  a  porcelain  slab  place 
several  separate  drops  of  dilute  iodine  solution.  With  a  glass  rod 
add  a  drop  of  the  mixture  in  the  test-tube  to  one  of  the  drops  of 
iodine  at  intervals  as  digestion  goes  on.  At  first  only  the  blue  colour 
given  by  starch  will  be  seen  ;  a  little  later  a  violet  colour,  due  to  the 
presence  of  erythrodextrin  in  addition  to  some  unaltered  starch.  A 
little  later  the  colour  will  be  reddish,  the  starch  having  disappeared 
and  the  erythrodextrin  reaction  being  no  longer  obscured.  Later 
still  no  colour  reaction  will  be  obtained,  the  erythrodextrin  having 
undergone  further  changes,  and  only  sugar  (maltose,  isomaltose,  and 
perhaps  a  trace  of  dextrose)  and  achroodextrin — a  kind  of  dextrin 
which  gives  no  colour  with  iodine — being  present. 

(g)  Put  two  pieces  of  glass  tube  filled  with  tinted  starch  paste 
(p.  422)  in  separate  test-tubes.  Cover  one  with  3  c.c.  and  the  other 
with  6  c.c.  of  saliva.  The  saliva  must  all  be  taken  from  the  same 
stock,  and  must  not  be  collected  separately.  Put  in  a  bath  at  380  C, 
and  when  a  fair  amount  of  digestion  has  taken  place  in  each,  measure 
the  length  of  the  column  digested,  and  determine  the  relation 
between  the  amount  digested  in  the  two  tubes  (p.  317). 

(h)  Dilute  2  c.c.  of  saliva  with  distilled  water  up  to  20  c.c,  and 
filter.  Take  six  test-tubes  of  the  same  width,  and  label  them  A,  B, 
C.  etc.  Measure  into  A  3  c.c.  of  the  diluted  saliva,  into  B  2  c.c, 
into  C  13  c.c,  into  D  00.  c.c,  into  E  o-6  c.c,  and  into  F  0-4  c.c. 
Thus  a  series  is  obtained  in  which  each  tube  contains  (approximately) 
two-thirds  as  much  ferment  as  the  one  it  follows.  Add  distilled 
water  to  tubes  B  to  F,  sufficient  to  make  up  the  volume  in  each  to 
3  c.c.  Place  the  tubes  in  a  beaker  of  iced  water  ;  add  to  each  10  c.c. 
of  a  1  per  cent,  solution  of  boiled  starch  previously  cooled  in  iced 
water,  and  shake  so  as  to  mix  the  contents.  Each  tube  now  con- 
tains starch  in  uniform  concentration,  and  ferment  in  varying  con- 
centration. The  low  temperature  prevents  digestion  till  all  the 
tubes  are  read  v.  Now  put  the  tubes  simultaneously  into  a  water- 
bath  at  400  C.  for  half  an  hour,  and  then  back  again  into  iced  water 
to  prevent  further  digestion.  Move  them  about  in  the  iced  water 
to  cool  rapidly.  Fill  up  the  tubes  with  distilled  water  nearly  to  the 
top,  add  a  drop  or  two  of  iodine  solution  to  each,  and  mix  uniformly. 

*  As  it  filters  slowly,  unaltered  saliva  may  be  used  for  F.xperiments 
(e).  (f).  and  (1). 


424  ■•'   M  '  v/    //    OF  PHYSIOLOG  Y 

1'hc  tubes  i"  which  the  smallesl  amounts  oi  saliva  were  added  will 
probably  still  show  a  distinct  blue  colour,  while  those  al  the  other 
end  oi  the  series  will  be  brown  or  yellow,  and  the  intermediate  tubes 
bluish-violet.  Suppose  D  is  the  last  tube  still  showing  a  bluish  tint, 
thm  in  the  next  higher  tube,  C,  all  the  starch  has  been  hydrolysed 
at  least  to  dextrin — that  is,  1*3  c.c.  of  the  ten-times  diluted  saliva, 
or  0-13  of  the  original  saliva,  has  been  sufficient  to  change  all  the 
starch  in  10  c.c.  of  the  1  per  cent,  solution.  With  anothei  specimen 
of  saliva  the  same  result  might  be  reached  in  tube  E,  containing  an 
amount  of  ferment  equal  to  that  in  006  c.c.  of  the  original  saliva. 
We  could  then  conclude  that  the  diastatic  power  of  the  second  saliva 
was  about  twice  as  great  as  that  of  the  first.  A  closer  approximation 
can  now  be  made  by  setting  up  two  fresh  tubes  (C  and  E  respe<  - 
tively  for  the  two  salivas)  and  determining  the  time  required  for  the 
blue  reaction  with  iodine  to  disappear,  taking  out  a  drop  from  time 
to  time  and  testing  on  a  porcelain  slab. 

(i)  Put  a  little  distilled  water  into  a  porcelain  capsule,  and  bring 
the  water  to  the  boil.  Now  put  into  the  mouth  some  boiled  starch 
paste,  and  move  it  about  as  in  mastication.  After  half  a  minute  spit 
the  starch  out  into  the  boiling  water.  Divide  the  water  into  two 
portions.  Test  one  for  sugar,  and  the  other  for  starch.  Repeat  the 
experiment,  but  keep  the  starch  two  minutes  in  the  mouth.  Report 
the  result. 

(/)  Starch  solution  to  which  saliva  has  been  added  is  placed  in  a 
dialyser  tube  of  parchment-paper  for  twenty-four  hours.  At  the  end 
of  that  time  the  dialysate  (the  surrounding  water)  should  be  tested 
for  sugar  and  for  starch.  Sugar  will  probably  be  found,  but  no 
starch.  If  no  reaction  for  sugar  is  obtained,  the  dialysate  should 
be  concentrated  on  the  water-bath,  and  again  tested. 

2.  Stimulation  of  the  Chorda  Tympani. — (1)  Having  previously 
studied  the  anatomy  of  the  mouth  and  submaxillary  region  in  the 
dog  by  dissecting  a  dead  animal  (Fig.  157),  put  a  good-sized  dog 
under  morphine.  Set  up  an  induction-machine  for  a  tetanizing 
current  (p.  184),  and  connect  it  with  fine  electrodes.  Fasten  the 
dog  on  the  holder,  give  ether  if  necessary,  and  insert  a  cannula  in 
the  trachea  (p.  186).  Then  make  an  incision  3  or  4  inches  long 
through  skin  and  platysma  muscle,  along  the  inner  border  of  the 
low^er  jaw  beginning  about  the  angle  of  the  mouth,  and  continuing 
backwards  towards  the  angle  of  the  jaw.  Such  branches  of  the 
jugular  vein  as  come  in  the  way  may  be  generallv  pushed  aside,  but 
if  necessary  they  may  be  doubly  ligated  and  divided.  Feel  for  tin- 
facial  artery,  so  as  to  be  able  to  avoid  it.  Divide  the  digastric  muscle 
about  its  anterior  third,  and  clear  it  carefully  from  its  attachments  ; 
or,  without  dividing  it,  pull  it  outwards  with  a  hook.  The  broad, 
thin  mylo-hyoid  muscle  will  now  be  seen  with  its  motor  nerve  lying 
on  it.  Divide  the  muscle  about  its  middle  at  right  angles  to  its 
fibres,  and  raise  it  carefully.  The  lingual  nerve  will  be  seen  emerging 
from  under  the  ramus  of  the  jaw.  It  runs  transversely  towards  the 
middle  line,  and  then,  bending  on  itself,  passes  forwards  parallel  to 
the  larger  hypoglossal  nerve.  In  its  transverse  course  the  lingual 
will  be  seen  to  cross  the  ducts  of  the  submaxillary  and  sublingual 
glands.  These  structures  having  been  identified,  the  lingual  net 
is  to  be  ligatured  before  it  enters  the  tongue  and  cut  peripherally  to 
the  ligature.  Then  a  glass  cannula  of  suitable  size  is  to  be  inserted 
into  the  submaxillary  duct  (the  larger  of  the  two),  just  as  if  it  were 
a  bloodvessel  (p.  55).       \  short  piece  of  narrow  rubber  tubing  is  care- 


/'A'  ICTIC  I!    EXERCIS1  S 


\  ■ 


fully  slipped  on  the  rn<l  ol  the  cannula.  The  Lingual  is  now  to  be 
lifted  by  means  of  the  Ligature,  and  traced  back  towards  the  jaw  till 
its  chorda  tympani  branch  is  seen  coming  off  and  running  ba<  kwards 
.di mil;  the  duct.  The  chordo -lingual  nerve  (Fig.  i  \  \,  p.  362)  is  then 
to  be  cut  centrallj  to  the  origin  of  the  chorda  tympani,  which  can 
now  be  easily  Laid  on  electrodes  by  means  oi  the  Ligature  on  the 
Lingual.  On  stimulating  the  chorda,  the  flow  of  saliva  through  the 
cannula  will  be  increased.  The  current  nerd  not  be  very  strong.  If 
the  rlow  stops  after  a  short  time,  it  can  be  again  caused  by  renewed 
stimulation  after  a  brief  rest.  A  quantity  of  saliva  may  thus  be 
collected,  and  the  experiments  already  made  with  human  saliva 
repeated. 

(2)  Expose  the  vago-sympathetic  nerve  in  the  neck  on  the  same 
side;  ligature  it;  divide  below  the  ligature;  and  note  the  effect 
produced  by  stimulation  of  the  upper  end  on  the  flow  of  saliva. 


Digastric 

Muscle  (cut). 


Fig.  157. 


Lingual     Wharton's 
Nerve.  Duct. 

-Dissection1  for  Stimulation  of  Chorda  Tympani   (after 
Bernard). 


(3)  Set  up  another  induction-machine,  and  connect  it  with  elec- 
trodes. Stimulate  the  chorda,  and  note  the  rate  of  flow  of  the 
saliva.  Then,  while  the  chorda  is  still  being  excited,  stimulate  the 
vago-sympathetic,  and  observe  the  effect.  If  the  experiment  is 
successful,  finish  by  stimulating  the  chorda  for  a  long  time.  Then 
harden  both  submaxillary  glands  in  absolute  alcohol,  make  sections, 
stain  with  carmine,  and  compare  them. 

3.  Effect  of  Drugs  on  the  Secretion  of  Saliva. — (1)  Proceed  as  in 
2  (1),  but,  in  addition,  insert  a  cannula  into  the  femoral  vein  (p.  200). 
On  the  cannula  put  a  short  piece  of  rubber  tubing,  filled  with  0-9  per 
cent,  salt  solution  and  closed  by  a  small  clamp,  or  a  small  piece  of 
glass  rod,  or  a  pair  of  bulldog  forceps.  While  the  chorda  is  being 
stimulated  inject  into  the  vein  10  to  15  milligrammes  of  sulphate 
of  atropine  by  pushing  the  needle  of  a  hypodermic  syringe  through 
the  rubber  tube.     This  will  stop  the  flow  of  saliva,  and  abolish  the 


1.26  l    1/  /  \r  //.  OF  PHYSIOLOGY 

effect  of  stimulation  of  the  chorda.     Sec  whether  the  sympathetic 
is  also  inactive,  and  repori  bhe  result. 

<>  ■.  empty  the  cannula  in  the  submaxillary  duel  by  means  of 
a  feather,  and  till  it  with  a  2  per  cent,  solution  of  pilocarpine  nitrate 

by  means  of  a  tine  pipette.     I 'ill  also  the  short  rubbei  tube  attached 
to  tlie  cannula,  and  close  it  again.     Compress  tlie  tube,  and  so  force 

into  the  duct  a  small  quantity  of  the  solution.  Open  the  tube. 
Secretion  of  saliva  will  again  begin,  and  stimulation  of  the  chorda 
will  again  cause  an  increase  in  the  flow.  But  alter  a  few-  minutes 
the  action  of  the  atropine  will  reassert  itself,  ami  the  How  will  stop. 
Renewed  secretion  may  be  caused  by  a  fresh  injection  of  pilocarpine. 
4.  Gastric  Juice. — (a)  Preparation  of  Artificial  Gastric  Juice. — 
Fake  a  portion  of  the  pig's  stomach  provided,  strip  oil  the  mucous 
membrane  (except  that  of  the  pyloric  end,  which  is  relatively  poor 
in  pepsin),  cut  it  into  small  pieces  with  scissors,  ami  put  it  in  a 
bottle  with  roo  times  its  weight  of  0-4  per  cent,  hydrochloric  acid. 
Label  and  put  in  a  bath  at  400  C.  for  three  hours,  and  then  in  the 
cold  for  twelve  hours.     Then  filter. 

(b)  Take  another  portion  of  the  mucous  membrane,  cut  it  into 
pieces,  and  rub  up  with  clean  sand  in  a  mortar.  Then  put  it  in  a 
small  bottle,  cover  it  with  glycerin,  label,  and  set  aside  for  two  or 
three  days.     The  glycerin  extracts  the  pepsin. 

(c)  Take  five  test-tubes,  A,  B,  C,  D,  E,  and  in  each  put  a  little 
washed  and  boiled  fibrin  or  a  small  cube  of  coagulated  egg-white. 
To  A  add  a  few  drops  of  glycerin  extract  of  pig's  stomach,  and  till 
up  the  test-tube  with  0-4  per  cent,  hydrochloric  acid.  To  B  add 
glycerin  extract  and  distilled  water  ;  to  C  glycerin  extract  and 
1  per  cent,  sodium  carbonate  ;  to  D  04  per  cent,  hydrochloric  acid 
alone  ;  to  E  glycerin  extract  which  has  been  boiled,  and  04  per 
cent,  hydrochloric  acid. 

Put  up  another  set  of  five  test-tubes  in  the  same  way,  except  that 
a  few  drops  of  a  watery  solution  of  a  commercial  pepsin  are  sub- 
stituted for  the  glycerin  extract.  Label  the  test-tubes  A',  B',  C\  D'.  E'. 

Into  another  test-tube  put  a  little  fibrin  (or  an  egg-white  cube), 
and  till  up  with  the  filtered  acid  extract  from  (a).  Label  it  F. 
Place  all  the  test-tubes  in  a  tumbler,  and  set  them  in  a  water-bath 
at  400  C.  Put  a  piece  of  a  Mctt's  tube  (p.  422)  into  each  of  two  test- 
tubes,  and  add  15  c.c.  of  0-4  per  cent,  hydrochloric  acid.  To  one 
tube  add  5  drops  and  to  the  other  10  drops  of  the  same  filtered 
glycerin  extract  of  gastric  mucous  membrane.  Put  the  tubes  in 
the  bath,  and  when  digestion  is  distinct  at  the  ends  of  both  tubes 
measure  the  length  of  the  column  digested  in  each.  What  is  the 
relation  between  the  two  (p.  317)  ?  The  experiment  can  be  repeated 
with  the  hydrochloric  acid  extract  of  the  mucous  membrane. 

After  a  time  the  fibrin  (or  egg-white)  will  have  almost  completely 
disappeared  in  A,  A',  and  F,  but  not  in  the  other  test-tubes.  Filter 
the  contents  of  A,  A',  and  F  into  one  dish. 

(d)  Test  the  filtrate  for  the  products  of  gastric  digestion  : 

(a)  Neutralize  a  portion  carefully  with  dilute  sodium 
hydroxide.  A  precipitate  of  acid-albumin  may  be 
thrown  down.      Filter. 

(£)  To  a  portion  of  the  filtrate  from  (a)  add  excess  of  sodium 
hydroxide  and  a  drop  or  two  of  very  dilute  copper 
sulphate.  A  rose  colour  indicates  the  presence  of 
proteoses  or  peptones.  The  cupric  sulphate  must  be 
very  cautiously  added,  because  an  excess  gives  a  violet 


/■/.'  i  cnc  it    i  xi  was  is  42- 

colour,  and  thus  obscures  the  rose  reaction,     if  still 
more  cupric  sulphate  be  added,  blue  cupric  hydroxide 
is  thrown  down,  and  nothing  can  be  inferred  as  to 
the  presence  or  the  nature  of  proteins  in  the  liquid. 
(7)    Meat  another  portion  of  the  filtrate  from  (a)  to  30°  C, 
and  add  crystals  of  ammonium  sulphate  to  satura- 
tion.    A   precipitate  of  proteoses  (albumoses)  may 
be  obtained.      Filter  off. 
(3)   Add  to  the  filtrate  from  (7)  a  trace  of  cupric  sulphate 
and  excess  of  sodium  hydroxide.     A  rose  colour  in- 
dicates  that    peptones   are   present.     More   sodium 
hydroxide  must  be  added  than  is  sufficient  to  break 
up    all    the    ammonium    sulphate,    for    the    biuret 
reaction  requires  the   presence  of  free  fixed  alkali. 
A  strong  solution   of  the  sodium  hydroxide  should 
therefore  be  used,   or  the  stick  caustic  soda.     The 
addition  of  ammonium  sulphate  will  cause  the  red 
colour  to  disappear  ;  so  will  the  addition  of  an  acid. 
Sodium    hydroxide    will    bring   it   back.     Ammonia 
does  not  affect  the  colour. 
(e)   Use  another  portion  of  the  filtrate  from   (a)  to  separate 
the  primary  and  secondary  albumoses  as  in  experi- 
ment (2)  (7)  (p-  10). 
(e)   To  some  milk  in   a  test-tube  add   a  drop  or  two   of  rennet 
extract,  and  place  in  a  bath  at  400  C.     In  a  short  time  the  milk  is 
curdled  by  the  rennin.      (See  p.  326.) 

5.  (1)  To  obtain  Normal  Chyme. — Inject  subcutaneously  into  a 
dog,  one  and  a  half  hours  after  a  meal  of  minced  meat  and  water, 
2  mg.  of  apomorphine.  Half  of  one  of  the  ordinary  tabloids  is 
enough.     Collect  the  vomit. 

(2)  To  obtain  Pure  Gastric  Juice. — If  the  laboratory  possesses  a  dog 
with  Pawlow's  double  oesophageal  and  gastric  fistula,  the  juice  may 
be  obtained  in  large  amount  by  sham  feeding  with  meat  (p.  374).      If 
not,  proceed  as  follows  :  Put  a  fasting  dog 
under  ether,  and  fasten  on  the  holder.    Clip 
the  hair  and  shave  the  skin  in  the  middle 
line   below  the  sternum.       Make    a   longi- 
tudinal incision  through  the  skin  and  sub- 
cutaneous tissue  from  the  xiphoid  cartilage 
downwards  for  3  or  4  inches.      The  linea 
alba  will  now  be  seen   as  a  white   mesial 
streak.     Open  the  abdomen  by  an  incision 

through  it.     Pull  over  the  stomach  towards         FlG-  158.— Stomach 
the   right,  and  stitch  it  to  the  abdominal  Cannula. 

wall,  open  it,  and  insert  a  stomach  cannula 

(Fig.  158).  Make  an  incision  through  the  serosa  and  muscularis. 
Doubly  ligate  and  divide  any  vessels  exposed  in  the  submucosa. 
Then  make  an  opening  in  the  mucosa  of  sufficient  size  to  just 
admit  the  gastric  cannula.  This  will  go  into  a  smaller  opening 
if  it  is  provided  with  a  nick  in  the  flange  which  enters  the 
stomach.  Be  careful  to  prevent  blood  from  getting  into  the 
stomach.  Immediately  stitch  the  wound  in  the  stomach  over  the 
flange  of  the  cannula,  but  do  not  pass  the  stitches  through  to  the 
internal  surface  of  the  mucosa.  Suture  the  muscles  and  skin 
separately.  Then  stitch  up  the  wound  in  the  abdomen.  Wash 
out  any  stomach  contents  with  warm  water.      Put  a  cork  in  the 


428  /    M  INV  U    OF  PHYSIOLOGY 

cannula,  and  cover  the  annual  with  a  cloth.  The  following  experi- 
ments may  now  be  performed.  Expose  both  vagi  in  the  neck. 
Connect  two  pairs  of  electrodes  with  the  secondary  coil  of  an  in- 
ductorium  arranged  for  single  shocks.  By  means  of  a  key  in  the 
primary  stimulate  the  nerves  with  slow  rhythmical  induction  shocks 
at  tin  rate  of  about  one  a  second.  Continue  the  stimulation  for 
fifteen  minutes,  collect  any  juice  that  may  nave  been  se<  reted,  and 
apply  the  tests  in  (3).  It  secretion  is  slow,  a  little  distilled  water 
may  be  put  Into  the  stomach,  and  the  vagus  stimulation  repeated. 
Mechanical  stimulation  of  the  mucous  membrane  with  a  feather 
causes  no  secretion  of  acid  gastric  juice,  but  may  cause  a  secretion 
of  alkaline  mucus. 

[a]   Test  the  reaction  to  litmus  of  the  chyme  obtained  in  (1), 
and  of  the  pure  juice  obtained  in  (2). 

(b)  Test  their  proteolytic  powers  by  putting  in  a  bath  at  40°  C. 
for  two  hours  two  test-tubes  containing  respe»  tively  tillered  chyme 
and  fibrin,  and  gastric  juice  and  fibrin.  The  fibrin  will  be  digested 
in  both.  Estimate  the  proteolytic  power  quantitatively  by  Mett's 
tubes  (p.  422). 

(c)  Add  a  few  drops  of  the  chyme  and  gastric  juice  to  milk  in  two 
test-tubes,  and  place  them  in  a  bath  at  40°  C.  Repeat  (c)  after 
neutralizing  the  liquids. 

(d)  Examine  a  drop  of  the  unfiltered  chyme  under  the  microscope. 
Partially  digested  fragments  of  the  food  will  be  seen — muscular 
fibres,  or  fat  cells.     Filter,  and  proceed  as  in  4  (d)  (p.  426). 

(4)  Test  the  filtrate  from  the  chyme  and  the  gastric  juice  for  lactic 
acid  by  Uffelmann's  test  or  Hopkins's  test  (p.  716),  and  for  hydro- 
chloric acid  by  Giinzburg's  reagent. 

Uffelmann's  Test  for  Lactic  Acid. — The  reagent  is  a  dilute  solution 
of  carbolic  acid  to  which  dilute  ferric  chloride  has  been  added  till 
the  colour  is  bluish  (say  a  drop  of  a  1  per  cent,  ferric  chloride  solution 
to  5  c.c.  of  a  1  per  cent,  carbolic  acid  solution).  The  blue  colour  of 
the  mixture  is  turned  yellow  by  lactic  acid,  but  not  by  dilute  hydro- 
chloric acid.  Since  Uffelmann's  test  is  given  also  by  phosphates, 
alcohol,  and  sugar,  which  may  sometimes  be  present  in  the  stomach 
contents,  it  is  best  to  shake  the  gastric  contents  with  ether,  dissolve 
the  ethereal  extract  in  water,  and  then  make  the  test  on  the  watery 
solution. 

Gunzburg's  Reagent  for  Free  Hydrochloric  Acid  in  Gastric  Juice 
is  made  by  dissolving  2  parts  of  phloroglucinol  and  1  part  of  vanillin 
in  30  parts  bv  weight  of  absolute  alcohol.  A  few  drops  of  the  reagent 
are  added  to  a  few  (hops  of  the  filtered  gastric  juice  in  a  small 
porcelain  capsule,  and  the  whole  evaporated  to  dryness  over  a  small 
bunsen  flame.  If  free  hvdrochloric  acid  is  present,  a  carmine-red 
residue  is  left.  If  all  the  hydrochloric  acid  is  united  to  proteins  in  the 
stomach  contents,  the  reaction  does  not  succeed.  It  is  also  hindered 
bv  the  presence  of  leucin. 

6.  Pancreatic  Juice. — (a)  Take  a  piece  of  the  pancreas  of  an  ox 
or  dog  which  has  been  kept  twenty-four  hours  at  the  temperature  of 
the  laboratorv.  and  make  a  glycerin  extract  in  the  same  way  as  in 
the  case  of  the  pig's  stomach  in  4  (b).  Put  in  a  small  bottle,  and 
set  aside  for  a  day  or  two. 

(b)  Put  a  little"  boiled  fibrin  into  each  of  six  test-tubes.  A,  B,  C, 
D,  E,  F.  To  A  add  a  few  drops  of  glycerin  extract  of  pancreas, 
and  till  up  with  a  1  per  cent,  sodium  carbonate  solution  :  to  P.  add 
glycerin    extract    and    distilled    water;    to   ('    glycerin    extract    and 


PRACTICAL   EXERCISES  429 

excess  <>t  0*05  per  cent,  hydrochloric  acid  ;  to  D  1  per  cenl  odium 
carbonate  alone  .  to  I  i  per  cent,  sodium  carbonate  in  which  a 
drops  of  glycerin  extract  of  pancreas  have  been  previously  boiled  ; 
glycerin  extract  and  excess  of  0*2  per  cent,  hvdrochloric  acid.* 
I  up  six  test-tubes,  A'.  B',  C,  1>'.  1'.'.  F',  in  the  same  way,  but 
substitute  a  few  drops  ol  a  solution  ot 'commercial  pancrcatin  for  the 
glycerin  extract.  Set  up  two  test  tubes  as  in  experiment  4  (p.  426 
\\  uli  Melt's  t  ubes.  I  'ut  all  the  test-tubes  in  a  tumbler,  and  place  in  a 
bath  at  40°  C.  The  fibrin  will  be  gradually  eaten  away  in  A  and  A'. 
by  the  action  of  the  trypsin,  but  will  not  swell  up  or  become  clear 
before  disappearing,  as  it  does  in  dilute  hydrochloric  acid  with 
•i  in  extract  of  stomach.  Filter  the  contents  of  these  test-tubes. 
Neutralize  the  filtrate  with  dilute  acid  ;  a  precipitate  will  consist  of 
alkali-albumin.  If  such  a  precipitate  is  obtained,  filter  it  off  and  test 
the  filtrate  for  proteoses  and  peptones  as  in  4  (d)  (p.  426).  Some 
digestion,  and  perhaps  a  considerable  amount,  may  also  have  taken 
place  in  F  and  F'  ;  less  or  none  at  all  in  C  and  C  ;  and  none  in  the 
other  test-tubes  (pp.  331,  394). 

(c)  Add  a  few  drops  of  the  glycerin  extract  to  a  test-tube  con- 
taining starch  mucilage,  which  has  been  previously  found  free  from 
reducing  sugar.  Put  in  a  bath  at  400  C.  After  a  short  time  abund- 
ance of  reducing  sugar  will  be  found,  owing  to  the  action  of  the 
ferment,  amylopsin. 

(d)  Mince  thoroughly  a  good-sized  piece  of  fresh  pancreas,  and 
shake  up  well  with  three  or  four  times  its  bulk  of  water.  Put  5  c.c. 
of  fresh  cream  into  a  test-tube,  then  10  c.c.  of  the  extract,  a  few 
drops  of  chloroform  to  prevent  the  growth  of  bacteria,  a  few  drops 
of  litmus  solution,  and  if  necessary  enough  of  very  dilute  sodium 
hydroxide  to  just  render  the  colour  distinctlv  blue.  Shake  up,  and 
divide  the  mixture  into  two  portions,  A  and  B.  Boil  one  portion  (B), 
and  place  the  test-tubes  at  40'  C.  Examine  from  time  to  time.  The 
blue  colour  will  disappear  in  A,  owing  to  the  formation  of  fatty  acids 
from  the  neutral  fats,  and  sodium  hydroxide  must  be  added  to  it  to 
restore  the  colour.  In  B  the  fat-splitting  ferment  has  been  destroyed 
by  boiling,  and  fat-splitting  will  not  occur.  Probably  a  distinct 
result  will  not  be  obtained  for  several  hours,  and  it  will  be  best  to 
leave  the  tubes  in  the  incubator  over-night. 

(e)  If  the  laboratory  possesses  an  animal  with  a  pancreatic  fistula, 
the  following  experiment  may  be  done  by  a  limited  number  of 
students  with  fresh  pancreatic  juice  f  collected  from  the  fistula. 
Take  five  test-tubes,  A,  B,  C.  D,  E.  Add  5  c.c.  of  pancreatic  juice 
to  each  tube.  Boil  E,  and  then  cool  it.  Put  into  A  and  B  small 
pieces  of  heat-coagulated  egg-white,  into  C  a  little  starch  mucilage, 
and  into  D  and  E  5  c.c.  of  fresh  cream.  Add  further  to  B  a  scraping 
of  the  mucous  membrane  of  the  upper  part  of  the  small  intestine 
which  has  first  been  washed  free  of  contents.     To  D  and  E  add  a 

*  With  hydrochloric  acid  of  different  strengths  the  rapidity  of  digestion 
of  boiled  fibrin  by  glycerin  extract  of  dog's  pancreas  (1  volume  of  extract 
to  25  of  acid)  was  found  about  the  same  for  0*3  and  o'iy  per  cent,  acid  ; 
much  less  for  o'oS  per  cent.,  while  in  0*04  per  cent,  acid  there  was  prac- 
tically no  digestion  at  all.  In  0*4  per  cent,  acid  digestion  took  place 
more  rapidly  than  in  o'oS  per  cent.,  but  much  less  rapidly  than  in  0*17  per 
cent.  In  acid  of  all  strengths  digestion  was  markedly  slower  than  in 
1  per  cent,  sodium  carbonate. 

t  A  considerable  flow  of  pancreatic  juice  can  be  obtained  from  a  dog 
with  a  pancreatic  fistula  by  injecting  intravenously  an  extract  of  intestinal 
mucous  membrane  containing  secretin  (p.  379). 


43o  I    W  INUAL  OF  PHYSIOLOGY 

drop  or  two  "I  litmus  solution,  and,  if  necessary,  enough  oi  dilute 
sodium  hydroxide  to  just  establish  a  blue  colour.  Then  put  the 
test-tubes  at  400  C,  and  examine  after  a  tunc  No  digestion  will 
have  taken  place  in  A,  because  the  pancreatic  juice,  as  secreted,  does 
not  contain  active  trypsin.  In  B  digestion  may  take  place,  because 
the  cnterokinase  in  the  intestinal  mucous  membrane  will  activate 
the  trypsinogen  to  trypsin.  In  C  and  I)  there  will  be  evidence  of  the 
production  of  reducing  sugar  and  fatty  acids  respectively,  since 
the  pancreatic  juice,  as  secreted,  contains  active  amylopsin  and 
steapsin.     E  will  be  unchanged  unless  by  bacterial  action. 

(/)  Leucin  and  Tyrosin. — -As  examples  of  amino-acids  formed  when 
pancreatic  digestion  of  proteins  (fibrin  or  casein,  e.g.)  is  allowed  to 
go  on  for  some  days,*  leucin  and  tyrosin  may  be  isolated.  Add 
bromine  water  by  drops  to  5  c.c.  of  the  digest :  a  pink  colour  indicates 
tryptophane.  If  the  '  digest  '  be  neutralized,  then  filtered,  and  the 
filtrate  concentrated  and  allowed  to  stand,  a  crop  of  tyrosin  crystals 
will  separate  out.  since  tyrosin  is  only  slightly  soluble  in  watery 
solutions  of  neutral  salts.  These  crystals  having  been  filtered  off, 
the  proteoses  (albumoses)  and  peptones  can  be  precipitated  together 
by  alcohol,  and  afterwards  separated,  if  that  is  desired,  by  redis- 
solving  the  precipitate  in  water  and  throwing  down  the  proteoses 
by  saturation  with  ammonium  sulphate.  The  alcoholic  filtrate  will 
contain  any  leucin  that  may  be  present,  since  that  body  is  mode- 
rately soluble  in  alcohol,  as  well  as  traces  of  tyrosin.  which,  however, 
is  much  less  soluble  in  this  medium.  On  concentration,  crystals  of 
both  substances  will  be  obtained.  Tyrosin  crystallizes  characteristi- 
cally from  animal  liquids  in  beautiful  silky  needles  united  into 
sheaves,  leucin  in  the  form  of  indistinct  fatty-looking  balls,  often 
marked  with  radial  striae  and  coloured  with  pigment  (Figs.  169  and 
170,  p.  452). 

7.  Bile. — (a)  Test  the  reaction  of  ox  bile.     It  is  alkaline  to  litmus. 

(b)  Add  dilute  acetic  acid.  A  precipitate  of  bile-mucin  (really 
nucleo-albumin)  falls  down.  Some  of  the  bile-pigment  is  also  pre- 
cipitated. Filter.  (Pig's  bile  contains  more  of  the  mucin-like 
substance  than  ox  bile.) 

(c)  Put  a  little  of  the  filtrate  from  (b)  or  of  the  original  bile  into  a 
porcelain  capsule,  add  a  drop  or  two  of  a  dilute  solution  of  cane- 
sugar,  and  mix  with  the  bile.  Then  add  a  few  drops  of  strong  sul- 
phuric acid,  and  stir.  Then  a  few  drops  more  of  the  sulphuric  acid, 
stirring  all  the  time.  A  purple  colour  appearing  at  once,  or  after 
gentle  heating,  shows  the  presence  of  bile-acids  (Pettenkofer's  reac- 
tion). The  bile  may  be  diluted  before  the  addition  of  the  sulphuric 
acid.  In  this  case  a  greater  amount  of  the  acid  must  be  added. 
Examine  the  purple  liquid  in  a  test-tube  with  a  spectroscope  p 
Dilute  the  liquid  with  water,  adding  some  sulphuric  acid  to  partially 
clear  up  the  precipitate  caused  bv  the  water.  Two  absorption  bands 
are  seen,  one  to  the  red  side  of  D.  and  the  other,  a  stronger  and 
broader  band,  over  and  to  the  right  of  E.  When  only  a  very  small 
amount  of  bile-salts  is  present,  the  reaction  is  made  more  sensitive  if  a 
solution  of  furfuraldehyde  (1  to  1,000)  is  used  instead  of  cane-sugar. 

(d)  Hay's  Sulphur  Test. — Sprinkle  a  little  sulphur  (in  the  form  of 
the  fine  powder  known  as  flowers  of  sulphur)  on  the  surface  of  some 
bile  in  a  small  beaker  or  deep  watch-glass.  The  sulphur  will  soon 
sink  to  the  bottom.  Repeat  with  water  ;  the  sulphur  will  float.  The 
reaction  is  due  to  the  diminution  of  the  surface  tension  produced  by 

*   A  little  chloroform  is  added  to  prevent  bacterial  growth. 


PR  [<   lK.ll.   EXERCISES  431 

the  bile  acids,  and  succeeds  also  in  a  solution  of  bile-salts.  The  I'  1 
is  very  sensitive.  But  in  stomach  contents,  vomit,  or  stool 
rarely  gives  good  results,  since  alcohol  or  acetic  acid  is  often  presenl 
in  the  gastric  liquid,  and  phenol  and  its  derivatives  in  intestinal 
contents,  and  all  of  these  cause  such  an  alteration  in  the  surfaci 
1  ension  that  the  sulphur  sinks.  Ether,  chloroform,  turpentine, 
benzine  and  its  derivatives,  anilin  and  soaps,  also  vitiate  the  test 
111  t  he  same  way. 

(c)  Add  yellow  nitric  acid  (containing  nitrous  acid)  to  a  little  bile 
on  a  white  porcelain  slab.  A  play  of  colours,  beginning  with  green 
and  running  through  blue  to  yellow  and  yellowish-brown,  indicates 
the  presence  of  bile-pigment  (Gmelin's  reaction).  The  reaction  may 
also  be  obtained  by  putting  some  yellow  nitric  acid  into  a  test-tube, 
and  then  running  a  little  bile  from  a  pipette  on  to  the  surface  of  the 
acid.  The  play  of  colours  is  seen  at  the  surface  of  contact.  Where 
the  bile-pigment  is  present  only  in  traces,  some  of  the  liquid  may  be 
filtered  through  white  filter-paper,  and  the  test  applied  by  putting 
a  drop  of  the  nitric  acid  on  the  paper. 

(/)  Cholesterin  (Fig.  159) — Preparation.  —  Extract  a  powdered 
gall-stone  (preferably  a  white  one)  with  hot  alcohol  and  ether  in  a 
test-tube.  Heat  the  test-tube  in 
warm  water,  not  in  the  free  flame. 
Put  a  drop  of  the  extract  on  a  slide. 
Flat  crystals  of  cholesterin,  often 
chipped  at  the  corners,  separate  out. 
(a)  Carefully  allow  a  drop  of  strong 
sulphuric  acid  and  a  drop  of  dilute 
iodine  to  run  under  the  cover-glass. 
A  play  of  colours — violet,  blue,  green, 
red — is  seen. 

{p)  Evaporate  a  drop  of  the  solu- 
tion of  cholesterin  in  a  small  porce- 
lain capsule,  add  a  drop  of  strong 
nitric  acid,  and  heat  gently  over  a 
flame.  A  yellow  stain  is  left,  which  FlG-  159- —  Crystals  of  Choles- 
becomes  red  when  a  drop  of  ammonia  terin  (   rey). 

is  poured  on  it  while  it  is  still  warm. 

(7)  Dissolve  a  little  cholesterin  in  chloroform.  Add  an  equal  bulk 
of  strong  sulphuric  acid,  and  shake  gently.  The  solution  turns  red 
and  the  subjacent  acid  shows  a  green  fluorescence. 

(5)  Put  a  drop  or  two  of  water  in  a  watch-glass,  and  add  a  drop 
of  an  ethereal  solution  of  cholesterin.  The  cholesterin  is  precipi- 
tated, and  will  not  dissolve  in  the  water  even  on  heating.  Repeat 
the  observation  with  bile  instead  of  water.  The  cholesterin  dis- 
solves in  the  bile. 

(g)  To  a  little  of  the  filtrate  from  a  peptic  digest  (e.g.,  fibrin  which 
has  been  digested  for  twenty-four  hours  with  pepsin  and  hydro- 
chloric acid)  add  some  bile.  A  precipitate  is  thrown  down,  which 
is  redissolved  in  excess  of  the  bile  (p.  341). 

(h)  Shake  up  a  little  bile  with  some  rancid  olive-oil  in  a  test-tube.  An 
emulsion  is  formed .  Repeat  the  experiment  with  the  same  quantities 
of  bile  and  oil,  but  use  perfectly  fresh  oil.  Compare  the  stability  of 
the  two  emulsions,  allowing  the  tubes  to  stand  together  for  a  while. 

(i)  To  some  starch  mucilage,  shown  to  be  free  from  sugar,  add  a 
little  bile,  and  place  in  a  bath  at  400  C.  After  a  time  test  for  reducing 
sugar.     Report  the  result.     Bile  often  has  a  slight  diastatic  power. 


432  I    M  INI    II    OF  PHYS10L0G  \ 

i/i  in  demonstrate  the  Presence  of  hmi  in  the  Liver  Cells. 
sections  ol  liver  in  a  solution  of  potassium  Eerrocyanide,  and  then  Id 
dilute  hydrochloric  acid.  <  >r  a  15  per  cent,  solution  ol  potassium 
Eerrocyanide  in  o"5  percent,  hydrochloric  acid  may  be  used.  (The 
iron  may  previously  be  fixed  in  the  tissue  bv  hardening  it  in  a 
mixture  ol  alcohol  and  ammonium  sulphide.)  The  sections  become 
bluish  Erom  the  formation  of  Prussian  blue.  A  fine-pointed  glass  rod 
or  a  platinum  lifter  should  be  used  in  manipulating  them.  A  steel 
needle  cannot  be  employed.  .Mount  in  glycerin  01  Farrant's  solu- 
tion, or  (after  dehydrating  with  alcohol  and  clearing  in  xylol)  in 
xylol-balsam.  Blue  granules  may  be  seen  under  the  microscope  m 
some  of  the  hepatic  cells.  Sections  of  spleen  may  also  be  examined 
for  this  reaction. 

8.  Microscopical  Examination  of  Faeces. —Examine  under  the 
microscope  the  slides  provided.  Draw,  and  as  far  as  possible  deter- 
mine the  nature  of,  the  objects  seen  (p.  396). 

9.  Absorption  of  Fat. — {a)  Feed  a  rat  or  frog  with  fatty  food  ;  kill 
the  rat  in  three  or  four  hours,  the  frog  in  two  or  three  days.  Imme- 
diately after  killing  the  rat  open  the  abdomen,  carefully  draw  out  a 
loop  of  intestine,  and  look  through  the  thin  mesentery.  The  white 
lacteals  will  probably  be  seen  ramifying  in  the  mesentery.  They 
appear  white  on  account  of  the  presence  of  globules  of  fat  in  the 
chyle  with  which  they  are  filled.  Strip  off  tiny  pieces  of  the  mucous 
membrane  of  the  small  intestine,  and  steep  them  in  £  per  cent,  solu- 
tion of  osmic  acid  for  forty-eight  hours.  Then  tease  fragments  of  the 
mucous  membrane  in  glycerin  and  examine  under  the  microscope. 
To  preserve  the  specimens  take  off  the  glycerin  with  blotting-paper 
and  mount  in  Farrant's  medium,  which  is  a  preservative  glycerin 
mixture.  Other  portions  of  the  mucous  membrane  may  be  hardened 
for  a  fortnight  in  a  mixture  of  z  parts  of  Midler's  fluid  and  1  part 
of  a  1  per  cent,  solution  of  osmic  acid.  Sections  are  then  made 
with  a  freezing  microtome  after  embedding  in  gum.  No  process 
must  be  used  by  which  the  fat  would  be  dissolved  out  (Schafer). 
(See  Fig.  156,  p.  413.) 

(b)  Feed  a  cat  with  30  grammes  of  butter  stained  a  deep  red  with 
the  dye  Sudan  III.  After  five  hours  anaesthetize  the  animal  with 
ether,  insert  a  cannula  in  the  carotid  artery,  and  obtain  a  sample 
of  blood.  Defibrinate  the  blood,  and  separate  the  serum  by  the 
centrifuge.  If  digestion  and  absorption  of  the  fat  have  proceeded 
normally,  the  serum  will  contain  numerous  fat  droplets,  and  will  be 
tinged  pink  by  the  dye,  which  can  be  dissolved  out  of  it  by  shaking 
up  with  ether.  On  opening  the  abdomen  it  will  be  seen  that  the 
mucous  membrane  of  the  small  intestine,  as  far  down  as  the  fat  lias 
reached,  is  stained  pink,  and  that  the  lacteals  in  t  he  mesentery  arc  also 
pink.    Observe  whether  any  of  the  pigment  has  passed  into  the  urine. 

10.*  Time  required  for  Digestion  and  Absorption  of  Various  Food 
Substances,  -heed  three  dogs.  A,  B,  and  C.  which  have  previously 
fasted  for  twenty-four  hours,  with  a  meal  containing  starch  (proved 
to  be  free  from  sugar),  lard,  and  meat. 

(i  i  After  fifteen  minutes  inject  subcutaneously  into  A  2  c.c.  of  a 
o- 1  per  cent,  solution  of  apomorphine.  Note  the  time  which  clap>e> 
before  the  animal  vomits.     Collect  the  vomit. 

*  Experiments  to  and  I  t  are  conveniently  done  in  a  class  by  assigning 
each  of  the  three  animals  to  a  separate  set  of  students.  The  contents  ot 
the  stomach  and  intestine  arc  divided  into  three  portions,  so  that  each 
set  has  a  sample  from  each  dog. 


PR  ICTh    \i    EXERCISES 

a)   Examine  a  little  oi  i1  under  the  microscope,  and  make  ou1  fat 
globules,  muscular  fibres  and  starcb  granules.     The  Latter  can  be 
ignised  l>v  their  being  coloured  blue  by  a  drop  or  two  oi  iodine 
solution. 

(h)  Filter  the  chyme,  mixing  it,  if  necessary,  with  a  little  water, 
and  test  ii  as  in  |  (d)  (p.  1.26)  for  the  products  01  digestion  of  proteins. 
In  addition,  test  tor  starch,  dextrin,  and  reducing  sugar. 

(2)  One  and  a  quarter  hours  after  the  meal  inject  apomorphine 
into  dog  B,  and  proceed  as  in  (1). 

(3)  Two  and  a  half  hours  alter  the  meal  inject  apomorphine  into 
dog  C,  and  proceed  as  in  (1).  Compare  the  results  from  the  three 
specimens  of  chyme. 

11.*  Quantity  of  Cane-sugar  inverted  and  absorbed  in  a  Given 
Time. — Take  three  dogs,  A,  B,  and  C,  which  have  fasted  for  twenty- 
four  hours.  The  animals  should  be  about  the  same  size.  Feed  A 
and  B  with  100  c.c.  of  a  standard  solution  of  cane-sugar  (about  a  20 
per  cent,  solution)  or  as  much  more  as  they  will  take.  If  the  dogs 
have  been  kept  without  water  for  a  day  they  will  more  readily  take 
the  sugar  solution.  Or  it  may  be  given  through  a  tube  passed  into 
the  stomach,  and  in  this  case  a  larger  quantity  of  sugar  can  be  given. 
A  gag  consisting  of  a  piece  of  wood  with  a  hole  in  the  middle  of  it, 
through  which  the  tube  is  passed,  must  first  be  secured  in  the  dog's 
mouth.  Feed  C  with  50  grammes  of  powdered  cane-sugar  mixed 
with  lard,  the  mixture  being  rolled  into  little  balls. 

(1)  After  a  quarter  of  an  hour  put  A  under  chloroform  or  the  A.C.E. 
mixture,  and  fasten  it  on  a  holder.  Kill  the  animal  with  chloroform, 
open  the  abdomen,  tie  the  oesophagus,  place  double  ligatures  on  the 
pyloric  end  of  the  stomach  and  the  lower  end  of  the  small  intestine, 
and  divide  between  them.  Cut  out  the  stomach  and  intestine  ; 
wash  their  contents  into  separate  vessels,  and  test  the  reaction  with 
litmus  paper.  Add  water  and  rub  up  thoroughly.  Filter.  Wash 
the  residue  repeatedly  with  small  quantities  of  water,  and  pass  all 
the  washings  through  the  filter.  Make  up  each  of  the  two  filtrates 
to  200  c.c. 

(a)  Test  the  filtrates  from  the  contents  of  the  stomach  and  intes- 
tines qualitatively  for  dextrose  by  Trommer's  (p.  10)  and  the  phenyl- 
hydrazine  test  (p.  488). 

(b)  If  no  reducing  sugar  is  present,  add  to  20  c.c.  of  each  filtrate 
1  c.c.  of  hydrochloric  acid,  boil  for  half  an  hour,  and  again  test  for 
reducing  sugar.     If  it  is  now  found,  some  cane-sugar  is  present. 

(c)  If  reducing  sugar  is  found,  estimate  its  amount  as  dextrose  by 
Fehling's  solution  (p.  489)  in  a  measured  quantity  of  the  original 
filtrate  of  the  gastric  or  intestinal  contents  before  and  after  boiling 
with  one-twentieth  of  its  volume  of  hydrochloric  acid. 

(d)  Estimate  in  the  same  way  the  amount  (as  dextrose)  of  the  invert 
sugar  in  the  standard  solution  of  cane-sugar  after  inversion,  and 
before  inversion  if  it  gives  the  qualitative  test  for  reducing  sugar 
before  it  has  been  boiled  with  acid. 

From  the  data  obtained  (and  taking  95  parts  of  cane-sugar  as 
equal  to  100  parts  of  dextrose)  calculate  the  amount  of  cane-sugar 
absorbed,  left  unchanged,  and  inverted,  though  not  absorbed. 

(2)  One  and  a  half  hours  after  the  meal  anaesthetize  B,  and  proceed 
as  in  ( 1 ) . 

(3)  Two  hours  after  the  meal  proceed  in  the  same  way  with  C. 
But  in   addition  observe  the  lacteals  in  the  mesentery,  by  gently 

*  See  note  on  p.  432. 

28 


434 


A    MANUAL  OF  PHYSIOLOGY 


lifting  up  a  loop  of  intestine  immediately  after  opening  the  abdomen. 
If  the  absorption  of  the  fat  lias  begun,  they  will  be  easily  visible,  as 
a  network  of  fine  milk-white  vessels.  Also  examine  the  gastric  and 
intestinal  contents  with  the  microscope  for  fat  globules.  Compare 
your  results  on  the  amount  of  sugar  obtained  from  the  three  animals. 
Probably  much  more  unabsorbed  sugar  will  be  found  in  C  than  in 
B,  as  the  lard  hinders  it  from  being  dissolved. 

12.  Auto-digestion  of  the  Stomach.  -In  some  of  the  previous 
experiments  the  stomach  of  an  animal  killed  (hiring  digestion  should 
be  removed  from  the  body  after  double  ligation  of  oesophagus  and 
duodenum,  and  placed  in  a  water-bath  at  400  C.  After  several 
hours  the  contents  should  be  washed  out,  and  the  mucous  membrane 
examined.     It  may  be  entirely  eaten  away  in  parts. 


CHAPTER    VI 
EXCRETION 

We  have  now  followed  the  ingoing  tide  of  gaseous,  liquid,  and 
solid  substances  within  the  physiological  surface  of  the  body. 
There  we  leave  them  for  the  present,  and  turn  to  the  considera- 
tion of  the  channels  of  outflow,  and  the  waste  products  which 
pass  along  them.  In  a  body  which  is  neither  increasing  nor 
diminishing  in  mass  the  outflow  must  exactly  balance  the  inflow  ; 
all  that  enters  the  body  must  sooner  or  later,  in  however  changed 
a  form,  escape  from  it  again.  In  the  expired  air,  the  urine,  the 
secretions  of  the  skin,  and  the  fseces,  by  far  the  greater  part  of 
the  waste  products  is  eliminated.  Thus  the  carbon  of  the 
absorbed  solids  of  the  food  is  chiefly  given  off  as  carbon  dioxide 
by  the  lungs  ;  the  hydrogen,  as  water  by  the  kidneys,  lungs  and 
skin,  along  with  the  unchanged  water  of  the  food  ;  the  nitrogen, 
as  urea  by  the  kidneys.  The  faeces  in  part  represent  unabsorbed 
portions  of  the  food.  A  small  and  variable  contribution  to  the 
total  excretion  is  the  expectorated  matter,  and  the  secretions 
of  the  nasal  mucous  membrane  and  lachrymal  glands.  Still 
smaller  and  still  more  variable  is  the  loss  in  the  form  of  dead 
epidermic  scales,  hairs,  and  nails.  The  discharges  from  the 
generative  organs  are  to  be  considered  as  excretions  with  refer- 
ence to  the  parent  organism,  and  so  is  the  milk,  and  even  the 
foetus  itself,  with  respect  to  the  mother. 

Excretion  by  the  lungs  and  in  the  fasces  has  been  already 
dealt  with.  All  that  is  necessary  to  be  said  of  the  expectoration 
and  the  nasal  and  lachrymal  discharges  is  that  the  first  two 
generally  contain  a  good  deal  of  mucin,  and  are  produced  in 
small  mucous  and  serous  glands,  the  cells  of  which  are  of  the 
same  general  type  as  those  of  the  mucous  and  seious  salivary 
glands.  The  lachrymal  glands  are  serous  like  the  parotid  ;  and 
the  tears  secreted  by  them  contain  some  albumin  and  salts,  but 
little  or  no  mucin.  The  sexual  secretions  and  milk  will  be  best 
considered  under  reproduction  (Chap.  XIV.),  so  that  there  remain 
only  the  urine  and  the  secretions  of  the  skin  to  be  treated  here 

43  5  28—2 


436  A    MANUAL  OF  PHYSIOLOGY 


I.  Excretion  by  the  Kidneys. 

The  Chemistry  of  the  Urine. — Normal  urine  is  a  clear  yellow 
liquid  acid  to  litmus  and  similar  indicators,  but  nearly  neutral 
or  very  weakly  acid  in  the  physico-chemical  sense  (p.  23).  The 
average  specific  gravity  is  about  1020,  the  usual  limits  being  1015 
and  1025,  although  when  water  is  taken  in  large  quantities,  or 
long  withheld,  the  specific  gravity  may  fall  to  1005,  or  even  less, 
or  rise  to  1035,  or  even  more.  The  quantity  passed  in  twenty- 
lour  hours  is  very  variable,  and  is  especially  dependent  on  the 
activity  of  the  sweat-glands,  being,  as  a  rule,  smaller  in  summer 
when  the  skin  sweats  much,  than  in  winter  when  it  sweats  little. 
The  average  quantity  for  an  adult  male  is  1200  to  1600  c.c.  (sav, 
40  to  50  oz.).* 

Composition  of  Urine. — This  is  very  closely  related  to  the 
quantity  and  quality  of  the  food.  Hence  it  is  impossible  to 
speak  of  a  definite  normal  composition  of  the  urine.  It  is 
essentially  a  solution  of  urea  and  inorganic  salts,  the  proportion 
of  the  latter  being  generally  about  15  per  cent.,  or  double  the 
usual  amount  in  physiological  liquids.  Besides  urea,  there  are 
other  nitrogenous  bodies  in  much  smaller  quantity,  such  as 
ammonia,  uric  acid,  and  the  allied  xanthin  bases,  hippuric  acid, 
and  kreatinin.  Some  of  these  at  least  are  products  of  the 
metabolism  of  proteins  within  the  tissues.  And  besides  the  in- 
organic salts  there  are  certain  organic  bodies — indoxyl.  phenyl, 
pyrokatechin,  skatoxyl — united  with  sulphuric  acid,  which  are 
primarily  derived  from  the  products  of  the  putrefaction  of 
proteins  within  the  digestive  tube. 

Folin  has  published  analyses  of  '  normal  '  urines  from  six  persons, 
weighing  from  566  to  70-9  kilos  (average  634  kilos),  who  were 
kept  for  seven  days  on  one  standard  uniform  diet.  The  diet  con- 
sisted of  500  c.c.  of  milk,  300  c.c.  of  cream  (containing  18  to  22  per 
cent,  of  fat),  450  grammes  of  eggs,  200  grammes  of  Hor lick's  malted 
milk,  20  grammes  of  sugar,  6  grammes  of  sodium  chloride,  water 
enough  to  make  the  whole  up  to  two  litres,  and  900  c.c.  of  additional 
water.  The  ingredients  contained  119  grammes  of  protein,  about 
148  grammes  of  fat,  and  225  grammes  of  carbo-hydrates.  The 
average  results  of  all  the  determinations  are  given  in  the  following 
table  : 

*  The  average  quantity  of  urine  varies  not  only  with  the  season,  but 
also  with  the  habits  of  the  person,  especially  as  regards  the  amount  of 
liquid  taken.  The  average  for  seventeen  healthy  (American)  students, 
whose  urine  was  collected  for  mx  to  eight  successive  days  in  winter,  was 
1 166  c.c.  The  highest  average  in  any  one  individual  for  the  observation 
p. -nod  was  1487  c.c.  (for  seven  days),  and  the  lowest  743  c.c.  (for  eight 
days).  The  greatest  quantity  parsed  in  any  one  period  of  twenty-four 
hours  was  2286  c.c.  (by  the  individual  whose  average  was  the  highest). 
The  smallest  quantity  passed  in  twenty-four  hours  was  650  c.c.  (by  the 
individual  whose  average  was  the  lov 


/  XCRETION 

437 

Grammes. 

Containing       Pen 
Nitroj                      1  ''■'' 
Grammes.         Nitrogen. 

I  rea           ... 

Ammonia  - 

Kreatinin 

I  ric  acid    - 

Nitrogen  in  other  compounds 

- 

29  8 

o-37 

I3.9               87-5 
070                4-3 

0-58            3-6 
0'12               o-8 
o-6o            3-75 

1 6-  00 

Total  nitrogen    - 

" 

2'92 

0-22 

o-i7 
3'3i 

3-87 
6-i 

Percentage  of  Total 
Sulphur. 

Inorganic  SO;! 
Kthereal  SO-, 
'  Neutral  '  SO, 

Total  sulphur  as  SO..     - 

Total  phosphates  as  P20-, 

Chlorine 

87-8 

6-8 
51 

^•,      ,    ,  ,         . ,.,      ■  r    ,     •  ,       -j      ^       \  mineral,  304. 

Titratable  acidity  in  c.c.  ot  decinormal  acid  -  017  j  organic    in, 


Indican  (Fehling's  solution  =100*) 
Volume  of  urine 


-  77 

-  1430  c.c. 

The  great  influence  of  diet  on  the  composition  of  the  urine  is 
illustrated  in  the  following  table.  Urine  I.  was  obtained  from  a 
man  weighing  87  kilos  on  the  standard  protein-rich  diet  described 
above.  Urine  II.  was  obtained  from  the  same  person  on  a  diet 
very  poor  in  protein  (400  grammes  of  starch  and  300  c.c.  of  cream), 
containing  only  about  1  gramme  of  nitrogen,  as  against  19  grammes 
in  the  first  diet. 


I. 

II. 

Volume  of  urine 

1170  c.c. 

385  c 

.c. 

Per  Cent. 

Grammes.     Per  Cent. 

Grammes. 

Total  nitrogen 

if5-8 

3-60 

Urea-nitrogen 

14-70    =  87-3 

2-20      = 

6l-7 

Ammonia-nitrogen 

0-49    =     3-0 

0-42      = 

n-3 

Uric  acid-nitrogen 

0-18    =      i-i 

o-og    = 

2'5 

Kreatinin-nitrogen 

0-58    =     3-6 

o-6o    = 

17-2 

Nitrogen  in  other  compounds 

0-85    =      4-9 

0-27    = 

7-3 

Total  S03       - 

3-64 

Inorganic  SO, 

3-27    =   90-0 

0-46    = 

60-5 

Kthereal  S03 

0-19    =     5-2 

o-io    = 

13-2 

Neutral  SO, 

0-18    =      4-8 

0-20     = 

26-3 

Total  phosphates  as  P.,0- 

4'i 

i-o 

Chlorine          ... 

6-i 

I-b 

Titratable  acidity  in  c.c  —  acid 

J  10 


1  mineral  398  1  mineral  123 

5  "|  organic  407  3-4  ,  organic  201 

Indican  (Fehling's  solution  =  100)  -     120     -         -         o 

*  The  indican  is  given  in  arbitrary  units,  the  indigo-blue  being  obtained 

from  the  urine  and  then  estimated  colorimetrically,  using  Fehling's  solu- 


438 


A    MANUAL    OF   PHYSIOLOGY 


The  titratab'e  acidity  of  urine  (see  p.  24)  is  chiefly  due  to  th< 
monobasi*  phosphates,  such  as  acid  sodium  phosphati  \.d  IJ'<  ),j. 
but  in  an  important  degree  also  to  organic  acids.  According  to 
Folin,  indeed,  the  organic  acidity  may  be  more  than  half  the  total 
acidity.  Normally  the  acidity  diminishes  distinctly,  or  even  gives 
place  to  alkalinity,  during  digestion,  when  the  acid  of  the  gastric 
juice  is  being  secreted.  This  is  sometimes  fancifully  denominated  the 
alkaline  tide.  After  a  fast,  as  before  breakfast,  the  opposite  condition, 
the  ac id  tide,  occurs. 

The  acidity  varies  with  the  quantity  of  vegetable  food  in  the  diet. 
The  urine  of  herbivora  and  vegetarians  is  alkaline,  and  is  cither  turbid 
when  passed,  or  on  standing  soon  becomes  turbid  from  precipitated 
carbonates  and  phosphates  of  earthy  bases,  while  that  of  carnivora 
and  of  fasting  herbivora.  which  are  living  on  their  own  tissues,  is 
stronglv  acid  and  clear.  Normal  human  urine  mav  deposit  urates 
soon  after  discharge,  as  they  are  more  soluble  in  warm  than  in  cold 
water.  They  carry  down  some  of  the  pigment,  and  therefore  usually 
appear  as  a  p:'nk  or  brick-red  sediment.  When  urine  is  allowed  to 
stand  after  being  voided,  what  is  generally  described  as  '  acid  fer- 
mentation '  occurs.  The  acidity  gradually  increases  ;  acid  sodium 
urate  is  produced  from  the  neutral  urate,  and  comes  down  in  the 
form  of  amorphous  granules,  while  the  liberated  uric  acid  is  deposited 


Fig.   160. — Uric   Acid 


Fig.   161. — Calcium  Oxalate. 


often  in  '  whetstone  '  crystals,  coloured  yellow  by  the  pigment  (Fig. 
160).  Calcium  oxalate  may  also  be  thrown  down  as  '  envelope,'  a,  b, 
or.  less  frequently,  '  sand-glass  '  crystals,  c  (Fig.  161).  If  the  urine 
is  allowed  to  stand  for  a  few  days,  especially  in  a  warm  place,  or  in  a 
place  where  urine  is  decomposing,  the  reaction  becomes  ultimately 
strongly  alkaline,  owing  to  the  formation  of  ammonium  carbonate 
from  urea  bv  the  action  of  micro-organisms  (Micrococcus  urea;,  Bac- 
terium iirece',  and  others)  which  reach  it  from  the  air,  and  produce  a 
soluble  ferment,  in  whose  presence  the  urea  is  split  up  with  assump- 
tion of  water.     Thus  : 

CON2H4+2H,,0      =     (NH4)2CO 

Urea.  Ammonium  carbonate. 

The  substances  insoluble  in  alkaline  urine  are  thrown  down,  the 
deposit  containing  ammonio-tnagnesic  or  triple  phosphate,  formed  by 
the  union  of  ammonia  with  the  magnesium  phosphate  present  in  fresh 
urine,  and  precipitated  as  clear  crystals  of  '  knife-rest  '  or  '  coffin-lid  ' 
shape  (Fig.  162),  along  with  amorphous  earthy  phosphates,  and  often 

tion  as  a  standard.  Fehling's  solution  is  employed  because  it  is  a  blue 
liquid  of  definite  depth  oi  tint  already  prepared  in  every  physiological 
laboratory. 


/  XCRETION 


439 


a<  id  ammonium  urate  in  the  form  of  dark  balls  occasionally  covered 
with  spines  (Fig.  165).  Calcium  phosphate  (CaHP04)  is  another 
phosphate  found  in  sediments  deposited  from  alkaline  or  faintly  acid 
unnc  It  is  usually  amorphous,  but  sometimes  in  the  form  of  long 
prismatic  crystals  arranged  in  star  fashion,  and  hence  spoken  of 
as  stellar  phosphate  (Fig.  164).      It  is  not  pigmented. 

It  is  only  in  pathological  conditions  that  the  alkaline  fermentation 
takes  place  within  the  bladder.  The  reaction  of  the  urine  can 
readily  be  made  alkaline  by  the  administration  of  alkalies,  alkaline 
carbonates,  or  the  salts  of  vegetable  acids  like  malic,  citric,  and 
tartaric  acid,  which  are  broken  up  in  the  body  and  form  alkaline 
carbonates  with  the  alkalies  of  the  blood  and  lymph.     It  is  not  so 


o 


Fig.    162. — Triple    Phosphate. 


Fig.   163. — Cystiv. 


easy  to  increase  the  acidity  of  the  urine,  although  mineral  acids  do 
so  up  to  a  certain  limit.  If  the  administration  of  acid  be  pushed 
farther,  ammonia  is  split  off  from  the  proteins,  and  is  excreted  in  the 
urine  as  the  ammonium  salt  of  the  acid. 

Determination  of  the  Acidity. — A  titration  method  is  described  in 
the  Practical  Exercises  (p.  477).  In  speaking  of  the  reaction  of 
blood,  it  has  already  been  mentioned  (p.  24)  that  we  cannot  deter- 
mine by  titration  the  true  acidity  or  alkalinity  of  a  liquid  in  the 
physico-chemical  sense — i.e.,  the  concentration  of  the  dissociated 
hydrogen  and  hydroxyl  ions  respectively.  E.g.,  when  we  titrate 
equal  quantities  of  decinormal*  acetic  acid  and  decinormal  hydro- 
chloric acid  with  decinormal  potassium  hydroxide,  using,  say,  phenol- 

W 


Fig.   164. — Stellar  Phosphate 
Crystals. 


Fig.   165. — Ammonium  Urate 
(after   Milroy). 


phthalein  as  the  indicator,  nearly  the  same  volume  of  the  potassium 
hydroxide  solution  will  be  needed  to  neutralize  each  acid.  Yet 
it  can  be  shown  by  physico-chemical  methods  that  the  acetic  acid 
in  the  strength  used  is  only  dissociated  to  the  extent  of  a  little  more 
than  1  per  cent.,  while  about  80  per  cent,  of  the  hydrochloric  acid 
is  dissociated.  The  concentration  of  the  hydrogen  ions  is  there- 
*  A  normal  solution  of  a  substance  contains  in  a  litre  a  number  of 
grammes  of  the  substance  equal  to  the  number  which  expresses  its 
equivalent  weight — a  decinormal  (usually  written  tV)  solution  one-tenth 
of  this  amount,  a  centinormal  one-hundredth,  etc.  Thus,  a  normal 
solution  of  potassium  hydroxide  contains  56  grammes  of  KOH,  and  a  deci- 
normal  solution    v^  grammes  in    1000   c.c. 


440  A    MANUAL  OF  PHYSIOLOGY 

fore  eighty  times  as  great  in  the  hydrochloric  as  in  the  acetic  aci<! 
solution.  What  we  determine  by  the  titration  is  not  the  true 
acidity,  but  the  total  amount  of  hydrogen  which  can  be  replaced 
by  metal.  The  concentration  of  the  hydrogen  ions  in  normal  urine 
is  very  small,  on  the  average  only  about  0-003  milligrammes  in  the 
litre,  or  about  thirty  times  as  much  as  is  present  in  the  purest  disl  died 
water.  Urine  departs  about  as  much  from  neutrality  in  the  one 
direction  as  blood  does  in  the  other. 

Urea,  CO(NH2)2,  is  the  form  in  which  by  far  the  greater  part  of 
the  nitrogen  is  under  ordinary  conditions  discharged  from  the  body. 
Its  amount  is  as  important  a  measure  of  protein  metabolism  as  the 
quantity  of  carbon  dioxide  given  out  by  the  lungs  is  of  the  oxidation 
of  carbonaceous  material.  Yet  a  glance  at  the  table  on  p.  437 
shows  that,  when  the  total  protein  metabolism  is  greatly  reduced 
by  diminishing  the  protein  in  the  food,  the  relative  as  well  as  the 
absolute  amount  of  nitrogen  eliminated  as  urea  suffers  a  great 
diminution.  The  relative  amount  of  the  other  nitrogenous  urinary 
constituents,  especially  of  the  kreatinin,  is  markedly  increased. 
The  significance  of  this  difference  is  alluded  to  in  speaking  of  the 
kreatinin  content  of  urine,  and  will  have  to  be  again  considered 
under  Protein  Metabolism.  Urea  is  soluble  in  water  and  in  alcohol, 
and  crystallizes  from  its  solutions  in  the  form  of  long  colourless 
needles,  or  four-sided  prisms  with  pyramidal  ends.  It  can  be 
easily  prepared  from  urine.  Urea  can  also  be  obtained  artificiallv 
by  heating  its  isomer,  ammonium  cyanate  (NH4  — O  — CN),  to 
ioo°  C.  This  reaction  is  of  great  historical  interest,  as  it  forms 
the  final  step  in  Wohler's  famous  synthesis  of  urea,  the  first 
example  of  a  complex  product  of  the  activity  of  living  matter 
being  formed  from  the  ordinary  materials  of  the  laboratory. 
Heated  in  watery  solution  in  a  sealed  tube  to  1800  C,  urea 
is  entirely  split  up  into  carbon  dioxide  and  ammonia,  a  change 
which  can  also  be  brought  about,  as  already  mentioned,  by 
the  action  of  micro-organisms.  Nitrous  acid,  hypochlorous  acid, 
and  salts  of  hypobromous  acid  carry  the  decomposition  still 
further,  carbon  dioxide,  nitrogen,  and  water  being  the  products  of 
their  oxidizing  action  on  urea.  Thus:  C0.2(NH2)  +  3NaBrO  = 
3XaBr+ 2H20+ C02+ N2.  This  reaction  is  the  basis  of  the  hypo- 
bromite  method  of  estimating  the  quantity  of  urea  in  urine  (Practical 
Exercises,  p.  480). 

Ammonia. — The  ammonia  in  urine  is  united  with  acids  in  the  form 
of  salts.  Its  formation  from  proteins  is  determined,  as  we  shall  see 
later  on,  by  the  necessity  of  neutralizing  certain  acids  produced  in 
metabolism — e.g.,  those  derived  from  the  sulphur  and  phosphorus 
of  the  proteins,  or  acids  administered  experimentally.  According 
to  some  observers,  the  percentage  amount  of  the  total  nitrogen  in 
the  urine  in  the  form  of  ammonia  remains  the  same  whether  the  food 
be  rich  or  poor  in  protein  (Schittenhelm,  etc.).  but  others  state  that 
when  the  protein  is  reduced,  there  is  a  relative  increase  in  the 
ammonia-nitrogen  (see  table  on  p.  437)  (Folin). 

Uric  acid  (C-H,N40.)  exists  in  large  amount  in  the  urine  of  birds. 
The  excrement  of  serpents  consists  almost  entirely  of  uric  acid.  In 
both  cases  it  is  mainly  in  the  form  of  acid  ammonium  urate.  In 
contrast  to  urea,  uric  acid  is  very  insoluble,  requiring  1,900  parts  of 
hot,  and  15,000  parts  of  cold,  water  to  dissolve  it.  In  man  and 
mammals  the  quantity  is  comparatively  small  in  health,  but  is 
increased  after  a  meal,  particularly  one  containing  substances  rich 


EXCRETION  441 

in  nucleins — e.g.,  the  thymus  -or  substances  containing  purin 
bases  e.g.,  liypoxanthin  in  meat.  When  the  amount  of  pro- 
tein in  the  food  is  greatly  reduced,  the  absolute  quantity  of  uric 
acid  is  diminished,  but  the  proportion  of  the  total  nitrogen  of  the 
urine  eliminated  as  uric  acid  is  increased,  since  the  '  endogenous  ' 
uric  acid  (p.  507)  still  continues  to  be  formed  and  excreted. 

The  purin  bases  (sometimes  called  the  nuclein  bases,  the  alloxuric 
bases,  or  the  xanthin  bases)  are  a  group  of  substances  allied  to  uric 
acid,  and  including,  besides  xanthin  itself,  hypoxanthin,  guanin, 
adenin,  and  other  bodies.  They  exist  in  very  small  amount  in  urine, 
but,  like  uric  acid,  are  increased  in  amount  *by  the  ingestion  of 
nuclein-containing  substances.  The  greater  part  of  the  purin  bases 
produced  in  the  body  is  transformed  into  uric  acid  ;  it  is  only 
the  untransformed  residue  which  appears  in  the  urine.  An  interest- 
ing fraction  of  the  purin  bases  in  the  urine  which  is  not  related  to 
the  nuclein  metabolism  is  composed  of  the  so-called  heteroxanthin. 
derived  from  caffeine  in  the  coffee  and  tea,  /-methylxanthin,  derived 
from  theobromine  in  the  cocoa,  and  paraxanthin.  derived  from  theo- 
phyllin  in  the  tea,  consumed  as  beverages. 

The  purin  bodies  are  so  called  because  they,  and  uric  acid  also,  are 
all  to  be  considered  chemically  as  derivatives  of  a  substance  called 
purin  (C-H4X4).  which,  however,  has  itself  never  been  discovered 
in  the  body.     Their  empirical  formulae  are  as  follows  : 

Purin  -  C5H4N4. 

Hypoxanthin  -  C6H4N40  -  Monoxypurin       ^  a  A 

Xanthin  -  C-H4X4C>2  -  -  Dioxy  purin 

Adenin  -  C;H3X4.XH2     -  -  Amino-purin 

Guanin  -  C-H^X4O.XH2-  -  Amino-oxypurin 

Uric  acid  -  C^H4X40;i  -  -  Trioxypurin. 

Hippuric  acid  (CyHuX03)  occurs  in  considerable  quantity  in  the 
urine  of  herbivora  (Practical  Exercises,  p.  486)  ;  in  the  urine  of 
carnivora  and  of  man  only  in  traces  ;  in  that  of  birds  not  at  all.  Its 
amount  is  much  more  dependent  on  the  presence  of  particular  sub- 
stances in  the  food  than  that  of  the  other  organic  constituents  of 
urine.  Anything  which  contains  benzoic  acid,  or  substances  which 
can  be  readily  changed  into  it  (such  as  cinnamic  and  quinic  acids), 
causes  an  increase  of  the  hippuric  acid  in  urine.  In  fact,  one  of  the 
best  ways  of  obtaining  the  latter  is  from  the  urine  of  a  person  to 
whom  benzoic  acid  is  given  by  the  mouth  ;  the  sweat  may  also  in 
this  case  contain  a  trace  of  hippuric  acid.  Chemically,  it  is  a  con- 
jugated acid  formed  by  the  union  of  benzoic  acid  and  glycin.     Thus  : 

C7H,;02  +  C2H,X02  =  CsHgNO,  +  H,0. 

Benzoic  acid.         Glycin.  Hippuric  acid.      Water. 

Benzoic  acid,  therefore,  meets  glycin  in  the  body,  and  combines  with 
it.  as  fatty  acids  meet  glycerin  and  combine  with  it.  But  while  a 
minute  amount  of  free  glycerin  has  been  found  in  the  plasma,  no 
free  glycin  has  been  detected  in  the  normal  blood  or  tissues.  Glycin. 
however,  has  been  demonstrated  in  the  blood  and  ascitic  fluid  in 
cases  of  nephritis. 

Amino-acids. — The  only  amino-acid  hitherto  detected  with  cer- 
tainty in  normal  urine  is  glycin. 

Oxalic  acid  is  always  present,  although  in  very  small  amount. 
Some  of  it  comes  from  the  oxalates  of  the  food,  but  a  portion  of  it 


r  -  x 
Jk.o 


44^ 


A   MANUAL  OF  1'llYSIOLOGY 


arises  in  the  metabolism  of  the  tissues  probably  from  the  de< 
position  of  uric  acid.      It  is  known  that  outside  of  the  body  uric  acid 
may   be   made  to  yield  oxalic  acid.     Calcium  oxalate  crystals  are 
often  seen  in  urinary  sediments. 

Kreatinin  ((',1 I7N  ;<  >). — Kreatinin  is  the  anhydride  oi  kreatin 
I  Fig.  [66).  Its  formula  differs  from  that  of  kreatin  only  in  possess- 
ing the  elements  of  one  molecule  of  water  less  ;  and  kreatinin  can  be 
obtained  by  boiling  kreatin  with  dilute  sulphuric  acid,  then  neu- 
tralizing with  barium  carbonate,  filtering,  evaporating  the  filtrate  to 
dryness  on  the  water-bath,  and  [extracting  the  residue  with.alcohol. 
From  its  alcoholic  solution  it  crystallizes  in  colourless  prisms 
Kreatinin  forms  crystallinejcompounds  with  various  acids  and  salts. 
One  of  the  best  known  of  these  is  kreatinin-zinc-chloride.  formed 
on  the  addition  of  zinc  chloride  to  an  alcoholic  or  watery  solution 
of  kreatinin,  often  in  the  shape  of  beautiful  thick-set  rosettes  of 
needles  (Fig.  167).  A  portion  of  the  urinary  kreatinin  is  derived 
from  the  kreatin  of  the  meat  taken  as  food.  But  this  is  not  its  only 
source,  for  on  a  meat-free 
diet  and  in  starvation  krea- 
tinin is  still  excreted.  The 
absolute  quantity  in  the  urine 
on  a.  meat-free  diet  is  con- 
stant for  one  and  the  same 
individual,  although  different 


Fig.   166. — Kreatin. 


Fig.   167. — Kreatinin-zinc-chloride. 


in  different  persons,  and  independent  of  the  total  amount  of  nitrogen 
eliminated.  Hence  on  a  diet  poor  in  protein  the  percentage  of  the 
total  nitrogen  excreted  as  kreatinin  is  much  greater  than  on  a  protein - 
rich  diet,  as  shown  in  the  table  on  p.  437  So  constant  is  the  quantity 
that  a  determination  of  the  kreatinin  may  be  used  as  a  check  upon 
the  complete  collection  of  the  urine. 

Carbo-hydrates  are  normally  present  in  human  urine,  but  only  in 
very  small  amount.  Three  are  known  with  certainty — dextrose, 
isomaltose.  and  the  so-called  animal  gum  or  urine  dextrin.  Cdycu- 
ronic  acid  (C6H10O7),  a  body  which  can  be  derived  from  dextrose, 
and  which  occurs  in  the  urine  in  increased  amount  after  the  adminis- 
tration of  chloroform,  chloral,  nitrobenzol,  camphor,  and  other 
drugs,  seems  also  to  be  constantly,  or  at  least  frequently  present  in 
small  amount,  probably  paired  with  phenol,  indoxyl  or  skatoxyl,  as 
a  potassium  salt.  It  gives  Fehling's  test,  and  thus  may  easily  be 
mistaken  for  sugar.  The  total  quantity  of  carbo-hydrates,  including 
glycuronic  acid,  excreted  in  the  urine  of  the  twenty-four  hours  has 
been   estimated   at   _•   to   3   grammes.      The  quantity  of  dextrose   in 


EXCRETION 


443 


normal  human  urine  is  aboul  0*02  per  cent.,  or  about  one-fifth  oi 
t  he  proport  ion  in  I  > l <  >od. 

Proteins,  mainly  serum-albumin,  are  also  found  in  normal  urine 
m  minute  quantities,  on  the  average  about  00036  per  cent.  (Morner). 

Pigments  of  Urine.  The  pigments  of  urine  have  not  hitherto  been 
exhaustively  studied  ;  but  we  already  know  that  normal  urine 
contains  several,  and  pathological  urines  probably  additional,  pig- 
mentary substances.  The  best-known  pigments  in  normal  urine  arc 
urochrome,  the  yellow  substance  which  gives  the  liquid  its  ordinary 
colour  ;  uroerythrin,  the  pink  pigment  which  often  colours  the 
deposits  of  urates  that  separate  even  from  healthy  urine;  and 
urobilin,  sometimes  termed  normal  urobilin,  to  distinguish  it  from 
the  so-called  febrile  urobilin,  which,  as  has  been  already  stated,  is 
identical  with  the  faxa!  pigment  stercobilin,  and  occurs  not  only 
in  many  febrile  conditions,  but  also  in  cases  with  no  fever,  such  as 
functional  derangements  of  the  liver,  dyspepsia,  chronic  bronchitis, 
and  valvular  diseases  of  the  heart.  Normal  and  febrile  urobilin  are 
said  to  show  certain  spectroscopic  differences,  but  are  nevertheless 
one  and   the  same  substance,  and    represent,  mainly  at  least,  the 


Fig.   168. — Pepsin  in  Urine.      Diastatic  Ferment  in  Urine. 
At  Different  Times  of  the  Day  (Hoffmann). 

portion  of  the  stercobilin  which  is  not  excreted  with  the  faeces,  but 
absorbed  from  the  intestine  into  the  blood.  The  urobilin  in  normal 
urine  only  exists  in  small  amount  in  the  fully-formed  condition, 
most  of  it  being  present  as  a  chromogen  or  mother-substance  (uro- 
bilinogen), which  by  oxidation,  as  on  standing  exposed  to  the  air, 
is  converted  into  urobilin.  On  the  addition  of  ammonia  and  zinc 
chloride  to  a  solution  of  urobilin  a  beautiful  green  fluorescence  is 
obtained,  and  the  solution  now  shows  an  absorption  band  between 
b  and  F.  Urobilin  and  urochrome  are  related  substances,  but  the 
exact  nature  of  the  relation  has  not  been  settled.  There  is  some 
evidence  that  a  portion  of  the  urobilin  of  urine  is  not  derived  from  the 
intestine,  but  manufactured  probably  in  the  liver.  In  hunger  urobilin 
is  still  excreted  in  the  urine,  although  in  greatly  reduced  amount. 
During  menstruation  it  is  markedly  increased,  both  in  fasting  and  in 
normally  fed  individuals.  Urorosein  is  a  red  pigment  which  is  pro- 
duced from  its  chromogen  by  the  action  of  mineral  acids — e.g.,  strong 
hydrochloric  acid — especially  in  the  presence  of  an  oxidizing  agent. 

The  pigments  of  the  blood  and  bile  and  some  of  their  derivatives 
are  of  common  occurrence  in  the  urine  in  disease.  H  cematoporphyrin 
has  not   only  been   found  in  some  pathological  conditions,   but  is 


ill  A  MANUAL    OF   PHYSI01  OG  1 

constantly  present  in  minute  traces  in  normal  urirn  <  i  rtain  drugs 
(■;■..  sulphonal  cause  an  increase  is  its  amount.  It  can  be  sepa- 
rated from  unnc  l>v  Hi'-  addition  of  sodium  or  potassium  hydroxide, 
which  precipitates  the  earthy  phosphates.  The  haematoporphyrin 
is  carried  down  with  the  precipitate,  and  may  be  dissolvi  a  ou1  with 
chloroform.  The  chloroform  is  then  evaporated  and  Hie  residue 
dissolved  in  alcohol  acidified  with  hydrochloric  acid.  The  al<  oholic 
solution  is  filtered,  and  examined  with  the  spectroscope.  In 
paroxysmal  hemoglobinuria,  methcemoglobin,  mixed  with  some  oxy- 
hemoglobin, is  found  in  the  urine  in  large  amount  ;  and  it  is  worthy 
of  note  that  it  is  not  formed  in  the  urine  after  secretion,  but  is  already 
present  as  such  when  it  reaches  the  bladder. 

In  the  rare  condition  termed  alkaptonuria  a  body,  alkapton,  now 
known  to  be  identical  with  homogentisinicae  id  (< ',  I  [s.(OH)aC]  tg.COOH), 
a  dioxyphenylacctic  acid,  is  present.  The  urine  bec<  >mes  dark  brown 
on  the  addition  of  an  alkali,  or  simply  on  exposure  to  air,  It  gives 
Fehling's  test  for  sugar.  The  substance  has  relations  to  the  aromatic 
amino-acids  tyrosin  and  phenyl-alanin,  and  when  either  of  these  is 
given  to  a  person  suffering  from  alkaptonuria,  the  amount  of  alkapton 
excreted  is  increased.  We  may  suppose,  thcrelore,  thai  in  this  con- 
dition the  normal  decomposition  of  these  products  of  proteolysis  is 
interfered  with. 

Ferments. — The  urine  contains  traces  of  proteolytic  and  anxio- 
lytic ferments  (Fig.  168).  These  may  be  easily  separated  from  it  by 
putting  a  little  fibrin,  which  has  the  power  of  fixing  (adsorbing) 
enzymes,  into  the  urine. 

Of  the  inorganic  constituents  of  urine  the  most  important 
and  most  easily  estimated  are  the  chlorine,  phosphoric  acid,  and 
sulphuric  acid. 

Chlorine. — Much  the  greater  part  of  the  chlorine  is  united  with 
sodium,  a  smaller  amount  with  potassium.  The  chlorides  of  the 
urine  are  undoubtedly  to  a  great  extent  derived  directly  from  the 
chlorides  of  the  food,  and  have  not  the  same  metabolic  significance 
as  the  organic,  and  even  as  some  of  the  other  inorganic  constituents. 
But  it  is  noteworthy  that  in  certain  diseased  conditions  the  chlorine 
may  disappear  entirely  from  the  urine,  or  be  greatly  diminished — 
e.g.,  in  pneumonia,  and  in  general  in  cases  in  which  much  material 
tends  to  pass  out  from  the  blood  in  the  form  of  effusions  (p.  .(771. 

Phosphoric  Acid.  -The  phosphoric  acid  of  the  urine  is  chiefly 
derived  from  the  phosphates  of  the  food,  but  must  partly  come  from 
the  waste  products  of  tissues  rich  in  phosphorus-containing  sub- 
stances, such  as  lecithin  and  nuclein.  The  phosphoric  acid  is  united 
partly  with  alkalies,  especially  as  acid  sodium  phosphate,  and  partly 
with  earthy  bases,  as  phosphates  of  calcium  and  magnesium.  The 
earthy  phosphates  are  precipitated  by  the  addition  of  an  alkali  to 
urine,  or  in  the  alkaline  fermentation.  In  some  pathological  urine-, 
they  come  down  when  the  carbon  dioxide  is  driven  ofl  l>v  heating  ;  a 
precipitate  of  this  sort  di  Hers  from  heat-coagulated  albumin  m  being 
readily  soluble  in  acids  (Practical  Exercises,  p.  480).  A  small  amount 
of  phosphorus  may  appear  in  the  urine  in  a  less  oxidized  form  than 
phosphoric  acid. 

Sulphuric  Acid.  —This  is  only  to  a  slight  extent  derived  from 
ready-formed  sulphates  in  the  food.  The  greater  part  of  it  is  formed 
by  oxidation  of  the  sulphur  of  proteins.     About  nine-tenths  of  the 


/  XCRl  TWh  44? 

sulphur  in  normal  urine  is  present  .is  inorganic  sulphates,  mainly 

those  of  potassium  and  sodium.  (  )l  the  ollur  tenth,  a  portion  I 
represented  by  ethereal  sulphates,  and  the  remainder  by  the  so- 
called  'neutral'  sulphur,  including  the  Sulphur  associated  with  the 
pigment  urochrome,  and  the  small  amounl  of  sulphur  occurring  in 
less  oxidized  forms  than  sulphates  in  such  compounds  as  the  sul- 
phocyanide,  which  is  probably,  in  part  but  not  entirely,  derived 
iroin  that  of  the  saliva  ;  and  ethyl  sulphide,  a  substance  with  a 
penetrating  odour,  which  appears  to  be  a  constant  constituent  of 
dog's  urine  (Abel). 

Thiosulphuric  acid  (H2S203)  occurs  almost  constantly  in  cat's 
urine,  often  in  dog's.     It  is  not  free,  but  combined  with  bases. 

The  ethereal  sulphates  are  compounds  in  which  the  sulphuric  acid 
is  united  with  aromatic  bodies  (indol,  phenol,  etc.).  Such  are 
potassium-phenyl-sulphate  (C(1H-,KSO.,),  potassium-kresyl-sulphatc 
(CdbKSO,),  potassium-indoxyl-sulphate  (C„H(;NKSO,),  potassium- 
skatoxyl-sulphate  (C$,H„NKS04),  and  two  double  sulphates  of 
potassium  and  pyrocatechin.     The  formation  of  potassium  indoxyl 

sulphate  may  be  thus  represented  :  Indol,  C,;H4<  -^tj'  on  absorp- 
tion from  the  intestine  is  changed  into  indoxyl,  C0H4<  bl;  ' 
which       +  SO./  qK       (potassium      hydrogen       sulphate)       yields 

S02\0K  ^  (potassium  indoxyl  sulphate)  +  HaO.  .The  'pairing' 
of  these  aromatic  bodies  with  sulphuric  acid  renders  them  innocuous 
to  the  organism.  Most  of  the  compounds  are  present  in  greater 
amount  in  the  urine  of  the  horse  than  in  the  normal  urine  of  man. 
But  in  disease  the  quantity  of  '  indican  '  in  the  latter  may  be  much 
increased  ;  and  to  a  certain  extent  it  must  be  looked  upon  as  an  index 
of  the  intensity  of  putrefactive  processes  in  the  intestine  and  of 
absorption  from  it.  Munk  made  the  observation  that  in  the  urine 
of  a  starving  dog  the  phenol-forming  substances  are  absent,  while 
in  the  urine  of  a  starving  man  they  are  present  in  abnormally  large 
amount.  The  indigo-forming  substances  ('  indican  '),  on  the  other 
hand,  are  in  hunger  excreted  in  considerable  quantity  by  the  dog, 
and  not  at  all  by  man  (Practical  Exercises,  p.  479). 

Phenol  and  kresol  can  easily  be  obtained  from  horse's  urine  by 
mixing  it  with  strong  hydrochloric  acid  and  distilling.  These  aro- 
matic bodies  pass  over  in  the  distillate.  Pyrocatechin  remains 
behind,  and  can  be  extracted  by  ether.  It  gives  a  green  colour  with 
ferric  chloride,  which  becomes  violet  on  the  addition  of  sodium 
carbonate. 

The  sulphur  of  the  inorganic  sulphates  is  the  fraction  of  the  total 
sulphur  which  fluctuates  in  proportion  to  the  total  protein  meta- 
bolism. In  this  regard  it  follows  the  variations  in  the  urea.  It 
represents  '  exogenous  '  metabolism.  The  neutral  sulphur  occupies 
a  position  analogous  to  that  of  the  kreatinin  :  the  smaller  the 
amount  of  protein  in  the  food,  and  the  smaller  therefore  the  total 
protein  decomposed,  the  larger  is  the  fraction  which  the  neutral 
sulphur  forms  of  the  total  sulphur.  The  neutral  sulphur  accordingly 
represents  endogenous  metabolism.  The  ethereal  sulphur  takes 
an  intermediate  position  in  this  regard,  but  upon  the  whole  it  also 
becomes  a  more  prominent  fraction  of  the  total  sulphur  when  the 
food  contains  little  or  no  protein.  The  ethereal  sulphates  are  there- 
fore not  entirely  derived  from  the  putrefaction  of  protein. 


44r> 


A   MA  VV  //.  OF  PHYSIOLOG  5 


Carbonates  of  sodium,  ammonium,  calcium,  and  magnesium  occur 
in  alkaline  urine  Their  source'  is  the  carbonates  and  the  vegetable 
organic  acids  of  the  food.  In  acid  urine  a.  certain  amount  of  carbon 
dioxide  is  present,  although  not  firmly  united  with  bases,  so  that 
most  of  it  can  be  pumped  out. 

Physico-chemical  Analysis  of  Urine.— The  Ereezing-poinl  of  urine 
is  often  determined  to  obtain  a  measure  of  the  molecular  concentra- 
tion, which  with  the  total  quantity  of  urine  secreted  in  a  given  time 
is  an  index  of  the  work  of  the  kidney.  The  greater  the  volume  of 
urine  secreted  per  unit  of  time,  and  the  greater  the  number  oi  mole- 
cules dissolved  in  unit  volume  of  it,  the  greater  is  the  work  of  the 
secretory  apparatus  in  separating  it  from  the  blood  (p.  465). 
Normally,  A  has  a  higher  value  for  urine  than  for  blood  i.e.,  the 
molecular  concentration  of  the  urine  is  higher  than  that  of  the  scrum. 
But  when  large  draughts  of  water  are  taken  A  may  be  lower  tor 
urine  than  for  blood,  and  in  general  it  varies  within  far  wider  limits 
(from  o-ii5°  to  2-546°  C,  according  to  Koppe).  The  following  table 
from  Kovesi  and  Roth-Schulz  shows  the  changes  in  A  under  the 
influence  of  water  : 


Time. 

I  liine  in  c.c 

A 

IO  to  2 

240 

i-8o 

2  to  6 

255 

1-72 

6  to  10 

161 

1-93 

IO  to  2 

131 

2- 18 

2  to  6 

160 

2-23 

6  to  10 

120 

i  -91 

I  I  to  1 2 

i-8  litres  '  Salvator  '  water  taken 

— 

12  to  12.30 

500 

0-12 

12.30  to  I 

444 

o-ii 

1  to  1.30 

II- 

o-io 

I.30  tO  2 

46 

0-78 

2  tO  2.30 

45 

I-30 

If  the  electrical  conductivity  is  determined,  we  obtain  an  approxi- 
mate measure  of  the  number  of  dissociated  ions  in  unit  volume,  mainly 
the  inorganic  salts.  Deducting  this  from  the  total  number  of  mole- 
cules per  unit  volume  (measured  by  A),  we  arrive  at  the  concentra- 
tion of  the  urine  in  non-dissociated  molecules,  mainly  urea  and  other 
organic  constituents.  Precision  is  added  to  such  calculations  by 
estimating  also  in  the  ordinary  way  (by  titration,  e.g.)  one  or  more 
of  the  inorganic  constituents,  especially  the  chlorine,  since  sodium 
chloride  is  quantitatively  the  most  important  of  the  salts.  Various 
formulae  have  been  deduced  from  such  determinations  connecting 
the  freezing-point  and  conductivity  with  other  physical  constants  of 

the  urine      E.g.,  =K=7S,  where  s  is  the  specific  gravity  and 

0     s  —  1 

K  a  constant  with  the  value  75  ;  t  =K=r45,  where  X  is  the 
specific  conductivity,  h  the  percentage  of  ash,  and  K  a  constant  = 
1-45.  The  quotient  N.  (T  representing  the  ratio  of  the  total  con- 
centration to  the  sodium  chloride  concentration  varies  within  rela- 


EXCRETION  447 

1 1\  ely  narrow  limits  in  hcall  h,  according  Id  Koranyi,  the  did  exercising 
no  influence  upon  it  whatever.     Thns,  in  a  large  number  oi  healthy 

individuals  ,T    ,.  fluctuated   only  between   1*23   and    1*69,  while  a 

varied  from  i-26°  to  2'35°,  and  the  percentage  of  sodium  chloride 
from  0*85  to  154.      This  is  illustrated  in  the  table  : 


Urine  in  c.C.  in 

_^ 

Percentage  of 

A 

Twenty-four  Hours. 

NaCl. 

NaCl. 

I.365 

1-43° 

1-08 

1-32 

1.745 

i-6o° 

1-24 

I-2g 

I,68o 

1    o,N 

1-28 

I-3I 

1,015 

I-84° 

i'i5 

l-6o 

865 

i-8i° 

1-26 

1-44 

1,360 

1-62° 

1-09 

1-49 

84O 

2-26° 

1-50 

i'5i 

I,6oo 

1-46° 

1-14 

1-28 

2,o8o 

i-33° 

0-85 

1-68 

The  Urine  in  Disease. — Although,  strictly  speaking,  a  truly 
pathological  urine  has  no  place  in  physiolog5^,  the  line  which 
separates  the  urine  of  health  from  that  of  disease  is  often  narrow, 
sometimes  invisible  ;  while  the  study  of  abnormal  constituents 
is  not  only  of  great  importance  in  practical  medicine,  but  throws 
light  upon  the  physiological  processes  taking  place  in  the  kidney, 
and  upon  the  general  problems  of  metabolism.  Even  in  health 
the  quantity  of  the  urine,  its  specific  gravity,  its  acidity,  ma}^ 
vary  within  wide  limits.  A  hot  day  may  increase  the  secretion 
of  sweat,  and  correspondingly  diminish  the  secretion  of  urine, 
and  the  deficiency  of  water  may  lead  to  a  deposit  of  brick-red 
urates.  A  meal  rich  in  fruit  or  vegetables  may  render  the  urine 
alkaline,  and  its  alkalinity  may  determine  a  precipitate  of  earthy 
phosphates.  But  neither  the  scanty  acid  urine  with  its  sedi- 
ment of  urates,  nor  the  alkaline  urine  with  its  sediment  of 
phosphates,  comes  into  the  category  of  pathological  urines  ; 
the  deviation  from  the  normal  does  not  amount  to  disease. 
The  maximum  deviation  from  the  line  of  health  is  the  total 
suppression  of  the  urine.  If  this  lasts  long,  a  train  of  symptoms, 
of  which  convulsions  may  be  one  of  the  most  prominent,  and 
which  are  grouped  under  the  name  of  uraemia,  appears.  At 
length  the  patient  becomes  comatose,  and  death  closes  the 
scene.  Suppression  of  urine  may  be  the  consequence  of  many 
pathological  conditions,  but  there  is  one  case  on  record  in  the 
human  subject  which,  in  effect,  though  not  in  intention,  belongs 
to  experimental  physiology.  A  surgeon  diagnosed  a  floating 
kidney  in  a  woman.  With  a  natural  impatience  of  loose  odds 
and  ends  of  this  sort,  he  offered  to  remove  it,  and  in  an  evil 


448  A   MANUAL  OF  PHYSIOLOGY 

hour  the  patient  consented.  The  surgeon,  a  perfectly  skilful 
man,  who  acted  for  the  best,  and  to  whom  no  blame  whatever 
attached,  carried  the  kidney  to  a  well-known  pathologist  for 
examination.  The  hitter,  to  the  horror  of  the  operator,  sug- 
gested, from  the  appearance  of  the  organ.  that  it  was  the  only 
kidney  the  woman  possessed.  This  turned  out  to  be  the  fact. 
Not  a  drop  of  mine  was  passed.  Apart  from  this  ominous 
symptom,  all  went  well  tor  seven  or  eight  days  ;  but  then  uremic 
troubles  came  on,  and  the  patient  died  on  the  eleventh  or 
thirteenth  day  after  the  operation.  The  autopsy  showed  that 
her  only  kidney  had  been  taken  away. 

In  disease  the  urine  may  contain  abnormal  constituents,  or 
ordinary  constituents  in  abnormal  amounts.  Of  the  normal 
constituents  which  may  be  altered  in  quantity,  the  most  im- 
portant are  the  water,  the  inorganic  salts,  the  urea,  the  uric 
acid,  and  the  aromatic  substances. 

Water. — A  marked  and  persistent  diminution  in  the  quantity 
of  urine — that  is  to  say,  practically  in  the  water,  with  or  with- 
out an  increase  in  the  specific  gravity — is  suggestive  of  disorgani- 
zation of  the  renal  epithelium.  In  some  infective  diseases  the 
kidney  is  liable  to  be  secondarily  involved,  its  secreting  cells 
being  perhaps  crippled  in  the  attempt  to  eliminate  the  bacterial 
poisons.  In  the  form  of  parenchymatous  or  tubal  nephritis 
which  so  frequently  complicates  scarlet  fever,  the  quantity  of 
urine  has  in  some  cases  fallen  to  50  or  60  c.c.  in  the  twenty-four 
hours. 

In  chronic  interstitial  nephritis  ('granular  kidney')-  on  the 
other  hand,  where  the  structural  changes  in  the  tubules  are,  for 
a  long  time  at  least,  comparatively  circumscribed,  the  quantity 
of  urine  is  often  increased  and  of  low  specific  gravity.  In  these 
cases  the  increase  in  the  blood-pressure,  associated  with  hyper- 
trophy of  the  heart,  may  be  a  factor  in  the  exaggerated  renal 
secretion.  In  diabetes  mellitus  the  quantity  of  urine  is  greatly 
increased,  perhaps  in  some  cases  because  more  urea  is  excreted 
than  normal,  and  urea  acts  as  a  diuretic,  perhaps  also  because 
the  elimination  of  sugar  draws  with  it  an  increased  excretion  of 
water  to  hold  it  in  solution.  Although  a  specific  gravity  as  low 
as  1002  has  been  seen  in  healthy  persons  (after  copious  potations), 
the  persistence  of  a  density  below  1010  should  suggest  hydruria. 
Watson  mentions  the  case  of  a  boy  with  diabetes  insipidus,  who 
voided  in  twenty-four  hours  g  or  10  pints  (5  to  6  litres)  of  urine 
with  a  specific  gravity  of  1002.  On  the  other  hand,  while  the 
specific  gravity  has  been  occasionally  observed  to  mount  in  health 
to  at  least  1036,  its  persistence  at  1025  or  1030  or  anything 
above  this,  especially  if  the  urine  is  pale  and  apparently  dilute, 
should  suggest  diabetes  mellitus. 


EXCRETION  449 

Inorganic  Salts. — The  changes  in  the  quantity  of  the  in- 
organic constituents  of  the  urine  in  disease  are  not,  in  the  present 
state  of  our  knowledge,  of  as  much  importance  as  the  changes 
in  the  organic  constituents.  The  chlorides  are  diminished  in 
most  acute  febrile  diseases  and  may  even  totally  disappear 
from  the  urine,  and  their  reappearance  after  the  crisis  is,  so 
far  as  it  goes,  a  favourable  symptom.  In  most  cases  in  which 
the  quantity  of  the  urine  is  markedly  lessened,  all  the  inorganic 
substances  are  diminished  in  amount. 

Urea. — The  quantity  of  urea  is,  as  a  rule,  increased  in  fever, 
either  absolutely  or  in  proportion  to  the  amount  of  nitrogen  in 
the  food.  In  the  interstitial  varieties  of  kidney  disease  the 
urea  is  usually  not  diminished,  but  when  the  stress  of  the  change 
falls  on  the  tubules  (parenchymatous  nephritis),  it  is  distinctly 
decreased — it  may  be  even  to  one-twentieth  of  the  normal. 

Uric  acid  is  diminished  in  the  urine  in  gout  (perhaps  to  one- 
ninth  of  the  normal),  not  only  during  the  paroxysms,  but  in 
the  intervals.  It  accumulates  in  the  blood  and  tissues,  and,  as 
sodium  urate,  mav  form  concretions  in  the  joints,  the  cartilage 
of  the  ear,  and  other  situations.  Watson  relates  the  case  of  a 
gentleman  who  used  to  avail  himself  of  his  resources  in  this 
respect  by  scoring  the  points  at  cards  on  the  table  with  his 
chalky  knuckles.  In  leukaemia  the  quantity  of  uric  acid  and  purin 
bases  in  the  urine  is  greatly  increased,  not  only  absolutely,  but 
also  in  proportion  to  the  urea.  As  much  as  4J  grammes  of  free 
uric  acid,  in  addition  to  about  ih  grammes  of  ammonium  urate, 
has  been  found  in  a  urinary  sediment  in  a  case  of  leukaemia. 

The  aromatic  bodies,  of  which  indoxyl  may  be  taken  as  the 
type,  are  increased  when  the  conditions  of  disease  favour  the 
growth  of  bacteria  in  the  intestine — -e.g.,  in  cholera,  acute  peri- 
tonitis, and  carcinoma  of  the  stomach.  A  marked  increase  in  the 
amount  of  the  '  indican  '  in  the  urine  may,  as  far  as  it  goes,  be 
taken  as  an  indication  that  the  bacteria  are  gaining  the  upper 
hand  in  the  intestinal  tract  ;  a  marked  diminution  is  usually  a 
sign  that  the  battle  has  begun  to  turn  in  favour  of  the  organism 
(Practical  Exercises,  p.  479).  Tryptophane,  a  substance  which 
we  have  already  recognised  among  the  products  of  the  tryptic 
digestion  of  proteins,  has  been  shown  to  be  a  precursor  of  indol, 
which  is  formed  from  it  under  the  influence  of  bacteria.  When 
trvptophane  is  injected  into  the  caecum  of  rabbits,  the  indican  in 
the  urine  is  markedly  increased.  Putrefactive  processes  in 
other  parts  of  the  body  than  the  intestine  may  also  increase  the 
indican  in  the  urine — e.g.,  a  collection  of  putrid  pus  in  the  pleural 
cavity. 

Abnormal  Substances  in  Urine. — Sugar,  proteins,  the  pig- 
ments of  bile  and  blood,   or   their   derivatives,   are  the  most 

29 


4SO  A  MAh  i  .11.  OF  PHYSIOLpGl 

important  abnormal  substances  tound  in  solution  in  the  urine. 
Normal  urine,  as  has  been  stated,  contains  a  trace  <>|  dextrose, 

but  so  little  that  it  cannot  be  detected  by  ordinary  lists,  and 
for  practical  purposes  it  may  be  considered  absent.  Dextrose  is 
the  sugar  tound  in  the  urine  in  diabetes.  In  the  urine  of  nursing 
mothers  lactose  may  be  present.  Pentoses,  sugars  with  five 
carbon  atoms  in  the  molecule  (instead  of  six,  as  in  the  hexoses,  of 
which  group  dextrose  is  a  member),  may  also  occasionally  occur 
in  urine.  Pentoses  give  the  ordinary  reduction  tests  for  sugar, 
and  yield  osazones,  but  do  not  ferment  with  yeast.  Various  plants 
contain  pentoses,  and  when  these  are  eaten  the  pentoses  are  ex- 
creted in  the  urine,  but  in  cases  of  true  pentosuria  they  originate 
in  the  body,  possibly  from  nucleo-proteins.  The  condition  has 
not  the  same  sinister  significance  as  diabetes.  Specific  toxic 
substances  produced  by  bacterial  action  have  been  demonstrated 
in  the  urine  in  certain  diseases.  Red  blood-corpuscles  and 
leucocytes  (pus  corpuscles,  white  blood-corpuscles,  mucus  cor- 
puscles) are  the  chief  organized  deposits  ;  but  spermatozoa  may 
occasionally  be  found,  as  well  as  pathogenic  bacteria-  e.g.,  the 
typhoid  bacillus  ;  and  in  disease  of  the  kidney  casts  of  the  renal 
tubules  are  not  uncommon.  These  tube-casts  may  be  composed 
chiefly  of  red  blood-corpuscles,  or  of  leucocytes,  or  of  the  epithe- 
lium of  the  tubules,  sometimes  fattily  degenerated,  or  of  struc- 
tureless protein,  or  of  amyloid  substance.  Abnormal  crystalline 
substances,  such  as  the  amino-acids,  leucin  (Fig.  169),  and  tyrosin 
(Fig.  170),  and  cystin  (Fig.  163)  may  be  on  rare  occasions 
found  in  urinary  sediments;  but  generally  the  unorganized 
deposits  of  pathological  urine  consist  oi  bodies  actually  contained 
in,  or  obtainable  from,  the  normal  secretion,  but  present  in 
excess,  either  absolutely,  or'relatively  to  the  solvent  power  of  the 
urine.  Cystin  is  of  interest  because  of  its  relations  to  the 
sulphur  of  the  protein  molecule  (p.  332).  It  is  not  found  in  the 
normal  organism.  It  very  occasionally  forms  calculi  in  the 
bladder.  There  are  individuals  who  constantly  pass  as  much  as 
one-fourth  of  all  the  sulphur  in  the  form  of  cystin,  without  any 
other  symptoms. 

Various  amino-acids  are  present  in  solution  in  the  urine  in 
many  pathological  conditions.  01  these  the  least  soluble  are 
leucin  and  tyrosin,  and  this  is  the  reason  why  t  hey  are  most  easily 
delected.  A  genera]  reaction  for  amino-acids  is  their  precipita- 
tion as  sparingly  soluble  compounds  (/2-naphthalinsulphones) 
by  j6-naphthalinsu%mochloride  in  the  presence  of  an  alkali 
(sodium  hydroxide).  In  acute  yellow  atrophy  of  the  liver 
leucin  and  tyrosin  have  been  found  in  large  amounts  in  the 
liver  itself,  as  well  as  in  the  mine.  In  phosphorus  poisoning 
these  amino  acids,  as   well    as  glycocoll,  have    been    detected    iu 


EXCRETION  45 1 

the  urine,  and  there  is  no  doubt  that  other  amino-acids, 
arising  from  the  decomposition  of  proteins,  are  also  present 
in  such  conditions. 

Sugar. — In  diabetes  mellitus,  although  the  quantity  of  urine  is 
usually  much  increased,  its  specific  gravity  is  above  the  normal ;  and 
this  is  due  chiefly  to  the  presence  of  sugar  (dextrose),  which  generally 
amounts  to  i  to  5  per  cent.,  but  may  in  extreme  cases_ reach  10  or 
even  15  per  cent.,  more  than  half  a  kilogramme  being  sometimes 
given  off  in  twenty-four  hours. 

The  name  of  the  tests  for  dextrose  is  legion.  They  are  mostly 
founded  on  its  reducing  action  in  alkaline  solution.  Hydrated  oxide 
of  bismuth  (Boettcher),  salts  of  gold,  platinum  and  silver,  indigo 
(Mulder),  and  a  host  of  other  substances,  are  reduced  by  dextrose, 
and  may  be  used  to  show  its  presence.  The  reduction  of  cupric 
salts  (Trommer),  fermentation  by  yeast,  and  the  formation  of  crystals 
of  phenyl-glucosazone  are  the  best  established  tests.  (See  Practical 
Exercises,  p.  488.) 

Proteins.— Serum-albumin  and  serum-globulin  are  the  proteins 
most  commonly  found  in  pathological  urine.  Both  are  coagulated 
by  heating  the  urine,  slightly  acidulated  if  it  is  not  already  acid,  or 
by  the  addition  of  strong  nitric  acid  in  the  cold.  Proteoses  (albu- 
moses)  are  also  occasionally  present,  e.g.,  in  the  disease  called 
'  osteomalacia  '  and  in  conditions  associated  with  the  formation  and 
especially  with  the  decomposition  of  pus.  They  may  be  recognised 
by  the  tests  given  in  the  Practical  Exercises  (p.  426).  It  is  doubtful 
whether  the  presence  of  true  peptone  has  as  yet  been  satisfactorily 
made  out. 

The  presence  of  bile-salts  may  be  shown  by  Hay's  test,  or  Petten- 
kofer's  test  (p.  430). 

The  pigments  of  blood  and  bile  may  be  detected  by  the  char- 
acters described  in  treating  of  these  substances  ;  the  spectrum  of 
oxyhemoglobin,  or  methaemoglobin,  or  any  of  the  other  derivatives 
of  haemoglobin,  with  the  formation  of  haemin  crystals,  would  afford 
proof  of  the  presence  of  the  former,  and  Gmelin's  test  of  the  latter. 
The  red  blood-corpuscles,  seen  with  the  microscope,  are  the  most 
decisive  evidence  of  the  presence  of  blood,  as  leucocytes  in  abundance 
are  of  the  presence  of  pus.  It  should  be  remembered  that  pus  in 
the  urine  of  women  has  sometimes  no  significance  except  as  showing 
that  there  has  been  an  admixture  of  leucorrheal  discharge  from  the 
vagina.     (See  Practical  Exercises,  pp.  65,  494.) 

The  Secretion  of  the  Urine. — We  have  now  to  consider  the 
mechanism  by  which  the  urine  is  formed  in  the  kidney  from  the 
materials  brought  to  it  by  the  blood.  And  here  the  same 
questions  arise  as  have  already  been  discussed  in  the  case  of  the 
salivary  and  other  digestive  glands  :  (1)  Are  the  urinary  con- 
stituents, or  any  of  them,  present  as  such  in  the  blood  ?  (2)  If 
they  do  exist  in  the  blood,  can  they  be  shown  to  be  separated 
from  it  by  processes  mainly  physical  or  mainly  '  vital ' — in  other 
words,  by  ordinary  filtration,  diffusion  and  osmosis,  or  by  the 
selective  action  of  living  cells  ?  In  the  case  of  the  digestive 
juices  it  has  been  seen  that  some  constituents  are  already  present 
in  the  blood,  but  that  physical  laws  alone,  so  far  as  we  at  present 

29 — 2 


452  A  MANUAL  OF  PHYSIOLOGY 

understand  them,  cannot  explain  the  proportions  in  which  they 

occur  in  the  secretions,  or  the  conditions  under  which  they  are 
separated  ;  while  other  constituents  and  these  the  more  specific 
and  important— are  manufactured  in  the  gland-cells. 

In  the  kidneys  the  conditions  seem  at  lirst  sight  favourable 
to  physical  separation,  as  opposed  to  physiological  secretion. 
Trine  has  been  described  as  essentially  ;i  solution  "1  urea  and 
salts,  and  both  are  ready  formed  in  the  blood.  The  arrange- 
ment of  the  bloodvessels,  too,  suggests  an  apparatus  for  filtering 
under  pressure. 


Fig.  169. — Leucin  Crystals.  Fig.  170. — Tyrosin  Crystals. 

Bloodvessels  and  Secreting  Tubules  of  Kidney. — The  renal  artery 
splits  up  at  the  hilus  into  several  branches,  which  pass  in  between 
the  Malpighian  pyramids,  and  form  at  the  boundary  of  the  cortex 
and  medulla  vascular  arches,  from  which  spring,  on  the  one  side, 
interlobular  arteries  running  up  into  the  cortex  between  the  pyramids 
of  Ferrein,  and,  on  the  other,  vasa  recta  running  down  into  the 
boundary  layer  of  the  medulla  (Fig.  171).  The  interlobular  arteries 
give  off  at  intervals  afferent  vessels  ;  each  of  these  soon  breaks  up 
into  a  glomerulus  or  tuft  of  vascular  loops,  which  gather  themselves 
up  again  into  a  single  efferent  vessel  of  somewhat  smaller  calibre  than 
the  afferent.  The  glomerulus  is  fitted  into  a  cup  or  capsule  (oi 
Bowman),  which  is  closely  reflected  over  it,  except  where  the  affe4feivt 
and  efferent  vessels  pass  through,  and  forms  the  beginning  of  a 
urinary  tubule.  If  we  suppose  the  tuft  pushed  into  the  blind  end  of 
the  tubule  so  as  to  indent  it.  it  will  be  easily  understood  that  the 
single  layer  of  flattened  epithelium  reflected  on  the  glomerulus  is 
continuous  with  that  lining  the  capsule,  which  in  its  turn  is  con- 
tinuous with  the  epithelial  layer  of  the  rest  of  the  urinary  tubule. 
This  has  been  divided  by  histologists  into  a  number  of  parts  which 
it  is  unnecessary  to  enumerate  here,  further  than  to  say  that  the 
urinary  tubule  proper  begins  in  the  cortex  in  Bowman's  capsule 
and  the  proximal  convoluted  tubule  (with  its  continuation,  the  spiral 
tubule),  and  ends  in  the  cortex  with  the  distal  convoluted  tubule, 
the  connection  between  the  two  being  made  by  a  long  loop  (Henle'sj 
with  a  descending  and  an  ascending  limb  (Fig.  172).  Between  the 
ascending  limb  and  the  distal  convoluted  tube  is  interposed  the 
zigzag  tubule.  The  tubule  throughout  its  length  is  bounded  by  a 
basement  membrane  lined  by  a  single  layer  of  epithelium,  winch 
differs  in  its  character  in  different  parts  of  the  tubule. 

The  distal  convoluted  tube  joins  by  means  of  the  short  con- 
necting tubule  one  of  the  straight  tubules  which  form  the  pyramids 
of  Ferrein  or  medullary  rays  in  the  cortex,  and  which  run  down  into 
the  medulla,  always  uniting  into  larger  and  larger  tubes  as  they 


EXCRETION 


Fig.  171. — Diagram  of 
Bloodvessels  of  Kidney 
(Klein,  after  Ludwig). 

ai,  interlobular  artery ;  vi, 
interlobular  vein  :  g,  glomer- 
ulus, to  which  an  afferent 
artery  is  seen  coming  from  the 
interlobular  artery,  and  from 
which  an  efferent  artery  pro- 
ceeds to  break  up  into  a  capil- 
lary network  surrounding  the 
renal  tubules  ;  vs,  vena  stel- 
lata ;  ar,  arteriae  rectae ;  vb, 
leash  of  venae  rectae  ;  vp,  vas- 
cular network  round  ducts  at 
apex  of  a  papilla. 


Fig.   172. — Diagram  of   Renal  Tubule 
(Klein). 

A,  cortex  ;  a,  layer  of  cortex  immediately  under 
capsule  containing  no  Malpighian  corpuscles ; 
a',  inner  layer  of  cortex  devoid  of  Malpighian  cor- 
pus<  les  ;  B,  boundary  layer  ;  C,  papillary  zone  of 
medulla  ;  1,  Bowman's  capsule  ;  2,  neck  of  cap- 
sule ;  3,  proximal  convoluted  tubule  :  4,  spiral 
tubule ;  5,  descending  part  of  Henle's  loop- 
tubule  ;  6,  the  loop  ;  7,  8,  and  9,  ascending  limb 
of  loop-tubule  ;  10,  irregular  tubule  ;  11,  distal 
convoluted  tubule;  12,  junctional  tubule;  13, 
collecting  tubule,  in  a  medullary  ray  or  pyra- 
mid of  Ferrein  14,  collecting  tubule  in  the 
boundary  layer ;  15,  large  collecting  tubule 
ending  in  a  duct  of  Bellini. 


454 


/    MANUAL  OF  PHYSIOLOGY 


go,  until  at  length  they  open  as  ducts  of  Bellini  on  the  apex  of  a 
papilla.  The  two  convoluted  tubules  (with  the  spiral  and  zigzag 
tubules)  are  lined  by  similar  epithelial  cells  with  granular  contents, 
and  the  tendency  of  the  granules  to  be  arranged  in  rows  jm  rpcn- 
dicular  to  the  basement  membrane  gives  theni  a  striated  or  '  rodded 
appearance  (Fig.  173).  The  granules  are  eosinophil*-  (p.  17),  which 
is  also  ;i  character  of  the  granules  of  other  secreting  cells.  Towards 
the  lumen  the  cells  may  show  a  brush  of  processes,  looking  like 
cilia,  but  in  mammals  these  are  not  motile.  The  ascending  part 
of  Henle's  loop  also  has  cells  of  the  same  general  character,  with 


Fig.   173. — From  a  Vertical  Section  of  Dog's  Kidney  to  show  the  Struc- 
ture of  different  portions  of  the   Renal  Tubule   (Klein). 

a,  Bowman's  capsule  enclosing  glomerulus)  the  capillaries  of  which  are  arranged 
in  lobules  separated  by  a  little  connective  tissue.  The  capsule  and  glomerulus 
together  constitute  a  Malpighian  body  or  corpuscle  ;  ;;.  ne<  k  of  capsule  :  c,  c,  con- 
voluted tubules,  cut  in  various  directions  ;  !>.  irregular  or  zigzag  tubule  :  ./.  e,  and 
/  are  straight  tubules,  which  take  part  in  tin-  formation  "t  .1  medullary  raj  "t- 
pyramid  of  Perrein ;  </.  collecting  tubule;  <-.  e,  spiral  tubule:  /,  narrow  pari  of 
ascending  limb  of  Henle's  loop-tubule ;  b,  c,  and  e  are  lined  with  rodded  epithelium. 

numerous  granules,  although  the  '  rodding  '  may  not  be  so  distinct. 
We  shall  see  directly  that  the  morphological  resemblance  is  the  index 
of  a  functional  likeness.  The  blood-supply  of  the  tubules,  especi- 
ally of  the  convoluted  portions,  is  exceedingly  rich,  the  efferent 
vessels  of  the  glomeruli  breaking  up  around  them  into  a  close- 
meshed  network  of  capillaries,  from  which  the  blood  is  collected 
into  interlobular  veins  running  parallel  to  the  interlobular  arteries 
between  the  pyramids  of  Ferrein.  The  straight  tubules  of  the 
medulla  are  also  surrounded  by  capillaries  given  oil  from  straight 
arteries  (artcri.e  rectae)  running  down  into  it  partly  from  the  arterial 
arches  and  partly  from  efferent  vessels  of  the  glomeruli  nearest  the 


EXCRETION  455 

boundary  layer,  the  blood  passing  away  by  straight  voins  (venae 
e)  which  join  the  larger  veins  accompanying  the  arterial  arches. 
[he  greater  part  of  the  blood  going  through  the  kidney  has  to  pass 
through  two  sets  of  capillaries,  one  in  the  glomeruli,  the  other  around 
the  tubules.  Even  the  portion  of  it  which  docs  not  go  through  the 
glomeruli  has  for  the  most  part  a  long  route  to  traverse  in  narrow 
arterioles  and  venules  to  and  from  its  capillary  distribution.  And 
the  mean  circulation-time  through  the  kidney  has  been  found  to  be 
longer  than  that  through  most  other  organs  (p.  125). 

Theories  of  Renal  Secretion. — To  come  back  to  our  problem 
of  the  nature  of  renal  secretion,  the  anatomical  structure  of  the 
kidney  might  be  expected  to  throw  light  upon  the  question. 
And,  indeed,  it  was  on  a  purely  histological  foundation  that 
Bowman  established  his  famous  '  vital  '  theory  of  renal  secre- 
tion. Impressed  with  the  resemblance  between  the  renal 
epithelium  and  the  epithelial  cells  of  other  glands,  and  with  the 
distribution  of  the  bloodvessels  in  the  kidney,  he  came  to  the 
conclusion  that  the  characteristic  constituents  of  urine,  in- 
cluding urea,  were  secreted  from  the  blood  by  the  tubules.  To 
the  Malpighian  bodies  he  assigned  what  he  doubtless  considered 
the  humbler  office  of  separating  water  from  the  blood  for  the 
solution  of  the  all-important  solids.  To  Ludwig,  on  the  other 
hand,  with  his  whole  attention  fastened  on  the  mechanical 
factors  by  which  the  flow  of  urine  could  be  influenced,  the 
tubules  seemed  of  secondary  importance,  while  the  glomeruli 
appeared  a  complete  apparatus  for  filtering  urine  from  the  blood 
into  Bowman's  capsule.  He  saw  that  the  efferent  vessel  was 
smaller  than  the  afferent  ;  that  it  was  therefore  easier  for  blood 
to  come  to  the  glomerulus  than  to  get  away  from  it,  and  that 
the  pressure  in  the  capillaries  of  the  tuft  must  be  higher  than  in 
ordinary  capillaries,  because  the  resistance  beyond  them  in  the 
comparatively  narrow  efferent  vessel,  and  especially  in  the 
second  plexus,  is  greater  than  the  resistance  beyond  a  single 
capillary  network.  And  experimental  investigation  soon  showed 
him  that  the  rate  at  which  urine  was  formed  could  be  greatly 
influenced  by  changes  in  the  blood-pressure. 

On  such  considerations,  Ludwig  founded  the  '  mechanical  ' 
theory  of  urinary  secretion,  which,  although  in  a  much  modified 
form ,  still  divides  with  the '  vital '  theory  the  allegiance  of  physiolo- 
gists. It  is  impossible  here  to  enter  in  detail  into  a  controversy 
t  hat  has  extended  over  more  than  half  a  century  and  produced  an 
extensive  literature.  The  result  of  the  discussion  has  been,  in 
our  opinion,  to  establish  in  its  essential  principles  the  '  vital  ' 
theory  of  Bowman,  or  at  least  to  show  that  no  purely  physico- 
chemical  theory  as  yet  constructed  will  account  for  all  the  facts. 

Ludwig  supposed  that  the  urine,  qualitatively  complete  in  all 
its  constituents,  was  simply  filtered  through  the  glomeruli,  the 


456  A  MANUA1    OF  PHYSIOLOGY 

work  done  in   this  filtration  being  performed  entirely  at   the 

expense  of  the  energy  of  the  heart-beat  represented  as  lateral 
pressure  in  the  vessels  of  the  tufts.  But  as  the  proportion  of 
salts,  and  especially  of  urea,  is  very  far  from  being  the  same 
in  urine  as  in  blood,  it  had  further  to  be  assumed  that  the  liquid 
which  passes  into  Bowman's  capsule  is  exceedingly  dilute,  and 
that  absorption  of  water,  and  perhaps  of  other  constituents, 
takes  place  in  its  passage  along  the  renal  tubules.  This  pro- 
cess of  reabsorption  he  pictured  as  a  purely  physical  diffusion 
between  the  dilute  urine  in  contact  with  the  free  ends  of  the 
epithelial  cells  lining  the  tubules  and  the  much  more  concen- 
trated lymph  with  which  their  deep  ends  are  bathed.  The 
great  length  of  these  tubules,  as  compared  with  those  of 
most  other  glands,  might  indeed  seem  to  indicate  a  long  sojourn 
of  the  urine  in  them,  and  the  probability  of  important  changes 
being  caused  in  its  passage  along  them.  But  if  we  consider  the 
immense  length  (60  to  70  cm.)  of  the  seminal  tubules  and  of 
their  gigantic  ducts  (epididymis  6  metres),  where,  of  course, 
absorption  of  water  on  a  large  scale  is  out  of  the  question,  it 
will  be  granted  that  little  can  be  built  upon  the  mere  length  of 
the  renal  tubules.  On  the  other  hand,  the  salivary  glands,  where 
there  are  no  glomeruli,  secrete  as  much  water  as  the  kidneys 
are  supposed  to  filter  ;  and  the  pancreas,  whose  capillaries  form 
the  first  of  a  double  set,  and  therefore  in  this  respect  correspond 
to  the  renal  glomeruli,  secretes  less  water  than  the  liver,  whose 
capillaries  correspond  to  the  low-pressure  plexus  around  the 
convoluted  tubules  of  the  kidney.  So  that  deductions  drawn 
from  the  anatomical  relations  of  the  bloodvessels  are  not  in  this 
case  of  much  value,  unless  supported  by  physiological  results. 

It  is  somewhat  unfortunate  that  systematic  writers  have  fallen 
into  the  habit  of  discussing  the  mechanism  of  urinary  secretion 
as  if  the  Ludwig  theory  and  the  Bowman  theory  presented  an 
exact  antithesis,  as  if  the  one  offered  a  complete  '  mechanical  ' 
explanation  of  a  process,  which  the  other  viewed  as  entirely 
'  vital,'  and  therefore  withdrawn  from  physical  explanation. 

We  need  not  concern  ourselves  here  with  the  historical  develop- 
ment of  this  discussion.  Three  main  questions  require  our  atten- 
tion : 

1.  Is  there  any  evidence  that  reabsorption  actually  occurs  in 
the  tubules  ?  If  reabsorption  on  an  important  scale  does  take 
place,  it  follows  at  once  that  there  must  be  a  difference  of  function 
between  the  two  parts  of  the  renal  apparatus,  through  which 
urinary  constituents  pass  in  opposite  directions. 

2.  But  if  there  is  no  reabsorption,  or  none  of  importance,  it 
may  still  be  asked  whether,  the  direction  of  movement  of  the 
urinary   constituents   through   the   glomeruli   and   the   tubular 


EXCR1  TION  457 

epithelium  being  the  same,  some  quantitative  or  qualitative 
difference  in  their  activity  may  not  exist,  certain  constituents, 
e.g.,  passing  numb  or  exclusively  through  the  one  or  the  other. 

;.  When  these  questions  have  been  settled,  we  are  in  a  position 
to  consider  the  nature  of  the  process  by  which  the  urinary  con- 
stituents find  their  way  from  the  Mood  into  the  lumen  of  the 
capsules  and  the  tubules,  or,  if  there  is  reabsorption,  out  of  the 
tubules  into  the  lymph  and  blood  again,  and  to  see  whether  or 
no  it  can  be  entirely  explained  on  mechanical  and  physico- 
chemical  principles. 

That  some  absorption  can  take  place  from  the  kidney  when 
the  pressure  in  the  ureter  is  abnormally  raised  need  not  be 
doubted,  and  when  substances  like  potassium  iodide  or  strych- 
nine are  introduced  into  the  ureter  or  the  pelvis  of  the  kidney 
under  these  circumstances,  they  can  speedily  be  detected  in 
the  blood.  When  the  ureter  pressure  (in  dogs)  is  only  slightly 
increased,  instead  of  evidence  of  reabsorption,  we  obtain  evidence 
of  increased  secretion.  The  volume  of  urine,  the  total  quantity 
of  sulphate  in  the  urine  when  sodium  sulphate  is  injected  into 
the  blood  as  a  diuretic,  and  the  total  amount  of  reducing  sugar 
when  phloridzin  is  injected,  are  all  greater  on  the  obstructed 
than  on  the  normal  side.  These  facts  are  quite  opposed  to  the 
idea  that  filtration  and  reabsorption  are  important  factors  in  the 
preparation  of  normal  urine  (Brodie  and  Cullis).  Changes  in  the 
blood-flow  through  the  kidney  have  nothing  to  do  with  the 
results,  since  the  small  increase  in  pressure  in  the  ureter  was  shown 
not  to  affect  the  rate  of  flow  of  the  blood.  The  attempt  has  been 
made  to  decide  whether  absorption  normally  occurs  by  removing 
as  much  of  the  tubules  as  possible,  and  seeing  whether  the 
character  of  the  urine  is  altered.  In  rabbits  the  whole  or  a  large 
portion  of  the  medulla  has  been  excised  from  one  kidney  and  the 
other  then  extirpated.  From  the  mutilated  kidney  two  or  three 
times  as  much  urine  was  said  to  flow  as  was  secreted  by  a  con- 
trol rabbit  operated  on  in  the  same  way,  except  for  the  removal 
of  the  renal  medulla  (Ribbert).  The  conclusion  was  drawn  that 
the  greater  quantity  of  urine  escaping  was  due  to  the  smaller 
opportunity  for  reabsorption  of  the  water.  But  experiments 
mentioned  on  p.  569  suggest  a  different  interpretation  of 
these  observations.  And  Boyd,  who  repeated  Ribbert's  work, 
obtained  quite  different  results  after  partial  removal  of  the 
medulla.  He  found  it  impossible  to  remove  the  whole.  So  that 
hitherto  the  direct  method  of  eliminating  the  tubules  has  left 
the  matter  where  it  wras. 

Some  light  has  been  thrown  on  this  question,  by  taking  ad- 
vantage of  the  anatomical  fact  that  the  kidney  of  batrachians, 
and,  indeed,  that  of  fishes  and  ophidia  as  well,  has  a  double 


458 


/    1/  /  \ ■/•  //    OF  PHYSIOLOGY 


blood-supply.  The  renal  artery  gives  <>li  afferenl  vessels  to 
the  glomeruli  :  the  vena  advehens,  or  renal  portal  vein,  breaks 
up,  like  the  portal  vein  in  the  liver,  into  a  plexus  oi  capillaries 
surrounding  the  tubules,  and  there  seems  to  be  no  communication 
between  the  two  vascular  systems. 

I'.\  tying  all  the  arteries  going  to  the  kidneys  in  frogs  the  circu- 
lation through  the  glomeruli  can  be  completely  cul  off,  while 
ligation  <>l  the  renal  portal  vein  does  not  affect  the  blood-supply 
of  the  glomeruli,  though  markedly  interfering  with  th.it  oi  the 
tubules.  Gurwitsch  has  found  that  after  ligation  of  the  renal 
portal  vein  oi  one  kidney  in  (male)  frogs,  the  flow  of  urine  from 
that  kidney  is  much  diminished  as  compared  with  the  other. 

He  argues  that  if  reabsorption 
of  dilute  urine  filtered  through 
the  glomeruli  takes  place  in  the 
tubules,  the  opposite  result  ought 
to  be  obtained,  since  the  glome- 
ruli are  not  affected,  while  any 
absorptive  power  of  the  tubules 
must  be  crippled  or  abolished. 

In  connection  with  the  second 
question,  and  also  incidentally 
with  the  first,  the  results  of  ex- 
periments on  the  distribution  of 
pigments  in  the  kidney  after  their 
injection  into  the  blood  have  oft  en 
been  appealed  to.  Heidenhain  in- 
jected indigo-carmine  into  the 
blood  of  rabbits,  and  after  a 
variable  time  killed  them,  cut 
out  the  kidneys,  and  flushed 
them  with  alcohol,  in  which  the 
pigmenl  is  insoluble.  His  results  were  as  follows  :  (i)  When  the 
spinal  cord  was  cul  before  the  injection  in  order  to  reduce  the 
blood-pressure,  the  bine  granules  were  found  in  the  '  rodded  ' 
epithelium  of  the  convoluted  tubules  and  the  ascending  limb  of 
Henle's  loop,  and  in  the  lumen  of  the  tubules,  but  nowhere  else. 
Bowman's  capsules  contained  no  pigment.  The  renal  cortex  was 
coloured  blue.  (_>)  When  the  spinal  cord  was  not  cut ,  the  pigment 
was  found  in  the  medulla  and  pelvis  ol  the  kidney,  as  well  as  in 
t  he  cortex,  but  always  in  the  lumen  ol  the  tubules,  and  not  in  the 
epithelium,  excepl  in  the  situations  mentioned.  (3)  It  a  portion 
of  thi'  cortex  of  the  kidney  had  been  cauterized  with  nitrate  (>t 
silver  before  injection  oi  the  pigment,  the  spinal  cord  being  left 
intact,  a  wedge  of  the  renal  substance,  corresponding  to  this 
area,  remained  coloured  only  in   the  cortex,  although  the  resl 


Fig.    174. — Diagram   of    Dis 
tion    of    I'k, mini     iv     Kidney 

AFTER    INJECTION    INTO    Bl.OOD. 

The  cortex  between  a  and  b  and 
between  c  and  1/  was  cauterized  be- 
fore the  injection.  In  the  black 
wedge-shaped  portions,  1,  there  was 
nc  1  pigment.  In  the  zones  shaded 
like  z  there  was  some  pigment,  but 
not  so  much  as  in  the  areas  shaded 
like  ;. 


EXCRETION  459 

was  blue  in  the  medulla  also.     The  '  rodded  '  epithelium  was 
filled  with  blue  granules  as  before  (Fig.  174). 

(1)  Shows  thai  the  epithelium  is  capable  of  excreting  some 
substances  a1  least.  (2)  Appears  to  show  thai  when  the  Mood- 
pressure  is  normal  water  is  poured  out  from  some  part  of  the 
tubule,  and  washes  the  pigment  separated  by  the  'rodded 
epithelium  down  towards  the  papillae.  (3)  Suggests  that  it  is 
through  the  glomeruli  thai  most  of  the  water  passes.  For 
cauterization  has  not  destroyed  the  power  of  the  epithelium 
to  excrete  pigment,  and  therefore,  presumably,  would  not  have 
destroyed  its  power  to  excrete  water  if  it  possessed  this  power 
in  any  great  degree  ;  and  the  glomeruli  and  their  capsules  are 
the  only  other  part  of  the  renal  mechanism  which  can  have 
been  affected.  The  fact  that  in  birds  and  serpents,  whose  urine 
is  solid  or  semi-solid,  the  glomeruli  are  smaller  than  in  mammals 
is  corroborative  evidence  that  the  glomeruli  have  to  do  with 
the  excretion  of  water. 

When  pigments  are  injected  into  the  dorsal  lymph-sac  of  a 
frog  without  interference  with  the  renal  circulation,  they  are 
found  plentifully  in  the  lumen  of  the  convoluted  tubules,  and 
also  in  the  epithelial  cells  lining  them.  The  suggestion  has  been 
made  that  the  pigments  have  been  absorbed  by  the  cells  from 
the  lumen  and  not  excreted  by  them  into  it.  And  certainly 
pigments  soluble  in  the  cytoplasm  or  in  the  substances  that 
form  the  envelopes  of  cells,  and  therefore  capable,  like  methylene 
blue,  of  staining  them  during  life,  might  be  taken  up  by  the 
renal  epithelium  if  excreted  into  the  tubules  by  the  glomeruli, 
and  might  cause  staining  of  them,  particularly,  of  course,  of  the 
free  ends  of  the  cells  next  the  lumen.  But  this  suggestion  is 
inadmissible  since  on  injection  of  the  same  pigments  after  ligation 
of  the  renal  portal  vein  the  convoluted  tubules  contain  little  or 
no  pigment  in  their  lumen.  And  when  the  urinary  flow  is  stopped 
on  one  side  in  mammals  by  temporary  compression  of  the  renal 
artery  the  corresponding  kidney  takes  up  fully  as  much  carmine 
as  its  fellow  (Carter).  There  is  no  doubt  that  not  only  pigments 
capable  of  '  vital  staining,'  like  methylene  blue,  but  also  pigments 
which  do  not  stain  living  cells,  are  taken  up  from  the  blood  (or 
lymph)  by  the  epithelial  cells,  and,  lying  in  vacuoles  in  their 
cytoplasm,  are  transported  towards  the  lumen,  and  there  ex- 
truded. It  is  not  the  solubility  of  the  pigments  in  lipoids,  and 
therefore  their  solubility  in  the  supposed  lipoid  envelope  of  the 
cells,  which  determines  whether  they  shall  be  excreted.  The 
degree  in  which  they  are  capable  of  being  presented  to  the  cells 
in  non-colloid  solution  appears  to  some  extent  to  be  a  determining 
factor.  The  pigments  not  taken  up  are  highly  colloidal  (Gurwitsch, 
Hober).      Shafer   has  recentlv   confirmed    Heidenhain's   state- 


46o  A   MANUAL  OF  PHYSIOLOGY 

Bients  as  to  the  place  of  excretion  of  indigo-carmine.  When 
leuco-indigo-carmine  (a  colourless  reduction-product  of  indigo- 
r, limine)  was  injected,  the  blue  oxidized  substance  \v;is  found  in 
the  lumen  of  the  convoluted  tubules  and  in  the<  ollei  ting  t  ubules, 
but  not  at  all  in  the  Bowman's  capsule.  The  cells  of  the  con- 
voluted tubules  were  colourless,  because  they  kepi  the  pigment 
in  its  reduced  condition,  and  it  only  became  oxidized  in  the 
lumina  of  those  parts  of  the  tubules  whose  contents,  according  to 
Dreser,  show  an  acid  reaction.  On  oxidation  by  peroxide  oi 
hydrogen  the  cells  of  the  convoluted  tubules  became  faintly  green, 
but  the  Bowman's  capsule  remained  colourless.  This  can  only 
be  explained  on  the  assumption  that  the  leuco-product  of  the 
pigment  was  excreted  by  the  cells  of  the  convoluted  tubules. 

But  these  cells  are  far  from  taking  up  all  pigments  indifferently. 
Some  pigments  are  extruded  mainly  by  one  part,  others  mainly 
by  another  part  of  the  renal  tubule,  and  some  even  by  the 
glomeruli,  as  shown  long  ago  for  ammonium  carminate.  The 
glomeruli,  however,  are  in  general  far  less  active  in  this  regard 
than  the  epithelial  cells,  and  the  fact  that  the  latter  pick  out  from 
the  blood  such  substances  as  these  foreign  pigments  which  pass 
through  the  Malpighian  tufts  unchallenged,  renders  it  likely  that 
the  tubules  also  exercise  a  special  function  in  the  secretion  of  the 
normal  constituents  of  urine.  More  direct  evidence  of  this  is 
not  wanting,  for  Bow  man  saw  crystals  of  uric  acid  in  the  epi- 
thelium of  the  convoluted  tubules  of  birds.  Heidenhain  found 
that  urate  of  soda  injected  into  the  blood  of  a  rabbit  is  excreted 
by  the  epithelium  of  the  convoluted  tubules  and  the  ascending 
part  of  Henle's  loop,  just  as  is  the  case  with  indigo-carmine. 
And  Nussbaum's  experiments,  although  not  quite  conclusive, 
have  made  it  probable  that  in  the  frog  urea  is  actually  separated 
by  the  epithelium  of  the  tubules.  They  were  founded  on  the 
anatomical  peculiarity  in  the  renal  circulation  of  the  frog  already 
mentioned.  By  tying  the  renal  arteries  in  that  animal,  he 
thought  he  could  at  will  stop  the  circulation  in  the  glomeruli,  and 
he  found  that  after  this  was  done  there  was  no  further  spon- 
taneous secretion  of  urine.  But  when  urea  was  injected  intra- 
venously the  secretion  of  urine  again  began,  urea  being  eliminated 
by  the  kidneys,  and  water  along  with  it.  Sugar,  peptone,  and 
egg-albumin,  injected  into  the  blood,  no  longer  passed  into  the 
urine,  even  when  the  secretion  was  excited  by  simultaneous 
injection  of  urea,  although  they  readily  did  so  when  the  arteries 
were  not  tied.  He  concluded  that  the  Malpighian  corpuscles 
have  the  power  of  excreting  water,  sugar,  peptone,  and  albumin, 
while  the  epithelium  of  the  tubules  excretes  urea  as  well  as  water. 

Beddard  has  confirmed  Nussbaum's  statemenl  that  when  all 
the  arteries  going  to  the  kidney  are  tied  the  glomeruli  are  com- 
pletely and  permanently  deprived  of  blood.     The  spontaneous 


/  KCRETION  461 

sea  etion  of  ui  ine  is  totally  stopped,  as  Nussbaum  found,  but  only 
111  three  experiments  out  <>!  eighteen  was  it  possible  to  starl  the 
mention  by  injection  oi  urea.  The  epithelium  of  the  tubules 
degenerated  and  desquamated  alter  complete  ligation  of  all  the 
renal  arteries,  showing  that  it  requires  some  arterial  blood  as 
well  as  the  venous  blood  from  the  renal  portal  to  maintain  its 
vitality.  The  degeneration  of  the  epithelium  can  be  prevented 
by  keeping  the  frogs  in  an  atmosphere  of  oxygen  after  ligation  of 
the  arteries.  In  six  such  frogs,  in  which  the  complete  elimination 
of  the  glomeruli  was  controlled  by  subsequent  injection,  secre- 
tion of  urine  followed  the  injection  of  urea,  alone  or  in  combina- 
tion with  dextrose,  phloridzin,  or  di-sodium  hydrogen  phosphate 
(Na2HP04).  In  all  the  cases  the  urine  contained  urea,  chlorides, 
and  sulphates,  and  was  acid  to  phenolphthalein.  In  one  case 
alter  injection  of  urea  and  dextrose,  and  in  another  after  urea  and 
phloridzin,  the  urine  reduced  Fehling's  solution,  and  therefore 
presumably  contained  dextrose  (Beddard  and  Bainbridge). 
When  the  frog's  kidney  is  perfused  in  situ  with  oxygenated  salt 
solution  a  certain  flow  of  urine  takes  place.  Substitution  of  non- 
oxygenated  saline  markedly  slows  the  flow  (Cullis). 

Apparently,  then,  the  tubules  have  the  capacity  to  secrete 
practically  all  the  constituents  of  urine,  and  when  the  flow  of 
urine  is  small,  probably  most  of  it  comes  from  the  tubules.  When, 
as  in  the  diuresis  produced  by  salt  solutions,  large  quantities  of 
water  and  salts  have  to  be  rapidly  excreted,  the  bulk  of  the  liquid 
comes  from  the  glomeruli,  but  also  by  a  process  of  secretion. 

Lindemann  has  endeavoured  to  exclude  the  glomeruli  in 
mammals  by  injecting  oil  through  the  renal  artery.  After  a 
short  time,  according  to  him,  the  oil  emboli  clear  away  from 
practically  all  parts  of  the  kidney  except  the  glomeruli,  which 
remain  plugged.  If  indigo-carmine  be  subsequently  injected  into 
the  blood,  it  is  not  only  taken  up  from  it  by  the  embolized  kidney 
as  well  as  by  a  normal  one,  but  is  excreted.  The  quantity  of 
urine  is  much  diminished  and  its  specific  gravity  increased,  but 
its  composition  is  not  essentially  altered.  He  infers  that  the 
tubules  are  in  a  high  degree  independent  of  the  glomeruli  as  an 
apparatus  for  the  secretion  of  urine. 

As  regards  our  first  two  questions  we  may  conclude  that 
there  is  no  good  evidence  that  reabsorption  of  water  or  other  con- 
stituents of  the  urine  in  the  renal  tubules  plays  an  important  part 
in  the  preparation  of  that  secretion.  Many  facts  favour  the  con- 
clusion that  the  glomeruli  and  the  renal  epithelium  act  as  separate 
although,  of  course,  mutually  supplementary  mechanisms,  the 
glomeruli  separating  the  larger  portion  of  the  water  and  salts,  the 
epithelium  the  larger  portion,  if  not  the  whole,  of  the  characteristic 
organic  constituents. 

As  regards  the  third  question,  it  is  now  generally  admitted, 


,...•  I    MANUAL  OF  PHYSIOLOG  V 

even  by  those  who  uphold  a  modified  '  mechanical  '  i  heory,  thai 
even  it  the  urine  is  originally  separated  from  the  blood  by  filtra- 
tion at  the  expense  of  the  energy  of  the  heart- In-. m  represented 
by  the  pressure  <>|  the  blood  in  the  glomeruli,  the  reabsorption 
in  the  tubules  cannot  be  attributed  to  simple  diffusion,  but 
must  be  a  selective  process  analogous  to  absorption  in  the  intes- 
tine and  entailing  the  expenditure  of  a  large  amount  <>!  work 
at  the  expense  of  the  food  materials  or  the  protoplasm  ol  the 
epithelial  cells.  Every  attempt  at  a  strictly  mechanical  explana- 
tion breaks  down  for  the  kidney,  as  for  other  glands. 

The  practical  absence  from  urine  of  the  proteins  and  sugar 
of  the  blood  under  normal  circumstances,  and  the  elimination 
by  the  kidney  of  egg-albumin,  peptone,  and  other  bodies  when 
injected  into  the  veins,  show  a  selective  power  inexplicable 
except  by  reference  to  the  vital  activity  of  cells.  Urea  and 
dextrose,  both  highly  diffusible  substances,  circulate  side  by  side 
in  the  bloodvessels  of  the  kidney.  The  one  is  taken  and  the  other 
left.  The  urea  is  a  waste-product  of  no  further  use  in  the 
economy.  The  sugar  is  a  valuable  food-substance.  The  kidney 
selects  with  unerring  certainty  the  urea,  of  which  only  4  parts 
in  10,000  arc  presenl  in  the  blood,  but  rejects  the  sugar,  of 
which  there  is  three  times  as  much. 

Egg-albumin  injected  into  the  blood  passes  through  the  renal 
circulation  side  by  side  with  the  serum-albumin  of  the  plasma. 
Both  are  indiffusible  through  membranes,  and  to  the  physical 
chemist  the  differences  between  them  may  appear  superficial  and 
minute.  But  the  kidney  does  not  hesitate  for  an  instant.  A 
large  part  of  the  egg-albumin  is  promptly  excreted  as  a  foreign 
substance  ;  the  serum-albumin  passes  on  untouched. 

Not  only  does  the  kidney  exercise  a  power  of  qualitative  selec- 
tion ;  it  also  takes  cognizance  of  the  quantitative  composition  of 
the  blood.  So  long  as  there  is  less  sugar  in  the  plasma  than  about 
_'  to  3  parts  in  1,000,  it  is  refused  passage  into  the  renal  tubules. 
But  when  this  limit  is  passed,  and  the  proportion  of  sugar  in  the 
blood  becomes  excessive,  the  kidney  begins  to  excrete  sugar,  and 
continues  to  do  so  till  the  balance  is  redressed. 

The  advocates  of  the  theory  of  filtration  through  the  glomeruli 
have  made  their  firmest  stand  on  the  excretion  of  the  inorganic 
constituents  of  the  urine,  and  have  laid  stress  particularly  on  the 
fact  that  the  hydraulic  plethora  caused  by  intravenous  injection 
of  salts  is  accompanied  by  diuresis.  It  is  true  that  the  direct  intro- 
duction of  water  into  the  blood,  or  its  attraction  from  the  lymph- 
spaces  when  the  osmotic  pressure  of  the  blood  is  increased  by  the 
injection  of  substances  like  urea,  sugar,  and  sodium  chloride,  may 
cause  a  condition  of  hydramiq  plethora,  and  that  this  plethora 
may  sometimes  be  associated  with  an  increase  of  pressure  in  the 
capillaries  in  general,  and  therefore  in  the  vessels  of  the  Mai- 


/  Xi  RETION 

pighian  tuft.  It  may  also  be  admitted  thai  such  an  incr< 
di  pressure  mighl  be  accompanied  by  an  increased  filtration  oi 
water  and  salts  into  Bowman's  capsule.  Even  in  the  excised 
kidney,  after  the  vital  activity  <>i  its  cells  may  be  presumed  to 
have  erased,  filtration  of  the  mosl  varied  solutions  occurs  when 
the  organ  is  perfused  with  them  through  the  renal  artery.  The 
liquid  which  escapes  from  the  ureter  always  has  the  same  com- 
position as  the  perfusion  fluid  (Sollmann).  It  would  certainly 
appear  unlikely  that  the  glomerular  epithelium  should  make  no 
use  whatever  for  the  furtherance  oi  its  task  of  the  difference  of 
hydrostatic  pressure  on  its  two  surfaces.  It  is  in  taking  advan- 
tage of  such  circumstances  for  the  promotion  of  its  specific  woi  k 
up  to  the  point  at  which  t  hey  cease  to  favour  it  that  a  great  part 
ot  t  he  true  secretory  activity  of  cells  may  be  supposed  to  consist. 
When  we  see  a  barge  passing  through  a  lock,  and  being  gradually 
lifted  to  the  proper  level  by  the  inrush  of  water,  we  never  dream 
of  saying  that  the  whole  thing  is  an  affair  of  the  laws  of  hydro- 
statics. We  know  that  the  part  played  by  the  lock-keeper,  the 
opening  and  closing  of  the  gates  and  sluices  at  the  proper  time, 
is  all-important,  although  he  does  not  lighten  by  one  ounce  the 
weight  which  the  water  must  lift.  He  uses  the  head  of  water  for 
a  specific  purpose — namely,  to  lift  the  barge.  In  like  manner 
it  is  to  be  expected  that  the  glomerular  epithelium,  when  the 
difference  of  pressure  on  its  two  surfaces  is  increased  by  hydraemic 
plethora,  will  use  the  increased  facility  of  filtration  to  rapidly 
excrete  a  portion  of  the  water.  But  who  will  believe  that 
the  addition  of  a  tumbler  of  water,  absorbed  from  the  alimentary 
canal,  to  4  or  5  litres  of  blood  circulating  in  a  system  of  vessels 
whose  capacity  can  and  does  vary  within  wide  limits,  should 
cause  in  the  capillaries  of  the  kidney  an  increase  of  pressure 
exactly  proportional  to  the  increase  in  the  elimination  of  water 
in  the  urine,  lasting  for  the  same  time  and  disappearing  at  the 
moment  when  the  normal  composition  of  the  blood  is  restored  ? 
Nor  is  it  easier  to  explain  on  any  mechanical  hypothesis  how- 
it  is  that  in  a  starving  animal,  the  quantity  of  inorganic  sub- 
stances eliminated  in  the  urine  drops  almost  to  zero,  while  the 
proportional  amount  in  the  blood  and  tissues  is  little,  if  at  all, 
affected.  In  a  rabbit  rendered  poor  in  sodium  chloride  by 
t ceding  it  with  salt-free  food  the  injection  of  a  solution  of 
sodium  chloride  isotonic  with  the  blood  produces  no  diuresis 
lor  a  considerable  time,  but,  on  the  contrary,  a  diminished  flow 
ot  urine,  while  a  similar  solution  injected  into  the  veins  of  a 
rabbit  previously  fed  with  salted  food  causes  an  immediate  and 
considerable  diuresis.  When  small  quantities  of  isotonic  solu- 
tions of  various  salts  are  injected,  those  not  normally  present  in 
the  blood  produce  a  greater  diuresis  thamnormal  constituents. 
Sodium  chloride,  which  is  present  in  normal  plasma  in  greater 


464  A   MANUAL  OF  I'lIYSIOLOGY 

amonnl  than  any  other  salt,  causes  the  smallesl  diuresis  of  all 
(Haake  and  Spiro).  Such  facts  suggesl  that  the  se<  reting  ''li- 
nt the  kidney  are  stimulated  or  inhibited  by  the  contact  of  blood 
or  lymph  in  which  the  normal  constituents  arc  present  in  too 
greal  or  in  too  small  amount,  and  that  the  intensity  of  the  action 
is  proportional  to  the  degree  of  deficiency  or  excess.  The  greater 
the  velocity  of  the  circulation  in  the  kidney,  the  more  effective  will 
be  the  stimulation  produced  by  any  given  sub-tain  «•  present  in 
excess,  and  therefore  the  greater  the  total  amount  of  it  eliminated 
in  a  given  time.  For  in  making  the  round  of  the  renal  circula- 
tion the  concentration  of  the  substance  in  any  given  portion  of 
blood  will  fall  less,  and  therefore  the  average  stimulation  exerted 
by  it  during  the  round  will  be  greater  the  faster  the  blood 
flows.  It  is  quite  in  agreement  with  this  that  when  plethora 
is  occasioned  by  transfusion  of  blood  there  is  little  or  no  diuresis, 
although  the  increase  of  arterial,  capillary,  and  venous  pressure, 
and  the  dilatation  of  the  kidney,  are  evident.  For  the  rapid 
passage  of  liquid  out  of  the  vessels  would  lead  to  a  great  increase  in 
the  relative  proportion  of  corpuscles  to  plasma — that  is  to  say, 
to  an  abnormal  condition  of  the  blood.  On  the  other  hand, 
when  plethora  is  produced  by  injection  of  serum  diuresis  occurs 
(Cushny).  This,  again,  is  what  we  should  expect,  since  the 
elimination  of  the  superfluous  liquid  will  restore  the  normal  pro- 
portion. The  diminished  viscosity  of  the  blood  (p.  22)  produced 
by  the  excess  of  serum  will  aid  the  flow  through  the  kidney  and 
therefore  increase  the  diuresis,  while  in  the  case  of  the  plethora 
produced  by  injection  of  blood  the  elimination  of  liquid  will  at 
once  increase  the  viscosity,  diminish  the  velocity  of  the  renal 
flow,  and  tend  to  lessen  diuresis. 

There  is,  then,  little  more  reason  to  assume  that  the  copious 
flow  of  urine  which  follows  the  absorption  of  a  large  quantity 
of  water  is  due  to  a  mere  process  of  filtration  than  there  is  to 
believe  that  filtration,  and  not  selective  secretion,  is  the  cause 
of  the  gush  of  saliva  which  precedes  vomiting,  or  the  sudden 
outburst  of  sweat  on  sudden  and  severe  exertion.  In  addition, 
there  are  the  positive  proofs  already  mentioned  that  the  '  rodded  ' 
epithelium  of  the  tubules,  which  no  one  supposes  to  be  abandoned 
more  to  mere  physical  influences  than  the  epithelium  of  the 
salivary  glands,  plays  a  part  in  the  secretion  of  some  of  the 
urinary  constituents. 

As  to  the  nature  of  the  mechanism  set  in  motion,  and  the 
series  of  events  that  take  place  as  the  constituents  of  the  urine 
journey  from  the  interior  of  the  bloodvessels  to  the  lumen  of 
the  tubules,  we  know  no  more  than  in  the  case  of  other  glands. 
This  alone  is  clear,  that  the  separation  of  the  urine  from  the 
blood  implies  the  performance  of  a  large  amount  of  work  by 


EXCRETION  465 

the  kidney.  For  the  osmotic  pressure  of  urine  is  several  times 
as  greal  as  thai  of  the  plasma  of  the  blood.  Blood-plasma 
freezes  at  -0-55°  to  -  0-65°  C.  (on  the  average,  say,  —  o-6°  ('.). 
The  osmotic  pressure  corresponding  to  —  o-6°  C.  is  5,662  milli- 
metres of  mercury  (p.  400),  or,  in  round  numbers,  75  metres  of 
water.  Human  urine,  lias  been  found  to  freeze  at  —1-38°  to 
2'U  ('.  (say,  on  the  average,  — 1-8°  C),  and  for  highly  con- 
centrated urines  the  depression  of  the  freezing-point  may  be 
considerably  greater.  The  osmotic  pressure  corresponding  to 
— 1'8°  C.  is  16,986  millimetres  of  mercury  or  225  metres  of 
water.  This  exceeds  the  osmotic  pressure  of  the  plasma  by 
150  metres  of  water.  In  separating  a  kilogramme  of  urine  from 
the  blood  the  kidney  accordingly  does  work  approximately 
equivalent  to  raising  a  weight  of  a  kilogramme  to  the  height 
'it  150  metres — i.e.,  150  kilogramme-metres.  It  is  evident  that 
the  excess  of  the  blood-pressure  in  the  glomeruli  over  the  pres- 
sure of  the  urine  in  the  tubules,  which,  even  if  we  neglect  the 
latter  altogether — since  there  is  only  slight  resistance  to  the  flow 
of  urine  towards  the  bladder — cannot  at  most  be  greater  than 
100  millimetres  of  mercury,  or  1-35  metres  of  water,  will  account 
for  only  an  insignificant  part  of  this  work.  The  rest  must  be 
done  at  the  expense  of  the  energy  of  the  food  materials  taken 
up  by,  and  transformed  in,  the  cells  concerned  with  the  secre- 
tion of  the  urine.  But  we  do  not  know  in  what  way  these  cells, 
by  applying  this  energy,  perform  the  remarkable  feat  of  per- 
manently maintaining  a  difference  of  fifteen  atmospheres  in  the 
osmotic  pressure  of  the  liquids  in  contact  with  their  attached 
and  free  surfaces.  A  token  of  the  intensity  of  the  metabolic  effort 
required  is  the  marked  increase  in  the  absorption  of  oxygen 
(as  much  as  0-28  c.c.  per  gramme)  which  occurs  during  diuresis, 
although  it  is  not  in  proportion  to  the  amount  of  the  diuresis. 
In  one  experiment  the  oxygen  absorbed  by  a  dog's  kidneys  was 
11  per  cent,  of  what  would  have  been  used  up  by  the  entire 
animal  under  normal  conditions.  There  is  no  definite  relation 
between  the  oxygen  taken  in  and  the  carbon  dioxide  given  out 
at  any  moment. 

What  is  the  significance  of  the  peculiar  arrangement  of  the 
glomerular  bloodvessels,  if  the  epithelium  of  the  capsules  has  secre- 
tive powers  like  that  of  ordinary  glands  ?  It  is  difficult  to  believe 
that  these  unique  vascular  tufts  have  not  a  near  and  important  rela- 
tion to  the  renal  function  ;  but  it  is  by  no  means  clear  what  that 
relation  is.  The  secretion  of  water,  and  even  its  rapid  secretion,  is 
not  at  all  bound  up  with  any  set  arrangement  of  bloodvessels. 
Gland-cells  all  over  the  body  secrete  water  under  the  most  varied 
conditions  of  blood-pressure,  although  a  comparatively  high  pressure 
is  upon  the  whole  favourable  to  a  copious  outflow. 

But  the  kidney  has  other  functions  than  mere  excretion  (pp.  50S, 
569).     And  it  may  be  that  the  simplest  part  of  the  latter  process, 

30 


466  A   MANUAL  OF  PHYSIOLOGY 

the  elimination  of  water  and  salts,  is  largely  thrown  upon  the 
Malpighian  corpuscles,  as  a  physiologically  cheaper  ma<  bine  than 
the  epithelium  of  the  tubules,  which  is  left  free  for  more  complex 
labours.  These  may  include  not  only  the  separation  of  aitrogi  nous 
metabolites,  but  also  synthetic  processes  possibly  concerned  in  the 
regulation  of  protein  metabolism.  One  characteristic  synthesis, 
the  union  of  benzoic  acid  and  glycin  to  hippuric  a<  id,  has  aheady 
been  referred  to.  As  will  be  shown  later  (p.  508),  it  takes  place 
mainly,  in  some  animals  perhaps  exclusively,  in  the  kidney.  I 
epithelium  of  the  glomerulus,  being  a  less  highly  organized  and  less 
delicately  selective  mechanism  than  that  of  the  convoluted  tubules, 
may  more  easily  respond  to  increase  of  blood-pressure  l>v  increased 
secretion.  At  the  same  time,  placed  as  it  is  at  the  last  flood-gate 
of  the  circulation,  where  the  escape  of  anything  valuable  means 
its  total  loss,  the  glomerular  epithelium  may  be  endowed  with  a 
general  power  of  resistance  to  transudation,  which  renders  a  com-» 
paratively  high  blood-pressure  a  necessary  condition  of  its  acting 
at  all.  And  as  a  matter  of  fact  water  ceases  to  be  secreted  by  the 
kidney  long  before  the  blood-pressure  in  the  glomeruli  can  have 
fallen  below  that  which  suffices  for  the  highest  activity  of  the  liver. 
Perhaps,  however,  the  high  minimum  pressure  required  (30  to  40  mm. 
of  mercury  in  the  dog)  is  merely  the  necessary  consequence  of  the 
long  and  difficult  path  which  most  of  the  blood  going  through  the 
kidney  has  to  take,  and  that  a  sufficient  blood-flow  cannot  be  kept 
up  with  less.  It  may  be,  too,  that  the  comparatively  small  surface 
of  the  glomeruli,  restricted  in  order  to  leave  room  for  the  more 
highly  organized  parts  of  the  renal  mechanism,  entails  the  more 
intense  and  concentrated  activity,  which  the  high  blood-pressure 
renders  possible,  and  the  simplicity  of  work  and  organization  renders 
harmless. 

An  obvious  result,  and  perhaps  an  important  one,  of  the  peculiar 
arrangement  of  the  bloodvessels  of  the  kidney  is  that  the  renal 
tubules  proper  are  shielded  from  an  excessive  blood-pressure  by  the 
interposition  of  the  glomeruli  as  a  block.  This  may  be  either 
because  the  epithelium  of  the  tubules  would  not  perform  its  work 
so  well  under  a  high  blood-pressure,  or  because  there  would  be  a 
danger  of  substances  which  ought  to  be  retained  being  cast  out  into 
the  urine.  In  this  connection  it  is  interesting  to  note  that  the  specific 
constituents  oi  urine  are  separated  by  epithelium  surrounded  by 
capillaries  of  the  s-cond  order,  and  therefore  with  a  smaller  blood- 
pressure  than  exists  in  the  capillaries  of  most  glands,  while  the 
same  is  true  of  bile,  another  (practically)  protein-free  secretion. 

The  maximum  secretory  pressure  in  the  kidney,  as  shown 
by  a  manometer  tied  into  the  divided  ureter,  is  about  60  mm. 
of  mercury  in  the  dog,  or  less  than  half  that  of  saliva.  If  tin- 
escape  of  the  urine  is  opposed  by  a  greater  pressure  than  this, 
or  if  the  ureter  is  tied,  the  kidney  becomes  cedematous.  Whether 
the  oedema  is  due  to  reabsorption  of  urine  or  to  the  pouring 
out  of  lymph  owing  to  the  pressure  of  the  dilated  tubules  on 
the  veins  has  not  been  definitely  settled.  It  has  been  already 
pointed  out  that  there  is  no  necessary  relation  between  the 
blood-pressure  in  the  capillaries  of  a  gland  and  its  secretory 
pressure  ;  and,  so  far  as  this  goes,  water  might  just  as  well  be 


RETION 


4'7 


secreted  at  a  pressure  of  60  mm.  of  mercury  from  the  low- 
pressure  blood  of  the  second  set  of  renal  capillaries  as  from  the 
high-pressure  blood  of  the  glomeruli.  By  obstruction  the  mole- 
cular concentration  of  the  urine  is  diminished  to  half  or  three- 
quarters  of  the  normal. 

The  Influence  of  the  Circulation  on  the  Secretion  of 
Urine. —  Although  the  activity  of  no  organ  in  the  body  is 
governed  more  by  the  indirect  effects  of  nervous  action  than 
that  of  the  kidney,  no  proof  has  been  given  of  the  existence  of 
secretory  fibres  for  it  comparable  to  those  of  the  salivary  glands. 
All  the  changes  in  the  rate  of  renal  secretion  which  follow  the 
section  or  stimulation  of  nerves  can  be  explained  as  the  conse- 
quences of  the  rise  or  fall  of  local  or  general  blood-pressure,  and 
of  the  corresponding 
variations  in  the 
velocity  of  the  blood 
in  the  renal  vessels. 


The  best  way  to 
study  variations  in 
the  calibre  of  the 
renal  vessels  is  the 
plethysmography 
method,  and  the  onco- 
meter of  Roy  is  a 
plethysmo  graph 
adapted  to  the  kid- 
ney. It  consists  of  a 
metal  capsule  lined 
with  loose  membrane, 
between  which  and 
the  metal  there  is  a 
space  filled  with  oil. 
The  two  halves  of  the 
capsule  open  and  shut 
on  a  hinge  ;  and  the 
kidney,  when  intro- 
duced into  it.  is  sur- 
rounded   on    all    sides 


p:r,.   175. — Diagram  of  Organ-Pletiiysmograph 
or   Oncometer. 

B,  metal  box  in  two  halves  opening  on  the  hinge 
H;  M,  thin  membrane:  A,  space  filled  with  oil; 
O,  organ  enclosed  in  oncometer  ;  V,  vessels  of  organ  ; 
/,  tube  for  filling  instrument  with  oil  ;  T,  tube  con- 
nected with  D,  which  opens  into  cylinder  C  ;  C  is 
also  filled  with  oil  ;  P,  piston  attached  by  E  to  a 
writing  lever. 


by  the  membrane,  the  vessels  and  ureter 
passing  out  through  an  opening.  The  oil-space  is  connected  with  a 
cvlinder  also  filled  with  oil,  above  which  a  piston,  attached  to  a  lever, 
moves.  The  lever  registers  on  a  drum  the  changes  in  the  volume  of 
the  kidney — i.e.,  practically  the  changes  in  the  quantity  of  blood  in 
it,  and  therefore  in  the  calibre  of  its  vessels.  A  still  better  oncometer 
is  that  of  Schafer,  in  which  air  is  employed  instead  of  oil. 

Nerves  of  the  Kidney. — Both  vaso-constrictor  and  vaso-dilator 
fibres  for  the  renal  vessels,  but  most  clearly  the  former,  have  been 
shown  to  leave  the  cord  (in  the  dog)  by  the  anterior  roots  of  the  sixth 
thoracic  to  second  lumbar  nerves,  and  especially  of  the  last  three 
thoracic.  They  run  in  the  splanchnics,  and  then  through  the  renal 
plexus — around  the  renal  artery — into  the  kidney.  The  vaso- 
constrictors predominate,  so  that  the  general  effect  of  stimulation  of 
the  nerve-roots,  the  splanchnics,  or  the  renal  nerves  is  shrinking  of 

30—2 


4^>8 


A    MANUAL  OF  PIJYSTOKH.Y 


the  kidney,  with  diminution  or,  cessation  of  the  Becretion  of  urine. 
Hul    slm\    rlivfimiH.il   stimulation   of  the   roots  causes  increa 
volume,  the  scanty  dilatorsxbeing  by  this  method  ex<  ited  in  prefer- 
ence to  the  constrictors. 

1 1,,-  renal  aerves,  entering  a1  the  bilum,  bran<  h  repeatedly,  so  as 
to  form  .i  wide  meshed  plexus  around  the  art<  ries,  and  a<  i  ompany 
them  even  to  their  finest  ramifications  in  the  cortex.  <  ommg  <>ii 
from  the  nerves  surrounding  the  arteries  are  fine  fibres  which  are 
distributed  to  the  convoluted  tubules,  Some  of  them  terminate  in 
-lobular  ends,  others  in  fine  threads  thai  pass  through  the  mem- 
brana  propria  (Bcrkcly). 


Fig.  176. — Nerves  of  Kidney  (Berkelv). 


(16)  medium -sized  artery  with  its  nerve  ■  plexus  ;  A  erminal  knobs  ; 
B  aberrant  branch  ending  in  terminal  knob  E  ;  the  dotted  ines  outline  he 
arterv  (17)  nerve-fibres  surrounding  a  Bowman's  capsule,  which  is  indicated 
bv  a  dotted  line  ;  some  of  the  endings  are  close  to  the  membrane  ;  (18)  convoluted 
tubule  shown  in  outline  with  fine  nerve-fibres  on  it,  which  seem  to  enter  the 
basement  membrane. 

Section  of  the  renal  nerves  is  followed  by  relaxation  of  the 

small  arteries  in  the  kidney,  and  consequent  swelling  of  the 
organ  The  flow  of  urine  is  greatly  increased,  and  sometimes 
albumin  appears  in  it,  the  excessive  pressure  in  the  capillaries 
(particularly  in  those  of  the  glomeruli)  being  supposed  to  favour 
the  escape  "of  substances  to  which  a  passage  is  refused  under 
normal  conditions. 

f  \n  experiment  which  is  sometimes  quoted  as  a  decisive  test 
of  the  relative  importance  of  changes  in  the  rate  of  flow,  and 
in  the  pressure  of  the  blood  within  the  glomeruli,  is  that  of 
tying  the  renal   vein.     This  undoubtedly   does   not    Lower   the 


EXCRETION 

intra-glomerular  pressure — on  the  contrary,  it  must  increase  it 
but  the  secretion  of  urine  stops.  If  the  venous  outflow  from 
the  kidney  is  only  partially  interfered  with,  the  flow  of  urine 
is  immediately  diminished,  but  the  administration  of  a  diuretic 
like  potassium  nitrate  causes  an  increase.  It  is  more  than  likely 
th.it  in  these  experiments  the  secretion  stops  or  slackens  not 
because  a  high  blood-pressure,  but  because  an  active  circulation 
is  its  necessary  condition.  When  the  blood  stagnates  in  the 
kidney  the  natural  stimulus  to  the  renal  apparatus  speedily 
disappears  owing  to  the  elimination  of  the  urinary  constituents 
to  the  neutral  or  indifferent  point  (p.  464).  The  experiment, 
however,  is  not  perfectly  conclusive.  For  few  glands  can  go 
on  performing  their  function  after  the  circulation  has  ceased. 
The  kidney  must  be  able  to  feed  itself  in  order  to  continue  its  work. 
Above  all  it  needs  oxygen  ;  and  it  might  be  urged  that  if  the  blood 
in  the  glomeruli  could  be  kept  at  the  normal  standard  of  arterial 
blood,  secretion  might  still  go  on  after  ligation  of  the  renal  vein. 

According  to  Ludwig,  indeed,  the  flow  of  urine  stops,  in  spite 
of  continued  filtration  through  the  glomeruli,  because  the 
swelling  of  the  veins  in  the  boundary  layer  compresses  the 
tubules,  and  may  even  obliterate  their  lumen.  There  is  no 
conclusive  experimental  evidence,  however,  and  no  a  priori 
probability,  that  the  obstruction  so  produced  is  sufficiently 
sudden  or  sufficiently  complete  to  cause  instant  and  total  cessa- 
tion of  the  flow.  It  is  even  less  justifiable  to  conclude  from  the 
experiment  that  the  liquid  part  of  the  urine  is,  at  any  rate,  not 
separated  by  the  epithelium  of  the  tubules,  since  the  blood- 
pressure  in  the  capillaries  around  the  tubules  must  rise  very 
greatly  after  ligature  of  the  vein,  and  yet  secretion  is  stopped. 
It  might  equally  well  be  argued  that  the  renal  epithelium  nor- 
mally secretes  water  under  a  low  blood-pressure,  but  is  dis- 
organized under  the  excessive  and  entirely  unaccustomed 
pressure  which  follows  the  closure  of  the  vein. 

It  is  not  only  through  nerves  directly  governing  the  calibre 
of  the  vessels  of  the  kidney  that  the  rate  of  urinary  secretion 
can  be  affected.  Any  change  in  the  general  blood-pressure,  if 
not  counteracted  by,  still  more  if  conspiring  with,  simultaneous 
local  changes  in  the  renal  vessels,  may  be  followed  by  an  in- 
creased or  diminished  flow  of  urine  ;  and  the  law  which  explains 
all  such  variations,  or  at  least  serves  to  sum  them  up,  is  that 
in  general  an  increase  in  the  rate  of  the  blood-flow  through  the 
kidney  is  followed  by  an  increase  in  the  rale  of  secretion.  It  will 
be  remarked  that  this  is  the  converse  of  the  great  law,  of  which 
we  have  already  seen  so  many  illustrations,  that  functional 
activity  increases  blood-flow.  It  is  probable  that  this  law  holds 
for  the  kidney  as  well  as  for  other  organs,  but  that  the  influ- 


170  A    MANV  II    OF  PHYSIOLOGY 

once  of  activity  on  blood-supply  is  subordinated  to  that  of 
blood-supply  on  activity,  while  in  most  tissues,  as  in  the  muscles, 
the  opposite  is  the  case.  It  is  evident  that  an  increase  in  the 
blood-flow  would  favour  the  secretory  activity  of  the  renal  cell-. 
since  the  average  concentration  of  the  blood  presented  to  them 
as  regards  those  constituents  which  they  select  would  remain 
relatively  high  in  its  circuit  through  the  kidney.  The  '  stimulus  ' 
to  secretion  would,  therefore,  be  relatively  intense. 

Destruction  of  the  medulla  oblongata  (i.e.,  of  the  vaso-motor 
centre),  or  section  of  the  cord  below  it,  diminishes  the  secretion 
of  urine,  because  the  arterial  pressure  is  lowered  so  much  as 
to  over-compensate  the  dilatation  of  the  renal  vessels,  which  the 
operation  also  brings  about.  If  the  blood-pressure  falls  below 
40  mm.  of  mercury,  the  secretion  is  abolished.  Stimulation  of 
the  medulla  or  cord  also  lessens  the  flow  of  urine  by  constricting 
the  arterioles  of  the  kidney  so  much  as  to  over-compensate  the 
rise  of  general  blood-pressure,  caused  by  the  constriction  of  small 
vessels  throughout  the  body. 

If  the  renal  nerves  have  been  cut,  stimulation  of  the  medulla 
oblongata  increases  the  urinary  secretion,  because  now  the  rise 
of  general  blood-pressure  is  no  longer  counterbalanced  by  con- 
striction of  the  renal  vessels.  An  increase  in  the  urinary  flow 
can  be  produced  in  the  rabbit  by  a  lesion  in  a  part  of  the 
funiculi  teretes,  which  can  be  reached  in  the  floor  of  the  fourth 
ventricle  (Eckhard),  perhaps  by  destroying  the  portion  of  the 
vaso-motor  centre  governing  the  renal  nerves,  while  the  rest 
remains  uninjured,  or  is  even  stimulated,  and  thus  keeps  up  or 
even  increases  the  general  blood-pressure.  There  is  either  no 
glycosuria,  or  it  is  very  slight. 

Section  of  the  splanchnic  nerves  causes  a  fall  of  arterial  pres- 
sure, which  is,  however  (in  animals  like  the  dog,  in  which  com- 
pensation soon  takes  place),  more  than  balanced  by  the  simul- 
taneous dilatation  of  the  renal  vessels,  and  therefore  for  some 
time  the  flow  of  urine  is  increased,  but  not  so  much  as  when  the 
renal  nerves  alone  are  cut.  In  the  rabbit  there  is  no  increase. 
On  the  other  hand,  stimulation  of  the  splanchnics  stops  the 
urinary  secretion,  because  the  general  rise  of  pressure  is  not 
enough  to  make  up  for  the  constriction  of  the  renal  vessels. 

Diuretics  arc  substances  that  incre  ise  the  flow  of  urine.  Some  of 
them  act  mainly  on  the  circulation,  as  by  increasing  the  general 
blood-pressure,  others  mainly  by  a  direct  influence  on  the  S<  1  reting 
mechanism.  Digitalis  is  a  representative  oi  the  first  class;  urea 
and  caffein  belong  to  the  second.  The  action  of  digitalis  is  to 
st  lengthen  the  beal  oi  the  hearl ,  which  is  a1  the  same  time  s<  imewhat 
slowed,  and  to  constrict  the  arterioles.  Both  effects  contribute  to 
the  increase  oi  pressure.  Bu1  the  accompanying  diuresis  is  due  to 
the  cardial  factor,  the  vaso-constriction  which  involves  the  renal 
vcss-ls  also,  bem-  oven  om  >en sated.     The  diuretic  effect  of  digitalis 


/  XCRETION  471 

is  much  greatei  in  cardia<  disease  with  dropsical  effusions  than 
in  health.  Caffein,  when  injected  into  the  blood,  affects  the 
pressure  but  little,  it  causes  dilatation  <>t  the  renal  vessels  after 
a  passing  constriction,  and  an  increase  in  the  flow  of  urine  alter  a 
temporary  diminution.  The  vascular  dilatation  is  not  the  chiei 
reason  for  the  diuretic  effect,  lor  the  latter  is  still  obtained  when  the 
vaso-motor  mechanism  lias  been  paralyzed  by  chloral  hydrate,  and 
even  after  the  secretion  of  urine  has  been  stopped  by  the  fall  of 
pressure  consequent  on  section  of  the  spinal  cord.  Caffein,  there- 
fore, acts  directly  on  the  renal  epithelium.  The  action  of  urea, 
potassium  nitrate,  and  the  saline  diuretics  is  probably  also  a  direct 
action  on  the  secreting  structures,  although  some  have  supposed  that 
their  primary  effect  is  to  cause  vaso-dilatation  in  the  kidney,  and  a 
consequent  local  increase  in  the  capillary  pressure.  The  influence 
of  anaesthetics  on  diuresis  is  of  practical  importance.  Ether  generally 
increases,  while  chloroform  generally  diminishes  the  flow  of  urine 
in  dogs.  A.C.E.  mixture  has  a  variable  effect,  but  there  is  always 
a  marked  after-increase.  A  mixture  of  ether  and  chloroform  con- 
stitutes the  ideal  anaesthetic  for  experiments  on  the  kidney,  since 
it  alters  the  diuresis  only  slightly  (Thompson). 

Summary. — Our  knowledge  of  renal  secretion  may  be  thus 
summed  up:  The  water  and  salts  of  the  urine  arc  chiefly  separated 
by  the  glomeruli  ;  the  process  is  not  a  mere  physical  filtration,  but 
a  true  secretion.  Substances  like  sugar,  peptone,  egg-albumin,  and 
hcemoglobin  when  injected  into  the  blood  arc  probably  excreted  mainly 
by  the  glomeruli  ;  and  so  is  the  sugar  of  diabetes.  Urea,  uric  acid, 
and  presumably  the  other  organic  constituents  of  normal  urine, 
with  a  portion  of  the  water  and  salts,  are  excreted  by  the  physio- 
logical activity  of  the  '  rodded  '  epithelium  of  the  renal  tubules.  The 
rate  of  secretion  of  urine  rises  and  falls  with  the  pressure,  and 
still  more  with  the  velocity,  of  the  blood  in  the  renal  vessels.  No 
secretory  nerves  for  the  kidney  have  been  found  ;  the  effects  of  section 
or  stimulation  of  nerves  on  the  secretion  can  all  be  explained  by  the 
changes  produced  in  the  renal  blood-flow.  Some  diuretics  act  by 
increasing  the  blood-flow,  others  directly  on  the  epithelium  of  the 
tubules  or  the  glomeruli. 

Micturition. — The  urine,  like  the  bile,  is  being  constantly 
formed  ;  although  secretion  varies  in  its  rate  from  time  to  time, 
it  never  ceases.  Trickling  along  the  collecting  tubules,  the  urine 
reaches  the  pelvis  of  the  kidney,  from  which  it  is  propelled  along 
the  ureters  by  peristaltic  contractions  of  their  walls,  and  drops 
from  their  valve-like  orifices  into  the  bladder.  When  this 
becomes  distended,  rhythmical  peristaltic  contractions  are  set 
up  in  it,  and  notice  is  given  of  its  condition  by  a  characteristic 
sensation,  which  is  perhaps  aided  by  the  squeezing  of  a  few  drops 
of  urine  past  the  tonically  contracted  circular  fibres  that  form 
a  sphincter  round  the  neck  of  the  bladder,  and  into  the  first  part 
of  the  urethra.  The  desire  to  empty  the  bladder  can  be  resisted 
for  a  time,  as  can  the  desire  to  empty  the  bowel.  If  it  is  yielded 
to,  the  smooth  muscular  fibres  in  the  wall  of  the  viscus  are  thrown 


472  A    WANV  U    "l    PHYSIOLOGY 

into  contraction.  This  is  aided  by  .in  expulsive  efforl  <>t  the 
abdominal  muscles.  The  sphincter  vesicae  is  relaxed  ;  and  the 
urine  is  forced  along  the  urethra,  its  passage  being  facilitated 
by  discontinuous  contractions  of  the  ejaculatoi  urinae  muscle, 
which  also  serve  to  squeeze  the  last  drops  of  urine  from  the 
urethral  canal  at  the  completion  of  the  a<  t. 

Regurgitation  into  the  ureters  is  to  a  great  extent  prevented 
by  their  compression  between  the  mucous  and  muscular  coats 
of  the  bladder,  where  they  run  for  more  than  half  an  inch  before 
opening  at  the  posterior  angle  of  the  trigone.  But  it  has  been 
shown  that  a  certain  amount  of  back  flow  can  take  place.  Small 
bodies  like  diatoms  suspended  in  water  and  pigments  dissolved 
in  it  have  been  found  in  the  pelvis  of  the  kidney,  the  renal 
tubules,  and  even  the  circulation  after  being  injected  into  the 
bladder, 

The  pressure  in  the  bladder  of  a  man  may  be  made  as  high  as 
10  cm.  of  mercury  during  the  act  of  micturition  ;  about  half  this 
amount  is  due  to  the  contraction  ol  the  vesical  walls  alone,  the 
rest  to  the  contraction  of  the  abdominal  muscles.  A  pressure 
of  id  to  26  mm.  ot  mercury  is  required  to  open  the  sphincter  of 
a  rabbit's  bladder  in  life. 

Although  the  whole  performance  seems  to  us  to  be  completely 
voluntary,  there  are  facts  which  show  that  it  is  at  bottom  a 
reflex  series  of  co-ordinated  movements,  that  can  be  started  by 
impulses  passing  to  a  centre  in  the  spinal  cord  from  above  or 
from  below — from  the  brain  or  from  the  bladder.  In  dogs,  with 
the  spinal  cord  divided  at  the  upper  level  of  the  lumbar  region. 
micturition  takes  place  regularly  when  the  bladder  is  full,  and 
can  be  excited  by  such  slight  stimuli  as  sponging  of  the  skin 
around  the  anus  (Goltz).  Here,  of  course,  the  act  is  entirely 
reflex  ;  and  the  centre  is  situated  at  the  level  of  the  fifth  lumbar 
nerves.  The  efferent  nerves  oi  the  bladder,  like  those  of  the 
rectum,  come  partly  from  the  cord  directly  through  the  sacral 
nerves,  and  partly  through  the  lumbar  sympathetic  chain 
(second  to  sixth  ganglia).  The  sacral  fibres  are  connected  with 
nerve  cells  in  the  hypogastric  plexus,  and  the  sympathetic. 
partly  at  least,  in  the  inferior  mesenteric  ganglia.  This  ana- 
tomical coincidence  acquires  interest  in  view  of  the  striking 
physiological  similarity  between  the  processes  of  micturition 
and  d<  la-cation,  a  similarity  which  is  emphasized  by  the  fa<  I 
that  the  latter  is  almost  invariably  accompanied  by  the  former. 
An  important  difference,  however,  is  that  the  will  can  far  more 
readily  set  in  motion  the  machinery  ot  micturition  than  that 
ol  deiaecation  ;  a  man  can  generally  empty  his  bladder  when  he 
like.-,  but  he  cannol  empty  his  bowels  when  he  V 

Sometimes  in  disease,  and  especially  in  disease  of  the  spinal 
cord,  the  mechanism  of  micturition  breaks  down;  the  bladder 


/  XCRE  I  ION  473 

is  no  longer  emptied;  it  remains  distended  with  urine,  which 
dribbles  away  through  the  urethra  as  fast  as  it  escapes  from 
the  ureters.  To  this  condition  the  term  incontinence  of  urine  is 
properly  applied. 

Reflex  emptying  of  the  bladder,  without  an  act  of  will  or 
during  unconsciousness,  is  not  true  incontinence.  The  in- 
voluntary micturition  of  children  during  sleep,  for  example, 
is  a  perfectly  normal  reflex  act,  although  more  easily  excited 
and  less  easily  controlled  than  in  adults.  Section  either  of  both 
nervi  erigentes,  or  of  both  hypogastrics,  is  never  followed  by 
more  than  quite  temporary  disturbance  of  function  of  the  bladder 
in  dogs,  both  male  and  female.  In  a  few  days  the  urine  is 
normally  passed.  In  bitches  the  same  is  true  when  both  pairs 
of  nerves  are  divided.  But  in  male  dogs  true  incontinence  of 
urine  follows  section  of  the  four  nerves,  as  well  as  intense  tenesmus 
due  to  paralysis  of  the  lower  part  of  the  large  intestine. 

II.  Excretion  by  the  Skin. 

Besides  permitting  of  the  trifling  gaseous  interchange  already 
referred  to  (p.  275),  the  skin  plays  an  important  part  in  the 
elimination  of  water  by  the  sweat-glands. 

Sweat  is  a  clear  colourless  liquid  of  low  specific  gravity  (1003 
to  1006),  consisting  chiefly  of  water  with  small  quantities  of 
salts,  neutral  fats,  volatile  fatty  acids,  and  the  merest  traces 
of  proteins  and  urea.  It  is  acid  to  litmus  except  in  profuse 
sweating,  when  it  may  become  neutral  or  even  alkaline.  It  is 
secreted  by  simple  gland- tubes,  which  form  coils  lined  with  a 
single  layer  of  columnar  epithelium,  in  the  subcutaneous  tissue, 
with  long  ducts  running  up  to  the  surface  through  the  true  skin 
and  epidermis.  Unless  collected  from  the  parts  of  the  skin  on 
which  there  are  no  hairs,  such  as  the  palm,  it  is  apt  to  be  mixed 
with  sebum,  a  secretion  formed  by  the  breaking  down  of  the 
cells  of  the  sebaceous  glands,  which  open  into  the  hair  follicles, 
and  consisting  chiefly  of  glycerin  and  cholesterin  fats,  soaps,  and 
salts.  Sebum  is  probably  of  considerable  importance  for  main- 
taining the  normal  condition  of  the  hair  and  skin. 

Although  it  is  only  occasionally  that  sweat  collects  in  visible 
amount  on  the  skin,  water  is  always  being  given  off  in  the  form 
of  vapour.  This  invisible  perspiration  leaves  behind  it  on  the 
skin,  or  in  the  glands,  the  whole  of  the  non-volatile  constituents, 
which  may  be  to  some  extent  reabsorbed  ;  and  since  even  the 
visible  perspiration  is  in  large  part  evapoiated  from  the  very 
mouths  of  the  glands  in  which  it  is  formed,  the  sweat  can  hardly 
be  considered  a  vehicle  of  solid  excretion,  even  to  the  small 
extent  indicated  by  its  chemical  composition. 

The  total  quantity  of  water  excreted  by  the  skin,  and  the 


474  A  MANUAL  OF  PHYSIOLOGY 

relative  proportions  of  visible  and  invisible  perspiration,  vary 
greatly.  A  drj  and  warm  atmosphere  increases,  and  a  moisl 
and  cold  atmosphere  diminishes  the  total,  and,  within  limits, 
the  invisible  perspiration.  Visible  sweat — given  the  condition 
of  rapid  heat-production  in  the  body  as  in  muscular  labour — 
is  more  readily  deposited  on  freely  exposed  surfaces  when  the 
air  is  moist  than  when  it  is  dry.  The  air  in  contact  with  surfaces 
covered  by  clothing  is  never  far  from  being  saturated  with 
watery  vapour.  Here,  accordingly,  a  comparatively  slighl 
increase  in  the  activity  of  the  sweat-glands  suffices  to  produce 
more  water  than  can  be  at  once  evaporated  ;  and  the  excess 
appears  as  sweat  on  the  skin,  to  be  absorbed  by  the  clothing 
without  evaporation,  or  to  be  evaporated  slowly,  as  the  pressure 
of  the  aqueous  vapour  gradually  diminishes  in  consequence  of 
diffusion.  The  power  of  imbibition  (p.  398)  of  water  by  the 
various  layers  of  the  skin  diminishes  as  we  pass  outwrards,  and 
the  cells  of  the  epidermis  are  characterized  by  the  rapidity  with 
which  they  return  from  a  condition  of  excessive  imbibition  to 
their  normal  state.  This  constitutes  a  protective  mechanism 
against  excessive  loss  of  water.  When  the  skin  is  thoroughly 
moistened  its  degree  of  imbibition  is  three  times  the 
normal. 

The  quantity  of  sweat  given  off  by  a  man  in  twenty-four  hours 
varies  so  much  that  it  would  not  be  profitable  to  quote  here  the 
numerical  results  obtained  under  different  conditions  of  tem- 
perature and  humidity  of  the  air  (but  see  p.  588).  It  is  enough  to 
say  that  the  excretion  of  water  from  the  skin  is  of  the  same  order 
of  magnitude  as  that  from  the  kidneys  :  a  man  loses  upon  the 
whole  as  much  water  in  sweat  as  in  urine.  But  it  is  to  be  care- 
fully noted  that  these  two  channels  of  outflow  are  complementary 
to  each  other  ;  when  the  loss  of  water  by  the  skin  is  increased,  the 
loss  by  the  kidneys  is  diminished,  and  vice  versa. 

The  Influence  of  Nerves  on  the  Secretion  of  Sweat. — The 
sweat-glands  are  governed  directly  by  the  nervous  system  ; 
and  though  an  actively  perspiring  skin  is,  in  health,  a  flushed 
skin,  the  vascular  dilatation  is  a  condition,  and  not  the  chief 
cause  of  the  secretion.  Stimulation  of  the  peripheral  end  of  the 
sciatic  nerve  causes  a  copious  secretion  of  sweat  on  the  pad  and 
toes  of  the  corresponding  foot  of  a  young  cat,  and  this  although 
the  vessels  are  generally  constricted  by  excitation  of  the  vaso- 
motor nerves.  Not  only  so,  but  when  the  circulation  in  the  foot 
is  entirely  cut  off  by  compression  of  the  crural  artery  or  by 
amputation  of  the  limb,  stimulation  of  the  sciatic  still  calls  forth 
some  secretion.  As  in  the  case  of  the  salivary  glands,  injection 
hi  atropine  abolishes  the  secretory  power  of  the  sciatic,  while 
leaving   its  vaso-motor    influence    untouched  ;  and  pilocarpine 


!  \(  RETION  47S 

increases  the  flow  of  sweal  by  direcl  stimulation  of  the  endings 
oi  the  secretory  nerves  in  the  glands. 

That  the  sweating  caused  by  a  high  external  temperature  is 
normally  brought  about  by  nervous  influence,  and  not  by  direct 
action  on  the  secreting  cells,  is  shown  by  the  following  experi- 
ments. One  sciatic  nerve  is  divided  in  a  cat,  and  the  animal 
put  into  a  hot-air  chamber.  No  sweat  appears  on  the  foot 
whose  nerve  has  been  cut,  but  the  other  feet  are  bathed  in 
perspiration.  Similarly,  a  venous  condition  of  the  blood  (in 
asphyxia)  causes  sweating  in  the  feet  whose  nerves  have  not 
been  divided,  but  none  in  the  other  foot  ;  and  stimulation  of  the 
central  end  of  the  cut  sciatic  has  the  same  effect.  All  this  points 
to  the  existence  of  a  reflex  mechanism  ;  and  it  is  certain  that 
asphyxia  acts  by  direct  stimulation  of  the  centre  or  centres. 
The  vaso-motor  centre  is  at  the  same  time  stimulated,  and  the 
bloodvessels  constricted,  as  in  the  cold  sweat  of  the  death 
agony.  Fear  may  also  cause  a  cold  sweat,  impulses  passing 
from  the  cerebral  cortex  to  the  vaso-motor  and  sweat  centres. 

It  is  probable  that  a  general  sweat-centre  exists  in  the  medulla 
oblongata,  but  its  position  has  not  been  exactly  determined  nor  even 
its  existence  definitely  proved.  On  the  other  hand,  it  is  known  that 
in  the  cat  there  are  at  least  two  spinal  centres,  one  for  the  fore-limbs 
in  the  lower  part  of  the  cervical  cord,  and  another  for  the  hind-limbs 
where  the  dorsal  portion  of  the  cord  passes  into  the  lumbar.  That 
this  latter  centre  does  not  exist  or  is  comparatively  inactive  in  man 
is  indicated  by  the  following  case:  A  man  fell  from  a  window  and 
fractured  his  backbone  at  the  fifth  dorsal  vertebra.  The  lower  half 
of  the  body  was  paralyzed  for  a  time,  but  recovered.  Ultimately, 
however,  the  paralysis  returned  ;  and  shortly  before  his  death 
(twentv-one  vears  after  the  accident)  it  was  noticed  that  a  copious 
perspiration  broke  out  several  times  on  the  upper  part  of  the  body, 
while  the  lower  portion  remained  perfectly  dry.  If  there  is  any 
functional  spinal  centre  in  man,  it  appears  to  lie  above  the  fifth  spinal 
segment.  For  it  was  seen  in  a  professional  diver  who  fractured  his 
neck  at  that  level,  and  lived  three  months  after  the  accident,  that 
sweat  frequently  appeared  on  parts  of  the  body  above  the  lesion,  but 
never  below.  At  the  autopsy  the  whole  thickness  of  the  cord, 
except  perhaps  a  small  portion  of  the  anterior  columns,  was  found 
destroyed.  Of  course,  it  may  be  that  in  man  the  spinal  centres, 
although  normally  active,  lose  their  function  for  a  long  time  after 
such  severe  injuries  to  the  cord  owing  to  the  condition  known  as 
shock. 

The  secretory  fibres  for  the  fore-limbs  (in  the  cat)  leave  the  cord 
in  the  anterior  roots  of  the  fourth  to  ninth  thoracic  nerves.  They 
pass  by  white  rami  communicantes  to  the  sympathetic  chain,  in  which 
they  reach  the  ganglion  stellatum,  where  they  are  all  connected  with 
nerve-cells.  Then,  as  non-medullated  fibres,  they  gain  the  brachial 
plexus  by  the  grey  rami,  and  run  in  the  median  and  ulnar  to  the 
pads  of  the  feet.  The  fibres  for  the  hind-limbs  leave  the  cord  in  the 
anterior  roots  of  the  twelfth  thoracic  to  the  third  or  fourth  lumbar 
nerves  ;  pass  by  the  white  rami  to  the  sympathetic  ganglia,  in  which 


476  A    MANUAL  OF  PHYSIOLOGY 

they  form  connections  with  ganglion  cells  ;  then,  as  non  medullated 
fibres,  run  along  the  grey  rami,  and  are  distributed  to  the  foot  in  the 
sciatic. 

The  evidence  of  the  direct  secretory  action  of  nerves  on  the 
sweat-glands  is  singularly  striking  and  complete,  in  contrast  to 
what  we  know  of  the  kidney.  In  the  latter,  blood-flow  is  the  im- 
portant factor  ;  increased  blood-flow  entails  increased  secretion. 
In  the  former,  the  nervous  impulse  to  secretion  is  the  spring 
which  sets  the  machinery  in  motion  ;  vascular  dilatation  aids 
secretion,  but  does  not  generally  cause  it.  It  would,  how- 
ever, be  easy  to  lay  too  much  stress  on  this  distinction,  for  in 
the  horse  the  mere  dilatation  of  the  bloodvessels  of  the  head 
after  section  of  the  cervical  sympathetic  has  been  found  to  be 
accompanied  by  increased  secretion  of  sweat,  and  urinary 
secretion  can  certainly  be  affected  by  the  direct  action  of  various 
substances  on  the  secretory  mechanism,  independently  of 
vascular  changes.  But  the  broad  difference  stands  out  clearly 
enough,  and  the  reason  of  it  lies  in  the  essentially  different 
purpose  of  the  two  secretions.  The  water  of  the  urine  is  in  the 
main  a  vehicle  for  the  removal  of  its  solids  ;  the  solids  of  the 
sweat  are  accidental  impurities,  so  to  speak,  in  the  water.  The 
kidney  eliminates  substances  which  it  is  vital  to  the  organism 
to  get  rid  of  ;  the  sweat-glands  pour  out  water,  not  because  it 
is  in  itself  hurtful,  not  because  it  cannot  pass  out  by  other 
channels,  but  because  the  evaporation  of  water  is  one  of  the  most 
important  means  by  which  the  temperature  of  the  body  is  con- 
trolled. In  short,  urine  is  a  true  excretion,  sweat  a  heat- 
regulating  secretion.  No  hurtful  effects  are  produced  when 
elimination  by  the  skin  is  entirely  prevented  by  varnishing  it, 
provided  that  the  increased  loss  of  heat  is  compensated.  A 
rabbit  with  a  varnished  skin  dies  of  cold,  as  a  rabbit  with  a 
closely-clipped  or  shaven  skin  does  ;  suppression  of  the  secretory 
function  of  the  skin  has  nothing  to  do  with  death  in  the  first 
case  any  more  than  in  the  second  (p.  276). 


PRACTICAL  EXERCISES  ON  CHAPTER  VI. 

Urine. 

For  most  of  the  experiments  human  urine  is  employed — in  the 
quantitative  work  the  mixed  urine  of  the  twentv-four  hours.  I  h-ine 
may  also  be  obtained  from  animals.  In  rabbits  pressure  on  the 
abdomen  will  usually  empty  the  bladder.  Dogs  may  be  taught  to 
micturate  at  a  set  time  or  place,  or  kept  in  a  cage  arranged  for  the 
collection  of  urine.     Or  a  catheter  may  be  used  (p.  609). 


PR  ICTIC  It    EXERCISl  S 


477 


i.  Specific  Gravity.     Pour  the   mine   into  a  glass  cylinder,   and 
remove  troth,  if  necessary,  with  filter-paper.     Place  a  urinometer 

(Fig.  1771  in  the  urine,  and  see  thai  it  docs  not  come  in  contact  with 
tlic  sidejof  tin-  vessel.     Read  ofl  on  the  graduated  stem  the  division 

which  corresponds  with  the  bottom  oJ  the  meniscus.     This  gives  the 
specific  gravity. 

2.  Reaction,  (a)  Test  with  litmus-paper.  Generally  the  litmus 
is  reddened,  but  occasionally  in  health  the  urine  first  passed  in  the 
morning  is  alkaline.  Sometimes  urine  has  an  amphicroi*  reaction 
i.e..  affects  both  red  and  blue  litmus-paper.  This  is  the  case  when 
there  is  such  a  relation  between  the  bases  and  acids  that  both  acid 
and  '  neutral  '  (dibasic)  phosphates  are  present  in  certain  propor- 
tions. The  acid  phosphate  reddens  blue  litmus,  and  the  'neutral' 
phosphate  turns  red  litmus  blue. 

(b)   Titratable  Acidity. — To  ij  c.c.  of  urine  add  15  to  20  grammes 
of  powdered   potassium  oxalate,   and   one  or  two  drops  of  a   1   per 
cent,  solution  of  phenolphthalein.      Shake  the  mixture  rapidly  for 
a  minute  or  two,  and  then  titrate  with  decinor- 
mal  sodium  hydroxide  at  once  (while  still  cold 
from  the  solution  of  the  oxalate)  till  a  faint  pink 
colour  remains  permanent  on  shaking.      The 
potassium  oxalate  is  added  to  counteract  the 
tendency  of   the    calcium  present  in  urine  to 
form   basic  phosphates,  which   would  be  pre- 
cipitated,  and  the  acidity  of  the  urine  thus 
increased  (Folin). 

3.  Chlorides — (a)  Qualitative  Test. — Add  a 
drop  of  nitric  acid  and  a  drop  or  two  of  silver 
nitrate  solution.  The  nitric  acid  is  added  to 
prevent  precipitation  of  silver  phosphate.  A 
white  precipitate  soluble  in  ammonia  shows  the 
presence  of  chlorides.  The  precipitate  appears 
to  be  incompletely  soluble  in  ammonia,  since 
the  ammonia  brings  down  a  small  precipitate 
of  earthy  phosphates. 

(b)  Quantitative  Estimation. — The  quantita- 
tive estimation  of  the  chlorine  in  urine  with- 
out previous  evaporation  and  incineration  is 
best  made  by  one  of  the  modifications  of 
Volhard's  method.  It  depends  upon  the  com- 
plete precipitation  of  the  chlorine  combined  with  the  alkaline 
metals,  and  also  of  sulphocyanic  acid,  by  silver  from  a  solution 
containing  nitric  acid  in  excess  ;  and  avoids  the  error  introduced 
into  simpler  methods,  like  Mohr's,  by  the  union  of  some  of  the 
silver  with  other  substances  than  chlorine.  A  given  quantity 
of  a  standard  solution  of  silver  nitrate  (more  than  sufficient 
to  combine  with  all  the  chlorine)  is  added  to  a  given  volume  of 
urine.  The  excess  of  silver  is  now  estimated  by  means  of  a  standard 
solution  of  ammonium  sulphocyanide,  which  precipitates  the  silver 
as  insoluble  silver  sulphocyanide.  A  fairly  strong  solution  of  the 
double  sulphate  of  iron  and  ammonium  (known  as  iron-ammonia- 
alum)  is  taken  as  the  indicator,  since  a  ferric  salt  does  not  give 
the  usual  red  colour  with  a  sulphocyanide  so  long  as  any  silver  in 
the  solution  is  uncombined  with  sulphocyanic  acid.  The  iron- 
ammonia-alum  forms  the  red  salt,  ferric  sulphocyanide,  when  any 
excess  of  ammonium  sulphocyanide  is  present,  but  it  does  not 
react  with  silver  sulphocyanide. 


478  A   MANUAL  OF  PHYSIOLOG\ 

The  standard  solution  of  silver  nitrate  can  be  made  by  dissolving 
20/063  grammes  oi  pure  fused  silver  nitrate;  in  distilled  water  and 
making  up  the  volume  of  the  solution  accurately  to  1  litre.  The 
solution  should  be  kepi  in  the  dark.  One  c.c.  "t  this  solution  corre- 
sponds to  o oi  gramme  NaCl  or  o'ooOoj  gramme  <  I 

rii<-  standard  solution  of  ammonium  sulphocyanide  is  prepared 
as  follows:  Dissolve  13  grammes  pure  ammonium  sulphocyanide 
(NHjCNS)  in  a  litre  of  distilled  water.  Measure  with  a  pipette  into 
a  beaker  20  c.c.  of  the  standard  silver  nitrate  solution,  and  add 
5  c.c.  of  the  iron  alum  solution  and  4  c.c.  of  pure  mine  acid  (specific 
gravity  1  -■  1  I'  ill  a  burette  with  the  sulphocyanide  solution,  and  run 
it  into  the  silver  nil  rate  solution  until  a  fainl  permanent  red  tinge  is 
obtained.  Note  the  number  of  c.c.  of  the  sulphocyanide  solution 
required,  and  then  dilute  the  solution  till  _•  c.c.  oi  the  sulphcx  yanide 
solution  correspond  exactly  to  1  c.c.  of  the  silver  solution,  so  as  just 
to  allow  of  the  end  reaction  with  the  iron  solution  being  seen,  and 
no  more. 

I  0  1  any  oui  the  method,  put  10  c.c.  of  urine,  which  must  be  free 
from  albumin,  in  a  stoppered  flask,  with  a  mark  corresponding  to 
100  c.c,  or  a  graduated  cylinder.  Add  50  c.c.  of  water.  4  c.c.  of  pure 
nitric  acid  (specific  gravity  vi),  and  15  c.c.  of  the  standard  silver 
solution  ;  shake  well,  till  with  water  to  the  mark,  and  again  shake. 
After  the  precipitate  has  settled,  filter  it  off.  Take  50  c.c.  of  the 
filtrate,  add  5  c.c.  of  the  solution  of  iron-ammonia-alum,  and  run 
in  from  a  burette  the  standard  solution  of  ammonium  sulphocyanide 
until  a  weak  but  permanent  red  coloration  appears. 

Suppose  x  c.c.  of  the  sulphocyanide  solution  arc  required,  then 
the  chlorine  in  10  c.c.  of  urine  evidently  corresponds  to  (15—  x), 
001  gramme  NaCl. 

4.  Phosphates — (1)  Qualitative  Tests. — (a)  Render  the  urine  alka- 
line with  ammonia.  A  precipitate  of  earthy  phosphates  (calcium 
and  magnesium  phosphates)  falls  down.  Filter.  The  nitrate  con- 
tains the  alkaline  phosphates.  To  the  nitrate  add  magnesia  mixture.* 
The  alkaline  phosphates  (sodium,  potassium,  or  ammonium  phos- 
phates) arc  precipitated  as  ammonio-magnesic  or  triple  phosphate. 
(b)  Add  to  urine  half  its  volume  of  nitric  acid  and  a  little  molybdate 
of  ammonium,  and  heat.  A  yellow  precipitate  of  ammonium  phos- 
pho-molybdate  shows  that  phosphates  are  present.  This  test  is 
given  both  by  alkaline  and  earthy  phosphates. 

(2)  Quantitative  Estimation.  The  quantitative  estimation  of  phos- 
phoric acid  in  urine  is  best  done  volume! ricallv.  by  titration  with  a 
standard  solution  of  uranium  nitrate,  using  ferrocyanide  of  potassium 
as  the  indicator.  Uranium  nitrate  gives  with  phosphates,  in  a  solu- 
tion containing  free  acetic  acid,  a  precipitate  with  a  constant  pro- 
portion of  phosphoric  acid.  As  soon  as  there  is  more  uranium  in 
the  solution  than  is  required  to  combine  with  all  the  phosphoric  acid, 
a  brown  colour  is  given  with  potassium  ferrocyanide.  due  to  the 
formation  of  uranium  ferrocyanide.  In  carrying  out  the  method. 
5  c.c.  of  a  mixture  of  acetic  acid  and  sodium  acetate  (there  are 
10  grammes  of  sodium  acetate  and  10  grammes  of  glacial  acetic  acid 
in  100  c.c.  of  the  mixture)  are  added  to  50  c.c.  of  urine,  which  is 
then  heated  in  a  beaker  on  the  water-bath  almost  to  boiling.  The 
standard  uranium  solution  (which  contains  355  grammes  of  uranium 
nitrate  in  the  litre,  and  1  c.c.  of  which  corresponds  to  0-005  gramme 

*  Magnesium  chloride  1 10  grammes,  ammonium  chloride  140  grammes, 
ammonia  (specific  gravity  O'qi)  250  c.c,  and  water  1,750  c.c. 


PRACTH    U    I  XERCIS1  S  479 

I'  (  >  1  is  now  nm  in  from  .1  burette,  until  ;i  drop  of  the  urine  gives, 
with  a  drop  of  potassium  ferrocyanide  solution,  on  a  porcelain  slab, 
,1  brown  colour.  Uranium  acetate  may  be  used  instead  ol  uranium 
nitrate,  but  the  latter  keeps  best.  When  uranium  acetate  is  employed 
it  is  not  necessary  to  add  the  sodium  a<  etate  mixture 

>  Sulphates     (1)  Qualitative  Test. — Add  to  mine  a  drop  of  hydro- 
chloric and  and  then  a  few  drops  of  barium  chloride.     A  white  pre 
1  ipitate  comes  down,  showing   that  inorganic  sulphates  are  present. 
I  h«-  hydrochloric  acid  prevents  precipitation  of  the  phosphates. 

<)  Quantitative  Estimation  of  the  Sulphates  {Inorganic  and 
Ethereal).  Add  to  50  c.c.  of  albumin-free  urine  in  a  200-c.c. 
Erlenmeyer  flask  5  c.c.  of  a  1  per  cent,  potassium  chlorate  solution 
and  5  c.c.  of  strong  hydrochloric  acid,  and  boil  the  mixture  to  break 
up  the  ethereal  sulphates.  In  five  to  ten  minutes  it  becomes  per- 
fectly colourless.  While  it  continues  to  boil,  25  c.c.  of  a  to  per 
cent,  solution  of  barium  chloride  arc  added  by  drops,  at  such  a 
rate  that  it  takes  about  five  minutes  to  add  this  quantity.  The 
flask  is  now  put  on  the  water-bath  for  one-half  to  one  hour,  till  the 
precipitate  has  settled.  Then  filter  through  an  ash-free  filter. 
Wash  the  precipitate  on  the  filter  for  half  an  hour  with  hot  water. 
During  the  first  twenty  minutes  of  the  washing,  at  intervals  of  a 
few  minutes,  substitute  hot  5  per  cent,  ammonium  chloride  solution 
for  the  water.  At  the  end  of  the  half-hour's  washing,  as  soon  as 
the  water  has  run  through  the  filter,  fold  up  the  latter  and  press  it 
gently  between  dry  filter-papers  to  remove  a  portion  of  the  water. 
Then  place  the  filter  in  a  weighed  porcelain  crucible.  Pour  into 
the  crucible  3  or  4  c.c.  of  alcohol,  and  ignite  it,  to  dry  and  partiallv 
burn  the  filter-paper.  Then  incinerate  till  all  the  carbon  is  burned 
off,  cool,  and  weigh.  From  the  wreight  of  the  barium  sulphate, 
the  sulphuric  acid  in  50  c.c.  of  urine  is  easily  calculated  (S04  in 
1  gramme  of  barium  sulphate,  0-41187  gramme)  (Folin). 

(3)  Quantitative  Estimation  of  the  Sulphuric  A  cid  united  with  A  romatic 
Bodies  (Aromatic  or  Ethereal  Sulphates) . — Put  200  c.c.  of  the  same 
urine  as  used  in  (2)  into  a  beaker.  Add  100  c.c.  of  10  per  cent, 
barium  chloride  solution  in  the  cold.  Let  stand  for  twenty-four 
hours.  Then  decant  off  the  clear  supernatant  liquid,  and  filter  it. 
Measure  150  c.c.  of  the  clear  filtrate,  corresponding  to  100  c.c.  of 
the  urine,  into  a40o-c.c.  Erlenmeyer  flask.  Add  10  or  15  c.c.  of  con- 
centrated hydrochloric  acid,  and  10  to  15  c.c.  of  4  per  cent,  potassium 
chlorate.  Heat  the  mixture  to  boiling,  and  proceed  as  in  (2). 
From  the  weight  of  the  barium  sulphate,  the  ethereal  sulphuric 
acid  in  100  c.c.  of  urine  can  be  calculated.  Deducting  this  from 
the  quantity  per  100  c.c.  of  urine  obtained  in  (2),  we  get  the^amount 
of  inorganic  sulphuric  acid  per  100  c.c.  (Folin). 

6.  Indoxyl  (contained  in  the  urine  as  indican,  the  potassium  salt 
of  indoxyl-sulphuric  acid)  can  be  oxidized  into  indigo,  and  so 
detected  and  estimated. 

A  Qualitative  test  is  the  following  :  Ten  c.c.  of  horse's  urine  is 
mixed  with  10  c.c.  of  Obermayer's  reagent  (pure  concentrated 
hydrochloric  acid  containing  2  to  4  parts  of  ferric  chloride  in  1,000), 
and  shaken  well  for  a  minute  or  two  ;  a  bluish  colour  appears  if,  as 
is  generally  the  case,  indoxyl  is  present,  indigo  (CieH10N2O2)  being 
formed  by  the  oxidizing  action  of  the  ferric  chloride  on  the  indoxyl, 
the  compound  of  which  wdth  sulphuric  acid  has  been  broken  up  by 
the  hydrochloric  acid.  The  urine  must  be  free  from  albumin .  In  per- 
forming the  test  in  human  urine,  which  contains  a  smaller  quantity 


$o  I   MANUAL  or  PHYSIOLOGY 

lit  t  lie  indigo-forming  substance,  the  faint  blue  Liquid  should  be  shaken 
iij)  wii.li  .1  few  drops  oi  chloroform.  The  latter  takes  up  the  colour. 
which  is  thus  rendered  more  evident,  [f  there  is  difficulty  in  obtain- 
ing the  reaction,  the  urine  may  first  be  decolourized  by  precipitatin 
with  acetate  of  Lead,  avoiding'excess.  The  pre<  irritate  is  altered  off, 
and  the  test  then  applied  to  the  clear  filtrate.  The  skatoxyl  of  urine 
can  also  be  oxidized  to  indigo,  bul  it  is  present  in  Ear  smaller  amount. 
The  average  quantity  of  indigo  obtained  from  a  Litre  ol  horse's  urine 
is  about  [50  milligrammes;  from  a  Litre  of  human  mine.  no1  .1 
1  went  ieth  of  that  amount . 

For  comparative  quantitative  determinations  the  method  <>f 
Iolin  may  be  used.  ( )nc-hun(lre(lth  of  the  t  wenty-four  hours'  urine 
is  taken.  In  this  the  indigo  is  developed  by  the  addition  of  an  equal 
volume  of  Obermayer's  reagent  (p.  470-.  and  1  he  indigo-blue  dissolved 
by  means  of  5  c.c.  of  chloroform.  The  chloroform  solution  is  then 
compared  colorimetrically  with  Fehling's  solution.  This  can  be 
done  by  putting  the  indigo  solution  and  5  c.c.  of  the  Fehling's 
solution  respectively  into  small  test-tubes  of  equal  calibre,  and 
comparing  the  depth  of  tint.  If  the  Fehling's  solution  is  stronger 
than  the  indigo  solution,  run  water  into  the  former  from  a  pipette. 
graduated  in  tenths  of  a  c.c,  shaking  up  after  each  addition,  till 
equality  of  tint  has  been  reached.  If  the  indigo  solution  has  a 
stronger  blue  colour  than  the  Fehling's  solution,  dilute  a  measured 
amount  of  it  first  of  all  with  such  a  quantity  of  chloroform  (say  an 
equal  volume)  as  will  make  its  tint  distinctly  weaker  than  that  of  the 
Fehling's  solution.  Then  dilute  the  Fehling's  solution  with  water,  as 
before,  till  the  tint  is  the  same.  From  the  amount  of  dilution  the 
quantity  of  indigo  can  be  expressed  in  arbitrary  units,  taking  Fehling's 
solution  as  100.     Thus,  if  1  c.c.  of  water  must  be  added  to  the  5  c.c.  ot 

Fehling's  solution,  the  indican  can  be  expressed  as  _        =  **      =83. 

5 
The  comparison  can  be  made  more  accurately  by  a  colorimeter,  if 
one    is    available.     To    determine   the    absolute    amount    of    indigo 
obtained,   comparison  must  be  made   with  a   standard   solution  of 
indigo. 

7.  Urea — (1)  Decomposition  of  Urea. — Heated  dry  in  a  test-tube, 
it  gives  off  ammonia.  The  residue  contains  biuret,  which,  when 
dissolved  in  water,  gives  a  rose  colour  with  a  trace  of  cupric  sulphate 
and  excess  of  sodium  hydroxide  (or  of  the  hydroxides  of  certain  other 
metals  of  the  alkalies  and  alkaline  earths,  p.  7).  Some  proteins — 
peptones  and  albumoses — in  the  presence  of  the  same  reagents,  give 
a  similar  colour,  the  so-called  biuret  reaction. 

(2)  Quantitative  Estimation — The  Hypobromite  Method. — -The  urea 
is  split  up  by  sodium  hypobromite  (p.  440),  and  the  carbon  dioxide 
being  absorbed  by  the  excess  of  sodium  hydroxide  used  in  preparing 
the  hypobromite,  the  nitrogen  is  collected  over  water  in  an  inverted 
burette.  It  is  easy  to  calculate  the  weight  of  urea  corresponding 
to  a  given  volume  of  nitrogen  measured  at  a  given  temperature  and 
pressure.  The  nitrogen  of  urea  is  $g,  or  ,7.  of  the  whole  molecular 
weight.  Now,  t  c.c.  of  N  weighs,  at  760  millimetres  of  mercury 
and  o°  C,  o-ooi25  gramme.  Therefore,  1  c.c.  of  N  corresponds  to 
o'ooi  25  x  y  =000268  gramme  urea.  Suppose,  now,  that  1  c.c.  of 
urine  was  found  to  yield  10  c.c.  of  N  measured  at  170  C.  and  750  milli- 
metres barometric  pressure.  Since  a  gas  expands  ..}..  part  of  its 
volume  at  o°  for  every  degree  above  o°,  we  must  correct  the  apparent 


PR  ICTIC  \L   EXERi  ISES 


481 


volume  of  nitrogen  l>v  multiplying  by  H,7,;;.  Since  the  volume  of 
a  gas  is  inversely  proportional  to  the  pressure,  we  must  further 
multiply  by  f,':,'!.  Thus  we  get  i<>  x  K7;;  x  ;,.;;;  •'.!'..',•,"'  =  >>-j(>  c.c. 
;is  the  volume  of  the  nitrogen  reduced  to  o°  C.  and  760  millimetres  of 
mercury.  Multiplying  this  by  o'oo268,  we  get  00249  gramme  urea 
for  1  c.c.  urine,  which  for  a  daily  yield  of  1,200  c.c.  would  correspond 
to  29'SS  grammes  urea. 

Asa.  matter  of  fact,  however,  it.  has  been  found  that  there  is  always 
a  deficiency  of  nitrogen  that  is,  a 
given  quantity  of  urea  yields  less 
than  the  estimated  amount  of  gas. 
A  gramme  of  urea  in  urine,  inslc.nl 
of  giving  off  373  c.c.  of  nitrogen, 
gives  only  354  c.c.  at  0°  C.  and  ~i»> 
millimetres  pressure.  We  must 
therefore  take  1  c.c.  of  N  as  corre- 
sponding to  0*00282  gramme,  in- 
stead of  o-oo268  gramme  urea.  But 
it  is  affectation  to  make  this  correc- 
tion if,  as  is  constantly  done  in 
hospitals,  the  temperature  is  not 
taken  into  account. 

A  convenient  apparatus  is  shown 
in  Fig.  178.  In  B,  place  10  c.c. 
of  a  solution  made  by  adding  bro- 
mine to  ten  times  its  volume  of 
40  per  cent,  sodium  hydroxide  solu- 
tion. Mix  5  c.c.  of  urine  with 
5  c.c.  of  water.  Put  5  c.c.  of  the 
mixture  into  the  thimble  A,  which 
is  then  set  in  the  small  bottle  B. 
The  cork  is  now  carefully  fixed  in 
B,  and  the  tube  F  being  open,  the 
level  of  the  water  in  the  burette  is 
read  off.  The  pinchcock  having 
been  closed,  the  bottle  B  is  now 
tilted  so  that  the  urine  in  the 
thimble  is  gradually  mixed  with  the 
hypobromite  solution,  and  the  nitro- 
gen given  off  is  added  to  the  air  in 
the  burette  and  its  connections. 
The  level  of  the  water  in  the  burette 
is  therefore  depressed.  When  gas 
ceases  to  be  given  off,  and  a  short 
time  has  been  allowed  for  the  whole 
to  cool,  the  tube  is  raised  till  the 
level  of  the  water  is  once  more  the  same  inside  and  out.  The 
level  is  again  read  off  ;  the  difference  of  the  two  readings  gives 
the  volume  of  nitrogen  at  the  temperature  of  the  air  and  the 
barometric  pressure.  In  order  that  the  temperature  of  the  water 
may  be  the  same  as  that  of  the  air,  the  cylinder  should  be  filled  a 
considerable  time  before  the  observations  are  begun. 

For  clinical  purposes  sufficiently  accurate  results  may  be  very 
easily  obtained  with  the  so-called  ureometer  of  Doremus  (Fig.  179). 
A  little  urine  is  poured  into  the  side-tube  A,  the  stopcock  C  being 
closed.     The  stopcock  is  then  opened  for  an  instant,  so  as  to  fill 

31 


Fig.    178. — Hypobromite    Method 
of  estimating  urea. 

A,  glass  thimble ;  B,  bottle, 
through  the  rubber  cork  of  which 
pass  two  short  glass  tubes,  one  con- 
nected by  the  rubber  tube  C  with 
a  burette  D,  and  the  other  armed 
with  a  short  piece  of  rubber  tube  F. 
F  is  provided  with  a  pinchcock. 
The  burette  is  supported  on  a  stand, 
and  immersed  in  water  contained  in 
the  glass  cylinder  E. 


■p- 


A    MANUAL  OF  PHYSIOLOGY 


its  bore,  and  then  closed  again.  Any  urine  which  lias  passed  into 
the  tube  B  is  washed  out  with  water,  and  B  is  then  Idled  with 
hypobromite  solution.  A  is  now  filled  up  with  urine  to  the  top  of 
tin-  graduation.     By  opening  the  stopcock,   i  c.c.  ol  urine  (or  Less 

if  the  urine  is  concentrated)  is  permitted  to  pas-,  into  B  and  t<>  mix 
with  tin-  hypobromite  solution.  The  nitrogen  collects  in  B.  and 
when  it  has  ceased  to  come  off,  the  menis<  us  oi  the  liquid  is  read 
off.  The  corresponding  degree  on  tin-  scale  gives  tie-  amount  of 
urea  in  grammes  contained  in  the  quantity  of  urine  employed. 

8.  Estimation  of  the  Total  Nitrogen.  It  is  sometimes  more  im- 
portant to  determine  the  total  nitrogen  oi  the  urine  than  tie-  urea 
alone  ;  and  this  is  conveniently  done  by  Kjeldahl's  method  (or  some 
modification  of  it),  which  can  also  be  applied  to  the  estimation  of  the 
nitrogen  in  the  faeces,  or  in  any  of  the  solids  or  liquids  of  the  body. 
It  depends  on  the  oxidation  of  the  nitrogenous  matter  (or.  rather, 
in  the  case  of  urine,  mainly  its  hydrolysis)  in  such  a  way  that  the 
nitrogen  is  all  represented  as  ammonia.  The  ammonia  is  then 
distilled  over,  collected  and  estimated,  and  from  its  amount  the 
nitrogen  is  easily  calculated.  In  urine  the 
method  can  be  carried  out  by  adding  to  a 
measured  quantity  of  it  (sav  5  c.c.)  four  times 
its  volume  of  strong  sulphuric  acid,  and  boiling 
in  a  long-necked  flask  (capacity  200  c.c).  after 
the  addition  of  a  globule  of  mercury  (about 
O"  1  c.c).  which  hastens  oxidatii  >n  and  i  >l>\ 
bumping.  A  part  of  the  mercuric  sulphate 
formed  remains  in  solution  ;  the  rest  forms  a 
crystalline  deposit.  The  heating  should  con- 
tinue for  half  an  hour,  or  until  the  liquid  is 
decolourized.  It  should  be  kept  gently  boiling. 
This  completes  the  process  of  oxidation  ;  and 
the  next  step  is  to  liberate  the  ammonia 
from  the  substances  with  which  it  is  united 
in  the  solution,  and  to  distil  it  over.  Dilute 
the  liquid  with  water,  after  cooling,  up  to  about 
150  c.c,  and  pour  into  a  larger  long-necked 
flask.  Add  enough  of  a  solution  of  sodium 
hydroxide  (specific  gravity  about  1*25)  to  render  the  liquid  alkaline, 
avoiding  excess,  as  this  favours  bumping.  The  proper  quantity  can  be 
found  by  determining  beforehand  how  much  of  the  alkali  is  needed  to 
neutralize  the  acid  used  for  oxidation,  and  a  little  more  than  this 
amount  should  be  added.  Twenty  c.c.  of  strong  sulphuric  acid  need-, 
about  :75  c.c.  of  40  per  cent,  sodium  hydroxide  to  neutralize  it. 
Bumping  may  further  be  prevented  by  the  addition  of  a  little  granu- 
lated zinc.  Shake  the  flask  two  or  three  times.  Add  also  about  1 2  c.c 
of  a  concentrated  solution  of  potassium  sulphide  (i  part  to  ij-  p. 
water),  which  favours  the  setting  free  of  the  ammonia  from  the 
amino-compounds  of  mercury  that  have  been  formed  during  oxida- 
tion. Commercial  '  liver  of  sulphur  '  will  do  quite  well.  Imme- 
diately connect  the  distilling-flask  with  the  worm,  as  shown  in 
Fig.  180.  and  distil  the  ammonia  over  into  50  c.c.  of  standard 
(decinormal)  sulphuric  acid  (see  footnote,  p.  139)  contained  in  a  flask 
into  which  a  glass  tube  connected  with  the  lower  end  of  the  worm 
dips.  Heat  the  distilling  flask  at  first  gently,  then  strongly,  and  boil 
for  three-quarters  of  an  hour,  or.until  about  two-thirds  of  the  liquid 
has  passed  over.     Then  lift  the  tube  out  of  the  standard  acid,  and 


Fig.  179. — Doremus 
Ureometer. 


PRACTIC  U    I  Xf-RCr.SES 


483 


continue  the  distillation  for  two  or  three  minutes  longer.  The 
ammonia  is  now  all  united  with  the  standard  acid,  a  certain  amount 
Hi  which  is  left  over.  By  determining  this  amount  we  arrive  at  the 
quantity  combined  with  ammonia,  and  therefore  at  the  quantity  of 
ammonia.  Fill  a  burette  with  a  decinormal  solution  of  potassium 
or  sodium  hydroxide.  Add  a  little  methyl-orange  solution  to  the 
standard  sulphuric  acid,  to  serve  as  indicator.  Then  run  in  the 
potassium  or  sodium  hydroxide  till  the  pink  tinge  gives  place  to[a 
permanent  but  just  recognisable  vellow.  Let  x  be  the  number  of 
c.c.  run  in.  Since  1  c.c.  of  any  decinormal  solution  is  equivalent  to 
1  c.c.  of  any  other,  x  represents  also  t  he  number  of  c.c.  of  the  standard 
sulphuric  acid  left  uncombined  with  ammonia;  and  50— #,  the 
quantity  combined  with  ammonia.  Then,  r  c.c.  of  decinormal 
sodium  or  potassium  hydroxide  being  equivalent  to  1  c.c.  of  deci- 


Fig.  180. 


-Arrangement  for  Distillation   in    E 
Nitrogen. 


iTIMATION    OF    TOTAL 


normal  ammonium1  hydroxide,  and  1  c.c.  of  decinormal  ammonium 
hydroxide  containing  00014  gramme  nitrogen,  we  get  (50  —  x)  x  0-0014 
as  the  quantity  of  nitrogen  in  5  c.c.  of  urine. 

Instead  of  mercury,  potassium  sulphate  and  copper  sulphate  may 
be  added  to  the  sulphuric  acid  in  order  to  aid  the  decomposition  in 
the  first  stage  of  the  estimation.  About  3  grammes  of  potassium 
sulphate  and  1  gramme  of  copper  sulphate  are  added  to  5  c.c.  of 
urine,  and  then  5  c.c.  of  sulphuric  acid.  The  liquid  is  gently  boiled 
for  an  hour,  or  until  it  is  quite  clear.  The  neutralization  and  dis- 
tillation are  conducted  as  before,  the  proper  quantity  of  sodium 
hydroxide  being  determined  in  advance.  No  potassium  sulphide  is 
added,  but  a  small  quantity  of  talc  may  be  put  in  to  prevent  bump- 
ing. Instead  of  methyl  orange.  '  alizarin  red,'  which  is  bright 
red  in  the!  presence  of  the  slightest  trace  of  alkali,  may  be  used. 

31—2 


484  A  MANUAL  OF   PHYSIOLOGY 

9.  Uric  Acid — (1)  Qualitative  Test  for  Uric  Acid — Murexide  Test. — 
A  small  quantity  of  uric  acid  or  one  of  its  salts  is  heated  with  a  little 
dilute  nitric  acid.  The  colour  of  the  residue  left  by  evaporation 
becomes  yellow,  and  then  red,  and  on  the  addition  of  ammonia 
changes  to  deep  purple-red.  Potassium  or  sodium  hydroxide  changes 
the  yellow  to  violet.  The  purple-red  substance  is  murexide  or 
ammonium  purpurate.  It  is  also  formed  by  the  action  of  nitric 
acid  and  ammonia  on  theobromine  (dimethylxanthin),  an  alkaloid 
in  cocoa,  and  theine  or  caffeine  (trimethylxanthin),  an  alkaloid  in 
tea  and  coffee,  which  arc  also  purin  derivatives  (p.  441). 

(2)  Quantitative  Estimation — (a)  Hopkins's  Method  of  Estimation 
of  Uric  Acid. — Add  about  25  grammes  of  ammonium  chloride  to 
100  c.c.  of  urine  in  a  beaker.  Stir  well  to  dissolve  all  the  salt. 
Then  add  2  c.c.  of  strong  ammonia.  Let  the  mixture  stand  till 
the  precipitate  of  ammonium  urate  which  is  formed  has  entirely 
settled  to  the  bottom  and  the  liquid  above  it  is  clear.  Then  filter 
through  a  small  filter-paper.  Wash  the  precipitate  on  the  filter 
twice  with  saturated  solution  of  ammonium  chloride  from  a  wash- 
bottle.  Then  wash  the  precipitate  into  a  porcelain  capsule  with 
hot  water  from  a  wash-bottle  with  a  fine  jet,  unfolding  the  filter- 
paper  over  the  capsule  so  as  to  get  it  all  off.  For  this  purpose 
not  more  than  20  to  30  c.c.  of  water  should  generally  be  necessary  : 
but  if  much  more  has  been  used  the  excess  should  be  got  rid  of  by 
evaporation  on  a  water-bath.  Pour  about  1  c.c.  of  strong  hydro- 
chloric acid  into  the  capsule,  heat  to  boiling,  and  then  allow  the 
capsule  to  stand  in  the  cold  till  the  uric  acid  crystallizes  out.  The 
time  required  for  this  is  2  to  12  hours,  being  shorter  the  lower  the 
temperature.  The  crystals  are  filtered  off  through  a  small  weighed 
filter,  the  filtrate  being  received  in  a  graduated  cylinder  and  measured . 
The  crystals  are  then  washed  on  the  filter  with  cold  distilled  water, 
till  the  washings  come  through  the  filter  free  from  chlorides,  as 
tested  by  silver  nitrate  (p.  477).  The  filter  with  the  crystals  is 
dried  in  the  oven  and  weighed.  To  the  weight  of  the  uric  acid 
thus  obtained  1  milligramme  must  be  added  for  each  15  c.c.  of 
the  filtrate  (the  mother  -  liquor)  collected  in  the  graduated 
cylinder. 

Or,  instead  of  being  estimated  by  weighing,  the  uric  acid  crystals 
may,  after  having  been  washed  with  the  cold  distilled  water  as 
described,  till  free  from  chlorides,  be  washed  again  with  hot  water 
off  the  filter  (which  need  not  in  this  case  be  a  weighed  one)  into  a 
capsule.  The  capsule  is  filled  up  with  distilled  water,  1  c.c.  of  10  per 
cent,  sodium  carbonate  solution  added,  and  the  contents  heated  to 
boiling  to  dissolve  the  uric  acid.  The  solution  is  allowed  to  cool, 
and  then  emptied  into  an  Erlenmeyer's  flask  with  a  mark  roughly 
corresponding  to  100  c.c.  The  solution  is  made  up  to  100  c.c.  with 
distilled  water.  A  burette  is  filled  with  standard  potassium  perman- 
ganate solution  (a  twentieth-normal  solution  made  by  dissolving  1581 
grammes  of  the  permanganate  in  a  litre  of  water).  Twenty  c.c.  of 
strong  sulphuric  acid  are  poured  into  the  flask,  which  is  then  shaken. 
The  permanganate  is  now  run  in  with  constant  shaking  of  the  flask. 
At  first  the  pink  colour  produced  where  the  drops  of  permanganate 
fall  into  the  liquid  disappears  at  once  without  spreading  through  the 
liquid.  When  a  certain  amount  has  been  run  in,  however,  the  whole 
liquid  becomes  pink,  although  the  colour  soon  disappears.  This 
indicates  that  enough  of  the  permanganate  has  been  added.  Each 
c.c.  of  the  permanganate  used  is  equivalent  to  000375  gramme  uric 


PRACTICAL   EXERCISES  485 

acid.  One  milligramme  must  be  added,  as  before,  to  the  result  for 
each  15  c.c.  of  the  mother-liquor  from  which  the  uric  acid  crystals 
were  deposited. 

(b)  Folin's  Modification  of  Hopkins's  Method. — The  chief  reagent 
is  a  solution  of  500  grammes  ammonium  sulphate,  5  grammes 
uranium  acetate,  and  60  c.c.  10  per  cent,  acetic  acid,  in  650  c.c. 
of  water. 

One  hundred  and  fifty  c.c.  of  urine  is  measured  into  a  tall,  narrow 
beaker  or  a  cylinder,  and  37 \  c.c.  of  the  reagent  added.  If  enough 
urine  is  available,  200  c.c.  of  urine  and  50  c.c.  of  reagent  are  to  be 
used.  Allow  the  mixture  to  stand  without  stirring  for  about  half 
an  hour.  The  uranium  precipitate  has  then  settled,  and  the  clear 
supernatant  liquid  is  removed  by  siphoning  or  decantation.  One 
hundred  and  twenty-five  c.c.  of  this  liquid  is  measured  into  another 
beaker,  5  c.c.  of  strong  ammonia  added,  and  the  mixture  set  aside 
till  next  day.  The  precipitate  is  then  filtered  off,  and  washed  with 
10  per  cent,  ammonium  sulphate  solution  until  the  filtrate  is  quite 
or  nearly  free  from  chlorides.  The  filter  is  then  removed  from  the 
funnel,  opened,  and  the  precipitate  rinsed  back  into  the  beaker. 
Enough  water  to  make  about  100  c.c.  is  added,  and  the  precipitate 
is  then  dissolved  by  means  of  15  c.c.  concentrated  sulphuric  acid, 
and  at  once  titrated  with  .?fl  (one-twentieth  normal)  potassium 
permanganate  solution,  each  c.c.  of  which  corresponds  to  3^75  milli- 
grammes of  uric  acid.  The  very  first  pink  coloration,  extending 
through  the  entire  liquid  through  the  addition  of  two  drops  of 
permanganate  solution,  marks  the  end  point.  A  correction  of  3  milli- 
grammes, owing  to  the  solubility  of  ammonium  urate,  is  added  to 
the  result. 

10.  Kreatinin. — Qualitatively,  kreatinin  may  be  recognised  in  very 
small  amounts  by  Weyl's  test.  A  few  drops  of  a  dilute  solution  of 
sodium  nitro-prusside  are  added  to  urine,  and  then  dilute  sodium 
hydroxide  drop  by  drop.  A  ruby-red  colour  appears,  which  soon 
turns  yellow.  If  the  urine  is  now  strongly  acidified  with  acetic  acid 
and  heated,  it  becomes  first  greenish  and  then  blue.  Enough  acid 
must  be  added  to  more  than  neutralize  the  alkali. 

Neubauer  has  made  the  reaction  of  kreatinin  with  zinc  chloride 
the  basis  of  a  method  for  its  quantitative  estimation  (Fig.  167,  p.  442), 
but  the  results  seem  to  be  somewhat  uncertain.  A  more  convenient 
method  is  that  of  Folin.  It  depends  upon  the  comparison  of  the 
colour  which  kreatinin  gives  with  picric  acid  in  an  alkaline  solution 
with  that  of  a  standard  solution  of  potassium  bichromate.  Ten  c.c. 
of  urine  is  measured  into  a  500  c.c.  measuring  -  flask  ;  15  c.c.  of 
a  saturated  picric  acid  solution  (containing  about  12  grammes 
per  litre),  and  5  c.c.  of  a  10  per  cent,  solution  of  sodium  hydroxide 
are  added.  The  mixture  is  allowed  to  stand  for  five  minutes. 
Then  water  is  added  up  to  the  500  c.c.  mark,  and  the  flask  shaken 
to  mix  uniformly.  Samples  of  the  liquid  are  then  at  once  com- 
pared colorimetrically  with  a  half  -  normal  solution  of  potassium 
bichromate  containing  24' 55  grammes  per  litre.  The  colour  of 
the  urine  does  not  introduce  a  sensible  error  on  account  of  the 
great  dilution.  For  exact  work  the  comparison  must  be  made 
with  a  good  colorimeter.  It  has  been  found  experimentally  that, 
when  10  milligrammes  of  kreatinin  are  present  in  500  c.c.  of  a 
solution  made  as  described,  a  layer  of  the  solution  8'i  millimetres 
in  thickness  has  the  same  depth  of  tint  as  8  millimetres  of  the 
bichromate    solution.     Suppose     it    takes    9    millimetres    of    the 


486  A    M  INUAL  OF  PHYSIOLOGY 

urine  -  picratc  solution  to  equal   8   millimetres  of  the   bichromate, 

then  the    10  c.c.   of    urine  contains   10  x        =9/0  milligrammes  of 

kreatinin. 

11.  Hippuric  Acid. — From  horse's  or  cow's  urine  hippuric  acid  is 
prepared  by  evaporating  to  a  small  bulk,  and  adding  strong  hydro- 
chloric acid.  The  crystalline  precipitate  is  washed  with  cold  water, 
then  dissolved  in  hot  water,  and  filtered  hot.  Hippuric  acid  separates 
out  from  the  filtrate  in  the  cold  in  the  form  of  Long  four-sided  prisms 
with  pyramidal  ends.  Heated  dry  in  a  test-tube,  the  crystals  melt, 
and  benzoic  acid  and  oily  drops  of  benzonitrilc.  a  substance  with  a 
smell  like  that  of  oil  of  bitter  almonds,  are  formed. 


ABNORMAL   SUBSTANCES    IN    URINE. 

12.  Proteins — (1)  Qualitative  Tests. — (a)  Boil  and  add  a  few  drops 
of  nitric  acid.  A  precipitate  on  boiling,  increased  or  not  affected 
by  the  acid,  shows  the  presence  of  coagulablc  proteins  (serum- 
albumin  or  globulin) .  A  precipitate  of  earthy  phosphates  sometimes 
forms  on  boiling.  It  is  distinguished  from  a  precipitate  of  proteins 
by  dissolving  on  the  addition  of  acid. 

(b)  Heller's  Test. — Put  some  nitric  acid  in  a  test-tube.  Pour 
carefully  on  to  the  surface  of  the  acid  a  little  urine.  A  white  ring  at 
the  junction  of  the  liquids  indicates  the  presence  of  albumin  or 
globulin.  If  much  albumose  is  present,  a  white  precipitate,  which 
disappears  on  heating,  may  be  formed.  When  this  test  is  performed 
with  undiluted  urine,  uric  acid  may  be  precipitated  and  cause  a 
brown  colour  at  the  junction.  A  similar  ring  may  be  found  in  the 
absence  of  proteins  when  the  test  is  made  on  the  urine  of  a  patient 
who  has  been  taking  copaiba.  In  very  concentrated  urine  a  white 
ring  of  nitrate  of  urea  may  be  formed.  A  coloured  ring  is  frequently 
seen,  owing  to  the  oxidation  of  certain  chromogens  of  urine. 

(c)  Filter  some  urine,  and  add  to  the  filtrate  its  own  volume  of  acetic 
acid.  A  precipitate  may  indicate  mucin  or  nucleo-albumin.  If  any 
is  formed,  filter  it  off,  and  add  to  the  filtrate  a  few  drops  of  potassium 
ferrocyanide.     A  white  precipitate  shows  the  presence  of  proteins. 

(d)  Test  for  Globulin  in  Urine. — Serum-globulin  probably  never 
occurs  in  urine  apart  from  serum-albumin .  It  may  be  detected  thus  : 
Make  the  urine  alkaline  with  ammonia,  let  it  stand  for  an  hour  and 
filter.  Half  saturate  the  filtrate  with  ammonium  sulphate — i.e.,  add 
to  it  an  equal  volume  of  a  saturated  solution  of  ammonium  sulphate. 
Scrum-globulin  is  precipitated,  scrum-albumin  is  not. 

(e)  Test  for  Albumose  in  Urine  (Albumosuria).- — Coagulablc  proteins 
are  removed  by  boiling  the  urine  (acidulated  if  necessary),  and  filter- 
ing off  the  precipitate  if  any.  The  filtrate  is  neutralized.  If  a 
further  precipitate  falls  down  it  is  filtered  off,  the  clear  filtrate  is 
heated  in  a  beaker  placed  in  a  boiling  water-bath,  and  there  saturated 
with  crystals  of  ammonium  sulphate.  A  precipitate  indicates  that 
albumoses  (proteoses)  are  present.  A  slight  precipitate  might  pos- 
sibly be  due  to  the  formation  of  ammonium  urate.  A  further  test 
may  be  performed  on  the  original  urine  if  it  is  free  from  coagulable 
proteins,  or  on  the  filtrate  after  their  removal.  Add  a  drop  or  two  of 
pure  nitric  acid.  If  albumoses  arc  present,  a  precipitate  is  thrown 
down  which  disappears  on  heating,  and  reappears  on  cooling  the  test- 
tube  at  the  cold-water  tap. 


PRACTh    U    i  XERCISES  487 

i/"i  Test  for  Peptone  in  Urine  {Peptonuria). — Place  some  of  the 
urine  in  a  beaker  on  a  boiling  water-bath  for  thirty  minutes,  and 
saturate  with  ammonium  sulphate  crystals.  Then  boil  over  a  small 
Same  or  in  an  air-bath  for  half  an  hour.  All  the  proteins,  including 
peptones,  are  precipitated.  But  the  peptones  can  still  be  redissolved 
by  water,  the  others  not.  Kilter  hot.  Wash  the  precipitate  on  the 
filter  with  a  boiling  saturated  solution  of  ammonium  sulphate.  Then 
extract  the  residue  with  cold  water,  filter,  and  test  the;  filtrate  by  the 
biuret  t<st  (addition  of  very  dilute  cupric  sulphate  and  excess  of 
sodium  hydroxide),  A  rose  colour  indicates  the  presence  of  peptone 
(p.  7),  but  it  the  reaction  is  only  a  faint  one,  it  may  be  due  to 
urobilin  (Stokvis).     True  peptone  is  rarely  found  in  urine. 

(2)  Quantitative  Estimation  of  Coagulable  Proteins  [Serum- Albumin 
and  Globulin) — (a)  Gravimetric  Method. — Heat  50  to  100  c.c.  of  the 
urine  to  boiling,  adding  a  dilute  solution  (2  per  cent.)  of  acetic  acid 
by  drops  as  long  as  the  precipitate  seems  to  be  increased.  Filter 
through  a  weighed  filter.  Wash  the  precipitate  on  the  filter  with  hot 
water,  then  with  hot  alcohol,  and  finally  with  ether.  Dry  in  an  air- 
bath  at  no°  C,  and  weigh  between  watch-glasses  of  known  weight. 

(b)  Method  of  Roberts  and  Stolnikow  [modified  by  Brandberg). — 
This  method  is  founded  on  the  fact  that  the  time  taken  for  the  white 
ring  to  appear  in  Heller's  test  depends  on  the  proportion  of  coagulable 
protein  present.  It  has  been  found  that  when  1  part  of  albumin  is 
contained  in  30,000  parts  of  an  albuminous  solution  (00033  per  cent.), 
the  ring  appears  in  two  and  a  half  to  three  minutes.  The  amount  of 
dilution  of  the  urine  which  is  necessary  to  delay  the  formation  of  the 
ring  for  this  length  of  time  is  what  has  to  be  determined.  To  do 
this,  proceed  as  follows  :  Dilute  a  portion  of  the  urine  (say  5  c.c.)  ten 
times — that  is,  add  to  it  nine  times  its  volume  of  distilled  water 
from  a  burette.  Place  some  pure  nitric  acid  in  a  test-tube  with  a 
pipette,  taking  care  not  to  wet  the  sides  of  the  test-tube  with  the 
acid.  Now  run  on  to  the  surface  of  the  nitric  acid  some  of  the 
diluted  urine.  Hold  the  test-tube  up  against  the  light  from  a  windowt 
Between  the  test-tube  and  the  window  hold  obliquely  a  dull  black 
surface  a  few  inches  from  the  test-tube,  moving  it  up  and  down  a 
little  below  the  junction  of  the  urine  and  acid.  Note  the  interval 
that  elapses  before  formation  of  the  white  ring.  If  it  is  more  than 
three  minutes,  the  diluted  urine  contains  less  than  1  part  in  30,000, 
and  the  undiluted  urine  less  than  1  part  in  3,000  [i.e.,  less  than  o'o33 
per  cent.)  of  coagulable  protein,  and  the  experiment  must  be  repeated 
with  urine  diluted  to  a  smaller  extent.  If  the  ring  appears  after  a 
shorter  interval  than  three  minutes,  the  diluted  urine  contains  more 
than  1  part  in  30,000  (the  original  urine  more  than  0*033  Per  cent.) 
and  must  be  further  diluted.  Fill  a  burette  with  the  diluted  urine. 
Run  1  c.c.  of  it  into  a  test-tube  and  add  9  c.c.  of  distilled  water. 
Repeat  the  test  with  this  second  dilution.  If  the  ring  appears  at  a 
longer  interval  than  three  minutes,  the  twice-diluted  urine  contains 
less  than  1  part  of  albumin  in  30,000,  and  the  original  undiluted 
urine  less  than  1  part  in  300 — i.e.,  less  than  033  per  cent.  So  far, 
then,  we  have  found,  let  us  suppose,  that  the  proportion  of  albumin 
in  the  original  urine  lies  between  0033  and  033  per  cent.  Now  run 
1  c.c.  of  the  urine  of  the  first  dilution  (the  urine  diluted  ten  times) 
into  a  test-tube,  and  add  4  c.c.  of  distilled  water — i.e.,  dilute  again  five 
times.     If  this  gives  the  white  ring  in  Heller's  test  in  three  minutes, 

the  original  urine  will  contain  1  part  of  albumin  in   — i.e.,  in 

0  r  10x5 


488 


J    MANl  AL  OF  PHYSIOLOGY 


600  parts,  or  o:  16  per  cent,  [f  the  interval  is  longer  or  shorter  than 
three  minutes,  the  urine  of  the  first  dilution  (i  to  10)  must  be  diluted 

less  or  more  than  five  times  until  the  into  rval  amounts  to  about 
three  minutes.  The  total  dilution  corresponding  to  a  percentage 
of  0*0033  of  albumin  is  thus  known,  and  the  percentage  in  the 
undiluted  urine  can  be  easily  calculated. 

(c)  Esbach's  Method. — Esbach's  reagent  is  made  by  dissolving 
10  grammes  of  picric  acid  and  20  grammes  of  citric  acid  in  boiling 
water  (800  or  900  c.c),  and  then  making  up  the  volume  to  a  litre. 
The  so-called  albuminimeter  is  simply  a  strong  glass  tube  graduated 
and  marked  in  a  certain  way.  Fill  the  tube  up  to  the  mark  l'  with 
the  urine.  Then  add  the  reagent  up  to  the  mark  R.  Close  the  tube 
with  the  rubber  cork,  and  invert  it  a  dozen  times  without  shaking. 

Set  the  tube  aside  for  twenty-four 
hours,  then  read  off  the  gradua- 
tion on  the  tube  which  corre- 
sponds with  the  top  of  the  pre- 
cipitate. The  figures  indicate  the 
number  of  grammes  of  dry  pro- 
tein in  a  litre  of  tie  urine.  Sup- 
pose the  top  of  the  sediment  is  at 
4,  this  will  indicate  4  grammes  per 
litre,  or  04  per  cent.  The  method 
is  of  some  clinical  importance, 
owing  to  its  simplicity,  although 
it  is,  of  course,  not  very  accurate 
13.  Sugar — (1)  Qualitative  Tests 
— (a)  Trommer's  Test  (seep.  10). — 
It  is  to  be  remarked  that  some  sub- 
stances present  in  small  amount  in 
normal  urine  reduce  cupric  sul- 
phate— e.g.,  uric  acid  (present  as 
urates)  and  kreatinin  —  but  al- 
though a  normal  urine  may  thus 
decolourize  the  copper  solution,  it 
rarely  causes  so  much  reduction 
that  a  yellow  or  red  precipitate  is 
formed,  as  is  the  case  in  diabetic 
urine.  Glycuronic  acid,  which  may 
occur  even  in  normal  urine  in  very 
slight  traces  (p.  442),  also  reduces 
cupric  salts,  as  does  alcapton  or 
homogentisinic  acid,  a  substance 
found  in  rare  cases  in  disease  (p.  444).  It  less  than  05  per  cent,  of 
sugar  is  present  in  the  urine,  no  precipitate  of  cuprous  oxide  will  be 
formed  till  the  urine  is  cooled.  The  test  may  also  be  performed  with 
Fehling's  solution. 

(6)  Phenyl-hydrazine  lest. — This  test  depends  upon  the  fact  that 
phenvl  -  hydrazine  forms  with  sugars  such  as  glucose  (dextrose), 
maltose,  isomaltose.  etc.,  but  not  with  cane-sugar,  characteristic 
crystalline  substances  (phenyl-glucosazone.  phenyl-maltosazone,  etc.) 
which  can  be  recognised  under  the  microscope,  and  are  distinguished 
from  each  other  bv  melting  at  different  temperatures.  Phenyl- 
glucosazone  (C18H22N.i04)  melts  at  205°  C.  To  perform  the  test  for 
dextrose  in  the  urine,  proceed  thus  :  Put  5  c.c.  of  urine  in  a  test- 
tube,  add  1  decigramme  of  hydrochlorate  of  phenyl-hydrazine  and 


Fig.  181. — Phenyl-glucosazone  and 

Phenyl-maltosazone  Crystals 

(Macleod  ). 

The  phenyl-glucosazone  crystals  are 
in  the  upper  part  of  the  figure,  the 
phenyl-maltosazone  in  the  lower. 


PR  h   l  h    II    I  XERCISES 

2  decigrammes  of  sodium  a<  etate  H  is  sufficiently  accural  bo  add 
as  much  phenyl-hydrazine  as  will  lie  <>n  a  sixpence  (or  a  dime)  and 
t  w  ice  .is  much  sodium  acetate  Heat  the  test-tube  in  a  boiling  wa 
bath  for  hall  an  hour.  Then  cool  at  the  tap  and  examine  th  d(  posit 
under  the  microscope  for  the  yellow  phenyl-glucosazone  crystals 
(Fig.  isn.  Sometimes  the  osazone  precipitate  is  amorphous.  Lesl 
this  should  be  the  case,  the  precipitate,  if  no  crystals  can  be  seen, 
must  be  dissolved  in  hot  alcohol.  The  solution  is  then  diluted 
with  water  and  the  alcohol  boiled  off,  when  the  osazone,  if  any  bo 
present,  will  crystallize  out.  Very  minute  traces  of  sugar  can  be 
detected  in  this  way  (as  little  as  o-i  per  cent,  in  urine).  Often 
in  normal  urine  yellow  crystals  are  deposited  during  the  first  fifteen 
minutes'  heating.  They' must  not  be  mistaken  for  glucosazone. 
They  probably  consist  of  a  compound  of  glycuronic  acid  and  phenyl- 
hydrazine.  They  are  changed  as  the  heating  goes  on  into  an  amor- 
phous brownish-yellow  precipitate  (Abel). 

(c)  The  Yeast  Test  is  an  important  confirmatory  test  for  dis- 
tinguishing the  fermentable  sugars  from  other  reducing  substances, 
but  it  is  not  very  delicate,  and  will  with  difficulty  detect  sugar 
when  less  than  0-5  per  cent,  is  present.  It  can  be  performed  thus  : 
A  little  yeast  (the  tablets  of  compressed  yeast  do  very  well)  is  added 
to  a  test-tube  half  filled  with  urine.  The  test-tube  is  then  filled  up 
with  mercury,  closed  with  the  thumb,  and  inverted  over  a  dish 
containing  mercury.  The  dish  may  be  placed  on  the  top  of  a  water- 
bath  whose  temperature  is  about  400  C.  After  twenty-four  hours 
the  sugar  will  have  been  broken  up  into  alcohol  and  carbon  dioxide. 
The  latter  will  have  collected  above  the  mercury  in  the  test-tube, 
and  the  former  will  be  present  in  the  urine.  The  tests  for  sugar 
will  either  be  negative  or  will  be  less  distinct  than  before.  A  con- 
trol test-tube  containing  water  and  yeast  should  also  be  set  up, 
as  impurities  in  the  yeast  sometimes  yield  a  small  amount  of  carbon 
dioxide.  Specially  constructed  tubes  are  also  often  used  for  per- 
forming the  test. 

(2)  Quantitative  Estimation  of  Sugar  in  Urine. — (a)  Volumetrically, 
the  sugar  can  be  estimated  by  titration  with  Fehling's  solution.  As 
this  does  not  keep  well,  two  solutions  containing  its  ingredients 
should  be  kept  separately  and  mixed  when  required.  Solution  I.  : 
Dissolve  34'64  grammes  pure  cupric  sulphate  in  distilled  water,  and 
make  up  the  volume  to  500  c.c.  Solution  II.  :  Dissolve  173  grammes 
Rochelle  salt  in  400  c.c.  of  water,  add  to  this  51-6  grammes  sodium 
hydroxide,  and  make  up  the  volume  with  water  to  500  c.c.  Keep  in 
well-stoppered  bottles  in  the  dark.  For  use,  mix  together  equal 
volumes  of  the  two  solutions.  Ten  c.c.  of  this  mixture  is  reduced  by 
0-05  gramme  dextrose.  To  estimate  the  sugar  in  urine,  put  10  c.c. 
of  the  mixture  into  a  porcelain  capsule  or  glass  flask,  and  dilute  it 
four  or  five  times  with  distilled  water.  Dilute  some  of  the  urine, 
say  ten  or  twenty  times,  according  to  the  quantity  of  sugar  indicated 
by  a  rough  determination.  Run  the  diluted  urine  from  a  burette 
into  the  Fehling's  solution,  bringing  it  to  the  boil  each  time  urine  is 
added,  until,  on  allowing  the  precipitate  to  settle,  the  blue  colour 
is  seen  to  have  entirely  disappeared  from  the  supernatant  liquid. 
The  observation  of  the  colour  must  be  made  while  the  liquid  is  still 
hot. 

Suppose  that  10  c.c.  of  Fehling's  solution  is  decolourized  by  20  c.c. 
of  the  ten-times  diluted  urine.  Then  2  c.c.  of  the  original  urine 
contains  0-5  gramme  dextrose.     If  the  urine  of  the  twenty-four  hours 


490  A   MANUAL  OF  PHYSIOLOGY 

(from  which  this  sample  is  assumed  to  have  been  taken    amounl 
4,000  c.c..  the  patient  will  havi  00     100  gran 

sugar,  in  twenty-four  hours.  Various  modifications  oJ  Fehling's 
solution,  which  have  for  their  object  the  pre>  ention  ol  the  pre(  ipitate 
of  cuprous  oxide,  with  its  disturbing  effect  upon  the  reading  of  the 
end-point,  have  been  devised.  Thus,  in  Pavy's  solution  ammonia 
holds  the  cuprous  oxide  in  solution,  and  the  end-point  is  the  dis- 
appearance of  the  blue  colour.  Ten  c.c.  of  Pavy's  solution  =  I  c.c. 
01  Fehling's  solution  =  o- 005  gramme  of  dextrose. 

(b)  The  polarimeter  affords  a  rapid  and.  with  practice,  a  delicate 
means  of  estimating  the  quantity  of  sugar  in  pure  and  colourless 
solutions,  but  diabetic  urine  must  in  general  be  first  decolourized 
by  adding  lead  acetate  and  filtering  off  the  precipitate.  Wh 
measured  is  the  amount  by  which  the  plane  of  polarization  of  a  ray 
of  polarized  light  of  given  wave-length  (say  sodium  light  1  is  rotated 
when  it  passes  through  a  layer  of  the  urine  or  other  optically  active 
solution  of  known  thickness.  Let  a  be  the  observed  angle  of  rota- 
tion. /  the  length  in  decimetres  of  the  tube  containing  the  solution, 
w  the  number  of  grammes  of  the  optically  active  substance  per  c.c.  of 
solution,  and  (a)D  the  specific  rotation  of  the  substance  for  light  of 
the  wave-length  of  the  part  of  the  spectrum  corresponding  to  the 
D  line  (i.e.,  the  amount  of  rotation  expressed  in  degrees  which  is 
produced  by  a  layer  of  the  substance  1  decimetre  thick,  when  the 

solution  contains  1   gramme  of  it  per  c.c).     Then  (a):>  =  ±     ,.     In 

this  equation  a  and  /  are  known  from  direct  measurement  ;  (a)„ 
has  been  determined  once  for  all  for  most  of  the  important  active 
substances,  and  therefore  w  is  easily  calculated.  For  dextrose  [a)B 
may  be  taken  as  5260.  It  varies  somewhat  with  the  concentration, 
but  for  most  investigations  on  the  urine  these  variations  may  be 
neglected. 

It  is  not  possible  to  describe  here  the  numerous  forms  of  polari- 
meter that  are  in  use.  Those  constructed  on  what  is  called  the  '  half- 
shadow  '  system  (Fig.  182)  give  sufficiently  satisfactory  results.  A 
half-shadow  polarimeter  consists,  like  other  polarimeters,  of  a  fixed 
Xicol's  prism  (the  polarizer),  and  a  nicol  capable  of  rotation  (the 
analyzer).  In  addition,  there  is  an  arrangement  which  rotates  by  a 
definite  angle  the  plane  of  polarization  in  one-half  of  the  field,  but  not 
in  the  other — e.g.,  a  small  nicol  occupying  only  half  of  the  field.  In 
the  zero  position  of  the  analyzer,  both  halves  of  the  field  arc  equally 
dark.  The  solution  to  be  investigated  is  placed  in  a  tube  of  known 
length,  the  ends  of  which  are  closed  by  glass  discs  secured  by  brass 
screw  caps.  The  glass  discs  must  be  slid  on,  so  as  to  exclude  all  air. 
The  tube  having  been  introduced  between  the  polarizer  and  analyzer, 
the  sharp  vertical  line  which  indicates  the  division  between  the  two 
half-fields  is  focusscd  with  the  eye-piece,  and  then  the  analyzer  is 
rotated  till  the  two  halves  are  again  equally  shadowed.  The  angle 
of  rotation,  a,  is  read  off  on  the  graduated  arc.  which  is  provided 
with  a  vernier. 

Pentoses  reduce  Fehling's  solution,  but  do  not  give  the  yeast  test. 
Thcv  give  the  following  characteristic  tests,  which  may  be  performed 
with  gum  arabic,  which  contains  arabinose,  one  of  the  pentoses  : 

(1)  Phloroglucin  Reaction. — Warm  in  a  test-tube  some  pure  con- 
centrated hvdrochloric  acid  to  which  an  equal  volume  of  distilled 
water  has  been  added.  Add  phlorogliu  in  until  a  little  remains  un- 
dissolved.    Add  a  small  quantity  of  gum  arabic,  and  keep  the  1 


/-/,'  \(  I  l<    II.   EXERCISES 


I'M 


lube  in  .1  water  bath  .d  [oo  C.  The  solution  becomes  cherry-red, 
and  -i  precipitate  gradually  separates,  which  may  be  dissolved  in 
amyl  alcohol.  The  solution  shows  with  the  spectroscope  a  band 
between  I )  and  E. 

(2)  Orcin  Reaction.  Use  orcis  instead  of  phloroglucin  in  (1). 
The  solution  becomes  reddish  blue  on  warming,  and  shows  a  band 
between  ("  and  D,  near  D.  The  colour  quickly  changes  from  violet 
to  blue  red,  and  finally  green.  A  bluish-green  precipitate  separates, 
which  is  soluble  in  amyl-alcohol.  Glycuronic  acid  gives  all  the  above 
reactions  of  pent<  ses. 

Bile-Salts  --{Hay's  Test). — Put  a  little  finely-divided  sulphur,  in 
the  form  of  flowers  of  sulphur,  on  the  top  of  a  glass  of  urine.     If  bilc- 


Fig.  182. — Mitscherlich's  Polarimeter. 
(Half-Shadow    Instrument.)      (Simple    Form.) 

salts  are  present  the  sulphur  will  sink  to  the  bottom.  If  there  are 
no  bile-salts  it  will  float  on  the  top.  The  difference  is  due  to  an  altera- 
tion in  the  surface  tension  of  the  urine  produced  by  the  bile-salts. 
We  must  exclude  the  presence  of  acetic  acid,  alcohol,  ether,  chloro- 
form, turpentine,  benzine  and  its  derivatives,  phenol  and  its  deriva- 
tives, anilin  and  soaps,  all  of  which  also  cause  such  an  alteration  in 
the  surface  tension  of  urine  that  the  sulphur  sinks  to  the  bottom. 
The  urine  should  be  fresh,  and  if  it  has  to  be  kept  it  should  be  pre- 
served from  decomposition  by  cyanide  of  mercury,  which  does  not 
alter  the  surface  tension.  The  reaction  has  the  great  advantage 
over  other  tests  of  being  easily  carried  out  at  the  bedside. 


(,,-•  A   .1/  !  \  /'.//.  OF  PHYSIOLOGY 

Acetone.  — (i)  Legal's  Test  (Rothera's  modification).  To  5  to 
10  c.c.  '>i  the  acetone  containing  urine  add  enough  ammonium  sul- 
phate  crystals  to  form  a  layer  at  the  bottom  of  the  test-tube,  then 
2  or  3  drops  of  a  fresh  5  per  cent,  solution  of  sodium  nitro-prusside 
.i.iul  1  to  j  c.c.  of  strong  ammonia.  The  development  of  a  colour 
like  that  of  permanganate  of  potassium,  often  in  the  form  of  a  ring 
.1  little  above  the  undissolved  salt,  indicates  the  present  1  "t  a<  etone. 
The  reaction  must  not  be  declared  negative  till  hull  an  hour  has 
elapsed.     The  colour  slowly  fades. 

(2)  Where  there  is  doubt  as  to  the  presence  oi  .net  one.  it  is 
best  first  to  distil  it  over.  Put  250  to  500  c.c.  of  the  urine  suspet  ted 
to  eontain  acetone  into  a  litre  flask.  Add  a  feu  c.c.  of  phosph 
acid  ;  connect  the  flask  with  a  worm  (sec  Fig.  [80,  p.  §.83),  and  distil 
over  the  urine  into  a  small  flask.  For  qualitative  tests  it  is  best  to 
collect  only  the  first  20  to  30  c.c,  as  most  of  the  acetone  is  contained 
in  this.     Test  the  distillate  for  acetone  by  (1)  or  by 

Lieben's  Test.— To  a  few  c.c.  of  the  distillate  in  a  test-tube  add  a  few 
drops  of  solution  of  iodine  in  potassium  iodide  and  then  sodium  or 
potassium  hydroxide.  A  precipitate  of  yellow  iodoform  crystals  (six- 
sided  tables)  is  thrown  down  if  acetone  be  present.  Examine  them 
under  the  microscope.  On  heating,  the  odour  of  iodoform  may  be 
recognised.  If  the  precipitate  is  amorphous  it  may  be  dissolved  in 
ether  (free  from  alcohol),  which  is  allowed  to  evaporate  on  a  slide. 
when  crystals  may  be  obtained. 

Determination  of  the  Freezing-point  of  Urine. — Study  Beckmann's 
apparatus  shown  in  Fig.  153,  p.  399.  Note  the  large  thermometer  1) 
graduated  in  hundredths  of  a  degree  centigrade.  It  is  inserted 
through  a  rubber  cork  into  the  inner  thick  test-tube  A.  A  platinum 
wire  F,  bent  at  the  lower  end  into  a  circle  or  a  spiral,  which  passes 
easily  up  and  down  between  the  bulb  of  the  thermometer  and  the 
tube,  serves  to  stir  the  urine.  The  thermometer  must  be  so  supported 
by  the  rubber  cork  that  the  bulb  is  in  the  axis  of  the  tube  and  a 
centimetre  or  two  from  the  bottom  of  it.  The  side-piece  E  on  the 
tube  A  is  not  absolutely  necessary,  but  it  is  convenient  for  '  inocu- 
lating '  the  urine  with  a  crystal  of  ice  at  the  proper  time.  A  passes 
through  a  rubber  cork  into  a  shorter  and  wider  outer  glass  tube  B. 
The  space  between  A  and  B  serves  as  a  badly  conducting  mantle, 
which  prevents  too  rapid  cooling  of  the  contents  of  A.  B  passes 
through  a  hole  in  the  metal  or  wooden  cover  of  a  strong  glass  jar  C, 
which  contains  the  freezing  mixture.  B  should  fit  the  hole  so  tightly 
that  it  docs  not  bob  up  out  of  the  mixture  when  A  is  removed.  In 
C  is  a  stirrer,  G,  of  strong  copper  wire,  the  end  of  which  passes  through 
the  lid.     This  serves  to  stir  up  the  freezing  mixture  from  time  to  time. 

Pulverize  some  ice  by  pounding  it  in  a  strong  wooden  box  with 
a  heavy  piece  of  wood.  Take  the  inner  tube  with  the  thermometer 
out  of  the  apparatus.  It  is  convenient  to  take  the  thermometer 
out  of  the  tube,  and  to  hang  it  up  carefully  on  a  stand  by  means  of 
a  fine  flexible  copper  wire  passing  through  the  eye.  The  rubber  cork 
can  be  taken  out  with  the  thermometer,  and  the  platinum  wire  also, 
the  bent  free  end  of  the  latter  supporting  it  in  the  cork,  or  it  may  be 
fastened  temporarily  to  the  thermometer  stem  by  a  small  rubber 
band,  which  is  slid  "up  over  the  cork  when  the  Thermometer  is  re- 
inserted. Tube  A  can  be  set  temporarily  in  a  specially  heavy  test- 
tube  rack.  Remove  the  lid  of  C,  and  with  it  tube  B.  Now  put  ice 
and  salt  alternately  into  C  until  it  is  nearly  full,  mixing  them  up  well. 
Add  some  cold  water  from  the  tap  till  the  stirrer  G  can  move  freely 


PRACTICAL  EXERCISES 

up  and  down  in  the  mixture.  For  very  exact  work  the  temperature 
of  the  breezing  mixture  musl  n<>i  be  more  than  a  few  degrees  below 
the  freezing-point  of  the  liquid  which  is  being  examined.  Put  on  the 
lid,  and  immerse  lube  B.  Into  A,  which  must  be  perfectly  clean, 
put  enough  pure  distilled  water  to  fully  cover  the  bulb  of  the  thermo- 
meter, and  introduce  the  latter.  For  ordinary  purposes  distilled 
water  previously  boiled  to  expel  the  carbon  dioxide,  and  then  cooled 
in  a  stoppered  flask,  is  sufficiently  pure.  Immerse  A  directlv 
in  the  freezing  mixture  through  the  hole  by  which  G  comes  out,  or 
through  a  separate  hole  (not  shown  in  the  figure)  till  some  ice  lias 
lorn  ied  in  t  he  water.  lake  A  out  of  the  mixture,  wipe  it  with  a,  cloth, 
and  hold  the  lower  part  of  it  in  the  hand  till  nearly  the  whole  of  the 
ice  has  melted.  If  there  is  a  cake  of  ice  at  the  bottom,  see  that  it  is 
displaced  by  the  platinum  stirrer.  A  trace  of  ice  being  still  left 
floating  in  the  water,  place  A  in  B,  and  allow  the  temperature  to  fall 
to  a  few  tenths  of  a  degree  below  the  freezing-point  you  expect  to 
get,  as  determined  by  a  previous  rough  experiment.  The  freezing 
mixture  is  stirred  up  occasionally.  The  meniscus  of  the  thermometer 
is  to  be  carefully  followed,  as  it  goes  on  falling,  by  means  of  a  weak 
hand  lens.  Now  stir  the  water  in  A  briskly.  Suddenly  it  will  be 
seen  that  the  mercury  begins  to  rise.  Keep  stirring  with  the 
platinum  wire,  and  read  off  the  maximum  height  of  the  mercury, 
at  which  it  is  stationary  for  some  time.  The  temperature  can  be 
estimated  between  the  graduations  to  thousandths  of  a  degree. 
Take  out  A,  and  observe  the  fine  ice  crystals  in  the  water.  Heat 
A  in  the  hand  as  before  till  nearly  all  the  ice  has  disappeared  ;  then 
replace  A  in  B,  and  make  another  freezing-point  determination.  A 
third  one  may  also  be  made,  and  the  mean  of  the  three  readings  taken. 

Take  out  the  thermometer,  and  dry  it  and  the  platinum  wire  with 
clean  filter-paper,  or  dip  them  in  some  of  the  urine,  which  is  then 
thrown  away.  Dry  A  or  rinse  it  with  urine.  Then  make  a  deter- 
mination of  the  freezing-point  of  the  urine  in  the  same  way  as  was 
done  with  the  water.  The  freezing-point  of  the  urine  will  lie  much 
lower  on  the  scale. 

Instead  of  freezing  the  liquid  first  and  then  leaving  a  little  ice  in  it 
when  A  is  placed  in  B,  A  may  be  put  into  B  before  any  ice  has  formed. 
Cooling  is  then  allowed  to  go  on  with  gentle  stirring  to  a  few  tenths 
of  a  degree  below  the  anticipated  freezing-point.  A  small  crystal  of 
clean  dry  ice  is  then  introduced  through  the  side-piece  on  a  clean 
splinter  of  wood  or  the  loop  of  a  cooled  platinum  wire,  the  end  of 
which  passes  through  a  piece  of  cork,  by  which  it  is  held  to  prevent 
conduction  of  heat.  The  platinum  stirrer  can  be  raised  to  receive 
the  crystal.  The  liquid  is  now  vigorously  stirred  ;  freezing  occurs, 
and  the  observation  is  made  as  before. 

Instead  of  the  above  method,  the  liquid  may  first  be  cooled  directly 
in  the  freezing  mixture,  but  not  so  much  that  ice  forms.  A  is  then 
put  in  B,  and  cooling  allowed  to  go  on  while  it  is  being  stirred. 
When  it  has  been  undercooled  to  a  certain  extent — i.e.,  cooled  below 
its  freezing-point — the  vigour  of  the  stirring  is  increased.  Ice  forms 
suddenly,  as  before,  and  the  temperature  rises  to  the  freezing-point. 
With  urine  this  method  is  sufficiently  satisfactory,  but  it  is  not 
usually  easy  to  get  freezing  of  the  distilled  water  till  the  under- 
cooling is  considerable,  and  it  has  been  shown  that  this  introduces 
some  error. 

Suppose  the  freezing-point  of  the  distilled  water  on  the  scale  of 
the  thermometer  was  52450  and  that  of  the  urine  36250,  the  value 


494  A   MAX  UAL  OF  PHYSIOLOGY 

of  A  for  the  urine  is  i620°.  Since  for  most  purposes  it  is  sufficient 
to  fix  the  second  decimal  point,  much  smaller  and  less  expensive 
thermometers  than  the  ordinary  Bcckmann  may  be  employed. 

In  the  same  way  the  freezing-point  of  blood-serum  (or  blood),  bile, 
and  other  physiological  liquids  can  be  determined. 

Systematic  Examination  of  Urine. — In  examining  urine,  it  is  con- 
venient to  adopt  a  regular  plan,  so  as  to  avoid  the  risk  of  overlooking 
anything  oi  importance.  The  following  simple  scheme  may  sen  i 
an  example  :  but  no  routine  should  be  slavishly  followed,  the  object 
being  to  get  at  the  important  facts  with  the  minimum  of  labour. 
More  extensive  information  must  be  sought  in  the  treatises  on 
examination  of  the  urine  for  clinical  purposes. 

i.  Anything  peculiar  in  colour  or  smell  ?      If  the  colour  suggests 
blood,  examine  with  spectroscope,  haemin  test,  guaiacum  test  (pp 
68,  71)  ;  if  it  suggests  bile,  test   tor  bile-pigments  by  (imelin's  test 
(p.  4^1),  and  for  bile-salts  by  Pettenkofer's test    p.  430)  and  by  Hay's 
test  "(pp.  430,  491). 

2.  Reaction. 

3.  Sediment  or  not  ?  Sediment  may  be  procured  by  letting  the 
urine  stand  in  a  conical  glass,  or  in  a  few  minutes  by  the  centrifuge. 
If  the  appearance  of  the  sediment  suggests  anything  more  than  a 
little  mucus,  examine  with  the  microscope.  The  sediment  may 
contain  organized  or  unorganized  deposits. 

Organized  Sediments. — (a)  Red  blood-corpuscles  (considerably 
altered  if  they  have  come  from  the  upper  part  of  the  urinary  tract). 

(b)  Leucocytes.  A  few  are  present  in  health.  A  large  number 
indicates  pus.  When  pus  is  present  the  sediment  may  be  white  to 
the  naked  eye. 

(c)  Epithelium  from  the  bladder,  ureters,  pelvis  of  the  kidney  or 
the  renal  tubules.  A  few  squamous  epithelial  cells  from  the  urethra 
are  always  present  in  normal  urine. 

id)  Tube  casts. 

(e)  Spermatozoa  (occasional). 

(/)  Bacteria. 

(g)  Parasites  (rare). 

(h)  Portions  of  tumours  (rare). 

Unorganized  Sediments. 

IN    ACID    URINE.  IX    ALKALIXK    URINE. 

Uric  Acid. — Crystals  coloured  Triple      Phosphate.    —   Clear, 

brownish  -  yellow    with    urinary  colourless,  coffin-lid  or  knife-rest 

pigment.     Various  shapes,  espe'-  crystals.     Also  deposited  in  the 

dally  oval  'whetstones,'  rhom-  form  of  feathery  stars  (Fig.  162). 
bic  tables,   and  elongated   crys-  Calcium    Hydrogen    Phosphate 

tals,  often  in  bundles  (Fig.  160).  ('  stellar  '   phosphate),   CaHP04. 

Urates. — Usuallv    amorphous.  — Crystals    often    wedge-shaped 

in    the    form    of    fine    granules.  and  arranged  in  rosettes.     May 

often   tinged   with   urinary   pig-  also  occur  in  a  dumb-bell  form, 

ment,       sometimes       brick-red.  (A  phosphate  of  calcium  is  also* 

Soluble  on  heating.    On  addition  occasionally  seen  in  weakly  acid 

of   acids    (including    acetic   acid)  urine.)      (Fig.  164,  p.  439.) 
they     dissolve     and     uric     acid  Calcium  Phosphate,  Ca^PO^o. 

crystals   appear   in   their   place.  — Amorphous. 
Acid    urate    of    sodium    and    of  Magnesium    Phosphate. — Long 


PRACTICAL  EXERCISES  495 

Unorganized  Sediments  (continued)  — 

IN    ACID    URINE.  IN    ALKALINE    URINE. 

ammonium     occasionally     found  rhombic  tablets,   which  are  dis- 

in  the  crystalline  form  (rosettes  solved   at    the  edges  by  ammo 

of  needles).  nium  carbonate  solution,  unlike 

Calcium  Oxalate.     Octahedral,  triple  phosphate.     All  the  above 

'envelope'    crystals,    not  are  soluble  in  acetic  acid^withoul 

coloured.      Insoluble     in      acetic  elk  rvescence. 
acid.     Soluble     in     hydrochloric  Calcium      Carbonate.  —  Small 

acid  (Fig.  161,  p.  438).  spherical    or    dumb-bell-shaped 

Cystin.  —  Hexagonal      plates.  bodies  soluble  in  acetic  acid  with 

Rare  (Fig.  [63,  p.  439).  effervescence. 

I  eucin     din/     Tyrosin      (Figs.  Ammonium         Urate.  —  Dark 

169,    170,    p.   452).-  -Rare.      Also  balls,  often  covered  with  spines. 

found  in  alkaline  urine. but  rarely.  Soluble  in  acetic  or  hydrochloric 

Triple  Phosphate. — Sometimes  acid,  with  formation  of  uric  acid 
found  in  weakly  acid  urine.             I   crystals  (Fig.  165,  p.  439). 

4.  Specific  gravity. 

5.  Quantity  of  urine  in  twenty-four  hours.  If  the  quantity  is 
abnormally  large  and  the  specific  gravity  high,  test  for  sugar. 

6.  Inorganic  constituents  not  generally  of  clinical  importance,  but 
in  special  diseases  they  should  be  examined — e.g.,  chlorides  in 
pneumonia. 

7.  Normal  organic  constituents.  Sometimes  quantitative  estima- 
tion of  urea  or  total  nitrogen  in  fever,  and  in  diabetes  and  Bright's 
disease. 

8.  Chemical  examination  for  abnormal  organic  constituents, 
especially  albumin  and  sugar. 

Albumin. — (1)  Heat  some  of  the  urine  in  a  test-tube  to  boiling.  A 
precipitate  insoluble  on  addition  of  a  few  drops  of  acetic  acid  consists 
of  coagulable  protein.  A  precipitate  soluble  in  acetic  acid  consists 
of  earthy  phosphates. 

(2)  Heller's  test.  Put  some  strong  nitric  acid  in  a  test-tube  and 
run  on  to  it  some  urine.     A  white  ring  indicates  protein. 

A  quantitative  estimation  may  be  made  by  the  method  of  Roberts 
and  Stolnikow  or  Esbach  (p.  487). 

Sugar. — (1)  Trommer's  test.  (Fehling's  solution  may  be  used.) 
If  the  result  is  indecisive  : 

(2)  Phenyl-hydrazine  test  (p.  488). 

(3)  In  case  of  doubt  confirm  by  yeast  test. 

A  quantitative  estimation  may  be  made  with  Fehling's  solution  or 
the  polarimeter. 


CHAPTER  VII 

METABOLISM,  NUTRITION  AND  DIETETICS 

We  return  now  to  the  products  of  digestion  as  they  are  absorbed 
from  the  alimentary  canal,  and,  still  assuming  a  typical  diet 
containing  proteins,  carbo-hydrates  and  fats,  we  have  to  ask, 
What  is  the  fate  of  each  of  these  classes  of  proximate  principles 
in  the  body  ?  what  does  each  contribute  to  the  ensemble  of  vital 
activity  ?  It  will  be  best,  rirst  of  all,  to  give  to  these  question^ 
what  roughly  qualitative  answer  is  possible,  then  to  look  at 
metabolism  in  its  quantitative  relations,  and  lastly  to  focus 
our  information  upon  some  of  the  practical  problems  of  dietetics. 
i.  Metabolism  of  Proteins. — The  two  chief  proteins  of  the 
blood-plasma,  serum-globulin  and  serum-albumin,  must,  as  has 
been  already  pointed  out,  be  recruited  from  proteins  absorbed 
from  the  intestine  and  for  the  most  part,  at  any  rate,  profoundly 
altered  in  its  lumen  and  in  their  passage  through  the  epithelium 
which  lines  it.  The  physiological  reasons  for  this  alteration  are 
in  a  measure  known,  and  have  already  been  alluded  to  in  con- 
nection with  the  digestion  of  proteins.  No  doubt  the  far-reaching 
decomposition  of  the  protein  molecule  ma}'  to  some  extent 
facilitate  the  absorption  of  protein  food.  No  doubt  also  it  is 
imperative  that  such  slightly  hydrolysed  products  as  peptone, 
and  particularly  proteose,  should  not  appear  in  quantity  in  the 
blood,  for  when  injected  they  cause  profound  changes  in  that 
liquid,  one  expression  of  which  is  the  loss  of  its  power  of  coagula- 
tion, and  are  rapidly  excreted  by  the  kidneys,  or  separated  out 
into  the  lymph.  But  the  passage  of  the  food  from  the  stomach 
is  so  gradual  an  affair,  the  quantity  of  digesting  protein  present 
at  one  time  in  any  loop  of  intestine  is  so  small,  and  the  rush  of 
blood  which  irrigates  the  active  mucosa  is  so  large,  that  the  con- 
centration of  peptone  or  proteose  necessary  to  produce  injurious 
effects  could  hardly  in  any  case  be  realized.  Again,  there  is  no 
i-vidence  that  the  simpler  decomposition  products  of  further 
hydrolysis  are  not  in  equal  concentration  as  poisonous  as  proteose 
and  peptone. 

496 


ME  TABOLISM,  NUTRITION  AND  DIETE  I  U  497 

Apart  from  any  influence  wliich  it  may  have  in  favouring 
absorption,  the  complete  shattering  of  the  protein  molecule  lias 
.1  double  significance.  In  the  first  place,  as  already  pointed  out, 
tlic  food-proteins  cannot  be  used  directly  in  the  upbuilding  and 
repair  of  the  protoplasm  (p.  419),  since  the  tissue-proteins  differ 
from  them  and  from  each  other  in  the  amount  and  nature  of  the 
amino-acids and  other  groups  in  their  molecule  (p.  2).  Secondly, 
under  ordinary  dietetic  conditions  a  surplus  of  nitrogen  in  the 
protein  food  has  to  be  got  rid  of  by  being  converted  into  urea 
without  being  built  up  into  the  tissue  substance.  Here  we  come 
upon  the  fundamental  fact  that  the  protein  katabolism  is  not  a 
single  uniform  process.  Two  forms  may  be  distinguished  which 
are  essentiallv  independent  in  course  and  character.  One  kind 
varies  extremelv  in  its  quantitative  relations,  according  to  the 
amount  of  protein  in  the  food.  Its  chief  end-products  are  urea, 
representing  the  nitrogen,  and  inorganic  sulphates,  representing 
the  sulphur  of  the  proteins.  Since  this  form  of  katabolism,  as  we 
shall  see  directly,  is  not  essentially  connected  with  the  life  and 
nutrition  of  the  living  substance,  it  is  termed  exogenous.  The 
other  varietv  is  practically  constant  in  amount  for  one  and  the 
same  individual,  and  independent  of  the  quantity  of  protein  in 
the  food.  Its  characteristic  end-products  are  kreatinin  and 
neutral  sulphur.  This  form  of  protein  katabolism  is  essentially 
an  expression  of  the  waste  of  the  living  substance  itself,  and  is 
therefore  spoken  of  as  endogenous. 

Some  have  supposed  that  the  intestinal  mucosa  has  as  one  of  its 
special  functions  the  resynthesis  of  a  great  part  of  the  digestive 
decomposition  products  into  the  proteins  of  the  blood-plasma. 
If  this  is  the  case,  these  proteins  must  be  again  decomposed  in 
the  cells  of  the  various  tissues  in  order  that  the  "  building- 
stones  "  may  be  recombined  to  form  the  tissue-proteins.  For 
the  proteins  of  the  organs  are  not  the  same  as  those  of  the  blood, 
and  the  proteins  of  different  organs  differ  characteristically  from 
each  other.  The  significance  of  the  synthetic  function  of  the 
intestinal  wall  would  then  lie  in  this :  that  from  the  varying 
mixture  of  amino-acids,  etc.,  derived  from  the  food-proteins  an 
always  uniform  and  suitable  protein  mixture  (the  blood-proteins) 
is  fabricated  for  the  feeding  of  the  tissues.  An  alternative 
assumption,  and  superficially  at  least  a  simpler  one,  is  that  no 
more  extensive  synthesis  of  proteins  occurs  in  the  wall  of  the 
alimentary  canal  than  is  necessary  for  the  needs  of  the  tissues 
composing  it,  and  that  the  decomposition  products  of  the 
proteins  are  mainly  absorbed  as  such,  and  pass  in  the  blood  to 
the  tissues  for  which  they  are  destined.  If  this  is  the  case,  the 
blood-proteins  can  no  longer  be  looked  upon  as  representing 
the  main  current  of  protein  supply  for  the  organs,  but  rather  the 

32 


498 


/   MANUAL  OF  PHYSIOLOGY 


store  "i  protein  material  proper  to  the  circulating  tissue  blood 
itself,  and  which  confers  on  it  certain  chemical  and  physico- 
chemical  properties  (e.g.,  the  due  degree  <»]  visensity)  necessary 
for  its  function.  Slowly  accumulated,  under  ordinan  erudition-. 
and  slowly  consumed,  this  protein  store  may,  of  course,  be  at  the; 
disposal  of  the  organs  in  an  emergency— for  instance,  in  starva- 
tion— or  may  be  rapidly  recruited  from  the  organ-proteins,  as 
after  haemorrhage,  just  as  in  prolonged  hunger  the  proteins  of 
skeletal  muscle  may  be  utilized  to  feed  the  heart.  It  is  imp<  >^si  ble, 
with  our  present  knowledge,  to  decide  definitely  between  these 
hypotheses.  There  is  some  evidence  that  serum-albumin  is 
more  directly  related  to  the  proteins  of  the  food  than  serum- 
globulin.  And  it  is  said  that  during  starvation  the  albumin  is 
relatively  diminished,  and  the  globulin  relatively  increased. 
It  is,  of  course,  not  at  all  improbable  that  the  plasma-proteins 
have  a  double  source — organ-proteins  on  the  one  hand,  food- 
proteins  on  the  other.  That  the  plasma-protein  mixture  main- 
tains a  very  constant  composition  in  the  face  of  wide  variations  in 
the  composition  of  the  food-proteins  is  indicated  by  the  following 
experiment  : 

A  horse  fed  mainly  on  hay  and  oats  was  bled  to  the  amount  of 
6  litres,  and  in  the  total  protein  of  the  serum  the  content  of  tyrosin 
and  glutaminic  acid  was  determined.  In  order  to  eliminate  the 
influence  of  remains  of  the  food  in  the  digestive  canal,  nothing  was 
given  to  the  animal  for  a  week.  Then  6  litres  of  blood  were  again 
removed,  and  the  tyrosin  and  glutaminic  acid  in  the  serum-protein 
again  estimated.  The  horse  was  now  fed  with  gliadin  obtained 
from  flour,  a  protein  which  contains  36-5  per  cent,  glutaminic  acid 
and  2*37  per  cent,  tyrosin — that  is,  about  the  same  amount  of 
tyrosin  as  the  serum-protein,  but  about  four  times  as  much  gluta- 
minic acid.  The  serum-protein  was  again  analyzed  for  the  two 
amino-acids  after  this  diet.  The  results  of  one  experiment  are 
shown  in  the  table  : 


Normal. 

2'43 
8-85 

After  8  Days' 
Hunger. 

After  Feeding        After  Feeding 
with  1,500          again  with  1,500 
Grammes                 Grammes 
1  rliadin.                  Gliadin. 

Tyrosin 
Glutaminic  acid- 

2"6o 
8-20 

2"24                       252 

7-88                 8-25 

No  increase  in  the  glutaminic  acid  content  of  the  serum-protein 
occurred,  although,  owing  to  the  loss  of  blood,  much  new  serum- 
protein  must  have  been  formed.  If  the  amino-acids  of  the  gliadin 
were  used  without  change  to  build  up  the  new  serum-protein, 
three-quarters  of  the  glutaminic  acid  must  have  been  superfluous, 
and  the  nitrogen  of  this  portion  may  have  been  straightway  changed 
into  urea  and  excreted.  But  the  possibility  that  one  amino-acid 
may  be  changed  into  another  in  the  body  cannot  be  excluded, 
although  there  is  no  evidence  that  it  occurs  (Abderhalden). 


METABOLISM,  M   TRITION  AND  DIETETICS 

Living  and  Dead  Proteins. — Carried  to  the  tissues,  the  decom- 
I  'Mtion^roducts  of  the  food-proteins,  or  the  regenerated  proteins 
"l  the  plasma,  which  in  ordinary  language  are  still  to  be  regarded 
as  dead  material,  arc  built  up  into  the  living  protoplasm,  at  any 
rate  to  the  extent  necessary  to  make  good  its  waste.  In  this  form 
they  sojourn  for  a  time  within  the  cells,  and  then  they  become 
dead  material  again.  The  nature  of  this  tremendous  transforma- 
tion has,  of  course,  been  the  subject  of  speculation,  but  the  truth  is 
that  we  do  not  understand  wherein  the  difference  between  a  living 
and  a  dead  cell,  between  a  living  and  a  dead  particle  in  one  and  the 
same  cell,  really  consists.  All  we  know  is  that  now  and  again  a 
livmg  protein  molecule  in  the  whirl  of  flying  atoms  which  we  call 
a  muscle-fibre,  or  a  gland-cell,  or  a  nerve-cell,  must  fall  to  pieces. 
Mow  and  again  a  molecule  of  protein,  hitherto  dead,  or  a  molecule 
of  a  particular  amino-acid,  or  perhaps  a  polypeptid  group  inter- 
mediate in  complexity  between  the  simple  amino-acid  and  the  pro- 
tein, coming  within  the  grasp  of  the  molecular  forces  of  the  living 
substance,  is  caught  up  by  it,  takes  on  its  peculiar  motions,  acquires 
its  special  powers,  and  is,  as  we  phrase  it,  made  alive.  Each,  cell 
has  the  power  of  selecting  and,  if  necessary,  further  decomposing 
or  further  synthesizing  the  protein  materials  offered  to  it  ;  so  that  a 
particle  of  serum-albumin  or  a  mixture  of  amino-acids  may  chance  to 
take  its  place  in  a  liver-cell  and  help  to  form  bile,  while  an  exactly 
similar  particle  or  mixture  may  furnish  constituents  to  an  endothelial 
scale  of  a  capillary  and  assist  in  forming  lymph,  or  to  a  muscular 
fibre  of  the  heart  and  help  to  drive  on  the  blood,  or  to  a  sperma- 
tozoon and  aid  in  transferring  the  pecuharities  of  the  father  to  the 
offspring.  And  just  as  a  tomb  and  a  lighthouse,  a  palace  and  a 
church,  may  be,  and  have  been,  built  with  the  same  kind,  of  material, 
or  even  in  succession  with  the  very  same  stones,  so  every  organ 
builds  up  its  own  characteristic  structure  from  the  common  quarry 
of  the  blood. 

It  is  not  any  difference  in  the  kind  of  protein  offered  them  which 
determines  the  difference  in  structure  and  action  between  one 
organ  and  another.  In  the  case  of  the  more  highly  developed 
tissues  at  least,  no  mere  change  of  food  will  radically  alter  structure. 
A  cell  may  be  fed  with  different  kinds  of  food,  it  may  be  over-fed, 
it  may  be  ill-fed,  it  may  be  starved  ;  but  its  essential  peculiarities 
remain  as  long  as  it  continues  to  five.  Its  organization  dominates 
its  nutrition  and  function. 

The  speculation  of  Pfluger,  that  the  nitrogen  of  living  protein 
exists  in  the  form  of  cyanogen  radicals,  whilst  in  dead  protein  it  is  in 
the  form  of  amides,  and  that  the  cause  of  the  characteristic  instability 
of  the  living  substance — its  prodigious  power  of  dissociation  and 
reconstruction — is  the  great  intramolecular  movement  of  the  atoms 
of  the  cyanogen  radicals,  is  interesting  and  ingenious,  but  it  remains, 
and  is  likely  to  remain,  a  speculation.  And  the  same  is  true  of  the 
suggestion  of  Loew  and  Bokorny,  that  the  endowments  of  living 
protoplasm  depend  on  the  presence  of  the  unstable  aldehyde  group 
H  —  C=(J.  Xor  do  the  known  differences  of  chemical  composition 
in  dead  organs  give  any  insight  into  the  pecuharities  of  organization 
and  function  which  mark  off  one  living  tissue  from  another.  In 
any  case,  the  living  protein  molecule,  whatever  function  it  may 
have  been  fulfilling  in  the  organized  elements  of  the  body,  has 
certainly  a  much  greater  tendency  to  fall  to  pieces  than  the  dead 
protein  molecule.     And  it  falls  to  pieces  in  a  fairly  definite  way, 

32—2 


5oo  A   MANUAL  OF  /'IIYSI0L0<,\ 

tin  ultimate  products,  under  the  influence  <>i  oxygen,  being  carbon 
dioxide,  water,  and  comparatively  simple  nitrogen-containing  sub- 
stances, which  after  further  changes  appear  in  the  urine  as  urea, 
kreatinin,  uric  acid,  and  other  bodies.  We  shall  see  later  on  that 
a  ^reat  part  of  the  urea  excreted  does  not  arise  in  the  decomposition 
of  living  protein  or  protoplasm,  but  is  the  form  in  which  '  surplus  ' 
nitrogen  is  eliminated  in  the  preparation  of  the  food-protein  for 
assimilation  by  the  tissues.  We  have  no  definite  information  as 
to  the  production  of  water  from  the  hydrogen  of  the  tissues,  except 
what  can  be  theoretically  deduced  from  the  statistics  of  nutrition 
(p.  540).  A  few  words  will  be  said  a  little  farther  on  about  the 
production  of  carbon  dioxide  from  proteins  ;  we  have  now  to  con- 
sider the  seat  and  manner  of  formation  of  the  nitrogenous  meta- 
bolites. And  since  in  man  and  the  other  mammals  urea  contains, 
under  ordinary  conditions,  by  far  the  greater  part  of  the  excreted 
nitrogen,  it  will  be  well  to  take  it  first. 

Formation  of  Urea. — The  starting-point  of  all  inquiries  into 
the  formation  of  urea  is  the  fact  that  it  occurs  in  the  blood  in 
small  amount  (4  to  6  parts  per  10,000  in  man ;  3  to  15  parts  per 
10,000  in  the  dog),  the  largest  quantity  being  found  when  the  food 
contains  most  protein  and  at  the  height  of  digestion,  the  smallest 
quantity  in  hunger  (Schondorfr).  Evidently,  then,  some,  at  least, 
of  the  urea  excreted  in  the  urine  may  be  simply  separated  by  Hie 
kidney  from  the  blood  ;  and  analysis  shows  that  this  is  actually 
the  case,  for  the  blood  of  the  renal  vein  is  poorer  in  urea  than  that 
of  the  renal  artery,  containing  only  one-third  to  one-half  as  much. 
If  we  knew  the  exact  quantity  of  blood  passing  through  the 
kidneys  of  an  animal  in  twenty-four  hours,  and  the  average 
difference  in  the  percentage  of  urea  in  the  blood  coming  to  and 
leaving  them,  we  should  at  once  be  able  to  decide  whether  the 
whole  of  the  urea  in  the  urine  reaches  the  kidneys  ready  made,  or 
whether  a  portion  of  it  is  formed  by  the  renal  tissue.  Although 
data  of  this  kind  are  as  yet  inexact  and  incomplete,  it  is  not 
difficult  to  see  that  all,  or  most  of,  the  urea  may  be  simply 
separated  by  the  kidney. 

If  we  take  the  weight  of  the  kidneys  of  a  dog  of  35  kilos  at 
160  grammes  („{r,th  of  the  body- weight  is  the  mean  result  of  a  great 
number  of  observations  in  man),  and  the  average  quantity  of  blood 
in  them  at  rather  less  than  one-fourth  of  their  weight,  or  35  grammes, 
and  consider  that  this  quantity  of  blood  passes  through  them  in  the 
average  time  required  to  complete  the  eirculation  from  renal  artery 
to  renal  vein,  or,  say,  ten  seconds,  we  get  about  300  kilos  of  blood  as 
the  flow  through  the  kidneys  in  twenty-four  hours.  Even  at  03  per 
1,000,  the  urea  in  300  kilos  of  blood  would  amount  to  go  grammes. 
Now,  Voit  found  that  a  dog  of  35  kilos  body- weight,  on  the  minimum 
protein  diet  (450  to  500  grammes  of  lean  meat  per  day)  which 
sufficed  to  maintain  its  weight,  excreted  35  to  40  grammes  of  urea 
in  the  twenty-four  hours.  If,  then,  the  renal  epithelium  separated 
somewhat  less  than  half  of  the  90  grammes  urea  offered  to  it  in  the 
circulating  blood,  the  whole  excretion  in  the  urine  could  be  accounted 
for,  and  the  blood  of  the  renal  vein  would  still  contain  more  than 


METABOLISM,    NUTRITION  AND  DIETETICS  501 

half  as  much  urea  as  that  d  the  renal  artery.  So  that  the  whole 
of  tho  urea  in  the  urine  may  be  simply  separated  by  the  kidney 
from  the  ready-made  urea  of  the  blood. 

Another  line  of  evidence  leads  to  the  same  conclusion  :  that 
the  kidney  is,  at  all  events,  not  an  important  seat  of  urea- 
formation.  When  both  renal  arteries  are  tied,  or  both  kidneys 
extirpated,  in  a  dog,  urea  accumulates  in  the  blood  and  tissues  ; 
and,  upon  the  whole,  as  much  urea  is  formed  during  the  first 
twenty-four  hours  of  the  short  period  of  life  which  remains  to 
the  animal  as  would  under  normal  circumstances  have  been 
excreted  in  the  urine. 

Where,  then,  is  urea  chiefly  formed  ?  If  the  main  source  of 
urea  were  the  decomposition  of  tissue-protein,  we  should  naturally 
look  first  to  the  muscles,  which  contain  three-fourths  of  the 
proteins  of  the  body  ;  but  we  should  look  there  in  vain  for  any 
great  store  of  urea — only  a  trace  is  normally  present.  The 
liver  contains  a  relatively  large  amount,  and  there  is  very  strong 
evidence  that  it  is  the  manufactory  in  which  the  greater  part  of 
the  nitrogenous  relics  of  broken-down  proteins  reach  the  final 
stage  of  urea.     This  evidence  may  be  summed  up  as  follows  : 

(1)  An  excised  '  surviving  '  liver  forms  urea  from  ammonium 
carbonate  mixed  with  the  blood  passed  through  its  vessels, 
while  no  urea  is  formed  when  blood  containing  ammonium  car- 
bonate is  sent  through  the  kidney  or  through  muscles.  Other 
salts  of  ammonium,  such  as  the  lactate,  the  formate,  and  the 
carbamate,  undergo  a  like  transformation  in  the  liver.  It  is 
difficult,  in  the  light  of  this  experiment,  to  resist  the  conclusion 
that  the  increase  in  the  excretion  of  urea  in  man,  when  salts  of 
ammonia  are  taken  by  the  mouth,  is  due  to  a  similar  action  of 
the  hepatic  cells.  •    ' 

(2)  If  blood  from  a  dog  killed  during  digestion  is  perfused 
through  an  excised  liver,  some  urea  is  formed,  which  cannot 
be  simply  washed  out  of  the  liver-cells,  because  when  the  blood 
of  a  fasting  animal  is  treated  in  the  same  way  there  is  no  apparent 
formation  of  urea  (v.  Schroeder).  This  suggests  that  during 
digestion  certain  substances  which  the  liver  is  capable  of  changing 
into  urea  enter  the  blood  in  such  amount  that  a  surplus  remains 
for  a  time  unaltered.  These  substances  may  come  directly  from 
the  intestine  ;  or  they  may  be  products  of  general  metabolism, 
which  is  increased  while  digestion  is  going  on  ;  or  they  may 
arise  both  in  the  intestine  and  in  the  tissues.  Leucin — which, 
as  we  have  seen,  is  constantly,  or,  at  least,  very  frequently, 
present  in  the  intestine  during  digestion — can  certainly  be 
changed  into  urea  in  the  body.  So  can  other  amino-acids  of 
the  fatty  series,  like  glycocoll  or  glycin,  and  aspartic  acid,  and 
it  has  been  shown  by  perfusion  experiments  that  this  change 


502  I    U  /  vr  !/    OF    PHYSIOLOGY 

lakes  place  in  the  liver.     Further,  the  blood  of  the  portal  vein 

during  digestion  contains  several  times  as  much  ammonia  a?  the 
arterial  blood,  and  the  excess  disappears  in  the  liver. 

(3)  I'm  acid— which  in  birds  is  the  chief  end-product  of 
protein  metabolism,  as  urea  is  in  mammals     is  formed  in  the 

se  largely,  and  almost  exclusively,  in  the  liver.  This  has 
been  most  clearly  shown  by  the  experiments  of  Minkowski,  who 
took  advantage  of  the  communication  between  the  portal  and 
renal-portal  veins  (p.  356)  to  extirpate  the  liver  in  geese.  When 
the  portal  is  ligatured  the  blood  from  the  alimentary  canal  can 
still  pass  by  the  roundabout  road  of  the  kidney  to  the  inferior 
cava,  and  the  animals  survive  for  six  to  twenty  hours.  While 
in  the  normal  goose  50  to  60  per  cent,  of  the  total  nitrogen  is 
eliminated  as  uric  acid  in  the  urine,  and  only  9  to  18  per  cent, 
as  ammonia,  in  the  operated  goose  uric  acid  represents  only 
3  to  6  per  cent,  of  the  total  nitrogen,  and  ammonia  50  to  60  per 
cent.  A  quantity  of  lactic  acid  equivalent  to  the  ammonia 
appears  in  the  urine  of  the  operated  animal,  none  at  all  in  the 
urine  of  the  normal  bird.  The  small  amount  of  urea  in  the 
normal  urine  of  the  goose  is  not  affected  by  extirpation  of  the 
liver.  And  while  urea,  when  injected  into  the  blood,  is  in  the 
normal  goose  excreted  as  uric  acid,  it  is  in  the  animal  that  has 
lost  its  liver  eliminated  in  the  urine  unchanged. 

(4)  After  removal  of  the  liver  in  frogs,  or  in  dogs  which  have 
survived  the  previous  connection  of  the  portal  vein  with  the 
inferior  vena  cava  by  an  Eck's  fistula  (p.  356),  the  quantity  of 
urea  excreted  is  markedly  diminished,  and  the  ammonium  salts 
in  the  urine  are  increased.  When  the  Eck's  fistula  is  established 
and  the  portal  vein  tied,  without  any  further  interference  with 
the  hepatic  circulation,  the  amount  of  urea  in  the  urine  is  not 
lessened  to  nearlv  the  same  extent,  evidently  because  the  sub- 
stances from  which  urea  is  formed  still,  for  the  most  part,  gain 
access  to  the  liver  through  the  hepatic  artery  and  by  means  of 
the  back-flow  which  is  known  to  take  place  through  the  hepatic 
vein.  Yet  while  in  normal  dogs  the  proportion  of  ammonia  to 
urea  in  the  urine  is  only  1  :  22  to  1  :  73,  in  dogs  with  Eck's 
fistula  it  rises  to  1 :  8  to  X  :  33.  If  the  animals  are  kept  on  a 
diet  poor  in  proteins,  no  symptoms  may  develop  for  a  considerable 
time.  But  if  much  protein  is  given,  characteristic  symptoms. 
including  convulsions,  always  appear.  These  may  be  produced 
by  the  saturation  of  the  organism  with  ammonia  compounds, 
which  are  formed  from  the  proteins  as  in  the  normal  animal, 
but  which  the  liver,  with  its  circulation  crippled,  is  unable  to 
cope  with,  and  to  completely  change  into  urea,  although  the 
statement  has  been  made  that  when  ammonia  or  ammonium 
salts  are  injected  into  the  blood  larger  quantities  must  be  present 


METABOLISM,    VUTRITION    IND  DI1  503 

to  produce  these  symptoms  than  are  found  in  animals  with  the 
Eck's  fistula.  Although  the  portal  vein  carries  to  the  liver  a 
much  greater  supply  of  blood  than  the  hepatic  artery,  ligation 
ol  the  latter  causes  a  greater  diminution  in  the  ratio  of  the 
amount  of  una  to  the  total  nitrogen  in  the  urine  than  ligation 
of  the  former.  This  indicates  that  a  good  supply  of  oxygen  is 
.111  important  factor  in  the  formation  of  urea  in  the  liver  (Doyon 
and  Dufourt).  But  this  is  no  proof  that  the  process  by  which 
it  is  formed  is  an  oxidation.  The  work  of  the  liver,  like  that  of 
other  tissues,  is  no  doubt  deranged  by  lack  of  oxygen. 

(5)  In  acute  yellow  atrophy,  and  in  extensive  fatty  degenera- 
tion of  the  liver,  urea  may  almost  disappear  from  the  urine, 
;md  leucin,  tyrosin,  and  other  amino-acids  may  appear  in  it  along 
with  a  much  larger  amount  of  ammonia  than  normal.  The 
amino-acids  and  ammonia  formed  in  the  intestine  in  the  digestion 
and  absorption  of  proteins  pass  unchanged  through  the  degener- 
ated liver,  and  are  excreted  by  the  kidney. 

Processes  by  which  Urea  is  Formed. — If  it  be  granted,  as  in  the 
face  of  the  evidence  it  must,  that  the  liver  plays  an  important  part 
in  the  formation  of  urea,  we  have  still  to  ask  what  the  materials  are 
upon  which  it  works,  in  what  organs  they  are  produced  before  being 
brought  to  the  liver,  and  by  what  process  they  are  there  changed 
into  urea.  To  the  last  question  it  may  be  at  once  replied  that  we 
know  but  little  of  the  process  by  which  urea  is  formed  in  the  body. 
In  the  laboratory  urea  can  be  obtained  from  protein  either  by  hydro- 
lysis or  by  oxidation.  We  have  already  remarked  that  when  a 
protein  is  split  up  by  boiling  with  dilute  acid  under  proper  conditions, 
very  much  the  same  decomposition  products  appear  as  in  tryptic 
digestion  (p.  332).  One  of  these,  arginin  (C6H14N402),  on  further 
hydrolytic  cleavage  by  barium  hydroxide,  yields  urea  and  ornithin 
(diamino- valerianic  acid),  half  of  the  nitrogen  of  the  arginin  appear- 
ing in  each.  The  amount  of  arginin,  and  therefore  the  amount  of 
urea  which  can  be  artificially  obtained  in  this  way,  varies  extremely 
with  the  different  proteins  and  protamins  (p.  2).  Thus,  salmin, 
a  substance  prepared  from  the  milt  of  salmon,  yields  843  per 
cent,  of  its  weight  of  arginin,  while  the  casein  of  cow's  milk 
yields  only  4'S  per  cent.,  and  gluten-fibrin,  one  of  the  proteins 
of  wheat,  only  3  per  cent.  In  the  body  the  hydrolysis  of  arginin 
to  urea  and  ornithin  is  accomplished  by  the  ferment  arginase. 
This  ferment  is  found  in  the  liver,  and  also  in  many  other 
organs.  The  urea  formed  in  this  way  appears  very  rapidly  in  the 
urine.  The  ornithin  itself  is  then  more  slowly  transformed  into 
urea.  Since  the  ordinary  food-proteins  are  poor  in  arginin,  the 
amount  of  urea  which  can  possibly  be  formed  in  mammalian  meta- 
bolism by  this  process  cannot  be  large,  even  if  most  of  the  arginin, 
as  is  the  case  when  it  is  fed  to  an  animal,  is  transformed  into  urea. 
Other  amino-acids,  as  already  mentioned,  also  cause  an  increased  pro- 
duction of  urea,  corresponding  to  their  nitrogen  content,  when 
administered  by  the  mouth  or  subcutaneously.  The  same  is  true 
when,  instead  of  simple  amino-acids,  polypeptids,  like  glycyl-glycin, 
alanyl-alanin,  or  leucyl-leucin,  are  given. 

Urea  has  also  been  artificially  obtained  from  protein  by  oxidation 


504  /    MANUAL  OF  PHYSIOLOGY 

with  an  ammoniacal  solution  of  permanganate  at  body-temperature. 
Winn  the  protein  is  first  split  into  its  cleavage  produi  ts  and  these  are 
then  oxidized,  a  very  large  amounl   <>t   urea  is  produced     e.g.,  as 

much  as  3  grammes  of  urea  from  10  grammes  of  ^lycin. 

While  these  facts  suggest  possible  ways  of  formation  oi  urea  in  the 
body,  we  cannot  assume  that  what  happens  in  the  test-tube  must 
happen  in  the  tissues.  It  is  now  known  that  the  greater  pari  oi 
the  una,  at  any  rate,  docs  not  come  from  tissue-protein,  either  by 
hydrolysis  or  by  oxidation,  but  that  much  of  it  arises  by  the  synl  h 
of  decomposition  products  of  the  food-proteins  simpler  than  itself 
viz.,  such  ammonium  compounds  as  have  been  already  mentioned  as 
being  transformed  into  urea  when  circulated  through  an  excised 
liver  (p.  501).  Ammonia  in  the  form  of  carbonate  or  carbamate  is 
constantly  found  in  the  blood,  and  the  portal  blood  contains  normally 
three  to  five  times  as  much  ammonia  as  arterial  blood.  Unquestion- 
ably, then,  a  portion  of  the  urea,  and  probably  a  large  portion, 
is  formed  from  such  ammonia  compounds,  and  if  we  still  ask  where 
these  compounds  arise,  and  what  their  immediate  precursors  are, 
the  only  reply  which  can  be  given  is  that  ammonia  is  known  to  be 
one  of  the  products  of  the  digestion  of  proteins,  and  that  there  is 
some  evidence  that  in  certain  ways  the  amide  (NH2)  groups  can  be 
split  off  from  amino-acids  and  then  utilized  as  ammonia  for  the 
formation  of  urea.  The  decomposition  products  of  the  food-pro- 
teins absorbed  from  the  intestine  are  thus  clearlv  indicated  as  a 
source  of  urea — namely,  of  that  large  fraction  which  represents  the 
surplus  nitrogen  eliminated  without  entering  into  the  metabolism 
of  the  cells.  It  is  of  importance  to  remark  that  such  hydrolytic 
cleavages  as  are  associated  with  the  splitting  of  protein  into  amino- 
acids,  etc.,  only  slightly  reduce  the  available  energy  of  the  com- 
pounds. If,  as  is  most  probable,  the  liberation  of  the  nitrogen  from 
the  amino-acids  is  also  accomplished  by  hydrolytic  cleavage,  tin- 
residue,  relatively  rich  in  carbon,  will  still  be  available  for  yielding 
to  the  body  by  its  oxidation  an  amount  of  energy  not  much  less  than 
could  be  obtained  from  the  original  protein. 

The  combination  of  ammonia  with  carbon  dioxide  and  the  con- 
version of  the  carbonate  into  urea  does  not  require  any  oxidation. 
But  if,  as  there  is  every  reason  to  believe,  a  part  of  the  carbonaceous 
residue  is  converted  into  carbo-hydrate,  a  certain  amount  of  oxida- 
tion must  occur  in  the  transformation.  It  would  be  an  error  to 
suppose  that  all  the  ammonia  or  other  forerunners  of  urea  come 
from  the  intestine,  or,  indeed,  that  all  the  urea  is  manufactured  in 
the  liver.  Urea  does  not  entirely  cease  to  be  produced  when  the  liver 
is  removed.  Some  of  the  urea  may  be  formed  '  on  the  spot.'  so 
to  speak,  in  the  endogenous  metabolism  of  all  the  tissues,  and 
perhaps  by  a  different  process  from  the  hepatic  urea  and  from 
different  intermediate  substances. 

Such  compounds  as  guanin,  sarkin  or  hypoxanthin.  xanthin,  uric 
acid,  and  kreatin,  used  to  be  cited  as  among  the  possible  intermediate 
substances.  But  while  there  is  now  complete  evidence  that  the 
first  three  bodies  can  be  and  are  converted  into  uric  acid,  there  is  no 
reason  to  believe  that  they  are  stages  on  the  way  to  urea.  I  Trie  acid 
is,  indeed,  very  closely  related  to  urea,  and  can  be  made  to  yield  it 
by  oxidation  outside  the  body.  Not  only  so,  but  it  is.  in  part  at 
least,  excreted  as  urea  when  given  to  a  mammal  by  the  mouth, 
and  it  replaces  urea  as  the  great  end-product  of  nitrogenous  meta- 
bolism almost  wholly  in  the  urine  oi  birds  and  reptiles,  and  partially 


i//  TABOLISM,    NUTRITION  AND  DIETETICS  505 

in  tlic  human  subject  in  Leukaemia.  But  none  of  these  things  can 
be  admitted  .is  evidence  that  in  the  normal  endogenous  metabolism 
of  mammals  uric  acid  lies  on  the  direcl  line  from  protein  to  urea 
ECreatin  exists  in  the  body  in  greater  amount  than  any  of  these, 
muscle  containing  from  0*2  to  o-.|  per  cent,  of  it  ;  and  the  total 
quantity  of  nitrogen  presenl  at  any  given  time  as  kreatin  is  not 
only  greater  than  thai  of  the  nitrogen  present  in  urea,,  but  greater 
than  the  whole  excretion  of  nitrogen  in  twenty-four  hours.  I'ail 
although  in  the  laboratory  kreatin  can  be  changed  into  kreatinin, 
and  kreatinin  into  urea,  there  is  no  proof  that  in  the  body  anything 
more  than  the  first  step  in  this  process  is  accomplished.  When 
kreatin  is  introduced  into  the  intestine  or  injected  into  the  blood, 
it  appears  in  the  urine,  not  as  urea,  but  as  kreatinin.  We  have 
already  seen  that  kreatinin  is  the  chief  nitrogenous  product  of 
endogenous  protein  metabolism. 

Ammonia  and  amino-acids  may  also  be  produced  from  tissue  - 
protein,  or  it  may  be  from  '  circulating  '  protein  (p.  536),  which 
has  not  been  built  up  into  protoplasm,  for  proteolytic  ferments  are 
everywhere  found  in  the  organs.  And  if  ammonia  and  amino- 
acids  are  formed  in  the  tissues,  there  is  no  reason  to  suppose  that 
they  will  not  yield  urea,  just  as  if  they  were  produced  in  the 
intestine. 

Formation  of  Uric  Acid. — Uric  acid,  like  urea,  is  separated 
from  the  blood  by  the  kidneys,  not  to  any  appreciable  extent 
formed  in  them.  In  birds,  and  often  in  man,  it  can  be  detected 
in  normal  blood.  It  is  present  in  increased  amount  in  the  blood 
and  transudations  of  gouty  patients,  in  whose  joints  and  ear- 
cartilages  it  often  forms  concretions.  '  Chalk-stones  '  may 
contain  more  than  half  their  weight  of  sodium  urate. 

As  to  the  place  and  manner  of  formation  of  uric  acid,  it  has 
already  been  stated  that  in  birds,  after  extirpation  of  the  liver, 
the  uric  acid  excretion  is  greatly  diminished,  and  that  ammonium 
lactate  appears  instead  in  the  urine.  It  has  been  further  shown 
that  when  blood  containing  ammonium  lactate  is  circulated 
through  the  surviving  liver  of  the  goose,  an  increase  in  the  uric 
acid  content  of  the  blood  occurs.  As  demonstrated  by  control 
experiments,  this  increase  is  too  great  to  be  due  merely  to  the 
sweeping  out  of  previously  formed  uric  acid  from  the  hepatic 
cells.  There  can  be  no  question,  then,  that  the  liver  in  birds 
is  the  seat  of  an  extensive  synthesis  of  uric  acid  from  such  simple 
materials  as  ammonia  and  lactic  acid.  A  similar  synthetic 
formation  of  uric  acid  from  ammonia  and  a  derivative  of  lactic 
acid  may  take  place  in  mammals,  and  probably  exclusively  in  the 
liver,  but  it  is  of  much  less  importance.  Another  way  in  which 
uric  acid  arises  both  in  mammals  and  in  birds  is  by  the  splitting 
and  oxidation  of  nucleins.  This  is  by  far  the  most  important  mode 
of  formation  in  mammals,  as  synthesis  is  the  chief  mode  of  for- 
mation in  birds.  In  both  groups  of  animals  the  oxidative  pro- 
duction of  uric  acid  takes  place,  not  in  any  particular  organ,  but 


506  A   MANUAL    of  PHYSIOLOGY 

in  the  tissues  in  general,  including  the  liver.  Tl  has  boon  shown 
thai  when  air  is  blown  through  a  mixture  of  splenic  pulp  and 
blood,  uric  acid  is  formed  from  purin  bodies  already  present  in 
the  spleen.     When  the  quantity  of  these  is  increased  by  the 

decomposition  of  nucleins  induced  by  slight  putrefaction,  the 
yield  of  uric  acid  is  also  increased.  Uric  acid  is  also  formed  by 
the  perfectly  fresh  surviving  spleen,  liver,  and  thymus  in  the 
presence  of  oxygen,  and  the  quantity  is  increased  when  purin 
bodies  are  artificially  added. 

As  to  the  source  of  the  uric  acid,  it  is  well  established  that 
in  the  bird  it  arises  both  from  the  end-products  of  protein  meta- 
bolism and  from  nuclein  compounds  and  their  derivatives  in  the 
food  and  tissues.  In  the  mammal,  the  taking  of  food  rich  in 
nucleated  cells,  and  therefore  in  nucleo-proteins  and  nucleins 
(thymus  gland,  pig's  pancreas,  and  herring  roe),  or  of  food  rich 
in  purin  bases  (Liebig's  meat  extract),  increases  the  quantity 
of  uric  acid  in  the  urine.  The  increase  is  mainly  due  to  the 
production  of  uric  acid  from  the  nuclein  substances.  But  this 
is  not  the  only  source  of  the  uric  acid,  since  extracts  of  the 
thymus  gland  containing  only  traces  of  nucleins  or  nucleic  acid 
cause,  when  injected,  a  characteristic  increase  in  the  uric  acid 
excretion,  just  as  the  entire  gland  does  when  taken  by  the 
mouth.  And  during  the  period  of  increased  nitrogen  excretion 
occasioned  by  a  meal  containing  protein  the  increase  in  the 
uric  acid  occurs  particularly  in  the  hours  immediately  following 
the  ingestion  of  the  food,  and  does  not  last  so  long  as  the  increase 
in  the  urea.  Now,  the  nucleins  of  the  food  are  comparatively 
little  affected  during  the  earlier  stages  of  digestion  (Hopkins  and 
Hope).  We  may  conclude,  therefore,  that  in  the  mammal,  as 
well  as  in  the  bird,  a  portion  of  the  uric  acid,  although  certainly 
a  far  smaller  portion  in  the  mammal,  is  derived  from  bodies  other 
than  the  nuclein  substances  of  the  food — that  is  to  say,  from  the 
nuclein  substances  of  the  tissues  contained  particularly  in  the 
cell-nuclei,  and  from  the  ordinary  proteins  of  both  food  and 
tissues.  The  portion  derived  from  the  proteins  is  that  small 
fraction  which  has  already  been  spoken  of  as  synthetically  f<  >rmed. 

Our  knowledge  of  the  metabolism  of  the  nucleo-proteins  and 
nucleins  has  been  greatly  augmented  in  recent  years.  When 
nucleo-protein  is  digested  by  gastric  juice  a  certain  amount  of 
protein  is  easily  split  off,  and  hydrolysed  to  peptone  and  the 
other  ordinary  products  of  proteolysis.  An  insoluble  residue  of 
nuclein  remains.  This  is  acted  upon  with  difficulty  by  gastric 
juice,  although  eventually  an  active  juice  will  split  it  up  also. 
By  heating  with  dilute  acids  it  is  more  easily  hydrolysed,  yielding 
a  further  quantity  of  protein  along  with  nucleic  acid.  This 
second  fraction  of  protein,  which  is  split  off  with  so  much  more 


METABOLISM,    NUTRITION     \ND  DIETETICS  507 

difficulty  than  the  first,  undergoes  proteolysis  in  the  usual  way. 
I  "i  the  decomposition  of  the  nucleic  acid  (or  rather  acids,  since 
different  nucleo-proteins  contain  different  nucleic  acids),  still 
more  drastic  treatment  is  required  -namely,  heating  with  hydro- 
chloric acid  in  a  sealed  tube.  Thus  treated,  nucleic  acid  yields 
a  number  of  products,  among  which  phosphoric  acid  and  purin 
bases  (adenin,  hypoxanthin,  guanin,  xanthin)  are  always  present, 
and  probably  a  carbo-hydrate  group  also.  Pyrimidin  bases 
(uracil,  cytosine,  thymine)  arc  also  present,  although,  perhaps, 
not  in  all  nucleic  acids.  The  empirical  formulae  for  the  purin 
bodies  of  greatest  physiological  interest  are  as  follows  : 

Purin  -  -  -  C,H4N,. 

["Hypoxanthin  (a  monoxvpurin)  -  C-H4N40. 

•§  v  I  Xanthin  (a  dioxypurin)    -  -  C-H4N40,. 

P  rt~|  Adenin  (an  amino-purin)   -  -  C-H:iN.,.NH.,. 

^•^  [Guanin  (an  amino-oxypurin)  -  C-H:iN4O.NH2. 

Uric  acid  (a  trioxypurin)    -  -  C-H4N40:i. 

Purin  has  not  been  found  in  the  body.  The  purin  bases  and 
uric  acid  are  widely  spread  in  the  tissues,  although  in  very  small 
amounts. 

As  to  the  manner  in  which  uric  acid  arises  from  the  nuclein 
substances  in  the  tissues,  we  may  picture  the  process  as  taking 
place  by  the  following  steps.  Certain  organs  have  been  shown 
to  contain  ferments  which  split  up  nucleo-proteins  into  protein 
and  nucleic  acid.  This  nucleic  acid,  or  nucleic  acid  arising  in 
other  ways  in  the  metabolism  of  nuclein,  and  also  the  nucleic 
acid  produced  in  the  alimentary  canal  in  the  digestion  of  nuclein- 
containing  substances,  are  then  decomposed  by  another  ferment, 
nuclease,  which,  along  with  phosphoric  acid  and  the  carbo- 
hydrate group,  liberates  purin  (and  pyrimidin)  bases,  especially 
adenin  and  guanin.  Then  follows  the  action  of  ferments 
(adenase  and  guanase),  which  remove  the  amino-group  from 
these  purin  bases,  transforming  adenin  into  hypoxanthin  and 
guanin  into  xanthin.  By  means  of  an  oxidizing  ferment  or 
oxydase  we  may  next  imagine  that  hypoxanthin  is  oxidized  into 
xanthin  and  xanthin  into  uric  acid.  Evidence  of  the  existence 
of  all  these  ferments,  and  of  their  wide  distribution,  has  been 
obtained  by  making  experiments  on  the  various  substances 
mentioned  with  extracts  of  different  tissues. 

The  portion  of  the  uric  acid  which  comes  from  the  food 
(mainly  from  the  purin  bodies  in  it)  is  sometimes  denominated 
the  exogenous  portion,  while  that  which  arises  from  the  tissues 
is  called  the  endogenous  portion.  The  latter  moiety,  which 
generally  amounts  to  about  0'6  gramme  in  the  twenty-four 
hours,  can  be  estimated  by  restricting  the  diet  to  articles  of 
food  free  from  purin  bodies,  such  as  bread,  milk,  cheese,  eggs. 


508  A   MANU  1/    OF  I'll  YSIOLOGY 

and  butter.  It  is  stated  ili.it  the  endogenous  uric  a<  id  remains 
pra<  tically  constant  in  the  same  individual  under  i  onstanl  con- 
ditions,  and  is  unaffected  by  changes  in  the  diet. 

The  total  excrel  ton  of  uric  acid  (and  the  other  purin  bodies)  is 
by  no  means  identical  with  the  sum  of  the  uric  acid  taken  in  as 
purin  liases  in  the  food  and  that  produced  in  the  body.  A  con- 
siderable destruction  of  uric  acid  (and  other  purin  bodies)  goes 
on  in  the  body,  and  mainly  in  the  liver.  A  ferment  called  the 
uricolytic  ferment  has  been  discovered  in  various  organs,  and  it  is 
believed  that  this  is  the  active  agent  in  the  normal  destruction 
of  uric  acid.  There  is  reason  to  think  that  one  of  the  factors  in 
the  production  of  gout  may  be  a  diminution  in  the  amount  or 
activity  of  this  ferment.  In  some  cases  it  is  said  to  be  entirely 
absent.  The  quantity  of  endogenous  uric  acid  excreted  by  the 
kidneys  bears  a  certain  ratio  to  the  total  amount  which  has 
entered  the  circulation.  This  ratio  varies  much  in  different 
mammalian  species.  In  man  a  full  half  is  excreted  and  about  a 
half  destroyed.  Some  of  the  exogenous  moiety  is  also  broken 
down.  When  uric  acid  is  heated  in  a  sealed  tube  with  strong 
hydrochloric  acid,  it  is  broken  up  into  glycin,  carbon  dioxide,  and 
ammonia.  There  are  grounds  for  believing  that  a  similar  decom- 
position takes  place  in  the  body,  and  that  the  products  are  then 
synthesized  to  urea  in  the  liver. 

Hippuric  acid  can  undoubtedly  be  produced  in  the  kidney. 

If  an  excised  kidney  is  perfused  with  blood  containing  benzoic 
acid,  or,  better,  benzoic  acid  and  glycin,  hippuric  acid  is  formed. 
The  kidney  cells  must  be  intact,  for  if  a  mixture  of  blood,  glycin, 
and  benzoic  acid  be  added  to  a  minced  kidney  immediately  after 
its  removal  from  the  body,  hippuric  acid  is  produced,  but  not  if 
the  kidney  has  been  crushed  in  a  mortar.  Nevertheless  there  is 
some  evidence  that  a  ferment  is  concerned  in  the  reaction.  In 
herbivora  hippuric  acid  cannot  normally  be  detected  in  the  blood  ; 
it  is  present  in  large  quantities  in  the  urine ;  it  must  therefore  be 
manufactured  in  the  kidney,  not  merely  separated  by  it.  In 
certain  animals,  as  the  dog,  the  kidney  is  the  sole  seat  of  the 
production  of  hippuric  acid.  But  in  the  rabbit  and  the  frog 
some  of  it  may  also  be  formed  in  other  tissues,  for  after  extirpa- 
tion of  the  kidneys  the  administration  of  benzoic  acid  causes 
hippuric  acid  to  appear  in  the  blood.  The  benzoic  acid  comes 
mainly  from  substances  of  the  aromatic  group  contained  in 
vegetable  food,  but  a  small  amount  is  produced  in  the  body, 
since  hippuric  acid  does  not  entirely  disappear  from  the  urine 
in  starvation.  It  is  not  known  in  what  form  the  nitrogenous 
glvcin  appears  on  the  spot  where  it  is  wanted  to  form  hippuric 
acid,  since  glycin  has  not  been  found  anywhere  in  the  tissues 
But  there  is  no  doubt   that  it  is  a  product  oi  tin   metabolism  oi 


Ml  I  IBOLISM,   M   TRITION  AND  I'll  TETICS 

proteins  (and  gelatin).  It  is  also  a  constituent  of  glycocholic  acid, 
ami  may  be  derived  in  pai  t  from  the  bile  which  is  reabsorbed. 

Kreatinin  can  be  so  readilj  obtained  from  kreatin  outside  the 
body  that  it  is  tempting  to  suppose  that  the  portion  of  the 

kreatinin  of  the  urine  which  is  not  formed  from  the  kreatin  in 
the  food  is  derived  from  the  kreatin  of  the  muscles  and  other 
tissues.  The  constancy  of  the  kreatinin  elimination  on  a  meat- 
tree  diet,  and  its  complete  independence  of  the  changes  in  the 
total  nitrogen  excretion,  show  that  it  has  a  different  significance 
in  protein  metabolism  from  the  urea.  There  is  some  reason  to 
suspect  that  the  kreatinin  may  represent  nitrogen  given  off  in 
the  constant  wear  and  tear  of  the  bodily  machinery.  The  fact 
that  the  amount  of  kreatinin  excreted  by  different  persons  seems 
to  be  related  to  the  weight  of  active  tissue  in  the  body,  excluding 
fat,  is  in  favour  of  this  suggestion.  The  statement  that  the 
content  of  the  urine  in  kreatinin  is  increased  by  muscular  work 
may  indicate  that  the  muscular  machine  wears  out  faster  during 
activity  than  during  rest,  or  perhaps  only  that  already  formed 
kreatin  leaves  the  muscles  in  greater  amount  when  the  blood- 
flow  is  increased.  As  to  the  manner  in  which  kreatin  is  changed 
into  kreatinin  in  the  body,  a  highly  suggestive  fact  is  the  presence 
of  ferments  in  various  organs  which  possess  this  power.  Ferments 
also  exist  which  can  decompose  both  kreatin  and  kreatinin. 

Formation  of  Carbon  Dioxide  from  Proteins. — We  cannot 
say  whether  any  carbon  dioxide  is  normally  produced  at  the 
moment  when  the  nitrogenous  portion  of  the  protein  molecule 
splits  off,  or  whether  a  carbonaceous  residue  may  not  always  hang, 
together  for  a  time  and  pass  through  further  stages  before 
the  carbon  is  fully  oxidized.  We  shall  see  that  under  certain 
conditions  some  of  the  carbon  of  proteins  may  be  retained  in 
the  body  as  glycogen  or  fat  ;  and  this  suggests  that  in  all  cases 
it  may  run  through  intermediate  products  as  yet  unknown 
before  being  finally  excreted  as  carbon  dioxide. 

Intracellular  Ferments — Autolysis.— As  to  the  agencies  by 
which  the  decomposition  of  the  proteins  is  carried  out  in  the 
cells,  we  have  already  spoken  of  the  oxidizing  cell  ferments,  or 
oxydases  (p.  264).  Reducing  ferments  or  reductases  are  also 
known,  and  can  be  extracted  from  most  organs,  if  not  all.  Like 
oxydases,  they  act  in  a  weakly  alkaline  medium,  causing  in  the 
presence  of  hydrogen  such  reductions  as  the  formation  of  nitrites 
from  nitrates.  There  is  some  evidence  that  one  and  the  same 
ferment  may  act  as  an  oxydase  or  a  reductase  according  to  the 
conditions.  Recent  researches  have  brought  to  light  in  addition 
hydrolytic  intracellular  ferments,  which  split  up  proteins  very 
much  in  the  same  way  as  the  proteolytic  ferments  of  the  digestive 
juices.     Not    only    do    unicellular    organisms,    like    leucocytes, 


510  A   MANUAL  OF  PHYSIOLOGY 

st-cells,  and  bactei  ia  possess  such  fa  ments,  but  their  existence 
has  been  demonstrated  in  practically  all  the  organs  oi  the  higher 

animals  and  man.  When  a  piece  of  liver,  e.g.,  is  removed  with 
aseptic  precautions  and  kept    at   body-temperature,  extensive 

auto-digestion  occurs,  and  ammonia,  and  other  basic  substances, 
glycin,  and  the  body  which  gives  the  tryptophane  reaction 
(p.  430),  appear  among  the  products.  Tyrosin  appears  so  early 
that  it  is  scarcely  possible  to  doubt  that  it  must  be  a  product 
of  protein  decomposition  in  the  liver-cells  under  normal  con- 
ditions. Similar  autolytic  processes  have  been  observed  in  the 
spleen,  muscle,  lymph-glands,  kidneys,  lungs,  stomach  wall 
(independently  of  pepsin),  thymus,  and  placenta,  also  in  patho- 
logical new  growths  like  carcinoma,  in  the  breaking  down  of 
which  and  in  the  removal  of  such  exudations  as  occur  in  the 
alveoli  in  pneumonia,  these  proteolytic  ferments  seem  to  plav  a 
part.  The  ferments  in  certain  cases  have  been  obtained  in 
extracts  of  the  organs,  and  have  been  found  still  active.  1'  is 
probable  that  the  syntheses  of  the  proteins  or  their  products, 
which  are  scarcely  less  characteristic  of  the  tissue  cells  than 
the  decompositions  effected  by  them,  are  also  due  to  the 
action  of  separate  intracellular  ferments  or  upon  the  reversed 
activity  of  the  proteolytic  ferments.  So  many  of  the  chemical 
reactions  of  the  body  have  been  found  to  depend  upon  enzymes 
that  modern  physiology  may  at  lirst  thought  seem  almost  to 
have  reverted  to  the  position  of  van  Helmont  and  his  school  in 
the  seventeenth  century,  who  resolved  all  difficulties  by  murmur- 
ing the  magic  word  '  ferment.'  No  fewer  than  eleven  ferments 
have  been  stated  to  be  present  and  active  in  the  liver  alone — 
viz.,  a  proteolytic  and  a  nuclein-splitting  ferment,  a  ferment 
which  splits  off  ammonia  from  amino-acids,  a  milk-curdling 
ferment,  a  nbrin  ferment,  a  bactericidal  ferment,  an  oxydase,  a 
lipase,  a  maltase,  a  ferment  called  glycogenase,  which  changes 
glycogen  into  dextrose,  and  an  autolytic  ferment.  In  the 
presence  of  such  an  array  of  enzymes  the  organs  might  seem  to 
be  little  more  than  incubators  in  which  the  ferments  do  their 
work.  It  must  not  be  supposed,  however,  that  the  intracellular 
ferments,  whether  they  cause  decomposition  or  synthesis, 
oxidation  or  reduction,  work  independently  of  what,  for  want  of  a 
better  name,  we  must  call  the  organization  of  the  cell.  We  may 
be  sure  they  are  the  servants  and  not  the  masters  of  the  proto- 
plasm, and  that  a  drop  of  an  extract  containing  intracellular 
ferments  has  very  different  powers  from  a  living  cell.  '  It  is  n<  >t 
in  the  existence  of  the  ferments,  but  in  their  combined  action  at 
the  proper  time  and  in  the  proper  intensity,  that  the  riddle  of 
metabolism  lies  '  (Hober). 

2.    Metabolism    of    Carbo  -  hydrates — Glycogen. — The    carbo- 


mi  r.ino/./sM,  \i i/:iri<>\   AND  mi  ii  i  511 

hydrates  of  the  food,  passing  into  the  blood  of  the  portal  rem  in 

the  form  of  dextrose,  are  in  part  arrested  in  the  liver,  and  stored 
up  us  glycogen  in  the  hepatic  cells,  to  be  gradually  given  out  again 
as  sugar  in  the  intervals  of  digestion.  The  proof  o\  this  statement 
is  as  follows  : 

Sugar  is  arrested  in  the  liver,  for  during  digestion,  especially 
of  a  meal  rich  in  carbo-hydi  ates,  the  blood  of  the  portal  contains 
more  sugar  than  that  of  the  hepatic  vein.  Popielski  on  the 
basis  of  experiments  in  which  he  fed  with  known  quantities  of 
sugar  dogs  whose  inferior  vena  cava  and  portal  vein  had  been 
united  by  an  Eck's  fistula,  and  determined  the  amount  of  sugar 
which  passed  into  the  urine,  estimates  the  quantity  of  sugar 
kept  back  by  the  liver  at  from  12  to  20  per  cent,  of  the  whole. 
In  the  liver  there  exists  a  store  of  sugar-producing  material 
from  which  sugar  is  gradually  given  off  to  the  blood,  for  in  the 
intervals  of  digestion  the  blood  of  the  hepatic  vein  contains  more 
dextrose  (2  parts  per  1,000)  than  the  mixed  blood  of  the  body  or 
than  that  of  the  portal  vein  (about  1  part  per  1,000).  When 
the  circulation  through  the  liver  is  cut  off  in  the  goose,  the 
blood  rapidly  becomes  free,  or  nearly  free,  from  sugar  (Min- 
kowski). And  a  similar  result  follows  such  interference  with 
the  hepatic  circulation  as  is  caused  by  the  ligation  of  the  three 
chief  arteries  of  the  intestine  in  the  dog,  even  when  the  animal  has 
been  previously  made  diabetic  by  excision  of  the  pancreas  (p.  518). 

The  nature  of  the  sugar-forming  substance  is  made  clear  by 
the  following  experiments  :  (1)  A  rabbit  after  a  large  carbo- 
hydrate meal,  of  carrots  for  instance,  is  killed  and  its  liver  rapidly 
excised,  cut  into  small  pieces,  and  thrown  into  acidulated 
boiling  water.  After  being  boiled  for  a  few  minutes,  the  pieces 
of  liver  are  rubbed  up  in  a  mortar  and  again  boiled  in  the  same 
water.  The  opalescent  aqueous  extract  is  filtered  off  from  the 
coagulated  proteins.  No  sugar,  or  only  traces  of  it,  are  found 
in  this  extract  ;  but  another  carbo-hydrate,  glycogen,  an  isomer 
of  starch  giving  a  port-wine  colour  with  iodine  and  capable  of 
ready  conversion  into  sugar  by  amylolytic  ferments,  is  present  in 
large  amount.     (See  Practical  Exercises,  p.  608.) 

(2)  The  liver  after  the  death  of  the  animal  is  left  for  a  time 
in  situ,  or,  if  excised,  is  kept  at  a  temperature  of  350  to  400  C, 
or  for  a  longer  period  at  a  lower  temperature  ;  it  is  then  treated 
exactly  as  before,  but  no  glycogen,  or  comparatively  little,  can 
now  be  obtained  from  it,  although  sugar  (dextrose)  is  abundant. 
The  inference  plainly  is  that  after  death  the  hepatic  glycogen 
is  converted  into  dextrose  by  some  influence  which  is  restrained 
or  destroyed  by  boiling.  This  transformation  might  theoretically 
be  due  to  an  unformed  ferment  or  to  the  direct  action  of  the 
liver-cells,  for  both  unformed  ferments  and  living  tissue  elements 


5i2  A   M  IM    If.  OF  PHYSIOLOGY 

are  destroyed  at  the  temperature  of  boiling  water.     It  has  been 
clearly  shown  thai   the  action  is  brought  about   by  a  di astatic 

enzyme,  which  some  writers  call  glycogen ase,  for  it  readily  occurs 
when  the  minced  liver  is  mixed  with  chloroform  water,  and  chloro- 
form kills  all  living  tissues.  Although  blood  contains  a  diastase 
in  small  amount,  the  change  does  not  depend  essentially  upon 
this,  since  thegly<  ■  -  ■  n  jKnimiln^irs  hydrolysis  (glycogenoh 
to  dextrose  when  all  the  blood  has  been  washed  out  of  the  organ. 
Lymph  also  contains  a  diastase,  but  there  is  eyidence  that  the 
post-mortem  glycogenolysis  is  chiefly  due  to  an  enzyme  contained 
in  the  hepatic  cells  (an  endo-enzyme)  (Macleod).  The  diastases 
in  the  blood  and  lymph  seem  to  be  '  discards  '  of  the  tissues 
which  are  on  the  way  to  destruction  or  elimination  (Carlson). 
The  post-mortem  change  is  to  be  regarded  as  an  index  of  a  similar 
action  which  goes  on  during  life  :  sugar  in  the  intact  body  is 
changed  into  glycogen  ;  glycogen  is  constantly  being  changed 
into  sugar.  There  is  no  reason  to  doubt  that  here,  too,  the 
hydrolysis  is  effected  by  the  endo-enzyme.  But,  as  in  the  case  of 
the  intracellular  proteolytic  ferments,  we  may  be  certain  that 
the  vital  action  of  the  hepatic  cells  is  a  most  important  factor  in 
controlling  the  rate  of  production  of  the  ferment  or  the  rate  at 
which  it  works. 

(3)  With  the  microscope,  glycogen,  or  at  least  a  substance 
which  is  very  nearly  akin  to  it,  which  very  readily  yields  it,  and 
which  gives  the  characteristic  port-wine  colour  with  iodine,  can 
be  actually  seen  in  the  liver-cells.  The  liver  of  a  rabbit  or  dog 
which  has  been  fed  on  a  diet  containing  much  carbo-hydrate  is 
large,  soft,  and  very  easily  torn.  Its  large  size  is  due  to  the 
loading  of  the  cells  with  a  hyaline  material,  which  gives  the 
iodine  reaction  of  glycogen,  and  is  dissolved  out  by  water, 
leaving  empty  spaces  in  a  network  of  cell-substance.  If  the 
animal,  after  a  period  of  starvation,  has  been  fed  on  protein 
alone,  less  glycogen  is  found  in  the  shrunken  liver-cells  ;  if  the 
diet  has  been  wholly  fatty,  little  or  no  glycogen  at  all  may  be 
found,  (dvcogen  can  even  be  formed  by  an  excised  liver  when 
blood  containing  dextrose  is  circulated  through  it. 

Formation  of  Glycogen  from  Protein.  In  the  liver-cells  of 
the  frog  in  winter-time  a  great  deal  of  this  hyaline  material 
— this  glycogen,  or  perhaps  loose  glycogen  compound — is  pre- 
sent ;  in  summer,  much  less.  The  difference  is  very  remarkable 
if  we  consider  that  in  winter  frogs  have  no  food  for  months, 
while  summer  is  their  feeding-time  ;  and  at  rirst  it  seems  incon- 
sistent with  the  doctrine  that  the  hepatic  glycogen  is  a  store 
laid  up  from  surplus  sugar,  which  might  otherwise  be  swept  into 
the  general  circulation  and  excreted  by  the  kidneys.  It  has  been 
found,  however,  that  the  quantity  of  glycogen  is  greatest  in 


METABOLISM,    \'   VRITION  AND  DIETETICS  513 

autumn  at  the  beginning  of  the  winter-sleep,  and  slowly 
diminishes  as  the  winter  passes  on,  to  fall  abruptly  with  the 

renewal  of  the  activity  of  the  animal  in  the  spring.  The  glyco- 
gen presenl  at  any  moment  is,  therefore,  believed  to  be  a  residue, 
which  represents  the  excess  of  glycogen  formed  over  glycogen 
used  up  ;  and  the  amount  is  larger  in  winter,  not  because  more 
is  manufactured  than  in  summer,  but  because  less  is  consumed. 
It  is  possible,  indeed,  to  produce  the  '  summer  '  condition  of 
the  hepatic  cells  merely  by  raising  the  temperature  of  the  air 
in  which  a  winter  frog  lives  ;  at  200  or  250  C,  glycogen  disappears 
from  its  liver.  Conversely,  if  a  summer  frog  is  artificially  cooled, 
a  certain  amount  of  glycogen  accumulates  in  the  liver.  The 
meaning  of  this  seems  to  be  that  at  a  low  temperature,  when  the 
wheels  of  life  are  clogged  and  metabolism  is  slow7,  some  substance, 
probably  dextrose,  is  produced  in  the  body  from  proteins  in 
greater  amount  than  can  be  used  up,  and  that  the  surplus  is 
stored  as  glycogen  ;  just  as  in  plants  starch  is  put  by  as  a  reserve 
which  can  be  drawn  upon — which  can  be  converted  into  sugar — 
when  the  need  arises.  That  carbo-hydrates  may  be  produced 
from  proteins  has  been  shown  by  feeding  dogs  with  almost  pure 
protein  (casein)  after  the  production  of  permanent  glycosuria  by 
removal  of  the  pancreas  (p.  518).  To  induce  the  animal  to  take 
the  casein  it  had  to  be  mixed  with  a  certain  amount  of  butter,  or 
serum,  or  meat  extract.  The  amount  of  sugar  excreted  was  much 
more  than  could  possibly  have  come  from  the  glycogen  originally 
present  in  the  animal's  body,  computing  it  on  the  most  generous 
scale  (41  grammes  per  kilogramme  of  body- weight,  according  to 
Pfluger),  or  from  free  carbo-hydrate  present  in  traces  in  the  food, 
or  as  prosthetic  groups  (p.  2)  in  the  ingested  protein.  That  the 
source  of  the  sugar  was  protein  and  not  fat  was  indicated 
by  the  fact  that  when  the  amount  of  protein  food  was 
increased,  the  dextrose  and  the  nitrogen  excreted  increased 
proportionally. 

Glycogen-formers. — As  true  glycogen-formers  in  the  higher 
animals,  only  a  few  substances  have  been  demonstrated,  such  as 
proteins  (including  gelatin),  the  fermentable  sugars,  and  glycerin. 
The  most  interesting  demonstration  of  the  transformation  of 
glycerin  into  glycogen,  because  the  most  direct,  has  been  afforded 
by  perfusing  the  liver  of  the  tortoise  with  blood  to  which  glycerin 
was  added.  The  glycogen  content  of  the  liver  was  very  distinctly 
increased.  The  monosaccharides  dextrose,  levulose,  and  galac- 
tose gave  a  similar  result,  while  the  disaccharides  cane-sugar  and 
lactose  caused  no  increase  in  the  glycogen  of  the  perfused  liver, 
since  the  liver  contains  no  ferment  capable  of  splitting  them 
into  monosaccharides.  It  is  said  that  even  such  small  mole- 
cules as  those  of  formaldehyde  (CH20)  can  be  condensed  to  glyco- 

33 


514  A   M.l  \  UAL  OF  PHYSIOLOGY 

gen  in  the  liver  (Grube).*  When  given  by  the  mouth  both  cane- 
sugar  and  lactose  form  glycogen,  being  hydrolysed  in  digestion. 
It  has  not  hitherto  been  proved  that  the  fatty  acid  component  of 
neutral  fats  can  be  converted  into  glycogen.  Many  other  bodies 
arc  known  to  influence  the  formation  of  glycogen  by  '  sparing  ' 
substances  which  are  true  glycogen  producers,  but  their  carbon 
does  not  actually  take  its  place  in  the  glycogen  molecule.  Some 
writers  deny  that  proteins  can  directly  form  giycogen  or  sugar 
apart  from  carbo-hydrate  groups  contained  in  the  protein  mole- 
cule. But  the  proteins  of  meat,  gelatin,  and  casein  are  capable 
of  forming  60  per  cent,  of  their  own  weight  of  dextrose  in  diabetic 
metabolism,  and  even  the  end  products  of  pancreatic  digestion  of 
meat  yield  so  much  sugar  that  the  greater  part  of  it  must  have 
come  from  the  amino-bodies,  and  not  from  a  sugar-group  in  the 
protein.  When  given  to  dogs  with  total  phloridzin  glycosuria 
(p.  521),  glycin  and  alanin  are  completely,  glutamic  and  aspartic 
acids  in  great  part,  converted  into  dextrose  (Lusk,  etc.). 

Extra-hepatic  Glycogen. — While  the  liver  in  the  adult  (con- 
taining as  it  does  from  2  to  10  per  cent,  of  glycogen,  or  even,  with 
a  diet  rich  in  sugar  or  starch,  more  than 
18  per  cent.)  may  be  looked  upon  as  the 
main  storehouse  of  surplus  carbo-hydrate, 
depots  of   glycogen  are  formed,  both   in 
adult   and  fcetal  life,  in  other  situations 
where  the  strain  of  function  or  of  growth 
is  exceptionally  heavy- — in  the  muscles  of 
the  adult  (o"3  to  05  per  cent,  of  the  moist 
skeletal  muscle,  or  on  a  carbo-hydrate  regi- 
Fig.     183.  —Cells    of    mcn  0-y  t0  ?y  per  cent.),  in  the  placenta, 
Placenta  containing  j       1      ■  ,1  1 

qLY(  ,,, ,j  N  in  many  developing  organs  in  the  embryo 

(muscles,  lungs,  epithelium  of  the  trachea, 
oesophagus,  intestine,  ureter,  pelvis  of  kidney,  and  renal 
tubules).  The  fcetus,  however,  is  not,  compared  with  the  adult, 
especially  rich  in  glycogen.  In  the  adult  under  favourable 
circumstances  the  absolute  amount  of  glycogen  in  the  muscles  may 
be  several  times  greater  than  that  in  the  liver,  and  usually  the 
hepatic  glycogen  makes  up  considerably  less  than  half  the  total 
glycogen  of  the  body.  That  the  muscles  do  not  derive  their 
glycogen  by  the  migration  of  hepatic  glycogen,  but  can  them- 
selves form  it  from  dextrose,  has  been  shown  by  injecting  that 
sugar  subcutaneously  into  frogs  after  excision  of  the  liver.  The 
muscle  glycogen  was  found  to  be  increased. 

The  glycogen  store  of  the  Liver  fulfils  a  different  function  from 
that  of  the  muscles.     This  is  indicated  1  ly  the  fact  that  when  dogs, 

*  Such  results,  however,  nerd  confirmation  in  view  oi   Pfluger's  receni 
analysis  oi  possible  errors  in  work  with  the  tortoise  liver. 


METABOLISM,   NUTRITION  AND  DIETETICS  515 

after  being  put  on  a  given  did  for  two  or  three  days,  are  stan  ed 
t(  >i  a  time,  and  then  put  again  on  the  original  diet,  the  hepatic  and 
t  Ik  muscular  glycogen  behave  differently  at  first  duringthe  period 
<>l  re-alimentation.  While  glycogen  accumulates  in  the  liver  in 
greater  quantity  than  under  normal  conditions  of  nutrition,  in  the 
muscles  it  at  first  accumulates  much  less  rapidly  than  normally. 

Function  and  Fate  of  the  Glycogen. — When  a  fasting  dog 
is  made  to  do  severe  muscular  work,  the  greater  part  of  the 
glycogen  soon  disappears  from  its  liver.  When  a  dog  is  starved, 
but  allowed  to  remain  at  rest,  the  glycogen  still  markedly 
diminishes,  although  it  takes  a  longer  time  ;  and  at  a  period  when 
there  is  still  plenty  of  fat  in  the  body,  there  may  be  only  a  trace 
of  hepatic  glycogen  left.  The  glycogen  which  is  usually  con- 
tained in  the  skeletal  muscles  also  diminishes  very  rapidly  in 
the  first  days  of  hunger,  but  the  heart  contains  the  normal 
amount  of  glycogen  at  a  time  when  the  proportion  in  the  skeletal 
muscles  has  sunk  to  ^  to  ¥\j  of  the  normal.  These  facts  have 
been  taken  to  indicate  that  glycogen  and  the  sugar  formed  from 
it  are  the  readiest  resources  of  the  starving  and  working  organism, 
for  the  transformation  of  chemical  energy  into  heat  and  mechani- 
cal work.  To  borrow  a  financial  simile,  the  fat  of  the  body  has 
sometimes  been  compared  to  a  good,  but  rather  inactive  security, 
which  can  only  be  gradually  realized  ;  its  organ-proteins  to  long- 
date bills,  which  will  be  discounted  sparingly  and  almost  with  a 
grudge  ;  its  glycogen,  its  carbo-hydrate  reserves,  to  consols, 
which  can  be  turned  into  money  at  an  hour's  warning.  Glycogen, 
On  this  view,  is  especially  drawn  upon  for  a  sudden  demand,  fat 
for  a  steady  drain,  tissue-protein  for  a  life-and-death  struggle. 

Although  it  cannot  be  doubted  that  much  of  the  hepatic 
glycogen  leaves  the  liver  as  sugar,  there  is  no  proof  that  it  all  does 
so.  It  is  known  that  fat  may  be  formed  from  carbo-hydrates 
(p.  524)  ;  and  globules  of  oil  are  often  conspicuous  among  the 
contents  of  liver-cells,  side  by  side  with  glycogen.  It  is  possible, 
therefore,  that  some  of  the  glycogen  may  represent  a  half-way 
house  between  sugar  and  fat,  or,  since  it  is  probable  that  fat 
can  also  be  formed  from  protein,  and  a  purely  protein  diet  pro- 
duces some  glycogen,  a  half-way  house  between  protein  and  fat. 

Pavy  has  put  forward  the  heterodox  view  that  the  glycogen 
formed  in  the  liver  from  the  sugar  of  the  portal  blood  is  never 
reconverted  into  sugar  under  normal  conditions,  but  is  changed 
into  some  other  substance  or  substances,  and  he  denies  that  the 
post-mortem  formation  of  sugar  in  the  hepatic  tissue  is  a  true 
picture  of  what  takes  place  during  life.  But  in  spite  of  the 
brilliant  manner  in  which  he  has  defended  this  thesis,  both  by 
argument  and  by  experiment,  it  must  be  said  that  the  older 
doctrine  of  Bernard,  which  in  the  main  we  have  followed  above, 

33—2 


516  A   MANX  AL  OF  PHYSIOLOGY 

is  attested  by  such  a  cloud  of  modern  witnesses  that  it  seems 
to  be  firmly  and  finally  established. 

Fate  of  the  Sugar — Glycolysis. — What,  now.  is  the  fate  of 
the  sugar  which  either  passes  right  through  the  portal  circula- 
tion from  the  intestine  without  undergoing  any  change  in  the 
liver,  or  is  gradually  produced  from  the  hepatic  glycogen  ? 
When  the  proportion  of  sugar  in  the  blood  rises  above  a  certain 
low  limit  (about  i-5  or  2  to  3  parts  per  1,000),  some  of  it  is 
excreted  by  the  kidneys  (Practical  Exercises,  p.  609). 

A  large  meal  of  carbo-hydrates  is  frequently  followed  by  a 
temporary  glycosuria,  but  much  depends  upon  the  form  in 
which  the  sugar-forming  material  is  taken.  Miura,  for  example, 
after  an  enormous  meal  of  rice  (equivalent  to  6*4  grammes  of 
ash-  and  water-free  starch  per  kilo  of  bod}'- weight),  which,  as  he 
mentions,  tasked  even  his  Japanese  powers  of  digestion  for  such 
food  to  dispose  of,  found  not  a  trace  of  sugar  in  the  urine. 
Dextrose,  cane-sugar  and  lactose,  on  the  other  hand,  when  taken 
in  large  amount,  were  in  part  excreted  by  the  kidneys,  as  was  also 
the  case  with  levulose  and  maltose  in  a  dog  (Practical  Exercises, 
p.  610).*  It  has  been  suggested  as  an  important  practical  rule 
that  a  person  who  can  tolerate  a  certain  amount  of  dextrose  (say 
2  grammes  per  kilo  of  body-weight  taken  not  less  than  two  hours 
after  a  meal)  without  excreting  a  portion  of  it  is  not  the  subject  of 
incipient  diabetes.    Many  healthy  persons  can  tolerate  much  more. 

Except  as  an  occasional  phenomenon,  glycosuria  other  than 
alimentary  is  inconsistent  with  health  ;  and  therefore  in  the 
normal  body  the  sugar  of  the  blood  must  be  either  destroyed  or 
transformed  into  some  more  or  less  permanent  constituent  of  the 
tissues.  The  transformation  of  sugar  into  fat  we  have  already 
mentioned,  and  shall  have  again  to  discuss  ;  it  only  takes  place 
under  certain  conditions  of  diet,  and  no  more  than  a  small  pro- 
portion of  the  sugar  which  disappears  from  the  body  in  twenty- 
four  hours  can  ever,  in  the  most  favourable  circumstances,  be 
converted  into  fat.  Accordingly,  it  is  the  destruction  of  sugar 
which  concerns  us  here,  and  there  is  every  reason  to  believe  that 
this  takes  place,  not  in  any  particular  organ,  but  in  all  active 
tissues,  especially  in  the  muscles,  and  to  a  less  extent  in  glands. 

*  Twenty-four  healthy  students,  whose  urine  had  previously  been 
shown  to  be  free  from  sugar,  ate  quantities  of  cane-sugar  varying  from 
250  grammes  to  750  grammes.  The  urine  was  collected  in  separate 
portions  for  twelve  to  twenty-four  hours  after  the  meal.  In  only  three 
cases  was  reducing  sugar  found  in  the  urine  (by  Fehling's  and  the  phenyl- 
hydrazine  test),  and  then  merely  in  traces.  In  eight  cases  cane-sugar 
was  found,  and  estimated  by  the  polarimeter,  and,  after  boiling  with 
hydrochloric  acid,  by  Fehling's  solution.  The  greatest  quantity  of  cane- 
sugar  recovered  from  the  urine  was  8  grammes  (7*92  grammes  by  Fehling's 
method  and  8'2g  grammes  by  the  polarimeter)  ;  the  highest  proportion 
of  the  quantity  taken  which  appeared  in  the  urine  was  2*5  per  cent.  When 
dextrose  was  found,  cane-sugar  was  always  present  as  well. 


METABOLISM,   NUTRITION  AND  DIETETICS  517 

Tt  has  been  asserted  thai  the  blood  which  leaves  even  a  resting 

muscle,  or  an  inactive  salivary  gland,  is  poorer  in  sugar  than 
that  coming  to  it  ;  and  the  conclusion  has  been  drawn  that  in 
the  metabolism  of  resting  muscle  and  gland  sugar  is  oxidized, 
the  carl  ion  passing  off  as  carbon  dioxide  in  the  venous  blood. 
This  is  indeed  extremely  likely,  for  we  know  that  when  the 
skeletal  muscles  of  a  rabbit  or  guinea-pig  are  cut  off  from  the 
central  nervous  system  by  curara,  the  production  of  carbon 
dioxide  falls  much  below  that  of  an  intact  animal  at  rest  ;  and 
the  carbon  given  off  l>v  such  an  animal  on  its  ordinary  vegetable 
diet  can  be  shown,  by  a  comparison  of  the  chemical  composition 
of  the  food  and  the  excreta,  to  come  largely  from  carbo-hydrates. 
But,  considering  the  relatively  feeble  metabolism  of  muscles 
and  glands  when  not  functionally  excited,  the  large  volume  of 
blood  which  passes  through  them,  the  difficulty  of  determining 
small  differences  in  the  proportion  of  sugar  in  such  a  liquid,  the 
possibilitv  that  even  in  the  blood  itself  sugar  maj^  be  destroyed, 
or  that  it  may  pass  from  the  blood,  without  being  oxidized, 
into  the  lymph,  too  much  weight  may  be  easily  given  to  the 
results  of  direct  analysis  of  the  in-coming  and  out-going  blood. 
And  although  the  results  of  Chauveau  and  Kaufmann,  obtained 
in  this  way,  fit  in  fairly  well  with  what  we  have  already  learnt 
by  less  direct,  but  more  trustworthy,  methods,  they  cannot  be 
accepted  as  yielding  exact  quantitative  information.  They 
found  that  in  one  of  the  muscles  of  the  upper  lip  of  the  horse  the 
quantity  of  dextrose  used  up  during  activity  (feeding  movements) 
was  3°5  times  as  much  as  in  the  same  muscle  at  rest,  and  this 
corresponded  with  the  deficit  of  oxygen  in  the  blood  entering  the 
muscle,  and  with  the  excess  of  carbon  dioxide  in  the  blood  leaving 
it.  More  dextrose  was  also  destroyed  in  the  active  than  in  the 
passive  parotid  gland  of  the  horse,  but  the  excess  per  unit  of 
weight  of  the  organ  was  far  less  than  in  muscle. 

Concerning  the  manner  in  which  dextrose  is  destroyed  in  the 
tissues,  we  are  in  the  same  position  as  in  the  case  of  the  proteins. 
It  cannot  be  definitely  stated  at  present  what  share  is  taken  by 
cleavage  and  what  by  oxidation  in  the  destruction  of  carbo- 
hydrates in  the  organism,  although  oxidation  is  known  to  play  an 
important  role.  Normal  blood  has  been  credited  with  a  ferment 
which  has  the  power  of  destroying  sugar  (glycolysis).  But  with 
rigid  aseptic  precautions  the  loss  of  sugar,  even  in  several  hours,  is 
small,  and  it  is  doubtful  whether  such  a  ferment  exists.  On  the 
other  hand,  Cohnheim  stated  that  while  no  glycolytic  ferment  can 
be  demonstrated  in  the  pancreas,  and  only  an  exceedingly  weak 
glycolytic  action  in  muscular  tissue  (Brunton),  by  combining 
pancreas  and  muscles  distinct  glycolysis,  due  to  a  ferment  action, 
could  be  produced.     He  suggested  that  the  glycolytic  ferment  is 


;iS  /    MANUAL  OF  PHYSIOLOGY 

activated  by  another  substance,  as  trypsinogen  is  activated  by 
enterokinase  (p.  343).  This  announcement  aroused  great  in- 
trust, since  it  is  known  that  the  pancreas  is  intimately  concerned 
in  the  metabolism  of  sugar.  Unfortunately,  however,  the  accu- 
racy of  Cohnheim's  observation  is  still  disputed.  Excision  of 
the  pancreas  in  dogs  causes  permanent  glycosuria  (pancreatic 
diabetes)  (v.  Mering  and  Minkowski),  which  is  prevented  if  a 
portion  of  the  pancreas  be  left  (p.  553).  Diabetes  in  man  is 
known  to  be  frequently  associated  with  pancreatic  lesions. 

Diabetes. — In  the  disease  known  as  diabetes  mellitus,  sugar 
accumulates  in  the  blood,  and  is  discharged  by  the  kidneys, 
and  it  has  been  supposed  that  a  derangement  in  the  glycogenic 
function  of  the  liver  is  sometimes  the  cause  of  this  accumulation 
and  of  this  discharge.  An  artificial  and  temporary  glycosuria, 
in  which  the  sugar  in  the  urine  undoubtedly  arises  from  the 
hepatic  glycogen,  can,  indeed,  be  caused  by  puncturing  the 
medulla  oblongata  in  a  rabbit  at  or  near  the  region  of  the  vaso- 
motor centre.  If  the  animal  has  been  previously  fed  with  a  diet 
rich  in  carbo-hydrates — that  is,  if  it  has  been  put  under  con- 
ditions in  which  the  liver  contains  much  glycogen — the  quantity 
of  sugar  excreted  by  the  kidneys  will  be  large.  If,  on  the  other 
hand,  the  animal  has  been  starved  before  the  operation,  so  that 
the  liver  is  free,  or  almost  free,  from  glycogen,  the  puncture  will 
cause  little  or  no  sugar  to  appear  in  the  urine.  That  nervous 
influences  are  in  some  way  involved  is  shown  by  the  absence 
of  glycosuria  if  the  splanchnic  nerves,  or  the  spinal  cord  above 
the  third  or  fourth  dorsal  vertebra,  be  cut  before  the  puncture 
is  made.  But  sometimes  these  operations  are  themselves 
followed  by  temporary  glycosuria.  Section  of  the  vagi  has  no 
effect  either  in  causing  glycosuria  of  itself  or  in  preventing  the 
'  puncture  '  glycosuria,  although  stimulation  of  the  central 
ends  of  these  and  of  other  afferent  nerves  may  cause  sugar  to 
appear  in  the  urine,  but  not  if  precautions  are  taken  to  prevent 
any  degree  of  asphyxia.  Asphyxia  produces  an  increase  in  the 
sugar  content  of  the  blood  (hyperglycemia),  an  increase  in  the 
flow  of  urine  and  glycosuria.  Under  normal  conditions  the  rate 
of  transformation  of  the  hepatic  glycogen  into  dextrose  is  ad- 
justed in  some  way  to  the  dextrose  content  of  the  blood,  so  that 
when  the  latter  tends  to  sink  more  dextrose  is  produced  in  the 
liver  ;  when  it  tends  to  rise  more  glycogen  is  laid  up  in  the 
hepatic  cells.  Thus,  the  great  function  of  the  glycogen  store  of 
the  liver  is  to  regulate  the  proportion  of  sugar  in  the  blood. 
Although  several  of  the  operations  which  lead  to  temporary 
glycosuria  undoubtedly  bring  about  changes  in  the  hepatic 
circulation,  it  is  as  yet  impossible  to  say  whether  the  whole 
phenomenon  is  at  bottom  a  vaso-motor  effect,  or  is  due  to  direct 


METABOLISM,    NUTRITION     IND  DIETETh  519 

nervous  stimulation  of  the  liver-cells,  or  to  withdrawal  0!  such 
stimulation  or  control  (sec  also  p.  470).     There  is  some  evidence 

that  excitation  of  the  uncut  great  splanchnic  nerve  (on  the  lefl 
side)  in  clogs  may  cause  an  increase  in  the  hyperglycemia, 
diuresis,  and  glycosuria,  even  under  conditions  in  which  as  far 
as  possible  circulatory  effects  are  eliminated.  But  absolute  proof 
of  the  existence  of  glycogenolytic  nerve  fibres  has  not  yet  been 
brought  forward  (Macleod). 

In  the  natural  diabetes  of  man,  as  in  all  the  forms  of  glycosuria 
mentioned,  the  immediate  cause  of  the  glycosuria  is  the  increase 
i>i  sugar  in  the  blood.  Instead  of  the  r  part  per  1,000,  or  a  little 
more  or  less,  which  constitutes  the  normal  proportion  in  a  healthy 
man,  in  diabetes  3  or  4  parts,  and  in  exceptional  cases  even 
7  to  10  parts  per  r,ooo  may  be  present.  The  riddle  of  diabetes 
is  the  explanation  of  this  persistent  hyperglycemia.  It  is 
possible  that  in  some  cases  the  sugar  coming  from  the  alimentary 
canal  passes  entirely  or  in  too  large  amount  through  the  liver, 
owing  to  a  deficiency  in  its  power  of  forming  glycogen.  But 
although  in  certain  cases  of  diabetes  specimens  of  the  hepatic 
cells,  obtained  by  plunging  a  trocar  into  the  liver,  have  been 
found  free  from  glycogen,  in  others  glycogen  has  been  present. 
The  muscles  also  are  usually  much  poorer  in  glycogen  than 
normal  muscles.  The  cause  of  this  defect  in  glycogen-forming 
power  has  been  supposed  by  some  to  be  the  absence  of  a  glycogen- 
forming  ferment,  or  its  production  in  too  small  an  amount.  But 
this  has  not  been  proved.  In  addition  to  an  interference  with 
the  due  and  regulated  storage  of  the  surplus  sugar  as  glycogen, 
it  is  necessary  for  a  rational  explanation  of  many  of  the  facts  of 
diabetes  to  assume  that  from  some  change  in  the  tissues  sugar 
has  ceased  to  be  a  food  for  them,  or  is  used  up  in  smaller  amount 
than  in  the  healthy  body.  The  change  may  be  the  loss  or  diminu- 
tion of  a  glycolytic  ferment  or  a  substance  necessary  for  the 
activation  of  such  a  ferment.  And  although  the  sugar-destroying 
power  of  blood  from  diabetic  patients,  or  from  animals  in  which 
glycosuria  has  been  caused  by  phloridzin,  is  not  at  all  inferior  to 
that  of  healthy  blood,  it  may  be  that  the  intracellular  glycolytic 
ferments,  if  such  really  exist,  are  much  less  active,  especially  in 
the  more  severe  forms  of  the  disease.  The  actual  primary  pro- 
duction of  sugar  may  be  no  greater  than  in  a  normal  person  with 
the  same  diet.  And  there  is  no  reason  to  suppose  that  an  over- 
production of  dextrose  is  ever  in  pathological  diabetes  the  proxi- 
mate cause  of  the  hyperglycemia  and  glycosuria.  But  a  secon- 
dary overproduction  of  sugar  unquestionably  occurs  in  many 
cases.  The  tissues,  bathed  as  they  are  in  liquids  rich  in  dex- 
trose, are  nevertheless  starving  for  sugar,  since  they  cannot  use 
what  is  offered  to  them,  and  the  bodv  labours  to  avert  the  famine 


./   MANUAL  OF  PHYSIOLOGY 

by  increasing  its  production  of  sugar,  the  sugar-forming  tissues 
being  stimulated  to  their  task  either  through  nervous  influences 
or  by  chemical  messengers  circulating  in  the  blood.  Why  the 
tissues  cannot  burn  dextrose  as  they  normally  do  is  a  question 
of  great  interest,  bul  as  yet  no  satisfactory  answer  can  be  given. 

Another  hypothesis,  which  endeavours  to  conned  the  impair- 
ment of  the  glycogenetic  function  with  the  impairment  of  the 
power  to  oxidize  dextrose,  is  that  it  is  only  sugar  which  has  been 
condensed  or  polymerized  to  glycogen  which  can  be  assimilated 
by  the  tissues,  and  therefore  burned  (v.  Noorden). 

It  is  remarkable  that  levulose  may  within  limits  be  entirely 
used  up  in  the  tissues  of  a  diabetic  patient,  or  of  a  dog  rendei  ed 
diabetic  by  extirpation  of  the  pancreas,  while  dextrose,  which  is 
so  closely  allied  to  it,  is  promptly  cast  out  by  the  kidneys. 
( dycogen  is  also  formed  from  levulose,  though  not  from  dextrose, 
in  the  depancreatized  dog.  This  is  not  easily  reconciled  with 
the  last-mentioned  theory  unless  we  suppose  that  the  glycogen 
which  levulose  gives  rise  to  is  somewhat  different  from  the 
glycogen  produced  by  the  condensation  of  dextrose.  The 
opposite  condition  is  also  seen  in  a  few  individuals — namely, 
intolerance  of  levulose  and  its  spontaneous  appearance  in  the 
urine  (levulosuria) — while  other  carbo-hydrates  are  normally  used 
up.     Like  pentosuria  (p.  450),  the  condition  is  not  a  serious  one. 

In  dogs  deprived  of  the  pancreas,  and  in  dogs  under  the 
influence  of  phloridzin,  glycerin,  given  by  the  mouth,  causes 
an  increase  in  the  excretion  of  sugar  up  to  two  or  three  times 
the  original  amount.  The  giving  of  fat  does  not  increase  the 
amount  of  sugar  excreted,  which,  however,  is  increased  by  such 
substances  as  egg-yolk,  which  contain  lecithin.  These  should 
accordingly  be  avoided  in  cases  in  which  a  strictly  antidiabetic 
diet  is  desired.  It  is  much  more  important  to  exclude  carbo- 
hydrates largely  or  entirely  from  the  food,  although  oatmeal  and 
potatoes  are  said  to  occupy  an  exceptional  position,  and  have 
even  been  recommended  as  beneficial.  Calcium  chloride  has 
been  stated  to  diminish  the  sugar  excretion  in  diabetes  (Boigey), 
and  it  has  a  similar  effect  in  certain  of  the  artificial  glycosurias 
(Brown,  Fischer). 

In  many  cases  even  when  carbo-hydrates  are  completely,  or 
almost  completely,  omitted  from  the  food,  sugar,  derived  from 
the  breaking-down  of  proteins,  and  possibly  to  some  extent  from 
fats,  still  continues  to  be  excreted,  although  in  smaller  quantity. 
Other  products  of  the  deranged  metabolism  of  proteins,  and 
especially  of  fats,  such  as  acetone,  aceto-acetic  acid,  and  oxy- 
butyric  acid,  may  also  appear  in  the  urine,  or,  accumulating  in 
the  blood,  may,  by  uniting  with  its  alkalies,  seriously  diminish  the 
quantity  of  carbon  dioxide  which  that  liquid  is  capable  of  cany- 


Ml  TABOLISM,    VI   TRITJON   AND  DIET1  I  521 

iii^.  and  thus  lead  to  the  condition  known  as  diabel Lc  coma.     The 
small  amounl  of  carbon  dioxide  in  the  venous  blood  may  also  be 

partly  due  to  the  hyper] ia,  marked  by  increased  depth  ol  the 

respiratory  movements  produced  by  stimulation  of  the  respira- 
tory centre  by  other  substances  than  carbon  dioxide.  The 
increased  ventilation  causes  .1  I. ill  in  the  carbon  dioxide  pressun 
in  the  alveolar  air,  and  therefore  an  increased  elimination  of  that 
gas  from  the  blood.  This  form  of  coma  appears  to  be  really  in 
part  an  acid-poisoning  comparable  to  the  condition  produced  in 
animals  by  doses  of  mineral  acids  too  large  to  be  neutralized  by 
the  ammonia  split  oil  from  the  proteins.  The  administration  of 
very  large  doses  of  alkalies  (sodium  bicarbonate,  for  instance, 
to  the  amount  even  of  hundreds  of  grammes)  has  been  recom- 
mended for  the  treatment  of  this  serious  complication,  and  in 
many  cases  it  is  successful  in  staving  it  off  for  a  time.  Often, 
however,  in  spite  of  a  prolonged  course  of  treatment,  during 
which  the  urine  has  continued  distinctly  alkaline,  fatal  coma 
eventually  occurs.  The  coma  then  is  not  merely  a  symptom  of 
acidosis,  but  is  also  due  to  the  specific  toxic  effects  of  the  acids 
even  when  neutralized.  Other  toxic  products  may  also  be 
formed  in  the  deranged  metabolism. 

Glycosuria  can  be  caused  in  many  other  ways  than  those 
already  mentioned — e.g.,  by  concussion  of  the  brain,  occlusion 
and  subsequent  release  of  the  arteries  supplying  the  brain  and 
cervical  cord,  acute  haemorrhage,  injection  of  water  or  physio- 
logical salt  solution  into  the  bile-ducts,  into  the  mesenteric 
veins,  or,  in  considerable  amount,  into  the  general  circulation. 
Carbon  monoxide  has  a  similar  action  owing  to  the  deficiency  of 
oxygen  occasioned  by  it.  Many  drugs  also  cause  glycosuria, 
including  curara,  morphine,  phloridzin,  adrenalin,  and  other 
substances.     Of  these  the  last  two  are  the  most  interesting. 

Phloridzin  glycosuria  agrees  with  pancreatic,  but  differs 
from  '  puncture  '  diabetes  in  this,  that  it  can  be  produced  in 
an  animal  free  from  glycogen,  and  is  accompanied  by  extensive 
destruction  of  proteins.  It  differs  from  other  forms  of  diabetes 
in  being  associated,  not  with  an  increase,  but  with  a  diminution 
in  the  sugar  of  the  blood.  This  is  best  explained  by  supposing 
that  the  phloridzin  acts  on  the  kidney  in  such  a  way  as  to  in- 
crease the  permeability  of  the  glomerular  epithelium  for  sugar, 
or  (in  terms  of  the  secretion  theory  of  urine  formation)  in  such  a 
way  as  to  increase  its  sensitiveness  to  the  stimulus  of  sugar 
circulating  in  the  blood.  The  sugar  is,  therefore,  rapidly  swept 
out  of  the  circulation,  and  this  leads  secondarily  to  an  increased 
production  of  sugar  to  make  good  the  loss.  In  addition,  within 
certain  limits  there  is  a  total  inabilitj^  on  the  part  of  the  body 
to  consume  dextrose. 


522  /    VTANUA1    OF  PHYSIOLOGY 

After  ilif  preliminary  sweeping  oul  of  the  sugar  already  in 
th<'  body  a  definite  ratio  is  established  between  the  dextrose 
and  the  nitrogen  eliminated  in  the  urine  (dextrose:  nitro 
:  :  3'6  or  37  :  [).  The  sugar  at  this  stage  is  produced  entirely 
from  proteins,  and  not  at  all  from  fat.  The  degree  oi  intoler- 
ance for  carbo-hydrates  in  pathological  diabetes  may  be  arrived 
a1  by  putting  the  patient  on  a  diel  of  protein  and  fal  (rich 
cream,  meat,  butter,  and  eggs),  and  determining  the  ratio  oi 
dextrose  to  nitrogen  excreted.  It  it  is  ;•(>  to  yy  :  1,  intolerance 
is  complete,  none  of  the  dextrose  produced  from  protein  being 
burned,  and  there  will  probably  be  a  quickly  fatal  issue  (Lusk 
and  Mandel).  There  is  some  evidence  that,  in  addition  to  the 
increased  permeability  of  the  kidney  to  sugar  and  the  diminished 
power  of  the  tissues  in  general  to  destroy  it,  the  renal  epithelium 
is  actually  an  important  seat  of  the  sugar  production  (Brodie). 

In  adrenalin  glycosuria  the  sugar-content  of  the  blood  is 
increased.  Subcutaneous  injection  of  adrenalin  chloride  causes 
a  mild,  intravenous  injection  a  greater  glycosuria,  and  intra- 
peritoneal injection  the  greatest  glycosuria  of  all  (Herter).  The 
best  evidence  is  that  the  glycosuria  is  produced  by  some  action 
on  the  liver,  possibly  through  the  excitation  of  sympathetic  fibres 
controlling  the  production  of  dextrose  from  glycogen  (I  nderhill 
and  Closson),  or  by  a  direct  effect  on  the  hepatic  cells,  which 
hastens  the  normal  transformation  of  glycogen  into  dextrose,  or 
hinders  the  normal  transformation  of  dextrose  into  glycogen. 
After  repeated  injections  of  adrenalin  a  tolerance  for  it  is 
established,  and  glycosuria  is  no  longer  caused. 

3.  Metabolism  of  Fat. — The  fat,  passing  along  the  thoracic 
duct  into  the  blood-stream,  is  very  soon  removed  from  tin- 
circulation,  for  normal  blood  contains  only  traces,  except  during 
digestion.     Where  does  it  go  ?     What  is  its  fate  ? 

The  presence  of  adipose  tissue  in  the  body  might  suggest  a 
ready  answer  to  these  questions.  The  fat-cells  of  adipose  tissue 
are  ordinary  fixed  connective-tissue  cells  which  have  become 
filled  with  fat,  the  protoplasm  being  reduced  to  a  narrow  ring, 
in  which  the  nucleus  is  set  like  a  stone.  It  would,  at  first 
thought,  seem  natural  to  suppose  that  the  fat  of  the  food  is 
rapidly  separated  by  these  cells  from  the  blood,  and  slowly  given 
up  again  as  the  needs  of  the  organism  require,  just  as  carbo- 
hydrate is  stored  in  the  liver  for  gradual  use.  And  it  has  been 
found  that  a  lean  dog,  fed  with  a  diet  containing  much  fat  and 
little  protein,  puts  on  more  fat,  as  estimated  by  direct  analysis, 
or  keeps  back  more  carbon,  as  estimated  by  measurements  of 
the  respiratory  exchange,  than  can  be  accounted  for  on  the 
supposition  that  even  the  whole  of  the  carbon  of  the  broken- 
down  protein  corresponding  to  the  excreted  nitrogen  has  been 


METABOLISM,    \>   VRITIOS     IND  DIETETICS 

laid  up  in  the  form  o\  fat,  Even  with  a  diet  of  purr  fa1  and 
with  such  a  diet  digestion  and  absorption  are  carried  on  under 
unfavourable  conditions —more  carbon  is  retained  than  can 
have  come  from  the  metabolism  of  the  proteins  of  the  body 
measured  by  the  nitrogen  given  off  in  the  urine  and  faeces  :  the 
i.it  passes  rapidly  from  the  Mood  into  the  organs,  and  especially 
into  the  liver  (Hofmann,  Pettenkofer  and  Voit).  It  is  thus  certain 
thai  some  of  the  absorbed  fat  may  be  stored  up  as  fat  in  the  body. 

This  is  borne  out  by  the  careful  experiments  of  Munk  and 
Lebedeff,  who  found  that  when  dogs  are  fed  with  excess  of  foreign 
fat  (linseed  oil,  rape  oil,  mutton  fat),  a  fat  is  laid  down  which  is 
quite  different  from  dog's  fat,  and  has  the  greatest  resemblance 
to  the  fat  of  the  food.  Thus,  when  rape  oil,  which  contains  a  fat  t  y 
acid,  erucic  acid,  not  found  in  animal  fat,  was  given,  erucic  acid 
could  be  detected  in  the  fat  laid  on.  When  the  dogs  were  fed 
with  mutton  fat,  whose  melting-point  is  much  higher  than  that  of 
dog's  fat,  the  fat  laid  on  did  not  melt  till  it  was  heated  to  400  C. 
or  more.  When  they  were  fed  with  linseed  oil,  the  body-fat 
was  found  liquid  even  at  o°  C.  We  have  already  referred  (p.  413) 
to  the  fact  that  neutral  fat  can  be  built  up  in  the  wall  of  the 
intestine  from  fatty  acids  given  in  the  food.  Munk  has  shown 
that  fat  formed  in  this  way  can  also  be  laid  down  as  body-fat. 
But  besides  the  fat  and  fatty  acids  of  the  food,  the  fat  of  the 
body  has  other  sources,  and  some  of  it  is  produced  by  more 
complex  processes. 

The  fat  of  a  dog  consists  of  a  mixture  of  palmitin,  olein,  and 
stearin.  When  a  starved  dog  was  fed  on  lean  meat  and  a  fat 
containing  palmitin  and  olein,  but  no  stearin,  the  fat  put  on 
contained  all  three,  and  did  not  sensibly  differ  in  its  composition 
from  the  normal  fat  of  the  dog  (Subbotin).  Stearin  must, 
therefore,  have  been  formed  in  some  way  or  other  in  the  body. 
If  it  was  produced  from  the  olein  and  palmitin  of  the  food,  the 
portion  of  these  deposited  in  the  cells  of  the  adipose  tissue  must 
have  undergone  changes  before  reaching  this  comparatively 
fixed  position.  But  there  is  conclusive  evidence  that  fat  may 
be  derived  from  other  sources,  certainly  from  carbo-hydrates,  and 
probably  from  proteins  ;  and  the  stearin  may  have  been  formed 
from  the  carbo-hydrates  or  proteins  of  the  food  or  tissues,  and  not 
directly  from  fat.  And  if  the  stearin  was  produced  from  proteins 
or  carbo-hydrates,  it  is  evident  that  the  olein  and  palmitin  might 
have  been  formed  in  this  way  too,  the  portion  of  the  carbo- 
hydrate or  protein  devoted  to  this  purpose  being  sheltered  from 
oxidation  by  the  combustion  of  the  fats  of  the  food.  It  is  well 
known  that  not  only  neutral  fats,  but  also  fatty  acids,  exert  such 
a  '  protein-sparing  '  action.  It  is  possible  also  that  the  fat  which 
is  normally  excreted  into  the   intestine  (p.  415),  and  which  is 


524  I    U  INU  U    OF  PHYSIOLOGY 

perhaps  derived  from  broken-down  proteins,  may  be  reabsorbed, 

and  take  its  place  among  the  fat  '  pul  on.' 

Formation  of  Fat  from  other  Sources  than  the  Fat  of  the 
Food — (i)  From  Carbo-hydrates.  It  has  been  found  thai  the 
addition  of  protein  to  a  diet  oi  fat,  and  especially  toa  diet  ol  carbo- 
hydrate, in  larger  amount  than  is  jusl  necessary  for  nitrogenous 
equilibrium  (p.  529),  leads  to  a  more  rapid  increase  in  the  carbon 
deficit  that  is,  in  the  tat  put  on  than  if  the  minimum  quantity 
of  protein  required  tor  nitrogenous  equilibrium  had  been  given. 
From  this  it  is  inferred  that  the  carbonaceous  residue  ot  the 
broken-down  protein  is  shielded  from  oxidation  by  tin-  fat.  and 
to  a  still  greater  extent  by  the  carbo-hydrates,  and  so  retained  in 
the  body  as  fat.  And  there  is  little  doubt  that  the  high  repute  of 
carbo-hydrates  as  fattening  agents  is  in  part  due  to  their  taking 
the  place  of  proteins  and  fats  in  ordinary  '  current  '  metabolism, 
and  so  allowing  body-fat  to  be  laid  down  from  these.  Voit, 
indeed,  has  gone  so  far  as  to  assert  that  this  is  the  only  sense  in 
which  carbo-hydrates  can  be  said  to  form  fat,  and  that,  in 
carnivorous  animals  at  least,  a  direct  conversion  never  occurs. 
But  the  experiments  of  Rubner  have  shown  that  in  a  dog  fed 
with  a  diet  rich  in  carbo-hydrates,  and  containing  but  little  fat 
and  no  proteins  at  all,  the  carbon  deficit  was  greater  than  could 
be  accounted  for  by  the  proteins  being  broken  down  in  the 
body  and  the  fat  of  the  food.  In  the  pig  and  goose,  too,  the  direct 
formation  of  fat  from  carbo-hydrates  has  been  demonstrated. 

For  example,  in  an  experiment  by  Tscherwinsky  two  young  pigs 
of  the  same  litter  were  taken.  They  weighed  respectively  7,300 
grammes  and  7,290  grammes.  One  was  killed,  and  the  amount 
of  fat  and  nitrogen  in  its  body  directly  estimated.  From  the 
nitrogen  the  maximum  quantity  of  protein  which  could  be  present 
was  calculated.  The  other  pig  was  fed  for  four  months  with  barley, 
which  was  analyzed.  The  excreta  were  also  analyzed  to  determine 
the  amount  of  unabsorbed  fat  and  protein.  At  the  end  of  the  four 
months  the  pig  was  killed.  It  now  weighed  24  kilogrammes,  and 
contained  2*52  kilogrammes  protein  and  9-25  kilogrammes  fat. 
Subtracting  the  protein  (0-96  kilogramme)  and  fat  (0-69  kilogramme) 
originally  present,  156  kilogrammes  of  protein  and  S'^o  kilogrammes 
of  fat  must  have  been  put  on.  The  amount  of  protein  taken  in  the 
food  was  7-49  kilogrammes,  and  of  fat  066  kilogramme.  There! 
5-93  kilogrammes  of  protein  must  have  been  used  up.  and  790  kilo- 
grammes of  fat  laid  on.  At  least  5  kilogrammes  of  this  fat  must 
have  come  from  the  carbo-hydrate  of  the  food.  Only  a  small  amount 
of  the  fat  put  on  could  possibly  have  come  from  the  protein. 

It  is  probable  that  in  the  formation  of  fats  the  carbo-hydrates 
are  first  split  up  to  some  extent,  and  that  the  fats  are  then  con- 
structed from  their  decomposition  products,  oxygen  being  lost 
in  the  process,  since  fat  is  poorer  in  oxygen  than  carbo-hydrate. 
The  production  of  wax  by  bees,  which  used  to  be  given  as  a  proof 
of  the  formation  of  fat  from  sugar,  is  not  decisive,  for  in  raw 


METABOLISM,    M   IKIIK)\    AND  nil  111  l< 

honey  proteins  are  present  ;  and  even  when  bees  fed  on  pure 
honey  or  sugar  manufacture  wax,  it  may  be  derived  from  the 
broken-down  proteins  of  their  own  bodies. 

(2)  From  Protein.  Dry  protein  contains  on  the  average  16  p<  r 
cent,  oi  nitrogen  and  50  per  cent,  oi  carbon,  and  urea  contains 
40  per  cent,  of  nitrogen  and  20  per  cent,  of  carbon.  Urea  is 
therefore  three  times  as  rich  in  nitrogen  as  the  protein  from 
which  it  is  derived,  but  two  and  a  half  times  poorer  in  carbon  ; 
and  less  than  one-seventh  of  the  carbon  of  protein  will  be 
eliminated  in  the  urea,  which  carries  off  all  the  nitrogen.  A 
carbonaceous  residue  is  left,  which,  it  is  extremely  probable,  may 
under  certain  circumstances  be  converted  into  fat,  as  we  know- 
it  may  into  carbo-hydrate;  yet  absolutely  flawless  experiments 
to  prove  the  direct  production  of  fat  from  protein  seem  still  to 
be  wanting. 

In  the  experiments  of  Bauer,  the  amount  of  oxygen  consumed 
and  of  carbon  dioxide  and  nitrogen  excreted  was  determined  in 
starving  dogs.  Phosphorus,  which,  as  is  well  known,  causes 
extensive  fatty  changes  in  the  organs,  was  then  administered  in 
small  doses  for  several  days.  The  excretion  of  nitrogen  was  doubled, 
the  excretion  of  carbon  dioxide  and  the  consumption  of  oxygen 
diminished  to  one-half.  When  the  animals  died,  in  a  few  days,  the 
organs  were  all  found  loaded  with  fat.  In  one  case  42*4  per  cent,  of 
the  solids  of  the  muscles  and  30  per  cent,  of  the  sohds  of  the  liver 
consisted  of  fat.  This  is  much  more  than  the  normal  amount.  It 
was  assumed  that  the  fat  could  not  have  been  simply  transferred 
from  the  adipose  tissue,  since  the  dog  had  been  starved  for  twelve 
days  before  the  phosphorus  was  given,  and  died  on  the  twentieth 
day  of  starvation.  Now,  after  such  a  period  of  hunger  the  amount 
of  fat  in  the  adipose  tissue  is  greatly  reduced.  It  was  therefore 
concluded  that  the  source  of  the  fat  could  only  have  been  the 
broken-down  protein.  Since  the  nitrogen  excretion  was  increased, 
while  the  carbon  excretion  was  diminished,  it  was  supposed  that  a 
residue  rich  in  carbon  must  have  been  spht  off  from  the  proteins, 
and,  remaining  unburnt  in  the  body,  must  have  been  converted 
into  fat.  Experiments  of  this  kind  are  open  to  criticism  on  several 
grounds,  but  especially  on  this  :  that  unless  the  fat-content  of  the 
whole  body  before  the  administration  of  the  poison  is  known,  it  is 
impossible  to  be  sure  that  the  fat  in  a  particular  tissue  has  not  been 
increased  simply  by  the  transportation  of  fat  from  some  other  tissue. 
It  has  been  conclusively  shown  that  migration  of  pre-formed  fat 
does  occur,  and  on  an  extensive  scale,  in  phosphorus  poisoning. 
For  example,  a  dog  was  fed  for  a  time  with  sheep's  tallow,  and  fat 
was  laid  down  in  its  adipose  tissue  with  the  physical  and  chemical 
characters,  not  of  dog's,  but  of  sheep's  fat.  The  animal  was  then 
poisoned  with  phosphorus,  and  the  fat  which  accumulated  in  the 
liver  examined.  It  also  resembled  sheep's  fat,  as  it  should  have 
done  had  it  migrated  from  the  adipose  tissue,  and  not  dog's  fat, 
as  it  might  have  been  expected  to  do  had  it  been  formed  in  the 
hepatic  cells  from  protein.  The  ease  with  which  connective-tissue 
fat — i.e.,  food  fat — migrates  to  the  liver  suggests,  with  other  facts, 
that  the  liver  has  a  special  relation  to  the  transformation  ot  this 


;    WANUAl    OF  PHYSIOLOGY 

i.ii  into  the  fat  <>i  the  organs.  This  'organized  '  intracellular  fat 
differs  in  various  ways  from  the  fats  oi  adipose  tissue.  Its  '  iodine 
value'  (p.  |.)  is  higher  (I.e. it  lies),  and  a  large  proportion  oi  it  consists 
"i  ph isphatide  Lipoids  | p.  337). 

The  mosl  convincing  evidence  that  fat  is  not  produced  in  in<  ri 
.Mm Hint  under  the  influence  of  phosphorus  has  been  obtained  by 
determining  by  actual  analysis  the  total  fat  in  animals.  ;md  then 
poisoning  similar  animals  with  phosphorus  and  again  estimating 
the  total  fat.  Far  from  being  increased,  the  fat  may  even  bi 
1  reased  in  the  poisoned  animals  (Taylor,  etc.).  There  is  no  ground, 
then,  for  the  assumption  that  phosphorus  and  other  substances, 
like  arsenic,  antimony,  etc.,  which  bring  about  so-called  '  fatty 
degeneration  '  of  the  organs,  act  by  causing  or  accelerating  the 
transformation  of  protein  into  fat.  Yet  there  is  good  evidence  that 
they  do  accelerate  the  decomposition  of  protein,  or  at  least  inter- 
fere with  its  normal  metabolism,  for  after  phosphorus  poisoning 
amino-acids  (leucin,  tyrosin,  glycin)  appear  in  the  urine.  The 
observations  of  Lusk  and  his  pupils  indicate  that  phosphorus  does 
not  directly  increase  the  amount  of  protein  broken  down,  but  does 
so  indirectly,  by  favouring  the  conversion  of  the  carbo-hydrate-like 
radicle  of  the  protein  molecule  into  leucin,  tyrosin,  and  perhaps 
fat,  and  thereby  necessitating  an  increased  consumption  of  protein. 

A  celebrated  experiment,  performed  nearly  forty  years  ago.  was 
long  supposed  to  furnish  an  absolute  proof  of  the  formation  of  fat 
from  protein,  under  strictly  physiological  conditions,  although  in  a 
humble  form  of  animal  life.  Maggots  were  allowed  to  develop  from 
the  egg  on  blood  containing  a  known  amount  of  fat.  The  quantity 
of  fat  in  the  eggs  was  also  known.  After  the  maggots  had  grown, 
ten  times  as  much  fat  was  found  in  them  as  had  been  contained  in 
the  blood  and  eggs  together.  The  trifling  quantity  of  sugar  in 
the  blood  was  utterly  inadequate  to  account  for  the  fat,  which,  it 
was  concluded,  must  therefore  have  come  from  the  proteins  of  the 
blood  (Hofmann).  It  can  be  objected  to  this  experiment  that  no 
precautions  were  taken  to  prevent  the  growth  of  micro-organisms 
on  the  blood,  and  fat  might  have  been  formed  by  them  from  the 
proteins.  Further,  the  fat  estimations  would  scarcely  pass  muster 
according  to  the  present  standards. 

The  experiments  of  Pettenkofer  and  Voit,  which  were  supposed 
to  have  demonstrated  that  in  the  higher  animals  also  fat  is  formed 
from  proteins  under  normal  conditions,  are  in  the  same  position. 
According  to  them,  a  dog  fed  for  a  time  on  a  liberal  diet  of  lean 
meat  may  go  on  excreting  a  quantity  of  nitrogen  equal  to  that  in  the 
food,  while  there  is  a  deficiency  in  the  carbon  given  oft.  Or  if  the 
clog  is  not  in  nitrogenous  equilibrium  (p.  529),  but  putting  on 
nitrogen  in  the  form  of  '  flesh,'  the  deficiency  in  the  carbon  given  off 
may  be  too  great  in  proportion  to  the  nitrogen  deficit  to  warrant  the 
assumption  that  all  the  retained  carbon  has  been  put  on  in  the  form 
of  protein.  In  cither  case,  carbon  in  large  amount  can  only  come 
from  the  proteins  of  the  food,  and  can  only  be  stored  up  in  the  body 
in  the  form  of  fat.  For  lean  meat  contains  but  a  trifling  quantity  of 
carbon  in  any  other  proximate  principle  than  protein,  and  the  non- 
protein carbon  of  the  animal  body  is  only  to  a  very  small  extent 
contained  in  carbo-hydrates  or  other  substances  than  fat. 

Pfliiger  has  criticised  these  experiments,  and  has  shown  that 
lean  meat  contains  more  fat  than  was  supposed,  and  this  is  now 
generally  admitted.      He  has  endeavoured  to  show  that  the  fat  and 


METABOLISM,    NUTRITION     IND  DIETETICS  ;>7 

glycogen  in  the  meal  given  to  the  animals  fullj  accounts  foi  th< 
carbon  retained.  Pfiiiger,  indeed,  takes  up  the  position  thai  th< 
tat  of  the  body  comes  exclusively  from  the  carbo-hydrates  and 
fats  "i  the  food,  and  not  at  all  from  the  proteins,  Bu1  there  is 
little  doubt  that  in  this  he  lias  gone  too  Ear,  although  his  criticism 
has  rendered  it  impossible  any  Longer  to  appeal  to  Pettenkofer  ami 
Voit's  results  as  good  evidence  on  the  other  side. 

If  none  of  the  supposed  quantitative  proofs  of  the  conversion 
oi  proteins  into  fat  which  have  hitherto  been  brought  forward  are 
free  from  flaw,  the  same  is  true  of  the  alleged  qualitative  indica- 
t  ions  of  its  possibility  and  of  its  actual  occurrence.  The  accumu- 
lation of  fat  between  the  hepatic  cells  caused  by  phloridzin  is,  at 
the  best,  no  better  evidence  than  the  accumulation  within  the 
cells  in  phosphorus  poisoning.  The  formation  of  adipocere  (a 
cheesy  substance,  rich  in  fatty  acids  united  with  calcium  or 
ammonium),  sometimes  seen  in  dead  bodies  which  have  remained 
a  long  time  under  water  or  in  moist  graveyards,  is  largely,  if  not 
entirely,  due  to  the  fat  ahead}7  present  in  the  parts  which  have 
undergone  the  change,  or  to  fat  removed  by  the  water  from  other 
parts  of  the  body.  If  any  portion  of  the  adipocere  represents 
fat  formed  from  protein,  this  transformation  may  well  be  credited 
to  the  numerous  micro-organisms  present,  and  throws  no  light 
upon  the  question  of  fat  formation  in  the  normal  organism. 
The  fat  in  the  cells  of  the  sebaceous  glands,  and  of  the  mammary 
glands,  maj7  be  produced  from  protein  by  a  transformation  of  the 
cell-substance.  But  absolutely  convincing  proof  is  wanting.  The 
rule  which  experience  has  taught,  that  a  woman  during  lactation 
requires  an  excess  of  proteins  in  her  food  corresponding  not  only 
to  the  proteins,  but  also  to  the  fat  given  off  in  the  milk,  suggests 
such  an  origin  for  the  milk-fat,  but  does  not  prove  it. 

As  to  the  ultimate  fate  of  the  fat,  from  whatever  source  it 
may  be  derived,  our  knowledge  may  be  compressed  into  a  single 
sentence  :  Sooner  or  later  it  is  split  and  oxidized  to  carbon  dioxide 
and  water,  its  energy  being  converted  into  heat  or,  directly  or  in- 
directly, into  mechanical  or  chemical  work  ;  some  of  the  fat  absorbed 
from  the  intestine  rapidly  undergoes  this  change  without  entering 
the  fat-cells  of  the  adipose  tissue.  A  portion  of  the  fat  may  be 
changed  into  carbo-hydrates.  This  has  been  proved  for  the  glycerin 
component ;  its  possibility  must  be  admitted  for  the  fatty  acids,  but 
complete  proof  has  not  yet  been  given. 

The  mechanism  of  the  transformation  of  fats  is  no  better  under- 
stood than  that  of  the  carbo-hydrates  or  the  proteins.  Many  ot 
the  tissues  contain  intracellular,  soluble,  fat-splitting  ferments 
called  lipases,  especially  the  liver,  the  active  mammary  gland, 
and  the  intestinal  mucosa.  We  have  already  seen  that  there 
is  evidence  that  these  lipases,  like  some  other  enzymes,  have  a 
reversible  action.     They  are  either  fat-splitting  or  fat-forming 


;  js  r  MANl  'AL  OF  PHYSIOLOGY 

ferments,  according  to  the  conditions  (Kastle  and  Loevenhart). 
The  perfectly  aseptic  blood  does  not  split  ordinary  neutral  I 
although  it   contains  a  ferment   which  splits  up  monobutyrin 
(glycerin  butyrate)  into  glycerin  and  butyric  acid. 

Summary.  At  this  point  let  us  sum  up  what  we  have  learnl 
as  to  the  relation  between  the  proximate  principles  oi  the  iUsur> 
and  the  proximate  principles  of  the  food.  Inside  the  body  we 
recognise  representatives  of  the  three  groups  of  organic  food-sub- 
stances in  a  typical  diet — proteins,  carbo-hydrates,  and  fats.  Bu1 
we  should  greatly  err  if  we  were  to  imagine  that  the  three  streams 
of  food-materials  have  flowed  from  the  intestines  into  the  tissues 
each  in  its  separate  channel,  neither  giving  to  nor  taking  from 
the  others.  The  fats  of  the  body  may,  indeed,  in  part  be  composed  of 
molecules  which  were  present  as  fat  in  the  food  ;  but  they  may  also 
be  formed  from  carbo-hydrates,  and  probably  from  proteins.  The 
carbo-hydrates  of  the  body — the  glycogen  of  the  liver  and  muscles,  the 
sugar  of  the  blood — may  undoubtedly  be  derived  from  carbo-hydrates 
in  the  food,  but  they  may  also  be  derived  from  proteins,  although 
probably  not  from  fats  (except  from  their  glycerin  constituent). 
The  proteins  of  the  body  arise  solely  from  the  proteins  of  the  food  ; 
neither  fats  nor  carbo-hydrates  can  form  proteins,  although  both  can 
economize  them  and  shield  them  from  an  over-hasty  metabolism. 

4.  The  Income  and  Expenditure  of  the  Body — (1)  Income  and 
Expenditure  of  Nitrogen. — 

Preliminary  Data. — The  office  of  the  food  is  to  maintain  the  con- 
stituents of  the  body  upon  the  whole  in  their  normal  proportions. 
A  knowledge  of  the  chemical  composition  of  the  body  is.  therefore, 
an  important  datum  in  the  consideration  of  the  statistics  of  its 
metabolism.  The  body  of  a  man  analyzed  by  Volkmann  had  the 
following  composition  : 

,    .  f  Water         -  059  per  cent. 

Inorganic  substances      lMineral  matter  .         .       ^        „ 

/Carbon  184  per  cent.  1 

1   *                   Hydrogen  2*7  ,,                w%.„ 

Organic  substances         j  Nitr0gen  2"6  „          f      "9  / 

I  Oxygen  6'o  ,,          J 

The  muscles,  the  adipose  tissue,  and  the  skeleton  form  nearly 
four-fifths  of  the  total  body-weight  in  the  adult.  The  following 
table  shows  the  percentage  amount  of  each  of  these  1  issues  in  a  man, 
a  woman,  and  a  child  (Bischoff)  : 


Man. 

Woman. 

New  lxjrn 
Child. 

Voluntary  muscles      -          41-8 
Adipose  tissue    -          -           18-2 
Skeleton    -          -          -           15-9 
Rest  of  body      -         -          24-1 

35-8 

28-2 

20-9 

23*5 

13-5 
15-7 
47-3 

METABOLISM,    NUTRITION   AND  HI  I  TETICS 

The  nitrogen  is  contained  chiefly  in  the  muscles,  glands,  and 
nervous  system,  and  in  the  constituents  of  the  connective  tissues, 
which  yield  gelatin,  various  mucoids,  and  elastin.  The  ordinary 
proteins  make  Up  about  o  per  cent,  of  the  weight  of  the  body,  or 
z 2  per  cent .  of  its  solids;  the  albuminoids  or  sclero  proteins  (gelatin 
yielding  material,  etc.)  (p.  2)  about  6  per  cent,  of  the  body-weight. 
Nitrogen  exists  in  proteins  to  the  extent  of  n>  per  cent.,  so  thai  the 
6-5  kilos  of  protein  of  a  70-kilo  body  contain  about  1  kilo  of  nitrogen. 

The  carbon  is  contained  chiefly  in  the  fat,  which  forms  a^very 
large  proportion  of  the  water-free  substance  of  the  body,  and  in  the 
proteins.  A  small  amount  is  present  as  calcium  carbonate  in  the 
bones.  In  the  body  of  a  strong  young  man  weighing  68*6  kilos, 
Voit  found  the  following  quantities  of  dry  fat  in  the  various 
tissues  : 

Adipose  tissue        -----  8809-4  grammes. 

Skeleton  ------  2617-2 

Muscles  ------  636-8  ,, 

Brain  and  spinal  coi'd    -  -  226-9         » 

Other  organs  -  73-2  ,, 


Total  -  -  -    12363-5  ,, 

equivalent  to  18  per  cent,  of  the  whole  body-weight,  or  44  per  cent, 
of  the  solids.  In  dry  fat  rather  more  than  75  per  cent,  of  carbon 
is  present,  and  in  protein  about  50  to  55  per  cent.  ;  so  that  while 
the  fat  of  the  body  analyzed  by  Voit  contained  more  than  9  kilos 
of  carbon,  only  about  a  third  of  this  amount  would  be  found  in  the 
proteins. 

In  the  fat  there  is,  roughly  speaking,  12  per  cent,  of  hydrogen, 
in  proteins  only  7  per  cent.  ;  so  that  from  three  to  four  times  as 
much  hydrogen  is  contained  in  the  fat  of  the  body  as  in  its  proteins. 

Oxygen  forms  about  12  per  cent,  of  fat,  and  20  to  24  per  cent,  of 
proteins  ;  the  protein  constituents  of  the  body,  therefore,  contain 
about  as  much  of  its  oxygen  as  the  fat. 

Of  the  inorganic  salts  calcium  phosphate,  Ca3(P04)o,  is  much  the 
most  abundant  owing  to  the  large  amount  of  it  in  bone,  in  the  ash 
of  which  it  is  found  to  the  extent  of  83  per  cent.,  along  with  13  per 
cent,  of  calcium  carbonate. 

Nitrogenous  Equilibrium. — It  is  a  matter  of  common  ex- 
perience that  the  weight  of  the  body  of  an  adult  may  remain 
approximately  constant  for  many  months  or  years,  even  when 
the  diet  varies  greatly  in  nature  and  amount.  And  not  only 
may  the  weight  remain  constant,  but  the  relative  proportions 
of  the  various  tissues  of  the  body,  so  far  as  can  be  judged,  may 
remain  constant  too.  Here  it  is  evident  that  the  expenditure 
of  the  body  must  precisely  balance  its  income  :  it  must  lose  as 
much  nitrogen  as  it  takes  in,  otherwise  it  would  put  on  flesh  ; 
it  must  lose  as  much  carbon  as  it  takes  in,  otherwise  it  would 
put  on  fat.  Or,  again,  the  body  may  be  losing  or  gaining 
fat,  giving  off  more  or  less  carbon  than  it  receives,  while 
its  '  flesh  '  (its  protein  constituents)  remains  constant  in 
amount,  the  expenditure  of  nitrogen  being  exactly  equal  to  the 

34 


S  jo 


A   MANUAL  OF  PHYSIOLOGY 


income.*  In  both  cases  we  say  that  the  body  is  in  nitrogenous 
equilibrium. 

A  starving  animal  or  a  fever  patient,  on  the  other  hand,  is 
living  upon  capital,  the  former  entirely,  the  latter  in  part  ;  the 
expenditure  of  nitrogen  is  greater  than  the  income.  A  growing 
child  is  living  below  its  income,  is  increasing  its  capital  of  flesh. 
In  neither  case  is  nitrogenous  equilibrium  present. 

The  starving  animal,  as  long  as  life  lasts,  excretes  kreatinin, 
urea  and  other  nitrogenous  substances,  and  gives  off  carbon 
dioxide  ;  but  its  expenditure,  and  especially  its  expenditure  of 
nitrogen,  is  pitched  upon  the  lowest  scale.  It  lives  penuriously, 
it  spins  out  its  resources  ;  its  glycogen  goes,  its  fat  goes,  a  certain 


I 

12/  Muscle 

"..",• '"IM , 

n 

Brain          Z 

202  Fal 

:          :      ~    "~ 

li.  m/          Z 

\,  9//M 
.7-  J  Bene  s 
4S  Litrtr 

3-6  Blood 
>  0 lid c .line. 
0  ■()  Hidn,  vs 
Q-H  S/tleen 
0-~  Lunas 
0-J  Panci  cm 
0 -J  Testes 
\0  LBramiCctd 

\Q-lH,4tlt 

J1I 1 

BBSBag 

m  H  H 

m  mm  mm  mssssssssms^ 

Bents       1'+ 
/-fane reus   /  7 

Inti&tiius.  £g 
Lunyz      J S 
Skin         2J 
Kid  in  if s    26 
Blood       2  7 
Muscles     Z/ 
Testes       £<J 
Lifer      SU 
Spleen     157 

Fa/       91 

■Br         mmmm 

hi    HH^i^i^H  ■             jw^^^^KmKotmmmmtm 
MB                 ■HHMMj 

Fig.    il 


-Diagram  showing  Loss  of  Weight  of  the  Organs  in 
Starvation. 


The  numbers  under  I.  are  the  percentages  of  the  total  loss  of  body-weight 
borne  by  the  various  organs  and  tissues.  The  numbers  under  II.  give  the 
percentage  loss  of  weight  of  each  organ  calculated  on  its  original  weight  as 
indicated  by  comparison  with  the  organs  of  a  similar  animal  killed  in  good 
condition. 

part  of  its  protein  goes,  and  when  its  weight  has  fallen  from  25  to 
50  per  cent.,  it  dies.  At  death  the  heart  and  central  nervous 
system  are  found  to  have  scarcely  lost  in  weight  ;  the  other  organs 
have  been  sacrificed  to  feed  them.  Fig.  184  shows  the  percentage 
loss  of  weight  and  the  proportion  of  the  total  loss  which  falls  upon 
each  of  the  organs  of  a  cat  in  starvation  (Yoit). 

For  the  first  day  of  starvation  the  excretion  of  urea  in  a  dog 
or  cat  is  not  diminished  ;  it  takes  about  twenty-four  hours  for 

*  For  long  experiments  extending  over  many  days  the  nitrogen  balance 
may  be  considered  as  practically  the  same  as  the  protein  balance,  but  this 
is  not  necessarily  true  of  short  periods  of  time,  since  the  stock  of  nitrogen 
present  in  the  body  in  other  forms  than  proteins,  although  relatively 
small,  is  subject  to  variations. 


METABOLISM,    VUTRITION     IND  DIETETICS 


53' 


JSjyraim 


lOgramsL 


all  the  nitrogen  corresponding  to  the  proteins  of  the  last  meal 
to  be  eliminated.  On  the  second  day  the  quantity  of  urea  sinks 
abruptly  ;  then  begins  the  true  starvation  period,  during  which 
the  daily  output  of  urea  remains  constant  or  diminishes  very 
slowly  until  a  short  time  before  death,  when  it  rapidly  falls, 
and  soon  ceases  altogether.  An  increase  in  the  excretion  may 
precede  the  final  abrupt  decline  (premortal  increase).  This 
seems  to  indicate  the  time  at  which  all  the  available  fat  has  been 
used  up,  ami  after  which  protein  is  no  longer  '  spared  '  by  tin- 
fat.*  If  the  animal  has  little  fat  in  its  body  to  begin  with,  the 
rise  in  the  urea  ex- 
cretion takes  place 
even  after  the  first 
few  days.  So  long 
as  the  fat  lasts 
the  rate  at  which 
it  is  destroyed — 
as  estimated  from 
the  amount  of  car- 
bon given  oil  minus 
the  carbon  corre- 
sponding to  the 
broken  -  down  pro- 
teins— remains  very 
nearly  constant  after 
the  first  day.  The 
fat  to  a  certain  ex- 
tent economizes  the 
proteins  of  the  star- 
ving body,  but  how- 
ever much  fat  may 
be  present,  a  steady 
waste  of  the  tissue- 
proteins  goes  on.  If  non-nitrogenous  food  in  the  form  of 
sugar  is  supplied  to  an  otherwise  starving  animal,  the  pre- 
mortal rise  in  the  nitrogen  excretion  does  not  occur.  By  giving 
a  sufficient  quantity  of  sugar,  or  of  sugar  and  fat,  but 
practically  no  protein  (so-called  nitrogen  starvation),  the  ex- 
cretion of  nitrogen  may  be  reduced  to  one-third  of  its  amount 
when  no  food  at  all  is  given.  This  is  true  both  in  animals  and 
man.     In  this  way  the  daily  excretion  of  nitrogen  in  a  man  has 


1  A15        A30        MS       A60    a?/ 

Bff  Bll         QI6         B22    P  ^ 


Fig.    185. — Excretion  of    Urea    in    Starvation. 

A  is  a  curve  representing  the  quantity  of  urea 
excreted  daily  by  a  fat  dog  in  a  starvation  period 
of  sixty  days.  B  is  the  curve  of  urea  excretion  in 
a  lean  young  dog  in  a  starvation  period  of  twenty- 
four  days.  Both  are  constructed  from  Falck's 
numbers,  but  in  A  only  every  third  day  is  put  in, 
in  order  to  save  space.  The  numbers  along  the 
vertical  axis  represent  grammes  of  urea ;  those 
along  the  horizontal  axis  days  from  the  beginning 
of  starvation. 


*  If  the  animal  has  been  for  some  time  on  a  diet  containing  an  abun- 
dance of  proteins,  several  days  may  elapse  before  the  constant  excretion  of 
urea  is  reached  ;  if  the  previous  diet  has  been  poor  in  protein,  the  constant 
starvation  output  may  be  at  once  established, 

34—2 


532  A   MANUAL  OF  PHYSIOLOGY 

been  reduced  to  4  grammes.  It  is  a  remarkable  fact  that 
while  a  mixture  of  carbo-hydrate  and  fat  will  act  just  as  well 
as  carbo-hydrate  alone  in  bringing  about  this  reduction  in  the 
nitrogen  output,  fat  without  carbo-hydrate  is  much  less  effec- 
tive. The  hypothesis  has  been  suggested  that  the  cells  must 
have  some  sugar,  and  that  when  fat  alone  is  given,  ;i  portion  of 
the  body-protein,  which  would  otherwise  have  been  saved,  is 
broken  down  to  supply  the  necessary  sugar  (Landergren). 

The  results  obtained  on  fasting  men  differ  in  some  respects 
from  those  obtained  on  starving  animals.  In  ten  days  of  hunger, 
Cetti,  a  professional  '  fasting  man  '  of  meagre  habit,  excreted 
112  grammes  nitrogen,  or  an  average  of  11  grammes  a  day. 
The  excretion  was  least  on  the  eighth,  ninth,  and  tenth  days — • 
namelv,  about  g  grammes  a  day.  On  the  third  day  it  was 
higher  than  on  the  second,  and  almost  as  high  on  the  fourth  as 
on  the  third.  A  similar  rise  in  the  nitrogen  excretion  on  the 
second  dav  has  been  observed  in  other  fasting  men,  but  is 
either  rare  or  absent  in  fasting  dogs.  The  explanation  appar- 
entlv  is  that  in  the  ordinary  food  of  man  there  is  a  greater 
abundance  of  carbo-hydrates  and  fats,  the  protein-sparing  action 
of  which  is  most  pronounced  at  the  very  beginning  of  the  starva- 
tion period.  The  quantity  of  chlorine  and  alkalies  in  the  urine 
was  also  diminished,  while  the  phenol  was  increased.  The 
respiratory  quotient  sank  to  o-66  to  o-6o, — even  less  than  the 
quotient  corresponding  to  oxidation  of  fats  alone.  The  mean- 
ing of  this,  in  all  probability,  is  that  some  of  the  carbon  of  the 
broken-down  proteins  was  laid  up  in  the  body  as  glycogen 
(Zuntz).  In  another  professional  fasting  man  (Succi)  with  a 
considerable  amount  of  body-fat,  the  excretion  of  nitrogen  was 
found  to  diminish  continuously  during  a  fast  of  thirty  days, 
being  less  than  7  grammes  on  the  tenth  day.  In  another  fast  of 
21  days  by  the  same  person  it  was  a  little  less  than  3  grammes 
on  the  last  dav.  The  surprisingly  small  nitrogenous  waste  in 
this  case  is  perhaps  to  be  accounted  for  by  the  protein-sparing 
action  of  the  abundant  body-fat.  The  nitrogenous  metabolism 
has  also  been  investigated  during  long-continued  hypnotic  sleep 
(Hoover  and  Sollmann).  The  results  were  very  much  the  same 
as  in  an  ordinary  starvation  experiment. 

It  might  be  supposed  that  if  an  animal  was  given  as  much 
nitrogen  in  the  food  in  the  form  of  proteins  as  corresponded 
to  its  daily  loss  of  nitrogen  during  starvation,  this  loss  would 
be  entirely  prevented,  and  nitrogenous  equilibrium  restored. 
The  supposition  would  be  very  far  from  the  reality.  If  a  dog 
of  30  kilos  weight,  which  on  the  tenth  day  of  starvation  excreted 
11/4  grammes  urea,  had  then  received  a  daily  quantity  of  protein 


METABOLISM,    .VI'/7,7/7()V     IX  I  >   DIETETICS 


533 


equivalent  to  this  amount — that  is  to  say,  about  34  grammes 
of  dry  protein,  or  175  grammes  of  lean  meat— the  excretion  of 
nitrogen  would  at  once  have  leaped  up  to  nearly  double  its 
starvation  value.  II  the  quantity  of  protein  in  the  diet  was 
progressively  increased,  the  output  of  urea  would  increase  along 
with  it,  but  at  an  ever-slackening  rate  ;  and  at  length  a  con- 
dition would  be  reached  in  which  the  income  of  nitrogen  exactly 
balanced  the  expenditure,  and  the  animal  neither  lost  nor  gained 
flesh. 

In  an  experiment  of  Voit's,  for  instance,  the  calculated  loss  of 
flesh  in  a  dog  with  no  food  at  all  was  190  grammes  a  day.  The 
animal  was  now  fed  on  a  gradually  increasing  diet  of  lean  meat,  with 
the  following  result. 


Flesh  in  the 

Flesh  used  up  in 

Net  Loss  of 

Food. 

the  Body. 

Body-flesh. 

O 

I90 

190 

25O 

341 

9rl 

350 

41  r 

6l 

4OO 

454 

54 

45° 

47i 

21 

480 

492 

12 

The  loss  of  nitrogen  in  the  urine  and  faeces  is  what  was  measured. 
Knowing  the  average  composition  of  '  body-flesh  '  (muscles,  glands, 
etc.),  it  is  possible  to  translate  results  stated  in  terms  of  nitrogen  into 
results  stated  in  terms  of  '  flesh.'  Muscle  contains  approximately 
34  per  cent,  of  nitrogen.  Here,  with  a  diet  of  480  grammes  of  meat, 
the  dog  was  still  losing  a  little  flesh  ;  it  would  probably  have  required 
from  500  to  600  grammes  for  equilibrium.  The  results  are  graphi- 
cally represented  in  Fig.  186,  p.  535. 

The  quantity  of  protein  food  necessary  for  nitrogenous 
equilibrium  varies  with  the  condition  of  the  organism  ;  an 
emaciated  body  requires  less  than  a  muscular  and  well-nourished 
body.  The  least  quantity  which  would  suffice  to  maintain 
in  nitrogenous  equilibrium  the  famous  35  kilo  dog  of  Voit, 
even  in  very  meagre  condition,  was  480  grammes  of  lean  meat, 
corresponding  to  16  grammes  of  nitrogen,  or  35  grammes  of 
urea — that  is,  about  three  times  the  daily  loss  during  starva- 
tion. From  this  lower  limit  up  to  2,500  grammes  of  meat  a 
day  nitrogenous  equilibrium  could  always  be  attained,  the 
animal  putting  on  some  flesh  at  each  increase  of  diet,  until  at 
length  the  whole  2,500  grammes  was  regularly  used  up  in  the 
twenty-four  hours.  A  further  increase  was  only  checked  by 
digestive  troubles.  A  man,  or  at  least  a  civilized  man,  can  con- 
sume a  much  smaller  amount  both  absolutely  and  in  proportion 


534  A    MANUAL  OF  PHYSIOLOGY      , 

to  the  body-weight.  Rubner,  with  a  body-weight  of  yz  kilos, 
was  able  to  digest  and  absorb  over  1,400  grammes  of  lean  meat  ; 
Rankc,  with  about  the  same  body-weight,  could  only  use  up 
1,300  grammes  on  the  first  day  of  his  experiment,  and  less  than 
1,000  grammes  on  the  third. 

So  much  for  a  purely  protein  diet.  When  fat  is  given  in 
addition  to  protein,  nitrogenous  equilibrium  is  attained  with 
a  smaller  quantity  of  the  latter.  A  dog  which,  with  protein 
food  alone,  is  putting  on  flesh,  will  put  on  more  of  it  before 
nitrogenous  equilibrium  is  reached  if  a  considerable  quantity 
of  fat  be  added  to  its  diet.  Fat,  therefore,  economizes  protein 
to  a  certain  extent,  as  we  have  already  recognised  in  the 
case  of  the  starving  animal.  On  the  other  hand,  when  protein 
is  given  in  large  quantities  to  a  fat  animal,  the  consumption 
of  fat  is  increased  ;  and  if  the  food  contains  little  or  none, 
the  body-fat  will  diminish,  while  at  the  same  time  '  flesh  '  may 
be  put  on.  The  Banting  cure  for  corpulence  consists  in  putting 
the  patient  upon  a  diet  containing  much  protein,  but  little  fat 
or  carbo-hydrate ;  and  the  fact  just  mentioned  throws  light 
upon  its  action. 

All  that  we  have  here  said  of  fat  is  true  of  carbo-hydrates.  To  a 
great  extent  these  two  kinds  of  food  substances  are  complementary. 
Carbo-hydrates  economize  proteins  as  fat  does,  but  to  a  greater 
extent,  and  they  also  economize  fat,  so  that  when  a  sufficient 
quantity  of  starch  or  sugar  is  given  to  an  otherwise  starving  animal, 
all  loss  of  carbon  from  the  body,  except  that  which  goes  off  in  the 
urea,  kreatinin,  etc..  still  excreted,  can  be  prevented.  Of  course,  the 
animal  ultimately  dies,  because  the  continuous,  though  diminished, 
loss  of  protein  cannot  be  made  good. 

It  is  only  necessary  to  add  that  peptone  can,  while  gelatin  cannot, 
replace  the  ordinary  proteins  in  the  food.  When  only  enough  protein 
is  taken  to  prevent  loss  of  nitrogen  from  the  body,  one-fifth  of  the 
necessary  nitrogen  can  be  supplied  in  the  form  of  gelatin.  When  the 
food  is  much  richer  than  this  in  ordinary  protein,  a  correspondingly 
greater  proportion  of  the  protein  can  be  replaced  by  gelatin.  The 
surplus  is  not  used  in  the  endogenous  metabolism  of  the  cells  (p.  497), 
but  supplies  energy  to  the  body  after  the  elimination  of  its  nitrogen 
as  urea,  just  as  the  surplus  protein  would  do.  Thus  gelatin  economizes 
protein  in  the  same  way  that  fat  and  carbo-hydrates  do.  but  also 
to  some  extent  in  a  different  way  by  supplying  '  building  stones  ' 
for  the  protoplasm.  Gelatin  contains  most  of  the  amino-acids  and 
other  groups  which  compose  the  body-proteins,  but  tyrosin,  trypto- 
phane, and  cystin  are  lacking  in  the  gelatin  molecule.  It  is  there- 
fore an  interesting  question  whether  gelatin  can  fully  replace  protein 
when  these  substances  are  given  in  addition.  Kauffmann  has 
shown  that  his  own  nitrogen  requirement  (1 52  grammes)  was  almost 
completely  covered  by  a  mixture  containing  93  per  cent,  of  the 
nitrogen  in  the  form  of  gelatin,  4  per  cent,  as  tyrosin,  2  per  cent, 
as  cystin,  and  1  per  cent,  as  tryptophane,  in  addition  to  the  same 
amounts  of  carbo-hydrate  and  fatty  food  as  in  the  comparison  diet, 


METABOLISM,  NUTRITION  AND  mill  lies 


535 


in  which  the  nitrogen  was  supplied  in  the  form  of  plasmon,  a  com- 
mercial preparation  of  casein. 

When,  instead  of  protein,  the  cleavage  products  of  pancreatic 
digestion  arc  given  to  an  animal,  nitrogen 
equilibrium  is  also  maintained.  This 
has  been  shown  for  casein.  But  if  the 
casein  has  been  hydrolysed  by  acid, 
the  products  will  not  preserve  nitrogen 
equilibrium,  perhaps  because  the  acid 
has  broken  up  all  the  polypeptides  (p.  2), 
which  the  cells  may  need  as  the  starting- 
point  of  protein  synthesis. 

The  Laws  of  Nitrogenous  Metabo- 
lism.— Within  the  limits  of  nitrogenous 
equilibrium,  which  is  the  normal 
state  of  the  healthy  adult,  the  body 
lives  up  to  its  income  of  nitrogen  ;  it 
lays  by  nothing  for  the  future.  In  the 
actual  pinch  of  starvation  the  organism 
becomes  suddenly  economical.  When 
a  plentiful  supply  of  protein  is  pre- 
sented to  the  starving  body,  it  seems 
to  pass  at  once  from  extreme  frugality 
to  luxury  ;  some  flesh  may  be  put  on 
for  a  short  time,  some  nitrogen  may  be 
stored  up  ;  but  the  consumption  is  soon 
adjusted  to  the  new  scale  of  supply, 
and  the  protein  income  spent  as  freely 
as  it  is  received.  This  is  the  first 
great  law  of  nitrogenous  metabolism, 
and  we  may  formulate  it  thus  :  Con- 
sumption of  protein  is  largely  determined 
by  supply  (Practical  Exercises,  p.  612). 

The  explanation  of  this  remarkable 
fact,  or  at  least  an  essential  part  of  the 
explanation,  has  already  been  given  in  de- 
fining the  differences  between  exogenous 
and  endogenous  protein  katabolism 
(p.  497).  It  is  to  the  exogenous  process, 
and  practically  to  that  alone,  that  the  law 
applies.  We  have  seen  that  a  large  pro- 
portion of  the  nitrogen  of  the  food-pro- 
teins split  off  by  hydrolysis  in  the  lumen 
of  the  alimentary  canal,  the  intestinal 
wall,  and  probably  also  in  the  liver, 
passes  by  a  short-cut  to  the  stage  of  urea 
without  ever  joining  the  protein  of  the 
blood,    much    less    that    of   the    organs. 


Fig.  186.  — ■  Curves  con- 
structed TO  ILLUSTRATE 
Nitrogenous  Equilib- 
rium (from  an  Experi- 
ment of  Voit's). 

The  loss  of  flesh  in  grammes 
is  laid  off  along  the  horizontal 
axis.  The  income  and  ex- 
penditure corresponding  to  a 
given  loss  are  laid  off  (in 
grammes  of  '  flesh  ')  along 
the  vertical  axis.  The  con- 
tinuous curve  is  the  curve  of 
income  ;  the  dotted  curve,  of 
expenditure.  With  no  in- 
come at  all  the  expenditure  is 
190  grammes  ;  with  an  in- 
come of  480  grammes  the 
expenditure  is  492  and  the 
loss  12  grammes.  Nitro- 
genous equilibrium  is  repre- 
sented as  being  reached  with 
an  income  of  about  530 
grammes  ;  here  the  two  curves 
cut  one  another. 


This 


not    a    form    of 


true    '  luxus-consumption.'      The  expenditure  is  apparently  but  not 


;    \l  l  \  i    \l    OF  PHYSIOLOGY 

really  wasteful,  sinci  the  greater  pari  oi  the  energy  oi  the  protein 
molecule  is  still  obtained  by  the  oxidation  oJ  the  carbon-rich 
n  sidue,  I  be  surplus  nitrogen  is  shunted  out  <>i  the  main  metabolic 
currenl  a1  its  very  source.  Some  writers  conceive  thai  in 
•i  short-cut  from  protein  to  urea  we  have  .1  land  oi  physioloj 
safety-valve  to  proteel  the  tissues  from  the  burden  oi  an  excessive 
metabolism.  And  ii  1>\-  this  is  meant  that  it  is  advantageous  to 
the  tissues  thai  a  special  mechanism  should  exisi  t<>  elimini 
surplus  of  nitrogen  which  they  do  not  require,  and  w  hi<  b  1  hej  i  annol 
store,  and  to  present  them  with  a  residue  which  they  <  an  utilize, 
the  conception  is  certainly  correct.  But  there  is  no  good  evid< 
that  in  the  presence  of  an  over-abundant  supply  oi  protein  the 
endogenous  protein  metabolism  would  be  essentially  modified. 
And  another  interpretation  of  the  preliminary  splitting  ofl  and 
elimination  of  nitrogen,  which  must  under  ordinary  conditions  oi 
diet  account  for  a  considerable  formation  oi  area,  has  been  alluded 
to  in  discussing  the  influence  of  the  food  on  the  serum-proteins 
(p.  498).  The  surplus  of  those  amino-acids  which  the  food-proteins 
contain  in  greater  quantity  than  the  body-proteins  cannol  be 
utilized  for  building  protein  in  the  tissues.  Also  at  any  momenl 
the  magnitude  of  this  non-utilizable  surplus  will  depend  upon  th< 
quantity  of  that  one  of  the  indispensable  amino-acids  which  is 
present  in  the  smallest  amount.  For  the  proper  proportion  must 
be  preserved  between  the  different  'stones'  out  of  which  the  mole- 
cule is  built.  When  a  single  amino-acid  is  introduced  into  the  body, 
it  is  at  once  changed  into  urea  and  excreted,  since  it  cannot  be 
utilized  by  itself  for  building  up  protein. 

The  relatively  small  and  constant  amount  of  the  endogenous 
metabolism  indicates  that  the  actual  protoplasmic  substance,  the 
living  framework  of  the  cell,  is  comparatively  stable;  that  it  dors 
not  break  down  rapidly;  and  that  only  a  small  and  fairly  constant 
amount  of  food-  or  circulating-protein,  or  of  the  decomposition 
products  of  protein,  is  required  to  supply  the  waste  of  the  organ- 
protein. 

<  >ther  explanations  of  the  relation  between  consumption  and 
supply  of  protein  have  been  put  forward.  Although  some  of  these 
may  now  possess  merely  a  historical  interest,  they  must  be  mentioned, 
all  the  more  as  it  has  not  been  shown  that  the  1  nod  net  ion  of  urea 
in  the  liver  from  decomposition  products  of  proteins  brought  to  it 
in  the  portal  blood  is  the  only  form  of  exogenous  protein  katabolism. 
The  famous  theory  of  Voit  assumes  that  the  food-protein  after 
absorption  (the  so-called  'circulating-protein')  is  carried  to  the 
tissues  and  taken  up  by  the  cells,  where  the  greater  part  of  it. 
without  being   incorporated   with  the   protoplasm,  is  neverthel 

d  upon,  rendered   unstable,  shaken  to  pieces,  as   it    were,    by  the 
whir]  of  life  in  the  organized   framework,  the  interstices  oi  which 

11  ails. 

Pfliiger,  on  the  other  hand,  has  maintained  that  we  have  no  right 
to  draw  a  distinction  between  the  consumption  of  organ-  and 
circulating-protein;  that  the  whole  of  the  latter  ultimately  rises 
to  the  height  of  organ-protein,  and  passes  on  to  the  downward  stage 
ol  metabolism  only  through  the  topmost  step  of  organization.  An 
increase  in  the  supplj  of  nitrogenous  material  in  the  blood  must,  on 
this  view,  be  accompanied  with  an  increased  tendency  to  the  break- 
up, the  dissociation,  as  Pfluger  puts  it.  of  the  living  substance, 
The  actual  organized  elements,  however,  the  existing  cells,  are  not 


Mil   IBOLISM,    NUTRITION     IND  DIETETICS  537 

supposed  1"  !"■  destroyed  ;  the  building  remains,  for  although  stones 
are  constantly  crumbling  in  its  walls,  oth.rs  are  being  constantly 

I. mil  in. 

\  much  less  plausible  view  is  that  the  tissue  elements  themselves  are 
short  lived  ;  tli.ii  the  <>M  cells  disappear  bodily  and  are  replaced  by 
new  cells  ;  and  that  the  whole  oi  the  proteins  of  the  food  take  pari 
in  this  process  oi  total  111111  and  reconstruction.  Histological 
evidence  is  strongly  against  this  idea.  Although  the  cells  oi  certain 
glands,  such  as  the  mammary,  and  perhaps  the  mucous  glands, 
exhibit  changes  which,  hastily  interpreted,  might  seem  to  indicate 
ih. 11.  hke  those  oi  the  sebaceous  glands  (p.  47.-;).  they  break  down 
bodily,  as  an  incident  oi  functional  activity,  there  is  no  proof  ..I 
the  production  of  new  cells  on  the  immense  scale  which  this  theory 
would  require. 

A  second  law  of  nitrogenous  metabolism  is  that  within  normal 
limits  it  is  nearly  independent  of  muscular  work — that  is  to  say, 
the  quantity  of  nitrogen  excreted  by  a  man  on  a  given  diet  is 
practicallv  the  same  whether  he  rests  or  works.  Before  this 
was  known  it  was  maintained  by  Liebig  that  proteins  alone  could 
supply  the  energy  of  muscular  contraction — that,  in  fact,  pro- 
teins were  solely  used  up  in  the  nutrition  and  functional  activity 
of  the  nitrogenous  tissues,  while  the  non-protein  food  yielded 
heat  by  its  oxidation.  As  exact  experiments  multiplied,  it 
was  found  that  muscular  work,  the  production  of  which  is  the 
function  of  by  far  the  greatest  mass  of  protein-containing  tissue, 
had  little  or  no  effect  upon  the  excretion  of  urea  in  the  urine. 
More  than  this,  it  was  shown  that  a  certain  amount  of  work 
accomplished  (by  Fick  and  Wislicenus  in  climbing  a  mountain) 
on  a  non-nitrogenous  diet  had  double  the  heat  equivalent  of 
the  whole  of  the  protein  consumed  in  the  body,  as  estimated  by 
the  urea  excreted  during,  and  for  a  given  time  after,  the  work. 
On  the  assumption  that  all  the  urea  corresponding  to  the  pro- 
tein broken  down  was  eliminated  during  the  time  of  this  experi- 
ment, a  part  at  least  of  the  work  must  have  been  derived  from 
the  energy  of  non-nitrogenous  material.  And  the  increase  in 
the  carbon  dioxide  given  off,  which  is  as  conspicuous  an  accom- 
paniment of  muscular  work  as  the  constancy  of  the  urea  excre- 
tion, showed  that  during  muscular  exertion  carbonaceous 
substances  other  than  proteins — that  is  to  say,  fats  and  carbo- 
hydrates— are  oxidized  in  greater  amount  than  during  rest . 

So  the  pendulum  of  physiological  orthodoxy  came  full-swing 
to  the  other  side.  Liebig  and  his  school  had  taught  that  pro- 
teins alone  were  consumed  in  functional  activity  ;  the  majority 
of  later  physiologists  have  denied  to  the  proteins  any  share 
whatever  in  the  energy  which  appears  as  muscular  contraction. 
The  proteins,  they  say,  '  repair  the  slow  waste  of  the  frame- 
work of  the  muscular  machine,  replace  a  loose  rivet,  a  worn-out 
belt,  as  occasion  may  require  ;  the  carbo-hydrates  and  fats  are 


538  [  MANUAl    OF  PHYSIOLOG  Y 

the  fuel  which  feeds  the  furnaces  of  life,  the  material  which,  dead 
itself,  is  oxidized  in  the  interstices  of  the  living  substance,  and 
yields  the  energy  for  its  work.' 

Now,  it  is  a  singular  circumstance,  and  full  of  instruction  for 
the  ingenuous  studenl  ol  science,  that  the  facts  whii  h  have  been 
supposed  absolutely  to  disprove  the  older  theory,  and  absolutely 
to  establish  its  modern  rival,  do  neither  the  one  thing  nor  the 
other.  The  fact — and  it  is  a  fact — that  the  excrel  ion  ol  nitrogen 
is  but  little  affected  by  muscular  contraction,  does  not  prove 
that  none  of  the  energy  of  muscular  work  comes  from  proteins  ; 
the  fact  that,  under  certain  conditions,  some  of  the  muscular 
energy  must  apparently  come  from  non-nitrogenous  materials, 
does  not  prove  that  these  are  the  normal  source  of  it  all.  The 
distinction  has  again  been  made  too  absolute.  The  pendulum 
must  again  swing  back  a  little  ;  and  the  experiments  of  Pfliiger 
and  others  have  actually  set  it  moving. 

In  the  first  place,  it  is  not  perfectly  correct  to  say  that  work 
causes  no  increase  in  the  excretion  of  nitrogen  ;  excessive  work 
in  man,  and  work,  severe  but  not  excessive,  in  a  flesh-fed  dog 
(Pfliiger),  do  cause  somewhat  more  nitrogen  to  be  given  off. 
On  the  first  day  of  work  the  increase  is  always  much  less  than 
on  the  second  and  third  ;  and  on  the  first  and  second  rest  days, 
following  work,  the  elimination  of  nitrogen  is  still  increased. 
After  excessive  exercise  in  man  not  only  is  the  urea  increased, 
but  also  the  ammonia,  kreatinin,  and  if  the  subject  is  in  poor 
training,  the  uric  acid  and  purin  bases  (Paton,  Stockman,  etc.). 
Moderate  exercise  causes  no  increase  on  the  first  day,  but  a 
slight  increase  on  the  second. 

In  the  second  place,  even  if  the  excretion  of  nitrogen  were 
entirely  unaffected  by  work,  this  would  not  prove  that  none  of 
the  energy  of  the  work  comes  from  proteins.  For,  as  we  have 
seen,  it  is  after  the  nitrogen  has  been  split  off  and  converted 
into  urea  that  the  energy  of  a  great  part  of  the  food-protein  is 
developed  by  oxidation.  Further,  since  the  animal  body  is  a 
beautifully-balanced  mechanism  which  constantly  adapts  itself 
to  its  conditions,  it  is  conceivable  that  it  maw  when  called  upon 
to  labour,  save  proteins  from  lower  uses  to  devote  them  to 
muscular  contraction.  In  this  case  the  excretion  ol  nitrogen 
would  not  necessarily  be  altered;  the  proteins  which,  in  the 
absence  of  work,  would  have  been  oxidized  within  the  muscular 
substance  or  elsewhere,  their  energy  appearing  entirely  .is  heat, 
may,  when  the  call  for  protein  to  take  the  pi. ice  of  that  broken 
down  in  muscular  contraction  arises,  be  diverted  to  this 
purpose. 

In  any  case,  there  is  no  doubt  that  a  dog  fed  on  lean  meat  may 
go  on  for  a  long  time  performing  far  more  work  than  can  be 


METABOLISM,   VUTRlTlON    IND  DIETETICS 

yielded  by  the  energy  of  Ea1  and  carbo-hydrates  occurring  in 
traces  in  the  food,  or  taken  from  the  stock  in  the  animal's  body 
a1  the  beginning  of  the  period  <>l  work.  A  large  portion,  and 
perhaps  the  whole,  of  the  work,  must  in  this  case  be  derived 
from  the  energy  of  the  proteins  (Pfliiger).  On  the  other  hand, 
it  is  well  established  thai  when  fats  and  carbo-hydrates  arc 
1  Hi-scut  in  sufficient  quantity  in  the  tissues  or  the  food,  they 
constitute  the  main  source  of  the  energy  of  muscular  contrac- 
tion (p.  669). 

Kxperience  has  shown  that  the  minimum  quantity  of  nitrogen 
required  in  the  food  of  a  man  whose  daily  work  involves  hard 
physical  toil  is  higher  than  the  minimum  required  by  a  person 
leading  an  easy,  sedentary  life.  This  is  evidently  in  accordance 
with  the  view  that  protein  is  actually  used  up  in  muscular  con- 
traction ;  but  it  is  not  inconsistent  with  the  opposite  view.  For 
the  body  of  a  man  fit  for  continuous  hard  labour  has  a  greater 
m  :ss  of  muscle  to  feed  than  the  body  of  a  man  who  is  only  fit 
to  handle  a  composing-stick,  or  drive  a  quill,  or  ply  a  needle  ; 
and  the  greater  the  muscular  mass,  the  greater  the  muscular 
waste.  But  if  an  animal  just  in  nitrogenous  equilibrium  on  a 
diet  of  lean  meat  when  doing  no  work  is  made  to  labour  day 
after  day,  it  will  lose  flesh  unless  the  diet  be  increased.  This 
must  mean  that  some  of  the  protein  is  being  diverted  to  mus- 
cular work,  and  that  the  balance  is  not  sufficient  to  keep  up  the 
original  mass  of '  flesh  '  (see  p.  548). 

(2)  Income  and  Expenditure  of  Carbon. — This  division  of 
the  subject  has  been  necessarily  referred  to  in  treating  of  the 
nitrogen  balance-sheet,  and  may  now  be  formally  completed. 

Carbon  Equilibrium.  —  A  body  in  nitrogenous  equilibrium 
may  or  may  not  be  in  carbon  equilibrium.  It  has  been  re- 
peatedly pointed  out  that  the  continued  loss  or  gain  of  carbon 
by  an  organism  in  nitrogenous  equilibrium  means  the  loss  or 
gain  of  fat  ;  and,  since  the  quantity  of  fat  in  the  body  may  vary 
within  wide  limits  without  harm,  carbon  equilibrium  is  less 
important  than  nitrogen  equilibrium.  It  is  also  less  easily 
attained  when  the  carbon  of  the  food  is  increased,  for,  the 
consumption  of  fat  is  not  necessarily  increased  with  the  supply 
of  fat  or  fat-producing  food,  and  there  is  by  no  means  the 
same  prompt  adjustment  of  expenditure  to  income  in  the  case 
of  carbon  as  in  the  case  of  nitrogen. 

Carbon  equilibrium  can  be  obtained  in  a  flesh-eating  animal, 
like  a  dog,  with  an  exclusively  protein  diet  ;  but  a  far  higher 
minimum  is  required  than  for  nitrogenous  equilibrium  alone. 
Voit's  dog  required  at  least  1,500  grammes  of  meat  in  the  twenty- 
four  hours  to  prevent  his  body  from  losing  carbon.  For  a  man 
weighing  70  kilos,  the  daily  excretion  of  carbon  on  an  ordinary 


A  M  \NVAL  OF  PHYSIOLOGY 

diet  is  250  to  |00  grammes.  Aboul  2,000  grammes  of  lean 
mr.it  would  be  required  to  yield  this  quantity  oi  carbon;  and, 
even  it  such  a  mass  could  be  digested  and  absorbed,  more  than 
three  times  the  necessary  nitrogen  would  have  to  undergo  pre- 
liminary cleavage  and  excretion  as  urea  or  be  thrown  upon  the 
ti>-ues. 

Not  only  may  carbon  equilibrium  be  maintained  for  a  si 
time  in  a  dog  on  a  diet  containing  fat  only,  or  fat  and  carbo- 
hydrates, but  the  expenditure  of  carbon  may  be  less  than  the 
income,   and    fat  may  be  stored  up.      But,  of   course,   if    this 
diet    is    continued,    the    animal    ultimately    dies    of     nitr>>. 
starvation. 

So  far  we  have  spoken  only  of  the  income  and  expenditure 
of  carbon  and  nitrogen  ;  and  from  these  data  alone  it  is  possible 
to  deduce  many  important  facts  in  metabolism,  since,  knowing 
the  elementary  composition  of  proteins,  fats,  and  carbo-hydrates, 
we  can,  on  certain  assumptions,  translate  into  terms  of  proteins 
or  fat  the  gain  or  loss  of  an  organism  in  nitrogen  and  carbon, 
or  in  carbon  alone.  But  the  hydrogen  and  oxygen  contained  in 
the  solids  and  water  of  the  food,  and  the  oxygen  taken  in  by 
the  lungs,  are  just  as  important  as  the  carbon  and  nitrogen  ;  it 
is  just  as  necessary  to  take  account  of  them  in  drawing  up 
a  complete  and  accurate  balance-sheet  of  nutrition.  Fortu- 
nately, however,  it  is  permissible  to  devote  much  less  time  to 
them  here,  for  when  we  have  determined  the  quantitative 
relations  of  the  absorption  and  excretion  of  the  carbon  and 
nitrogen,  we  have  also  to  a  large  extent  determined  those  of  the 
oxygen  and  hydrogen. 

(3)  Income  and  Expenditure  of  Oxygen  and  Hydrogen. — 
The  oxygen  absorbed  as  gas  and  in  the  solids  of  the  food  is  given 
off  chiefly  as  carbon  dioxide  by  the  lungs  ;  to  a  small  extent  as 
water  by  the  lungs,  kidneys,  and  skin  ;  and  as  urea  and  other 
substances  in  the  urine  and  faces.  The  hydrogen  of  the  solids 
of  the  food  is  excreted  in  part  as  urea,  but  in  far  larger  amount 
as  water.  The  hydrogen  and  oxygen  of  the  ingested  water 
pass  off  as  water,  without,  so  far  as  we  know,  undergoing  any 
chemical  change,  or  existing  in  any  other  form  within  the  body. 
But  it  is  important  to  recognise  that  although  none  of  the  water 
taken  in  as  such  is  broken  up,  some  water  is  manufactured  in  the 
tissues  by  the  oxidation  of  hydrogen.  We  have  already  con- 
sidered (p.  242)  the  gaseous  exchange  in  the  lungs,  and  we  have 
seen  that  all  the  oxygen  taken  in  does  not  reappear  as  carbon 
dioxide.  It  was  stated  there  that  the  missing  oxygen  goes  to 
oxidize  other  elements  than  carbon,  and  especially  to  oxidize 
hydrogen.  We  have  now  to  explain  more  fully  the  cause  of 
this  oxygen  deficit. 


METABOLISM,   NUTRITION  AND  hi  Ell.  I  S4, 

The  Oxygen  Deficit.  The  carbo-hydrates  contain  in  themselves 
enough  oxygen  to  form  water  with  all  their  hydrogen  ;  they  account 
for  a  part  of  the  water-formation  in  the  body,  but  for  none  of  the 

oxygen  deficit. 

Ilif  fats  iir  mix  different  :  their  hydrogen  can  be  nothing  like 
completely  oxidized  by  their  oxygen.  A  gramme  of  hydrogen  is 
contained  in  8'5  grammes  of  dry  fat,  and  needs  8  grammes  of  oxygen 
for  its  complete  combustion.  Only  i  gramme  of  oxygen  is  yielded 
by  the  hit  itself  ;  so  that  if  a  man  uses  [00  grammes  of  fat  in  twenty- 
four  hours,  rather  nunc  than  So  grammes  of  the  oxygen  taken  in 
must  go  to  oxidize  the  hydrogen  of  the  fat. 

The  proteins  also  contribute  to  the  deficit.  In  ioo  grammes  of 
dry  proteins  there  are  1 5  grammes  of  nitrogen,  7  grammes  of 
hydrogen,  and  21  grammes  of  oxygen.  The  carbon  does  not  concern 
us  at  present.  The  n  grammes  of  urea,  corresponding  to  100 
grammes  of  protein,  contains  15  grammes  of  nitrogen,  a  little  more 
than  2  grammes  of  hydrogen,  and  a  little  less  than  9  grammes  of 
oxygen.  There  remain  5  grammes  of  hydrogen  and  12  grammes  of 
oxygen.  But  5  grammes  of  hydrogen  needs  for  complete  combustion 
40  grammes  of  oxygen  ;  therefore  28  grammes  of  the  oxygen  taken 
in  must  go  to  oxidize  the  hydrogen  of  100  grammes  of  protein. 
Taking  140  grammes  of  protein  as  the  amount  in  a  liberal  diet  for 
a  man,  we  get  39  grammes  as  the  required  quantity  of  oxygen.  This, 
added  to  the  80  grammes  needed  for  the  hydrogen  of  the  fat,  makes  a 
total  of,  say,  120  grammes,  equivalent  to  about  85  litres  of  oxygen. 
A  small  amount  of  oxygen  also  goes  to  oxidize  the  sulphur  of  proteins. 

With  a  diet  containing  less  fat  and  protein  and  more  carbo- 
hydrate, the  oxygen  deficit  would  of  course  be  less. 

The  Production  of  Water  in  the  Body. — One  gramme  of  hydrogen 
corresponds  to  9  grammes  of  water.  In  140  grammes  of  proteins 
and  100  grammes  of  fat  there  are,  in  round  numbers,  22  grammes 
of  hydrogen  ;  in  350  grammes  of  starch,  21*5  grammes.  With  this 
diet,  435  grammes  of  hydrogen  is  oxidized  to  water  within  the  body 
in  twenty-four  hours,  corresponding  to  a  water  production  of  391 
grammes,  or  1 5  to  20  per  cent,  of  the  whole  excretion  of  water.  It 
has  been  observed  that  during  starvation  the  tissues  sometimes 
become  richer  in  water,  even  when  none  is  drunk.  The  only  explana- 
tion is,  that  the  elimination  of  water  does  not  keep  pace  with  the 
rate  at  which  it  is  produced  from  the  hydrogen  of  the  broken-down 
tissue-substances,  or  set  free  from  the  solids  with  which  it  is 
(physically  ?)  united. 

Inorganic  Salts. — The  inorganic  salts  of  the  excreta,  like 
the  water,  are  for  the  most  part  derived  from  the  salts  of  the 
food,  which  do  not  in  general  undergo  decomposition  in  the 
body.  A  portion  of  the  chlorides,  however,  is  broken  up  to  yield 
the  hydrochloric  acid  of  the  gastric  juice.  Within  the  body  some 
of  the  salts  are  more  or  less  intimately  united  to  the  proteins  of 
the  tissues  and  juices,  some  simply  dissolved  in  the  latter. 
The  chlorides,  phosphates  and  carbonates  are  the  most  im- 
portant ;  the  potassium  salts  belong  especially  to  the  organized 
tissue  elements,  the  sodium  salts  to  the  liquids  of  the  body  ; 
calcium  phosphate  and  carbonate  predominate  in  the  bones.  The 
amount  and  composition  of  the  ash  of  each  organ  only  change 


542  /    V  l.vr  //    OF  PHYSIOLOGY 

within  narrow  limits.  In  hunger  the  organism  clings  to  its 
inorganic  materials,  as  it  clings  to  its  tissue-proteins  :  the  former 
are  just  as  essential  to  life  as  the  latter.  In  a  starving  animal 
chlorine  almost  disappears  from  the  urine  at  a  time  when  there 
is  still  much  chlorine  in  the  body  ;  only  the  inorganic  salts  which 
have  been  united  to  the  used-up  proteins  are  excreted,  so  that 
a  starving  animal  never  dies  for  want  of  salt-. 

When  sodium  chloride  is  omitted  as  ail  addition  to  the  food 
of  man,  the  decomposition  of  protein  seems  to  be  slightly  at  i  eler- 
ated,  but  for  a  time,  at  least,  there  are  no  serious  symptoms 
(Belli).  The  Hereros  in  Damaraland,  who  are  physically  one 
of  the  finest  races  in  Africa,  are  said  not  to  use  salt  (R6clus). 
On  the  other  hand,  when  an  animal  is  fed  with  a  diet  as  fai 
possible  artificially  freed  from  salts,  but  otherwise  sufficient, 
it  dies  of  salt-hunger.  The  blood  first  loses  inorganic  material, 
then  the  organs.  The  total  loss  is  very  small  in  proportion  to 
the  quantity  still  retained  in  the  body;  but  it  is  sufficient  to 
cause  the  death  of  a  pigeon  in  three  weeks,  and  of  a  dog  in  six, 
with  marked  symptoms  of  muscular  and  nervous  weakness. 
A  deficiency  of  lime  salts  causes  changes  particularly  in  the 
skeleton,  although  the  nutrition  of  the  rest  of  the  body  is  also 
interfered  with.  These  changes  are  of  course  most  marked  in 
young  animals,  in  which  the  bones  are  growing  rapidly.  In 
pigeons  on  a  diet  containing  very  little  calcium  the  hones  of  the 
skull  and  the  sternum  become  extremely  thin  and  riddled  with 
holes,  while  the  bones  concerned  in  movement  scarcely  suffer 
at  all  (E.  Voit). 

It  is  not  indifferent  in  what  form  the  calcium  is  taken,  nor  can  it 
be  replaced  to  any  great  extent  by  oilier  earthy  bases,  as  magnesium 
or  strontium.  Weiske  fed  five  young  rabbits  of  the  same  fitter  on 
oats  a  food  relatively  poor  in  calcium.  One  of  the  rabbits  received 
in  addition  calcium  carbonate,  another  calcium  sulphate,  a  third 
magnesium  carbonate,  and  a  fourth  strontium  carbonate.  At  the 
end  of  a  certain  time  it  was  found  that  the  skeleton  of  the  rabbit  f<  d 
with  calcium  carbonate  was  the  heaviest  and  strongest  of  all,  and 
contained  the  greatest  proportion  of  mineral  matter.  Then  came 
the  rabbit  fed  with  calcium  sulphate.  The  animal  which  received 
only  oats  had  the  worst-developed  skeleton  ;  the  condition  of  tin- 
animals  fed  with  magnesium  and  strontium  carbonates  was  but  little 
better. 

Milk  is  a  food  rich  in  calcium  and  also  in  phosphorus,  a  cir- 
cumstance evidently  related  to  the  rapid  development  of  the 
skeleton  in  the  young  child.  As  in  the  other  natural  foods,  the 
calcium  and  phosphorus  are  partly  in  the  form  of  organic  com- 
pounds, united  with  the  proteins,  the  calcium  especially  with 
caseinogen,  and  partly  in  the  form  of  inorganic  salts.  Both  of 
these  elements  are  more  easily  assimilated  by  the  body  in  the 


METABOLISM,   NUTRITION   AND  I'll  n  Tli  543 

organic  than  in  the  inorganic  form.  And  the  same;  is  true  <>i 
iron,  which  exists  in  organic  combination  in  the  bran  of  wheat, 
in  the  haemoglobin  of  the  blood  and  of  muscular  fibres,  in  the 
nuclei  of  most  cells,  vegetable  and  animal,  and  conspicuously  in 
the  nuclein  of  the  yolk  of  the  egg.  Attempts  have  been  made 
to  increase  the  amount  of  iron  in  hen's  eggs  by  giving  them  food 
mixed  with  preparations  of  iron — e.g.,  iron  citrate.  An  increase 
takes  place,  but  only  alter  a  long  time.  Tims  in  one  experiment 
100  grammes  of  egg-substance  contained  4-4  milligrammes  of 
Fea03  before  the  administration  of  the  iron  was  begun  ;  after 
feeding  with  iron  for  three  and  a  half  weeks  the  amount  was 
4-5  milligrammes,  after  more  than  two  months  7-4  milligrammes  ; 
and  after  a  year  only  7-3  milligrammes.  Although,  as  we  have 
seen,  inorganic  iron  can  be  absorbed,  it  is  certainly  the  case 
that  under  ordinary  conditions  all  the  iron  that  the  body  receives 
or  needs  is  taken  in  the  form  of  organic  compounds,  since  there 
is  no  inorganic  iron  in  the  natural  food  substances.  Stockman, 
from  careful  estimations  of  the  quantity  of  iron  in  a  number  of 
actual  dietaries,  finds  that  it  only  amounts  to  about  8  to  10  milli- 
grammes a  day.  He  concludes  that  the  greater  part  of  it  must 
be  retained  in  the  body  and  used  over  and  over  again. 

Milk  is  poor  in  iron,  but  this  does  not  hinder  the  develop- 
ment of  the  young  child,  except  when  it  is  weaned  too  late, 
when  it  is  apt  to  become  anaemic  unless  the  milk  is  supplemented 
with  a  food  rich  in  iron,  such  as  yolk  of  egg.  The  explanation 
is  that  the  foetus,  especially  in  the  last  three  months  of  intra- 
uterine life,  accumulates  a  store  of  iron  in  the  liver  and  other 
organs  ;  so  that,  in  proportion  to  its  body-weight,  it  is  at  birth 
several  times  richer  in  iron  than  the  adult.  This  iron,  of  course, 
all  comes  from  the  mother,  and  the  loss  is  not  exactly  balanced 
by  the  excess  of  iron  in  her  food  ;  certain  of  her  organs,  the 
spleen,  for  instance,  though  not  apparently  the  liver,  are  im- 
poverished as  regards  their  content  of  iron. 

DIETETICS. 

There  are  two  ways  in  which  we  can  arrive  at  a  knowledge 
of  the  amount  of  the  various  food  substances  necessary  for  an 
average  man  :  (a)  By  considering  the  diet  of  large  numbers  of 
people  doing  fairly  definite  work,  and  sufficiently,  but  not  ex- 
travagantly, fed — e.g.,  soldiers,  gangs  of  navvies,  or  plantation 
labourers  ;  (b)  by  making  special  experiments  on  one  or  more 
individuals. 

Voit,  bringing  together  a  large  number  of  observations,  con- 
cluded that  an  '  average  workman,'  weighing  70  to  75  kilos, 
and  working  ten  hours  a  day,  required  in  the  twenty-four  hours 


;t4  '    1/  '  VUA1    OF  PHYSIOLOGY 

ri8  grammes  protein,  56  grammes  fat,  and  500  grammes  carbo- 
hydrate, corresponding  to  aboul  18*8  grammes*  nitrogen,  and 
at  Least  328  grammes  carbon. 

Ranke  Found  the  following  a  sufficient  diet  for  himself,  with 
a  body-weighl  of  74  kilns : 

Proteins        -  100  grammes. 

Fat       -         -         -         -         -100 
Carbo-hydrates     -         -        -240 

This  corresponds  to  only  16  grammes  nitrogen  and,  say,  230 
grammes  carbon.  * 

A  German  soldier  in  the  field  receives  on  the  average  : 

Proteins         -  -  -  151  grammes. 

Fat       -         -         -         -         -        1 '  • 
Carbo-hydrates      -         -  -     5-- 

representing  about  24  grammes  nitrogen  and  340  grammes 
carbon.  The  average  ration  for  four  British  regiments  in  peace- 
time contained  133  grammes  protein,  115  grammes  fat,  and 
424  grammes  carbo-hydrate  (=3,400  calories).  But  in  addition 
the  soldiers  constantly  obtained  at  their  own  expense  a  supper, 
generally  comprising  meat  (Pembrey).  The  Russian  army  war 
ration  in  the  Manchurian  campaign  is  said  to  have  comprised 
187  grammes  protein  and  775  grammes  carbo-hydrate,  but 
onlv  27  grammes  fat  (=4,900  calories).  The  diet  of  certain  miners 
(Steinhefl)  and  lumberers  (Liebig)  contained  respectively  133  and 
112  grammes  protein,  113  and  309  grammes  fat,  and  634  and 
691  grammes  carbo-hydrates.  The  diet  of  prize-fighters  and 
of  athletes  in  training  is  richer  in  protein  than  any  of  these. 
The  members  of  two  college  football  teams  are  stated  to  have 
consumed  on  the  average  225  grammes  protein,  334  grammes  fat, 
and  633  grammes  carbo-hydrates  (  =  6,800  calories).  Caspari,  from 
a  studv  of  the  phenomena  of  training,  concluded  that  continuous 
bodily  work  at  a  rate  above  the  ordinary  requires  a  large  amount 
of  protein  (2  to  3  grammes  a  day  per  kilo  of  body-weight).  But 
there  seems  to  be  a  considerable  difference  between  different 
individuals.  So  that  a  definite  and  typical  diet  for  severe  labour 
does  not  exist.  And  although  perhaps  the  hardest  physical  work 
ever  done  in  the  world  is  to  break  athletic  records,  to  cut  and 
handle  timber,  to  mine  coal,  and  to  make  war,  the  diet  on  which 
these  things  are  accomplished  is  very  variable. 

Recent  observations  tend  to  reduce  the  amount  of  protein 
considered  necessary  for  a  person  under  ordinary  conditions. 
Siven  remained  in  nitrogen  equilibrium,  for  a  time  at  least,  with 
an  intake  of  only  0-07  to  o-o8  gramme  of  nitrogen  (0-4  to  05 
gramme  of  protein)  per  kilo  of  body-weight,  or  not  much  more 
*  Taking  the  percentage  of  nitrogen  in  protein  .it  16. 


METABOLISM,    VUTRITIOh    AND  DIETETh    ■  545 

than  one-third  of  the  amount   in   Ranke's  diet.     It   is  obvious 
thai    the  endogenous  protein   katabolism  sets  the  limit  below 

which  it  must  be  impossible  permanently  to  reduce  the  allowance 
of  protein.  But  it  would  be  very  hazardous  to  assume  that  this 
theoretical  minimum  limit  corresponds  with  the  permissible 
physiological  limit.  From  experiments  on  men  of  various  callings 
extending  over  many  months,  Chittenden  has  concluded  that 
the  average  man  eats  at  least  twice  as  much  protein  as  he  really 
requires.  We  have  already  seen  that  the  amount  of  nitrogen 
required  to  repair  the  actual  waste  of  the  tissues  is  comparatively 
small,  and  th%t  with  the  ordinary  amount  of  protein  in  the  food 
a  very  large  fraction  of  the  total  nitrogen  is  rapidly  excreted  as 
urea.  There  is  no  doubt,  also,  that  many  persons  consume  too 
much  protein,  at  any  rate  in  the  form  of  animal  food,  and  would 
feel  better,  work  better,  and  probably  live  longer,  if  they 
restricted  themselves  in  this  regard.  But  there  is  no  evidence 
that  the  digestion  of  such  quantities  of  protein  as  the  average 
healthy  man  eats,  or  the  elaboration  and  excretion  of  the  corre- 
sponding amounts  of  urea,  '  strain  '  in  the  least  the  digestive 
apparatus,  the  liver,  or  the  kidneys.  And  it  may  just  as  well 
be  argued  that  it  is  advantageous  that  much  more  than  the 
minimum  protein  requirement  should  be  offered  to  the  tissues, 
so  that  the  appropriate  amino-acids,  even  the  scarcest  of  them, 
may  be  sure  to  be  present  in  sufficient  amount,  rather  than  that 
the  organs  should  be  subjected  to  the  unnecessary  '  strain  '  of 
reconstructing  some  of  the  amino-acids  themselves,  supposing 
that  they  possess  this  power.  In  a  question  of  this  sort  the 
immemorial  experience  and  instinct  of  mankind  cannot  be 
lightly  waved  aside. 

If  we  decide  the  matter  merely  on  physiological  grounds,  we 
may  say  that  for  a  man  of  70  kilos,  doing  fairly  hard,  but  not 
excessive,  work,  15  grammes  nitrogen  and  250  grammes  carbon 
are  a  sufficient  allowance.  The  15  grammes  nitrogen  will  be 
contained  in  95  grammes  dry  protein,  which  will  also  yield 
50  grammes  of  the  required  carbon.  The  balance  of  200  grammes 
carbon  could  theoretically  be  supplied  either  in  450  grammes 
starch  or  in  260  grammes  fat.  But  it  has  been  found  by  experi- 
ment and  by  experience  (which  is  indeed  a  very  complex  and 
proverbially  expensive  form  of  experiment)  that  for  civilized 
man  a  mixture  of  these  is  necessary  for  health,  although  the 
nomads  of  the  Asian  steppes,  and  the  herdsmen  of  the  Pampas, 
are  said  to  subsist  for  long  periods  on  flesh  alone,  and  a  dog  can 
live  very  well  on  proteins  and  fat.  The  proportion  of  fat  and 
carbo-hydrates  in  a  diet  may,  however,  be  varied  within  wide 
limits.  Probably  no  '  work  '  diet  should  contain  much  less 
than  40  grammes  of  fat,  but  twice  this  amount  would  be  better  ; 

35 


5  i<> 


I   M.l\  UAL  OF  PHYSIOLOGY 


80  grammes  iat  give  aboul  60  grammes  carbon,  so  thai  from 
proteins  and  fal  we  have  now  got  no  grammes  ot  the  nei  essary 
250,  leaving  140  grammes  carbon  to  be  taken  in  aboul  310 
grammes  starch,  or  an  equivalent  amount  <>i  cane-sugar  or 
dextrose.  Adding  30  grammes  inorganic  salts,  we  can  pul  down 
as  the  solid  portion  of  a  normal  did  sufficient  from  the  physio- 
logical point  of  view  for  a  man  of  70  kilos : 


95  grammes  proteins 

fat 
310  „  carbo-hydrates 

30  ,,  salts. 


-,',„  <>i  body-weight. 


525 


solid  food 


Now,  knowing  the  composition  of  the  various  food-stuffs,  we 
can  easily  construct  a  diet  containing  the  proper  quantities  oi 
nitrogen  and  carbon,  by  using  a  table  such  as  the  following  : 


Quantity 

Quantity 

required 

N  in 

C  in 

Protein 

Fat  in 

hydrate 

Water 

to  5  ield 

to  yield 

100 

100 

in  100 

100 

in  100 

1 5  Grins. 

'  N. 

250  Grin-, 

c. 

1  inn   . 

( inns. 

<  inns. 

( inns. 

Grins. 

Cheese* 

(Gruyi  re) 

300 

640 

5 

39 

J3 

3i 

— 

34 

Peas  (dried)     - 

430 

700 

3*5 

35"7 

22 

2 

55 

15 

Lean  meat 

440 

i860 

3  "4 

I3"5 

21 

3-5 

— 

Wheat-flour    - 

650 

625 

2"3 

39-8 

I  J 

2 

7o 

15 

Oatmeal 

580 

620 

2-6 

403 

*3 

5  "5 

65 

15 

3 

790 

1700 

1-9 

147 

ix-5 

12 

— 

75 

.Maize 

810 

610 

1-85 

40*9 

10-5 

7 

65 

15 

Wheat 

bread  - 

1200 

II20 

I"25 

-'-   1 

8 

15 

49 

40 

Rice 

1530 

685 

0-9 

366 

5 

1 

83 

10 

Milk 

2380 

3540 

06 

7 

4 

4 

5 

85 

Potatoes 

3750 

2380 

04 

i"  , 

- 

015 

21 

Good   butter 

1 0000 

360 

0-15 

69 

1 

90 

8 

Economic  and  social  influences — prices  and  habits  —and  not 
purely  physiological  rules,  fix  the  diet  of  populations.  The  Chii 
labourer,  for  example,  lives  on  a  diet  which  no  physiolo 
would  commend.  In  order  to  obtain  15  grammes  nitrogen  or 
95  grammes  protein,  he  must  consume  more  than  1,500  grammes 
rice,  which  will  yield  700  grammes  carbon,  or  twice  as  much  as  is 
required  ;  but  ii'  the  Chinese  labourer  could  not  live  on  rice,  he 
could  not  live  at  all.  The  Irish  peasant  is  even  in  worse  case  :  he 
must  consume  nearly  4  kilos  of  potatoes  to  obtain  his  15  grammes 


*  A  cheese  manufactured  from  whole  milk,  curdled  before  the  in-. mi 

has  had  time  to  rise,  and  therefore  rich  in  fat. 


W/  /   IBOLISM,   Nl   rRITION  AND  hi  III  TICS  $47 

nitrogen,  while  little  more  than  half  this  amount  would  furnish 
the  necessary  250  grammes  carbon.  Of  course  a  diet  consisting, 
week  in  week  out,  entirely  oi  potatoes  or  rice,  would  represenl 
.111  extreme  case.  A  certain  amount  of  the  necessary  nitrogen  is 
obtained  even  by  the  poorest  populations,  in  the  form  of  iish, 
milk,  eggs,  or  bacon.  A  man  attempting  to  live  on  flesh  alone 
would  be  well  fed  as  regards  nitrogen  with  500  grammes  of  meat, 
but  nearly  four  times  as  much  would  be  required  to  yield 
250  grammes  of  carbon.  Oatmeal  and  wheat-flour  contain 
nitrogen  and  carbon  in  nearly  the  right  proportions  (1  N  :  15  C), 
oatmeal  being  rather  the  better  of  the  two  in  this  respect  ;  and 
the  best-fed  labouring  populations  of  Europe  still  live  largely 
on  wheaten  bread,  while,  one  hundred  years  ago,  the  Scotch 
peasant  still  cultivated  the  soil,  as  the  Scotch  Reviewer  the  Muses, 
'  on  a  little  oatmeal.'  But  although  bread  may,  and  does,  as 
a  rule,  form  the  great  staple  of  diet,  it  is  not  of  itself  sufficient. 

It  is  necessary  to  recognise  that  habit  has  much  to  do  with 
the  quantity  as  well  as  with  the  quality  of  the  food  used  by  an 
individual  or  a  community.  Some  concession  may  be  made  to 
custom  in  what  is,  after  all,  not  a  purely  physiological  question, 
and  in  this  country  it  is  probable  that  20  grammes  of  nitrogen 
and  300  grammes  of  carbon,  while  a  liberal  is  not  an  excessive 
allowance,  although  it  is  certain  that  a  man  can  maintain  a 
normal  body-weight  and  perform  a  normal  amount  of  work  on 
considerably  less,  in  some  cases  even  with  advantage  to  his  health. 

We  may  take  500  grammes  of  bread  and  250  grammes  of 
lean  meat  as  a  fair  quantity  for  a  man  fit  for  hard  work.  Add- 
ing 500  grammes  milk,  75  grammes  oatmeal  (as  porridge), 
30  grammes  butter,  30  grammes  fat  (with  the  meat,  or  in  other 
ways),  and  450  grammes  potatoes,  we  get  approximately 
20  grammes  nitrogen  and  300  grammes  carbon  contained  in 
135  grammes  protein,  rather  less  than  100  grammes  fat,  and 
somewhat  over  400  grammes  carbo-hydrates.     Thus — 


N. 

C. 

Proteins. 

Fat. 

Carbo- 
hydrates. 

Salts. 

z.)  250  grms.  lean  meat    - 

8 

53 

55 

8-5 

— 

4 

■z.)  500  grms.  bread 

6 

112 

40 

7'5 

245 

b'5 

(J  pint)  500  grms.  milk 

3 

35 

20 

20 

25 

3'5 

(1  oz.)  30  grins,  butter    - 

20 

— 

27 

— 

05 

/..)  30  grms.  fat 

— 

22 

— 

30 

— 

— 

oz.)  450  grms.  potatoes    - 

15 

47 

10 

— 

95 

4"5 

(3  oz.)  75  grms.  oatmeal 

1 '7 

30 

10 

4 

48 

- 

20*2 

299 

135 

97 

413 

21 

This  would  be  a  fair   '  hard  work  '   diet   for  a  well-nourished 
labourer.     But  the  great  elasticity  of  dietetic  formulae  is  shown 

35—2 


548 


A   MANU  U    OF  PHYSIOLOGY 


in  the  following  tables,  which  give  the  ration  ot  the  German 
soldier  in  peace  and  war  and  the  minimum  allowance  per  '  statute 
adult  '  prescribed  in  the  British  regulations  concerning  passenger 
ships  from  Great  Britain  to  America. 


Ration  of  the  German  Soldier. 


War. 


Bread          -         -     750  grammes. 

Bread 

- 

-     750  grammes 

Meat                     -     150         „ 

Biscuit 

- 

-     5°° 

Rice                    -      50        ,, 

Meat 

- 

-     375 

or  barley  groats     120          ,, 

Smoked  meat 

250 

Legumes              -     230         ,, 

or  fat 

-     170         „ 

Potatoes              -   1500         ,, 

Rice 

- 

-     125 

or  barley  groats     125 

Legumes 

-     250 

Minimum  Ration 

for  Passenger  Ships. 

Bread  or  biscuit    - 

- 

227 

grammes. 

Wheaten  flour 

- 

65 

>> 

or  bread    - 

- 

81 

j  ? 

Oatmeal 

- 

97 

>j 

Rice      - 

- 

97 

?> 

Peas     - 

- 

97 

jy 

Potatoes 

- 

130 

9? 

Beef     - 

- 

81 

Pork  or  preserved  meat 

65 

,, 

Sugar   - 

- 

05 

,, 

or  treacle  - 

- 

97 

,, 

Tea       - 

- 

8 

?> 

or  coffee  or  cocoa 

- 

M 

,, 

Salt      - 

- 

S 

}> 

Mustard 

- 

2 

?? 

Pepper- 

- 

1 

9J 

Vinegar  or  pickles 

- 

20 

c.c. 

In  prisons  the  object  is  to  give  the  minimum  amount  of  the  plainest 
food  which  will  suffice  to  maintain  the  prisoners  in  health.  A 
'  hard  work  '  prison  diet  in  Munich  was  found  to  contain  104 
grammes  proteins,  38  grammes  fat,  and  521  grammes  carbo- 
hydrates ;  a  '  no- work  '  diet,  only  87  grammes  proteins,  22  grammes 
fat,  and  305  grammes  carbo-hydrates.  Here  we  recognise  the 
influence  of  price  ;  carbon  can  be  much  more  cheaply  obtained  in 
vegetable  carbo-hydrates  than  in  animal  fats  ;  the  cheapest  possible 
diet  contains  a  minimum  of  animal  fat  and  proteins. 

Many  poor  persons  live  on  a  diet  which  would  not  maintain  a 
strong  man,  for  an  emaciated  body  has  a  smaller  mass  of  flesh  to 
keep  up,  and  therefore  needs  less  protein  ;  it  can  do  little  work,  and 
therefore  needs  less  food  of  all  kinds.  A  London  needlewoman, 
according  to  Playfair,  subsists,  or  did  subsist  thirty  years  ago,  on 
54  grammes  protein,  29  grammes  fat,  and  292  grammes  carbo- 
hydrates. But  this  is  the  irreducible  minimum  of  the  deepest 
poverty,  not  so  much  in  the  protein  content,  perhaps,  as  in  the 
very  low  heat  equivalent  (1,600  calories)  ;  and  a  woman,  with  a 
smaller  mass  of  flesh  and  leading  a  less  active  life  than  a  man, 
requires  less  food  of  all  sorts.  Even  the  Trappist  monk,  who  has 
reduced  asceticism  to  a  science,  and,  instead  of  eating  in  order  to 


METABOLISM,    XUTRlTfOX  AND  DTETETH  ;49 

live,  lives  in  order  not  to  eat,  consumes,  according  to  Voit,  68 
grammes  protein,  1 1  grammes  fat,  and  469  grammes  carbo-hydrates  ; 
but  manual  labour  is  a  part  of  the  discipline  of  the  brotherhood, 
and  this  must  be  still  above  the  lowest  subsistence  diet. 

The  question  whether  it  is  best  to  derive  the  proteins  (and  fats) 
of  the  food  mainly  from  plants  or  mainly  from  animals  is  one  which 
is  never  left  to  physiology  alone  to  decide.  But  it  has  been  definitely 
proved  that  vegetable  proteins  and  vegetable  fats  are  (when  properly 
prepared)  digested  and  absorbed  as  completely  as  those  of  animal 
origin,  and  play  the  same  part  in  the  metabolism  of  the  body. 

A  growing  child  needs  far  more  food  than  its  weight  alone 
would  indicate ;  for,  in  the  first  place,  its  income  must  exceed 
its  expenditure  so  that  it  may  grow  ;  and,  in  the  second  place, 
the  expenditure  of  an  organism  is  pretty  nearly  proportional, 
not  to  its  mass,  but  to  its  surface.  Now,  speaking  roughly,  the 
cube  of  the  surface  of  an  animal  varies  as  the  square  of  the 
mass  ;  when  the  weight  is  doubled,  the  surface  only  becomes 
V4,  or  one  and  a  half  times  as  great.  The  surface  of  a  boy 
of  six  to  nine  years,  with  a  body-weight  of  18  to  24  kilos,  is 
two-fifths  to  one-half  that  of  a  man  of  70  kilos  ;  and  he  should 
have  about  half  as  much  food  as  the  man.  A  child  of  four 
months,  weighing  5-3  kilos,  consumed  per  diem  food  containing 
06  gramme  nitrogen  per  kilo  of  body- weight,  or  3- 18  grammes 
nitrogen  altogether,  as  against  a  daily  consumption  of  only 
0-275  gramme  nitrogen  per  kilo  in  a  man  of  71  kilos  (Voit). 

An  infant  for  the  first  seven  months  should  have  nothing 
except  milk.  Up  to  this  age  vegetable  food  is  unsuited  to  it  ; 
it  is  a  purely  carnivorous  animal.  By  careful  observations  on 
the  amount  of  carbon  dioxide  and  nitrogen  excreted  by  a  child 
nine  weeks  old,  fed  exclusively  on  its  mother's  milk,  it  has  been 
shown  that  the  absorption  and  assimilation  of  milk  in  the  infant 
is  very  complete,  over  91  per  cent,  of  the  total  energy  being 
utilized  ;  while  an  adult,  taking  as  much  milk  as  is  necessary  for 
the  maintenance  of  nitrogenous  equilibrium,  does  not  utilize 
at  most  more  than  84  per  cent.  Human  milk  contains  about 
2  per  cent,  of  protein  (mainly  caseinogen),  3  per  cent,  of  fat, 
5  or  6  per  cent  of  carbo-hydrate  (lactose  or  milk-sugar),  and 
from  02  to  03  per  cent,  of  salts.  Cow's  milk  contains  about 
4  per  cent,  of  protein,  4  to  6  per  cent,  of  fat,  4  per  cent,  of  lactose, 
and  o-7  per  cent,  of  salts.  When  given  to  infants  it  should,  as 
a  general  rule,  be  diluted  with  water,  and  some  sugar  should  be 
added  to  it.  Ass's  milk  has  about  the  same  amount  of  protein, 
lactose,  and  salts  as  human  milk,  but  less  than  half  as  much  fat. 
It  is  very  well  borne  and  very  completely  absorbed. 

As  to  the  place  of  water  and  inorganic  salts  in  diet,  it  is 
neither  necessary  nor  practicable  to  lay  down  precise  rules. 
In  most  well-settled  countries  they  cost  little  or  nothing  ;  very 


1   MANUAL  OF  PHYSIOLOGY 

different  quantities  can  be  taken  and  excreted  without  harm  ; 
and  both  economics  and  physiology  may  well  leavi  :nan 

to  his  taste  in  the  matter.  Salt  is  indeed  for  the  mo>t  part  u 
not  as  a  special  article  of  diet,  but  as  a  condiment  to  tii 
relish  to  the  food,  just  as  a  great  deal  more  water  than  is  actually 
led  is  often  drunk  in  the  form  of  beverages.  It  is  certain 
that  the  quantity  of  salt  required,  in  addition  to  the  salts  of  the 
food,  to  keep  the  inorganic  constituents  of  the  body  at  their 
normal  amount,  is  very  small.  A  30-kilo  dog  obtains  in  his  diet 
'0  grammes  of  lean  meat  only  06  gramme  sodium  chloride. 
and  needs  no  more.  An  infant  in  a  litre  of  its  mother's  milk, 
which  is  a  sufficient  diet  for  it  at  six  to  nine  months,  gets  only 
o-8  gramme  sodium  chloride.  Bunge,  however,  has  shown  that  the 
proportion  of  potassium  and  sodium  salts  in  the  food  is  a  factor  in 
determining  the  quantity  of  sodium  chloride  required.  A  double 
decomposition  takes  place  in  the  body  between  potassium 
phosphate  and  sodium  chloride,  potassium  chloride  and  sodium 
phosphate  being  formed  and  excreted  ;  and  the  loss  of  sodium 
and  chlorine  in  this  way  depends  on  the  relative  proportions 
of  potassium  and  sodium  in  the  food.  In  most  vegetables  the 
proportion  of  potassium  to  sodium  is  much  greater  than  in 
animal  food,  so  that  vegetable-feeding  animals  and  men  as  a 
rule  desire  and  need  relatively  great  quantities  of  sodium  chloride. 
But  it  is  stated  that  the  inhabitants  of  a  portion  of  the  Soudan 
use  potassium  chloride  instead  of  sodium  chloride,  obtaining 
the  potassium  salt  by  burning  certain  plants  which  leave  an  ash 
poor  in  carbonates,  and  then  extracting  the  residue  with  water 
and  evaporating  (Dvbowski*.  A  beef-eating  English  soldier  in 
India  consumes  about  7  grammes  (J  oz.),  a  vegetarian  S< 
about  18  grammes  (f  oz.).  of  common  salt  per  day. 

Wine,  beer,  tea,  coffee,  cocoa,  etc.,  belong  to  the  important 
class  of  stimulants.  Some  of  them  contain  small  quantities 
of  food  substances,  but  these  are  of  secondary  interest.  In  beer, 
for  example,  there  are  not  inconsiderable  amounts  of  proteins, 
dextrin,  and  sugar.  But  14  litres  of  beer  would  be  required  to 
yield  15  grammes  nitrogen,  and  10  litres  to  give  250  grammes 
carbon  ;  and  nobodv,  except  a  German  corps  student,  could 
consume  such  quantities.  The  minimum  nitrogen  require- 
ment, however,  as  well  as  the  necessary  heat  value,  could 
theoretically  be  covered  by  6  or  7  litres  of  good  German 
beer. 

In  some  cocoas  there  is  as  much  as  50  per  cent,  of  fat,  4  per 
cent,  of  starch,  and  13  per  cent,  of  proteins  ;  and  in  the  cheaper 
cocoas  much  starch  is  added.  Still,  a  large  quantity  of  the 
ordinary  infusion  would  be  needed  for  a  satisfying  meal. 
Frederick   the  Great,   indeed,   in   some  of  his   famous  marches 


METABOLISM,  NUTRITION  AND  DIETETICS  551 

dined  off  .1  cup  of  chocolate,  and  beat  combined  Europe  on  it  ; 
but  his  ordinary  menu  was  much  more  varied  and  substantial. 

Alcohol. — The  great  social  and  hygienic  evils  connected  with 
the  abuse  of  alcohol,  as  well  as  its  applications  in  therapeutics, 
render  it  necessary,  or  at  least  permissible,  to  state  a  little  more 
fully,  though  only  in  the  form  of  summary,  some  of  the  chief 
conclusions  that  may  be  drawn  as  to  its  action  and  uses. 

(1)  In  small  quantities  alcohol  is  oxidized  in  the  body,  a  little 
of  it,  however,  being  excreted  unchanged  in  the  breath  and 
urine.  A  certain  amount  of  protein  is  saved  from  decomposi- 
tion when  alcohol  is  taken,  just  as  when  fat  or  sugar  is  taken. 
For  example,  the  addition  of  130  grammes  of  sugar  to  the  daily 
food  of  an  individual  caused  a  '  sparing  '  of  03  gramme  nitrogen. 
The  substitution  of  72  grammes  alcohol  for  the  sugar  caused 
o-2  gramme  nitrogen  to  be  spared  (Atwater  and  Benedict). 
Alcohol  is  therefore  to  some  extent  a  food  substance,  although 
it  is  not,  under  ordinary  circumstances,  taken  for  the  sake  of  the 
energy  its  oxidation  can  supply,  but  as  a  stimulant. 

(2)  There  is  no  reason  to  suppose  that  this  energy  cannot  be 
utilized  as  a  source  of  work  in  the  body.  Indeed,  a  certain  amount 
of  alcohol  seems  to  be  normally  formed  in  the  tissues  as  one  of 
the  intermediate  products  in  the  oxidation  of  sugar.  Heat  can 
certainly  be  produced  from  it,  but  this  is  far  more  than  counter- 
balanced by  the  increase  in  the  heat  loss  which  the  dilatation 
of  the  cutaneous  vessels  caused  by  alcohol  brings  about. 

(3)  It  is  a  valuable  drug,  when  judiciously  employed,  in  certain 
diseases — -e.g.,  pneumonia  and  puerperal  insanity  (Clouston). 

(4)  Alcohol  is  occasionally  of  use  in  disorders  not  amounting 
to  serious  disease— e.g.,  in  some  cases  of  slow  and  difficult 
digestion.  In  these  cases  it  may  act  by  increasing  the  flow  of 
certain  of  the  digestive  secretions,  as  saliva  and  gastric  juice. 
This  effect  seems  to  more  than  counterbalance  the  retarding 
influence  which,  except  when  well  diluted,  it  exerts  on  the 
chemical  processes  of  digestion. 

(5)  Alcohol  is  of  no  use  for  healthy  men. 

(6)  Alcohol  in  strictly  moderate  doses,*  properly  diluted  and 
especially  when  taken  with  the  food,  is  not  harmful  to  healthy 
men,  living  and  working  under  ordinary  conditions. 

(7)  Modern  experience  goes  to  show  that  in  severe  and  con- 
tinuous exertion,  coupled  with  exposure  to  all  weathers,  as  in 
war  and  in  exploring  expeditions,  alcohol  is  injurious,  and  it  is 
well  known  that  it  must  be  avoided  in  mountain  climbing. 

Tea,  coffee,  and  cocoa  are  more  suitable  stimulants  for  healthy 
persons,  because  they  are  less  dangerous  than  alcohol,  and  they 

*  Not  more  than  1$  oz.  of  absolute  alcohol,  corresponding  to  about 
4  oz.  of  whisky,  or  2  to  3  wineglasses  of  sherry  or  port,  or  a  pint  of  claret, 
or  a  couple  of  pints  of  light  beer  in  24  hours. 


552  A  MANUAL  OF  PHYSIOLOGY 

leave  no  unpleasant  effects  behind  them.  But  it  should  be 
remembered  that  there  is  no  stimulant  which  is  not  liable  to  be 
abused.  It  has  been  shown  by  ergographic  experiments  (p.  649) 
that,  like  alcohol,  tea,  coffee,  mate,  and  cola-nut,  which  all 
contain  the  alkaloid  theine  or  caffeine,  restore  the  power  of  per- 
forming muscular  work  after  exhaustion,  but  only  if  food  has 
been  recently  or  is  simultaneously  taken. 

Certain  organic  acids  contained  in  fresh  vegetables,  although 
neither  in  the  ordinary  sense  foods  nor  condiments,  seem  to  In- 
necessary  for  the  maintenance  of  health,  for  in  circumstances  in 
which  these  cannot  be  obtained  for  long  periods,  scurvy  is  liable 
to  break  out.  It  is  prevented  by  the  use  of  lime  or  lemon- 
juice,  in  which  citric  and  a  trace  of  malic  acid  are  contained. 


INTERNAL  SECRETION. 

It  is  long  since  Caspar  Friedrich  Wolff  expressed  the  idea  that 
'  each  single  part  of  the  body,  in  respect  of  its  nutrition,  stands 
to  the  whole  body  in  the  relation  of  an  excreting  organ,'  and 
thus  emphasized  the  importance  of  substances  produced  by  the 
activity  of  one  kind  of  cell  for  the  normal  metabolism  of  another. 
But  it  is  only  in  recent  years  that  it  has  become  possible  to 
illustrate  this  mutual  relation  by  any  large  number  of  experi- 
mental facts. 

Certain  of  the  substances  taken  in  from  the  blood  by  the 
liver  find  their  way,  after  undergoing  various  changes,  into  the 
biliary  capillaries,  and  are  excreted  as  bile  ;  certain  other  sub- 
stances, such  as  sugar  and  the  precursors  of  urea,  are  taken  up 
by  the  hepatic  cells,  transformed  and  sometimes  stored  for  a 
time  within  them,  and  then  given  out  again  to  the  blood.  Bile 
we  may  call  the  external  secretion  of  the  liver,  glycogen  and 
urea  constituents  of  its  internal  secretion.  In  one  sense  it  is 
evident  that  all  tissues,  whether  glands  in  the  morphological 
sense  or  not,  may  be  considered  as  manufacturing  an  internal 
secretion.  For  everything  that  an  organ  absorbs  from  the 
blood  and  lymph  it  gives  out  to  them  again  in  some  form  or 
other  except  in  so  far  as  it  forms  or  separates  a  secretion  that 
passes  away  by  special  ducts.  But  it  is  usual  to  employ  the  term 
only  in  relation  to  organs  of  glandular  build,  whether  provided 
with  ducts  or  not.  For  convenience  the  action  of  extracts  of 
some  other  tissues,  such  as  nervous  tissue,  will  also  be  con- 
sidered here,  although  there  is  no  reason  to  suppose  that  they 
form  any  specific  internal  secretion. 

The  capacity  of  manufacturing  internal  secretions  of  high 
importance  can  neither  be  attributed  to  all  glands  with  ducts 


Ml  TABOLISM,    NUTRITION  AND  DIETETICS 

nor  denied  to  all  other  organs.  For  the  salivary,  mammary, 
and  gastric  glands  may  be  completely  removed  without  causing 

any  serious  effects,  while  death  follows  excision  of  the,  so  far  as 
mere  hulk  is  concerned, apparently  insignificant  masses  of  tissue  in 
the  ductless  thyroid,  parathyroid,  suprarenal  or  pituitary  bodies. 

It  is  known  that  in  the  case  of  the  liver  the  internal  secretion 
is  more  important  than  the  external,  for  an  animal  cannot 
survive  without  its  liver,  while  it  may  be  but  little  affected  by 
the  continuous  escape  of  the  bile  through  a  fistulous  opening. 

Pancreas. — -The  internal  secretion  of  the  pancreas  is  also 
indispensable.  For  when  the  pancreas  is  excised  death  follows 
in  many  species  of  animals,  and  especially  in  carnivorous  animals  ; 
and  in  man  severe  and  ultimately  fatal  diabetes  is  often  associated 
with  pancreatic  disease,  while  the  mere  loss  of  the  pancreatic 
juice  through  a  fistula  does  not  necessarily  shorten  life,  although 
the  absorption  of  fat  is  seriously  interfered  with. 

The  ultimate  cause  of  death  seems  to  be  a  profound  disturbance 
of  metabolism,  of  which  the  most  significant  token  is  the  in- 
creased proportion  of  sugar  in  the  blood,  and  its  speedy  appear- 
ance in  the  urine — in  dogs  always  within  twenty-four  hours 
following  total  removal  of  the  organ.  Associated  with  the 
glycosuria  is  an  increase  in  the  quantity  of  the  urine  (polyuria), 
excessive  thirst  (polydipsia),  and  a  ravenous  appetite  (poly- 
phagia), in  spite  of  which  the  animal  becomes  more  and  more 
emaciated — in  short,  the  classical  symptoms  of  a  severe  type  of 
pathological  diabetes  in  man,  but,  of  course,  far  more  acute  in 
their  onset,  and  far  more  rapid  in  their  progress  towards  the 
inevitable  end.  Dogs  rarely  survive  more  than  two  or  three 
weeks,  the  immediate  cause  of  the  rapidly  fatal  result  being 
perhaps  the  extensive  suppuration  which  is  apt  to  ensue  on 
slight  and  practically  unavoidable  superficial  injuries.  The 
resistance  of  the  tissues  to  bacterial  invasion  and  their  tendency 
to  spontaneous  healing  are  reduced  by  the  overloading  of  the 
blood  and  tissue  liquids  with  sugar.  Even  when  carbo-hydrates 
are  excluded  from  the  food,  or  when  no  food  at  all  is  given, 
sugar  continues  to  be  excreted  in  large  amounts.  The  destruction 
of  proteins  is  increased.  It  is  a  significant  fact  that  glycosuria 
does  not  appear  or  is  only  transient  when  the  pancreas  is  partially 
removed,  so  long  as  a  comparatively  small  fraction  of  the  gland 
(one-quarter  or  one-fifth)  is  left.  Even  when  such  a  remnant 
is  transplanted  from  its  original  position,  care  being  taken  not 
to  interfere  with  its  circulation,  and  grafted  in  the  peritoneal 
cavity  or,  indeed,  under  the  skin,  the  animal  remains  in  good 
health.  In  the  dog  this  operation  can  be  practised  on  the 
lowest  part  of  the  descending  division  of  the  pancreas,  which  is 
not  united  with  the  duodenum,  but  lies  free  in  the  mesentery. 


554  I    V  \NUAL  OF  PHYSIOLOGY 

Removal  of  the  fragment  of  pancreas  is  followed  by  the  whole 
train  of  symptoms  associated  with  total  extirpation  of  the 
organ. 

Although  as  vd  we  are  ignorant  of  the  precise  manner  in 
which  the  pancreas  influences  the  metabolism  of  the  body,  it  is 
impossible  to  doubt,  in  view  of  the  facts  we  have  mentioned, 
that,  like  the  liver,  in  addition  to  carrying  on  the  exchanges 
necessary  for  the  preparation  of  the  ordinary  or  external  secre- 
tion,  the  gland  has  other  important  relations  with  the  circu- 
lating fluids,  giving  to  them  or  taking  from  them  substances 
on  the  manufacture  or  destruction  of  which  the  normal  metabolic 
processes  depend.  It  has  been  suggested  that  the  pancreas 
neutralizes  or  renders  harmless  some  toxic  substance  formed 
elsewhere  in  the  body,  the  action  of  which  produces  glycosuria. 
But  no  evidence  of  the  existence  of  an}'  such  substance  has  been 
obtained,  and  the  transfusion  into  a  normal  dog  of  blood  from 
a  depancreatized  animal,  which  ought  to  be  laden  with  the 
hypothetical  toxic  material,  does  not  cause  glycosuria.  It  is 
much  more  probable  that  the  hyperglycemia  on  which  the 
glycosuria  depends  is  caused  by  the  absence  of  something 
normally  produced  by  the  pancreas,  and  which  is  indispensable  for 
the  due  regulation  of  the  sugar-content  of  the  blood.  This  some- 
thing, as  already  pointed  out  in  discussing  pathological  diabetes, 
may  either  be  necessary  to  regulate  the  transformation  of 
sugar  into  glycogen,  so  that  too  great  a  surplus  of  sugar  does 
not  remain  unchanged,  or  to  regulate  the  transformation  of 
glycogen  into  dextrose  and  prevent  too  hastv  and  too  extensive 
action  by  the  glycogenase,  or,  finally,  to  regulate  and  to  aid  in  the 
normal  combustion  of  the  sugar  in  the  organs  (p.  517).  The  seat 
of  the  internal  secretion  of  the  pancreas  seems  to  be  the  very 
vascular  epithelioid  tissue  which  is  peculiar  to  this  gland,  and 
occurs  in  islands  between  the  alveoli  (islands  or  islets  of  Langer- 
hans)  (Schafer) .  For  animals  survive  the  complete  atrophy  of  the 
ordinary  secreting  epithelium  caused  by  the  injection  of  paraffin 
into  the  ducts,  and  no  sugar  appears  in  the  urine.  The  islets 
remain  intact.  When  a  portion  of  the  pancreas  is  separated 
from  the  rest,  and  its  duct  ligated,  it  undergoes  extensive  atrophy, 
a  tissue  remaining  which  is  apparently  composed  of  enlarged 
islands  of  Langerhans  and  remains  of  pancreatic  ducts.  If  the 
rest  of  the  gland  is  now  removed,  no  glycosuria  occurs,  even  when 
considerable  quantities  of  dextrose  are  injected.  But  when  the 
atrophied  remnant  is  also  removed,  typical  pancreatic  glycosuria 
at  once  ensues  (W.  G.  MacCallum). 

As  further  evidence  that  the  islets  have  a  different  function 
from  the  pancreatic  alveoli  may  be  cited  the  statement  that  in 
teleostean  fishes,  in  which  the  islands  are  so  large  that  they  can 


METABOLISM,    VUTRITIOh    AND  DIETETK  555 

parated  from  the  resl  of  the  tissue,  the  cells  oi  the  islets, 
instead  oi  containing  an  amylolytic  ferment  like  the  alveolar 
cells,  contain  a  glycolytii  ferment,  or  ai  leasl  possess  t!  e  power 
oi  destroying  sugar.  Ye1  the  question  oi  the  significant  e  oi  the 
islets  can  hardly  be  considered  settled,  and  there  are  good 
observers  who  believe  thai  they  do  no1  differ  essentially  from 
the  alveolar  tissue,  bu1  are  formed  by  certain  changes  in  the 
arrangement  and  properties  oi  the  alveolar  elements.  For  example, 
after  the  gland  has  become  exhausted  under  the  influence  oi 
secretion,  a  great  part  of  the  alveoli  are  said  to  be  converted 
into  islet  tissue,  which  after  a  period  of  rest  is  again  altered, 
so  as  to  yield  the  characteristic  histological  picture  of  the 
secretory  alveoli  (Dale).  While,  then,  the  importance  of  the 
pancreas  in  carbo-hydrate  metabolism  is  certain,  and  the 
dependence  of  this  function  upon  an  internal  secretion  is  highly 
probable,  it  is  not  yet  definitely  settled  whether  this  secretion 
is  formed  in  the  organ  as  a  whole  or  only  in  the  islets.  That 
lesions  of  the  pancreas  may  be  concerned  in  pathological 
diabetes  is  well  established,  and  it  is  of  interest  in  connection 
with  the  question  we  have  just  been  discussing  that  in  a  certain 
number  of  cases  the  changes  observed  have  been  in  the  islands 
(Opie).  And  in  diabetes  accompanying  cirrhosis  of  the  liver, 
which  has  usually  been  considered  to  depend  upon  the  hepatic 
changes,  it  has  been  shown  that  in  many,  if  not  all,  of  the  cases 
the  pancreas  is  also  affected  by  a  growth  of  connective  tissue 
outside  the  acini  (Steinhaus).  Some  authors,  indeed,  have  gone 
so  far  as  to  say  that  in  all  cases  of  diabetes  mellitus  there  is 
disease  of  the  pancreas,  but  of  this  there  is  no  evidence. 

Ligation,  or  the  establishment  of  a  fistula,  of  the  thoracic 
duct,  causes  glycosuria  in  dogs.  It  is  possible  that  this  is  really 
a  mild  form  of  pancreatic  diabetes,  due  to  interference  with 
the  supply  of  the  internal  secretion  of  the  pancreas,  or  of  that 
part  of  it  which  reaches  the  blood  by  the  lymph-stream  (Tuckett). 

Quite  recently  Pfliiger  has  brought  forward  evidence  which  he 
considers  to  show  that  it  is  not  the  removal  of  the  pancreas,  as  such, 
but  the  section  of  certain  nerves  running  into  or  through  it  from 
the  duodenum,  which  is  the  cause  of  the  glycosuria.  For  when  these 
nerves  are  divided  or  the  duodenum  removed  while  the  pancreas 
remains  untouched,  the  result  is  the  same  as  if  the  pancreas  itself 
had  been  excised.  He  imagines  that  these  nerves  are  '  antidiabetic  ' 
— that  is.  in  some  way  oppose  the  production  of  sugar — while  nerves 
coming  from  the  so-called  '  sugar  centre  '  in  the  bulb  (the  centre 
assumed  to  be  affected  in  the  puncture  experiment)  favour  sugar 
production.  Between  these  the  normal  balance  is  struck  in  health  ; 
it  is  the  upsetting  of  this  balance  by  the  crippling  of  the  duodenal 
fibres  which  is  at  the  bottom  of  '  pancreatic  '  diabetes.  It  is  too 
early  to  appraise  /the  value  of  this  conception,  especially  as  the  facts 
upon  which  it  is  founded  have  only  been  clearly  established  for 


I    MANUAL    OF  PHYSIOLOGY 

frogs,  and  it  is  doubtful  whether  they  can  be  extended  to  mammals. 
But  if  these  nerves  end  in  the  pancreas,  and  do  not  simply  run 
through  it,  say.  to  the  liver,  it  is  possible  that  they  act  on  the  sugar 
metabolism  by  regulating  the  internal  secretion  of  the  pancreas. 

Sexual  Organs. — The  influence  of  castration  in  preventing 
the  physical  and  psychical  changes  that  normally  occur  at 
puberty  is  no  doubt  also,  in  part  at  least,  due  to  the  loss  of  the 
internal  secretion  of  the  testes.  In  partially  castrated  cocks 
it  was  seen  that  so  long  as  a  portion  of  one  testicle  remained,  the 
male  characters  were  preserved,  but  after  removal  of  this 
residue  the  comb  and  wattles  withered  in  a  few  weeks  (Hanau). 
At  the  breeding-time  the  muscles  of  the  forearm  of  the  brown 
land  frog  (Rana  fusca)  become  hypertrophied  in  the  male,  so 
that  it  can  more  tightly  hold  the  female.  At  the  same  time  the 
balls  of  the  toes  increase  in  size,  and  become  covered  with  a 
peculiar  black  growth.  After  the  breeding  season  these  secondary 
sexual  characters  disappear.  If  the  male  frog  is  castrated,  the 
periodical  return  of  these  phenomena  does  not  occur,  but  the 
presence  of  one  testicle  suffices  for  their  development  on  both 
sides.  When  pieces  of  testicle  from  normal  frogs  are  introduced 
under  the  skin  of  the  castrated  frogs,  the  phenomena  occur  just 
as  if  the  animals  had  not  been  castrated  (M.  Xussbaum).  The 
exact  experiments  of  Loewy  and  Richter  on  the  metabolism 
of  bitches  before  and  after  castration  throw  light  upon  the 
changes  which  follow  that  operation,  and  afford  decisive  proof 
that  they  are  connected  with  the  absence  of  substances  specific 
to  the  ovary.  They  conclude  that  in  the  castrated  animal  the 
oxidative  energy  of  the  cells  is  lessened.  The  oxygen  consump- 
tion sinks,  even  although  protein  is  laid  on  and  the  total  amount 
of  active  tissue  thus  increased.  Under  certain  circumstances 
this  specific  diminution  of  metabolism  may  be  balanced  by 
conditions  which  cause  an  increase  in  the  metabolism.  The 
lessening  of  the  oxidative  power  is  due  to  the  loss  of  ovarian 
substance,  for  the  administration  of  an  extract  of  the  ovary 
(oophorin)  not  only  neutralizes  it,  but  actually  causes  an  increase 
in  the  gaseous  metabolism  to  far  above  the  original  amount, 
while  it  has  no  effect  on  the  metabolism  of  the  uncastrated 
animal.  It  is  not  the  decomposition  of  proteins,  but  of  non- 
nitrogenous  substances,  which  is  accelerated.  Oophorin  also 
brings  about  a  notable  increase  in  metabolism  in  the  castrated 
male  dog,  while,  curiously  enough,  extract  of  testicle  causes 
only  a  small  increase,  due  to  a  basic  substance,  spermin  (C5N2H14). 
which  can  be  isolated  from  the  testicle.  But  the  orchitic 
extract  is  not  without  influence  in  other  ways.  It  certainly 
increases  the  capacity  for  muscular  work,  as  tested  by  the 
ergograph    (p.   650),    and   this   distinct    physiological    action   is 


Ml  TABOLISM,  NUTRITION    AND  hi  1. 1 1  1  557 

sufficient  to  encouragr  the  hope  that  it  may  possess  some  thera- 
peutic value,  although  far  from  what  has  been  claimed  for  it 
by  its  more  enthusiastic  advocates.  The  only  constituent  of 
extracts  of  the  testicle  made  with  salt  solution  which  causes 
any  pronounced  effect  on  the  blood-pressure  when  injected  into 
the  circulation  is  a  nucleo-protein,  the  most  plentiful  of  the  pro- 
tein substances.  The  pressure  falls,  mainly  owing  to  inhibition 
of  the  heart,  but  partly  through  vaso-dilatation  in  the  splanchnic 
area  (DLxon). 

The  testicles  also  influence  the  growth  of  the  bones.  In 
eunuchs  and  in  young  men  with  atrophy  of  the  testicles  a  ten- 
dency has  been  observed  for  the  long  bones  to  go  on  growing 
far  beyond  the  usual  period.  This  has  been  shown  by  the 
Rongten  rays  to  be  due  to  delay  in  the  ossification  of  the  epi- 
physes. The  same  has  been  observed  in  animals,  and  is  supposed 
to  be  caused  by  the  loss  of  some  substance  normally  formed  in 
the  testicle  which  influences  the  metabolism  of  the  bones  and 
the  deposition  of  the  bone  salts. 

A  temporary  diminution  in  the  haemoglobin  and  in  the  number 
of  the  erythrocytes  has  been  observed  in  castrated  bitches,  an 
observation  which,  so  far  as  it  goes,  is  in  favour  of  the  view  that 
an  insufficient  internal  secretion  of  the  ovaries  is  the  cause  of 
the  form  of  anaemia  known  as  chlorosis. 

Evidence  has  recently  been  brought  forward  that  the  corpus 
luteum  is  a  gland  with  an  internal  secretion,  whose  function 
is  connected  with  menstruation  and  with  the  implantation  of 
the  ovum  and  the  subsequent  growth  of  both  ovum  and  uterus 
in  pregnancy  (Born,  Fraenkel)  (Chap.  XIV.). 

Thymus. — It  is  well  known  that  in  castrated  animals  the 
thymus  is  larger  and  persists  longer  than  in  entire  animals.  In 
bulls  and  unspayed  heifers  the  normal  atrophy  of  the  thymus, 
which  begins  after  the  period  of  puberty,  is  greatly  accelerated 
when  the  bulls  have  been  used  for  breeding,  and  when  the  heifers 
have  been  pregnant  for  several  months.  There  is  a  reciprocal 
influence  of  the  thymus  on  the  testicles,  and  removal  of  the 
thymus  before  the  time  at  which  it  naturally  atrophies  is  fol- 
lowed by  a  more  rapid  growth  of  the  testes  (in  guinea-pigs) 
(Paton).  In  young  mammals  the  loss  of  the  thymus  causes 
transient  disturbances  of  nutrition,  a  temporary  decrease  in 
the  number  of  all  varieties  of  leucocytes,  and  a  diminished 
resistance  to  the  pus-forming  micrococci,  probably  connected 
with  the  relatively  feeble  leucocytosis  (or  increase  in  the  number 
of  leucocytes)  by  which  the  animals  react  to  the  infection.  In 
the  frog  the  thymus  persists  throughout  life.  Yet  the  removal 
of  it  is  not  fatal  if  precautions  against  infection  be  taken.  In 
mammals    (including   man)    the   thymus   does   not    completely 


A   Ml  Mil    OF  I'll  YSIOLOG  \ 


disappear  in  the  adult,  [slands  of  thymus  tissue  are  found 
at  all  ages  among  the  fal  by  which  the  bulk  <>t  the  organ  i> 
replaced.  The  chief  effect  of  intravenous  injection  oi  extract 
of  human  or  ox  thymus  is  a  Lowering  of  blood-pressure.      In 

this  respect  it  resembles  thyroid  extract.  The  heart  may  be  a1 
the  same  time  accelerated. 

Thyroids  and  Parathyroids. —The  thyroid  consists  oi  two 
lobes  connected  by  an  isthmus  across  the  middle  line  in  man 
and  some  animals,  but  often  separate.     In  the  neighbourhood 

of  the  thyroid,  or  em- 
bedded in  its  tissue,  are 
certain  bodies  called  para- 
thyroids, consisting  of 
solid  columns  of  epithelial 
cells.  The  number  and 
situation  of  the  parathy- 
roids are  not  constant. 
As  a  rule,  there  are  four 
in  mammals,  two  on  each 
side,  but  this  number  is 
subject  to  variations  in 
different  individuals  of 
the  same  species.  The 
variability  in  their  ana- 
tomical relations  to  the 
thyroid  is  of  greater  signi- 
ficance. For  much  of  t he- 
uncertainty  in  which  the 
whole  question  of  the 
symptoms  following  ex- 
tirpation of  the  thyroids 
was  until  lately  involved 
arose  from  ignorance  or 
insufficient  recognition  of 
this  variability.  In  most 
animals  the  inferior,  anterior,  or  external  pair  of  parathy- 
roids is  more  or  less  distinctly  separated  from  the  thyroid. 
The  separation  is  especially  evident  in  the  herbivora,  in  the 
monkey,  and  in  man,  and  this  pair  of  parathyroids  is  much  larger 
than  the  other.  In  carnivorous  animals,  as  the  dog  and  cat,  t  he 
anterior  pair  of  parathyroids  is  closely  adherent  to  the  thyroid 
capsule.  The  superior,  posterior,  or  internal  pair,  both  in  herbi- 
vora and  carnivora,  is  always  very  closely  associated  with  the 
capsule  of  the  thyroid,  and  frequently  embedded  in  the  substance 
of  the  gland.  The  consequence  of  this  arrangement  is  that  in 
the  older  experiments  the  chief  masses  of  parathyroid  tissue  were 


Fig.   187. — Parathyroid  (Vincent  and 
Jolly). 

A  small  portion  of  parathyroid  of  cat 
embedded  in  thyroid  tissue.  It  consists  for 
the  most  part  of^solid  columns  of  epithelial 
cells  (3,  5,  8)  with  strands  oi  vascular  con- 
nective tissue  (6).  A  thyroid  vesicle  (11)  and 
portions  of  two  others  (1.  10)  are  seen  in  the 
Lower  part  of  the  figure,  separated  fnun  the 
parathyroid  by  a  fibrous  capsule  (2).  4,  7, 
bloodvessels  ;  9,  lower  boundary  of  the  para- 
thyroid tissue.      (  x  5°o.) 


METABOLISM,    NUTRITION  AND  DIETETIi    i  J59 

much  more  likely  to  escape  removal  with  the  thyroid  in  th< 
<>!  herbivorous  than  in  the  1  ase  <>l  carnivorous  animals. 
Bui  even  in  one  and  the  same  species  considerable  variations 

may  exist.  It  is  easy  to  see,  then,  that  in  removing  the  thyroid 
the  parathyroids  would  sometimes  be  completely  removed  as 
well,  while  at  other  times  all  or  some  of  the  parathyroid  tissue 
would  be  spared.  Add  to  this  that  sporadic  masses  of  thyroid 
tissue  (accessory  thyroids),  often  existing  as  far  down  as  the 
root  of  the  aorta  (always,  indeed,  in  certain  animals — e.g.,  the 
dog),  must  necessarily  be  spared  in  the  most  complete  thy- 
roidectomy, and  it  will  cease  to  excite  surprise  that  the  symptoms 
and  pathological  changes  described  after  that  operation  should 
have  been  so  various  and  so  contradictory.  We  know  now  that 
the  parathyroids  are  perfectly  distinct  organs  from  the  thyroid 
in  histological  structure,  in  function,  and  in  the  consequences 
of  their  removal.  Nor  do  they  show  any  compensatory  hyper- 
trophy when  the  thyroid  alone  is  excised,  or  any  changes  which 
would  indicate  a  definite  relation  to,  still  less  an  active  participa- 
tion in,  the  pathological  processes  occurring  in  the  thyroid  in 
goitre.  The  parathyroids  contain  no  iodine,  while  iodine  is  a 
characteristic  constituent  of  the  thyroid. 

Parathyroidectomy. — Total  extirpation  of  the  parathyroids  is 
followed  by  a  train  of  acute  symptoms,  ending  fatally,  as  a  rule, 
in  from  one  to  ten  days.  The  typical  nervous  symptoms  follow- 
ing the  operation  have  been  described  as  those  of  '  tetany,'  and  the 
tetany  which  used  to  be  included  among  the  consequences  of 
removal  of  the  thyroid  is  now  known  to  be  due  to  the  simul- 
taneous excision  of  the  parathyroids  (Kocher).  A  cat,  after  the 
combined  operation,  is  perfectly  well  on  the  first  day.  On  the 
second  day  a  curious  shaking  of  the  paws  is  seen,  tremors  of 
central  origin  soon  appear,  and  increase  in  severity  until  at  length 
they  culminate  in  general  spasmodic  attacks.  Even  when  the 
animal  is  at  rest  the  fore-legs  tend  to  be  flexed,  while  the  hind- 
legs  are  extended,  and  this  attitude  is  exaggerated  in  the  con- 
vulsions. In  the  later  stages  unconsciousness  is  associated  with 
the  onset  of  the  convulsions.  Similar  results  follow  excision  of 
the  parathyroids  alone  in  dogs.  Although  the  tetany  is  the  most 
striking  symptom,  it  is  only  one  token  of  a  profound  general  dis- 
turbance of  nutrition.  The  pulse-rate  and  the  rate  of  respiration 
are  markedly  increased.  There  is  profuse  salivation,  with  dilata- 
tion of  the  stomach  and  duodenum,  and  fever.  The  exact  signifi- 
cance of  these  symptoms  is  unknown.  The  administration  of 
calcium  completely  relieves  them,  and  by  its  use  death  may  be 
long  or  perhaps  indefinitely  postponed  (W.  G.  MacCallum).  The 
mode  of  action  of  the  calcium  has  not  been  made  clear  as  yet.  It 
does  not  seem  to  be  so  efficacious  in  rabbits  as  in  dogs  (Arthus). 


560  A  M  1X1    li.  OF  PHYSI0LOG\ 

Thyroidectomy.  The  symptoms  that  follow  removal  ol  the 
thyroid  alone  are  perfectly  different.  The  metabolic  disturbance 
is  eventually,  in  tno9l  animals,  not  less  far-reaching  than  that 
which  ensues  when  the  parathyroids  are  alone  excised.  Bui  it  is 
far  more  chronic,  reveals  itself  by  totally  distincl  changes,  is 
not  amenable  to  calcium,  but  is  completely  corrected  by  the 
administration  of  thyroid  substance.  While  qo  animals  which 
have  been  examined  survive  the  total  removal  ol  the  para- 
thyroids, certain  species — e.g.,  the  goat — are  but  slightly  affected 
by  thyroidectomy,  and  survive  indefinitely.  In  man,  before  the 
consequences  of  thyroidectomy  were  known,  the  whole  -land 
not  infrequently  excised  for  goitre.  If  the  parathyroids  hap- 
pened also  to  be  completely  involved  in  the  operation,  death 
quickly  followed.  But  where  only  the  thyroid  itself,  or  the 
thyroid  plus  the  small  internal  pair  of  parathyroids,  was  extir- 
pated, the  condition  called  cachexia  strumipriva  was  observed  to 
supervene.  The  symptoms  resemble  those  of  the  disease  known 
as  myxcedema,  in  which  the  characteristic  anatomical  change  is 
an  increase  (a  hyperplasia)  of  the  connective  tissue  in  and  under 
the  true  skin.  Newly-formed  connective  tissue  always  contains 
an  excess  of  mucin,  and  for  this  reason  in  the  early  stages  oi 
myxcedema  there  is  somewhat  more  than  the  usual  amount  of 
that  substance  in  the  subcutaneous  tissue.  The  skin  is  dry, 
and  the  hair  falls  off.  The  features  arc  swollen  and  heavy, 
the  movements  clumsy  and  trembling.  As  the  disease  pro- 
gresses the  mental  powers  deteriorate  too  ;  the  patient  becomes 
stupid  and  slow,  and  perhaps,  at  last,  imbecile.  When  the 
gland  is  so  affected  in  early  life  that  extensive  atrophy  of  the 
true  secreting  tissue  occurs,  a  peculiar  condition  of  idiocy 
(cretinism)  results. 

In  animals  there  is  a  great  difference  in  the  results  ol  total 
cision  of  the  thyroids,  both  between  different  groups  and  between 
different  individuals  of  the  same  group.  In  young  animals  the 
symptoms  come  on  more  rapidly,  and  are  more  severe  than  in 
old.  Monkeys  develop  symptoms  resembling  those  ot  myx- 
cedema. 

The  older  descriptions  of  the  very  acute  onset  of  the  symptoms 
and  the  quickly  fatal  result  in  carnivorous  animals  were  vitiated 
by  the  circumstance  that,  for  the  anatomical  reason  already 
alluded  to,  the  parathyroids  were  also  involved  in  the  operation. 
Nevertheless,  the  consequences  of  complete  removal  of  the  thy- 
roid proper  are  in  general  more  serious  in  the  carnivora  than  in 
the  herbivora.  Muscular  weakness  soon  becomes  marked  ;  the 
tissues  waste,  the  temperature  becomes  subnormal,  and  this  is 
associated  with  changes  in  the  heat  regulation  (p.  593).  If  a 
portion  of  the  thyroid  be  left,  or  a  graft  be  made  of  some  thyroid 


METABOLISM,    NUTRITION     IND  DIETETICS 


tissue  from  an  animal  oi  the  same  species,  these  effects  are  en 

tirelv  obviated  so  Ion-  .1^  the  grafl  survives.  It  has  not  been 
established  th.it  a  hetero  thyroid  grafl  i.e.,  a  grafl  o\  thyroid 
tissue  from  an  animal  ot  .1  different  kind  even  temporarily 
succeeds.  The  alien  thyroid  cells  are  destroyed  by  cytolysins 
(p.  29)  in  the  serum  and  tissue  liquids  of  the  animal.  When  a  small 
pari  of  a  thyroid  is  left,  it  max-  undergo  1^1  ci  1  hypertrophy,  and 
the  same  is  true  of  the  aeeessoi'v  thyroids.  'Hie  administration 
of  extracts  of  thi"  thyroid  glands  or  the  glands  themselves  l>v 
the  month  brings  about  a.  cure,  permanent  so  long  as  the  thyroid 
treatment  is  continued,  in  cases  of  myxedema  in  man,  and 
prevents  the  development 
of  the  symptoms  in  ani- 
mals or  removes  them 
when  they  have  appeared. 
The  same  is  true  of 
a  compound  rich  in 
iodine,  the  so-called  thy- 
roiodin,  which  has  been 
extracted  from  the  organ. 
Under  this  treatment  the 
total  metabolism,  which  in 
myxcedema  is  below  the 
normal,  is  markedly  in- 
creased. This  is  partly 
due  to  an  increase  in  the 
metabolism  of  protein. 
An  increase  in  the  de- 
struction of  protein  is  also 
caused  in  normal  persons. 
For  this  reason  the  use  of 
thyroid  preparations  to 
reduce  weight  in  cases  of 
obesity,  without  evidence 
of  thyroid  insufficiency,  is  a  dangerous  remedy.  For  while 
a  fat  man  can  very  well  spare  a  great  deal  of  his  fat, 
he  cannot  spare  much  of  his  tissue-protein.  The  question 
whether  the  thyroid  or  parathyroid  is,  in  addition,  concerned 
in  the  carbo-hydrate  metabolism  is  at  present  the  subject  of 
lively  discussion,  but  the  data  are  so  contradictory  that  it 
would  not  be  advisable  to  enter  into  the  matter  here. 

The  relations  of  iodine  to  the  gland  itself,  and  the  modifications 
in  its  structure  and  function  determined  by  the  giving  or  with- 
holding of  iodine,  recently  studied  by  Marine,  are  of  great 
interest.  In  all  animals,  so  far  as  examined,  the  normal  thyroid 
contains  iodine.     The  amount  is  variable,   but   the  minimum 

36 


Fig.  188. — Microphotograph  of  Active 
Thyroid  Hyperplasia  from  a  Case  of 
Exophthalmic  Goitre   (Marine). 

The  characteristic  changes  in  the  hyper- 
plastic gland — the  infoldings  and  plications  of 
the  alveolar  epithelium,  the  great  reduction  in 
the  colloid,  and  the  increase  in  the  stroma — 
are  shown. 


;'>j 


A    MANUAL  OF  PHYSIOLOGY 


percentage  of  iodine  necessary,  if  the  norma]  histological  struc- 
ture is  to  be  maintained,  is  quite  constanl   for  a  given  species. 

So  also  the  tiighesl  per- 
i  entage  ol  iodine  asso- 
ciated wit  h  anv  decree  o\ 
active  hyperplasia  (de- 
veloping goitre)  is  always 
below  the  normal  mini- 
mum, as  shown  by  Marine 
in  the  dog,  sheep,  man, 
and  ot  her  mammals.  As 
act  ive  hyperplasia  ot  the 
thyroid  (goitre)  (Fig.  i 
develops,  the  iodine  con- 
tent of  the  gland,  both 
relative  and  absolute,  de- 
creases, until  in  extreme 
degrees  ot  the  condition 
there  may  be  no  demon- 
strable iodine  presenl  at 
all.  since  the  iodine  is 
contained  in  the  colloid 
as  an  iodine-protein  com- 
pound, the  generalization 
may  be  made  that  in  the  thyroid  the  iodine  varies  directly 
with  the  amount  of  colloid,  and  inversely   with   the  degree  of 

hyperplasia.  The  ad- 
ministration of  any  iodine- 
containing  substance  to 
animals  with  actively  hy- 
I  >ei]  >last  ie  t  hyroids  (goitres) 
quickly  (in  two  to  three 
weeks  in  dogs)  induces  a 
histological  change,  the 
end  stage  of  which  is  the 
so-cal  le<  1  ci  »1  loid  goi  t  re  ( Fig. 
is .|i.  This  is  a  reversion 
to  the  normal  histological 
structure  (Fig.  190),  so  far 
as  this  is  possible  in  a  gland 
which  has  once  undergone 
hyperplasia.  The  physio- 
logical influence  of  iodine 
on  the  thyroid  may  be 
summed  up  as  follows  :  Iodine  is  absolutely  essential  for  the 
normal  activity  of  the  gland.     It  prevents  spontaneous  hyper- 


flg.    189. —  mlcrophotograph  01   v  colloid 
Gland  (Goitre)  (Marine). 

The  effect   of   administration  oi  iodine   is 
shown    in    the   return    towards    the    normal 

structure  from  .1  preceding  active  hyperplasia, 
such  as  is  shown  in  Fig.  188. 


I'h,.   190.     M11  rophoi oor  \i'H  of  Norm  w 
Human  Thyroid  (Marine). 


METABOLISM,    NUTRITION  AND  DIETETICS  563 

plasia  (goitre),  and  also   the  compensatory  hyperplasia   which 
follows  partial  removal  of  the  thyroid.     It  exercises  a  curative 
effecl   on  active    hyperplasias.     The   physiological    and    th< 
peutical'activitv  of  1 1 1  \-i-« »i<  1  substance  varies  directly  with  the 
amount  rof  iodine  in  it  in  organic  combination  (thyroiodin). 

As  in  the  case  of  other  glands  forming  an  internal  secretion, 
it  has  been  debated  whether  the  function  of  the  thyroid  is  to 
destroy  toxic  bodies  or  to  form  substances  indispensable  or 
advantageous  to  the  organism.  While  the  precise  role  played 
by  the  organ  in  the  economy  remains  obscure,  it  is  evident  that 
in  most  animals  and  in  man  its  secretion  is  of  great  importance, 
whether  it  be  solely  the  quasi-external  secretion  of  '  colloid,' 
containing  the  thyroiodin,  that  collects  in  its  alveoli  and  slowly 
passes  out  of  them  by  the  lymphatics,  or  perhaps,  in  addition, 
some  other  substance,  which,  like  the  glycogen  of  the  liver, 
never  finds  its  way  into  the  lumen  of  the  gland-tubes  at  all. 
It  may  also  be  admitted  that,  by  aiding  in  the  maintenance  of 
the  normal  level  of  general  nutrition,  particularly  that  of  the 
central  nervous  system,  the  ability  of  the  organism  to  cope  with 
toxic  substances  introduced  from  the  outside  or  manufactured 
in  the  body  is  favoured.  There  is,  however,  no  evidence  that 
an  actual  destruction  or  neutralization  of  toxic  substances 
occurs  in  the  gland  itself. 

Although  no  clear  proof  has  yet  been  given  that  the  secretion 
of  the  thyroid  is  influenced  by  nerves,  it  is  probable  that  this  is 
the  case.  Section  of  the  superior  and  inferior  thyroid  nerves 
going  to  the  gland  is  followed  by  degenerative  changes  in  it. 

Suprarenal  Capsules. — It  had  been  observed  by  Addison  that 
the  malady  which  now  bears  his  name,  and  in  which  certain 
vascular  changes,  with  muscular  weakness,  anaemia,  and  pig- 
mentation or  '  bronzing  '  of  the  skin,  are  prominent  symptoms, 
was  associated  with  disease,  usually  tuberculous,  of  the  supra- 
renal or  adrenal  bodies.  This  clinical  result  was  soon  supple- 
mented by  the  discovery  that  extirpation  of  the  adrenals  in 
animals  is  incompatible  with  life  (Brown-Sequard).  Our  know- 
ledge of  the  functions  of  these  hitherto  enigmatic  organs  was 
greatly  extended  by  the  experiments  of  Oliver  and  Schafer,  who 
investigated  the  action  of  extracts  of  the  suprarenals  (of  calf, 
sheep,  dog,  guinea-pig,  and  man),  when  injected  into  the  veins 
of  animals.  The  arteries  are  greatly  contracted,  and  this  mainly 
through  direct  action  on  the  vaso-motor  nerve-endings  or  some 
structure  intermediate  between  them  and  the  smooth  muscle  of 
the  vessels,  but  partly  through  the  vaso-motor  centre.  The 
blood-pressure  rises  rapidly,  although  the  heart  may  be  inhibited 
through  the  vagus  centre.  The  heart  is  at  the  same  time  directly 
stimulated,   so  that,   although  it   beats  slowly,  the  beats  are 

36—2 


564  »    MA  vr  //    OF  PHYSIOLOGY 

stronger  than  before.     When  the  vagi  are  cut  the  action  oi 
heart   is  markedly  augmented,  and   the  arterial   pressure  rises 
enormously  (it  may  be  to  four  or  five  times  it-  original  amount). 
Stimulation  oi  the  depressoi  is  oi  no  avail  in  combating  this  in- 
crease   of    blood-pressure.     The    generalization    may    be    made 
that   suprarenal  extract  or  adrenalin,   its  active  principle,    acts 
upon   all   plain   muscle  and  gland-cells  that  are  supplied  with 
sympathetic  nerve-fibres,  and  the  result  of  the  action,  whether 
augmentation  or  inhibition,  is  the  same  as  would  be  produced  by 
stimulation  of  the  sympathetic  fibres  going  to  the  muscle  or 
gland  in  question.     Yet  it  is  not   through  excitation  of   tl 
fibres  that  the  adrenalin  acts,  for  its  effect  is  even  more  pro- 
nounced when  the  nerve-fibres  have  been  caused  to  degenerate, 
in  the  case  of  the  pupillo-dilator  fibres,  e.g.,  by  excision  of  the 
superior  cervical  ganglion.     Xor  is  the  effect  a  direct  one  on  the 
muscular  fibres.     For  smooth  muscle  which  is  not,  and  never  has 
been,   in  functional  union  with  sympathetic  nerve-fibres  is  in- 
different to  adrenalin  (Elliott).     It  seems,  then,  to  act  on  some 
structure  intermediate  between  the  nerve  and  the  muscle,  but 
so  related  to  the  latter  that  it  continues  to  live  so  long  as  it  is 
in    connection    with    the    muscle    fibre.     Instead    of    a    definite 
histological  structure,  the  seat  of  the  action  may  be  a  special 
'  receptive  '  substance  at  the  myoneural  junction.     Thus  adrenalin 
causes  marked  diminution  of  tone  in  the  small  intestine,  with 
disappearance  of  the  peristalsis  and  pendulum  movements.     The 
same  effect  is  produced  on  an  isolated  loop  of  intestine  immersed 
in   Locke's    solution,  and   the   action    is   therefore  local.     The 
drug  is  effective  even  in  a  dilution  of  1  :  1,000,000.     A  similar 
action  has  been  observed  on  the  stomach.     The  vessels  of  the 
conjunctiva  are  constricted  by  local  action  when  an  extract  of 
the  capsules  is  dropped  into  the  eye,  a  fact  which  has  proved  of 
value    in    ophthalmological    practice.     Inhibition    of    the    con- 
traction of  the  stomach,   intestine,   urinary   bladder,  and   gall- 
bladder ;  contraction  of  the  uterus,   vas  deferens,  and  seminal 
vesicles  ;  dilatation  of  the  pupil  and  retraction  of  the  nictitating 
membrane  ;  stimulation  of  the  salivary  and  lachrymal    secre- 
tions,   are    among   its   actions    (Langley).     The   curve   of   con- 
traction  of  the  skeletal  muscles  is  lengthened  as  in   veratrine 
poisoning    (p.    654),    though    to    a    less    extent.     Adrenalin    or 
suprarenin    (C9H13X03)    is    solely  contained    in    the   medulla   of 
the  gland,   and  such   is   its   extraordinary  power,   that   a  dose 
of  one  -  millionth   of   a  gramme    per    kilo   of    body  -  weight    is 
sufficient  to  cause  a  distinct  effect  upon  the  heart   and  blood- 
Is    (a   rise    of    pressure   of    14    millimetres    Hg).     Another 
delicate,   and   for  certain    purposes   a   convenient,   reaction   for 
the  detection  and  the  physiological  assay  of  adrenalin  is  the 


Mil  \BOl  tSM,    \  UTR1  HON    IND  nil  1 1  in 

dilatation  oi  the  pupil  in  the  excised  eyeball  oi  the  frog,  first 
introduced  by  Meltzer,  and  afterwards  developed  1>\  Em 
mann.  The  increase  in  the  tone  and  the  acceleration  and 
strengthening  oi  the  rhythmical  contractions  of  an  isolated  ring 
ol  rabbil  's  uterus  have  also  been  employed  as  a  clinical  test  even 
for  such  minute  amounts  of  adrenalin  as  can  exist  in  the  circu- 
lating blood  (Practical  Exercises,  Chap.  XIV.).  The  alkaloid  is 
used  in  medicine  in  the  form  of  a  dilute  solution  of  adrenalin 
chloride,  as  a  styptic,  and  for  reducing  congestion  in  accessible 
parts.  The  intense  local  anaemia  which  it  causes  when  given 
subcutaneously  or  by  the  mouth  is  one  reason,  perhaps  the  most 
important,  for  the  slow  absorption  on  which  depends  the  absence 
of  its  general  effects,  including  that  on  the  blood-pressure,  when 
it  is  administered  in  this  way.  The  function  of  the  capsules,  or 
rather  of  the  so-called  '  chromaffin  '  cells,  which  constitute  the 
medulla  and  stain  brown  with  chromic  acid  or  chromates,  is  to 
secrete  this  substance,  which  is  probably  of  great  physiological 
importance  for  maintaining  the  tonicity  of  the  muscular  tissues 
in  general,  and  especially  of  the  heart  and  arteries.  Adrenalin 
was  entirely  absent  from  the  suprarenals  of  a  person  who 
had  died  of  Addison's  disease.  There  is  some  evidence  that 
the  active  substance  is  really  given  off  to  the  blood,  and  that 
normal  plasma  contains  adrenalin  in  sufficient  amount  to  be 
detected  by  that  effect  on  the  uterus  which  has  just  been  men- 
tioned. But  statements  which  connect  the  increased  blood- 
pressure  in  such  conditions  as  chronic  nephritis  with  hypertrophy 
of  the  chromaffin  tissue,  an  increased  adrenalin  production,  and 
an  increased  adrenalin  content  of  the  blood,  must  be  received 
with  caution.  In  a  series  of  cases  with  high  blood-pressure 
Fraenkel  found  no  distinct  difference  in  this  regard  between 
the  pathological  and  normal  sera.  The  so-called  experimental 
arterio-sclerosis  produced  by  repeated  injections  of  adrenalin 
into  the  blood  of  rabbits  throws  little  light  upon  the  question, 
for  the  vascular  changes,  in  so  far  as  they  have  not  been  con- 
founded with  similar  lesions  occurring  spontaneously  in  a  con- 
siderable proportion  of  rabbits,  differ  from  those  observed  in 
pathological  arterio-sclerosis  (M.  C.  Hill).  An  artificial  adrenalin 
or  suprarenin  has  been  synthetically  prepared.  Chemically  it  is 
identical  with  the  natural  adrenalin  obtained  from  the  suprarenal 
glands,  but  while  the  natural  adrenalin  rotates  the  plane  of 
polarization  to  the  left,  the  artificial  substance  is  optically  in- 
active. This  is  because  it  consists  of  equal  parts  of  laevo- 
rotatory  and  dextro-rotatory  adrenalin.  The  artificial  adrenalin 
has  approximately  half  the  effect  of  the  natural  on  the  blood- 
pressure,  from  which  it  may  be  inferred  that  the  dextro-rotatory 
isomer  has  only  a  very  slight   pressor  effect.     Quite  recently 


566  A  MANUAL  OF  PHYSIOLOGY 

the  Lefl  and  right  rotatory  moieties  have  beer  separated.     The 
former  has  exactly  the  same  power  of  raising  the  blood-pressure 

as  the  natural  adrenalin,  the  latter  only  ,'._.  to  ,',  as  much. 
Practically  the  same  proportion  holds  when  the  power  oi  the 
two  isomers  in  producing  glycosuria  is  compared.  This  con- 
stitutes important  corroboration  of  the  view  already  referred 
to  (p.  522)  that  adrenalin  glycosuria  is  caused  by  an  action  on 
the  sympathetic  system.  For  the  effect  on  the  blood-pn  ssure 
is  known  to  be  thus  produced  (Cushny).  The  function  oi  the 
cortex  is  unknown.  It  is  stated  that  it  contains  cholin,  a  sub- 
stance which  lowers  the  blood-pressure,  instead  of  raising  LI 
adrenalin  does.  It  has  been  suggested  that  the  adrenal  glands 
have  thus  a  double  chemical  grip  upon  the  circulation,  and  can 
influence  it  in  either  direction,  just  as  the  bulb  can  influence  it 
through  its  double  nervous  grip.  But  it  is  possible  that  the 
depressor  substance  of  the  cortex  may  be  only  a  toxic  hody 
neutralized  or  destroyed  in  the  glands.  In  any  case  the  func- 
tional difference  between  cortex  and  medulla  is  easily  under- 
stood when  we  reflect  that  the  morphological  history  of  the  two 
tissues  is  quite  different.  The  medulla  is  developed  from  cells 
which  push  their  way  into  the  gland  from  the  rudiments  of  the 
sympathetic  ganglia  at  that  level,  and  is  therefore  of  ectoderm i« 
origin.  The  cortex  is  derived  from  the  same  mesodermic 
structure  which  gives  rise  to  the  kidneys  and  genital  organs. 

The  existence  of  secretory  fibres  for  the  adrenal  glands 
in  the  splanchnic  nerves  has  been  rendered  probable  by  the 
experiments  of  Dreyer,  who  finds  that  the  amount  of  active 
substance  in  the  blood  of  the  suprarenal  vein,  as  tested  by  its 
physiological  effect  when  injected  into  an  animal,  is  increased 
by  stimulation  of  those  nerves. 

Pituitary  Body.  In  the  pituitary  body  three  parts  may  be 
distinguished  :  (1)  The  anterior  lobe  proper,  or  pars  anterior, 
consisting  of  epithelial  cells,  many  of  which  are  filled  with 
granules  of  the  type  seen  in  glandular  epithelium,  and  abun- 
dantly provided  with  bloodvessels  ;  (2)  the  pars  intermedia, 
consisting  of  epithelial  cells,  less  granular  and  less  richly  supplied 
with  bloodvessels  than  those  of  the  pars  anterior;  (3)  the  pos- 
terior lobe  proper,  or  pars  nervosa,  consisting  chiefly  of  neuroglia 
close! v  invested  by  epithelial  cells  of  the  pars  intermedia,  and 
invaded  by  the  colloid  secreted  by  these  cells.  These  differences 
in  the  structure  of  the  anterior  and  posterior  lobes  of  the  pituitary 
body  correspond  to  a  difference  in  their  dew  lopment,  the  anterior 
lobe,  with  the  pars  intermedia,  being  derived  from  an  inpushing 
of  the  ectoderm  of  the  buccal  cavity,  and  the  posterior  lobe  from 
an  extension  of  the  neural  ectoderm,  which  grows  backwards  as 
the  infundibular  process  till  it  meets  and  blends  with  that  por- 
tion of  the  buccal  invagination   which  gives  rise  to  the  pars 


METABOLISM,   NUTRITION     IND  DIETETIi  567 

intermedia.  When  the  pituitary  body  is  complete^  removed, 
death  speedily  and  invariably  ensues,  in  dogs,  011  the  average 
within  twenty-four  to  forty-eight  hours.  The  much  longer 
periods  oi  surviva]  occasionally  witnessed  are  due  to  failure  to 
remove  some  small  portion  of  the  hypophyseal  epithelium.  On 
the  day  after  the  operation  the  animals  may  be  able  to  walk 
about,  to  eat  and  drink,  and  may  show  an  interest  in  their  sur- 
roundings. The  temperature,  pulse,  and  respiration  at  this  time 
may  be  normal.  Soon,  however,  they  become  lethargic,  then 
comatose,  with  characteristically  incurved  spine,  slow  respira- 
tion, with  long-drawn  inspiration,  a  feeble  pulse,  perfectly  limp 
muscles,  and  often  a  subnormal  temperature.  This  deep  coma 
passes  into  death,  with  no  perceptible  transition,  and  without  a 
struggle   (Paulesco,    Cushing).     The   ablation   of  a  part   of  the 


.       w,wW 


Fig.    191. — Action  of  Extract  of  Hypophyseal  Lobe  of  Pituitary  on  the 
Blood-pressure  (W.  W.  Hamburger). 

The  signal  line  at  the  top  shows  the  time  and  length  of  injection  of  the  saline 
extract  into  the  blood.  Time  trace  (at  bottom)  shows  second  intervals.  The 
figure  is  to  be  read  from  left  to  right. 

cortical  substance  of  the  anterior  (epithelial)  lobe  of  the  hypo- 
physis is  compatible  with  permanent  survival,  and  gives  rise 
to  no  symptom  of  disorder.  The  same  is  true  when  only  the 
posterior  lobe  is  removed.  On  the  other  hand,  complete  removal 
of  the  anterior  lobe  causes  death,  just  as  if  the  whole  gland  had 
been  taken  away.  Of  all  the  structures  included  in  the  pituitary 
body,  the  most  important  from  the  functional  point  of  view 
appears  to  be  the  superficial  layer  of  the  anterior  lobe.  It  has 
been  asserted  that  the  pituitary  undergoes  (compensatory  ?) 
hypertrophy  after  thyroidectomy.  Some  observers  have  accord- 
ingly assumed  a  similarity  of  function  for  these  organs.  It 
has  even  been  stated  that  the  production  of  colloid  material  by 
the  cells  of  the  pars  intermedia  (lying  between  the  anterior  lobe 
and  the  nervous  tissue  of  the  posterior  lobe,  and  investing  the 
latter)  is  increased,  and  that  colloid  accumulates  in  the  nervous 


A   MANUAL  OF  PHYSIOLOGY 

portion  of  the  posterior  lobe.  But  this  colloid,  whatever  its 
function  may  be,  is  very  different  from  th.it  oi  the  thyroid 
alveoli,  for  the  (sheep's)  pituitary  contains  no  iodine  after  ex- 
tirpation of  the  thyroid  any  more  than  before  (Simpson  and 
Hunter).  And  in  man  pathological  changes  (tumours)  in  the 
pituitary  body  are  associated,  not  with  myxcedema,  or  othei 
disease  connected  with  changes  in  the  thyroid,  but  with  another 
condition,  called  acromegaly,  in  which  the  hones  oi  the  limbs  and 
face,  especially  the  hands  and  feet  and  the  lower  jaw,  become 
hypertrophied. 

Another  condition  often  associated  with  tumours  of  the 
pituitary  is  gigantism — a  condition  occurring  before  the  normal 
growth  of  the  hones  is  completed,  and  resulting  in  a  great  in- 
crease in  the  length  of  the  bones  both  in  the  limbs  and  the  trunk. 

The  effects  on  the  vascular  system  of  intravenous  injection 
of  extracts  of  the  pituitary  gland  are  also  very  different  from 
those  caused  by  thyroid  extracts.  The  posterior  lobe,  or  in- 
fundibular body,  including  the  pars  intermedia,  contains  two 
active  substances,  one  pressor  and  the  other  depressor.  The 
former  is  soluble  in  salt  solution,  but  insoluble  in  absolute 
alcohol  and  ether  ;  while  the  latter  is  soluble  in  salt  solution  as 
well  as  in  alcohol  and  ether.  The  pressor  substance  causes  a 
great  rise  of  blood-pressure,  due  partly  to  constriction  of  the 
arterioles  and  partly  to  an  increase  in  the  force  ol  the  heart- 
beat, both  of  which  are  brought  about  by  direct  action.  Tin- 
rise  of  pressure  lasts  for  a  considerable  time,  and  is  sometimes 
accompanied  by  a  slowing  of  the  heart.  A  second  dose  injected 
before  the  effect  of  the  first  has  passed  off  is  inactive  ;  and  this 
distinguishes  the  pituitary  from  the  suprarenal  extract.  As- 
sociated with  the  pressor  effect  is  an  increase  in  the  flow  of  the 
urine.  Whether  this  is  due  to  a  separate  diuretic  substance, 
as  some  maintain,  has  not  been  definitely  settled.  The  pressor 
substance,  unlike  adrenalin,  directly  stimulates  smooth  muscle 
fibres  (especially  the  arteries,  uterus,  and  spleen)  irrespective 
of  their  innervation  (Dale).  The  depressor  substance  produces 
a  marked  fall  of  blood-pressure,  even  when  it  is  injected  during 
the  rise  of  pressure  caused  by  an  injection  of  the  pressor  sub- 
stance. The  anterior  lobe,  or  hypophysis,  also  contains  a  de- 
pressor substance.  Intravenous  injection  of  a  saline  extracl 
causes  a  distinct  fall  of  blood-pressure,  accompanied  usually  by 
acceleration  and  weakening  of  the  heart  (Fig.  191).  A  second 
injection  immediately  following  the  fust  produces  no  change  in  the 
pressure.  Bui  extracts  of  many  organs,  including  the  nervous 
tissues,  produce  a  similar  tall  of  pressure,  and  there  is  no  evidence 
that  the  depressor  substance  oi  the  anterior  lobe  is  specific  to 
the  pituitary  (W.  YV.  Hamburger). 


\n  r  IBOLIS  \i     \  r  /'/,'/  n<>\     I  \!>  DIET1  i  h 

It  is  not  at  present  possible  to  deduce  from  such  clinical  and 
experimental  observations  .is  those  described  any  coherenl 
theory  of  the  function  of  the  pituitary.  That  there  is  some  con- 
nection between  the  normal  action  oi  the  gland,  and  in  particular 
oi  its  anterior  lobe,  and  the  normal  growth  and  nutrition  of  the 
skeleton  is  scarcely  to  he  doubted.  The  fact  that  administration 
of  the  dried  gland  substance  to  dogs  causes  an  increased  excretion 
oi  calcium  on  a  diet  rich  in  calcium  is  a  further  indication  of  its 
influence  on  the  metabolism  of  bone  (Malcolm).  But  so  far  is 
the  precise  nature  of  this  influence,  if  it  exists,  from  being  fully 
understood,  that  authorities  of  repute  arc  still  divided  on  the 
question  whether  the  symptoms  of  acromegaly  and  gigantism 
are  due  to  atrophy  or  to  hypertrophy  of  the  active  elements  of 
tin1  gland,  to  loss  of  its  internal  secretion,  or  to  its  manufacture  in 
excessive  amount.  There  is  evidence  that  the  colloid  secretion 
of  the  posterior  lobe,  probably  formed  by  the  epithelial  cells  of 
the  pars  intermedia,  passes  through  the  nervous  portion  to 
enter  the  infundibulum  and  the  third  ventricle  of  the  brain, 
where  it  breaks  down  in  the  cerebro-spinal  fluid  (Herring).  And 
it  has  been  suggested  that  in  virtue  of  the  action  of  the  hormones 
(p.  375)  in  this  secretion  on  the  vascular  system  in  general,  and  on 
the  renal  cells  and  the  renal  circulation  in  particular,  the  posterior 
lobe  constitutes  a  mechanism  for  the  control  of  the  secretion  of 
urine.     But  this  suggestion  is  still  in  the  realm  of  hypothesis. 

Extracts  of  nervous  tissue  (sciatic  nerve,  white  matter  of  brain,  and 
spinal  cord,  but  especially  grey  matter  of  brain)  cause,  on  injection 
into  the  veins,  a  decided  fall  of  arterial  blood-pressure,  which  soon 
passes  off,  and  can  be  renewed  by  a  fresh  injection.  The  fall  of 
pressure  is  due  to  direct  action  upon  the  bloodvessels  of  a  depressor 
substance  in  the  extracts,  and  not  to  the  action  of  vaso-motor  nerves. 
It  can  be  obtained  after  section  of  the  vagi. 

Extracts  of  muscular  tissue  also  cause  a  distinct  though  transient 
fall  of  pressure,  but  not  so  great  a  fall  as  in  the  case  of  extracts  of 
nervous  tissue.  Saline  decoctions  of  other  tissues  (testis,  kidney, 
spleen,  pancreas,  liver,  mucous  membrane  of  stomach  and  intestine, 
lung,  and  mammary  gland)  all  produce  a  fall  of  blood-pressure 
(Osborne  and  Vincent).  The  same  is  true  of  bone-marrow  (Brown 
and  Guthrie  ;  Figs.  192,  193).  It  must  be  repeated  that  there  is 
no  evidence  that  these  depressor  substances  are  specific  internal 
secretions  in  the  same  sense  as  adrenalin. 

Kidney. — The  experiments  of  Bradford,  which  seemed  to  indicate 
that  the  kidney,  in  addition  to  its  function  as  an  excretory  organ. 
plays  an  important,  and  indeed  indispensable,  part  in  protein 
RKlabolism,  possibly  by  forming  something  of  the  nature  of  an 
internal  secretion,  have  not  been  confirmed.  He  stated  that  when 
the  half  or  two-thirds  of  one  kidney  and  the  whole  of  the  other  have 
been  removed  from  a  dog  by  successive  operations,  death  ensues, 
although  the  quantity  both  of  water  and  urea  excreted  by  the  frag- 
ment of  renal  substance  that  remains  is  far  above  the  normal.  In 
spite  of  the  increased  elimination  of  urea,  that  substance  was  said 


57° 


/    \l  l  Mil    OF  PHYSIOLOGY 


i  u in  11 1. it <  in  the  tissues,  showing  th.it  the  destruction  oi  prot<  in 
was  incri  conclusion   which  seemed  t<>  derive  supporl   from 

the  wasting  oi  the  animal.  It  lias  since  been  shown  that  an  in- 
creased  output  oi  aitrogen  is  uo1  oi  constant  occurrence,  and  only 
takes  place   under  the  same  conditions  .is  in   starvation   (p.   331). 


wmmmiis&^KWn 


WKMMmmmi.. 


Fig.  192. — Effect  of  Bone-marrow  on  Blood-pressure.     Intravenous 
Injection  of  Saline  Extract.     Vagi  Intact. 

The  uppermost  line  is  a  signal  trace  showing  the  time  and  length  of  injection. 
Below  this  i>  the  record  oi  tin-  respiratory  movements,  and  lowest  the  blood- 
;  ><  ssure  trai  ing.     To  be  read  from  left  to  right. 

As  a  matter  of  fact,  the  animals  waste  and  die  within  a  few  day 
weeks   largely  because  they  refuse   to  eat.     Polyuria    (increas 
urine  beyond  the  normal)   does  not  necessarily  occur.     It  is  well 
known  that  when  only  one  kidney  is  extirpated  the  other  hyper- 
trophies, and  no  ill-effects  ensue. 

The  statement  that  extracts  of  the  kidney  when  injected  into  the 

veins  of  an  animal  cause  a  rise 
^  '  of  arterial   blood-pressure,   es- 

sentially through  direct  action 
on  the    peripheral    vaso-motor 
mechanism,  is  of  consider 
jjfc  interest,    for    it    may    possibly 

Wljlf^P   1^  have  some  bearing  on  the  rise 

W  utff/f/tiHlL  pressure     and     consequent 

Ifc  jj|^rTPT     hypertrophy  of  the  heart  asso- 

\  Jf  ciated    with    certain   renal  dis- 

^4u        j^r  s-     |lu1  there  is  not  as  yel 

^tmfl0r  sufficient     evidence     that     the 

hypothetical  pressor  substano  . 
to  which  the  name  '  renin  '  has 
been  given,  in  any  sense  te- 
ats .m  internal  secretion 
of  the  kidney.  The  pn 
substance  (so-called  "  urohypertensine  ")  which  1  an  be  extracted  by 

r  from  normal  human  urine  (Abelous)  is  probably  only 
by  the  kidney,  and  perhaps  arises  from  the  putrefaction  of  proteins 
in  the-  intestine.    For  it  has  been  shown  that   in  the  putrefaction 
of  (horse-)  meat  bases  are  formed  which,  when  injected  intravenously, 
cause  a  rise  of  blood-pressure.     The  most  active  of  these  is  a  body 


Fig.    193. — Injection    01     Extract   of 
bonl  -marrow  w]  1  ii    i  iii    v*agi   i  i  i 

1  o  be  read  from  left  to  right. 


METABOLISM,    VUTRITION    IND  DIETETICS  571 

known  .is  p-hydroxyphenj  lethylamine,  Eormed  from  tyrosin  (B  1 
and  Walpi  »le) 

I'll.-  spleen  does  no1  produce  an  Internal  secretion  necessary  to 
life,  for  it  can  be  removed  both  in  animals  and  in  man,  not  only 
without  causing  death,  bu1  often  without  the  development  of  any 
serious  symptoms.  Its  blood  forming  and  blood  -  destroying 
functions  (p.  21)  are  taken  on  by  other  structures  (particularly  th< 
r<-d  bone  marrow),  but  the  formation  of  the  bile-pigment  is  inter- 
fered with,  and  its  amounl  reduced  by  more  than  50  per  cent. 
(Pugliese).  The  production  of  trypsinogen  by  the  pancreas  is  al  0 
said  to  be  diminished,  whereas  it  an  extract  of  spleen  be  injected 
into  the  circulation  of  an  animal  deprived  of  its  spleen,  the  amount  of 
trypsinogen  is  increased.  It  has,  therefore,  been  supposed  that  the 
spleen  forms  a  substance  (protrypsinogen)  which,  passing  into  the 
blood,  is  taken  up  by  the  pancreas  and  elaborated  into  trypsinogen 
(p.  382). 

The  salivary  glands  may  be  extirpated  without  any  sensible 
change  being  produced  in  the  normal  metabolism.  There  is  evidence, 
however,  that  the  secretion  cf  the  gastric  juice  is  diminished.  It 
has  been  supposed  that  this  may  be  due  to  the  absence  of  a  hormone 
(p.  375)  normally  produced  in"  the  salivary  glands.  A  temporary 
increase  in  the  gastric  secretion  is  caused  when  extracts  of  the 
glands  cf  normal  dogs  are  injected  into  the  veins  or  into  the 
peritoneal  cavity  of  dogs  deprived  of  their  salivary  glands 
(Hemmeter). 

Extracts  of  the  pineal  gland  injected  into  the  circulation  have 
no  effect  other  than  that  due  to  the  inorganic  constituents  of  the 
'  brain  sand.' 


CHAPTER    VIII 

ANIMAL  HEAT 

From  the  earliest  ages  it  must  have  been  noticed  that  th<'  bodies 
of  many  animals,  and  particularly  of  men,  arc  warmer  than 
the  air  and  than  most  objects  around  them.  The  '  vulgar 
opinion  '  of  Bacon's  time,  '  that  fishes  are  the  least  warm  intern- 
ally, and  birds  the  most,'  if  it  does  not  imply  a  very  extensive 
knowledge  of  animal  temperature,  at  least  shows  that  the 
fundamental  distinction  of  warm  and  cold-blooded  animals, 
which  is  to-day  more  accurately  expressed  as  the  distinction 
between  animals  of  constant  temperature  (homoiothermal)  and 
animals  of  variable  temperature  (poikilothermal),  had  been 
grasped,  and  was  even  popularly  known.  Since  that  time  the 
accumulation  of  accurate  numerical  results,  and  the  advance 
mI  physical  and  physiological  doctrine,  have  given  us  definite 
ideas  as  to  the  relation  of  animal  heat  to  the  metabolic  pro- 
cesses of  the  body.  It  is  impossible  to  understand  the  present 
I  .option  of  the  subject  without  an  elementary  knowledge  of  the 
science  of  heat.  For  this  the  student  is  referred  to  a  text-book 
of  physics.  All  that  can  be  done  here  is  to  preface  the  physio- 
logical portion  of  the  subject  by  a  few  remarks  on  the  physical 
methods  and  instruments  employed  : 

Temperature. -Two  bodies  arc  at  the  same  temperature  if,  when 
placed  in  contact,  no  exchange  of  heat  takes  place  between  them. 
They  are  at  different  temperatures  if,  on  the  whole,  heat  passes  from 
one  to  the  other,  and  that  body  from  which  the  heal  passes  is  .it  the 
higher  temperature.  It  is  known  by  experiment  that  if  two  bodies 
of  different  temperature  are  placed  in  contact,  heat  will  pass  from 
one  to  the  other  till  they  come  to  have  the  same  temperature.  I*. 
then,  we  have  the  means  of  finding  out  the  temperature  of  any  on< 
body,  we  can  arrive  at  the  temperature  of  any  other  by  placing  the 
two  in  «  ontai  t  for  a  sufficiently  long  time,  under  the  proviso  th  ;  the 
quantity  of  h<  iry  to  bring  tin-  temperature  of  the  first  body, 

which  mav  be  called  the  '  measuring  '  body,  to  equality  with  th.  I 
the  second,  i^  so  small  as  not  to  make  a  sensible  difference  in  the 
...     This  is  tin-  principle  on  which  thermometric  measurements 
ml.     A  men  urial  thermometer  consists  of  a  quantity  of  mercury 

572 


ANIM  \L  HEAT 


573 


ordinarily  contained  in  a  thin  glass  bulb,  the  cavity  of  which  is  con- 
tinued into  a  tube  of  very  fine  bore  in  the  stem.  Like  most  other 
substances,  mercury  expands  when  the  temperature  rises,  and  con- 
tracts when  it  sinks,  and  the  amounl  of  expansion  or  contraction  is 

shown  by  the  rise  or  fall  of  t lie  mercurial  column  in  the  stem  ot  the 
thermometer.     The  point  at  which  the  meniscus  stands  when 

bulb  is  immersed  in  melting  ice  or  ice-cold  water  is,  on  the  centi- 
grade scale,  taken  as  zero;  the  point  at  which  it  stands  when  the 
thermometer  is  surrounded  by  the  steam  rising  from  a  vessel  oi 
boiling  water  is  taken  as  [oo  degrees.  The  intermediate  portion  of 
the  stem  is  divided  into  degrees  and  fractions  of  degrees.  When, 
now.  we  measure  the  temperature  of  any  part  of  an  animal  with  such 
a  thermometer,  we  place  the  bulb  in  contact  with  the  part  until  the 
mercury  has  ceased  to  rise  or  fall.  We  know  then  that  the  mercury 
has  ceased  to  expand  or  contract,  and  therefore  that  its  temperature 
is  stationary,  and  presumably  the  same  as  that  of  the  part.  It  is  to 
be  noted  that  we  have  earned  no  information  whatever  as  to  the 
amount  of  heat  in  the  body  of  the  animal.  We  h  ive  only  observed 
that  the  mercury  of  the  thermometer  when  its  temperature  is  the 
same  as  that  of  the  given  part  expands  to  an  extent  marked  by  the 
division  of  the  scale  at  which  the  column  is  stationary.  And  we  know 
that  if  the  mercury  rises  to  the  same  point  when  the  thermometer  is 
applied  to  another  part,  the  temperature  of  the  latter  is  the  same 
as  that  of  the  first  part  ;  if  the  mercury  rises  higher,  the  temperature 
is  greater  ;  if  not  so  high,  it  is  less.  The  thermometer,  then,  only 
informs  us  whether  heat  would  flow  from  or  into  the  part  with  which 
it  is  in  contact  if  the  part  were  placed  in  thermal  connection  with  any 
other  body  of  which  the  temperature  is  known.  In  other  words,  the 
temperature  is  a  measure  of  the  heat  '  tension,'  so  to  speak  :  and 
difference  of  temperature  between  two  bodies  is  analogous  to  differ- 
ence of  potential  between  the  poles  of  a  voltaic  cell  (p.  615),  or  to 
difference  of  level  between  the  surface  of  a  mill-pond  and  the  race 
below  the  wheel. 

The  temperature  of  an  animal  is  measured  in  one  of  the  natural 
cavities,  as  the  rectum,  vagina,  mouth,  or  external  ear,  or  in  the 
axilla,  or  at  any  part  of  the  skin.  For  the  cavities  a  mercury 
thermometer  is  nearly  always  used;  the  ordinary  little  maximum 
thermometer  is  most  convenient  for  clinical  purposes.  The  tem- 
perature of  the  skin  may  be  measured  by  an  ordinary  mercury  ther- 
mometer, the  outer  portion  of  the  bulb  of  which  is  covered  by  some 
badly  conducting  material.  An  uncovered  thermometer,  heated 
nearly  to  the  temperature  expected,  will  also  give  results  sufficiently 
accurate  for  most  purposes,  especially  if  the  bulb  is  flat  or  in  the  form 
of  a  flat  spiral,  which  can  be  easily  applied  to  the  surface.  A 
theoretically  better  method,  but  more  laborious  in  practice,  is  the 
use  of  a  thermo-electric  junction,  or  a  resistance  thermometer  formed 
of  a  grating  cut  out  of  thin  lead-paper  or  tinfoil  (Fig.  194).  This 
is  especially  useful  for  comparing  the  temperature  of  two  portions 
of  skin.  The  temperature  of  the  solid  tissues  and  liquids  of  the  bodv 
may  also  be  measured  or  compared  by  the  insertion  of  mercurial  or 
resistance  thermometers  or  thermo-electric  junctions  (p.  664). 

Calorimetry. — The  quantity  of  heat  given  off  by  an  animal  is 
generally  measured  by  the  rise  of  temperature  which  it  produces  in 
a  known  mass  of  some  standard  substance.  Sometimes,  however, 
as  in  the  ice-calorimeter  of  Lavoisier  and  Laplace  and  the  ether 
calorimeter  of  Rosenthal,  a  physical  change  of  state — in  the  one 


574 


A   MANUAL  ()!■    filYSIOLOGY 


case  liquefaction  of  ice,  in  the  other  evaporation  oi  ether— is  taken 
as  token  .iiul  incisure  oi  ileal  received  by  the  measuring  substance* 
the  number  oi  units  oi  heat  corresponding  to  liquefaction  of  unit 
mass  of  ice  or  evaporation  of  unit  mass  of  ether  being  known.  The 
unit  generally  adopted  in  the  measurement  of  heat  is  the  quantity 
required  to  raise  the  temperature  of  a  kilogramme  of  water  i°  C, 
which  is  called  a  calorie,  or  kilocalorie,  or  large  calorie.  The 
adth  pari  of  this,  the  quantity  needed  to  raise  the  temperature 
of  a  gramme  oi  water  by  i°,  is  termed  a  small  calorie  or  millicalorie. 

In  the  calorimeters  which  have  been  chiefly  used  in  physiology 
either  water  or  air  has  been  taken  as  the  measuring  substance.  The 
amplest  Eorm  of  water  calorimeter  is  a  box  with  double  walls,  tin- 
space  between  which  is  filled  with 
a  weighed  quantity  of  water.  The 
animal  is  placed  inside  the  vessel,  and 
the  temperature  of  the  water  noted  at 
the  beginning  and  end  of  the  experi- 
ment. Suppose  that  the  quantity  of 
water  is  10  kilos,  and  that  the  tem- 
perature rises  i°  in  thirty  minutes, 
then  the  amount  of  heat  lost  by  the 
animal  is  10  calories  in  the  half-hour, 
or  480  calories  in  the  twenty-four 
hours  ;  and  if  the  rectal  temperature  is 
unchanged  this  will  also  be  the  amount 
of  heat  produced. 

Here  we  assume  (1)  that  all  the  heat 
lost  by  the  animal  has  gone  to  heat  the 
water  and  none  to  heat  the  metal  of 
the  calorimeter  ;  (2)  that  none  has  been 
radiated  away  from  the  outer  surface 
of  the  latter.  The  first  assumption 
will  seldom  introduce  any  sensible  error 
in  a  prolonged  physiological  experi- 
ment ;  but  it  is  very  easy  to  determine 
by  a  separate  observation  the  water- 
equivalent  of  the  calorimeter — that  is, 
the  quantity  of  water  whose  tempera- 
ture will  be  raised  i°  by  a  quantity  of 
heat  which  just  suffices  to  raise  the 
temperature  of  the  metal  by  i° 
(p.  613).  Then  the  water-equivalent 
is  added  to  the  quantity  of  water 
actually  present,  and  the  sum  is  multiplied  by  the  rise  of  tempera- 
ture. If  the  temperature  of  the  room  is  constant,  as  will  be 
approximately  the  case  in  a  cellar,  any  error  due  to  interchange  of 
heat  between  the  calorimeter  and  its  surroundings  may  be  eliminated 
by  making  the  initial  temperature  of  the  water  as  much  less  than  that 
of  the  air  as  the  final  temperature  exceeds  it.  Then  if  the  loss  of 
heat  by  the  animal  is  uniform,  as  much  heat  is  gained  during  the  first 
half  of  the  experiment  by  the  calorimeter  from  the  air  as  is  lost  by 
it  to  the  air  during  the  last  half.  Or,  without  lowering  the  tem- 
perature of  the  water,  the  amount  of  heat  lost  by  the  calorimeter 
during  an  experiment  may  be  previously  determined  by  a  special 
observation,  and  added  to  the  quantity  calculated  from  the  observed 
rise  of  temperature.     Or,  finally,  two  similar  calorimeters  may  be 


Fig.  194.  —  Resistance  Ther- 
mometer for  Measuring 
Tkmperature  of  Skin. 

G,  grating  of  lead-paper,  at- 
tached to  a  cover-slip,  and 
mounted  on  a  holder  ;  W,  W, 
wires  to  the  Wheatstone's  bridge. 
An  increase  of  temperature 
causes  an  increase  in  the  re- 
sistance of  the  lead.  The  balance 
of  the  bridge  is  thus  disturbed. 
By  experimental  graduation  the 
temperature  value  of  the  deflec- 
tion, or  of  the  change  of  resist- 
ance that  balances  it,  is  known 
(p.   617). 


ANIMAL  HEAT 


175 


used,  one  containing  the  animal  ind  the  other  ;i  hydrogen  fla  tne,  01  a 
coil  of  wire  traversed  by  a  voltaic  current,  which  is  regulated  so  as 
to  keep  the  temperature  the  same  in  the  two  calorimeters.  From 
the  quantity  of  hydrogen  burnt,  or  electricity  passed,  the  heat- 
production  of  the  animal  can  be  calculated. 

In  Atwatcr's  great  respiration  calorimeter  (Fig.  195)  both  the  heat 
production  and  the  respiratory  exchange  are  measured.     The  heal 


Fig.  195* — Respiration  Calorimeter  (Atwater). 

Interior  of  chamber.  A  corner  of  the  inner  copper  wall  is  supposed  to  be  taken 
away.  The  ventilating  air-current  enters  the  chamber  at  the  lower  end  of  W, 
and  leaves  the  chamber  through  the  long  tube  fastened  above  W.  The  copper 
tubes  H,  H  are  surrounded  by  copper  discs  I,  I,  fastened  on  them  like  a  string 
of  beads  to  inrrease  the  surface.  These  tubes  constitute  the  arrangement 
through  which  the  stream  of  water  flows  which  removes  the  heat  formed  in 
the  chamber.  J,  J  are  copper  troughs  which  receive  the  water  dropping 
from  H.  H.  M,  M,  M  are  electrical  thermometers  which  show  the  temperature 
of  the  chamber  ;  N,  N,  similar  thermometers  which  show  the  temperature  of  the 
copper  wall. 


produced  by  the  person  in  the  calorimeter  is  carried  away  from  it 
by  a  stream  of  water  flowing  through  the  chamber  in  a  series  of 
tubes,  the  temperature  within  the  calorimeter  being  kept  constant  by 
regulating  the  temperature  and  velocity  of  the  entering  stream  of 
water.     The  quantity  of  the  escaping  water  and  the  increase  in  its 


A    .UAXCAL  OF  PHYSIOLOGY 


temper  lure  are  measured,  and  the  heat  production  can  then  be 
d.  The  apparatus  consists  of  a  chamber  in  which  a  human 
being  can  live  for  several  days  and  nights.  \  s1  ream  of  air  is  supplied 
and  the  chemical  changes  produced  in  tins  are  investigated  in  the 
manner  already  described  (p.  241). 

Air    calorimeters    have    sometimes    been    used    for    physio! 
purposes.     A  diagram  of  one  is  shown  in   Fig.    196.     :  |,,r'- 

meters  are  really  thermometers  with  an  immense  radiating  surl 
for  only  a  small  proportion  of  the  heat  given  off  by  the  animal 
to  heat  the  measuring  substance.     The  heat  required  to  raise  the 


^raJp; 


M 

Fig.   196. — Air  Calorimeter. 

cross-section  ;    (//.),   longitudinal   section  ;    A,   cavity   of 
calorimeter  for  animal  ;  B,  copper  cylinder  corrugated  so  as  to 
increase  the  radiating  surface  ;  C,  air  space  enclosed  between  B 
and  a  concentric  copper  cylinder  F  :  C  is  air-tight,  and  is  connected  by  the  tube  2 
with  the  manometer  M.     The  other  end  of  the  manometer  is  connected  with  an 
exactly  similar  calorimeter,  in  which  a  hydrogen  flame  is  burnt  in  the  space  cor- 
roding to  A,  or  in  which  the  air  in  A  is  heated  by  a  1  oil  oi  wire  traversed  by 
an  electrical  current.     The  flame  or  current  is  regulated  so  as  to  keep  the  coloured 
Leum  or  mercury  in  the  manometer  M  at  thi  1  in  both  limbs  j  the 

amount  of   heat  given  off  to  the  one  calorimeter  by  the  flame  or  current  is  then 
equal  to  that  given  oft  by  the  animal  to  the  other.     I)  is  an  external  cylinder 

per  or  tin  perforated  by  holes  (6,  7)  at  intervals.  The  purpose  of  it 
prevent  draughts  from  affecting  the  loss  of  heat  from  F  ;  4.  5.  are  tubes  through 
which  thermometers  can  be  introduced  into  C  :  1  is  the  terminal  of  a  spiral  tube, 
which  is  coiled  in  the  end  portion  of  the  air  space  C.  The  sections  of  the  coils 
are  indicated  by  small  circles.  The  other  end  of  the  spiral  tube  is  3  j  through 
this  tube  air  is  su<  ked  out,  and  so  the  proper  ventilation  of  the  animal  is  kept  up. 
The  object  of  the  spiral  arrangement  is  that  the  air  aspirated  out  of  A  maj 
up  its  heat  to  the  air  in  C  before  passing  out.  E  is  1  door  with  double  glass 
walls. 

temperature  of  a  litre  of  air  by  i°  is  very  small  in  comparison 
with  that  required  to  raise  the  temperature  of  a  litre  of  water 
by  the  same  amount.  Hence  a  given  quantity  of  heat  r. 
the  temperature  of  an  air  calorimeter  much  more  than  that  of  a 
water  calorimeter  of  the  same  dimensions  ;  and  the  loss  of  heat  to 
the  surroundings  being  proportional  to  the  elevation  of  temperature, 
in  the  water  calorimeter  the  chief  part  of  the  heat  is  actually  retained 
in  the  water,  while  in  an  air  calorimeter  the  greater  portion  passes 
through  the  air  space,  and  is  radiated  away.  When  the  amount  of 
heat  lost  by  the  calorimeter  becomes  equal  to  that  gained  from  the 
animal,  the  '  steady  '  reading  of  the  instrument  is  taken,  and  from 
this    the    heat    production    can    be    deduced    by    an    experimental 


1X1  1/  //.  HEAT  577 

graduation  oi  the  apparatus.  One  advantage  oi  an  air  calorimeter 
is  thai  H  follows  more  i  Losely  rapid  variations  in  the  beat-production 
oi  the  animal,  or,  to  speak  more  correctly,  in  the  heat  loss.  It 
should  be  carefully  noted  that  in  calorimetry  what  is  directly 
measured  is  the  quantity  of  heat  given  out  by  the  animal,  not  the 
quantity  produced.  The  two  quantities  are  identical  only  when  the 
temperature  of  the  animal  has  remained  unchanged  throughout  the 
experiment.  I!  the  temperature  has  fallen,  the  quantity  of  heat 
produced  is  equal  to  the  quantity  measured  by  the  calorimeter  minus 
the  difference  between  the  quantity  in  the  animal  at  the  beginning 
and  at  the  end  of  the  observation.  This  difference  is  equal  to  the 
average  specific  heat  of  the  animal  multiplied  by  its  weight  and  by 
the  fall  of  temperature.  It  can  be  approximately  found  by  multiply- 
ing the  weight  (in  kilogrammes  or  grammes)  by  the  fall  of  rectal 
temperature  (in  degrees),  since  the  average  specific  heat  of  the  body 
is  not  very  different  from  that  of  water,  and  the  specific  heat  of  water 
is  taken  as  unity. 

All  the  higher  animals  (mammals  and  birds)  have  a  prac- 
tically constant  internal  temperature  (fowl  410  to  440  C,  mouse 
3j°  to  38°,  dog  380  to  39°,  man  370  in  the  rectum),  but  a  few 
hibernating  mammals,  such  as  the  marmot,  are  homoiothermal 
in  summer,  poikilothermal  during  their  winter  sleep.  In  the 
lower  forms  the  body-temperature  follows  closely  the  tempera- 
ture of  the  environment,  and  is  never  very  much  above  it  (frog 
0*5°  to  2°  above  external  temperature).  Both  in  a  frog  and  in 
a  pigeon  heat  is  evolved  as  long  as  life  lasts  ;  but  per  unit  of 
weight  the  amphibian  produces  far  less  than  the  bird,  and  loses 
far  more  readily  what  it  does  produce.  The  temperature  of 
the  frog  may  be  300  C.  in  June  and  50  in  January.  The  structure 
of  its  tissues  is  unaltered  and  their  vitality  unimpaired  by  such 
violent  fluctuations.  But  it  is  necessary,  not  only  for  health, 
but  even  for  life,  that  the  internal  temperature  (the  tempera- 
ture of  the  blood)  of  a  man  should  vary  only  within  relatively 
narrow  limits  around  the  mean  of  370  to  380  C. 

Why  it  is  that  a  comparatively  high  temperature  should  be 
needed  for  the  full  physiological  activity  of  the  tissues  of  a 
mammal,  while  the,  in  many  respects,  similar  tissues  of  a  fish 
work  perfectly,  although  perhaps  more  sluggishly,  at  a  much 
lower  temperature,  is  not  quite  clear  ;  nor  do  we  know  the 
precise  significance  of  that  relative  constancy  of  temperature  in 
the  warm-blooded  animal,  which  is  as  important  and  peculiar  as 
its  absolute  height.  The  higher  animals  must  possess  a  superior 
delicacy  of  organization,  hardly  revealed  by  structure,  which 
makes  it  necessary  that  they  should  be  shielded  from  the  shocks 
and  jars  of  varying  temperature  that  less  highly  -  endowed 
organisms  endure  with  impunity.  Leaving  the  discussion  of  the 
local  differences  and  periodic  variations  of  the  temperature  of 
warm-blooded  animals  to  a  future  page,   let  us  consider  now 

37 


57$  I    1/  /  \  r  it    hi    PHYSIOLOGY 

the  mechanism  by  which  the  loss  <»l  heal  is  adjusted  to  its  pro- 
duction, so  that  upon  the  whole  the  one  balances  til''  other; 

Heat-loss.  Heal  is  lost  (i)  from  the  surfaces  oi  the  body 
by  radiation,  conduction,  and  convection;  (2)  as  latenl  heal  in 
the  watery  vapour  given  "it'  by  the  skin  and  lungs  :  and  (3)  in 
the  excreta.  Even  in  the  bulky  excremenl  <>i  herbivora  a  com- 
paratively trilling  part  of  the  total  heat  is  lost.  The  second 
channel  of  elimination  is  much  more  important  ;  the  lust  is  in 
general  the  most  important  of  all. 

I  lie  loss  of  heat  by  direct  radiation  from  a  portion  of  the  skin 
or  clothes,  or  from  hair,  fur,  or  feathers  covering  the  skin,  ma)' 
be  measured  by  means  of  a  thermopile  or  a  resistance  radiometer 
(bolometer).  The  latter  instrument  is  similar  in  principle  and  allied 
in  construction  to  the  resistance  thermometer  used  in  measuring 
superficial  temperatures,  and  already  described  (Fig.  194,  p.  57.4). 
It  may  consist  of  a  grating  of  lead-paper  or  tinfoil  fixed  vertically 
in  a  small  box  which  protects  it  from  draughts.  The  box  has  a 
sliding  lid.  which  is  kept  closed  till  the  moment  of  the  observation, 
when  it  is  withdrawn  and  the  portion  of  skin  applied  to  the  opening 
at  a  fixed  distance  (5  to  10  cm.)  from  the  grating.  The  intensity 
of  radiation  depends  on  the  excess  of  temperature  of  the  radiating 
surface  over  that  of  the  surroundings,  as  well  as  on  the  nature  of  the 
surface.  The  uncovered  parts  of  the  skin  (face  and  hands  in  man) 
radiate  more  per  unit  of  area  than  the  clothes  or  hair  ;  and  the  warm 
forehead  more  than  the  comparatively  cool  lobe  of  the  car  or  tip  oJ 
the  nose.  When  a  man  is  sitting  at  rest  in  a  still  atmosphere,  pure 
radiation  plays  a  greater,  and  conduction  and  convection  play  a 
smaller,  part  in  the  total  loss  of  heat  from  the  skin  than  when  he  is 
walking  about  or  sitting  in  a  draught.  The  more  rapidly  the  air  in 
contact  with  the  skin  and  clothes  is  renewed,  the  lower,  other  things 
being  equal,  the  temperature  of  the  radiating  surfaces  is  kept,  the 
greater  is  the  loss  of  heat  by  conduction  to  the  adjacent  portions  of 
air,  and  the  smaller  the  loss  by  radiation  to  the  walls  of  the  room. 
the  furniture,  and  other  surrounding  objects.  It  is  probable  that . 
under  the  most  favourable  conditions,  the  amount  of  heat  lost  from 
the  surface  by  true  radiation  does  not  exceed  the  amount  lost  by 
conduction  and  convection. 

The  loss  of  heat  by  evaporation  of  water  from  the  skin  can  be 
calculated  if  we  know  the  quantity  of  water  so  given  off.  Fo 
gramme  of  water  at  the  ordinary  temperature  (say  iy  C 
°'555  calories  to  convert  it  into  aqueous  vapour  at  the  average  tern]  >era- 
ture  of  the  skin.  If  we  take  the  average  quantity  of  water  excreted 
as  sweat  in  twenty-four  hours  as  750  c.c,  this  will  be  equivalent 
to  a  heat-loss  ol  416-25 — say,  in  round  numbers.  .400  calories. 

The  quantity  of  heat  given  off  by  the  lungs  may  be  also  dei 
from  calculation,  the  data  being  (1)  the  weight,  temperature,  and 
specific  heat  of  the  expired  air.  and  (2)  the  excess  of  water  it  contains 
in  the  form  of  aqueous  vapour  over  that  contained  in  the  inspired 
air.  Helmholtz  calculated  the  quantity  of  heat  needed  to  warm  the 
air  expired  by  a  man  in  twenty-four  hours  from  an  initial  temperature 
of  200  to  body-temperature,  at  70  calories,  and  that  required  to 
1  \  aporate  the  water  given  off  by  the  lungs  at  397,  making  the  total 
heat-loss  by  the  lungs  in  thes<  proi  esses  from  400  to  500  calorics.  A 
certain  amount  oi  heal  is  also  absorbed  in  connection  with  the  escape 


i.\!  w  //    HE  I  I 


..t  the  i  arbon  dioxide.  The  reason  why  a  great  deal  more  water  and 
therefore  more  heat  is  not  given  of  by  the  lungs  with  their  enonm  ius 
suit. nf.  .iihI  the  high  degree  of  imbibition  (p.  $98)  oi  the  epithelium 
of  the  alveoli  is  thai  the  air  is  already  saturated  with  aqueous  vapour, 
or  nearly  so,  before  i1  reaches  the  alveoli.  By  direct  calorimetric 
observations  it  was  found  that  a  man  of  70  kilos  weight  gave  off  in 
normal  breathing,  with  .m  air-temperature  of  r2°to  150  C,  from  350 
to  450  calories.     Forced  respiration,  as  might  be  expected,  increased 

B,  copper  tube  with  mouth- 
piece, connected  with  the  thin 
brass  capsule  1  ;  .(  is  connected 
with  a  similar  capsule  (3)  by  a 
short  tube,  which  passes  out 
from  it  at  the  side  opposite  to 
that  at  which  B  enters  ;  2  and  1 
are  similar  capsules.  From  1  an 
outlet  tube  (C)  passes  off.  The 
whole  is  set  in  a  copper  cylinder 
(A)  filled  with  water.  A  piece 
is  supposed  to  be  cut  out  of  A 
in  order  to  show  the  capsules. 
A  is  placed  in  another  wider 
copper  cylinder. 

Fig.  197. — Respiration  Calorimeter. 

the  amount  often  to  double  or  even  treble.  A  diagram  of  a  respira- 
tion calorimeter  (for  measuring  the  heat  given  off  in  respiration)  is 
shown  in  Fig.  197.     (See  Practical  Exercises,  p.  613.) 

The  following  table  gives  an  analysis  of  the  heat -loss  of  an 
average  man.  It  must  be  understood  that  the  figures  are  only 
approximate.  In  round  numbers  we  may  say  that  two-thirds 
of  the  heat-loss  is  due  to  radiation,  conduction,  and  convection, 
and  one-third  to  the  evaporation  of  water. 


("Evaporation  of  water  - 
Skin   -  Radiation* 

I  Conduction  (and  convection) 
j  f Evaporation  of  water   - 

&   t  Heating  the  expired  air 
Heating  the  excreta 


Per  Cent. 

15       } 

40       J 

15       \ 

2'5i 


80 


*TS 


Calories. 
4OO 
65O 

I,()00 

f4°° 

\   7° 

70 


100     2,590 

In  the  rabbit,  according  to  Nebelthau,  the  heat  lost  by  evapora- 
tion of  water  is  about  16  per  cent,  of  the  whole,  or  about  half  the 
proportion  in  man,  according  to  the  above  calculation.  This  is  not 
surprising  when  we  reflect  that  the  rabbit  does  not  sweat,  and 
drinks  comparatively  little  water. 

Sources  of  the  Heat  of  the  Body — Heat-production. — Some 
heat  enters  the  body  as  such  from  without — in  the  food,  and 
by  radiation  from  the  sun  and  from  fires.     The  ultimate  source 

*  The  relative  amounts  lost  by  radiation  and  conduction  cannot  be 
accurately  fixed.     The  proportion  is  extremely  variable. 

37—2 


58o  A    MANUAL  OF  PHYSIOLOGY 

<>t  all  the  heal  produced  in  the  body  is  the  chemical  energy  oi 
the  food  substances.  Whatever  intermediate  forms  this  energy 
may  assume — whether  the  mechanical  energy  of  muscular  con- 
traction ;  the  energy  of  electrical  separation  by  which  the 
currents  of  the  tissues  are  produced  ;  the  energy  of  the  nerve 
impulse  ;  or  the  energy,  be  it  what  it  may,  which  enables  the 
living  cells  to  perform  their  chemical  labours — it  all  ultimately, 
except  so  far  as  external  mechanical  work  may  be  done,  appears 
in  the  form  of  heat.  We  do  not  know  at  what  precise  stage  of 
metabolism  the  chief  outburst  of  heat  takes  place.  But  it  is 
known,  as  already  pointed  out  (p.  504),  that  the  fraction  of  the 
total  energy  liberated  in  the  processes  of  hydrolytic  cleavage 
is  comparatively  small.  Most  of  the  heat  is  set  free  in  the 
oxidative  processes  which  accompany  or  follow  the  hydrolytic 
changes. 

Thus  the  energy-value  of  a  gramme-molecule  (p.  398)  of  maltose, 
cane-sugar,  or  lactose  is  a  little  more  than  1,350  calories  ;  that  of  the 
two  gramme-molecules  of  dextrose  formed  by  hydrolysis  of  the 
maltose  is  13474  calories  ;  that  of  the  gramme-molecule  each  of 
dextrose  and  levulose  formed  from  the  cane-sugar,  1349/6  ;  and 
that  of  the  gramme-molecule  each  of  dextrose  and  galactose  formed 
from  the  lactose,  13436  calories.  That  is  to  say,  the  hydrolysis  of 
these  disaccharides  to  monosaccharides,  which  is  the  first  step  in 
their  metabolism,  is  accomplished  with  the  liberation  of  very  little 
heat.  The  same  is  true  of  the  splitting  of  the  fats  and  proteins. 
The  dried  residue  of  a  filtered  pancreatic  digest  was  found  to  yield, 
when  burned  in  the  calori metric  bomb,  only  10  per  cent,  less  heat 
than  the  same  weight  of  dry  meat.  Much  the  greater  part  of  this 
deficiency  was  accounted  for  by  the  leucin  and  tyrosin  which  had 
crvstallized  out,  and  the  derivatives  of  higher  fatty  acids  in  the 
meat,  as  these  would  be  removed  from  the  digest  by  filtration. 

It  has  been  shown  that  the  law  of  the  conservation  of  energy 
holds  for  the  animal  body  ;  in  other  words,  there  is  a  practically 
exact  agreement  between  the  potential  energy  of  the  food  and 
the  kinetic  energy  into  which  it  is  transformed  in  the  body  both 
during  rest  and  during  work.  This  kinetic  energy  is  represented 
by  the  heat  given  off  plus  the  heat -equivalent  of  any  mechanical 
work  done  (Atwater).  In  other  words,  the  food,  whether  it  is 
burned  in  a  calorimeter  to  simple  end-products  like  carbon 
dioxide  and  water,  or  more  slowly  oxidized  in  the  body,  yields 
the  same  amount  of  heat,  provided  always  that  in  both  cases  it 
is  entirely  consumed,  and  that  no  work  is  transferred  to  the 
outside.  In  the  body  the  combustion  of  carbo-hydrates  and  fats 
is  complete  ;  but  the  nitrogenous  residues  of  the  proteins — urea, 
uric  acid,  etc. — can  be  further  oxidized,  and  the  remnant  of 
energy  which  they  yield  must  be  taken  into  account  in  any 
calculation  of  the  total  heat-production  founded  on  the  heat  of 


/  v/u  ,/.  ///   f  / 

combustion  of  the  food  substances.  From  careful  experiments, 
it  has  been  found  thai  a  gramme  of  dry  protein  (egg-albumin), 
ulu-n  burned  in  a  calorimeter,  yields  57. ;5  calories  of  heat,  a 
gramme  of  dextrose  3*742,  and  a  gramme  of  animal  fat  9*500 
calories  (Stohmann). 

Calories. 

I  leat-equivalent  of  1  gramme  of  albumin  -  5'735 

Albumin  (minus  area  produced  from  it)  -  4'949 

(  ane-sugar         -----  3-955 

Kreatin  (water-free)      -  4'275 

Starch    -  -  -  -  -  -  4tSj 

In  applying  such  results  to  the  calculation  of  the  heat-production 
of  the  body,  it  is  not  sufficient  to  deduct  from  the  heat  of  combustion 
of  the  proteins  the  heat  which  the  residual  urea  would  yield  if  fully 
oxidized.  For  other  incompletely  oxidized  products  arise  from 
proteins  when  consumed  in  the  body,  and  Rubner  has  shown,  by 
actually  determining  the  heat  of  combustion  of  the  urine  and  faeces, 
that  the  real  equivalent  of  a  gramme  of  albumin  is  at  most  only 
44 20  calories.  The  heat-equivalent  of  our  less  liberal  specimen  diet 
(p.  545)  will  be  approximately  : 

Calories. 

Protein,  95  grammes  x      4^420  =  4T9'9 

Fat,  80  grammes  x      9'50o  =  7600 
Carbo-hydrate   (reckoned    as 

dextrose),  320  grammes  $*742  =  IrI97'4 

2-377'3 

The  heat-equivalent  of  the  more  generous  specimen  diet  (p.  546) 
would  be  2,878  calories. 

But  this  is  the  diet  of  a  man  doing  a  fair  day's  work,  and  to 
get  the  quantity  of  energy  which  actually  appears  as  heat,  the  heat- 
equivalent  of  the  mechanical  work  performed  must  be  deducted. 
A  fair  day's  work  is  about  150,000  kilogramme-metres— that  is,  an 
amount  equal  to  the  raising  of  150,000  kilogrammes  to  the  height 
of  a  metre.  Xow,  a  kilogramme-degree  or  calorie  of  heat  is 
equivalent  to  4255  kilogramme-metres  of  work,  and  a  kilogramme- 
metre  to  calorie.  The  heat-equivalent  of  the  day's  work 
425'5 

is,  therefore,   150,000  x  -         =352  calories.     Deducting  this  from 

425'5 
the  heat-equivalent  of  the  food,  we  get  in  round  numbers  2,520  calo- 
ries as  the  heat  given  off  on  the  more  liberal  diet.     This  corresponds 
fairly  well  with  the  calculated  heat-loss  (p.  579)- 

The  following  table,  based  on  the  direct  calorimetric  observations 
of  Atwater  and  Benedict,  shows  the  average  heat-production  in  a 
large  number  oi  experiments  on  several  individuals  at  rest  and  doing 
measured  amounts  of  work,  with  a  stationary  bicycle,  for  instance. 
This  was  connected  with  a  small  dynamo,  which  transformed  the 
greater  part  of  the  work  into  electrical  energy.  The  electrical  energy 
in  its  turn  was  changed  into  heat,  the  current  passing  through  a 
lamp  : 


582 


A    MANV  \l    OF  PHYSIOLOGY 


.So 

Heal  eliminated  per  Hour. 

1    tal  Heat 
I  [ours. 

-  3 

- 

Daj 

time. 

Night-time. 

■J  ± 

Day-time.        Night-time. 

SB.S 

ei   1 1 

7  a.m. 
to 

I    p   Ml. 

to 

7  p.m.     1  a.m. 
to             to 

7  a.m. 
to 

1  p.m. 

to 

7  p.m.     1  a.m. 
to          to 

Hpj 

1  p.m. 

7  P-m. 

1  a  in.      7  a.m. 

a. 

1  p.m. 

7  p.m. 

1  a.m.    7  a.m. 

Resl      experi- 

ments  - 

2,262 

ro6'3 

104-4 

98-3      67-9 

94"3 

-;•; 

J'.-  1 

Work   experi 

merits   - 

[,22S 

2317 

235-6 

I  iS-i 

— 

— 

—         — 

1  [eat  -  equiva- 

lent oi  work 

451 

58-5 

56-8 

Total  for  work 

experiments 

4,676 

2QO-2 

292-4 

I  1  s- 1 

[94-8 

37 '2 

37' S 

l5-2      !(>•  1 

The  heat-production  during  the  hours  of  sleep,  in  the  second  night 
period,  is  much  less  than  in  the  waking  hours  of  rest,  and  of  course 
enormously  less  than  in  the  hours  of  work.  After  work  the  heat- 
production  in  the  period  of  sleep  is  only  a  little  greater  than  after  rest. 

As  already  indicated  (p.  580),  it  is  permissible  to  calculate  tin 
production  from  the  diet,  and  Rubner  has  done  this  for  various 
classes  of  men.  reducing  everything  to  the  standard  of  a  body-weight 
of  67  kilos.  The  fasting  man,  of  67  kilos  bodv-weight,  produces 
2,303  calories  in  the  twentv-four  hours.  The  class  of  brain-workers, 
represented  by  physicians  and  officials,  produce  only  a  little  more 
heat  than  the  fasting  man,  viz.,  2.445  calories.  The  second  class, 
represented  by  soldiers  (presumably  in  time  of  peace)  and  day- 
labourers  (probably  of  a  cautious  and  conservative  type),  work  up  to 
2,868  calories.  The  third  class,  composed  of  men  who  work  with 
machines  and  other  skilled  labourers,  attain  a  heat-production  of 
3,362  calories.  The  fourth  class,  typified  by  miners  (who  are 
engaged,  usually  by  the  piece  and  not  by  the  day,  in  severe  and 
exhausting  toil),  produce  as  much  as  4.790  calories.  In  the  fifth 
and  last  class,  represented  by  lumberers  and  other  out-of-door 
labourers  (who.  in  addition  to  excessive  exertion,  have  often  to  face 
intense  cold),  the  heat-production  rises  to  5,360  calorics.  The  diet 
of  ordinarv  prisoners  in  Scotland  doing  light  work,  chiefly  of  a 
sedentary  character,  was  found  to  correspond  to  3.115.  and  that  of 
convicts  on  '  hard  labour  '  to  3,707  calories.  It  is  a  fair  presump- 
tion that  in  Scotch  prisons  the  total  heat  value  supplied  is  not 
excessive.  From  the  general  agreement  of  calculated  results  with 
actual  measurements  we  can  safely  conclude  that  most  healthy  adults 
produce  between  2,000  and  3,000  calories  (35  to  40  per  kilo  of  body- 
weight)  on  a  '  rest  '  day,  or  a  day  of  light  labour,  and  between  3,000 
and  4,000  (45  to  60  per  kilo  of  body-weight)  on  a  (lav  of  hard  manual 
work. 

What  has  been  already  said  in  connection  with  standard  dietaries 
(p.  545)  indicates  that  the  work  of  the  world  might  possibly  be 
accomplished  as  well  with  a  smaller  transformation  of  energy  in 
the  human  machine,  at  least  in  the  more  prosperous  countries,  ami 
that  in  the  body,  as  in  an  engine,  more  careful  '  stoking  '  might 
result  in  a  saving  of  fuel.  It  is  extremely  improbable,  however, 
that  any  argument  of  this  sort  will  have  much  effect  upon  the 
deep-rooted  dietetic  habits  of  mankind. 


AN1  \l  U    III    I  l 

In  any  case  it  must  be  carefully  remembered  that  the  question 
o1  the  minimum  amount  oi  protein  necessary  in  a  permanent 
is  quite  distinct  from  the  question  of  the  minimum  beat  value  of  the 
diei  for  a  man  of  given  body  weight  doing  a  definite  amount  of  work 
under  definite  conditions.  Whether  the  protein  allowance  be  scanty 
oi  liberal,  the  total  heat  value  cannol  be  permanently  reduced  below 
i.  certain  minimum  depending  on  the  work  done,  the  climate,  and 
nt her  conditions!  Mc<  ay  points  out  that  while  Bengalis  subsist  on 
food  containing  only  about  one-third  the  amount  of  protein  in  such 
a  '  standard  '  diet  as  Voit's.  and  may  therefore  be  supposed  to  be 
immune  from  the  dangers  of  an  excessive  protein  metabolism,  the 
large  intake  of  carbo-hydrate  rendered  necessary  by  the  poverty  of 
the  food  in  protein  is  associated  with  perhaps  greater  evils,  among 
them  a  marked  predisposition  to  diabetes  and  renal  troubles.  Their 
weight,  chest  measurement,  and  muscular  development  are  inferior 
tot  hose  of  other  Asiatics  living  in  the  same  climate  but  with  dietetic 
habits  which  ensure  them  a  larger  supply  of  protein. 

The  Seats  of  Heat-production. — We  have  already  recognised 
the  skeletal  muscles  as  important  seats  of  heat-production.  A 
frog's  muscle,  contracting  under  the  most  favourable  con- 
ditions, does  not  convert  at  most  more  than  one-fourth  or 
one-fifth  of  the  energy  it  expends  into  mechanical  work  ;  at 
least  three-fourths  or  four-fifths  of  the  energy  appears  as  heat. 
The  muscles  of  mammals  and  of  man  in  the  intact  body  work, 
upon  the  whole,  more  economically  than  the  excised  frog's 
muscles  at  their  maximum  efficiency.  Under  the  best  con- 
ditions— that  is,  when  the  work  is  moderate  and  not  too  rapidly 
done — about  one-third  of  the  chemical  energy  expended  may  be 
transformed  into  mechanical  work,  and  only  two-thirds  into  heat 
(Zuntz).  In  hard  work  three-quarters  of  the  energy  may  be 
changed  into  heat  ;  but  even  then  the  efficiency  of  the  muscles 
far  outstrips  that  of  the  best  steam-engines,  which  convert  only 
an  eighth  of  the  total  energy  into  work. 

Notwithstanding  the  splendid  efficiency  of  the  muscular 
machine,  the  gaseous  metabolism  easily  rises  during  muscular 
work  to  five  times,  and  in  severe  labour  to  nine  times  its  resting 
value,  although  persons  inured  to  toil  work  more  economically 
than  amateurs.  In  one  of  Atwater's  '  severe  work  '  experi- 
ments the  work  done  in  twenty-four  hours  had  a  heat-equivalent 
of  1,482  calories  (equal  to  over  630,000  kilogramme-metres).  The 
total  heat-production  (including  the  equivalent  of  the  work) 
was  9,314  calories.  It  is  not  difficult  to  show  that  the  greater 
part  of  the  metabolism  and  heat-production  of  a  man  doing 
ordinary  work  is  accounted  for  by  the  contraction  of  the  voluntary 
and  involuntary  muscles. 

Even  in  muscles  completely  at  rest  metabolism  goes  on,  and  some 
heat  is  produced.  By  analyzing  the  gases  of  the  arterial  and  venous 
blood  Zuntz  compared  the  oxygen  consumption  and  carbon  dioxide 
production  in  the  hind-legs  of   dogs  when  the  sciatic  and  anterior 


./    MANUAL  OF  I'HYSIOLOGY 


crural  nerves  were  divided  and  intact.      In  both  •  muscles 

were-  at  n-st  in  the  ordinary  sense.  But  in  the  second  experiment 
the  central  '  tonus  ,    was  preserved,  while  in  the  first  it  was 

abolished.  In  one  experiment  in  which  the  nerves  wen-  intact  the 
oxygen  consumed  amounted  to  ['22  c.c.  and  the  carbon  dioxide 
produced  to  i  S-  c.c,  per  kilo  of  tissue  per  minute.  In  the  experi- 
ment in  which  the  nerves  were  severed,  the  corresponding  numbers 
were  o*68  c.c.  for  the  oxygen  and  0*63  c.c.  for  the  carbon  dioxide. 
Although  it  is  probable,  from  the  results  of  (  hauveau  and  Kauffmann 
already  referred  to  (p.  263),  that  these  figures  are  too  low  for  tin- 
normal    resting    muscle,    they    still    demonstrate   that,  even    in    th  ■ 


NUTRIENTS.        CRAMS 

2 

DO           4 

00         6  00         6 

00          10  00         12  00 

POTENTIAL    ENERCY.     CALORIES 

IC 

ee     ao 

00        3O00        40 

00     5000     60100 

DIETARY     STANDARDS. 

i 

SUBSISTENCE    DIET  (PLAYFAIR) 

1 

■ 

MAN  AT    MODERATE    W0RK(V0IT) 

-■■    1    *.   .  SV\ 

MAN    AT    HARD    WORK  (ATWATER) 

«,jai          ^«^^«5 

MAN    WITH    MODERATE  EXERCISE  (PLAYFAIR) 

iwi.££miMabi 

ACTUAL       DIETARIES- 

LAWYER,  MUNICH,  GERMANY. 

.  ^IIB 

PHYSICIAN,  MUNICH, GERMANY. 

til  Jlill 

•    «1^& 

1IHM1 

... 

WELL-CED   BLACKSMITH,  ENGLAND. 

MIVIi 

1  ^^^^           vk 

GERMAN  SOLDIERS,  PEACE   FOOTING. 

WBkz 

wm&mmOmM       BB  HI 

■■hbI                      urn 

GERMAN   SOLDIERS,  WAR    FOOTING. 

BB 

31 

U.S.  ARMY     RATION. 

*.jj 

I         II 

U.S.  NAVY      RATION. 

MM\ 

^^.>*i^^*  bb   II 

]"^j"             ""M"TI 

■  <     1 

B 

. 

1 

Fig.   198. — Diagram  showing  the  Heat-equivalent  of  various  Dietaries 
A,  proteins  ;  B,  fats  ;  C,  carbo-hydrates  ;  D,  heat-equivalent. 


absence  of  innervation  from  the  central  nervous  system,  the  meta- 
bolism, and  therefore  the  heat-production  of  the  muscles,  are  by  no 
means  negligible  ;  068  c.c.  of  oxygen  per  minute  corresponds  to 
408  c.c.  per  hour,  or  more  than  one-tenth  of  the  oxygen  consumption 
per  kilo  per  hour  of  a  fasting  dog  lying  at  rest  (Zuntz). 

If  the  work  of  the  heart  is  taken  as  16,600  kilogramme-metres  in 
twenty-four  hours  (p.  127).  the  total  heat  produced  by  this  organ 
will  be  equivalent  (on  the  assumption  that  it  converts  one-third  of 
its  energy  into  work)  to  about  50,000  kilogramme-metres,  or  not 
much  less  than  120  calories,  since,  practicallv.  the  whole  work  is 
expended    in    overcoming   the   friction  of   the    vessels,  and    finally 


IX/M  II,   Ill    I  /  585 

appears  aa  heat.  Enough  energy  is  transformed  in  twenty-four 
hours  in  the  hear!  oi  the  colonel  oi  a  regiment  of  [,000  men  to  lift 
the  whole  regimenl  to  the  height  oi  the  mess-table,  if  it  could  be  all 
changed  into  mechanical  work.  Barcroft  and  Dixon  have  <  al<  ulated 
tlu  energy  of  the  heart's  contraction  on  the  assumption  that  it  is 
derived  from  the  oxidation  of  a  carbo-hydrate  by  the  oxygen 
absorbed  by  the  organ.  They  concluded  that  the  energy  set  free 
in  the  heart  of  a  dog  weighing  12  kilos  corresponds  on  the  average 
to  7-86  kilogramme-metres  per  minute,  which  is  equivalent  to 
26'6  calorics  in  twenty-four  hours.  Allowing  for  the  fact  that  the 
heart  of  a  small  animal  pumps  more  blood  in  proportion  to  the 
body-weight  than  the  heart  of  a  large  animal  (p.  127).  this  result 
agrees  very  well  with  that  deduced  from  the  work  of  the  heart. 
The  work  of  the  inspiratory  muscles  may  be  reckoned  at  13,000  kilo- 
gramme-metres, equal  to  30-5  calories,  and  the  heat  produced  by 
them  at,  say,  go  calories.  In  sum,  the  muscular  work  cf  the  circula- 
tion and  respiration  is  responsible  for  the  production  of  about 
210  calorics  (without  including  the  heat  produced  by  the  smooth 
muscle  of  the  bronchi  and  bloodvessels),  or  nearly  one-twelfth  of 
the  total  production  of  a  man  doing  ordinary  labour. 

The  glands,  and  then  the  central  nervous  system,  rank  after 
the  muscles,  though  at  a  great  distance,  as  seats  of  heat-produc- 
tion. The  liver  and  brain  (?)  are  the  hottest  organs  in  the  body  ; 
and  that  this  is  not  altogether  due  to  their  being  well  protected 
against  loss  of  heat  is  shown,  in  the  case  of  the  liver,  by  the 
excess  of  temperature  of  the  blood  of  the  hepatic  over  that  of 
the  portal  vein.  In  view,  however,  of  the  exaggerated  impor- 
tance which  some  have  given  to  these  organs  as  foci  of  heat- 
production,  it  may  be  well  to  point  out  that  although  many  of 
the  chemical  changes  in  the  animal  body  are  undoubtedly 
associated  with  the  setting  free  of  heat  (exothermic  reactions), 
other,  and  not  less  weighty  and  characteristic,  reactions  may 
cause  the  absorption  of  heat  (endothermic  reactions)  ;  and  it  is 
possible  that  some  of  the  syntheses  which  many  of  the  tissues 
are  capable  of  performing  may  be  included  in  this  latter  category. 
For  example,  when  urea  is  decomposed  so  as  to  yield  ammonium 
carbonate  (p.  438),  heat  is  set  free.  We  must  assume  that  if 
ammonium  carbonate  were  transformed  into  urea  in  the  liver, 
an  equal  amount  of  heat  would  be,  on  the  whole,  absorbed. 
So  that  the  heat-production  of  an  organ  may  depend,  not  only 
upon  the  quantity,  but  also  upon  the  quality,  of  its  chemical 
activity.  In  all  the  tissues,  including  the  muscles,  it  is  necessary 
to  assume  that  some  of  the  energy  transformed  is  expended  in 
so-called  '  restitution  '  processes — that  is,  in  replenishing  the 
store  of  nutritive  material  within  the  cells  and  in  building  up  the 
protoplasm.  Claude  Bernard  observed  an  excess  of  o-6°  C.  in 
the  temperature  of  the  blood  of  the  hepatic  vein  over  that  of 
the  portal  during  hunger,  and  as  much  as  r6°  at  the  height  of 
digestion,    although   at   the   beginning   of   digestion   the   portal 


586  /    U  /  vr  //    OF  PHYSIOLOGY 

blood  was  the  hotter  by  0-4°.  But  such  observations,  like 
the  corresponding  ones  on  the  salivary  glands,  are  "pen  to 
many  errors,  and  when  we  consider  the  enormous  tide  of  blood 
which  during  digestion  sets  through  the  portal  system,  we  shall 
look  with  suspicion  upon  results  that  announce  a  difference 
of  more  than  a  small  fraction  of  a  degree  in  the  temperature 
of  the  incoming  and  outgoing  blood  of  the  liver.  Probably  not 
less  than  200  litres  of  blood  pass  in  twenty-four  hours  through  the 
liver  of  a  2-kilo  rabbit.  If  the  temperature  of  this  blood  is 
raised  even  one-tenth  of  a  degree  in  its  passage  through  the 
hepatic  capillaries,  this  would  correspond  to  a  heat -product  ion 
of  20,000  small  calories,  or  one-tenth  of  the  whole  heat  produced 
in  the  animal. 

In  the  case  of  the  brain  there  is  some  evidence,  obtained  by  com- 
parison of  the  gases  of  blood  taken  from  the  carotid  and  from  the 
venous  sinuses  (torcula  Herophili),  that  the  metabolism  is  feebl 
compared  even  with  that  of  resting  muscles  (Hill).  Nor  is  it  possible 
to  demonstrate  any  marked  or  constant  increase  when  the  cerebral 
cortex  is  roused  to  such  an  active  discharge  of  impulses  as  leads  to 
general  epileptiform  convulsions.  The  rise  of  temperature  of  certain 
regions,  especially  the  occipital  portion,  of  the  scalp,  which  some 
observers  nave  stated  to  take  place  during  mental  activity,  cannot 
be  supposed  to  be  due  to  conduction  of  heat  from  the  brain  through 
the  skull.  It  is  perhaps  caused  by  vaso-motor  changes  in  the  scalp, 
associated,  it  may  be.  with  corresponding  changes  in  related  areas  of 
the  cortex.  The  increase  observed  by  Mosso  in  the  temperature  of 
the  brain  during  intense  psychical  activity,  sometimes  to  o'2°  C, 
or  o-3°  C.  above  the  rectal  temperature,  may  also  have  been  due, 
in  part  at  least,  to  vascular  changes.  And,  indeed,  if  wc  remember 
how  large  a  proportion  of  the  central  nervous  system  is  made  up  of 
nerve-fibres,  in  which,  or  at  any  rate  in  the  fibres  of  peripheral 
nerves,  no  sensible  production  of  heat  has  ever  been  demonstrated, 
it  will  not  appear  surprising  if  even  a  considerable  increase  in  the 
metabolism  of  the  really  active  elements  should  fail  to  make  itself  felt. 

With  regard  to  the  muscles,  we  are  as  yet  in  the  dark  as  to 
the  precise  relation  of  the  energy  which  appears  as  heat  and  of 
that  which  is  converted  into  work.  The  original  source  of  both 
is,  of  course,  the  oxidation  (and  cleavage)  of  the  food  substances, 
but  it  has  been  the  subject  of  discussion  whether  in  a  muscle, 
as  in  a  heat-engine,  the  chemical  energy  is  first  converted  into 
heat,  and  part  of  the  heat  then  transformed  into  work,  or 
whether  the  chemical  energy  is  immediately  changed  into  work, 
or  whether  there  is  an  intermediate  form  of  energy  other  than 
heat.  Some  have  supposed  that  the  chemical  energy  is  first 
converted  into  electrical  energy  (p.  640). 

It  has  been  very  generally  admitted  thai  the  chief  seat  of 
excessive  metabolism  in  fever  is  the  muscles  ;  but  U.  Mosso  has 
stated  that  cocaine  fever — the  marked  rise  of  temperature 
produced  by  injection  of  cocaine — can  be  obtained  in  animals 


INIMA1    III    I  /  587 

paralyzed  by  curara.  This,  even  it'  true,  would  no1  support  the 
conclusion  that  a  '  nervous  fever  '—that  is  to  say,  a  fever  due 
solely  to  increased  metabolism  in  the  nervous  system— exists  ; 
for  in  a  curarized  animal  a  large  amount  of  'active'  tissue 
(glands,  heart,  smooth  muscle)  still  remains  in  physiological 
connection  with  the  brain  and  cord.  But,  as  a  matter  of  fact, 
in  an  animal  under  a  dose  of  curara  sufficient  to  completely 
paralyze  the  skeletal  muscle  cocaine  causes  no  appreciable  rise 
of  rectal  temperature  ;  and  this  is  strongly  in  favour  of  the  view 
that  the  fever  produced  in  the  non-curarized  animal  is  con- 
nected with  excessive  muscular  metabolism. 

Regulation  of  Temperature  or  Thermotaxis. — What,  now,  is 
the  mechanism  by  which  the  balance  is  maintained  in  the  homoio- 
thermal  animal  between  heat -production  and  heat-loss  ?  In 
answering  this  question  we  have  to  recognise  that  both  of  these 
quantities  are  variable,  that  a  fall  in  the  production  of  heat  may 
be  compensated  by  a  diminution  of  heat-loss,  and  an  increase 
in  the  loss  of  heat  balanced  by  a  greater  heat-production. 

The  loss  of  heat  from  the  surfaces  of  the  body  may  be  regu- 
lated both  by  involuntary  and  by  voluntary  means.  It  is  greatly 
affected  b}^  the  state  of  the  cutaneous  vessels,  and  these  vessels 
are  under  the  influence  of  nerves.  A  cold  skin  is  pale,  and  its 
vessels  are  contracted.  In  a  warm  atmosphere  the  skin  is 
flushed  with  blood,  its  vessels  are  dilated,  its  temperature  is 
increased  ;  an  effort,  so  to  speak,  is  being  made  by  the  organism 
to  maintain  the  difference  of  temperature  between  its  surface 
and  its  surroundings  on  which  the  rate  of  heat-loss  by  radiation 
and  conduction  depends.  A  still  more  important  factor  in  man, 
and  in  animals  like  the  horse,  which  sweat  over  their  whole 
surface,  is  the  increase  and  decrease  in  the  quantity  of  water 
evaporated  and  of  heat  rendered  latent.  It  is  owing  to  the 
wonderful  elasticity  of  the  sweat-secreting  mechanism,  and  to 
the  increase  of  respiratory  activity  and  the  consequent  increase 
in  the  amount  of  watery  vapour  given  off  by  the  lungs,  that  men 
are  able  to  endure  for  days  an  atmosphere  hotter  than  the 
blood,  and  even  for  a  short  time  a  temperature  above  that  of 
boiling  water.  The  temperature  of  a  Turkish  bath  may  be  as 
high  as  650  to  8o°  C.  Blagden  and  Fordyce  exposed  themselves 
for  a  few  minutes  to  a  temperature  of  nearly  1270  C.  Although 
meat  was  being  cooked  in  the  same  chamber  by  the  heat  of  the 
air,  they  experienced  no  ill  effects,  nor  was  their  body-temperature 
even  increased.  But  a  far  lower  temperature  than  this,  if  long 
continued,  is  dangerous  to  life.  During  the  '  hot  waves, '  not  infre- 
quently experienced  in  summer  in  the  United  States,  hundreds 
of  persons  have  died  within  a  few  days  from  the  excessive  heat. 
It  is  stated  that  during  the  unusually  hot  summer  of  1819  the 


588  /    1/  l  \r  \i    OF  PHYSIOLOGY 

temperature  at  Bagdad  ranged  for  a  considerable  time  between 
co8  and  [20  1-  (42  i"  ('I  C),  and  there  was  greal  mortality. 
A  Him  li  higher  temperature  may  be  borne  in  dry  air  than  in  air 
saturated  with  watery  vapour.  A  shade  temperature  oi  too  I 
(377  C.)  in  the  dry  air  oi  the  South  African  plateaux  is  quite 
tolerable,  while  a  temperature  <>i  85  F.  (29*4  C.)  in  the  moisture- 
Laden  atmosphere  oi  Bombay  may  be  oppressive.  The  reason  is 
thai  in  dry  air  the  sweat  evaporates  freely  and  cools  the  skin, 
while  in  moist  air,  although  according  to  Rubner  the  loss  oi 
heat  by  radiation  and  conduction  is  increased,  the  loss  oi  heat 
by  evaporation  of  sweat  is  diminished  in  a  still  greater  degree. 
In  saturated  air  at  the  body-temperature  qo  loss  oi  heat  by 
perspiration  or  by  evaporation  from  the  pulmonary  surface  is 
possible  ;  the  temperature  of  an  animal  in  a  saturated  atmosphere 
it  350  to  400  C.  soon  rises,  and  the  animal  dies.  In  animals 
like  the  dog,  which  sweat  little  or  not  at  all  on  the  general  sur- 
face, the  regulation  of  the  heat  doss  by  respiration  is  relatively 
more  important  than  in  man. 

The  observations  of  Boycott  and  Haldane  in  a  deep  mine,  in  the 
incubating-room  of  a  laboratory,  and  in  a  Turkish  bath  illustrate 
the  important  influence  of  the  humidity  oi  the  air.  In  still  air  the 
body-temperature  rose  above  normal  when  the  wet -bulb  thermo- 
meter rose  above  310  C.  (88°  F.),  and  it  remained  normal  whal 
the  external  temperature  might  be  so  long  as  the  reading  of  the  wet- 
bulb  thermometer  did  not  exceed  that  level.  The  more  the  wet-bulb 
thermometer  rose  above  310  the  more  rapid  was  the  increase  in  the 
body-temperature.  In  moving  air  a  greater  degree  of  humidity 
could  be  borne  without  increase  in  the  body-temp<  rature,  which  did 
not  occur  till  the  temperature  shown  by  the  we1  bulb  thermometer 
exceeded  350  C.  The  great  increase  in  the  evaporation  of  sweat 
when  the  temperature  of  the  air  is  high  is  shown  by  the  observation 
that  on  a  warm  day  (dry  bulb,  79°  F.  ;  wet  bulb.  O75  F)  the  average 
loss  of  moisture  from  the  body  was  1,816  grammes  for  four  soldiers 
during  a  march  of  seven  miles,  while  on  a  cold  day  (dry  bulb.  4^  F.  ; 
wet  bulb,  38°  F.)  it  was  only  |  10  grammes  during  the  same  march  by 
the  same  men  (Pembrey). 

The  winter  fur  of  Arctic  animals  is  a  special  device  of  Nature 
to  meet  the  demands  of  a  rigorous  climate,  and  combat  a  ten- 
dency to  excessive  loss  of  heat.  The  experiments  of  Hdsslin. 
and  the  experience  of  squatters  in  Australia,  go  to  show  that 
even  domesticated  animals  have  a  certain  power  of  responding 
to  long-continued  changes  in  external  temperature  by  changes 
in  the  radiating  surfaces  which  affect  the  loss  of  heat.  It  is 
said  that  in  the  hot  plains  of  Queensland  and  New  South  Wales 
the  fleeces  of  the  sheep  show  a  tendency  to  a  progressive  decrease 
in  weight.  And  Hosslin  found  that  a  young  dog  exposed  for 
eighty-eight  days  to  a  temperature  of  50  (\  developed  a  thick 
coat  of  fine  woolly  hairs.  Another  dog  of  the  same  litter,  ex- 
posed for  the  same  length  of  time  to  a  temperature  of   ;i  5    to 


I  \  /  1/   II.    Ill     /  / 

i  .  had  a  much  scantier  covering.  I  lie  in<  reased  protection 
againsl  heat-loss  in  i  be  case  oi  I  lie  '  cooled  '  dog  was  not  suffi<  i<  m 
fully  t<'  compensate  for  the  Lowered  externa]  temperature.  Mm 
metabolism  that  is  to  say,  the  bieat-production — was  also 
increased.  And  although  the  food  was  exactly  the  same  for 
both  animals  in  quantity  and  quality,  the  dog  at  50  C.  put  on 
less  than  hall  as  much  iat  in  the  period  of  the  experiment  as 
the  '  heated  '  dog,  but  the  same  amount  of  '  flesh.' 

The  voluntary  factor  in  the  regulation  of  the  heat-loss  is  oi 
great  importance  in  man.  Clothes,  like  hair  and  oilier  natural 
coverings,  retard  the  loss  of  heat  from  the  skin  chiefly  by  main- 
taining a  zone  of  still  air  in  contact  with  it,  for  air  at  rest  is  an 
1  \i  eedingly  bad  conductor  of  heat.  A  man  clothed  in  the 
ordinary  way  has  two  or  three  concentric  air-jackets  around  him. 
The  air  in  the  intervals  between  the  inner  and  outer  garments 
is  of  importance  as  well  as  that  in  the  pores  of  the  clothes  them- 
selves ;  and  it  is  for  this  reason  that  two  thin  shirts  put  on  one 
above  the  other  are  warmer  than  the  same  amount  of  material 
in  the  form  of  a  single  shirt  of  double  thickness.  When  a  man 
feels  himself  too  hot  and  throws  off  his  coat,  he  really  removes 
one  of  the  badly  conducting  layers  of  air,  and  increases  the  rate 
of  heat-loss  by  radiation  and  conduction.  At  the  same  time 
the  water-vapour,  which  practically  saturates  the  layer  of  air 
next  the  skin,  is  allowed  a  freer  access  to  the  surface,  and  the 
loss  of  heat  by  the  evaporation  of  the  sweat  becomes  greater. 
The  power  of  voluntarily  influencing  the  heat-loss  must  be 
looked  upon  in  man  as  one  of  the  most  important  means  by 
which  the  equilibrium  of  temperature  is  maintained.  In  the 
lower  animals  this  power  also  exists,  but  to  a  much  smaller  extent. 
A  dog  on  a  hot  day  puts  out  its  tongue  and  stretches  its  limbs 
so  as  to  increase  the  surface  from  which  heat  is  radiated  and 
conducted.  The  mere  placing  of  a  rabbit  on  its  back,  with  its 
legs  apart,  may  cause  in  an  hour  or  two  a  fall  of  ic  to  2°  C.  in 
the  rectal  temperature.  The  power  of  covering  themselves  with 
straw  or  leaves,  of  burrowing  and  of  forming  nests,  may  be 
included  among  the  voluntary  means  of  regulation  of  the  heat- 
loss  possessed  by  animals.  A  man  opens  the  window  when  he 
is  too  hot,  and  pokes  the  fire  when  he  feels  cold.  Both  actions 
are  a  tribute  to  his  status  as  a  homoiothermal  animal,  and 
illustrate  the  importance  of  the  voluntary  element  in  the 
mechanism  by  which  his  temperature  is  controlled. 

The  production  of  heat,  like  the  loss,  is  to  a  certain  extent 
under  voluntary  control.  Rest,  and  especially  sleep,  lessens 
the  production  ;  work  increases  it.  The  inhabitants  of  the 
tropics,  human  and  brute,  often  tide  over  the  hottest  part  of 
the  day  by  a  siesta  ;  and  it  is  as  natural,  and  as  much  in  accord- 


59Q  /    MANUAL  OF  PHYSIOLOGY 

ance  with  physiological  laws,  that  a  man  overpowered  by  the 
heal  should  lie  down  as  it  is  that  he  should  walk  about  and 
stamp  his  feet  or  (dap  Ins  hands  on  a  cold  winter  morning.  In 
the  one  case  a  diminution,  in  the  other  an  increase,  in  the  heat- 
production  is  aimed  at  by  a  corresponding  change  in  the  amount 
of  muscular  contraction.  The  quantity  and  quality  oi  the  food 
also  influence  the  production  of  heat.  The  Eskimo,  who  revels 
in  train-oil  and  tallow-candles,  unconsciously  illustrates  the 
experimental  fact  that  the  heat  of  combustion  of  fat  is  high  ; 
the  rice  diet  of  the  ryot  of  the  Carnatic,  with  its  low  heat-equiva- 
lent, seems  peculiarly  adapted  to  the  dweller  in  tropical  lands. 
But  it  would  be  easy  to  attach  too  much  weighl  to  considerations 
such  as  these.  The  Arctic  hunter  eats  animal  fat,  and  the 
Indian  peasant  vegetable  carbo-hydrate,  not  only  because  fat 
has  a  high  and  carbo-hydrate  a  low  heat-equivalent,  but  because 
in  the  climate  of  the  Far  North  animals  with  a  thick  coating  of 
badly-conducting  fat  are  plentiful,  and  vegetable  food  scarce  ; 
whereas  in  the  river-valleys  of  India  Nature  favours  the  growth 
of  rice,  and  religion  forbids  the  killing  of  the  sacred  cow. 

The  production  of  heat  is  also  controlled  by  an  involuntary 
nervous  mechanism,  through  which  the  'chemical'  regulation 
of  the  body-temperature  is  achieved,  as  the  '  physical  '  regulation 
is  accomplished  by  the  nervous  mechanisms  that  control  the 
circulation,  the  sweat-glands,  and  the  respiratory  movements. 
It  is  a  matter  of  everyday  experience  that  cold  causes  involuntary 
shivering — involuntary  muscular  contractions — the  object  of 
which  seems  a  direct  increase  in  the  heat-production.  But 
besides  this  visible  mechanical  effect,  the  application  of  cold  to 
a  warm-blooded  animal,  when  not  carried  so  far  as  to  greatly 
reduce  the  rectal  temperature,  is  accompanied  by  a  marked 
increase  in  the  metabolism,  as  shown  by  an  increased  produc- 
tion of  carbon  dioxide  and  consumption  of  oxygen.  In  cold- 
blooded animals  like  the  frog  the  metabolism,  on  the  other 
hand,  rises  and  falls  with  the  external  temperature  ;  there  is 
no  automatic  mechanism  which  answers  an  increased  drain  upon 
the  stock  of  heat  in  the  body  by  an  increased  supply.  Or,  in 
the  light  of  recent  experiments,  we  ought  rather  to  say  that, 
although  the  rudiments  of  a  heat-regulating  mechanism  may  exist 
in  such  animals  as  the  frog,  the  newt,  and  even  the  earthworm 
(Vernon),  it  is  only  able  to  modify  to  a  certain  extent  the  effects 
of  changes  of  external  temperature,  not  to  balance  or  even 
override  them,  as  in  the  homoiothermal  animal.  The  warm- 
blooded animal  loses  its  heat-regulating  power  when  a  dose  oi 
curara  sufficient  to  paralyze  the  voluntary  muscles  is  given.  A 
curarized  rabbit,  kept  alive  by  artificial  respiration,  reacts  to 
changes  of  external  temperature  like  the  cold-blooded  frog. 
Now,  the  only  action  of  curara  adequate  to  account  for  this 


INIM  II.  Ill    I  I 

effed  is  its  power  of  paralyzing  the  motor  innervation,  and 
so  cutting  off  from  the  skeletal  muscles  impulses  which  in  the 
intact    animal    would    have    reached    them.      The   excitation    by 

cold  of  the  cutaneous  nerves,  or  some  of  them,  which  in  the 
unpoisoned  animal  is  reflected  along ^the -motor  nerves  to  the 
muscles,  and  causes  the  increase  of  metabolism,  is  now  blocked 
at  the  end  of  the  motor  path  ;  and  the  muscles,  the  great  heat- 
producing  tissues,  are  abandoned  to  the  direct  influence  of  the 
external  temperature  (Plhiger). 

How  is  it,  then,  that  nervous  impulses  from  the  skin  produce 
in  the  intact  animal  their  effect  upon  the  chemical  processes  in 
the  muscles  ?  We  know  that  the  heat-production  of  a  muscle 
is  greatly  increased  when  it  is  caused  to  contract  ;  but  it  has  not 
hitherto  been  possible  by  artificial  stimulation  to  demonstrate 
that  any  chemical  or  physical  effect  is  produced  in  a  muscle 
by  excitation  of  its  motor  nerve  unless  as  the  accompaniment 
of  a  mechanical  change.  When  the  gastrocnemius  of  a  frog 
poisoned  with  not  too  large  a  dose  of  curara  is  laid  on  a  resistance 
thermometer  (p.  664),  and  its  nerve  stimulated  from  time  to 
time  as  the  curara  paralysis  deepens,  heating  of  the  muscle  is 
observed  as  long  as,  and  only  as  long  as,  there  is  any  visible 
contraction.  The  gaseous  metabolism  of  a  rabbit  immersed  in 
a  bath  of  constant  temperature  may  sink  by  as  much  as  30  to 
40  per  cent,  when  curara  is  given.  One  obvious  cause  of  this 
is  the  complete  muscular  relaxation.  And  the  whole  secret  of 
the  regulation  of  the  heat-production  might  be  plausibly  supposed 
to  lie  in  the  bracing  effect  of  cold  upon  the  skeletal  muscles 
and  the  relaxing  effect  of  heat.  Indeed,  in  man  it  has  been 
observed  that  exposure  to  moderate  cold  causes  no  metabolic 
increase  when  shivering  is  prevented  by  a  strong  effort  of  the 
will  (Loewy).  Nevertheless,  the  explanation  is  inadequate  in 
the  case  of  small  animals,  such  as  guinea-pigs,  rabbits,  and  cats  ; 
for  very  great  changes  in  the  metabolism  may  be  brought  about 
by  external  cold  without  any  outward  token  of  increased  mus- 
cular activity.  In  a  man  also  a  fall  in  the  external  temperature 
from  230  to  150  C.  caused  a  certain  increase  in  the  output  of 
carbon  dioxide  (from  27' 9  to  32* 3  grammes  per  hour),  although 
no  shivering  was  observed.  As  the  temperature  of  the  air  is 
lowered,  the  point  is  soon  reached  at  which  shivering  can  no 
longer  be  suppressed,  and  then  it  is  neither  practicable  nor 
perhaps  very  important  to  distinguish  clearly  the  portion  of  the 
increased  heat-production  associated  with  the  visible  muscular 
contractions  and  the  portion  due  to  quickened  muscular  met- 
abolism without  contraction.  Lefevre  found  that  in  man  a 
marked  increase  in  the  heat-loss,  such  as  is  caused  by  immersion 
for  a  considerable  time  (one  to  three  hours)  in  cold  water  (at  a  tem- 
perature of   70  to  150  C),  was  accompanied  by  a  great  increase 


/   MANUAL  OF  PHYSIOLOGY 

in  the  production  of  heat,  so  that  the  axillary  temperature  tell 
comparatively  little  —  e.g.,  only  i°  C.  during  a  stay  of  three 
hours  in  a  bath  at  150  C.  With  short  periods  ot  immersion,  a 
characteristic  reaction  occurs  after  the  person  comes  out  of  the 
hath.  The  rectal  temperature  falls  to  a  minimum,  which  is 
reached  in  twenty  to  thirty  minutes  after  exit  from  the  bath, 
and  then  gradually  returns  to  normal.  This  fall  of  internal 
temperature  is  due  to  the  heating  of  the  superficial  portions  of 
the  body  at  the  expense  of  the  central  portions.  By  training, 
the  fall  of  temperature  is  greatly  lessened,  the  heat-regulating 
mechanism  acquiring,  so  to  speak,  with  practice,  greater  prompti- 
tude and  precision  of  adjustment. 

It  must  be  admitted,  then,  that — especially  in  the  smaller 
homoiothermal  animals — the  metabolic  changes  normally  going 
on  in  the  resting  muscles  may  be  reflexly  increased  without  the 
usual  accompaniment  of  mechanical  contraction,  and  that  such 
an  increase  of  '  chemical  tone  '  is  an  important  means  by  which 
the  temperature  is  regulated.  It  is  possible  that  other  organs 
besides  the  muscles  may  be  concerned,  though  not  to  a  sufficient 
extent  to  secure  the  due  regulation  of  temperature  during 
curara  paralysis.  It  is  obvious  that  in  man,  whose  environment 
is  so  much  under  his  own  control,  a  mere  automatic  regulation 
is  less  required  than  in  the  inferior  animals,  and  that  a  regulative 
power,  if  present  in  rudiment,  would  tend  to  '  atrophy  '  l>v 
disuse,  or,  at  all  events,  to  become  less  sensitive  to  slight  changes 
of  temperature.  In  the  larger  animals,  again,  mere  bulk  is  an 
important  safeguard  against  any  sudden  change  of  internal 
temperature.  To  reduce  the  temperature  of  a  horse  or  an 
elephant  by  i°,  a  considerable  quantity  of  heat  must  be  lost, 
while  a  very  slight  loss  would  suffice  to  cool  a  mouse  by  that 
amount.  Not  only  so,  but  the  surface  by  which  heat  is  lost  is 
greater  in  proportion  to  the  mass  of  the  body  in  small  than  in 
large  animals.  The  power  of  rapidly  increasing  the  heat-pro- 
duction to  meet  a  sudden  demand  is,  therefore,  far  more  im- 
portant to  the  mouse  than  to  the  horse  ;  and  the  fact  (p.  549) 
that  the  metabolism  of  an  animal  varies  approximately  as  its 
surface,  and  not  as  its  mass,*  is  an  illustration  of  the  nice  adjust- 
ment by  which  heat-equilibrium  is  maintained. 

*  The  relation  between  mass  (M)  and  surface  (S)  in  man  is  approxi- 

mately    given    by    the    equation   — ^=-    =K,    and    the    relation    between 

surface,  mass,  length  of  body   (L),  and  circumference  of  chest  (C)   just 
above  the  nipples  in  the  '  mean  '  position  of  respiration,  by  the  equation 

>x  '     '  V      =K'.     M  is  expressed  in  grammes,  S  in  square  centimetres, 

MLC 
L  and  C  in  centimetres.     K  is  a  constant  whose  mean  value  is  12*3,  and 
K'  a  constant  whose  mean  value  is  45  (Meeh). 


I  \7  1/   1/     ///     I  / 


The  following  table  shows  bow  close  is  the  agreement  in  the  heal 
production  per  unit  of  surface  calculated  by  the  Formula  for  animals 
nt  different  species  and  very  different  body-weight. 


Caloi  ies  pi  i  dui  ed  in  -'.|  1  [ours. 

\\  i  ight  in 

Pei  Kilo 

Metre 

i.f  Sui 

Horse 

.          . 

■I  1  1 

i  i'3 

948 

.Man    - 

- 

- 

&4'3 

32M 

[,042 

Dog    - 
Rabbit 

without  ears)  - 

23 

5i"5 
75* 

1.(13*. 
'"  7 

Fowl  - 

.Mouse 

- 

_ 

2 

o  •  o  1 8 

71  0 

2I2'0 

943 
1,188 

The   next    table,    calculated    by    Rubner    from   the   quantity    of 

tissue-protein  and  fat  consumed,  gives  the  relative  intensity  of  heat- 
production  in  fasting  dogs  of  different  sizes  : 


Body-weight. 

Calories  per  Kilo 
per  Hour 

31   K 

24 

20 
18 
10 

6 

3 

1-58 
I-70 

1-87 

192 

255 

2-84 

378 

Rubner  has  found  that  animals  abundantly  fed  do  not  show  so 
much  change  in  the  production  of  heat  when  the  external  tempera- 
ture is  varied  as  starving  animals,  perhaps  because  the  thicker  coat 
of  subcutaneous  fat  so  steadies  the  rate  at  which  heat  is  lost  that  it 
becomes  easy  for  the  vaso-motor  mechanism  alone  to  hold  the 
balance  between  loss  and  production.  In  well-fed  animals  it  is  the 
heat-loss  which  is  chiefly  affected,  and  it  may  be  that  this  has  some- 
thing to  do  with  the  explanation  of  Loewy's  results  on  man  (p.  591). 

Lorrain  Smith  discovered  the  interesting  fact  that  after  removal 
of  the  thyroid  glands  (in  cats),  the  heat-production,  as  measured 
by  the  amount  of  carbon  dioxide  given  off,  is  more  sensitive  to 
changes  of  external  temperature  than  in  the  normal  animal. 

But  it  must  not  be  imagined  that  the  production  of  heat  can  be 
increased  indefinitely  to  meet  an  increased  heat-loss.  The  organism 
can  make  considerable  efforts  to  protect  itself,  but  the  loss  of  heat 
may  easily  become  so  great  that  the  increase  of  metabolism  fails  to 
keep  pace  with  it.  The  internal  temperature  then  falls,  and  if  the 
fall  be  not  checked,  the  animal  dies.  A  mammal,  when  cooled  arti- 
ficially to  the  temperature  of  an  ordinary  room  (150  to  200  C),  does 
not  recover  of  itself,  but  may  be  revived  by'the  employment  of  arti- 
ficial respiration  and  hot  baths,  even  when  the  rectal  temperature 
has  sunk  to  50  to  10°  C.     If  the  skin  of  a  rabbit  be  varnished,  and 

38 


594  A   MANUAL  OF  PHYSIOLOGY 

the  air  which  it  is  the  function  of  the  fur  to  maintain  at  rest  around  it 
be  thus  expelled,  the  animal  dies  of  cold,  unless  the  loss  of  heat  is 
artificially  prevented.  If,  without  varnishing  at  all,  tin-  greater 
portion  of  the  skin  of  a  rabbit  or  guinea-pig  be  closely  clipped  or 
shaved,  similar  phenomena  are  observed.  Prevented  from  covering 
itself  with  straw,  the  animal  dies,  sometimes  in  twenty-four  hours. 
The  radiation  from  the  skin,  as  measured  by  the  resistance-radio- 
meter (p.  574),  is  greatly  increased  ;  the  animal  shivers  constantly, 
and  the  rectal  temperature  falls.  Placed  in  a  warm  chamber  before 
the  temperature  in  the  rectum  has  fallen  below  250,  the  animal 
recovers  perfectly.  If  the  fall  is  allowed  to  go  on,  it  dies.  If  it 
is  kept  from  the  first  in  the  warm  chamber,  no  fall  of  temperature 
occurs.  When  the  increased  loss  of  heat  is  less  perfectly  compen- 
sated— when,  for  example,  the  animal  is  left  at  the  ordinary  tem- 
perature, but  supplied  with  sufficient  straw  to  cover  itself,  or  allowed 
to  crouch  among  other  animals — a  curious  phenomenon  may  some- 
times be  seen.  The  rectal  temperature,  which  has  fallen  sharply 
during  the  operation,  remains  subnormal  (as  much  as  2°  to  30  below 
the  ordinary  temperature)  for  a  time  (a  week  or  more),  and  then 
gradually  rises  as  the  coat  again  begins  to  grow.  The  meaning  of 
this  seems  to  be  that  the  power  of  regulating  the  temperature  by 
increasing  the  metabolism  is  overtasked  by  the  removal  of  the 
natural  protective  covering,  unless  the  escape  of  heat  is  artificiallv 
diminished.  When  the  loss  of  the  fur  is  entirely  compensated,  no 
fall  of  temperature  occurs  ;  when  it  is  not  compensated  at  all.  the 
animal  cools  till  it  dies  ;  when  it  is  partially  compensated,  the 
increased  metabolism  may  only  suffice  to  maintain  a  temperature 
lower  than  the  normal,  although  constant  muscular  contractions 
(shivering)  are  brought  in  to  supplement  the  efforts  of  the  regulative 
chemical  processes. 

Hitherto  we  have  only  spoken  of  a  reflex  regulation  of  the 
heat-production  called  into  play  by  external  cold.  It  might 
be  supposed — and,  indeed,  has  often  been  assumed — that  heat 
would  lessen  the  metabolism,  as  cold  increases  it  ;  and  there  are 
indications  that  in  the  smaller  animals  this  is  the  case,  although 
the  influence  of  heat  seems  to  be  much  smaller  than  the  influence 
of  cold.  But  neither  experimental  results  nor  general  reasoning 
have  as  yet  shown  that  in  man,  either  in  the  tropics  (Eykman) 
or  in  the  north  temperate  zone  (Loewy),  the  chemical  tone  is 
diminished  by  a  rise  of  external  temperature  much  above  the 
mean  of  an  ordinary  English  summer,  apart  from  the  effect  of 
the  muscular  relaxation  which  heat  induces.  In  a  man,  indeed, 
at  rest  in  a  hot  atmosphere,  the  production  of  carbon  dioxide 
and  consumption  of  oxygen  are,  if  anything,  greater  than  at 
the  ordinary  temperature.  The  regulation  of  temperature  in 
an  environment  warmer  than  the  normal  seems,  in  fact,  to  be 
brought  about  more  by  an  increase  in  the  loss  than  a  decrease 
in  the  production  of  heat.  Evaporation  from  the  skin  and  lungs 
is  an  automatic  check  upon  overheating  as  important  as  the 
involuntary  increase  of  metabolism  upon  excessive  cooling. 

While  it  is  known  that  the  skeletal  muscles,  and  perhaps  the 


I  MM  \L  HEAT  595 

glands  and  other  tissues,  are  at  one  end  of  the  reflex  arc  by 
which  the  impulses  pass  that  regulate  the  temperature  through 
the  metabolism,  we  are  as  yet  ignorant  of  the  precise  paths  by 
which  the  afferent  impulses  travel,  of  the  nerve-centres  to  which 
they  go,  and  even  of  the  end-organs  in  which  they  arise.  There 
arc  nerves  in  the  skin  which  minister  to  the  sensation  of  tempera- 
ture (Chap.  XIII.).  A  change  of  temperature  is  their  '  ade- 
quate '  and  sufficient  stimulus  ;  and  it  is  a  tempting  hypothesis 
that  these  are  the  afferent  nerves  concerned  in  the  reflex  regula- 
tion of  temperature — that  impulses  carried  up  by  them  to  some 
centre  or  centres  in  the  brain  or  cord  are  reflected  down  the 
motor  nerves  to  control  the  metabolism  of  the  skeletal  muscles, 
and  down  the  vaso-motor  nerves  to  control  the  loss  of  heat  from 
the  skin. 

It  is  more  than  doubtful,  however,  whether  the  whole  chemical 
regulation  can  be  attributed  to  such  stimuli.  For  it  has  been 
found  that  the  relation  between  heat-production  and  extent  of 
surface  in  animals  (guinea-pigs)  of  different  size  is  unaltered  when 
the  air  temperature  is  made  so  nearly  the  same  as  that  of  the  skin 
that  the  temperature  nerves  can  hardly  be  supposed  to  be  excited. 

There  is  some  evidence  that  the  bioplasm — the  living  substance — of 
different  animals,  even  when  the  external  conditions  are  the  same, 
may  differ  specifically  in  the  average  intensity  of  metabolism  to 
which  it  is  pitched.  When  exposed  to  a  temperature  about  equal 
to  that  of  warm-blooded  animals,  the  green  lizard  (Lacerta  viridis) 
and  the  bull-frog,  which  live  in  the  temperate  zone,  and  for  which 
a  temperature  of  370  C.  is  highly  abnormal,  double  their  heat-pro- 
duction, and  soon  die.  Tropical  poikilothermal  animals,  such  as  the 
alligator,  also  double  their  heat-production,  but  the  highest  values 
reached  are  only  one-half  that  of  the  lizard  at  250  C.  Apparently 
the  bioplasm  of  the  tropical  animals  has  adapted  itself  to  a  high 
external  temperature,  and  works  very  economically  even  at  the 
highest  temperatures  (Krehl). 

Heat  Centres. — It  is  known  that  certain  injuries  of  the  central 
nervous  system  are  related  to  disturbance  of  the  heat-regulating 
mechanism.  Puncture  of  the  median  portion  of  the  corpus 
striatum  in  the  rabbit  by  a  needle  thrust  through  a  trephine  hole 
in  the  skull  is  followed  in  a  few  hours  by  a  rise  of  temperature  in 
the  rectum  (i°  to  2°),  and  still  more  in  the  duodenum,  which  is  nor- 
mally the  hottest  part  of  the  body  in  this  animal.  The  heat-pro- 
duction, the  respiratory  exchange,  and  the  nitrogen  excretion  are 
increased.  These  phenomena  may  last  for  several  days  (Ott, 
Richet,  Aronsohn,  and  Sachs),  and  are  due  to  stimulation  of  the 
portions  of  the  brain  in  the  immediate  neighbourhood  of  the  injury. 
Electrical  stimulation  of  this  region  has  a  similar  effect.  When  the 
temperature  has  returned  to  normal,  a  fresh  puncture  may  again 
cause  a  rise. 

Some  observers  hold  that  the  chief  seat  of  the  increased  metabolism 
is  the  skeletal  muscles,  others  the  liver.  The  question  turns 
largely  upon  the  success  of  the  puncture  experiment  after  the 
previous  administration  of  curara  on  the  one  hand,  and  of  strychnine 
on  the  other.  For  curara  cuts  out  the  motor  innervation  of 
the    skeletal    muscles,    and    strvchnine    convulsions    exhaust    the 

38—2 


596  •/    MANUAL  OF  PHYSIOLOGY 

store  of  hepatic  glycogen.  Certain  investigators  have  found  that 
after  an  adequate  dose  of  curara  no  puncture  fever  can  be  obtained, 
and  they  Locate  the  increased  metabolism  associated  with  the  fever 

in  the  muscles.  Others  maintain  that  even  after  curara  the  puncture 
is  followed  by  fever,  but  is  not  followed  by  fever  if  strychnine  has 
first  been  given.  They  accordingly  conclude  that  the  rapid  com- 
bustion of  the  glycogen  (or  the  dextrose  derived  from  it)  is  the 
primary  factor  in  the  increased  metabolism.  It  may  be  pointed  out, 
however,  that  neither  experiment  is  a  crucial  test.  For  if  strychnine 
reduces  the  liver  glycogen,  it  also  reduces  the  glycogen  of  the  muscles. 
And  if  in  the  puncture  fever  the  liver  glycogen  is  transformed  into 
dextrose  more  rapidly  than  usual,  the  dextrose  is  probably  in  great 
part  used  up  in  the  muscles  more  rapidly  than  usual,  else  it  would 
appear  in  the  urine.  The  effect  of  strychnine  on  the  puncture  fever, 
then,  is  no  proof  that  the  muscles  are  not  essentially  concerned  in  it. 
On  the  other  hand,  the  alleged  absence  of  the  fever  after  curara  is 
not  sufficient  to  show  that  the  muscles  arc  alone  concerned.  I  or 
curara  causes  a  lowering  of  the  body-temperature,  which,  if  it  be 
not  overcompensated,  may  mask  the  fever.  The  positive  result 
of  the  puncture  in  curarized  animals,  which  some  observers  say  they 
have  obtained,  would,  if  confirmed,  be  important  evidence  that  the 
primary  effect  is  not  on  the  muscles,  or,  at  least,  not  solely  on  them, 
but  would  not  prove  that  it  is  on  the  liver.  That  the  liver  is  con- 
cerned, however,  is  more  directly  indicated  by  the  fact  that  during 
the  puncture  fever  the  liver  continues  to  be  what  it  is  under  normal 
conditions,  the  warmest  organ  in  the  body,  warmer  than  the  blood 
in  the  root  of  the  aorta  by  about  i  °  C.  The  most  probable  conclusion 
is  that  the  increased  production  of  heat  in  this  form  of  experimental 
fever  is  due  to  an  increased  metabolism  of  carbo-hydrate  (glycogen) 
both  in  the  liver  and  in  the  muscles. 

Injury  to  various  portions  of  the  cortex  cerebri  in  the  dog  and 
other  animals,  and  lesions  of  the  pons,  medulla  oblongata  and  cord 
in  man  may  also  be  followed  by  increase  of  temperature.  When  the 
spinal  cord  is  cut  below  the  level  of  the  vaso-motor  centre,  the 
increased  loss  of  heat  from  the  skin  due  to  dilatation  of  the  cutaneous 
vessels  masks  any  increase  of  the  heat-production  which  may 
possibly  have  taken  place,  and  the  internal  temperature  falls  ;  but 
if  the  loss  of  heat  is  diminished  by  wrapping  the  animal  in  cotton- 
wool the  temperature Jrmay  rise.  From  such  phenomena  it  has  been 
surmised  that  certain  'centres  '  in  the  brain  have  to  do  with  the 
regulation  of  temperature  by  controlling  the  metabolism  vol  tin- 
tissues  ;  that  they  cause  increased  metabolism  when  the  internal 
temperature  threatens  to  sink,  diminished  metabolism  when  it 
tends  to  rise.  The  cutting  off,  it  is  said,  of  the  influence  of  the 
'  heat  centres  '  by  section'of  the  paths  leading  from  them  allows  the 
metabolism  of  the  tissues  to  run  riot,  and  the  temperature  to  increase. 

The  behaviour  of  hibernating  mammals,  such  as  the  marmot, 
dormouse,  hedgehog,  and  bat,  is  of  interest  in  connection  with 
the  temperature  regulation.  In  the  active  waking  state  these 
animals  are  homoiothermal,  but  in  profound  winter  sleep  they 
are  poikilothermal,  the  body-temperature  rising  and  falling 
with  that  of  the  air.  The  rectal  temperature  may  be  as  low  as 
2°  C.  There  is  an  intermediate  state  in  which  the  animal  is 
partially  awake,  though  inactive,  and  its  temperature  is  much 


I.Y/.V  XL   III    I  /  S97 

t ».  1< >w  the  normal,  1ml  considerably  above  that  of  its  environ- 
ment. In  this  condition  it  lias  an  imperfecl  t  Ik  rmotaxis,  some- 
thing like  that  of  an  ordinary  mammal  (including  the  human 
infant)  in  the  period  of  immaturity,  immediately  after  birth. 
When  the  hibernating  mammal  awakes  the  rise  of  temperature 
is  enormous  and  abrupt.  The  temperature  of  a  dormouse  rose 
in  an  hour  from  13*5°  C.  to  3570  C,  and  that  of  a  bat  in  fifteen 
minutes  from  17"  C.  to  340  C.  (lYmbrey). 

Fever  is  a  pathological  process  generally  caused  by  the 
poisonous  products  of  bacteria,  and  characterized  by  a  rise  of 
temperature  above  the  limit  of  the  daily  variation  (p.  605). 
It  is  further  associated  with  an  increase  in  the  rate  of  the  heart 
and  the  respiratory  movements,  and  a  diminution  in  the  alkalies 
and  carbon  dioxide  of  the  blood.  The  total  excretion  of  nitrogen 
is  increased,  at  least  in  proportion  to  the  amount  of  protein 
ingested,  indicating  an  increase  in  the  consumption  of  tissue- 
protein.  The  distribution  of  the  nitrogen  among  the  urinary 
constituents  is  altered.  The  ammonia  (in  the  form  of  ammonium 
salts  of  organic  acids),  the  uric  acid,  and  to  a  smaller  extent 
the  kreatinin  (Leathes),  are  increased,  while  the  urea  is  relatively 
decreased,  even  when  its  absolute  amount  is  greater  than  normal. 
Kreatin,  which  is  not  normally  present  in  urine,  unless  the  food 
contains  it,  may  also  appear  in  fever  (Shaffer).  It  has  been 
suggested  that  the  proximate  cause  of  fever  is  the  action  of 
bacterial  poisons  or  of  other  substances  on  the  '  heat  centres,' 
and  that  antipyretics,  or  drugs  which  reduce  the  temperature 
in  fever,  do  so  by  restoring  the  centres  to  their  normal  state,  by 
preventing  the  development  of  the  poisons,  aiding  their  elimina- 
tion, or  antagonizing  their  action.  In  favour  of  this  view,  it 
has  been  stated  that  when  the  basal  ganglia  are  cut  off,  by 
section  of  the  pons,  from  their  lower  nervous  connections,  fever 
is  no  longer  produced  by  injection  of  cultures  of  bacteria  which 
readily  cause  it  in  an  intact  animal,  while  antipyrin  has  no 
influence  upon  the  temperature  (Sawadowski).  But  some 
observers  have  been  unable  to  find  any  clear  evidence  of  the 
existence  of  '  heat  centres  ' — that  is,  of  localized  portions  of 
the  central  nervous  system  specially  concerned  in  the  regulation 
of  the  body-temperature.  And  while  it  is  almost  certain  that 
some  pyrogenic  or  fever-producing  agents — cocaine,  e.g. — act 
indirectly,  through  the  brain  or  cord,  it  is  quite  possible  that 
others  affect  directly  the  activity  of  the  tissues  in  general,  just 
as  some  antipyretics  or  fever-reducing  agents,  such  as  quinine, 
act  immediately  upon  the  heat-forming  tissues,  so  as  to  diminish 
their  metabolism,  while  others,  like  antipyrin,  affect  them 
through  the  nervous  system.  Quinine  has  no  influence  upon 
'  puncture  '  fever  in  rabbits.     A  still  more  important  action  of 


598 


A   .U  ixr  II.  OF  PHYSIOLOGY 


antipyrin,  and  the  group  oi  antipyretics  to  which  il  belongs,  is 
the  increase  in  the  heat-loss  which  they  bring  about  by  the 
dilatation  oi  the  bloodvessels  of  the  skin.  This  effecl  is  also 
produced  through  the  nervous  system. 

Fever  is  a  condition  so  interesting  from  a  physiological  point 
nt  view,  and  of  such  importance  in  practical  medicine,  that  it 
will  be  well  to  consider  a  little  more  closely  the  possible  ways 
in  which  a  rise  of  temperature  may  occur.  It  must  not  be  for- 
gotten that  the  febrile  increase  of  temperature  is  always  accom- 
panied by  other  departures 
from  the  normal,  and  that 
all  t  he  fundamental  febrile 
<  hanges  may  even,  in 
tain  cases,  be  present  with- 
out elevation,  and  even 
with  diminution  ot  tem- 
perature. But  here  we 
have  only  to  do  with  the 
disturbance  of  the  normal 
equilibrium  between  the 
loss  and  the  production  of 

heat  ;  and  it  is  evident  that 
any  of  the  five  conditions 
illustrated  in  the  diagram 
(Fig.  199)  may  give  rise  to 
an  increase  of  temperature. 
It  is  not  necessary  to  dis- 
cuss whether  cases  of  fever 
can  actually  be  found  to 
illustrate  every  one  of 
these  possibilities.  It  is 
probable  that  not  infre- 
quent ly  diminished  loss  and 
increased  production  may 
be  both  involved  ;  and  it 
ought  to  be  remembered 
that  the  healthy  standard  with  which  the  heat-production  oi  a 
fever  patient  should  be  compared  is  not  that  of  a  man  doing  hard 
work  on  a  full  diet,  but  that  of  a  healthy  person  in  bed,  and  on 
the  meagre  fare  of  the  sick-room.  When  this  is  kept  in  view, 
the  comparatively  low  heat -production  and  respiratory  exchange 
which  have  sometimes  been  found  in  fever  cease  to  excite  sur- 
prise. But  in  any  case,  no  mere  change  in  the  relative  propor- 
tions of  heat  formed  and  lost  is  sufficient  to  explain  the  febrile 
rise  of  temperature.  That  an  increase  in  heat-production  is  not 
of  itself  enough  to  produce  fever  is  proved  by  the  fact  that  severe 


Fig.  199. — Diagram  to  show  the  Possible 
Relations  between  Heat-production 
and  Heat-loss  in  Fever. 


AN1M  //.  ///■  '  / 

muscular  work,  which  increases  the  metabolism  more  than 
high  fever,  only  causes  in  a  healthy  man  a  rise  of  about  i°  C. 
in  the  rectal  temperature.  When  the  work  is  over,  the  tempera- 
ture comes  rapidly  back  to  normal.  The  essence  of  the  change 
in  fever  is  ;i  derangement  of  the  mechanism  by  which  in  the  healthy 
body  excess  or  defect  of  average  metabolism,  or  of  average  heat- 
loss,  is  at  once  compensated  and  the  equilibrium  of  temperature 
maintained. 

This  derangement  only  lasts  as  long  as  the  temperature  is 
rising.  When  it  becomes  stationary  at  its  maximum  we  have 
again  adjustment,  again  equality  of  production  and  escape  of 
heat  ;  but  the  adjustment  is  now  pitched  for  a  higher  scale  of 
temperature.  A  rough  analogy,  so  far  as  one  part  of  the  pro- 
cess is  concerned,  may  be  found  in  the  behaviour  of  the  ordinary 
gas-regulator  of  a  water-bath.  It  can  be  '  set  '  for  any  tempera- 
ture. That  temperature,  once  reached,  remains  constant  within 
narrow  limits  of  oscillation  ;  but  the  regulator  can  be  equally 
well  adjusted  for  a  higher  or  a  lower  temperature.  It  is,  how- 
ever, important  to  note  that  the  equilibrium  is  more  unstable  in 
fever  than  in  health,  so  that  changes  of  external  temperature 
more  easily  depress  or  increase  the  temperature  of  a  fever  patient 
than  of  a  healthy  man. 

Rosenthal  has  concluded  from  calorimetric  observations  that, 
in  the  first  stage  of  fever,  while  the  temperature  is  rising,  there 
is  always  increased  retention  of  heat.  Maragliano  actually 
found  evidence,  by  means  of  the  plethysmograph,  that  the 
cutaneous  vessels  are  at  this  stage  constricted,  and  that  the 
constriction  may  even  precede  the  rise  of  temperature.  Both 
observations  lend  support  to  the  famous  '  retention  '  theory  of 
Traube.  In  the  great  majority  of  cases  the  production  of  heat 
is  also  increased,  on  the  average  by  20  to  30  per  cent,  of  the 
normal  production  of  a  resting  man.  The  increase  may 5 be 
much  greater  during  the  chill  which  ushers  in  so  many  infections 
on  account  of  the  muscular  contractions  in  shivering.  During 
the  period  of  rising  temperature  the  production  of  heat  is  not 
necessarily  increased.  At  the  height  of  the  fever  there  is  often, 
though  apparently  not  always,  an  increase  in  the  heat-production. 
After  the  crisis,  while  the  fever  is  subsiding,  the  rate  at  which 
heat  is  being  lost  rises  sharply.  As  to  the  explanation  of  the 
increase  of  metabolism  in  fever,  and  especially  of  the  increased 
metabolism  of  tissue-protein,  various  views  have  been  held. 
Some  have  gone  so  far  as  to  say  that  the  increase  is  merely  the 
consequence,  not  the  cause,  of  the  rise  of  temperature.  But  the 
rebutting  evidence  which  has  been  brought  against  this  view  is 
strong  and,  indeed,  overwhelming.  It  is  perfectly  true  that, 
when  the  temperature  of  the  body  is  artificially  raised  by  pre- 


6oo  ./   MANUAL  OF   PHYSIOLOGY 

venting   the   free   loss  oi    heal    for  a  sufficient    time   (so-called 
physiological   fever),  the  destruction   of  protein   is  augmented. 
\    asting  dog  whose  temperature  was  increased  to  \>>   or  41    < 
for  twelve  hours  eliminated  37  per  cent,  inure  nitrogen  than  when 
the    body-temperature  was  normal.     But   this  increase  in  the 
protein  metabolism  could  be  entirely  prevented  by  giving  the 
animal    a    sufficient    amount    of   carbo-hydrate.      Similar    results 
have  been  obtained  in  man.     The  carbon  dioxide  excretion  and 
oxygen  absorption  are,  of  course,  also  markedly  increased.  Bui  the 
increase  in  the  nitrogt  n  excretion  is  often  much  greater  in  fever 
than  any  increase  which  can  he  broughl   about   by  artificially 
raising  the  temperature  of  a  healthy  individual  l>v  means  of  hot 
hat  lis.     A  typhoid  patient  was  found  to  lose  io*8  grammes  of 
nitrogen  a  day  (corresponding  to  318  grammes  of  muscle]  during 
eight  days  of  fever  (F.  Miiller).     A  portion  of  the  loss  of  nitrogen 
on  the  routine  fever  regimen  maybe  due  to  the   tact    that   the 
ordinary   typhoid   patient   is  really   on   a   semi-starvation   diet, 
the  heat-equivalent  of  which  is  not  much  more  than  half  his 
heat-production.     Yet   it  has  not  been  found  possible  to  com- 
pletely prevent  the  loss  of  nitrogen  by  putting  the  fever  patient 
on  a  diet  rich  in  protein,  or  on  a  diet   containing  a  moderate 
amount   of   protein   with   a   large   quantity   of    fat    and   carbo- 
hydrate, even  when  the  total  heat-value  of  the  diet  is  much  in 
excess  of  the  32  or  ^3  calories  per  kilo  of  body-weight  which 
corresponds  to  the  heat-production  of  a  resting  man.     Another 
suggestive  fact  is  that  the  excessive  excretion  of  nitrogen  does 
not  run  parallel  with  the  rise  of  temperature  in  fever,   but  is 
often  most  marked  after  the  crisis.     During  the  stage  of  defer- 
vescence an  enormous  amount  of  urea  is  sometimes  given  off. 
In  a  case  of  typhus,  in  the  mixed  urine  of  the  third  and  fourth 
days  after  the  crisis,   no  less  than   160  grammes  of  urea   was 
found  (Naunyn),  or  nearly  three  times  the  normal  amount  for 
a  man  on  full  diet.     Again,  when  fever  is  caused  by  the  injection 
of  bacteria  or  their  products,  the  increase  in  the  carbon  dioxide 
eliminated  and  oxygen  consumed  occurs  even  when   the  tem- 
perature  is   prevented    from    rising   by   cold    baths.     It    seems 
perfectly  clear,  then,  that  the  increase  of  metabolism  is,  in  many 
cases  at  least,  a  primary  phenomenon  of  fever.     Its  course  ami 
incidence,  falling  as  it  does  so  largely  upon  the  proteins,   the 
steady  loss  of  tissue  nitrogen,  and  the  inability  of  the  tissues  to 
recoup  their  losses  from  the  protein  of    the  food  or  to  shield 
their   own    protein    by   burning  more  carbo-hydrate  or  fat,  all 
suggest  that    the  cells  are  poisoned  by  toxic  products  of  the 
infective  process.     The  poisoned   bioplasm    falls  an   easy  prey 
to  the  hydrolyzing  and  oxidizing  agents  always  present  in  the 
tissues.      It  breaks  down  more  rapidly  and  builds  itself  up  more 


i xi  1/  1/   ///■  ;  /  '<"' 

slowly    than    aormal    bioplasm.     Tins   increased,  and    to   some 
.Aleut  perverted,  metabolism,  far  from  being  occasioned  by  the 
febrile  temperature,  is  quite  probably  the  cause  <>i  the  thermo 
regulative  upsel  which  we  call  fever.     For  Mandel  has  shown 

hat  one  of  the  I'm  in  bases  (xantbin)  causes  fever  in  monkeys  ; 
(_■)  that  the  purin  bases  in  the  urine  are  increased  both  in  infective 
lexers  and  the  so-called  aseptic  or  surgical  lever  that  is,  in 
cases  where  the  temperature  rises  alter  such  injuries  as  extensive 
crushing  of  tissues  without  infection.  There  is  a  constant 
relation  between  the  height  of  the  fever  and  the  quantity  oi 
purin  bases  excreted.  The  source  of  the  purin  bases  in  aseptic 
fever  is  presumably  the  autolysis  of  the  injured  tissue,  from 
which  they  pass  into  the  blood  without  being  oxidized  to  uric 
acid.  The  xanthin  fever  can  be  prevented  by  salicylates,  though 
not  by  antipyrin. 

It  remains  to  ask  whether  the  rise  of  temperature  is  anything 
more  than  a  superficial  and,  so  to  speak,  an  accidental  circum- 
stance. The  orthodox  view  for  many  ages  has  undoubtedly  been 
that  the  increase  of  temperature  is  in  itself  a  serious  part  of  the 
pathological  process,  a  symptom  to  be  fought  with  and,  if 
possible,  removed.  And,  indeed,  it  is  not  denied  by  anyone 
that  the  excessive  rise  of  temperature  seen  in  some  cases  of 
febrile  disease  (to  430  C,  or  even  to  450)  is,  apart  from  all  other 
changes,  a  most  imminent  danger  to  life,  unless,  as  is  sometimes 
the  case  (in  influenza,  e.g.,  where  a  temperature  of  440  has  been 
observed),  the  high  temperature  lasts  only  a  short  time.  Experi- 
mental heat  paralysis,  a  condition  in  which  all  voluntary  and 
reflex  movements  are  abolished,  is  produced  in  frogs  by  raising 
the  internal  temperature  to  about  340  C.  On  cooling,  the  animal 
recovers.  A  similar  condition  can  be  induced  in  mammals,  but, 
of  course,  at  a  higher  temperature.  The  central  nervous  system 
succumbs  before  the  peripheral  structures.  The  superior  cervical 
ganglion  in  the  cat  or  rabbit  loses  the  power  of  transmitting 
nerve  impulses  at  500  C.  But  some  evidence  has  been  brought 
forward,  mostly  from  the  field  of  bacteriology,  to  support  the 
idea  that  in  infective  processes  the  rise  of  temperature  is  of  the 
nature  of  a  protective  mechanism,  that  the  fever  is,  indeed,  a 
consuming  fire,  but  a  fire  that  wastes  the  body,  to  destroy  the 
bacteria.  The  streptococcus  of  erysipelas,  for  example,  does 
not  develop  at  390  to  400  C,  and  is  killed  at  39-5°  to  410  C,  and 
erysipelas  infections  in  rabbits  are  less  virulent  if  the  body-tem- 
perature be  artificially  raised.  Anthrax  bacilli,  kept  at  420  to 
43°  C.  for  some  time,  are  attenuated,  and  when  injected  into 
animals  confer  immunity  to  the  disease.  Heated  for  several 
days  to  410  to  420  C,  pneumococci  render/rabbits  immune  to 
pneumonia,  and  in  rabbits  in  which  '  puncture  '  fever  has  been 


/    1/  INUAL  OF  PHYSIOLOGY 

induced  pneumococcus  infections  run  a  milder  course.  These 
bacteriological  results  arc  supported  to  a  certain  extent  by  clinical 
experience.  For  it  has  been  observed  that  a  cholera  patient 
with  distinct  fever  has  a  better  chance  of  recovery  than  a  case 
which  shows  no  fever.  But  too  much  weight  ought  not  to  be 
given  to  isolated  facts  of  this  sort,  and  adverse  evidence  can  l>< 
produced  both  from  the  laboratory  and  the  hospital.  For 
although  hens  are  immune  to  anthrax  under  ordinary  conditions, 
but  can  be  infected  by  inoculation  when  artificially  cooled,  frogs, 
equally  immune  at  the  temperature  of  the  air,  become  susceptible 
when  artificially  heated.  And  it  is  impossible  t<>  den)  that  the 
use  of  cold  baths  in  typhoid  fever  is  sometimes  of  remarkable 
benefit. 

Distribution  of  Heat — Temperature  Topography. — The  great 
foci  of  heat-formation — the  muscles  and  glands — would,  if  heal 
were  not  constantly  leaving  them,  in  a  short  time  become  much 
warmer  than  the  rest  of  the  body  ;  while  structures  like  the 
bones,  skin,  and  adipose  tissue,  in  which  chemical  change  and 
heat-production  are  slow,  would  soon  cool  down  to  a  temperature 
not  much  exceeding  that  of  the  air.  The  circulation  oi  the 
blood  insures  that  heat  produced  in  any  organ  shall  be  carried 
away  and  speedily  distributed  over  the  whole  body  ;  while 
direct  conduction  also  plays  a  considerable  part  in  maintaining 
an  approximately  uniform  temperature.  The  uniformitv.  how- 
ever, is  only  approximate.  The  temperature  of  the  liver  is 
several  degrees  higher  than  that  of  the  skin,  and  the  temperature 
of  the  brain  several  degrees  higher  than  that  of  the  cornea. 
The  blood  of  the  superficial  veins  is  colder  than  that  of  the 
corresponding  arteries. 

The  crural  vein,  for  example,  carries  colder  blood  than  the  crural 
artery,  and  the  external  jugular  than  the  carotid.  The  heat  pro- 
duced in  the  deeper  parts  of  the  regions  which  they  drain  is  more 
than  counterbalanced  by  the  heat  lost  in  the  more  superficial  parts. 
When  loss  of  heat  from  the  surface  is  sufficiently  diminished  by  an 
artificial  covering,  or  prevented  by  the  protected  situation  of  any 
organ  with  an  active  metabolism,  the  venous  blood  leaving  it  is 
warmer  than  the  arterial  blood  coming  to  it.  The  temperature  of 
Hie  blood  passing  from  the  levator  labii  superioris  muscle  of  the 
horse  during  mastication  may  be  sensibly  higher  than  that  of  the 
blood  which  feeds  it  ;  the  blood  in  the  vena  profunda  femoris,  and 
in  the  crural  vein  of  a  dog  with  the  leg  wrapped  in  cotton-wool,  is 
warmer  by  oi°  to  03°  than  the  blood  of  the  crural  artery.  This 
difference  of  temperature  is  due  to  the  heat  produced  in  the  muscles, 
and  it  is  not  difficult  to  show  that  the  difference  ought  to  be  of  this 
order  of  magnitude.  The  epiantity  of  blood  in  a  7-kilo  dog  is  about 
\  kilo  ;  \  of  this,  or  1  kilo,  is  in  the  skeletal  muscles,  and  the  avei 
circulation -time  through  them  may  be  taken  as  ten  seconds.  Six 
times  in  the  minute,  or  360  times  in  the  hour,  J  kilo  of  blood  passes 
through  the  muscles,  and  is  heated  on  the  average  by  020.     If  we 


/  \7  1/   //.    ///     /  / 

take  the  specific  heal  oi  blood  as  about  equal  to  that  of  water,  this 

represents  a  heat-production   <>i   '  '   x  — ,  or  9  calorics  per  hour. 

Now,  the  tol.il  lieu  production  <»f  a  7-MI0  dog  is  about  tg  calories 
per  liour.  of  which  somewhat  less  than  one-half  is  probably  formed 

mi  t  hr  skeletal  muscles. 

The  blood  of  the  interior  vena  cava  at  the  level  of  the  kidneys 
may  be  o'l°  colder  than  that  of  the  abdominal  aorta,  but  is  warmer 
than  the  blood  of  the  superior  cava.  The  right  heart,  therefore, 
receives  two  streams  of  blood  at  different  temperatures,  which 
mingle  in  its  cavities.  A  controversy  was  long  carried  on  as  to  the 
relative  temperature  of  the  blood  of  the  two  sides  of  the  heart  ; 
but  the  researches  of  Heidenhain  and  Korner  have  shown  that  a 
thermometer  passed  into  the  right  ventricle  through  the  jugular 
vein  stands,  as  a  rule,  slightly  higher  than  a  thermometer  introduced 
through  the  carotid  into  the  left  ventricle.  They  consider  that  the 
method  gives  not  so  much  the  temperature  of  the  blood  in  the  two 
cavities  as  that  of  their  walls.  The  thin-walled  right  ventricle, 
according  to  them,  is  heated  by  conduction  from  the  warm  liver, 
from  which  it  is  only  separated  by  the  diaphragm,  while  the  left 
ventricle  loses  heat  to  the  cooler  lungs.  They  deny  that  the  differ- 
ence of  temperature  is  caused  by  cooling  of  the  blood  in  its  passage 
through  the  pulmonary  capillaries,  for  even  when  respiration  is  sus- 
pended, they  find  a  difference  of  temperature  between  the  two  sides 
of  the  heart.  Under  ordinary  circumstances,  they  say,  the  inspired 
air  is  already  heated  almost  to  body-temperature  before  it  reaches 
the  alveoli.  But,  while  this  is  the  case,  a  fall  of  less  than  ^  in  the 
temperature  of  the  blood  passing  through  the  lungs  would  account 
for  all  the  heat  lost  by  the  expired  air.  If  half  of  the  loss  took  place 
in  the  upper  air-passages,  less  than  ^j0  would  be  sufficient.  A  slight 
difference  of  temperature  in  the  blood  of  the  two  ventricles  might  be 
caused,  even  in  the  absence  of  respiration,  by  the  heat  developed  in 
the  cardiac  muscle  itself  during  contraction,  a  large  proportion  of 
which  must  be  conveyed  by  the  blood  of  the  coronary  veins  into  the 
right  side  of  the  heart. 

The  surface  temperature  varies  between  rather  wide  limits  with 
the  temperature  of  the  environment.  The  temperature  of  cavities 
like  the  rectum,  vagina,  and  mouth,  and  of  secretions  like  the  urine, 
approximates  to  that  of  the  blood  in  the  great  vessels  or  the  heart, 
and  undergoes  only  slight  changes.  An  increase  in  the  velocity  of 
the  blood  causes  the  internal  and  surface  temperatures  to  come  nearer 
to  each  other,  the  former  falling  and  the  latter  rising.  When  the  loss 
of  heat  from  a  portion  of  the  surface  is  prevented,  the  temperature 
of  this  portion  approaches  the  internal  temperature.  For  this  reason 
a  thermometer  placed  in  the  axilla  approximately  measures  the 
internal  temperature,  and  not  that  of  the  skin  ;  and  a  thermometer 
in  the  groin  of  a  rabbit,  and  completely  covered  by  the  flexed  thigh, 
may  stand  as  high  as,  or,  it  is  said,  even  higher  than,  a  thermometer 
in  the  rectum  (Hale  White).  The  temperature  in  the  mouth  is  not 
a  very  reliable  index  of  the  deep  temperature  of  the  body,  especially 
in  cold  weather  or  after  exercise,  as  it  is  apt  to  be  influenced  by  the 
inspired  air.  The  mouth  must,  of  course,  be  kept  closed  during 
the  measurement.  On  the  average  its  temperature  is  about  the 
same  as  that  of  the  axilla,  and  o-4°  C.  below  that  of  the  rectum.  The 
rectal  temperature  is  02°,  or  030  above  that  of  the  urine.  In  point 
of  accuracy  rectal  observations  are  the  best,  and  next  to  them 
determinations  of  the  temperature  of  the  stream  of  urine.     The 


/    1/  l  xi    //.  OF  PHYSIOLOGY 

latter  method,  although  subjeci  to  obvious  limitations,  is  rapid  and 
tnc  from  the  danger  of  com  eying  infection  to  the  person  1 1  'embrey). 

The  surface  temperature  is  a  rough  index  of  the  rate  ol  heal 
the  internal  temperature,  of  the  rate  oi  heat-production.  A  normal 
skm  temperature  and  a  rising  rectal  temperature  would  probably 
indicate  increased  production  oi  beal  ;  an  increased  rectal  tempera- 
ture, in  conjunction  with  a  diminished  surface  temperature,  as  in  the 
cold  stage  of  ague,  might  be  due  either  to  diminished  In  a1  loss  while 
the  heat-production  remained  normal,  or  to  diminished  he, it-loss 
plus  increased  heat  -production. 

lln  Eollowing  tables  illustrate  the  differences  oi  temperature 
found  in  the  body.  It  should  be  remembered  that  the  numbers  are 
not  strictly  comparable  with  each  other;  the  temperature  of  the 
mammals  in  which  direct  observations  have  been  made-  on  the  blood 
is  not  exactly  the  same  as  that  of  man.  the  temperature  of  the  dog, 
for  example,  being  a  little  (about  i  C.)  higher.  Then  in  the  same 
animal  there  is  no  very  constant  ratio  between  the  temperature  of 
the  blood  in  two  vessels  or  of  the  skin  at  two  points.  Even  in  the 
same  vessel  the  temperature  may  vary  with  many  circumstan 
such  as  the  velocity  of  the  stream,  and  the  state  of  activity  of  the 
organ  from  which  it  comes.  Apart  from  physiological  variations. 
experimental  fallacies  sometimes  cause  a  want  of  constancy,  es] 
ally  in  measurements  of  blood  temperature.  The  insertion  of  a 
mercurial  thermometer  into  a  vessel  is  very  likely  to  obstruct  the 
passage  of  the  blood  ;  and  if  the  blood  lingers  in  a  warm  organ,  it 
will  be  heated  beyond  the  normal. 

/  hod.      (Dog.) 

Right  heart         -  -     ( 

I,  It  ..  ....      386 

Aorta  -  -  -  -  -     38"  7 

Superior  vena  cava    -  -         -     36*8 
Inferior               ..            -  -      38'] 

(rural  vein         -  -         -     37*2* 

Crural  artery      -  -  -  -     380 

Profunda  femoris  vein  -  -     38*2 

Portal  vein         -         -  38-39      (  Varies  with  activity* 

Hepatic  vein      -  -  38'4-39"7  J  of  digestive  organs. 

Tissues. 

Brain  ....         -     ^o° 

Liver  ...  -     40*6-  jo  o 

Subcutaneous    tissue    21    lower 

than  that  of  subjacent  muscles 

(man ) . 

Anterior  chamber  oi  eye    -         -     319  j  (rabbit). 

\  it  icons   humour        ...      36'!  \  v 

*  The    following    numbers    were    obtained    (in    an    anaesthetized    d 
rectal   temperature  had   fallen   a0  C.)   for  the  temperature  oi   the  watts  of  the 
crural  artery  and  vein,  .is  measured  by  an  electrical  resistance  thermometer. 


/  1     of  1/";'  lightly  wrapped  in  u 

1 

ural  artery            .... 

vein              .... 

•      UT" 

Re<  turn,  j6*a 

Leg  iii">,-  carefully  wrapped  up. 

Air.           163 

ural  artery            .... 

vein              .... 

\NIMAL  III    II 


605 


Cavities. 

Axilla         - 
Rectum     - 
MouthS      " 
Vagina 
Uterus 

External   auditory  meatus 
Bladder     (temperai  ure 
the  escaping  urine) 


Of 


(Man.) 

36'3-37'5' 

36-37-8 

37'25 

37'5"38 

37'7-38-3 

37'3-37'8 

36-0-37-5 


C.  (Q7-3-99-.50  I7 


Air 
temperature, 

n°  c. 


Respiratory  Passages. 

Middle  of  nasal  cavity 
trachea 


(Horse.) 

234°  C. 

324  C.  in  inspiration. 
344  C.  in  expiration. 


(Man) 

Room 

temperature, 

*T5° 


Natural  Surfaces. 

Cheek  (boy,  immediately  after  running)  - 
Anterior  surface  of  forearm     - 
Posterior         ,, 

Skin  over  biceps      -  -  - 

,,     head  of  tibia  ... 

immediately  below  xiphoid  cartilage 
1      ,,     over  sternum  -  -         - 

On  hair  (boy)  - 

Under  hair  over  sagittal  suture  (boy) 
Shaved  skin  of  neck  (rabbit)  - 
On  hair      ,,  ,,  -  - 

,,         between  eyes      ,, 

A  rtificial  Surfaces . 
Room         I  Surface  of  trousers  over  thigh 
temperature,  I  »  coat  over  arm 

\„.  o  „  waistcoat        - 

l7  5  v 


36-25° 

33'5-34'4 

34'° 

35° 

3i'9 

347 

33'2 

300 

337-34'° 

36-5 
3 1  "5 
30-7 


237-28-7° 

26-8 

26*0 


Normal  Variations  in  the  Temperature. — The  internal  tem- 
perature, as  has  been  already  said,  is  not  strictly  constant.  It 
varies  with  the  time  of  day  ;  with  the  taking  of  food  ;  with  age  ; 
to  some  extent  with  violent  changes  in  the  external  temperature, 
such  as  those  produced  by  hot  or  cold  baths  ;  and  possibly  with 
sex.  On  the  average  the  range  of  variation  in  the  temperature 
of  the  rectum  or  urine  of  a  healthy  man  is  from  36-0°  C.  (96-8°  F.) 
to  37-8°  C.  (ioo-o°  F.). 

In  the  monkey  a  very  distinct  and  constant  diurnal  variation 
has  been  observed,  and  the  range  is  much  wider  than  in  man, 
(as  much  as  5-4°  F.),  the  maximum  falling  between  6  and  8  p.m. 
and  the  minimum  between  2  and  4  a.m.  (Simpson). 

The  daily  curve  of  temperature  shows  a  minimum  in  the  early 
morning,  between  two  and  six  o'clock  (36-3°  C),  and  a  maximum 
in  the  evening,  between  five  and  eight  o'clock  (37- 50  C.)  (Fig.  200). 
The  daily  range  in  health  may  be  taken  as  a  little  over 
i°  C,  or  about  2°  F.     In  fever  it  is  generally  greater,  but  the 


6o6 


A   MANUAL  OF  PHYSIOLOGY 


maximum  and  minimum  fall  at  the  same  periods  ;  and  it  is  of 
scientific,  and  also  of  practical,  interest  that  the  early  morning, 
when  the  temperature  and  pulse-rate  are  at  their  minimum,  is 
often  the  time  at  which  the  flagging  powers  of  the  sick  give  way. 
From  two  to  >ix  o'clock  in  the  morning  the  daily  tide  <>f  life 
may  be  said  to  reach  low-water  mark.  Even  in  a  Easting  man 
the  diurnal  temperature  curve  runs  its  course,  but  tin-  varia- 
tions are  not  so  great.  The  taking  of  food  of  itself  causes  an 
increase  of  temperature,  although  in  a  healthy  man  this  rarely 
amounts  to  more  than  half  a  degree.  The  rise  of  temperature 
is  certainly  due  in  part  to  the  increased  work  of  the  alimentary 
canal,  but  it  is  also  connected  with  the  increase  of  metabolic 
activity  which  the  entrance  of  the  products  of  digestion  into  the 
blood  brings  about.     The  heat-production  is  especially  increased 

by  proteins.  The  ris 
temperature  during  di- 
ion  is  gradual,  the 
maximum  being  reached 
during  the  fourth  hour, 
or  even  later.  The  great- 
est increase  of  heat-pro- 
duction takes  place  during 
the  first  hour  after  feeding 
(Reichert). 

The  cause  of  the  daily 
variation  of  temperature 
has  been  much  discussed. 
There  is  no  doubt  that 
several  factors  are  con- 
cerned, among  the  most 
important  being  the  vari- 
ation in ,- the  amount  of  contraction  of  the  skeletal  muscles 
and  the  influence  of  food.  Muscular  exercise  is  capable  of 
causing  a  considerable  rise  in  the  temperature  of  the  rectum 
and  urine,  to  385°  C.  (101-3°  F.)  or  even  38-9°  C.  (102°  F.) 
without  producing  any  feeling  of  distress.  Other  unknown 
influences  seem  also  to  be  involved,  as  is  shown  by  the  fact 
that  in  persons  who  work  at  night  and  sleep  during  the 
day  the  curve  of  temperature,  although  greatly  altered,  is 
not  reversed.  Recent  observations  on  this  subject  are  those 
of  Benedict.  By  means  of  a  resistance  thermometer  in  the 
rectum,  readings  were  taken  usually  every  four  minutes.  With 
such  a  thermometer  no  disturbance  of  the  person's  sleep  is 
necessary  to  obtain  a  reading.  He  can  sit  without  discomfort 
in  anv  position,  walk  about  the  room  (returning  to  the  observer's 
table  for  the  observations),  and  even  ride  a  stationary  bicycle. 
Even  years  of  night-work  do  not  eliminate  the  tendency  to  a 


Fin. 


200. — Curve      showing     thl      Daily 
Variation  of  Body-temperature. 


ANIMAL  HEAT 


Coy 


fall  of  temperature  at  night,  a  minimum  in  the  early  morning 
and  a  morning  rise. 

As  to  the  relation  of  age  and  sex  to  temperature,  it  is  only 
necessary  to  remark  that  the  mean  temperature  both  of  the 
young  child  and  of  the  old  man  is  somewhat  higher  than  that 
of  the  vigorous  adult  ;  hut  a  point  of  more  importance  is  the 
relative  imperfection  of  the  heat-regulation  in  infancy  and 
age,  and  the  greater  effect  of  accidental  circumstances  on  the 
mean  temperature.  Thus,  old  people  and  young  children  are 
specially  liable  to  chills, 
and  a  lit  of  crying  may 
be  sufficient  to  send  up 
the  temperature  of  a 
baby.  In  infants  an 
hour  or  two  old  the 
temperature  may  be  as 
low  as  340  C.  (93-2°  F.) 
or  33-0°  C.  (91-4°  F.) 
even  when  they  are  fully 
clothed  in  a  room  at 
15°  C.  (59°  F.).  It  rises 
gradually  during  the  first 
day  or  two,  but  shows 
marked  variations.  On 
the  fifth  day  after  birth, 
e.g.,  the  rectal  tem- 
perature ranged  from 
36-2°  C.  (97-16°  F.)  to 
33'5°  C.  (92-3°  F.)  in  a 
child  weighing  5|  pounds 
(Babak).  The  tempera- 
ture of  women  is  gene- 
rally a  little  higher  than 
that  of  men,  and  is  also 
somewhat  more  variable. 

After  death  the  body  cools  at  first  rapidly,  then  more  slowly 
(Fig.  201).  But  occasionally  a  post-mortem  rise  of  temperature 
may  take  place.  In  certain  acute  diseases  (like  tetanus)  associ- 
ated with  excessive  muscular  contraction  this  has  been  especially 
noticed  ;  in  bodies  wasted  by  prolonged  illness  it  does  not  occur. 
Nearly  an  hour  after  death,  in  a  case  of  tetanus,  the  temperature 
was  found  to  be  45-  30,  while  before  death  it  was  44-7°  (Wunder- 
lich).  In  dogs  a  slight  post-mortem  rise  may  be  demonstrated, 
especially  when  the  body  is  wrapped  up  ;  but  when  an  animal 
has  been  long  under  the  influence  of  anaesthetics  no  indication 
whatever  of  the  phenomenon  may  be  obtained.  The  explana- 
tion of  post-mortem  rise  of  temperature  is  to  be  found  :  (1)  In 


Fig.  201. — Curve  of  Cooling  after  Death  : 
Guinea-pig. 

Time  marked  along  horizontal,  and  tempera- 
ture along  vertical  axis.  At  a  ether  and 
chloroform  given  to  kill  animal  ;  death,  as 
indicated  by  stoppage  of  the  heart,  took  place 
at  b.  The  dotted  line  shows  the  course  the 
curve  would  have  taken  if  death  had  occurred 
at  the  moment  the  anassthetics  were  given.  Air 
of  room  i7'6°. 


/    u  /  \r  \l    OF  PHYSIOLOGY 

the  continued  metabolism  "I  the  tissues  for  some  time  after  the 
head  has  i  rased  'to  beat,  for  the  cell  dies  harder  than  the  body. 
(2)  In  the  diminished  loss  of  heal,  due  to  the  stoppage  of  the 
circulation.  (3)  To  a  small  extent  in  physical  changes  (rigor 
mortis,  coagulation  of  blood)  in  which  heat  is  set  free. 


PRACTICAL  EXERCISES  ON  CHAPTERS  VII.  AND  VIII. 

1.  Glycogen* — (1)  Preparation. — (a)  Cut  an  oyster  into  two  or 
three  pieces,  throw  it  into  boiling  water,  and  boil  for  a  minute  or  two. 
Rub  up  in  a  mortar  with  clean  sand,  and  again  boil.  Filter. 
Precipitate  any  proteins  which  have  not  been  coagulated,  l>v  adding 
alternately  a  drop  or  two  of  hydrochloric  acid  and  a  few  drops  of 
potassio-mercuric  iodide  so  long  as  a  precipitate  is  produced.  (  tally 
a  small  quantity  of  these  reagents  will  be  required,  as  the  greater 
part  of  the  proteins  has  been  already  coagulated  by  boiling.  Filter 
it  any  precipitate  has  formed.  The  filtrate  is  opalescent.  Precipi- 
tate the  glycogen  from  the  filtrate  (after  concentration  on  the 
wrater-bath  if  it  exceeds  a  few  c.c.  in  bulk)  by  the  addition  of  four 
or  five  times  its  volume  of  alcohol.  Filter  off  the  precipitate,  wash  it 
on  the  filter  with  alcohol,  and  dissolve  it  in  a  little  water.  To  some 
of  the  solution  add  a  drop  or  two  of  iodine  ;  a  reddish-brown  (port 
wine)  colour  is  produced,  which  disappears  on  heating,  returns  on 
cooling,  is  removed  by  an  alkali,  restored  by  an  acid.  Add  saliva 
to  some  of  the  glycogen  solution,  and  put  in  a  bath  at  400  C.  In  a 
few  minutes  reducing  sugar  (maltose)  will  be  found  in  it  by  Trommer's 
test  (p.  10). 

Note  that  dextrin  (crythrodextrin)  gives  the  same  colour  with 
iodine  as  glycogen  does.  Dextrin  is  also  precipitated  by  alcohol, 
but  a  greater  proportion  must  be  added  to  cause  complete  precipita- 
tion. Glycogen  is  completely  precipitated  by  saturation  with  mag- 
nesium sulphate  or  ammonium  sulphate,  so  that  the  filtrate  no  longer 
gives  the  reddish  colour  with  iodine.  A  pure  solution  of  erythro- 
dextrin  is  not  precipitated.  On  the  addition  of  a  drop  or  two  of 
a  solution  of  basic  lead  acetate  to  a  solution  of  glycogen  in  distilled 
water,  a  precipitate  forms  immediately.  Wherf  the  same  reagent 
is  added  to  a  solution  of  dextrin  in  distilled  water  there  is  no 
immediate  precipitate.  Maltose  is  formed  when  dextrin  is  digested 
with  saliva. 

(b)  Cut  another  oyster  into  pieces,  throw  it  into  boiling  water 
acidulated  with  dilute  acetic  acid,  and  boil  for  a  few  minutes.  Rub 
up  in  a  mortar  with  sand,  boil  again,  and  filter.  Test  a  portion  of 
the  filtrate  with  iodine  for  glycogen.  Precipitate  the  rest  with 
alcohol,  filter,  dissolve  the  precipitate  in  water,  and  test  again  for 
glycogen.  On  boiling  some  of  the  opalescent  solution  for  a  few 
minutes  after  the  addition  of  a  few  drops  of  sulphuric  acid  the 
opalescence  disappears,  and  when  the  solution  has  been  neutralized 
with  sodium  hvdroxide  it  gives  Trommer's  test,  owing  to  the 
hydrolysis  of  the  glycogen  into  dextrose. 

*  For   the   quantitative  estimation   of   glycogen   in   organs,   Pfluger's 

method  is  the  best.  The  organ  is  minced  and  heated  with  strong  (60  per 
cent.)  potassium  hydroxide.  Cue  glycogen  is  precipitated  with  alcohol, 
and  then,  after  hydrolysis  with  hydrochloric  acid,  estimated  as  dextrose. 


PR  It'  I  /('.!/    EXERCISl  S 

(2)  Deeply  etherize  a  dog  or  rabbit  five  hours  after  a  meal  rich  in 
carbo-hydrates — e.g.,  rice  and  potatoes  in  the  case  of  the  dog. 
carrots  in  the  case  <>f  the  rabbit.  Fasten  it  on  a  holder.  CUp 
ofl  the  hair  over  the  abdomen  in  the  middle  line.  Make  a  mesial 
incision  through  the  skin  and  abdominal  wall  from  the  ensiform  car- 
tilage to  the  pubis.  The  liver  will  now  be  rapidly  cut  out  (bv  the 
demonstrator)  and  divided  into  two  portions,  one  of  which  will  be 
(distributed  among  the  class  and)  treated  as  in  (a)  or  (b)  ;  the  other 
will  be  kept  for  an  hour  at  a  temperature  of  400  C,  and  then  sub- 
jected to  process  (a)  or  (b).  Little,  if  any.  sugar  and  much  glycogen 
will  be  found  in  the  portion  which  was  boiled  immediately  after 
excision.  Abundance  of  sugar  will  be  found  in  the  portion  kept  at 
400  C.  ;  it  may  or  may  not  contain  glycogen. 

2.  Catheterism. — In  many  physiological  experiments  it  is  neces- 
sary to  obtain  urine  from  the  bladder  by  means  of  a  catheter.  It 
is  possible  to  pass  a  fine  rubber  catheter  into  the  bladder  of  a  male 
dog.  A  larger  one  is  easily  passed  in  a  male  rabbit,  and  a  still 
larger  in  a  bitch,  which  is  often  used  for  experiments  on  metabolism. 
Even  in  the  bitch  the  opening  of  the  urethra  lies  entirely  concealed 
within  the  vagina,  much  deeper  than  the  cul-de-sac  in  the  mucous 
membrane,  into  which  the  beginner  usually  tries  to  force  the 
catheter.  For  a  first  attempt  the  animal  should  be  etherized  and 
fastened  on  a  holder.  The  little  or  index  finger  of  the  left  hand  is 
passed  into  the  vagina  till  the  symphvsis' pubis  can  be  felt.  A  little 
below  this  is  the  opening  of  the  urethra.  With  the  right  hand  the 
point  of  a  catheter  of  suitable  calibre  is  directed  along  the  finger, 
and  after  a  little  '  guess  and  trial  '  it  slips  into  the  bladder,  its 
entrance  being  announced  by  the  escape  of  urine.  A  glass  tube 
drawn  out  to  a  sufficiently  small  calibre  and  bent  near  the  point  is 
the  easiest  form  of  catheter  to  pass  in  a  bitch.  The  point  must,  of 
course,  be  rounded  in  the  flame. 

When  the  bitch  is  to  be  used  in  a  long  series  of  experiments  an 
operation  is  sometimes  performed  first  of  all  to  render  the  urethral 
orifice  more  accessible. 

3.  Glycosuria, — (1)  (a)  Weigh  a  dog  (female  by  preference)  or 
rabbit.  Fasten  on  a  holder,  and  etherize.  Insert  a  glass  cannula 
into  the  femoral  or  saphena  vein  of  the  dog,  or  into  the  jugular 
of  the  rabbit  (p.  200).  Fill  a  burette  with  a  2  per  cent,  solution 
of  dextrose  in  physiological  salt  solution,  connect  it  with  the 
cannula  by  means  of  an  indiarubber  tube,  taking  care  that  there 
are  no  air-bubbles  in  the  tube,  and  slowly  inject  as  much  of  the 
solution  as  will  amount  to  \  or  f  grm.  of  sugar  per  kilo  of  body-weight. 
Tie  the  vein,  remove  the  cannula,  and  in  half  an  hour  evacuate  the 
bladder  by  passing  a  catheter,  by  pressure  on  the  abdomen,  or,  if 
both  of  these  methods  fail,  by  tapping  the  bladder  with  a  trocar 
pushed  through  the  linea  alba  (supra-pubic  puncture).  In  an  hour 
again  draw  off  the  urine.     Test  both  specimens  for  sugar. 

In  this  experiment  the  opportunity  may  also  be  taken  to  demon- 
strate that  egg-albumin,  when  injected  into  the  blood,  is  excreted  by 
the  kidneys,  a  filtered  solution  containing  the  albumin  of  one  egg 
and  sugar  in  the  quantity  mentioned  being  injected. 

The  catheter  may  be  inserted  before  the  injection  is  begun,  and 
the  bladder  evacuated.  After  the  injection  the  urine  that  drops 
from  the  catheter  may  be  collected  in  test-tubes,  first  every  two 
minutes,  and  then,  as  soon  as  sugar  is  found,  every  ten  minutes. 
Determine  the  interval  between  injection  and  the  appearance  of  the 

39 


610  A   MANUAL  OF  PHYSIOLOGY 

first  trace  of  sugar  and  albumin.  If  a  sufficient  amount  of  urine  is 
obtained,  the  quantity  of  sugar  in  successive  specimens  may  bo 
estimated  and  compared.  The  rate  of  flow  of  the  urine  as  measured 
by  the  number  of  drops  falling  from  the  catheter  may  also  be  esti- 
mated from  time  to  time,  in  order  to  determine  whether  diuresis  is 
1  aking  place. 

If  a  rabbit  is  used  for  this  experiment,  the  sugar  solution  may 
be  injected  into  the  ear  vein.  The  vein  is  caused  to  swell  up  by 
pressing  on  it  with  the  finger  and  thumb,  and  the  hypodermic  needle 
is  then  inserted  towards  the  heart. 

(b)  Instead  of  collecting  the  urine  by  a  catheter  in  the  bladder 
the  abdomen  of  the  dog  may  be  opened,  and  a  cannula  tied  into 
each  ureter.  The  two  cannulas  are  then  connected  by  short  rubber 
tubes  with  a  glass  Y-piecc.  on  the  stem  of  which  a  test-tube  is  tied 
for  collecting  the  urine.  Replace  the  test-tube  by  a  fresh  one  from 
time  to  time.  The  urine  already  in  the  bladder  is  removed  by 
pressure  or  by  a  trocar,  and  tested  for  sugar,  since  the  anaesthetic 
itself  may  cause  a  certain  amount  of  glycosuria.  Test  the  samples 
of  urine  obtained  from  the  ureters  for  sugar,  and  in  those  in  which 
it  is  present  estimate  its  amount.  Note  also  any  changes  in  the 
rate  of  secretion  of  urine,  and  any  abnormal  constituents,  as  albumin. 

(2)  Phloridzin  Glycosuria. — Dissolve  \  grm.  of  phloridzin  in  warm 
water,  and  inject  it  subcutaneously  into  a  rabbit.  Obtain  a  sample 
of  the  urine  at  the  end  of*two  hours,  by  pressure  on  the  abdomen 
with  the  thumb  or  by  passing  a  catheter,  and  test  for  sugar.  If  none 
is  present,  wait  for  another  interval,  and  again  test  the  urine. 

This  experiment  can  also  be  performed  without  risk  on  man. 
One  grm.  of  phloridzin  has  been  injected  twice  a  day  without  dis- 
turbing the  individual.  Much  sugar  is  found  in  the  urine,  but  it 
disappears  the  day  after  the  administration  of  phloridzin  is  stopped. 
The  phloridzin  may  also  be  given  by  the  mouth,  but  more  is  required, 
and  it  is  not  very  easily  absorbed,  and  often  causes  diarrhoea 
(v.  Mcring). 

(3)  Alimentary  Glycosuria. — The  urine  having  been  tested  for 
sugar  for  two  successive  days,  and  none  being  found. 

(a)  A  large  quantity  of  dextrose  is  to  be  taken  in  the  form  which 
is  most  agreeable  to  the  student  some  hours  after  a  meal.  The  urine 
of  the  next  twenty-four  hours  is  to  be  collected  and  measured.  A 
sample  of  it  is  then  to  be  tested  for  reducing  sugar  by  Trommer's  and 
the  phenyl-hydrazine  test.  If  any  sugar  is  found,  the  reducing  power 
of  a  definite  quantity  of  the  urine  is  to  be  determined  by  titration 
with  Fehling's  solution  (p.  489). 

(b)  Instead  of  dextrose  use  cane-sugar  and  proceed  as  in  (a).  But 
estimate  the  reducing  power  of  the  urine  (a)  before  and  (<3)  after 
boiling  with  hydrochloric  acid  (p.  433). 

(c)  A  large  meal  of  rice  and  arrowroot,  sweetened  with  as  much 
dextrose  as  the  observer  can  induce  himself  to  swallow,  is  to  be 
taken,  and  the  urine  treated  as  in  (a). 

(d)  A  large  number  of  sweet  oranges  may  be  eaten.* 

4.  Milk. — (1)  Examine  a  drop  of  fresh  cow's  milk  with  the  micro- 
scope.    Note  the  fat  globules  of  various  sizes. 

(2)  Determine  the  specific  gravity  of  the  milk  with  a  hydrometer 
(lactometer).  Then  centrifugalize  some  of  the  milk  to  separate  the 
cream,  which  rises  to  the  top  of  the  tubes.      Remove  the  cream  and 

*  These  experiments  may  be  distributed  among  the  class  so  that  each 
student  does  one. 


PR  ICTIi    II.   EXERCISES  6n 

determine  the  specific  gravity  of  the  skimmed  milk.  Tt  will  be  found 
to  have  increased  since  the  Cat  is  of  lower  specific  gravity  than  the 
rest  of  the  milk.  Normal  cow's  milk  has  a  specific  gravity  of  1,028 
1 11"  1.034.  skimmed  milk  1,033  to  1,037. 

(3)  Test  the  reaction  of  the  milk  to  litmus-paper.  It  is  slightly 
alkaline. 

(4)  (a)  Put  to  c.c.  of  milk  in  a  t(  si-tube,  and  nearly  fill  it  up  witli 
water.  Add  strong  acetic  acid  drop  by  drop.  A  precipitate  of 
caseinogen  is  thrown  down  which  entangles  the  fat,  and  carries  it 
down  mechanically  along  with  it.  Filter  oh  the  precipitate.  Keep 
the  filtrate  for  (b).  Wash  the  precipitate  with  water,  scrape  a 
portion  of  it  off  the  filter,  and  add  to  it  some  2  per  cent,  sodium 
carbonate  solution.  The  caseinogen  dissolves,  while  the  fat  remains  in 
suspension .     The  solution  gives  the  colour  reactions  for  proteins  (p.  7) . 

(6)  Test  some  of  the  filtrate  by  Trommer's  test  (p.  10)  for  lactose. 
Add  dilute  sodium  carbonate  solution  to  another  portion  till  it  is 
only  slightly  acid.  Boil,  and  lactalbumin  is  coagulated.  Remove 
the  lactalbumin  by  filtering,  and  test  this  filtrate  for  earthy  (i.e., 
calcium  and  magnesium)  phosphates  by  adding  a  few  drops  of 
ammonia,  which  precipitates  them  as  a  slight  cloud. 

(c)  To  5  c.c.  of  milk  add  an  equal  volume  of  saturated  ammonium 
sulphate  solution.  The  caseinogen  is  precipitated,  entangling  the 
fat.  Filter  off.  The  filtrate  may  be  used  to  test  for  lactalbumin 
by  boiling.  The  addition  of  water  to  the  precipitate  of  caseinogen 
(and  fat)  on  the  filter  causes  the  caseinogen  to  dissolve,  as  it  is  soluble 
in  weak  salt  solutions.  Caseinogen  can  also  be  precipitated  by 
saturating  milk  with  sodium  chloride  or  magnesium  sulphate. 

(5)  To  5  c.c.  of  milk  add  a  couple  of  drops  of  20  per  cent,  sodium 
or  potassium  hydroxide,  and  then  a  few  c.c.  of  ether.  Shake  up. 
The  ether  dissolves  the  fat,  and  the  opacity  of  the  milk  diminishes. 
Take  off  the  ether  with  a  pipette,  evaporate  away  most  of  it  on  a 
water-bath,  and  place  a  drop  or  two  of  the  remainder  on  a  filter- 
paper.  A  greasy  stain  is  left,  showing  the  presence  of  the  fat  of  the 
milk  or  butter. 

(6)  Clotting  of  Milk. — (a)  To  a  few  c.c.  of  milk  in  a  test-tube  add 
a  few  drops  of  rennet.  Place  the  tube  in  a  bath  at  400  C.  In  a  short 
time  a  clot  or  curd  is  formed,  consisting  of  casein,  which  is  derived 
from  the  caseinogen.  The  fat  is  entangled  in  the  clot.  On  standing 
some  time  the  clot  contracts,  and  exudes  the  whey.  Boil  some  of 
the  whey  after  slight  acidulation  with  acetic  acid  ;  the  lactalbumin  and 
whey-protein  are  coagulated .  Test  another  portion  of  whey  for  proteins 
by  one  of  the  general  protein  tests  (p.  7) — e.g.,  the  xanthoproteic. 

(b)  Repeat  (a)  but  use  rennet  which  has  been  previously  boiled .  The 
milk  is  not  curdled,  because  the  ferment  has  been  inactivated  by  boiling. 

(c)  To  10  c.c.  of  milk  add  3  c.c.  of  1  per  cent,  potassium  oxalate. 
Divide  the  oxalated  milk  into  three  portions — A,  B,  and  C.  To  A 
add  a  few  drops  of  rennet,  to  B  1  c.c.  of  2  per  cent,  calcium  chloride, 
solution  and  a  little  rennet,  and  to  C  1  c.c.  of  2  per  cent,  calcium 
chloride  solution  alone.  Put  the  tubes  at  400  C.  Clotting  will 
occur  in  B,  but  not  in  A  or  C. 

5.  Cheese. — (1)  Rub  up  some  finely-grated  cheese  in  a  mortar 
with  2  per  cent,  sodium  carbonate  solution.  Filter.  The  filtrate 
contains  casein,  which  can  be  precipitated  by  adding  dilute  acetic 
acid  by  drops  to  a  portion  of  the  filtrate.  The  precipitate  is  soluble 
in  excess  of  the  acid.  With  another  portion  of  the  filtrate  perform 
some  of  the  general  protein  tests  (p.  7).  r._. 

39—2 


6ra  AM  \MUAL  OF  PHYSIOLOGY 

(2)  Shake  up  some  finely-grated  cheese  in  a  dry  test-tube  with 
ether.  Take  oil  the  ether  with  a  pipette,  and  evaporate  on  a  water- 
bath  till  only  .1  lew  drops  remain.  With  a  Ldass  rod  pul  a  drop  of  the 
ether  on  a  piece  of  filter-paper.  A  greasy  spol  is  left,  showing  that 
fat  is  present. 

6.  Flour. — (1)  Mix  some  wheat-flour  with  a  Little  water  into  1 
stiff  dough.  Let  it  stand  for  a  few  minutes  at  body-temperature 
to  facilitate  the  formation  oi  gluten.  Wrap  a  piece  in  1  neese  1  Loth, 
forming  a  kind  of  bag,  and  knead  it  with  the  fingers  in  a  capsule  of 
water.  The  starch  grains  come  through  the  cheese-cloth.  Pour 
the  water  into  a  beaker.  It  is  opaque,  and  on  standing  the  starch 
grains  sink  to  the  bottom,  (a)  Test  for  starch  with  the  iodine  test, 
and  also  examine  microscopically.  The  grains  are  round,  with  a 
central  hilum,  and  are  smaller  than  those  of  potato  starch  (p.  1  1). 
(b)  Test  for  sugar  by  Trommer's  test  (p.  10).  None  is  present 
unless  the  flour  has  been  made  from  inferior  grain  in  which  some 
germination  has  taken  place. 

(2)  Go  on  kneading  the  dough  till  no  more  starch  comes  through. 
The  sticky  mass  which  remains  in  the  bag  is  a  protein  calleil  gluten, 
which  is  formed  from  certain  globulins  and  other  proteins  in  the  flour 
on  addition  of  water.  Oatmeal,  ground  rice,  and  other  grains  poor 
in  gluten-forming  globulins  do  not  form  dough  when  mixed  with  water. 
Suspend  some  of  the  gluten  in  water  in  a  test-tube,  and  apply  to  it 
the  general  protein  colour  tests  (p.  7). 

7.  Bread. — (1)  Rub  up  a  small  piece  of  the  crumb  of  a  stale  loaf 
in  a  mortar  with  water.  Strain  through  cheese-cloth.  The  fluid 
which  passes  through  contains  starch  grains,  (a)  Filter  it,  and 
test  a  portion  of  the  filtrate  for  dextrose  by  Trommer's  test.  A 
positive  result  is  obtained.  Test  another  portion  with  iodine  for 
crythrodextrin.  (b)  Test  a  portion  of  the  residue  of  the  bread 
which  has  not  passed  through  the  cheese-cloth  for  protein  by  the 
general  protein  tests — e.g.,  the  xanthoproteic  or  Millon's  tests. 

(2)  Repeat  (1)  using  the  crust  of  the  bread.  Both  dextrose  and 
erythrodextrin  are  present  in  the  cold-water  extract,  but  the  dextrose 
is  less  plentiful  than  in  the  crumb,  having  been  converted  into 
caramel  in  the  baking.  The  sugar  and  dextrin  are  formed  from  the 
starch  of  the  flour  by  the  ferments  of  the  yeast  employed  to  make  the 
bread  rise. 

8.  Variations  in  the  Total  Nitrogen  (p.  535)  and  in  the  Quantity 
of  Urea  Excreted,  with  Variations  in  the  Amount  of  Proteins  in  the 
Food. — The  student  should  put  himself,  or  somebody  else  if  he  can. 
for  two  days  on  a  diet  poor  in  proteins,  then  (after  an  interval  of 
forty-eight  hours  on  his  ordinary  food)  for  two  days  on  a  diet  rich 
in  proteins.  A  suitable  table  of  diets  will  be  supplied.  The  urine 
should  be  collected  on  the  six  days  of  the  period  of  experiment,  on 
the  day  before  it  begins,  and  on  the  day  after  it  ends.  Small 
samples  of  the  mixed  urine  of  the  twenty-four  hours  for  each  of 
these  eight  days  should  be  brought  to  the  laboratory,  and  the 
quantity  of  urea  determined  by  the  hypobrordite  method.  The 
volume  of  the  urine  passed  in  each  interval  of  twenty-four  hours 
being  known,  the  total  excretion  of  urea  for  the  twenty-four  hours 
can  be  calculated,  and  a  curve  plotted  to  show  how  it  varies  during 
the  period  of  experiment.*     If  sufficient  time  is  available,  the  experi- 

*  In  17  healthy  students  the  average  amount  of  urea  exent  id  m  twenty- 
four  hours  on  the  ordinary  diet  was  29-51  grammes  (minimum  19*35 
grammes,  maximum  46-007  grammes)  ;  on  a  diet  poor  in  protein,  average 


PR  ICTIi    II    I  XI  RCISES  »>i3 

men!  will  be  made  still  more  instructive  by  determining  the  total 
nitrogen  in  each  sample  in  addition  to  the  urea.  A  curve  showing 
the  variation  in  the  total  nitrogen  can  then  be  plotted  on  the  same 
paper  as  the  urea  curve,  and  a  table  calculated  giving  the  percen 
oJ  the  total  nitrogen  contained  in  the  urea  for  each  clay  of  the 
experiment . 

9.  Measurement  of  the  Quantity  of  Heat  given  off  in  Respiration. 

This  may  be  done  approximately  as  follows  :  Put  in  the  inner 
copper  vessel,  A.  of  the  respiration  calorimeter  (Fig.  197,  p.  579)  a 
measured  quantity  of  water  sufficient  to  completely  cover  the  series 
of  brass  discs.  Place  A  in  the  wide  outer  cylinder,  the  bottom  of 
which  it  is  prevented  from  touching  by  pieces  of  cork.  The  outer 
cylinder  hinders  loss  of  heat  to  the  air.  Suspend  a  thermometer  in 
the  water  through  one  of  the  holes  in  the  lid.  In  the  other  hole 
place  a  glass  rod  to  serve  as  a  stirrer.  Read  off  the  temperature  of 
the  water.  Put  the  glass  tube  connected  with  the  apparatus  in  the 
mouth,  and  breathe  out  through  it  as  regularly  and  normally  as 
possible,  closing  the  opening  of  the  tub;  with  the  tongue  after  each 
expiration  and  breathing  in  through  the  noso.  Continue  this  for 
five  or  ten  minutes,  taking  care  to  stir  the  water  frequently.  Then 
read  off  the  temperature  again.  If  \Y  be  the  quantity  of  wai 
in  c.c.,  and  z1  the  observed  rise  of  temperature  in  degrees  Centigrade, 
\\7  equals  the  quantity  of  heat,  expressed  in  small  calories  (p.  574b 
given  off  by  the  respiratory  tract  in  the  time  of  the  experiment,  on 
tin-  assumptions  (1)  that  "all  the  heat  has  been  absorbed  by  the 
water.  (2)  that  none  of  it  has  been  lost  by  radiation  and  conduction 
from  the  calorimeter  to  the  surrounding  air.  Calculate  the  loss  in 
twenty-four  hours  on  this  basis  ;  then  repeat  the  experiment, 
breathing  as  rapidly  and  deeply  as  possible,  so  as  to  increase  the 
amount  of  ventilation.  The  quantity  of  heat  given  off  will  be  found 
to  be  increased.* 

In  an  experiment  of  short  duration  (2)  is  approximately  fulfilled. 
As  to  (1),  it  must  be  noted  that  in  the  first  place  the  metal  of  the 
calorimeter  is  heated  as  well  as  the  water,  and  the  water-equivalent 
of  the  apparatus  must  be  added  to  the  weight  of  the  water  (p.  574)- 
The  water-equivalent  is  determined  by  putting  a  definite  weight  of 
water  at  air  temperature  T  into  the  calorimeter,  and  then  allowing 
a  quantity  of  hot  water  at  known  temperature  T'  to  run  into  it, 
stirring  well,  and  noting  the  temperature  of  the  water  when  it  has 
ceased  to  rise.  Call  this  temperature  T".  Enough  hot  water  should 
be  added  to  raise  the  temperature  of  the  calorimeter  about  20  C. 
The  quantity  run  in  is  obtained  by  weighing  the  calorimeter  before 
and  after  the  hot  water  has  been  added.  Suppose  it  is  m.  Let  the 
mass  of  the  cold  water  in  the  calorimeter  at  first  be  M,  and  let 
M'=the  mass  of  water  which  would  be  raised  i°  C.  in  temperature 
by  a  quantity  of  heat  sufficient  to  increase  the  temperature  of  all 
the  metal,  etc.,  of  the  calorimeter  by  i° — in  other  words,  the  water- 
equivalent  of  the  calorimeter. 

The  mass  m  of  hot  water  has  lost  heat  to  the  amount  of  m  (T'  —  T"), 
and  this  has  gone  to  raise  the  temperature  of  a  mass  of  water  M, 

2075  grammes  (minimum  9*517  grammes,  maximum  32*857  grammes)  ; 
on  a  diet  rich  in  protein,  average  38-83  grammes  (minimum  23^265  grammes, 
maximum  67"82  grammes). 

*  The  average  heatdoss  by  the  lungs  for  5 1  men  (calculated  for  the 
24  hours)  was  312,000  small  calories  for  normal,  919,000  for  the  fastest, 
and  195,000  for  the  slowest  breathing. 


614 


A    MANUAL  OF  PHYSIOLOG  Y 


and  metal  equivalent  to  a  mass  of  water  M\  by  (T*  — T)  d< 

.-.  ,„  (T'-T")=M(T"-T)  +  M'(T/"-T).  Everything  in  this  equa- 
tion except  M'  is  known,  and  .'.  M ',  the  water-equivalent  of  the 
calorimeter,  can  be  deduced,  and  must  be  added  in  all  exact  experi- 
ments to  the  mass  of  water  contained  in  it. 

Secondly,  all  the  excess  of  heat  in  the  expired  over  that  in  the 
inspired  air  is  not  given  off  to  the  calorimeter,  for  the  air  pass* 
of  it  at  a  slightly  higher  temperature  than  that  of  the  atmosphere. 
At  the  beginning  of  the  experiment  this  excess  oi  temperature  is 
zero.  If  at  the  end  it  is  i°  C,  the  mean  excess  is  05  I 
when  respiration  is  carried  on  in  a  room  at  a  temperature  of  io°  C. 
the  expired  air  has  its  temperature  increased  by  nearly  300  C. 
About  ,.',,  of  the  heat  given  off  by  the  respiratory  tr.u  1  in  raising  the 
temperature  of  the  air  of  respiration  would 
accordingly  be  lost  in  such  an  experiment. 
But  since  the  portion  of  the  heat  lost  by  the 
lungs  which  goes  to  heat  the  expired  air  is 
only  }  of  the  whole  heat  lost  in  respiration 
(p.  579),  the  error  would  only  amount  to  .,,',,  <>! 
the  whole,  and  this  is  negligible. 

Thirdly,  the  air  leaves  the  calorimeter  satu- 
rated with  watery  vapour  at,  say,  to 
while  the  inspired  air  is  not  saturated  for 
10°  C.  Now.  the  quantity  oi  heal  rendered 
latent  in  the  evaporation  of  water  sufficient 
to  saturate  a  given  quantity  of  air  at  |o  I 
(the  expired  air  is  saturated  for  body-tem- 
perature) is  six  times  that  required  to  saturate 
the  same  quantity  of  air  at  ro°.  If.  then, 
the  inspired  air  is  half  saturated,  the  error 
under  this  head  is  ,'._..  or  8|  per  cent.  If  the 
inspired  air  is  three-quarters  saturated,  the 
<nor  is  ._,',.  or  about  4  per  cent.  If  the  air 
is  fully  saturated  before  inspiration,  as  is  the  case  when  it  is 
drawn  in  through  a  water- valve  (Fig.  202)  by  a  tube  fixed  in  one 
nostril,  the  only  error  is  that  due  to  the  slight  excess  of  temperature 
of  the  air  leaving  the  calorimeter  over  that  of  the  inspired  air. 
The  latent  heat  of  the  aqueous  vapour  in  saturated  air  at  io'5°  C. 
is  about  ..',,  more  than  the  latent  heat  of  the  aqueous  vapour  in 
the  same  mass  of  saturated  air  at  io°  C.  or  about  ^hs  °f  the 
latent  heat  in  saturated  air  at  400.  The  error  in  this  case  would 
therefore  be  under  1  per  cent.  The  tubes  must  be  wide  and  the 
bottle  large. 


Fig.    202. — B  qttle 

A  ]<]k  A  \  (.  1    I)        FOR 
\\    \  I  I :  R  -  VALVE. 


CHAPTER    IX 
MUSCLE 


It  is  impossible  to  understand  the  general  physiology  of  muscle  and 
nerve  without  some  acquaintance  with  electricity.  It  would  be  out 
of  place  to  give  even  a  complete  sketch  of  this  preliminary  but 
essential  knowledge  here  ;  and  the  student  is  expressly  warned  that 
in  this  book  the  elementary  facts  and  principles  of  physics  are 
assumed  to  be  part  of  his  mental  outfit.  But  in  describing  some  of 
the  electrical  apparatus  most  commonly  used  in  the  study  of  this 
portion  of  our  subject,  it  may  be  useful  to  recall  the  physical  facts 
involved. 

Batteries. — The  Daniell  cell  is  perhaps  better  suited  for  physio- 
logical work  than  any  other  voltaic  element,  although  for  special 
purposes  Bunsen,  Grove,  Le- 
clanche,  and  bichromate  of 
potassium  batteries  may  be 
employed.  Dry  batteries  are 
very  convenient  for  work  in 
which  the  current  does  not 
need  to  be  very  constant,  and 
where  it  is  only  closed  for  a 
short  time. 

The  Daniell  is  a  two-fluid  cell. 
Saturated  solution  of  sulphate 
of  copper  is  contained  in  an 
outer  vessel,  and  a  dilute  solu- 
tion of  sulphuric  acid  in  a 
porous  pot  standing  in  the 
copper  sulphate  solution.  The 
latter  is  kept  saturated  by  a 
few  crystals  of  copper  sulphate. 
A  piece  of  sheet-copper,  gener- 
ally bent  so  as  to  form  a  hollow  cylinder,  dips  into  the  sulphate  of 
copper,  and  a  piece  of  amalgamated  zinc  into  the  contents  of  the 
porous  pot.  Inside  the  cell  the  current  (the  positive  electricity) 
passes  from  zinc  to  copper  ;  outside,  from  copper  to  zinc.  The  copper 
is  called  the  positive,  the  zinc  the  negative,  pole.  When  the  current 
is  passed  through  a  tissue,  the  electrode  by  which  it  enters  is  termed 
the  anode,  and  that  by  which  it  leaves  the  tissue  the  kathode.  The 
anode  is,  therefore,  the  electrode  connected  with  the  copper  of  the 
Darnell's  cell  ;  the  kathode  is  connected  with  the  zinc. 

Potential — Current  Strength — Resistance. — -We  do  not  know  what 
in  reality  electricity  is,  but  we  do  know  that  when  a  current  flows 

615 


Fig.  203 . — Daniell  Cell. 

A,  outer  vessel  ;  B,  copper  ;  C,  porous 
pot  ;  D,  zinc  rod  ;  D  is  supposed  to  be 
raised  a  little  so  as  to  be  seen. 


616  A    MANU  ll.  OF    I'll  YSIOl  OG  I 

along  ;i  wire  energy  is  expended,  just  as  energy  is  expended  when 
water  flows  from  a  higher  to  a  lower  level.  Many  ol  the  phenomena 
of  current  electricity  can,  in  fact,  be  illustrated  by  the  laws  of  flow 
of  an  incompressible  liquid.  The  difference  of  level,  in  virtue  of 
which  the  flow  of  liquid  is  maintained,  corresponds  to  the  difference 
of  electrical  level,  or  potential,  in  virtue  of  which  an  electrical  current 
is  kept  up.  The  positive  pole  of  a  voltaic  cell  is  at  a  higher  potent  Lai 
than  the  negative.  When  they  are  connected  by  a  conductor,  a  flow 
of  electricity  takes  place,  which,  if  the  difference  of  level  or  potential 
were  not  constantly  restored,  would  soon  equalize  it.  and  the  current 
would  cease  ;  just  as  the  flow  of  water  from  a  reservoii  would  ulti- 
mately stop  if  it  was  not  replenished.  If  the  reserv<  >ir  was  small,  and 
the  discharging-pipe  large,  the  flow  would  only  last  a  short  time ; 
but  if  water  was  constantly  being  pumped  up  into  it,  the  flow  would 
go  on  indefinitely.  This  is  practically  the  case  in  the  Danicll  cell. 
Zinc  is  constantly  being  dissolved,  and  the  chemical  energy  which 
thus  disappears  goes  to  maintain  a  constant  difference  of  potential 
between  the  poles.  Electricity,  so  to  speak,  is  continuallv  running 
down  from  the  place  of  higher  to  the  place  of  lower  potential,  but 
the  cistern  is  always  kept  full. 

The  difference  of  electrical  potential  between  two  points  is  called 
the  electromotive  force  ;  and  from  its  analogy  with  difference  of 
pressure  in  a  liquid,  it  is  easy  to  understand  that  the  intensity  or 
strength  of  the  current — that  is,  the  rate  of  flow  of  the  electricity 
between  two  points  of  a  conductor — does  not  depend  upon  the 
electromotive  force  alone,  any  more  than  the  rate  of  discharge  of 
water  from  the  end  of  a  long  pipe  depends  alone  on  the  difference  of 
level  between  it  and  the  reservoir.  In  both  cases  the  resistance  to 
the  flow  must  also  be  taken  account  of.  With  a  given  difference  of 
level,  more  water  will  pass  per  second  through  a  wide  than  through 
a  narrow  pipe,  for  the  resistance  due  to  friction  is  greater  in  the 
latter.  In  the  case  of  an  electrical  current,  a  wire  connecting 
the  two  poles  of  a  Daniell's  cell  will  represent  the  pipe.  A  thick 
short  wire  has  less  resistance  than  a  thin  long  wire  ;  and  for  a  given 
difference  of  potential,  of  electric  level,  a  stronger  current  will  flow 
along  the  former.  But  for  a  wire  of  given  dimensions,  the  intensity 
of  the  current  will  vary  with  the  electromotive  force.  The  relation 
between   electromotive   force,    strength   of   current,    and   resistance 

were  experimentally  determined  by  Ohm,  and  the  formula  C=  — , 

R 
which  expresses  it,  is  called  Ohm's  Law.  It  states  that  the  current 
varies  directly  as  the  electromotive  force,  and  inversely  as  the 
resistance. 

For  the  measurement  of  electrical  quantities  a  system  of  units  is 
necessary.  The  common  unit  of  resistance  is  the  ohm,  of  current 
the  ampere,  of  electromotive  force  the  volt.  The  electromotive  force 
of  a  Daniell's  cell  is  about  a  volt.  An  electromotive  force  of  a  volt, 
acting  through  a  resistance  of  an  ohm,  yields  a  current  of  one 
ampere  ;  but  the  current  produced  by  a  Daniell's  cell,  with  its  poles 
connected  by  a  wire  of  i  ohm  resistance,  would  be  less  than  an 
ampere,  because  the  internal  resistance  of  the  cell  itself — that  is,  the 
resistance  of  the  liquids  between  the  zinc  and  the  copper — must  be 
added  to  the  external  resistance  in  order  to  get  the  total  resistance, 
which  is  the  quantity  represented  by  R  in  Ohm's  Law. 

Measurement  of  Resistance. — To  find  the  resistance  of  a  con- 
ductor, we  compare  it  with  known  resistances,  as  a  grocer  finds  the 


MUSCLE 


617 


weight  of  a  packet  of  tea  by  comparing  it  with  known  weights.     Th< 
\\  beatstone  s  bridge  method  oi  measuring  resistance  depends  on  the 

i.ut  lh.it  it  tour  resistances,  A  P.,  AD,  BC,  CD,  are  connected,  as  in 
Fig.    204,    with    each    other,    and    with    a    galvanometer,    <■',    and    a 
battcrv  F,  no  current    will  flow   through   the  galvanometer  when 
AM     IH 
AD"(IV 

For  when  no  current  passes  through  the  galvanometer,  B  and  D 
are  at  the  same  potential.  Let  the  tall  of  potential  from  C  to  B  or 
fromfC  to  D  be  «  ;  then,  since  the  total  fall  of  potential  from  C  to  A 
must  be  the  same  along  cither  of  the  paths  CBA  or  CDA,"the  fall 


Fig.  204. — Wheat- 
stone's  Bridge. 


Fig.    205.- 


-Diagram    of    Resistance 
Box. 


from  B  to  A  must  be  equal  to  that  from  D  to  A.  Call  this  fl.  Now. 
the  fall  of  potential  which  takes  place  in  any  given  portion  of  a 
circuit  is  to  the  whole  fall  of  potential  in  the  circuit  as  the  resistance 
of  the  given  portion  is  to  the  whole  resistance.     That  is, 

a  BC 

a  +  p     BC  +  AB' 

/J  AB  .     «_BC 

«  +  ^~BC  +  AB  ;  *'  /3~"AB' 

c.     ..     .       «      CD      .     BC     CD         AB     BC 
Similarly:  3=^;  .  .  m=^,  or  AD=Q& 

In  making  the  measurement,  a  resistance  box,  containing  a  large 
number  of  coils  of  wire  of  different  resistances,  is  used  (Fig.  205). 
The  resistances  corresponding  to  AB  and  AD,  called  the  arms  of  the 
bridge,  may  be  made  equal,  or  may  stand  to  each  other  in  a  ratio 
of  1  :  10,  1  :  100,  etc.  Then,  the  unknown  resistance  being  CD, 
BC  is  adjusted  by  taking  plugs  out  of  the  box  till,  on  closing  the 
current,  there  is  either  no  deflection,  or  the  deflection  is  as  small  as 
it  is  possible  to  make  it  with  the  given  arrangement. 

Galvanometer. — A  galvanometer  is  an  instrument  used  to  detect  a 
current,  to  determine  its  direction,  and  to  measure  its  intensity. 
Since,  by  Ohm's  law,  electromotive  force,  resistance,  and  current 
strength  are  connected  together,  any  one  of  them  may  be  measured 
by  the  galvanometer.  A  galvanometer  of  the  kind  ordinarilv  used 
in  physiology  consists  essentially  of  a  small  magnet  suspended  in  the 
axis  of  a  coil  of  wire,  and  free  to  rotate  under  the  influence  of  a 
current  passing  through  the  coil.  The  most  sensitive  instruments 
possess  a  small  mirror,  to  which  the  magnet  is  rigidly  attached.     A 


618  /    1/  \m    II    OF  PHYSIOLOGY 

ray  oi  [ighl  is  allowed  to  fall  on  the  mirror,  from  which  it  is  reflected 
on  to  a  scale  ;  and  the  rotation  of  the  mirror  is  magnified  and 
measured  by  the  excursion  of  the  spot  of  light  on  the  scale.  In 
the  Thomson  galvanometers  the  magnet  is  vcrv  light.  A  strip  or 
two  of  magnetized  watch-spring  docs  very  well.  The  magnet  is 
'damped'  that  is,  its  tendency,  when  once  displaced,  to  go  '>n 
oscillating  about  its  new  position  of  equilibrium  is  overcome  by 
enclosing  it  in  a  narrow  air  space.  In  tin-  Wiedemann  instrument 
the  magnet  is  heavier  (Fig.  206).  It  swings  in  a  chamber  with 
copper  walls.  Every  movement  of  the  magnei  'induces'  currents 
in  the  copper  ;  these  tend  to  oppose  the  movement,  and  so  '  damping  ' 
is  obtained.  It  is  usual  to  read  the  deflections  oi  the  Wiedemann 
galvanometer  by  means  of  a  telescope.  An  inverted  scale  is  placed 
over  the  telescope  at  a  distance  of,  say,  a  metre  from  the  mirror  ;  an 
upright  image  of  the  scale  is  formed  in  the  telescope  after  reflection 
from  the  mirror,  and  with  every  movement  of  the  latter  the  scale 
divisions  appear  to  move  correspondingly.  The  method  oi  reading 
by  a  telescope  can  be  applied  to  any  minor  galvanometer,  and  is 


Fig.  206. — Scheme  of  Wiedemann's  Galvanometer  (withT]  li  scopj  Ri  ading). 

T.  telescope  ;  S,  scale  :  M,  mirror  ;  m,  ring  magnet  suspended  between  the  two 
galvanometer  coils  G,  the  distance  of  which  from  m  cm  be  varied  ;  F,  fibre 
suspending  mirror  and  magnet . 

often   extremely   convenient   in   physiological   work.     Sometime 
small  scale  is  fastened  on  the  mirror  itself,  and  observed  directly 
through  a  low-power  microscope. 

A  suspended  magnet,  if  no  other  magnets  arc  near,  takes  up  a 
definite  position  under  the  influence  of  the  earth's  magnetism  ;  its 
long  axis,  in  the  position  of  rest,  lies  in  a  vertical  plane,  called  the 
plane  of  the  magnetic  meridian  at  the  given  place.  The  '  marked  ' 
or  north  pole  points  north,  the  south  pole  south.  If  the  magnet  is 
disturbed  from  this  position,  it  tends  to  return  to  it  as  soon  as  the 
disturbing  force  ceases  to  act.  If,  for  instance,  the  north  pole  is 
displaced  in  an  eastward  direction,  the  earth's  magnetism  will 
produce  a  couple  (a  pair  of  parallel  forces  acting  in  opposite  direc- 
tions), one  member  of  which  mav  be  considered  to  pull  the  north  pole 
towards  the  west,  and  the  other  to  pull  the  south  pole  towards  the 
east.  Displacement  of  the  magnet,  then,  is  opposed  by  this  couple  ; 
and  where  the  displacing  force  is  small — that  is.  the  current  passing 
through   the  galvanometer  weak,   as  is  usually  the  case  in   physio- 


MUS<  I  i 


6ig 


logical  observations  it  becomes  important  to  reduce  the  effect  o\ 
the  magnetism  oi  the  earth,  in  other  words,  the  strength  o\  thi 
magnetic  6eld,  as  much  .is  possible.  This  can  be  done  by  bringing 
a  magnet  into  the  neighbourhood  of  the  galvanometer  with  its  north 
pole  pointing  north.  This  pole,  which  is  the  one  attracted  by  the 
earths  north  pole,  is  magnetized  in  the  opposite  sense;  and  by 
properly  adjusting  its  distance  from  the  galvanometer  magnet,  the 
influence  of  the  earth  on  the  latter  can  be  almost  neutralized,  and 
tin  system  made  nearly  'astatic'  In  many  galvanometers  the 
magnets  attached  to  the  mirror  form  an  'astatic'  pair  (Fig.  207). 
Two  small  magnets  of  nearly  equal  strength  arc  connected  to  a 
light  slip  <>!  horn  or  an  aluminium  wire,  with  their  poles  in  opposite 
directions.  The  earth's  magnetism  affects  them  oppositely,  so  that 
the  resultant  action  is  nearly  zero.  It  is  not  possible  to  make  the 
magnets  exactly  equal  in  strength,  nor  is 
it  desirable,  for  then  the  system  would 
not  tend  to  come  to  rest  in  any  definite 
position,  and  the  zero  point  would  be 
constantly  shifting.  Either  one  or  both 
magnets  may  be  surrounded  by  the  gal- 
vanometer coils.  If  both  are  so  sur- 
rounded, each  must  be  within  a  separate 
coil,  and  the  current  must  pass  in  oppo- 
site directions  in  the  two  coils,  otherwise 
they  would  neutralize  each  other.  In 
the  d'Arsonval  galvanometer  the  current 
passes  through  a  small  coil  of  fine  wire 
suspended  in  the  field  of  a  strong  magnet. 
When  the  current  passes  the  coil  is  de- 
flected, carrying  with  it  a  small  mirror 
attached  to  the  suspending  filament.  A 
great  advantage  of  this  galvanometer  in 
many  situations  is  that  it  is  unaffected  by 
neighbouring  currents. 

The  deflection  of  a  magnet  by  a  current 
of  given  strength  is  proportional  to  the 
number  of  turns  of  wire  around  it. 
Where  an  increase  in  the  number  of  turns 
does  not  sensibly  cut  down  the  current, 
as  in  experiments  on  tissues  like  nerves, 
whose  resistance  is  large  in  comparison 
with  that  of  the  galvanometer,  an  instru- 
ment wdth  a  great  number  of  turns  of  wire 
galvanometer — is  suitable.  The  resistance  of  the  galvanometers 
generally  used  in  electro-physiology  varies  from  3,000  or  4,000  ohms 
up  to  five  times  as  much. 

The  string  galvanometer  of  Einthoven  has  peculiar  merits  for 
certain  physiological  purposes.  It  consists  of  a  silvered  quartz-fibre 
stretched  in  a  very  strong  magnetic  field.  When  traversed  by  a  cur- 
rent the  fibre  is  deflected,  and  by  means  of  a  beam  of  light  the  deflec- 
tion is  greatly  magnified.  Bv  photographing  the  beam  a  record  of 
the  swing  of  the  fibre  caused  by  a  momentary  current  can  be  obtained. 
In  this  way  the  instrument  may  be  employed  to  record  the  electrical 
changes  occurring  in  the  human  heart  with  each  beat  (p.  732). 

A  rheocord  is  an  instrument  bv  means  of  which  a  current  may  be 
divided,  and  a  definite  portion  of  it  sent  through  a  tissue  (Fig.  208). 


Fig.  207. — Astatic  Pair  of 
Magnets. 

SX  and  NS  are  the  mag- 
nets, fixed  to  the  vertical 
piece  P.  M  is  a  mirror. 
The  arrow-heads  show  the 
direction  of  a  current  which 
deflects  both  magnets  in  the 
same  direction. 

—that  is,  a  high-resistance 


Hjn 


/    MANV  \L  OF  PHYSIOLOGY 


A   compensator  is  simply  a  rheocord   from   which  .1   branch  of  a 
current  is  led  off,  to  balance  or  '  compensate  '  any  electrical  differ 

in  a  tissue,  like    thai    h  hi*  h    • 
11       i"    t  he    <  in  renl    oi    rest    oi 
muscle,  for  example  1 1  ig 

An  electrometer  is  an  instrumenl 
for  measuring  ele<  1  romol  \\  e  for*  e 
— that  is.  different  es  oJ  ele<  1 1  li 
potent  Lai.  Lippmann's  <  apillary 
<  !<'  1  rometer  is  rnui  h  employed  in 
physiology.  A  1  onvenienl  form  oi 
it  is  shown  in  Fig.  210.  A  simple 
form,  suitable  for  students  working 
in  a  class  where  .1  1  onsiderable 
number  oi  1  opieslof  the  instrumenl 
is  needed,  can^  be  1  onvenienl  ly 
made  as  follows':  A  -1  is  1  tub 
drawn   ou1    to  a    i    pill  try   a1 


Fig      208. — Diagram    of     Rheocord 
(after  Du  Bois-Kevmond's  Modi  l). 


209.     1  i 


Description  of  Fig.  208  :  I.  to  VII.  arc  pieces  oi  brass  connei  ted  with  the  wires 
a  to  /  in  such  a  way  that  by  taking  out  any  of  the  brass  pln^s  1  to  5,  a  greater  1 1 
less  resistance  may  be  interposed  between  the  binding  screws  A  and  B.  The 
two  wires  a  are  connected  by  a  slider  s,  tilled  with  mercury  or  otherwise  making 
contact  between  the  wires.  The  current  from  the  batter)  B  dh  ides  at  A  and  B, 
part  of  it  passing  through  the  rheocord,  part  through  X.  the  nerve,  muscle,  or 
other  conductor  which  forms  the  alternative  circuit.  When  a  sufficient  resistance 
R  is  interposed  in  the  chiei  circuit  to  make  the  total  strength  of  the  current 
independent  of  changes  in  the  resistance  of  the  rheocord,  the  strength  <>t  the 
current  passing  through  X  will  vary  inversely  as  the  resistance  of  the  rheocord. 

When  all  the  plu^s  are  in.  and  the  slider  (lose  up  to  A.,  there  is  practically  QO 
resistance  in  the  rheocord.  and  all  the  current  passes  across  the  brass  pieces  and 
plugs  to  I'..  and  thence  back  to  the  battery.  As  s  is  moved  farther  away  from  A. 
the  resistance  of  the  rheocord  is  increased  more  and  more,  and  the  intensity  of 
the  current  passing  through  X  becomes  greater  and  greater.      The  --(ale  s  shows 

the  length  of  wire  interposed  lor  any  position  Of  S,  and  tins  gives  a  rough  measure 
Oi  the  frad ol  the  current   passing  through   X.       When  pin-   i   or  J  is  taken  on!, 

a  resistance  equal  to  that  of  the  two  wires  «  is  interposed  ;  plug  .;.  twice  that  "I  </  . 
plug  4.  five  t  imes  ;  plug  5,  ten  times. 

Description  oi  Fig.  209  :  W  is  a  wire  stretched  alongside  a  scale  S.  A  battery 
B  is  connected  to  the  binding  screws  at  the  ends  oi  the  wire.  \  pair  ol  unpolariz- 
able  electrodes  an-  connei  ti  d,  one  with  a  slider  m<>\  ing  i  d  a  wire,  the  other  through 
a  galvanometer  with  one  oi  the  terminal  binding-screws.  In  the  figure  a  nerve 
is  shown  on  the  electrodes,  one  ot  which  is  in  contact  with  an  uninjured  portion. 
the  other  witli  an  injured  part.  The  slider  is  moved  until  the  twig  ot  the  com- 
pensating current  just  balances  the  demarcation  current  ot  the  nerve  and  the 
galvanometer  shows  no  deflection. 


MISCLE 


<>2l 


end  and  filled  with  mercury.  The  tube  is  inserted  into  .i  small 
glass  bottle,*  and  fastened  in  its  neck  by  a  cork  or  a  plug  of 
sealing-wax    which   docs    not    quite    (ill    the   opening,   so   thai    the 

interior  of  the  bottle  is  still  in  communication  with  the  ex- 
ternal air.  The  upper  end  of  the  tube  is  connected  by  a  short 
piece  of  rubber-tubing  with  .1  glass  T-tube  as  in  Fig.  211.  The 
bottle  is  partially  filled  with  5  to  10  per  cent,  sulphuric  acid,  under 
which  the  capillary  dips.  By  means  of  a  small  reservoir  made  from 
a  piece  of  glass-tubing  tilled  with  mercury,  and  connected  with  the 
stein  of  the  T-tnbe,  a  little  mercury  is  forced  through  the  capillary 


Fig.  210. — Capillary  Electrometer  (after  Frey),  as  arranged  for  Mount 
ing  on   the  Microscope  Stage. 

The  electrometer  consists  (i)  of  a  small  table  carrying  a  parallel-sided  glass 
vessel  containing  mercury  and  sulphuric  acid.  (2)  The  capillary  tube,  which 
can  be  moved  in  two  directions  at  right  angles  to  each  other,  and  so  adjusted 
in  the  field  of  the  microscope.  (3)  A  pressure-vessel,  and  a  manometer 
connected  with  it  for  measuring  the  pressure.  (4)  Two  binding-screws  con- 
nected by  wires  to  the  mercury  in  the  capillary  tube  and  in  the  parallel-sided 
vessel.  The  binding-screws  can  be  short-circuited  by  closing  the  friction-key  shown 
at  the  right  side  of  the  figure,  thus  preventing  any  difference  of  electro-motive  force 
between  two  points  connected  with  the  screws  from  affecting  the  electrometer. 

so  as  to  expel  the  air  in  it.  When  the  pressure  is  lowered  again, 
sulphuric  acid  is  drawn  up,  and  now  lies  in  the  capillary  in  contact 
with  the  meniscus  of  the  mercury.  A  platinum  wire  fused  through 
*  A  parallel-sided  bottle  is  best,  as  it  gives  the  clearest  image  of  the 
meniscus.  But  it  is  easiest  to  make  a  cylindrical  bottle  from  a  piece  of 
wide  glass-tubing,  and  to  insert  a  platinum  wire  into  it  before  closing  it 
at  the  bottom  in  the  blow-pipe  flame.  The  tube  can  then  be  firmly 
fastened  with  sealing-wax  in  a  depression  in  a  piece  of  wood,  the  wire 
being  brought  out  through  a  hole  in  the  wood.  Once  the  instrument  is 
arranged,  there  is  little  chance  of  the  capillary  getting  broken,  and  there 
is  very  little  evaporation  of  the  acid. 


622 


/    MANUAL  OF  PHYSIOLOGY 


the  tube,  or  simply  inserted  through  its  upper  end,  dips  into  the 
mercury.  Another,  passing  through  the  cork,  or,  better,  fused 
through  the  bottom  of  the  bottle,  makes  contact  with  the  sulphuric 
acid  through  some  mercury.  The  bottle  is  fastened  on  the  stage 
of  a  microscope,  the  capillary  brought  into  focus,  and  the 
meniscus  adjusted  by  raising  or  lowering  the  reservoir.  When  the 
platinum  wires  are  connected  with  points  at  different  potential,  a 
current  begins  to  pass  through  the  instrument,  and  the  meniscus  of 
the  mercury  in  the  capillary  tube,  where  the  current  density  is  the 
greatest,  becomes  polarized  by  the  ions  separated  from  the  sulphuric 


B,  bottle  containing  sulphuric  acid  ; 
Hg,  mercury  ;  E,  R',  platinum  wires. 
E  dips  into  the  mercury  in  the  vertical 
tube,  and  E'  is  fused  through  the 
bottom  of  B,  so  as  to  make  contact  with 
the  mercury  in  B,  the  other  end  of  it 
passing  out  through  a  small  hole  in  the 
wooden  platform  /•',  on  which  B  rests. 
F  is  fastened  to  the  stage  of  the  micro- 
scope, S,  by  a  pin,  G,  passing  through 
one  of  the  clip-holes,  and  to  the  wooden 
upright,  1),  by  the  pin,  H.  1)  fits  tightly 
over  the  microscope  stage,  but  can  be 
moved  laterally  a  little  so  as  to  bring 
the  capillary  into  the  middle  of  the  field. 
/,  stem  of  glass  T-tube  passing  through 
a  hole  in  I).  L,  rubber  tube  connecting 
the  capillary  point  with  the  vertical 
portion  of  the  T-tube.  A  is  a  reservoir 
containing  mercury  connected  by  the 
rubber  tube  .1/  to  /.  A  can  be  raised  or 
lowered  by  sliding  it  in  the  clips  A'. 
In  the  figure  the  capillary  tube  appears 
as  if  the  mercury  extended  to  the  very 
point  of  it.  This  should  not  be  the 
case  ;  the  sulphuric  acid  should  rise  for 
some  distance  in  the  capillary,  so  that 
the  mercury  shows  a  finely-bounded 
meniscus  in  the  tube  as  is  represented 
in  C,  the  magnified  image  of  the  capillary 
as  seen  with  the  microscope. 


Fig.   2ii. — A  Simple   Capillary 
Electrometer. 


acid  at  the  surface  of  contact  between  the  acid  and  the  mercury,  so 
that  the  meniscus  is  no  longer  in  equilibrium  in  the  tube.  The 
surface  tension  is  diminished  when  the  direction  of  the  current  is 
from  mercury  to  acid  (mercury  at  a  higher  potential  than  acid),  and 
is  no  longer  able  to  counterbalance  the  hydrostatic  pressure  of  the 
mercury.  The  meniscus  therefore  moves  down  in  the  tube.  With 
the  opposite  direction  of  current  (mercury  at  a  lower  potential  than 
acid)  the  surface  tension  is  increased,  and  the  meniscus  moves  up. 
The  polarization  develops  itself  almost  instantaneously,  and  thus  an 
electromotive  force  is  at  once  established  in  the  opposite  direction 
to  that  between  the  points  connected  with  the  electrometer,  and 
equal  to  it  so  long  as  the  external  electromotive  force  is  not  sufti- 


MUSCLE 


623 


cicntly  great  to  cause  continuous  electrolysis  of  the  acid — that  is,  so 
long  as  it  is  below  about  2  volts.  The  external  current  is  therefore 
.it  once  compensated,  and  after  the  first  moment  no  current  passes 
through  the  instrument,  which  is  accordingly  not  a  measurer  of 
current,  but  of  electromotive  force.  It  is  very  suitable  for  detecting 
and  measuring  such  small  differences  of  potential  as  occur  in  animal 
t  issues. 

Induced  Currents. — When  a  coil  of  wire  in  which  a  current  is 
(lowing  is  brought  up  suddenly  to  another  coil,  a  momentary  current 
is  developed  in  the  stationary  coil  in  the  opposite  direction  to  that 
in  the  moving  coil.  Similarly,  if  instead  of  one  of  the  coils  being 
moved  a  current  is  sent  through  it,  while  the  other  coil  remains  at 
rest  in  its  neighbourhood,  a  transient  oppositely-directed  current  is 
set  up  in  the  latter.  When  the  current  in  the  first  coil  is  broken,  a 
current  in  the  same  direction  is  induced  in  the  other  coil. 

Du  Bois-Reymond's  Sledge  Inductorium  (Fig.  212). — This  consists 


Fig.  212. — Du  Bois-Reymond's  Inductorium. 

B,  primary,  B\  secondary,  coil ;  H,  guides  in  which  B'  slides,  with  scale  ; 
D,  electro-magnet ;  E,  vibrating  spring  ;  i,  wire  connecting  wire  of  D  to  end  of 
primary  ;  v,  screw  with  platinum  point,  connected  with  other  end  of  primary  ; 
A,  A',  binding-screws,  to  which  are  attached  the  wires  from  battery.  A'  is 
connected  with  the  wire  of  the  electro-magnet  D,  and  through  it  and  i  with  the 
primary. 


of  two  coils,  the  primary  and  the  secondary,  the  former  having  a 
comparatively  small  number  of  turns  of  fairly  thick  copper  wire, 
the  latter  a  large  number  of  turns  of  thin  wire.  The  object  of 
this  is  that  the  resistance  of  the  primary,  which  is  connected  with 
one  or  more  voltaic  cells,  may  not  cut  down  the  current  too  much  ; 
while  the  currents  induced  in  the  secondary,  having  a  high  electro- 
motive force,  can  readily  pass  through  a  high  resistance,  and  are 
directly  proportional  in  intensity  to  the  number  of  turns  of  the 
wire. 

By  means  of  various  binding-screws  and  the  electro-magnetic 
interrupter,  or  Neef's  hammer,  shown  in  the  figure  and  explained 
below  it,  the  current  can  be  made  once  in  the  primary  or  broken 
once,  or  a  constant  alternation  of  make  and  break  can  be  kept  up. 
We  can  thus  get  a  single  make  or  break  shock  in  the  secondary,  or  a 


,  A    VISUAL  OF  PHYSIOLOGY 

series  of  shocks,  sometimes  called  an  interrupted  or  farad ic  current. 
Such  a  series  of  stimuli  can  also  be  got  by  making  and  lire. iking  a 
voltaic  current  at  any  given  rate. 

A  '  self-induced  '  current  can  also  be  obtained  from  a  single  coil  ; 
for  instance,  from  the  primary  coil  alone  of  the  induction  apparatus. 
The  reason  of  this  is,  that  when  a  current  begins  to  flow  through  any 
turn  of  a  coil  of  wire,  it  induces  in  all  the  other  turns  a  current  in 
the  opposite  direction,  and,  when  it  ceases  to  flow,  a  current  in  the 
same  direction  as  itself.  The  former  current,  '  the  make  extra  shock,' 
being  in  the  opposite  direction  to  the  inducing  current,  is  retarded  in 
its  development,  and  reaches  its  maximum  more  slowly  than  '  the 
break  extra  shock.'  But,  as  we  shall  see,  the  suddenness  with  which 
an  electrical  change  is  brought  about  is  one  of  the  most  important 
factors  in  electrical  stimulation,  and  therefore  the  break  extra  shock 
is  a  much  more  powerful  stimulus  than  the  make.  Owing  to  these 
self-induced  currents,  the  stimulating  power  of  a  voltaic  stream  may 
be  much  increased  by  putting  into  the  circuit  a  coil  of  wire  of  not 
too  great  resistance. 

The  self-induction  of  the  primary  also  affects  the  stimulating 
power  of  the  currents  induced  in  the  secondary  ;  the  shock  induced 
in  the  secondary  by  break  of  the  primary  current  is  a  stronger 
stimulus  than  that  caused  at  make  of  the  primary.  The  reason  is 
that  with  a  given  distance  of  primary  and  secondary,  and  a  given 
intensity  of  the  voltaic  current  in  the  primary,  the  abruptness  with 
which  the  induced  current  in  the  secondary  is  developed  depends 
upon  the  rapidity  with  which  the  primary  current  reaches  its  maxi- 
mum at  closing,  or  its  minimum  (zero)  at  opening.  Now,  the  make 
extra  current  retards  the  development  of  the  primary  current,  while 
in  the  opened  circuit  of  the  primary  coil  the  current  intensity  falls 
at  once  to  zero. 

The  inequality  between  the  make  and  break  shocks  of  the 
secondary  coil  can  be  greatly  reduced  by  means  of  Helmholtz's  wire. 
Connect  one  pole  of  the  battery  with  v  (Fig.  212),  and  the  other 
with  A'.  Join  A  and  A'  by  a  short,  thick  wire.  With  this  arrange- 
ment the  primary  circuit  is  never  opened,  but  the  current  is  alter- 
nately allowed  to  flow  through  the  primary,  and  short-circuited 
when  the  spring  touches  v.  The  '  make  '  now  corresponds  to  the 
sudden  increase  of  intensity  of  the  current  in  the  primary  when  the 
short-circuit  is  removed,  and  the  '  break  '  to  its  sudden  decrease 
when  the  short-circuit  is  established.  In  both  cases  self-induced 
currents  are  developed,  and  therefore  both  shocks  are  weakened. 
But  the  opening  stimulus  is  now  slightly  the  weaker  of  the  two, 
because  the  opening  extra  shock  has  to  pass  through  a  smaller 
resistance  (the  short-circuit)  than  the  closing  extra  shock  (which 
passes  by  the  battery),  and  therefore  opposes  the  decline  of  current 
intensity  on  short-circuiting  more  than  the  closing  shock  opposes 
the  increase  of  current  intensity  on  long-circuiting  through  the 
primary. 

By  means  of  wires  connected  with  the  terminals  of  the  secondary 
coil,  and  leading  to  electrodes,  a  nerve  or  muscle  may  be  stimulated  ; 
and  it  is  usual  to  connect  the  wires  to  a  short-circuiting  key  (Fig. 
215),  by  opening  which  the  induced  current  is  thrown  into  the  tissue 
to  be  stimulated.  For  some  purposes  the  electrodes  may  be  of 
platinum  ;  but  all  metals  in  contact  with  moist  tissues  become 
polarized  when  currents  pass  through  them — that  is,  have  decom- 
position products  of  the  electrolysis  of  the  tissues  deposited  on  them- 


MUSCLE 


625 


Fig.  213. — Unpolarizable   Electrodes. 

A,  hook-shaped  ;  B.  U -tubes  ;  C,  straight.  D,  clay 
in  contact  with  tissue  :  S,  saturated  zinc  sulphate 
solution  ;  Z,  amalgamated  zinc  wire. 


Ami  as  any  slighl  1  hemicaJ  difference,  or  even  perhaps  a  difference 
oi  phj  ii«    I  state,  between  the  two  electrodes  will  cause  them  and  the 

tissues  in  form  a  battery  evolving  a  continuous  current,  it  is  often 
desirable  to  use  unpolarizable  electrodes. 

Unpolarizable  Electrodes.  Some  convenient  forms  of  these  are 
represented  in  Fig.  213.  A  piece  of  amalgamated  zinc  wire  dips  into 
saturated  zinc  sulphate  solution  cont/jned  in  the  upper  part  of  a 
-lis.  tube.  The  lower  end  of  the  tube  may  be  straight,  but  drawn 
out  so  as  to  terminate 
in  a  not  very  large 
opening,  or  it  may  be 
bent  into  a  hook,  in 
the  bend  of  which  a 
hole  is  made.  Before 
the  tube  is  filled  with 
the  zinc  sulphate  solu- 
tion, the  lower  pirt 
of  it  is  plugged  with 
china  clav  made  nn 
with  physiological  s-,lt 
solution.  The  clay  just 
projects  through  the 
opening,  and  thus 
comes  in  contact  with 
the  tissue.  When  these 

electrodes  are  properly  set  up,  there  is  very  little  polarization  for 
several  hours,  but  for  long  experiments,  U-shaped  tubes,  filled 
with  saturated  zinc  sulphate  solution,  are  better.  The  amalga- 
mated zinc  dips  into  one  limb,  and  a  small  glass  tube  filled  with  clay, 
on  which  the  tissue  is  laid,  into  the  other. 

Pohl's  Commutator  (Fig.  214)  consists  of  a  block  of  paraffin  or 
wood  with  six  mercury  cups,  each  in  connection  with  a  binding-screw 
(not  shown  in  the  figure).  Cups  1  and  6  and  2  and  5  are  connected 
by  copper  wires,  which  cross  each  other 
without  touching.  The  bridge  consists 
of  a  glass  or  vulcanite  cross-piece  a,  to 
which  are  attached  two  wires  bent 
into  semicircles,  each  connected  with  a 
straight  wire  dipping  into  the  cups  3 
and  4  respectively.  With  the  bridge  in 
the  position  shown  in  the  figure,  a 
current  coming  in  at  4  would  pass  out 
by  the  wire  connected  with  1 ,  and  back 
again  by  that  connected  with  2,  in  the 
direction  shown  by  the  arrows.  When 
the  bridge  is  rocked  to  the  other  side 
so  that  the  bent  wires  dip  into  5  and  6, 
the  direction  of  the  current  is  reversed.  The  cross-wires  may  be 
taken  out  altogether,  and  the  commutator  used  to  send  a  current 
at  will  through  either  of  two  circuits,  one  connected  with  1  and  2, 
and  the  other  with  5  and  6. 

Du  Bois-Reymond's  Short-circuiting  Key. — A  cheap  and  con- 
venient form  is  shown  in  Fig.  215. 

Time-markers — Electric  Signal. — It  is  of  importance  to  know  the 
time  relations  of  many  physiological  phenomena  which  are  graphi- 
cally recorded  ;  for  example,  the  contraction  of  a  skeletal  muscle  or 

40 


Fig.  214. — Pohl's  Com- 
mutator. 


626 


.1    M  INUAL  OF  PHYSIOLOGY 


the  beat  of  a  heart.  For  this  purpose  a  tracing  showing  the  speed 
of  the  travelling  surface  in  a  given  time  is  often  taken  simultaneously 
with  the  record  of  the  movement  under  investigation.  For  a  slowly- 
moving  surface  it  is  sufficient  to  mark  intervals  of  one  or  two  seconds, 
and  this  is  very  readily  done  by  connecting  an  clectro-m  ignctic 
marker  (such  as  the  electric  signal  of  Deprez)  with  a  circuit  which  is 


Fig.   215 — Short-circuiting 
Key. 


Time-marker. 


Arrangement  for  marking  2  second 
intervals.  D,  seconds  pendulum, 
with  platinum  point  E  soldered  on  ; 
A,  mercury  trough,  into  which  E 
dips  at  end  of  its  swing  ;  B,  Daniell 
cell;  C,  electro  -  magnets  which 
draw  down  writing-lever  F  when 
the  current  is  closed  by  E  dipping 
into  A  ;  G,  spring  (or  piece  of  india- 
rubber),  which  raises  F  as  soon  as 
current  is  broken. 


closed  and  broken  by  the  seconds  pendulum  of  an  ordinary  clock 
(Fig.  216)  or  a  metronome  (Fig.  76.  p.  179).  For  shorter  intervals 
a  tuning-fork  is  used,  which  makes  and  breaks  a  circuit  including  an 
electromagnetic  marker,  or  writes  on  the  drum  directly  bv  means  of 
a  writing-point  attached  to  one  of  the  prongs. 

In  all  the  great  functions  of  the  body  muscular  movements 
play  an  essential  part.  The  circulation  and  the  respiration, 
the  two  functions  most  immediately  essential  to  life,  are  kept 
up  by  the  contraction  and  relaxation  of  muscles.  The  move- 
ments of  the  digestive  canal,  the  regulation  of  the  blood-supply 
to  its  glands  and  to  all  parts  of  the  body,  and  that  immense  class 
of  movements  which  we  call  voluntary,  are  all  dependent  upon 
muscular  action,  which,  again,  is  indebted  for  its  initiation, 
continuance,  or  control,  to  impulses  passing  along  the  nerves 
from  the  nerve-centres.  Hitherto  we  have  not  gone  below 
the  surface  fact,  that  muscular  fibres  have  the  power  of  con- 
tracting, either  automatically,  or  in  response  to  suitable  stimuli. 
In  this  chapter  and  the  two  next  we  shall  consider  in  detail 
the  general  properties  of  muscle,  nerve,  and  the  other  excitable 
tissues. 


MUSCLE  627 

Lying  deeper  than  the  peculiarities  of  individual  muscles, 
muscular  tissue  has  certain  common  properties — physical, 
chemical,  and  physiological.  The  biceps  muscle  flexes  the  arm 
upon  the  elbow,  and  the  triceps  extends  it.  The  external  rectus 
rotates  the  eyeball  outwards.  The  intercostal  muscles  elevate 
the  ribs.  The  sphincter  ani  seals  up  by  a  ring-like  contrac- 
tion the  lower  end  of  the  alimentary  canal.  These  actions  are 
very  different,  but  the  muscles  that  carry  them  out  are  at  bottom 
very  similar.  And  it  cannot  be  doubted  that  the  functional 
differences  are  due  entirely,  or  almost  entirely,  to  differences 
of  anatomical  connection,  on  the  one  hand  with  bones  and 
tendons,  on  the  other  with  the  nerve-cells  of  the  spinal  cord  and 
brain.  The  common  properties  in  which  all  the  skeletal  muscles 
agree  are  the  subject-matter  of  the  general  physiology  of  striated 
muscle. 

The  cardiac  muscle  differs  more,  both  in  structure  and  in 
function,  from  the  skeletal  muscles  than  these  do  among  them- 
selves ;  the  smooth  muscle  of  the  intestines  and  bloodvessels 
still  more.  But  every  muscular  fibre,  striped  or  unstriped, 
resembles  every  other  muscular  fibre  more  than  it  does  a  nerve- 
fibre  or  a  gland-cell  or  an  epithelial  scale.  The  properties 
common  to  all  muscle  make  up  the  general  physiology  of  mus- 
cular tissue. 

A  nerve-fibre  is  at  first  sight  very  different  from  a  muscular 
fibre.  It  has  diverged  more  widely  from  the  primitive  type 
of  undifferentiated  protoplasm.  It  has  lost  the  power  of  con- 
traction, or  contractility,  but  it  retains,  in  common  with  the 
muscle-fibre,  susceptibility  to  stimulation,  or  excitability,  the 
capacity  for  growth,  and  to  a  limited  extent  the  capacity  for 
reproduction.  This  inheritance  of  primitive  properties,  retained 
alike  by  both  tissues,  is  the  basis  of  the  general  physiology  of 
muscle  and  nerve. 

The  electrical  organ  of  the  Torpedo  or  the  Malapterurus  is 
intermediate  in  some  respects  between  muscle  and  nerve,  and 
has  properties  common  to  both.  In  the  gland-cell  the  chemical 
powers  of  native  protoplasm  have  been  specialized  and  de- 
veloped. Contractility  has  been,  in  general,  entirely  l;>st; 
but  excitability  remains.  The  idea  that  certain  common 
endowments  find  expression  in  the  action  of  muscle,  nerve, 
electrical  organ,  gland,  etc.,  in  the  midst  of  all  their  apparent 
differences,  is  the  basis  of  the  general  physiology  of  the  excitable 
tissues. 

Amoeboid  movement  is  the  most  primitive,  the  least  elabo- 
rated form  of  contraction.  An  amoeba  may  be  seen  under 
the  microscope  to  send  out  pseudopodia,  or  processes,  of  its 
substance,  and  to  retract  them,  and  it  is  able  by  such  movements 

40 — 2 


628  A   MANUAL  OF  PHYSIOLOGY 

to  change  its  place  and  to  take  in  and  expel  food  and  foreign 
bodies.  The  maximum  velocity  of  the  amoeboid  movement  has 
been  reckoned  at  o-oo8  millimetre  a  second.  Stimulation  with 
the  constant  current  or  induction  shocks  causes  the  whole  of  the 
processes  to  be  drawn  in,  and  the  amoeba  to  gather  itself  into  a 
ball.  This  illustrates  a  universal  property  of  protoplasm, 
excitability,  or  the  power  of  responding  to  certain  influences, 
or  stimuli,  by  manifestations  of  the  peculiar  kind  which  we 
distinguish  as  vital  or  physiological.  Many  other  unicellular 
organisms  and  the  chief  varieties  of  the  white  blood-corpuscles 
behave  like  the  amoeba  ;  and  we  have  already  dwelt  upon  some 
of  the  important  functions  fulfilled  by  such  amoeboid  move- 
ment in  the  higher  animals  and  in  man.  But  a  great  distinction 
between  this  kind  of  contraction  and  that  of  a  muscular  fibre 
is  that  it  takes  place  in  any  direction. 

Cilia. — Cilia  possess  a  higher  and  more  specialized  grade  of 
contractility.  They  are  very  widely  distributed  in  the  animal 
kingdom  ;  and  analogous  structures  are  also  found  in  many 
low  plants,  such  as  the  motile  bacteria. 

In  the  human  subject  ciliated  epithelium  usually  consists  of 
several  layers  of  cells,  the  most  superficial  of  which  are  pear- 
shaped,  the  broad  end  being  next  the  surface,  and  covered  with 
extremely  fine  processes,  or  cilia,  about  8  /x  in  length,  which  are 
planted  on  a  clear  band.  It  lines  the  respiratory  passages,  the 
middle  ear  and  Eustachian  tube,  the  Fallopian  tubes,  the  uterus 
above  the  middle  of  the  cervix,  the  epididymis,  where  the  cilia 
are  extremely  long,  and  the  central  cavity  of  the  brain  and 
spinal  cord. 

Ciliary  motion  can  be  readily  studied  by  placing  a  scraping 
from  the  palate  of  a  frog,  or  a  small  portion  of  the  gill  of  a  fresh- 
water mussel  under  the  microscope  in  a  drop  of  physiological  salt 
solution.  The  motion  of  the  cilia  is  at  first  so  rapid  that  it  is 
impossible  to  make  out  much,  except  that  a  stream  of  liquid, 
recognised  by  the  solid  particles  in  it,  is  seen  to  be  driven  by 
them  in  a  constant  direction  along  the  ciliated  edge.  When  the 
motion  has  become  less  quick,  which  it  soon  does  if  the  tissue  is 
deprived  of  oxygen,  it  is  seen  to  consist  in  a  swift  bending  of 
the  cilia  in  the  direction  of  the  stream,  followed  by  a  slower 
recoil  to  the  original  position,  which  is  not  at  right  angles  to 
the  surface,  but  sloping  streamwards.  All  the  cilia  on  a  tract 
of  cells  do  not  move  at  the  same  time  ;  the  motion  spreads  from 
cell  to  cell  in  a  regular  wave.  The  energy  of  ciliary  motion 
may  be  considerable,  although  far  inferior  to  that  of  muscular 
contraction.  The  work  which  cilia  are  capable  of  performing 
can  be  calculated  by  removing  the  membrane,  fixing  it  on  a 
plate  of  glass,  cilia  outwards,  putting  weights  on  the  glass  plate, 


MUSCLE 


629 


and  allowing  the  cilia,  like  an  immense  number  of  feet,  to  carry 
it  up  an  inclined  plane.  Bowditch  found  in  this  way  that  the 
cilia  on  a  square  centimetre  of  mucous  membrane  did  nearly 
7  gramme-millimetres  of  work  per  minute  (equal  to  the  raising 
of  7  grammes  to  a  height  of  a  millimetre). 

Since  the  cilia  in  the  respiratory  tract  all  lash  upwards,  they 

must  play  an  important  part  in 
carrying  up  foreign  particles  taken 
in  with  the  air,  and  the  mucus 
in  which  they  are  entangled,  as 
well  as  pathological  products.  En- 
gelmann  found  that  the  energy  of 
ciliary  motion  increases  as  the  tem- 
perature is  raised  up  to  about  400  C, 
after  which  it  diminishes  quickly. 
Over-heating  causes  cilia  to  come 
to  rest,  but  if  the  temperature  has 


Fig.  217. — Ciliated  Cell 
(M.  Heidenhain). 

From  a  '  liver  duct  '  of 
the  garden  snail  x  2,500. 


jifK   A 

Fig.   218. — Ciliated  Cell 
(Schneider). 

From  a  flatworm  (P  I  a  n  o  c  e  r  a 
folium).  1,  space  between  two  ad- 
joining ciliated  cells  ;  2,  basal  bodies  : 
4,  inner  granule  ;  5,  '  cilia  roots  '  ; 
6.  boundary  laver. 


not  been  too  high,  and  has  not  acted  too  long,  they  recover  on 
cooling. 

It  is  not  well  understood  in  what  way  the  contraction  of  the 
cilia  depends  upon  their  connection  with  the  body  of  the  ciliated 
cell.  Very  few  cases  occur  in  which  cilia  have  the  power  of  inde- 
pendent  motion    when   severed   from  the   cell-body.     It   has  been 


630  a   .1/  \\r  \i    ()!■    PHYSIOLOGY 

observed  in  certain  low  forms  of  animals  thai  cilia  which  have 
been  broken  ofl  from  the  cell  are  still  able  to  contract  when  a 
small  portion  of  the  substance  of  the  cell-body  at  the  pohrl  w  here  the 
cilinm  is  attached  to  the  cell,  the  so-called  basal  piece,  or  basal  body 
(Fig.  218),  has  come  off  along  with  them.  In  other  forms  isolated  cilia 
1  .111  contract  in  the  absence  of  anything  corresponding  to  the  basal 
piece.  It  cannot,  therefore,  be  said  that  continuity  with  the  basal 
piece  is  absolutely  necessary.  Nor  is  it  known  what  significance  tor 
the  ciliary  movements  is  possessed  by  the  long  fibrilla-,  called  the 
'  roots  of  the  cilia,'  which  in  some  animals  run  down  through  the  cell 
from  the  basal  bodies  (Figs,  217,  218).  The  theory  has  been  pu1  for- 
ward by  Schafer  that  the  cilia  arc  hollow  processes  of  the  cell-body, 
and  that  their  contraction  is  caused  by  the  passage  of  liquid  into 
them  from  the  cell.  He  believes  that  the  direction  of  movement  is 
determined  by  the  investing  membrane  of  the  cilium  being  thicken-  d 
(or  less  extensible)  along  one  side  or  in  a  spiral  line.  In  some  worms 
and  molluscs  ciliated  cells  are  supplied  with  nerve-fibres,  but  this 
has  not  been  demonstrated  for  the  higher  animals. 

Muscle. — Since  most  of  our  knowledge  of  the  general  physio- 
logy of  muscle  has  been  gained  from  striped  muscle,  in  what 
follows  we  always  refer  to  ordinary  skeletal  muscle,  unless  it 
is  otherwise  stated.  The  sartorius  and  the  gastrocnemius  are  the 
classical  objects  for  experiments  on  striated  muscle.  For  smooth 
muscle  the  adductor  muscle  of  Anodon,  the  fresh-water  mussel,  a 
ring  cut  from  the  middle  portion  of  the  frog's  stomach,  the  rabbit's 
ureter  and  uterus,  and  the  cat's  bladder,  have  been  most  used. 

Physical  Properties  of  Muscle — Elasticity. — All  bodies  may  have 
their  shape  or  volume  altered  by  the  application  of  force.  Some 
require  a  large  force,  others  a  small  force,  to  produce  a  sensible 
amount  of  distortion.  The  elasticity  of  a  body  is  the  property  in 
virtue  of  which  it  tends  to  recover  its  original  form  or  bulk  when 
these  have  been  altered.  Liquids  and  gases  have  only  elasticity  i  ■! 
volume  ;  solids  have  also  elasticity  of  form.  .Most  solids  recover 
perfectly,  or  almost  perfectly,  from  a  slight  deformation.  The  limits 
of  distortion  within  which  this  occurs  are  called  the  limits  of  elasticity, 
and  they  vary  greatly  for  different  substances.  Living  muscle  has 
very  wide  limits  of  elasticity  ;  it  may  be  deformed — stretched,  for 
example— to  a  very  considerable  extent,  and  yet  recover  its  original 
length  when  the  stretching  force  ceases  to  act. 

The  extensibility  of  a  body  is  measured  by  the  ratio  of  the  increase 

of  length,  produced  by  unit  stretching  force  per  unit  of  area  of  the 

cross-section,  to  the  original  length  of  a  uniform  rod  of  the  substance. 

Is 
If  e  is  the  extensibility,  £=__.,  where  I  is  the  increase  of  length, 

L  the  original  length,  s  the  cross-section,  and  F  the  stretching  force. 
Suppose  we  wish  to  compare  the  extensibility  of  two  substances. 
Let  A  and  B  be  strips  or  rods  of  the  substances,  the  length  of  A 
being  500  mm.,  that  of  B  1,000  mm.  ;  the  cross-section  of  A,  100 
sq.  mm.,  of  B,  200  sq.  mm.  Let  the  elongation  produced  by  a 
weight  of  1  kilo  be  10  mm.  in  each,  then  the  extensibility  of  A   is 

I O  X  TOO  .   , ,  r   T-,   .       IO  X  200  .,  , ,  ,     , 

=  2  ;  and  that  of  B  is  =■  2  ;  that  is,  the  substances 

500  x  1  1,000  x  r 

are  equally  extensible      Young's  modulus  of  elasticity,  or  the  co- 


WUSCL1 


631 


efficient  oi  elastii  ity  is  the  quotii  nt  of  the  deforming  force  acting  on 
unit  area  of  the  given  body  by  the  deformation  produced  (within  the 

F.   /    .,    ,  .     LF. 


limits  lit  elasticity).      In  the  above  example  it  is 


T  ,  that  is,    , 
L  Is 


the  reciprocal  of  the  extensibility  e.  For  steel  the  coefficient  of 
elasticity  1--  very  large,  for  muscle  small.  Or.  as  we  may  otherwise 
express  it,  living  muscle  within  its  limits  of  elasticity  is  very  ex- 
tensible  ;  a  small  force  per  unit  area  of  cross-section  of  a  prism  of  it 
will  produce  a  comparatively  great  elongation.  The  extensibility, 
however,  diminishes  continually  with  the  elongation,  so  that  equal 
increments  of  stretching  force  produce  always  less  and  less  extension. 
Tf,  for  instance,  the  sartorius  or  semi-membranosus  of  a  frog  be 
connected  with  a  lever  writing  on  a  blackened  surface,  and  weights 
increasing  by  equal  amounts  be  successively  attached  to  it,  the 
recording  surface  being  allowed  to  move  the  same  distance  after  the 
addition  of  each  weight,  a  series  of  vertical  lines,  representing  the 
amount  of  each  elongation,  will  be  traced.  When  the  lower  ends  of 
all  the  vertical  lines  are  joined,  a  smooth  curve  with  the  concavity 
upwards  is  obtained  (Fig.  219).  This  is  a  property  common  to 
living  and  dead  muscle  and  to  other 
animal  structures,  such  as  arteries. 
Marev's  method,  in  which  the  weight 
is  continuouslv  increased  from  zero 
and  then  continuously  decreased  to 
zero  again  by  the  flow  of  mercury  into 
and  out  of  a  vessel  attached  to  the 
muscle,  gives  directly  the  curve  of 
extensibility. 

The  elongation  of  a  steel  rod  or  other 
inorganic  solid  is  proportional  within 
limits  to  the  extending  force  per  unit 
of  cross-section  ;  and  a  curve  plotted 
with  the  weights  for  abscissae  and  the 
amounts  of  elongation  for  ordinates 
would  be  a  straight  line.  But  this  is 
not  a  fundamental  distinction  between 
animal   tissues,    and  the  materials  of 

unorganized  nature,  as  some  writers  seem  to  suppose.  For  when 
the  slow  after-elongation  which  follows  the  first  rapid  increase  in 
length  in  the  loaded,  excised  muscle  is  waited  for,  the  curve  of 
extensibilitv  comes  out  a  straight  line  (Wundt),  and  within  limits 
this  is  also  the  case  for  human  muscles  in  the  intact  body.  And 
although  a  steel  rod  much  more  quickly  reaches  its  maximum  elon- 
gation for  a  given  weight  when  loaded,  and  its  original  length  when 
the  weight  is  removed,  than  does  a  muscle,  time  is  required  in  both 
cases,  and  the  difference  is  one  of  degree  rather  than  of  kind.  When 
muscle  (striated  or  smooth)  is  not  stretched  beyond  the  limit  of 
physiological  relaxation,  the  amount  of  stretching  is  proportional 
to  the  weight,  and  the  same  is  true  of  all  the  simple  tissues  of  the 
body  (Haycraft). 

Dead  muscle  is  less  extensible  than  living,  and  its  limits  of 
elasticity  are  much  narrower.  In  the  state  of  contraction  the 
extensibility  is  increased  in  excised  frog's  muscle.  When  fatigue 
comes  on  after  many  excitations,  the  after-elongation  becomes  more 
pronounced,  but  the  return  after  unloading  is  very  incomplete. 
Donders  and   Van  Mansveldt  have  found  that  contraction  causes 


Fig.    219. — Curves   of    Exten- 


sibility. 


M,  of  muscle  ;  S,  of  an  ordinary 
inorganic  solid. 


532  A   M  INUAL  OF  PHYSIOLOGY 

little^  difference  in  the  muscles  of  ;i  living  man,   although   fatigue 

increases  the  extensibility. 

The  greal  extensibility  and  elasticity  of  muscle  must  play  a 
considerable  part  in  determining  the  calibre  of  the  vessels,  and  in 
lessening  the  shocks  and  strains  which  the  heart  and  the  vascular 
system  in  general  are  called  upon  to  bear,  and  must  contribute  much 
to  the  smoothness  with  which  the  movements  of  the  skeleton  are 
carried  out,  and  immensely  reduce  the  risk  of  injury  to  the  bones 
as  well  as  to  the  muscles  themselves,  the  tendons  and  the  other 
soft  tissues.  And  not  only  is  smoothness  gained,  but  economy  also  ; 
for  a  portion  of  the  energy  of  a  sudden  contraction,  which,  if  the 
muscles  were  less  extensible  and  elastic,  might  be  wasted  as  heal 
in  the  jarring  of  bone  against  bone  at  the  joints,  is  stored  up  in  the 
stretched  muscle  and  again  given  out  in  its  elastic  recoil.  The 
skeletal  muscles,  too,  are  even  at  rest  kept  slightly  on  the  stretch, 
braced  up,  as  it  were,  and  ready  to  act  at  a  moment's  notice  without 
taking  in  slack.  This  is  shown  by  the  fact  that  a  transverse  wound 
in  a  muscle  '  gapes,'  the  fibres  being  retracted,  in  virtue  of  their 
elasticity,  towards  the  fixed  points  of  origin  and  insertion.  Smooth 
muscle,  as  we  meet  it  in  the  hollow  viscera,  is  highly  distensible  and 


Fig.   220. — Extensibility  of  Smooth  Muscle  (Grutzner). 

The  upper  group  of  four  cells  (i  to  4)  is  from  a  hollow  organ,  whose  walls  are 
contracted,  and  its  lumen  almost  abolished  :  the  under  group  represents  the  same 
fibres  when  the  organ  is  full.  The  fibres  are  longer  ami  somewhat  darker.  They 
are  also  displaced  somewhat  along  each  other. 

elastic,  as  is  suited  to  organs  whose  capacity  is  continually  varying 
within  wide  limits  (Fig.  220). 

In  the  further  study  of  muscle  it  is  necessary  first  of  all  to  consider 
the  means  we  have  of  calling  forth  a  contraction — in  other  words, 
the  various  kinds  of  stimuli. 

Stimulation  of  Muscle. — A  muscle  may  be  excited  or  stimu- 
lated either  directly  or  through  its  motor  nerve.  It  is  usual  to 
classify  stimuli  as  electrical,  mechanical,  chemical,  or  thermal. 
Electrical  stimuli  are  by  far  the  most  commonly  employed,  and 
will  be  discussed  in  detail.  A  prick,  a  cut,  or  a  blow  are  examples 
of  mechanical  stimuli.  The  action  of  a  fairly  strong  solution  of 
common  salt  or  of  a  dilute  solution  of  a  mineral  acid  is  usually 
described  as  chemical  stimulation.  But  in  considering  the 
excitation  of  nerve  (p.  680)  we  shall  see  that  physical  changes  are 
often  mixed  up  with  so-called  chemical  stimulation.  The  con- 
traction caused  is  not  a  single  brief  twitch,  as  is  the  case  with  a 
not  too  severe  mechanical  excitation,  but  a  sustained  contraction 
or  a  tetanus.     Sudden  cooling  or  heating  acts  as  a  stimulus  for 


WUS(  II  633 

muscle,  bu1  thermal  stimulation  is  somewhat  uncertain.  Ii  is 
not  quite  settled  whether  the  contraction  which  can  be  obtained 
from  a  muscle  when  it  is  subjected  to  brief  local  heating— to  a 
'  thermic  shock,'  as  some  writers  prefer  to  say  {e.g.,  by  the  mo- 
mentary glow  of  a  platinum  wire  below  but  not  touching  it) — is  an 
ordinary  muscular  contraction,  or  a  physical,  although  transient, 
contracture  analogous  to  that  caused  by  certain  drugs  (Waller). 
Smooth,  like  striped,  muscle  is  susceptible  to  electrical,  mechani- 
cal, thermal,  and  chemical  stimulation.  In  addition,  in  certain 
situations  it  can  be  excited  by  light  (photic  stimulation),  as  in  the 
case  of  the  excised  iris  of  fish  and  amphibia.  In  all  artificial 
stimulation  there  is  an  element  of  sudden  or  abrupt  change,  of 
shock,  in  other  words  ;  but  we  cannot  tell  in  what  the  '  natural ' 
or  '  physiological  '  stimulus  to  muscular  contraction  in  the 
intact  body  reallv  consists,  nor  how  it  differs  from  artificial 
stimuli.  All  we  know  is  that  there  must  be  a  wide  difference, 
and  that  our  methods  of  excitation  must  be  very  crude  and  in- 
exact imitations  of  the  natural  process. 

Direct  Excitability  of  Muscle. — The  famous  controversy  on 
the  existence  of  independent  '  muscular  irritability  '  has  long 
been  forgotten,  and  has  no  further  interest  except  for  the  anti- 
quaries of  science,  if  such  exist.  The  direct  excitability  of 
muscle  in  the  modern  sense  is  not  quite  the  same  as  the  '  muscular 
irritability,'  the  discussion  of  which  occupied  Haller  and  his 
contemporaries.  What  the  modern  physiologists  have  been 
called  upon  to  decide  is  whether  muscular  fibres  can  be  caused 
to  contract  except  by  an  excitation  that  reaches  them  through 
their  nerves.  In  this  sense  there  can  exist  no  doubt  that  muscle 
is  directly  excitable,  and  some  of  the  proofs  are  as  follows  : 

(1)  The  ends  of  the  frog's  sartorius  contain  no  nerves, 
yet  they  respond  to  direct  stimulation.  (2)  Certain  chemical 
stimuli — ammonia,  for  instance — excite  muscle  but  not  nerve. 
(3)  When  the  motor  nerves  of  a  limb  are  cut  they  degenerate, 
and  after  a  certain  time  stimulation  of  the  nerve-trunk  causes 
no  muscular  contraction,  while  the  muscles,  although  atrophied, 
can  be  made  to  contract  by  direct  stimulation.  (4)  Finally, 
there  is  the  celebrated  curara  experiment  of  Claude  Bernard, 
which  is  described  in  a  somewhat  modified  form  in  the  Practical 
Exercises,  p.  706.  A  ligature  is  tied  firmly  round  one  thigh  of 
a  frog,  omitting  the  sciatic  nerve  ;  then  curara  is  injected,  and 
in  a  short  time  the  skeletal  muscles  are  paralyzed.  That  the 
seat  of  the  paralysis  is  not  the  contractile  substance  of  the  muscles 
itself  is  shown  by  their  vigorous  response  to  direct  stimulation. 
The  '  block  '  is  not  in  the  nerve-trunk,  nor  above  it  in  the  central 
nervous  system,  for  the  ligated  leg  is  often  drawn  up — that  is,  its 
muscles    are    contracted — although    the    poison    has    circulated 


<>;  i 


/     1/  J  \'/     If.   OF   I'UYSIOI.OGY 


freely  in  the  sacral  plexus  and  the  spinal  cord.  Further,  if  the 
nerve  <>i  the  ligated  leg  be  prepared  as  high  up  ;il»)ve  the 
ligature  us  possible,  where  the  curara  must  undoubtedly  have 
reached  il  (just  above  the  ligature  the  nerve  has  been  isolated 
and  the  circulation  in  it  more  or  less  interrupted),  stimulation 
of  it  will  cause  contraction  of  the  muscles  of  the  limb  ;  while 
excitation  of  the  other  sciatic  is  ineffective. 

It  can  be  also  shown,  by  means  of  the  negative  variation  oi 
current  of  action  (p.  719),  that  a  nerve-trunk  on  which  curara 
has  acted  remains  excitable,  and  capable  of  conducting  the 
nerve-impulse.  The  conclusion,  therefore,  is  that  the  curara 
paralyzes  neither  nerve-fibre  nor  the  contractile  substance  of  the 


Fig.   221. — Frog's  Motor  Nerve -Ending  (Wilson). 

A,  B,  C,  three  muscle-fibres.  The  medullated  nerve  a  loses  its  medullary  sheath 
and  breaks  up  on  B  at  1.  It  gives  off  at  2  a  large  non-medullated  branch, 
which  also  breaks  up  on  B.  The  nerve-endings  send  ultraterminal  fibrilla1  to 
A,  B,  and  C,  some  of  which  were  seen  to  end  in  small  knobs.  A  separate  non- 
inedullated  nerve,  n,  is  shown,  which  forms  a  small  plexus  on  B,  one  fibre  ol 
which  penetrates  to  a  lower  plane  than  the  other,  and  ends  by  forming  a  knob 
under  the  sarrolemma. 


muscular  fibre,  but  some  link  between  the  two.  If  the  assump- 
tion be  made  that  the  efferent  medullated  nerve-fibres  within  the 
muscle,  since  they  are  anatomically  similar  to  those  in  the  nerve- 
trunk  till  near  their  terminations,  are  similarly  affected  by  curara 
— and  it  is  a  justifiable  assumption — the  seat  of  the  curara 
paralysis  must  either  be  the  nerve-ending  or  some  mechanism, 
physiological  if  not  anatomical,  interposed  between  the  nerve- 
ending  and  the  contractile  substance.  Now,  Langley  has  shown 
that  the  contractions  caused  by  the  local  application  of  dilute 
nicotine  solution  to  points  of  the  skeletal  muscles  of  the  frog, 
both  in  normal  muscles  and  in  muscles  whose  motor  nerves  and 
nerve-endings   have   degenerated   after   section   of   the   nerves, 


MUSC1.I  635 

are  in  either  case  prevented  by  curara.  He  therefore  conclude-, 
that,  since  nicotine  produces  its  effects  by  a  direct  action  on 
muscle,  and  not  by  an  action  on  nerve-endings  or  on  any  special 
structure  (such  as  the  protoplasmic  mass  or  '  sole  '  at  the  nerve- 
ending  in  many  animals)  interposed  between  the  nerve  and  the 
muscle,  no  such  special  structure  existing  in  the  frog  (Fig.  221), 
curara  must  also  act  directly  on  the  muscle.  But  obviously 
curara  does  not  paralyze  the  general  contractile  substance  of 
the  muscle,  else  the  curarized  muscle  would  not  contract  on  direct 
stimulation.  Langley  accordingly  assumes  that,  in  addition  to 
the  contractile  or  '  general  '  substance,  '  receptive  '  substances 
exist  in  the  fibre,  through  which  the  excitation  is  transferred  to 
the  contractile  substance  when  the  motor  nerve  is  stimulated. 
He  pictures  these  receptive  substances  as  '  side-chains  '  of  the 
contractile  molecule,  in  accordance  with  Ehrlich's  theory  of 
immunity  (p.  29),  and  distinguishes  those  in  the  neighbourhood 
of  the  nerve-ending  from  those  present  throughout  the  muscle 
fibre.  Both  the  slow  local  tonic  contraction  and  the  quick, 
brief  conducted  contractions  or  twitches  set  up  in  a  muscle 
fibre  by  nicotine,  but  especially  the  latter,  are  much  more  easily 
elicited  in  that  part  of  it  which  lies  under  the  nerve-ending  than 
elsewhere.  Indeed,  the  position  of  the  nerve-endings  in  the 
superficial  fibres  of  a  muscle  can  be  ascertained  by  observing 
the  points  which  respond  most  readily  to  nicotine.  Nicotine 
and  curara,  etc.,  are  supposed  to  combine  with  the  receptive 
substance,  which  is  then  in  both  cases  rendered  incapable  of  being 
affected  by  nerve  impulses.  In  the  case  of  nicotine  an  additional 
action  results  from  the  combination  with  the  receptive  substance 
— viz.,  the  change  in  the  contractile  substance  which  leads  to 
contraction.  Curara  paralyzes  the  transmission  of  the  excitation 
from  the  motor  nerves  to  smooth  muscle — the  muscles  of  the 
bronchi,  for  instance — with  much  greater  difficulty  than  to 
ordinary  skeletal  muscle,  and  the  same  is  true  of  the  inhibitory 
nerves  of  the  heart. 

The  action  of  curara  gives  us  the  means  of  stimulating  muscle 
directly  ;  when  electrical  currents  are  sent  through  a  non-curarized 
muscle,  there  is  in  general  a  mixture  of  direct  and  indirect  stimula- 
tion, for  the  nerve-fibres  within  the  muscle  are  also  excited.  Induced 
currents  stimulate  nerve  more  readily  than  muscle.  Voltaic  currents 
may  excite  a  muscle  whose  nerves  have  degenerated,  while  induced 
currents  are  entirely  without  effect. 

For  direct  stimulation,  a  curarized  frog's  sartorius  or  semi- 
membranosus is  generally  used  on  account  of  their  long  parallel 
fibres.  For  indirect  excitation,  a  muscle-nerve  preparation,  com- 
posed of  a  frog's  gastrocnemius  with  the  sciatic  nerve  attached 
to  it,  is  commonly  employed,  as  it  is  easy  to  isolate  the  muscle 
without  hurting  its  nerve. 

Stimulation  by  the  Voltaic  Current. — -While  the  current  continues 


636  A   MANUAL  OF  PHYSIOLOGY 

to  pass  through  a  nerve  without  any  sudden  or  great  change  in  its 
intensity,  there  is  no  stimulation,  and  the  muscle  connected  with 
the  nerve  remains  at  rest.  The  same  is  true  of  striated  muscle  when 
a  weak  current  is  passed  directly  through  it.  Rut  in  muscle  the 
constancy  of  the  rule  is  more  and  more  frequently  broken  by 
exceptional  results  as  the  current  is  strengthened,  a  st;ite  of  perma- 
nent contraction  being  very  apt  to  show  itself  during  the  whole  time 
of  flow  (Wundt)  (Fig.  222).  Above  a  certain  intensity  of  current  a 
greater  or  less  degree  of  permanent  contraction  is  invariably  produced. 
This  is  sometimes  called  the  '  closing  tetanus.'  It  is,  however,  not 
a  true  tetanus,  but  a  tonic  contraction,  which  is  strongest  in  the 
neighbourhood  of  the  kathode,  and  docs  not  spread  far  from  it.  A 
similar  condition,  the  so-called  galvanotonus,  is  normally  seen  in 
human  muscles  when  they  or  their  motor  nerves  are  traversed  by  a 
stream  of  considerable  intensitv.  Under  certain  conditions,  too — 
e.g.,  when  a  strong  current  is  allowed  to  flow  for  a  comparatively 


Fig.   222. — Tonic  Contraction    of    Muscle  during  Passage  of  Constant 

Current. 

Two  sartorius  muscles  of  frog  connected  by  pelvic  attachments.  Current  from 
12  small  Daniell  cells  in  series  passed  through  their  whole  length.  Current  closed 
at  m,  opened  at  b.     Time  trace,  two-second  intervals. 

long  time  through  a  muscle — the  muscle  remains  contracted  after 
the  opening  of  the  current  (so-called  '  opening  or  Ritter's  tetanus  '). 
Smooth  muscle  is  excited  to  contraction  even  when  a  voltaic  current 
is  very  gradually  passed  into  it  and  slowly  increased,  and  again  when 
it  is  caused  very  gradually  to  disappear.  Rut  striped  muscle  is  not 
stimulated  under  these  conditions. 

For  nerve,  and  with  these  qualifications  for  muscle,  too,  we  may 
lay  down  the  law  that  the  voltaic  current  stimulates  at  make  and  at 
break,  but  not  during  its  passage.  Or,  generalizing  this  a  little, 
since  it  has  been  shown  that  a  sudden  increase  or  decrease  in  the 
strength  of  a  current  already  flowing  also  acts  as  a  stimulus,  we 
may  say  that  the  voltaic  current  stimulates  only  when  its  intensity  is 
suddenly  and  sufficiently  increased  or  diminished,  but  not  while  it 
remains  constant.* 

*  This  law  of  du  Rois-Reymond  has  been  questioned  by  Hoorweg  and 
others.  It  seems  to  need  modification,  but  the  subject  cannot  be  discussed 
here. 


MUSI' I  I 


<>37 


When  a  strong  current  is  closed  through  a  muscle  there:  is  an 
immediate  sharp  contraction  (initial  contraction).  The  muscle  then 
promptly  relaxes,  but  incompletely.  When  the  current  is  opened, 
there  is  another  contraction  (Fig.  223).  The  force  of  the  initial 
contraction,  as  measured  by  the  resistance  necessary  to  prevent  it, 
is  greater  than  that  of  the  tonic  contraction  which  follows  it. 

A  second  law  of  great  theoretical  importance  is  that  of  polar 
stimulation.  At  make  the  stimulation  occurs  only  at  the  kathode  ;  at 
break  only  at  the  anode.  This  is  true  both  for  muscle  and  nerve,  but 
it  is  most  directly  and  simply  demonstrated  on  muscle.  A  long 
parallel-fibred  curarized  muscle  is  supported  about  its  middle  ;  the 
two  ends,  which  hang  down,  arc  connected  with  levers  writing  on  a 
revolving  drum,  and  a  current  is  sent  longitudinally  through  the 
muscle.  It  is  not  difficult  to  see  from  the  tracings  that'^at  make  the 
lever  attached  to  the 
kathodic  end  moves 
first,  and  that  the 
other  lever  only 
moves  when  the  con- 
traction started  at 
the  kathode  has  had 
time  to  reach  it  in  its 
progress  along  the 
muscle.  Similarly, 
at  break  the  lever 
connected  with  the 
anodic  end  moves 
first.  The  law  of 
polar  excitation 
holds  both  for  stri- 
ated and  for  smooth 
muscle.  Not  only  is 
there  no  excitation 
of  unstriped  muscle 
at  the  anode  on  clo- 
sure of  the  current, 
but  a  previously  ex- 
isting contraction 
disappears.  For 
skeletal    muscle    the 

make  is  stronger  than  the  break  contraction 
that  this  is  the  case  for  smooth  muscle. 

The  Muscular  Contraction. — When  a  muscle  contracts,  its 
two  points  of  attachment,  or,  if  it  be  isolated,  its  two  ends,  come 
nearer  to  each  other  ;  and  in  exact  proportion  to  this  shortening 
is  the  increase  in  the  average  cross-section.  The  contraction  is 
essentially  a  change  of  form,  not  a  change  of  volume.  The  most 
delicate  observations  fail  to  detect  the  smallest  alteration  in 
bulk  (Ewald).  Living  fibres  kept  contracted  by  successive 
stimuli  can  be  examined  under  the  microscope  ;  or  fibres  may  be 
'  fixed  '  by  reagents  like  osmic  acid,  and  sometimes  a  verjr  good 
opportunity  of  studying  the  microscopic  changes  in  contraction 
is  given  by  a  group  of  fibres  in  which  the  '  fixing  '  reagent  has 


Fig.   223. — Tonic  Contraction  during  and   after 
Flow  of  Voltaic  Current. 

Curve  from  frog's  gastrocnemius.  At  M  constant 
current  closed,  at  B  broken.  Contracture  continues 
after  opening  of  current.  Time  trace,  two-second 
intervals. 


It  has  not  been  proved 


638  ;    1/  INUAL  OF  PHYSIOLOGY 

caught  a  wave  of  contraction,  and,  so  to  speak,  pinned  it  down. 
It  is  then  seen  thai  the  process  of  contraction  in  the  fibre  is  .1 
miniature  <.|  that  in  the  anatomical  muscle.  The  individual 
fibres  shorten  and  thicken,  and  the  sum-total  oi  tins  shortening 
and  thickening  is  the  muscular  contraction  which  we  sec  with  the 
naked  eye.  The  phenomena  of  the  muscular  contraction  may 
be  classified  thus:  (1)  Optical,  (2)  Mechanical,  (3)  Thermal, 
(4)  Chemical,  (5)  Sonorous.  (6)  Electrical.  (5)  will  be  treated 
under  '  Voluntary  Contraction  '  ;  (6)  in  Chapter  XI. 

(1)  Optical  Phenomena  Microscopic  Structure  of  Striped  Muscle. 
The  s1  ructure  of  striped  muscle  lias  long  been  t  he  enigma  of  histology  ; 
and  the  labours  of  many  distinguished  men  have  not  sufficed  to 
make  it  clear.  On  the  contrary,  as  investigations  have  multiplied, 
new  theories,  new  interpretations  of  what  is  to  be  seen,  have  multi- 
plied in  proportion,  and  a  resolute  brevity  has  become  the  chief  duty 
of  a  writer  on  elementary  physiology  in  regard  to  the  whole  question. 

The  muscle-fibre,  the  unit  out  of  which  the  anatomical  muscle  is 
built  up,  is  surrounded  by  a  structureless  membrane,  the  sarcolemma. 
The  length  and  breadth  of  a  fibre  vary  greatly  in  different  situations. 
The  maximum  length  is  about  4  cm.  ;  the  breadth  may  be  as  much 
as  70  n  and  as  little  as  10  fi.  When  we  come  to  analyze  the  muscle- 
fibre  and  to  determine  out  of  what  units  it  is  built  up,  the  difficulty 
begins.  The  fibre  shows  alternate  dim  and  clear  transverse  stripes, 
and  can  actually  be  split  up  into  discs  by  certain  reagents,  ft  also 
shows  a  longitudinal  striatum,  and  can  be  separated  into  fibrils. 
Some  have  supposed  that  the  discs  are  the  real  structural  units 
which,  piled  end  to  end,  make  up  the  fibre.  The  fibrils  they  con- 
sider artificial.  This  view  is  erroneous.  It  seems  certain  that  the 
fibres  are  built  up  from  fibrils  ranged  side  by  side,  and  that  the  discs 
are  artificial.  The  contents  of  the  muscle-fibre  appear  to  consist  of 
two  functionally  different  substances,  a  contractile  substance,  and  an 
interstitial,  perhaps  nutritive,  non-contractile  material  of  more  fluid 
nature.  The  contractile  substance  is  arranged  as  longitudinal  fibrils 
embedded  in  interfibrillar  matter  (sarcoplasm).  In  a  muscle  im- 
pregnated with  chloride  of  gold  the  interfibrillar  matter  appears  as  a 
network. 

Schafer  has  described  the  contractile  elements  of  the  muscle-fibre 
(Figs.  224,  225)  as  fine  columns  (sarcostyles),  divided  into  segments 
(sarcomeres)  by  thin  transverse  discs  (Krausc's  membranes),  occupy- 
ing the  position  of  the  middle  of  each  light  stripe.  Each  sarcomere 
contains  a  sarcous  clement  (a  portion  of  the  dark  stripe)  with  a  clear 
substance  at  its  ends,  filling  up  the  space  between  the  sarcous 
element  and  Krausc's  membrane,  and  constituting  a  portion  of  the 
light  stripe.  The  sarcous  element  is  itself  double,  and  if  the  fibre 
be  stretched,  the  two  portions  separate  at  a  line  which  runs  trans- 
versely across  the  middle  of  tlie  dim  stripe  (llensen's  line).  Schafer 
considers  that  the  appearance  of  longitudinal  fibrillation  in  the  sarcous 
elements  is  due  to  the  presence  in  them  of  fine  longitudinal  canals  or 
pores. 

Rutherford  has  given  a  somewhat  different  account  of  the  matter. 
According  to  him,  each  fibril  is  made  up  of  a  longitudinal  row  of 
segments  of  two  kinds,  alternating  with  each  other  (Fig.  226)  : 
(1)  '  Bowman's  elements,'  shaped  like  an  elongated  hour-glass,  and 


WUS(  I  I 


containing  a  substance  readily  stained  by  various  dyes;  (2)  an 
'intermediate  segment  '  <>i  cylindrical  shape,  the  general  substance 
of  which  does  no1  readily  stain.  The  intermediate  segmenl  con- 
tains in  its  centre  a  globule  (Dobie's  globule),  which  is  easily  stained.* 
The  fibrils  are  regularly  arranged  in  bundles  within  the  fibre.  The 
apposition  of  Bowman's  elements  gives  rise  to  the  dim  stripe  ;  the 
apposition  of  the  intermediate  segments  to  the  clear  stripe  ;  the  appo 
sit  ion  of  the  Dobie's  globules  to  a  line  in  the  middle  of  the  clear  stripe 
(Dobie's  line).  Dobie'sfline  has  by  sonic  been  considered  to  represent 
a  membrane  made  up  of  the  apposed  Krause's  membranes  of  all 
the  fibrils.      But  the  Krause's  membrane  of  the  individual  fibrils  is 

scarcely  ever  visible  in  an  intact 
mammalian     fibre     (Schafer), 

tot.* ..a  arui  the  apparent  line  in  the 

clear  stripe  of  an  intact  fibre 
is  an  optical  appearance  due 
to  interference  of  the  light. 
Kiihne,    who    was    fortunate 


Fig.  224. — Living  Muscle  of 
Water-beetle  (Highly  Magni- 
fied) (Schafer). 

s,  sarcolemma ;  a,  dim  stripe 
b,  bright  stripe  ;  c,  row  of  dots  in 
bright  stripe,  which  appear  to  be 
the  enlarged  ends  of  rod-shaped 
particles,  d,  but  in  reality  represent 
expansions  of  the  interstitial  substance 
(sarcoplasm). 


Fig.  225. — Portion  of 
Leg  Muscle  of  Insect, 
treated  with  Dllute 
Acetic  Acid  (Schafer). 

S,  sarcolemma  ;  D,  dot- 
like enlargement  of  sarco- 
plasm ;  K,  Krause's  mem- 
brane. The  sarcous  ele- 
ments have  been  swollen 
and  dissolved  by  the  acid. 


enough  to  find  one  day  a  small  nematode  worm  moving  in  the 
interior  of  a  fibre,  saw  it  pass  along  the  fibre  with  perfect  freedom, 
ignoring  Krause's  membrane.  Possibly,  however,  it  was  moving  in 
the  sarcoplasm,  the  fibrils  being  simply  pushed  aside. 

Changes  during  Contraction. — When  a  muscle  contracts,  according 
to  Schafer,  the  clear  substance  between  the  Krause's  membrane  and 
the  sarcous  element  passes  into  the  canals,  which  are  open  towards 
Krause's  membrane,  but  closed  towards  Hensen's  line.  The  sarcous 
element  therefore  swells  up,  and  the  sarcomere  is  shortened.  In  the 
extended  muscle  the  clear  substance  leaves  the  pores  of  the  sarcous 
element,   and   accumulates  in  the  space  between  it  and   Krause's 

*  In  the  muscles  of  certain  invertebrate  animals,  though  not  in  those 
of  vertebrates,  the  intermediate  segment  contains,  in  addition  to  Dobie's 
globule,  two  pear-shaped  bodies  (Flogel's  elements),  each  of  which  occupies 
an  intermediate  position  between  Dobie's  globule  and  the  end  of  the 
adjoining  Bowman's  element.  Flogel's  elements  also  stain  well,  and  are 
doubly  refracting. 


640 


./    MANUAL  OF   PHYSIOLOGY 


l>\ 


U 


!>rane.  The  sarcomere  is  thus  length- 
en <l  and  narrowed.    While  the  existence 

hafer's  pores  is  not  admitted  t>v  all 
oba  rvers,  there  is  a  pretty  genera]  . 

mcnt  that  the  sarcomere,  like  tin-  cytoi 
of  an  amoeboid  cell,  does  consist  01  two 
substances,  one  of  which  (the  hyaloplasm 
oi  the  cell,  the  clear  material  of  the  a 
mere]  interpenetrates  the  other  (spongio- 
plasm  of  the  cell,  substance  of  the  sai 
element)  ;  and  that  in  relaxation  the  clear 
fluid  passes  from  the  sarcous  element  to 
the  ends  of  the  sarcomeres,  whereas  in  con- 
traction it  passes  in  the  reverse  dirt 
into  the  sarcous  elements.  Whether  the 
fluid  passes  into  and  out  of  the  meshes  of 
an  actual  network,  or  along  actual  physical 
pores  in  the  sarcous  element,  or  wh 
it  is  transferred  by  some  process  like  mole- 
cular imbibition  (p.  398),  need  not  be  dis- 
cussed here,  since  it  is  not  definitely  known 
The  fundamental  question  by  what  pn 
the  transference  is  determined  when  the 
muscle  is  excited  also  remains  unsettled. 
So  far  as  is  known  at  present,  it  is  probable 
that  the  mechanical  energy  of  the  contract- 
ing muscle  must  be  derived  from  the  trans- 
formation  of  chemical  energy  into  one  of 
three  forms:  energy  associated  with  os- 
motic processes,  energy  associated  with  im- 
bibition, and  energy  associated  with  ch. 
of  surface  tension.  It  is  not  difficult  to  see 
that  a  sudden  increase  in  the  osmotic  con- 
centration in  the  sarcous  element,  due  to 
the  breaking  up  of  large  molecules  or  col- 
loid aggregates  into  small  molecules,  or  the 
liberation  of  electrolytes  from  the  colloids, 
might  lead  to  the  rapid  passage  of  water 
into  it  from  the  bright  bands.  A  sudden 
change  of  permeability  of  the  sarcous 
elements  for  dissolved  substances  in  the 
clear  fluid  would  have  a  similar  effect. 
The  same  is  true  of  a  change  in  their 
power  of  imbibition.  But,  according  to 
Bernstein,  it  is  scarcely  to  be  supposed  that 
the  extraordinarily  rapid  movement  of 
water  molecules  which  must  occur  in  con- 
traction can  be  accounted  for  cither  by 
osmosis  or  by  imbibition.  A  more  plausible 
theory  is  that  the  surface  tension — say 
between  the  substance  of  the  sarcous  ele- 
ment and  the  clear  fluid — is  altered.  Some 
writers  assert  that  in  contraction  there  is 
such  a  transference  of  substance  between 
the  light  and  dim  stripes  that  the  former  becomes  dim,  and  the  latter 
light.  This  so-called  reversal  of  the  stripes  is  not  really  a  re- 
versal in  the  sense  of  being  a  bodily  exchange  of  the  whole  of  the 


C: 


16 


fo    1 


Fig.  226. — Crah-  Mi  si  1.1. 
in  dipfi  reni  Stages 
of  Contraction  (after 
Rutherford). 

Three  fibrillar  arc  shown  : 
;.   i  omplete   relaxation  ;   /. 
lete  contraction 

sarcous      elements  ;      d-d?, 
Dobie's  granules  ;  /,  Fl« 
granules. 


MUSCLE 


'■  l ' 


materia]  of  the  dim  and  light  stripes.  Schaier  has  explained  it.  as  due 
t.>  tin-  squeezing  >>i  sarcoplasm  from  between  the  sarcous  elements 
into  the  position  of  tin-  light  stripe,  when  tiny  bulge  laterally  in 
contraction.  This  accuiuul.it  ion  of  sarcoplasm  in  the  stripes  that 
were  previously  light  makes  them  look  darker  in  comparison  with 
the  true  dim  stripe. 

Appearance  of  the  Fibres  in  Polarized  Light. — A  ray  of  ordinary 
light  consists  of  vibrations  of  the  ether  in  all  planes  at  right  angles 
to  the  direction  of  the  ray.  In  a  ray  of  plane  polarized  light  all  the 
particles  vibrate  in  one  plane.  A  ray  of  light  which  has  b&  Q 
polarized  by  a  Xicol's  prism  cannot  pass  through  another  Xicol's 
prism  with  its  principal  plane  at  right  angles  to  that  of  the  first. 
If  the  second  or  analyzing  prism  be  rotated  so  that  the  principal 
planes  are  no  longer  at  right  angles,  some  of  the  light  will  pass 
through.  The  same  effect  is  produced  if,  without  altering  the 
original  '  crossed  '  position  of  the  nicols,  a  substance  capable  of 
rotating  the  polarized  ray  is  introduced  between  the  prisms.  A 
rough  illustration  will  perhaps 
tend  to  make  this  point  clearer. 
Suppose  that  a  string  fixed  at 
one  end  is  set  vibrating  in 
various  directions  by  a  twist- 
ing movement.  If  the  string 
has  to  pass  through  a  narrow 
vertical  slit — e.g.,  between  two 
fingers  held  vertically — all  vi- 
brations except  those  in  the 
vertical  plane  will  be  extin- 
guished ;  but  vertical  vibra- 
tions will  be  able  to  pass  be- 
yond the  slit.  The  movement 
may  be  said  to  be  plane  polar- 
ized, and  the  effect  of  the  slit 
corresponds  to  that  of  the  first 
nicol.  Now  make  the  string 
pass  also  through  a  horizontal 
slit  ;  the  vertical  vibrations 
will  then  be  extinguished  too  ; 
in  other  words,  none  of  the 
movements  will  pass  beyond 


Fig.   227. — Living  Muscular  Fibre 
(from  Geotrupes  stercorarius). 

1,  in  ordinary  ;  2,  in  polarized  light. 
(Van  Gehuchten.)  In  living  muscle  (at 
least  in  fibres  which  are  not  extended)  in 
contrast  to  dead  muscle  after  treatment 
with  reagents,  the  doubly  refracting  or 
anisotropous  substance  is  present  hi  the 
greater  part  of  the  fibre ;  and  with  crossed 
nicols  the  position  of  the  singly  refracting 
or  isotropous  material  is  indicated  only 
by  narrow  transverse  black  lines  or  rows 
of  dark  dots. 


the  '  crossed  '  slits.  This  cor- 
responds to  the  dark  field  of  the  crossed  nicols.  But  if  the  vertical 
vibrations  which  have  passed  the  first  slit  could  be  in  any  way 
changed  into  horizontal  vibrations,  they  would  no  longer  be  ex- 
tinguished by  the  second.  This  would  correspond  to  rotation  of 
the  plane  of  polarization  through  900.  A  ray  of  light  polarized 
by  the  first  nicol  will,  if  its  plane  of  polarization  be  rotated  through 
900,  pass  entirely  (except  for  loss  by  ordinary  reflection  and  absorp- 
tion) through  the  second.  If  the  angle  of  rotation  is  less  than  900, 
a  portion  will  pass  through. 

The  substance  of  the  sarcous  element  which  forms  the  dark  stripe 
is  doubly  refracting,  and  therefore  rotates  the  plane  of  polarization, 
but  the  clear  substance  of  the  light  stripe  is  singly  refracting.  When 
an  uncontracted  fibre  is  viewed  with  crossed  nicols,  the  dim  stripe 
accordingly  appears  bright  in  the  otherwise  dark  field.  In  the  con- 
tracted fibre  the  doubly  refractive  material  remains  in  the  stripe 

41 


642  ./    MANX    1/    OB   PHYSIOLOGY 

which  is  dim  in  ordinary  light.     There  is  no  transference  oi  it.  and 
no  real  reversal  ol  the  stripes. 

Diffraction  Spectrum  of  Muscle. — When  a  beam  oi  white  light 
pisses  through  a  striped  muscle,  it  is  broken  up  into  its  constitu*  m 
colours,  and  a  series  of  diffraction  spectra  are  produced,  just  as 
happens  when  the  light  passes  through  a  diffraction  grating  (a  piece 
of  ,nlass  on  which  are  ruled  a  number  of  fine  parallel  equidistant 
lines).  The  nearer  the  lines  are  to  each  other,  the  greater  is  the 
displacement  of  a  ray  of  light  of  any  given  wave-length.  It  has 
accordingly  been  found  that  when  a  muscular  fibre  contracts,  the 
amount  oi  displacement  of  the  diffraction  spectra  increases.  At  the 
same  time  the  whole  fibre  becomes  more  transparent 

(2)  Mechanical  Phenomena. — The  muscular  contraction  may 
be  graphically  recorded  by  connecting  a  muscle  with  a  lever  which 
is  moved  cither  by  its  shortening  or  by  its  thickening.  The  lever 
writes  on  a  blackened  surface,  which  must  travel  at  a  uniform  rate 
if  the  form  and  time-relations  of  the  muscle  curve  are  to  be  studied, 
but  may  be  at  rest  if  only  the  height  of  the  contraction  is  to  be 
recorded.  The  whole  arrangement  for  taking  a  muscle-tracing  is 
called  a  myograph  (Fig.  261,  p.  707).  The  duration  of  a  'twitch' 
or  single  contraction  (including  the  relaxation)  of  a  frog's  muscle  is 
usually  given  as  about  one-tenth  of  a  second,  but  it  may  vary  con- 
siderably with  temperature,  fatigue,  and  other  circumstances.  It 
is  measured  by  the  vibrations  of  a  tuning-fork  written  immediately 
below  or  above  the  muscle  curve.  When  the  muscle  is  only  slight  lv 
weighted,  it  but  very  gradually  reaches  its  original  length  after 
contraction,  a  period  of  rapid  relaxation  being  followed  bv  a  period 
of  'residual  contraction,'  during  which  the  descent  of  the  Lever 
towards  the  base-line  becomes  slower  and  slower,  or  stops  altogether 
some  distance  above  it.  The  duration  of  the  contraction  of  smooth 
muscle  evoked  by  a  single  momentary  stimulus  is  much  greater  than 
that  of  striped  muscle  (two  to  seven  seconds  for  the  rabbit's  ureter  ; 
five  to  fifteen  seconds  for  the  cat's  nictitating  membrane  ;  one  to 
two  minutes  for  the  frog's  stomach). 

Latent  Period. — If  the  time  of  stimulation  is  marked  on  the 
tracing,  it  is  found  that  the  contraction  does  not  begin  simul- 
taneously with  it,  but  only  after  a  certain  interval,  which  is  called 
the  latent  period. 

This  can  be  measured  by  means  of  the  pendulum  myograph 
(Fig.  229)  or  the  spring  myograph  (Fig.  228),  in  both  of  which 
the  carrier  of  the  recording  plate  opens,  at  a  definite  point  in  its 
passage,  a  key  in  the  primary  coil  of  an  induction  machine,  and  so 
causes  a  shock  to  be  sent  through  the  muscle  or  nerve,  which  is  con- 
nected with  the  secondary.  The  precise  point  at  which  the.  stimulus 
is  thrown  in  can  be  marked  on  the  tracing  by  carefully  bringing  the 
plate  to  the  position  in  which  the  key  is  just  opened,  and  allowing 
the  lever  to  trace  here  a  vertical  line  (or,  rather,  an  arc  of  a  circle). 
The  portion  of  the  time-tracing  between  this  line  and  a  parallel  line 
drawn  through  the  point  at  which  the  contraction  begins  gives  the 
latent  period. 

I  [elmholtz  measured  the  length  of  the  latent  period  by  means  of 
the  principle  of  Pouillet,  that  the  deflection  of  a  magnet  by  a  current 
of  given  strength  and  of  very  short  duration  is  proportional  to  the 
time  during  which  the  current  acts  on  the  magnet.  He  arranged 
that  at  the  moment  of  stimulation  of  the  muscle  a  current  should 
be   sent  through   a  galvanometer,   and   should   be   broken   by  the 


VUSi  I  i 


Hi 


contraction  of  the  muscle  the  moment  it  began.     In  this  way  ho 

obtained  the  value  of  ,,',,,  second  lorthe  latent  period  of  frog's  muscle. 
The  tendency  of  later  observations  has  been  to  make  the  latent  peri  ml 
Bhorter.     Burdon  Sanderson  found  that  the  change  of  form  begins  in 

muscle  with  direct  stimulation  in  ,,,',,,,  second  after,  and  the  electrical 
change  (p.  721)  simultaneously  with,  the  excitation.  It  is  known 
that  the  apparent  latenl  period  depends  upon  the  resistance  which  the 
muscle  has  to  overcome  in  beginning  its  contraction.  A  heavily- 
weighted  muscle,  for  instance,  cannot  begin  to  shorten  until  as  much 
energy  has  been  developed  as  is  necessary  to  raise  the  weight  ;  and  its 
latent  period  will  be  distinctly  longer  than  that  of  unweighted  or  very 
slightly  weighted  muscles,  such  as  those  with  which  Sanderson  worked. 


Fig.   228. — -Spring  Myograph. 

A,  B,  iron  uprights,  between  which  are  stretched  the  guide-wires  on  which  the 
travelling  plate  a  runs  ;  k,  pieces  of  cork  on  the  guides  to  gradually  check  the  plate 
at  the  end  of  its  excursion,  and  prevent  jarring  ;  b,  spring,  the  release  of  which 
shoots  the  plate  along  ;  h,  trigger-key,  which  is  opened  by  the  pin  d  on  the  frame 
of  the  plate. 

The  maximum  shortening,  or  '  height  of  the  lift,'  depends  upon 
the  length  of  the  muscle,  the  direction  of  the  fibres,  the  strength  of 
the  stimulus,  the  excitability  of  the  tissue,  and  the  load  it  has  to  raise. 

In  a  long  muscle,  other  things  being  equal,  the  absolute  shortening 
and  therefore  the  maximum  height  of  the  curve,  will  be  greater  than 
in  a  short  muscle  ;  in  a  muscle  with  fibres  parallel  to  its  length — 
the  sartorius,  for  instance — it  will  be  greater  than  in  a  muscle  like 
the  gastrocnemius,  with  the  fibres  directed  at  various  angles  to  the 
long  axis.  For  stimuli  less  than  maximal,  the  absolute  contraction 
increases  with  the  strength  of  stimulation,  and  a  given  stimulus 
will  cause  a  greater  contraction  in  a  muscle  with  a  given  excitability 
than  in  a  muscle  which  is  less  excitable.  Under  ordinary  experi- 
mental conditions  at  least,  weak  stimuli  cause  a  smaller  contraction 
than  strong,  not  only  because  each  stimulated  fibre  contracts  less,  but 

41 — 2 


644 


A    MANUAL  OF  PHYSIOLOGY 


because  a  smaller  number  of  fibres  are  excited  (p.  141).     The  obi 
used  for  the  study  of  muscular  contraction  contain  many  fibres,  and 
it  Mint  in  genera]  possible  to  distribute  the  stimulus  equally  to  all. 
This  is  true  for  smooth  muscle  as  well  as  for  striped.    Finally,  increase 


Fig.  229. — Pendulum  Myograph. 

At  the  left  as  seen  from  the  side,  at  the  right  as  seen  from  the  front.    A,  bearings 
on  which  the  pendulum  swings:   P,  pendulum ;  G,  lates  earned  in 

the  frames  T,  T  ;  a,  pin  which  opens  the  trigger-key.     The  key,  when  1  I 

is  in  contact  with  c,  and  so  completes  the  circuit  <>t  the  primary  coiL 

of  the  load  per  unit  of  cross-section  of  the  muscle  diminishes  abi". 
certain  limit  the  '  height  of  the  lift,'  although  below  that  limit  it  may 
increase  it. 

Influences  which  affect  the  Time-relations  of  the  Muscular  Con- 


ur.sv/  / 


645 


traction.  —Many  circumstances  affect  the  form  of  the  muscle  curve 
and  its  time-relations. 

1  Influence  of  the  Load.  The  firsl  effect  of  contraction  is  to 
suddenly  stretch  the  muscle,  and  the  more  the  muscle  is  loaded  the 

iter  will  this  elongation  be.  So  thai  at  the  beginning  of  the 
actual   shortening    part    of    the   energy   oi    contraction    is   already 


Fig.    230. — Curve  of  a  Single   Muscular   Contraction   or  Twitch  taken 
on  Smoked  Glass  with  Spring  Myograph  and  Photographed. 

Vertical  line  A  marks  the  point  at  which   the  muscle  was  stimulated;   time 
tracing  shows  ,,',,-,  ol  a  second  (reduced). 

expended  without  visible  effect,  and  has  to  be  recovered  from  the 
elastic  reaction  during  the  ascent  of  the  lever. 

Then  the  inertia  of  the  lever  itself  and  of  its  load  comes  into  play, 
and  may  carry  the  curve  too  high  during  the  up-stroke  and  too  low 
during  the  down-stroke.  This  can  be  minimized  by  making  the 
lever  very  light,  and  attaching  the  weight  close 
to  the  fulcrum,  so  that  it  has  onlv  a  small  range 
of  movement,  and  never  acquires  more  than  a 
small  velocity.  The  contraction  of  a  muscle 
loaded  by  a  weight  which  is  not  increased  or 
diminished  during  the  contraction  is  said  to 
be  iso-tonic,  for  here  the  tension  of  the  muscle 
is  the  same  throughout,  and  its  length  alters. 
When  the  muscle  is  attached  very  near  the  ful- 
crum of  the  lever,  so  that  it  acts  upon  a  short 
arm,  while  the  long  arm  carrying  the  writing- 
point  is  prevented  from  moving  much  by  a 
spring,  the  muscle  can  only  shorten  itself  very 
slightly  ;  but  the  changes  of  tension  in  it  will 
be  related  to  those  in  the  spring,  and  therefore 
to  the  curve  traced  by  the  writing-point.  Such 
a  curve  is  called  iso-metric,  since  the  length 
of  the  muscle  remains  almost  unaltered.  In 
the  body  muscles  usually  contract  under  con- 
ditions more  nearly  allied  to  those  of  the  iso- 
metric than  to  those  of  the  iso-tonic  contraction. 

The  maximum  of  the  iso-metric  curve  (the 
maximum  tension  with  practically  constant 
length)  is  sooner  reached  than  that  of  the  iso- 
tonic (the  maximum  contraction  with  constant  tension).  From 
this  it  has  been  concluded  that  as  the  muscle  shortens  its  coefficient 
of  elasticity  continuously  diminishes  (Fick),  or,  what  comes  to  the 
same  thing,  its  extensibility  continuously  increases.  It  follows  that 
the  tension  of  a  muscle  contracting  against  resistance,  especially  at 
the  beginning  of  its  contraction,  is  greater  than  would  be  the  case 
when  the  muscle,  contracting  isotonically,  had  attained  the  same 
length. 


Cat's 
(C.       C. 


Fig.  231. — Contrac- 
tions of  Smooth 
Muscle 
Bladder 
Stewa;;t). 

Stimulated  with  pro- 
gressively  stronger  in- 
duction shocks.  The 
lowest  line  is  the  time 
trace  (10-second  inter- 
vals). Immediately  he- 
low  the  muscular  con- 
tractions are  marked 
the  points  at  which  the 
stimuli  were  thrown  in. 


. 


A    MANUAL  OF  PHYSIOLOGY 


The  work  done  by  a  muscle  in  raising  a  weight  is  equal  to  the 
product  of  the  weight  by  the  height  to  which  it  is  raised.  Beginning 
with  no  load  at  all.  it  is  found  that  the  weight  can  be  increa 


Fig.    232. — Influence  of  Load  on  the   Form   op  thi    M  RVE. 

1,  curve  taken  with  unloaded  lever  :  2,  3,  4,  weight  successively 
5,  abscissa  line  :  time  trace,  Ti„  second  (reduced). 

a  certain  limit  without  diminishing  the  height  of  the  contraction  ; 
perhaps  the  height  may  even  increase.  Up  to  this  limit,  then,  the 
work  evidentlv  increases  with  the  load.  If  the  weight  is  made  still 
greater,  the  contraction  becomes  less  and  less,  but  up  to  another 


Fig.   233. — Influence  of  Temperature  on  the  Striated  Muscle  Curve. 

2,  air  temperature  ;  1,  25° — 30°  C.  ;  3,  70 — io°  C.  ;  4,  ice  in  contai  t  with  mu 
The  fifth  rurve  was  taken  at  a  little  al  ; ■<  rature. 

limit  the  increase  of  weight  more  than  comj"  r  the  diminu- 

tion of   'lift.'  and  the    work   still   increases.      Beyond  this,   further 
increase  of  weight  can  no  longer  make  up  for  the  Lessening  of  the 


MUSCLl 


647 


lift,  and  the  work  falls  of)   till   ultimately  the  muscle  is  unable  to 
raise  the  weight  at  all. 

The  manner  <>f  application  of  the  weight  has  an  influence  on  the 
work  done  by  the  muscle.  If  it  is  applied  before  the  contraction 
begins,  so  that  the  muscle  is  already  stretched  at  the  moment  <>t 
stimulation,  a  cause  of  error  and  uncertainty  is  introduced  ;  for  it  is 
known  that  mere  stretching  of  muscle  affects  its  metabolism,  and 
therefore  its  functional  power.  So  that  it  is  usual  in  experiments 
of  this  kind  to  after-load  the  muscle — that  is,  to  support  the  lever 
and  its  load  in  such  a  way  that  the  weight  does  not  come  upon  the 
muscle  till  contraction  lias  just  begun.  The  'absolute  contractile 
force  '  of  an  active  muscle  may  be  measured 
on  this  principle  by  determining  the  weight 
which,  brought  to  bear  upon  the  muscle  at  the 
instant  of  contraction,  is  just  able  to  prevent 
shortening  without  stretching  the  muscle.  It, 
of  course,  depends,  among  other  things,  on  the 
cross-section  of  the  muscle.  During  the  con- 
traction the  absolute  force  diminishes  continu- 
ally, so  that  a  smaller  and  smaller  weight  is 
sufficient  to  stop  any  further  contraction,  the 
more  the  muscle  has  already  shortened  before 
it  is  applied.  At  the  maximum  of  the  con- 
traction the  absolute  force  is  zero.  Hence  a 
muscle  works  under  the  most  favourable  con- 
ditions,  when   the   weight   decreases   as   it  is 


pIG     234_ — Influence   of   Temperature   om   the   Smooth   Muscle   Curve 
Cat's  Bladder  (C.   C.   Stewart). 
Contractions  at  different  temperatures  with  the  same  strength  of  stimulus. 
The  temperatures  (Centigrade)  are  marked  on  the  curves. 

raised,  and  this  is  the  case  with  many  of  the  muscles  of  the  body. 
During  flexure  of  the  forearm  on  the  elbow,  with  the  upper  arm  hori- 
zontal, a  weight  in  the  hand  is  felt  less  and  less  as  it  is  raised,  since 
its  moment,  which  is  proportional  to  its  distance  from  a  vertical  line 
drawn  through  the  lower  end  of  the  humerus,  continually  diminishes. 
(b)  Influence  of  Temperature  on  the  Muscular  Contraction. — 
Increase  of  temperature  of  the  muscle  up  to  a  certain  limit  dimin- 
ishes the  latent  period  and  the  length  of  the  curve,  and  increases  the 
height  of  the  contraction,  but  beyond  this  limit  the  contractions  arc 
lessened  in  height  (Fig.  233).  Marked  diminution  of  temperature 
causes,  in  general,  an  increase  in  the  latent  period  and  length,  and 
a  decrease  in  the  height  of  the  contraction.  It  is  evident  that  much 
depends  upon  the  normal  temperature  which  we  start  from,  and 
moderate  cooling  may  increase  the  height  of  the  curve.     In  the  heart 


648 


I     MANUAL  OF  PHYSIOLOGY 


the  cftcri  of  cold  in  strengthening  the  beat  is  often  very  marked, 
temperature  affects  the  contraction*curve  of  smooth  muscle  much 
in  the  same  way  asjthat  of  striated  muscle  (Fig.  234).     Up  to  40 

there  is  an  increase  in  the 
height  and  a  diminution  in 
the  length  of  the  curve. 
Above  1  liai  temperai m 
height  is  diminished.  The 
latent  period  is  markedly 
diminished  by  heat  ffrom 
3*5  seconds  at  io°  ('.  to 
o'2  seconds  at  400  1 
(C.  C.  Slew  art  1. 


(c)  Influence  of  Previous 
Stimulation  Fatigue. — If 
a  muscle  is  stimulated  by 
a  series  of  equal  shocks 
thrown  in  at  regular  in- 
tervals, and  the  contrac- 
tions recorded,  it  is  seen  that 
af  first  each  curve  overtops  its 
predecessor  by  a  small  amount. 
This  phenomenon,  which  is 
regularly     observed     in     fresh 


Fig.  235. — Automatic  Muscle  Interruptor. 

K.  battery  ;  P,  primary;  S,  secondary  coil; 
A.  axis  of  lever  ;  N,  needle  ;  Hg,  mercurv  cup. 


Fig.  236. —  Fatigue  Curve  of  Muscle: 
Frog's  Gastrocnemius. 

The  arrangement  with  which  the 
curve  figured  was  obtained  was  a  so- 
called  automatic  muscle  interruptor 
(Fig.  235).  A  wire  on  the  lever  is  made 
to  close  and  open  the  primary  circuit 
of  an  inductorium,  the  muscle  or  nerve 
being  connected  with  the  secondary. 
Every  time  the  needle  touches  the 
mercury  the  muscle  is  stimulated  auto- 
matically. Another  arrangement  is 
shown  in  Fig.  237. 


Fig. 


>37. — Automatic  Musi  I  1 
I  s  I  1  rruptor. 


A,  femur  with  gastroi  nemiu: 
tached,  supported  in  clamp  :  C,  metal 
hook  with  fine  wire  attached  to  lever  F. 
The  wire  is  continued  along  the  lever 
and  connected  with  a  sewing-needle,  tin- 
point  of  which  just  dips  "it"  the  mere  tiry 
cup  D.  A  wire  from  one  pole  of  the 
Daniell  cell  E  dips  permanently  into  the 
mercury  :  the  wire  B  from  the  other  pole 
is  attached  to  the  upper  end  of  the 
muscle  or  the  clamp. 

skeletal  muscle  (Fig.  238),  although  it  was  at  one  time  supposed 
to  be  peculiarly  a  property  of  the  muscle  of  the  heart  (Fig.  239), 
is  called  the  'staircase,'  and  seems  to  indicate  that  within  limits 


MUS(  II 


the  muscle  is  benefited  by  contraction  and  its  excitability 
increased  for  a  new  stimulus.  Soon,  however,  in  an  isolated 
preparation,  the  contractions 
begin  to  decline  in  height,  till 
the  muscle  is  at  length  utterly 
exhausted,  and  reacts  no  longer 
to  even  the  strongest  stimulation 
( Figs.  236,  241,  242). 

A  conspicuous  feature  of  the 
contraction-curves  of  fatigued 
muscle  is  the  progressive  length- 
ening, which  is  much  more 
marked  in  the  descending  than 
in  the  ascending  periods  ;  in  other 
words,  relaxation  becomes  more 
and  more  difficult  and  imperfecl 
(Fig.  241).  In  smooth  muscle 
(cat's  bladder  or  ring  from  frog's 
stomach)  fatigue  can  be  very 
easily  demonstrated  in  the  same 
way,  and  the  curves  present 
similar  features,  with  the  exception  that,  instead  of  becoming 
longer  in  fatigue,  the  successive  contractions  become  shorter. 

It  is  by  no  means  so  easy  to  fatigue  a  muscle  still  in  connec- 
tion with  the  circulation  as  an  isolated  muscle.  But  even  the 
latter,  if  left  to  itself,  will  to  some  extent  recover,  and  be  again 


Fig.    238. — 'Staircase'   in  Skele- 
tal Musi  1.1   :   Frog. 

Stimulation  by  arrangement  shown 
in    Fig.    237. 


Fig.  239. — '  Staircase  '  ix  Cardiac  Muscle. 

1  Contractions  recorded  on  a  much  more  quickly  moving  drum  than  in  Fig.  23S. 
The  contractions  were  caused  by  stimulating  a  heart  reduced  to  standstill  by  the 
first  Stannius'  ligature  (p.  151).     The  contractions  gradually  increase  in  height. 

able  to  contract,  although  exhaustion  is  now  more  readily 
induced  than  at  first. 

In  man,  muscular  fatigue  can  be  studied  by  means  of  an 
arrangement  called  an  ergograph  (Fig.  240).  A  record  of  suc- 
cessive contractions,  say,  of  one  of  the  flexor  muscles  of  a  finger, 
in  raising  a  weight  (iso-tonic  method)  or  in  deforming  a  spring 
(iso-metric  method)  is  taken  on  a  drum.    When  the  contractions 


650 


/    1/  \NUAL  OF  PHYSIOLOGY 


are  repeated  every  second,  or  every  half-second,  distincl  evidence 
of  fatigue  is  seen  on  the  tracing  after  a  longer  01  shorter  period, 
according  to  the  conditions. 

What  is  the  cause  of  muscular  fatigue  ?  An  exacl  answer  is 
not  possible  in  the  presenl  state  of  our  knowledge,  bu1  we  may 
fairly  conclude  thai  in  an  isolated  preparation  it  is  twofold  : 
(1)  The  material  necessary  for  contraction  is  used  up  more 
quickly  than  it  can  be  reproduced  or  brought  to  the  place  where 
it  is  required  ;  (2)  waste  products  are  formed  by  the  active 
muscle  faster  than  they  can  be  removed.  That  even  an  isolated 
muscle  has  a  certain  store  of  the  materials  needed  for  contraction 
which  cannot  be  all  exhausted  at  once,  or  which  can  to  a  certain 
evtent  he  replenished  by  processes  going  on  in  the  muscle,  is 
shown    by    the    beneficial    effect    of   mere   rest.     Among   these 


Fig.  240. — Ercograph  (Mosso's.  modified  by  Lombard). 


materials  oxygen  holds  a  conspicuous  place.  An  isolated  muscle 
is  necessarily  an  asphyxiated  muscle,  and  the  favourable  action 
of  an  atmosphere  of  oxygen  on  restoration  of  its  contractile  power 
after  exhaustion  (Fig.  no,  p.  261)  shows  that  asphyxia  is  itself 
an  important  condition  in  the  onset  of  fatigue.  Injection  of 
arterial  blood,  or  even  of  an  oxidizing  agent  like  potassium 
permanganate,  into  the  vessels  of  an  exhausted  muscle  also 
causes  restoration  (Kronecker).  The  depletion  of  the  available 
store  of  carbo-hydrate  in  the  form  of  glycogen  (and  dextrose) 
seems  to  be  another  factor.  That  the  accumulation  of  fatigue 
products  has  something  to  do  with  the  exhaustion  is  shown  by 
the  fact  that  the  muscles  of  a  frog,  exhausted  in  spite  of  the 
continuance  of  the  circulation,  can  he  restored  by  bleeding  the 
animal,  or  washing  out  the  vessels  with  physiological  salt  solution, 


MUSCLE 


651 


while  injection  of  a  watery  extract  of  exhausted  muscle  into  the 
bloodvessels  of  a  curarized  muscle  renders  it  less  excitable 
(Ranke).  This  observer  supposed  thai  it  was  specially  the 
removal  of  the  acid  products  of  contraction  which  restored  the 

muscle.  Such  acid  products  as  carbon  dioxide  and  lactic  acid, 
when  they  act  on  muscle  in  more  than  a  certain  concentration, 
produce  the  same  effects  on  its  power  of  contraction  as  are  pro- 
duced by  fatigue.  In  smaller  concentration,  on  the  contrary, 
they  increase  the  excitability  of  the  muscle,  and,  according  to 
1  ee,  the  phenomenon  of  the  '  staircase  '  is  due  to  the  augmenting 


.'■-...■-'.-. 


Fig.  241. — Fatigue  Curve  of  Skeletal  Muscle  :  Gastrocnemius  of  Frog. 

Indirect    stimulation  ;  taken  with  arrangement   shown   in  Fig.  261  (p.  707). 
Time  tracing,  yl^  of  a  second. 

action  of  these,  and  perhaps  other  fatigue  substances,  before  they 
have  accumulated  sufficiently  to  cause  fatigue  (p.  649). 

Seat  of  Exhaustion  in  Fatigue. — When  a  fatigued  muscle 
responds  no  longer  to  indirect  stimulation,  it  can  still  be  directly 
excited.  The  seat  of  exhaustion  must  therefore  be  either  the 
nerve-trunk  or  the  nerve-endings.  It  is  not  the  nerve-trunk 
which  is  first  fatigued,  for  this  still  shows  the  negative  variation 
(p.  719)  on  being  excited.  And  if  the  two  sciatic  nerves  of  a  frog 
or  rabbit  be  stimulated  continuously  with  interrupted  currents  of 
equal  strength,  while  the  excitation  is  prevented  from  reaching 


632 


;    1/  i\r  1/    OF  PHYSIOLOGY 


the  muscles  of  one  limb  till  those  of  the  other  cease  to  contract, 

it  will  Ik-  found  that  when  the  'block'  is  removal  the  cor- 
responding  muscles  contract  vigorously  on  stimulation  of  their 
nerve.  The  passage  of  a  constant  current  through  a  portion  of 
the  nerve  or  the  application  of  ether  between  the  poinl  ol  stimula- 
tion and  the  muscles  may  be  used  to  prevent  the  excitation  from 
passing  down  (p.  708).  Or  a  dose  of  curara  jusl  sufficient  to 
paralyze  the  motor  innervation  may  be  given  to  a  rabbit,  ami  tin- 
animal  kept  alive  by  artificial  respiration.  The  sciatic  i>  now 
stimulated  for  man\-  hours.  Nevertheless,  as  soon  .1^  the 
influence  of  the  curara  begins  to  wear  off,  the  muscles  of  the  leg 
contract. 

The  possible  seats  of  fatigue  caused  by  voluntary  muscular 
contraction  are  (1)  the  muscle :  (2)  the  nerve-endings  (or  the  recep- 


Fig.   242.— Fatigue   Curve   taken-   on   a   Slowly    Moving   Drum   (Reduced 

to  Half):  Frog's  Gastrocnemius. 

Excited  through  the  sciatic  nerve  by  maximal  shocks  <>ncc  in  six  seconds. 

tive  substances  in  the  muscle  p.  634)  :  (3)  the  nerve-trunk  :  and 
the  path  of  the  voluntary  motor  impulses  in  the  central 
nervous  system,  which  includes  the  pyramidal  cells  in  the  motor 
region  of  the  cerebral  cortex  (p.  774),  the  fibres  of  the  pyramidal 
tract,  and  the  motor  cells  in  the  anterior  horn  of  the  spinal  cord. 
Although  the  matter  cannot  be  considered  definitely  settled.ergo- 
graphic  experiments  (Mossoand  Maggiora,  Lombard,  etc.)  (p.  ; 
have  been  interpreted  as  showing  that  fatigue  after  voluntary 
effort  is  die  to  <  entral  changes,  and  not  entirely  to  changes  in  the 
muscles  and  nerves  themselves.  Thus,  electrical  stimulation, 
either  of  a  '  tired  '  muscle  or  of  its  nerve,  is  readily  responded  to 
at  a  time  when  the  weight  cannot  be  raised  by  voluntary  con- 
traction. Now,  it  is  argued,  there  is  no  reason  to  suppose  that 
the  nerve-fibres  in  the  central  nervous  svstem  differ  essentially 
from  those  of  peripheral  nerves,  and  therefore  no  reason  for 
placing  the  seat  of  the  fatigue  anywhere  in  the  pyramidal  fibres, 


MUSCLE  053 

ex<  epl  perhaps  in  their  synapses  (p.  775)  in  the  cord,  which  1  orre- 

spond  to  the  endings  ol  the  peripheral  fibres  in  the  muscles.     Thai 

the  synapses  easibj  lose  their  power  of  conducting  nerve  impulses 

under  the  influence  oi  repeated  excitations  is  indicated  by  the  ex- 

perimentsof  Sherrington  on  fatigue  of  reflex  mechanisms  in  which 

two  or  more  afferenl  paths  can  cause  discharge  along  a  common 

efferenl  path  (p.  800).  When  excitation  of  one  of  the  afferent  paths 

has  ceased  to  be  effective,  the  reflex  contractions  can  still  be 

obtained  on  exciting  the  other.   In  this  case  the  motor  neuron  from 

cell-body  to  nerve-ending  and  the  muscle  are  eliminated  as  the  seats 

of  the  fatigue  block.     Whether  the  temporary  loss  of  conduction 

111  this  case  is  comparable  to  the  fatigue  of  muscle,  or  is  a  perfectly 

different  phenomenon  ('  pseudo-fatigue  '  of  Lee),  scarcely  bears 

on  our  present  question.     For  if  '  pseudo-fatigue  '  of  afferent 

synapses  can  cause  a  reflex  to  miss  fire,  this  at  least  shows  that  the 

conductivity  of  the  synapse  is  very  easily  affected  by  repeated 

excitation,  just  as  it 

is  known  to  be  very 

easily    affected    by 

anaemia.     The  only 

other  portions  of  the 

voluntary        motor 

path    besides   these 

synapses  that  seem  „  TT  „ 

,.,    , x  ,  Fig.  243. — Veratrine  Curve:  Frogs 

likely      to      become  Gastrocnemius. 

easily   fatigued    are        The  curve  shows  a  peak>  the  lfiver  falling  a  llttle 

the    nerve  -  ceils     Of      before  the  sustained  contraction  begiiib. 

the  cortex  and  the 

cord.  These  central  structures  are  usually  considered  the 
weakest  links  in  the  chain,  the  next  weakest  link  being  the 
motor  endings  in  the  muscles,  and  the  strongest  the  nerve-fibres. 
The  motor  endings  do  not,  in  general,  break  down  in  voluntary 
contraction,  because  the  central  apparatus  becomes  sooner 
fatigued.  It  is  not  inconsistent  with  these  facts  that  a  muscle, 
fatigued  by  direct  electrical  stimulation,  can  still  be  voluntarily 
contracted.  For  the  voluntary  excitation  may  be  more  effective 
than  any  artificial  stimulus. 

It  has  been  shown  that  the  injection  of  the  blood  of  an  animal 
exhausted  by  running  or  other  muscular  effort  into  the  circula- 
tion of  a  normal  animal  produces  in  the  latter  all  the  symptoms 
of  fatigue.  Here  the  fatigue-producing  substances  will  have 
the  opportunity  of  acting  on  both  the  central  and  the  peripheral 
mechanisms.  There  are  reasons  for  believing  that  the  fatigue 
process  is  fundamentally  the  same  in  different  tissues.  The 
fatigue  substances  produced  in  muscle,  and  not  immediately 
eliminated  or  transformed  during  active  muscular  exertion,  may 


"54 


;    1/  INUAL  OF  PHYSIOLOGY 


there  tore  wry  well  l>e  a  factor  in  inducing  fatigue  oi  the  central 
nervous  mechanisms  in   addition   to   the   formation  ol    fatigue 
products,   and   the   using   up   of    necessary   material   in    tl 
mechanisms  themselves.     Cent  ran  wise,  active  and  long-<  ontinued 
mental  exertion  may  occasion  muscular  fatigue  (Fig.   244). 

(d)  The  Influence  of  Drugs  on  the  Contraction  of  Muscle.  -The 
total  work  which  a  muscle  can  perform,  its  excitability  and  the 
absolute-  force  of  the  contraction,  may  all  be  altered  either  in  the  plus 
or  the  minus  sense  by  drugs.     But  in  connection  with  our  present 

subject  those  drugs  which  conspicuously  alter  the  form  and  time- 
relations  o! 'tlu-  muscle-curve  have  most  interest.  Of  these  veratrine 
is  especially  important.     When  a  small  quantity  of  this  substance 


Fig.  244. — Influence  of  Mental  Fatigue  on  Muscular  Contraction. 

1,  series  of  contractions  of  flexors  of  middle  finger  before,  and  2,  series  of  con- 
tractions immediately  after,  a  period  of  three  and  a  half  hours'  hard  mental  work. 
In  both  cases  the  muscles  were  stimulated  directly  every  two  seconds  by  .111 
electrical  current,  and  caused  to  raise  a  certain  weight  till  temporary  exhaustion 
occurred.  In  the  first  series  fifty-three  contractions  were  found  possible,  in  the 
second  only  twelve  (Maggiora). 

is  injected  below  the  skin  of  a  frog,  spasms  of  the  voluntary  mus> 
well  marked  in  the  limbs,  come  on  in  a  few  minutes.  These  are 
attended  with  great  stiffness  of  movement,  for  while  the  animal  cut 
contract  the  extensor  muscles  of  its -legs  so  as  to  make  a  spring,  they 
relax  very  slowly,  and  some  time  elapses  before  it  can  spring  again. 
If  it  be  killed  before  the  reflexes  are  completely  gone,  the  peculiar 
alterations  in  the  form  of  the  muscle-curve  caused  by  veratrine  will 
be  most  marked.  The  poisoned  muscle,  stimulated  directly  or 
through  its  nerve,  contracts  as  rapidly  as  a  normal  muscle,  while  the 
lit  of  the  curve  is  about  the  same,  but  the  relaxation  is  enormously 
prolonged  (Fig.  245).  This  effect  seems  to  be  to  a  considerable 
degree  dependent  on  temperature,  and  it  may  temporarily  disappear 
when  the  muscle  is  made  to  contract  several  times  without  pause. 
Adrenalin,  barium  salts,  and,  in  a  less  degree,  those  of  strontium  and 


MUSC1  I 


655 


calcium,  have  an  action  on  muscle  similar  to  thai  "i  vei  itrine. 
Sometimes  the  curve  shows  a  peals  (Fig.  2  pp.  due  to  a  rapid  *  1 «  scent 
oi  the  lever  for  a  certain  distance.  This  is  followed  by  ;l  slow 
relaxation.  The  peak  appears  to  be  analogous  to  the  initial  con- 
traction when  a  strong  voltaic  current  is  passed  through  a  mu 
.mil  the  rest,  of  the  curve  to  the  ionic  contraction. 

(e)  The  individuality  of  the  muscle  itself  has  an  influence  on  the 
muscle-curve.  Not  only  do  the  muscles  oi  differenl  animals  vary 
in  the  rapidity  of  contraction,  but  there  are  also  differences  in  the 
skeletal  muscles  of  the  same  animal. 

In  the  rabbit  there  are  two  kinds  ol  striped  muscle,  the  red  and 
the  pale  (the  semitendinosus  is  a  red.  and  the  adductor  magnus  a 
pale  muscle),  and  the  contraction  of  the  former  is  markedly  slower 
than  that  of  the  latter.  In  many  fishes  and  birds,  and  in  sonic 
insects,  a  similar  difference  of  colour  and  structure  is  present, 
although  a  physiological  distinction  has  not  here  been  worked  out. 

Even  where  there  is  no  distinct  histological  difference,  there  may 
be  great  variations  in  the  length  of  contraction.     In  the  frog,  for 


JWWWVWWWWWWWl^^ 


Fig.  245. — Veratrixe  Curve  compared  with  Normal  :  Frog's 
Gastrocnemius. 

The  tuning-fork  marks  hundredths  of  a  second.  Between  i  and  z  a  portion 
of  the  tracing  corresponding  to  one  and  a  half  seconds  has  been  cut  out,  and 
between  2  and  3  a  portion  corresponding  to  one  second.  The  veratrine  curve 
does  not  show  a  peak.     At  3  it  has  not  yet  fallen  to  the  base-line. 

instance,  the  hyoglossus  muscle  contracts  much  more  slowly  than 
the  gastrocnemius.  The  wave  of  contraction,  which  in  frogs' 
striped  muscle  lasts  only  about  C07  second  at  any  point,  may  last  a 
second  in  the  forceps  muscle  of  the  crayfish,  though  only  half  as 
long  in  the  muscles  of  the  tail.  In  the  muscles  of  the  tortoise  the 
contraction  is  also  very  slow.  The  muscles  of  the  arm  of  man 
contract  more  quickly  than  those  of  the  leg. 

Summation  of  Stimuli  and  Superposition  of  Contractions. — 
Hitherto  we  have  considered  a  single  muscular  contraction  as  arising 
from  a  single  stimulus,  and  we  have  assumed  that  the  muscle  has 
completed  its  curve  and  come  back  to  its  original  length  before  the 
next  stimulus  was  thrown  in .  We  have  now  to  inquire  what  happens 
when  a  second  stimulus  acts  upon  the  muscle  during  the  contraction 
caused  by  a  first  stimulus,  or  during  the  latent  period  before  the  con- 
traction has  actually  begun  ;  and  what  happens  when  a  whole  series 
of  rapidly-succeeding  stimuli  are  thrown  into  the  muscle. 

First,  let  us  take  two  stimuli  separated  by  a  smaller  interval 
than  the  latent  period  (p.  642).  If  they  are  both  maximal — i.e., 
if  each  by  itself  would  produce  the  greatest  amount  of  contraction 


656  A   .1/  \NU  U-  OF  PHYSIOLOGY 

oi  which  the  muscle  is  capable  when  excited  by  ;i  single  stimulus — 
th<  second  has  do  effect  whatever;  the  contraction  is  precisely  the 
same  .is  n  it  had  never  acted.  But  if  they  are  1<  ss  than  maximal, 
the  contraction,  although  it  is  a  single  contra*  tion,  is  n  ater  than 
would  have  hern  due  to  the  first  stimulus  alone  ;  in  other  words,  the 
stimuli  have  been  summed  or  added  to  each  other  during  the  latent 
period  so  as  to  produce  a  single  result. 

Next,  l(  t  us  consider  the  ease  of  two  stimuli  separated  by  a  greater 
interval  than  the  latent  period,  so  that  the  second  tails  into  the 
muscle  during  the  contraction  produced  by  the  first.  The  result 
lure  is  very  different  :  traces  of  two  contractions  appear  upon  the 
muscle-curve,  the  second  curve  being  that  which  the  second  stimulus 
would  have  caused  alone,  but  rising  from  the  point  which  the  first 
had  reached  at  the  moment  of  the  second  shod.  Al- 

though the  first  curve  is  cut 
short  in  this  manner,  the  total 
height  of  the  contraction  is 
greater  than  it  would  have 
been  had  only  the  first  stimu- 
lus acted  :  and  this  is  true  <-\  en 
when  both  .stimuli  are  maxi- 
mal. Under  favourable  cir- 
cumstances, when  the  second 
Curve  rises  from  the  apex  oi 
the  first,  the  total  height  may 
be  twice  as  -real  .is  that  <>t 
Fig.  246.  Superposition  of  Contrac-  the  contraction  which  one 
iio_\s.  stimulus    would    have    caused 

1  is  the  curve  when  only  one  stimulus  (?■  7")-  [t  is  worthy  of  note 
is  thrown  in ;  2,  when  a  second  stimulus  tnat  striated  muscle  has  no 
acts  at  the  tune  when  curve  1  lias  nearly  power  of  summation  of  sub- 
reached  its  maximum  height.  minimal  stimuli  each  of  which 

is  just  too  weak  to  cause  con- 
traction. No  matter  how  rapidly  they  are  thrown  in.  the  muscle 
remains  at  rest.  It  is  otherwise,  with  smooth  muscle.  Stimuli 
which  are  singly  ineffective  cause  contraction  when  repeated. 

Tetanus. — Not  only  may  we  have  superposition  or  fusion  of 
two  contractions,  but  of  an  indefinite  number  ;  and  a  series  of 
rapidly  following  stimuli  causes  complete  tetanus  of  the  muscle, 
which  remains  contracted  during  the  stimulation,  or  till  it  is 
exhausted  (Fig.  247). 

The  meaning  of  a  complete  tetanus  is  readily  grasped  if, 
beginning  with  a  series  of  shocks  of  such  rapidity  that  the 
muscle  can  just  completely  relax  in  the  intervals  between  suc- 
cessive  stimuli,  we  gradually  increase  the  frequency  (p.  711). 
As  this  is  done,  the  ripples  on  the  curve  become  smaller  and 
smaller,  and  at  last  fade  out  altogether.  The  maximum  height 
of  the  contraction  is  greater  than  that  produced  by  the  strong 
single  stimulus  :  and  even  after  complete  fusion  has  been  attained, 
a  further  increase  of  the  frequency  of  stimulation  may  cause  the 
curve  still  to  rise. 

It  is  evident  from  what  has  been  said  that  the  frequency  of 


\£US(  i  '  65; 

stimulation  necessary  foi  complete  tetanus  will  depend  upon 
the  rapidity  with  which  the  muscle  relaxes;  and  everything 
which  diminishes  this  rapidity  will  lessen  the  necessary  frequi 
of  stimulation.  A  fatigued  muscle  may  be  tetanized  by  a 
smaller  number  oi  stimuli  per  second  Hum  a  fresh  muscle,  and 
.1  cooled  by  a  smaller  number  than  a  heated  muscle.  The  striped 
muscles  of  insects,  which  can  contract  a  million  times  in  an 
hour,  require  joo  stimuli  per  second  for  complete  tetanus,  those 
o\  birds  too,  of  man  40,  the  torpid  muscles  of  the  tortoise  only  3. 
The  pale  muscles  of  the  rabbit  need  20  to  40  excitations  a  second, 
the  red  muscles  only  10  to  20;  the  tail  muscles  of  the  crayfish 
40,  but  the  muscles  of  the  claw  only  6  in  winter  and  20 in  summer. 


Fig.  247. — Analysis  of  Electrical  Tetanus  (Reduced  10  §). 
Four  curves  showing  the  effect  of  increasing  frequency  of  stimulation  of  the 
frog's  gastrocnemius  through  its  nerve.  In  the  lowest  curve  the  frequency  is 
such  that  the  muscle  relaxes  almost  completely  between  the  successive  con- 
tractions. In  the  uppermost  curve,  with  a  frequency  more  than  three  times  greater, 
the  contractions  are  almost  completely  fused.  In  all  the  curves  the  fusion  becomes 
more  nearly  complete  as  stimulation  goes  on,  owing  to  the  slower  relaxation  of 
the  fatigued  muscle. 

The  gastrocnemius  of  the  frog  requires  30  stimuli  a  second,  the 
hyoglossus  muscle  only  half  that  number  (Richet).  The  fre- 
quency of.,  stimulation  necessary  for  complete  tetanus  of  un- 
striped  muscle  is  much  less  than  for  striped  muscle.  Smooth 
tetanus  of  a  band  of  muscle  from  the  frog's  stomach  was  obtained 
with  strong  opening  induction  shocks  at  the  rate  of  1  in  5  seconds. 

We  see,  then,  that  there  is  a  lower  limit  of  frequency  of  stimula- 
tion below  which  a  given  muscle  cannot  be  completely  tetanized, 

4-2 


6sfi  A    M  INI    U    (>}■   PHYSIOLOGY 

.mi]  the  question  arises  whethei  there  is  also  an  uppi  i  limil  i>  yond 
which  a  series  oi  stimuli  becomes  too  rapid  to  product  complete 
i.i  hi  us.  in .  indeed,  to  cause  contraction  .it  .ill  \\  e  maj  b(  certain 
ili.ii  every  stimulus  requires  .1  finite  time  to  produce  an  effe<  1.  and 
it  is  1 M i-vm  1  ill ■  that  it  the  duration  oi  eai  b  shot  K  wen-  reduced  b<  low  a 
certain  minimum,  withoul  Lessening  .it  the  same  timi  the  interval 
between  successive  excitations,  no  contraction  would  be  caused  by 
anj  or  .ill  oi  the  stimuli  in  the  series  Bu1  abovi  tins  minimum 
then  apparently  lies  .1  frequency  oi  stimulation  ai  least,  when 
the  interval  between  the  stimuli  is  reduced  exactly  in  th<  Bame 
proportion  as  the  duration  a1  wIihIi.ui  interrupted  currenl  <  onus 
tn  ,nt  like  a  constant  current,  causing  a  singli  twitch  a1  its  com* 
1  inn  1 1  11 H  nt  1  n  ■  .1.1  its  end,  bu1  no  contraction  during  i1     | 

\s  do  this  lasi  hunt .  on  the  fixing  oi  whi<  h  mucb  labour  has  been 
expended,  it  undoubtedly  does  nol  depend  upon  the  frequent 
stimulation  alone;  the  intensitj  oi  the  individual  excitations,  the 
temperature  oi  the  muscle,  and  probablj  othei  factors,  affed  it. 
li.i  Bernstein  found  thai  with  moderate  trength  of  stimulus 
tetanus  failed  a1  aboui  250  per  second,  and  was  replaced  1>\  an 
initial  contraction;  with  strong  stimuli  a1  more  than  [,700  per 
31  nd,  tetanus  could  still  be  obtained.  Kronecker  and  Stirling, 
stimulating  the  muscle  1  >\  induced  currents  sel  up  in  .1  coil  1>\  the 
longitudinal  vibrations  of  ;i  magnetized  bar  oi  iron,  savi  tetanus 
.  vi  11  with  the  utmosl  Erequem  \  attainable,  4,000  shot  ks  .1  second, 
.11 1  ording  to  Roth;  while  v.  Kries  in  .1  cooled  muscle  found  tetanus 
replaced  by  the  simple  initial  twitch  .it  too  stimuli  per  second, 
although  in  a  muscle  ai  38  C.  stimulation  of  ten  times  1  lus  frequency 
still  caused  tetanus.  Recently  Einthoven,  exciting  the-  nerve  oi  .1 
frog's  nerve-muscle  preparation  with  extremely  fre  [uent  os<  illatory 
1  ondenserdisi  barges,  observed  tetanus  up  to  even  a  million  vibrations 
.1  so  oikI,  if  the  '  uncut  intensity  was  .it  the  same  time  very  greatly 
1111  leased  (to  more  than  16,000  times  the  intensity  needed  with  a 
constant  current).  These  results  are  not  really  so  discordant  as 
they  appear  ;  for  ii  is  known  that  with  electrical  stimulation  the 
number  oi  excitations  is  not  necessarily  the  same  as  the  nominal 
number  of  shocks.  By  applying  a  telephone  to  a  muscle  excited 
through  its  motor  nerve,  it  lias  been  shown  that  the  pitch  oi  the 
note  produced  by  the  tetanized  muscle  corresponds  exactly  to  the 
rate  oi  excitation  up  to  a  certain  frequency.  This  frequency  is 
about  200  per  second  for   frog's  and  aboui    [,00  cond   for 

mammalian  muscle  under  the  besl  conditions.  If  the  rate  oi  ex- 
citation is  still  further  increased,  there  is  no  corresponding  increase 
in  the  pitch.  Therefore,  some  oi  the  stimuli  are  now  producing  no 
effeci  '  falling  Hat.'  so  to  speak  (Wedenskj  <  >ne  reason  for  tins 
1sih.1i  even  very  briei  currents  leave  alterations  oi  conductivity 
and  excitability  behind  them  (Sewall),  which  we  shall  have  to 
discus  -  in  am  ithei  chaptei  (p  68  . 

li  is  only  while  the  actual  short  iking  place  thai  a  tetan- 

ized muscle  can  do  external  work  But,  although  durinj  the 
maintenance  oi  the  contraction  no  w  ork  is  done,  energy  Is  n  \  < 1  Un- 
less being  expended,  for  the  metabolism  oi  a  muscle  during  tetanus 
is  greater  than  during  rest.  Anion-  other  changes,  the  carbon 
dioxide  given  ofl  is  increased,  and  lactic  acid  produced.  And  upon 
the  whole  a  muscli  Is  more  quicklj  exhausted  by  tetanus  than  l>> 
successive  single  contractions,  although  there  are  great  differences 
between  different  muscli  •  For  example,  the  muscles  which  close 
the-  forceps  of  the  crayfish  or  lobster  have,  as  everyone  knows,  the 


MUSCLE  659 

power  "i  mosi  obstinate  imhii.uIi.ih  Richel  tetanized  one  for 
over  scventj  minutes,  and  anothei  for  an  tour  and  a  half,  before 
exhaustion  came  on,  while  a  tetanus  oi  a  single  minute  exhausted 
tlic  muscles  oi  the  1  raynsh's  tail,  ["he  gastroi  aemius  oi  a  summer 
frog  kept  up  for  twelve  minutes,  and  a  tortoise  muscle  for  forty 
minutes. 

Continuous  stimulation  is  nol  always  ue<  essary  for  the  production 
oi  continuous  contraction  :  in  some  conditions  a  single  stimulus  is 
sufficient.  \  blow  with  a  hard  instrument  maj  cause  a  dying  or 
exhausted,  and  in  thin  persons  even  .1  fairly  normal,  muscle  to  pass 
into  Long-continued  contraction  Mm.  s. >  railed  '  idio-muscular  ' 
contraction  seems  to  depend,  in  pari  .if  Least,  on  the  greai  intensity 
of  the  stimulus  It  can  sometimes  I"  obtained  in  1  lie  frog's  gastroc- 
nemius, particularly  in  spring  after  the  winter  East.  it  is  not  a 
mis  and  is  not  propagated  along  the  muscular  fibres,  as  an 
electrical  tetanus  is,  bul  remains  localized  a1  the  spot  where  rl  .irises. 
Similar  nun  -tetanic  contractions  have  already  been  mentioned, 
such  .is  (he  tonic  contraction  during  (he  passage  oi  .1.  strong  voltaii 
current  and  the  sustained  veratrine  contraction.  Ammonia  causes 
also  a  Long  but  non  tetanic  contraction,  and  tins,  too,  does  nol  spread 
when  the  substance  has  acted  only  on  .1.  pint  urn  oi  the  muscle.  The 
contraction  force  >>i  .ill  these  tonic  contractions,  as  measured  by  the 
resistance  necessary  to  overcome  or  prevent  them,  is  less  than  the 
contraction  force  in  electrical  t (dan us  (Sehcnek). 

The  rate  at  which  the  wave  of  muscular  contraction  travels  may 
be  measured  In-  stimulating  the  muscle  .it.  one  end.  and  recording, 
by  means  of  Levers,  the  movements  of  two  points  of  its  surface  as 
far  apart  from  each  other  .is  possible.  Time  is  marked  on  the 
tracing  by  means  of  a  tuning-fork,  and  the  distance  between  the 
points  at  which  the  two  curves  begin  to  rise,  from  the  base-line 
divided  by  the  time  gives  the  velocity  of  the  wave.  Another 
method  is  founded  upon  the  measurement  of  the  rate  at  which  the 
negative  variation  (p.  719)  passes  over  the  muscle,  this  being  the 
same  as  the  velocity  of  the  contraction-wave.  In  frog's  muscle  it 
is  about  three  metres  a.  second,  or  six  miles  an  hour.  Rise  of  tem- 
perature increases,  fall  of  temperature  lessens  it. 

When  a  muscle  is  excited  through  its  nerve,  the  contraction 
springs  up  first  of  all  about  the  middle  of  each  muscular  fibre  where 
the  nerve-fibre  enters  it.  and  then  sweeps  out  in  both  directions 
towards  the  ends.  But  so  long  is  the  wave,  th.it  all  parts  of  the 
fibre  are  at  the  same  time  involved  in  some  phase  or  other  of  the 
contract  ion.  And  this  is  the  case  even  when  the  end  of  a  long 
muscle  like  the  sartorius  is  artificially  stimulated. 

The  wave  of  contraction  in  unstriped  muscle  lasts  a  relatively 
long  tune  at  any  given  point,  and  in  tubes  like  the  intestines  and 
ureter...  the  walls  of  which  arc  largelv  composed  of  smooth  muscle 
arranged  in  rings,  the  wave  shows  itself  as  a  gradually-advancing 
constriction  travelling  from  end  to  end  of  the  organ.  There  is  no 
evidence  that  the  contraction  of  smooth  muscular  fibres  is  discon- 
tinuous— that  is,  composed  of  summated  contractions  like  a  tetanus  ; 
it  appears  to  be  a  greatly-prolonged  simple  contraction.  An  artificial 
stimulus,  mechanical  or  electrical,  causes,  after  a  long  latent  period. 
a  very  definitely-localized  contraction  in  a  rabbit's  ureter,  which 
slowly  spreads  in  a  peristaltic  wave  in  one  or  both  directions  alon^ 
the  muscular  tube.  Here,  as  in  the  cardiac  muscle,  the  excitation 
passes  from  fibre  to  fibre,  while  in  striped  skeletal  muscle  only  the 
fibres  excited  directly  or  through  their  nerves  contract.     That  the 

42—2 


I    i/!Vi    1/    OF   PHYSIOLOGY 

rhytlmiK.il  contraction  oi  the  heart  is  nol  a  tetanus  has  already 
been  seen,  it  Is  a  simple  contraction,  intermediate  in  its  duration 
,iik1  other  characters  between  the  twitch  <>t  voluntary  muscle  and 
the  contraction  of  smooth  muscli  rh<  contraction  both  oi  unstriped 
.md  oi  <  ardiac  must  le  is  lengthened  and  made  strong!  r  by  distension 
oi  the  viscera  in  whose  walls  they  occur,  just  as  a  skeletal  muscle 
(  ontra<  ts  more  powerfully  against  resistan 

Voluntary  Contraction.  There  is  evidence  thai  the  volun- 
tary contraction  is  a  tetanus.  One  oi  the  strongesi  butti 
the  theory  oi  natural  tetanus  has  been  the  muscle-sound,  a  low 
rumbling  note  which  can  be  heard  by  listening  with  ;i  stetho- 
scope over  the  contracting  biceps,  or,  when  all  is  still,  by  stopping 
the  ears  with  the  fingers  and  strongly  contracting  the  mass 
.md  the  other  muscles  concerned  in  closing  the  jaws.*  Dis- 
covered aboul  ninety  years  ago,  firsi  by  Wollaston  and  then  by 
Erman,  halt  a  century  passed  away  before  it  was  investigated 
more  fully  by  Helmholtz.  The  latter  observer,  confirming  the 
results  of  his  predecessors,  pu1  down  the  pitch  "I  the  sound  at 
36  to  4<i  vibrations  per  second.  He  found,  however,  thai  little 
vibrating  reeds  with  a  rate  oi  oscillation  of  aboul  its  pei  second 
were  more  affe<  ted  when  atta<  hed  to  muscle  thrown  into  volun- 
tary contraction,  than  those  that  vibrated  al  a  smaller  or  a 
iter  rate.  He  therefore  concluded  thai  the  1nndanicnt.il 
tone  "t  the  muscle  corresponded  to  this  frequency,  although, 
since  such  a  lovt  note  is  noi  easily  apprei  iated,  the  sound  actually 
heard  was  reallj  its  01  tave  or  firsi  harmonic  (p.  280). 

The  objection  has  been  br<  tught  forward  that  the  resonance  tone  of 
the  ear  also  corresponds  to  a  vibration  frequency  oi  j6to  }<>  a  second. 
In  other  words,  this  is  the  natural  rati'  of  swing  oi  the  clastic  struc- 
tures in  the  middle  ear.  the  rate  they  will  most  easily  tall  into  it 
set  moving  by  an  irregular  mixture  oi  faint,  low-pitched  tones  and 
noises,  .md  not  compelled  to  vibrate  at  some  other  rate  l>v  a  distini  t 
sound  "i  definite  pitch.  Now.  this  resonance  tone  might  he  elicited 
by  a  quivering  muscle  if.  among  many  diverse  rat' s  "i  o»  illation  oi 
different  porti  ms  oi  its  substance,  the  rate  oi  s"  1"  40  a  second  any- 
where appeared,  and  the  note  corresponding  to  the  real  rate  of  vibra- 
tion of  the  muscle  as  a  whole  might  be  overpowered.  « >r,  even  if  there 
were  no  regular  rate  oi  \  ibral  ion  oi  the  whole  muscle,  but.  instead,  a 
ulai  tremors  or  pulls  due  to  irregularities  in  the  con- 
traction, ted  with  a.  want  ol  co-ordination  of  all  the  fibres 
>  might  from  time  to  time  pick  nut  of  the  turmoil 
ol  feeble  a<  rial  waves  those  corresponding  to  its  resonance  tone,  just 
as  a  tuning-fork  or  a  piano-string  attuned  to  a  particular  note  would 
.  it  up  amid  a  thousand  other  sounds  and  strengthen  it. 

But  while  this  renders  it  highly  probable  that  the  resonance  of 
the  ear  contributes  to  the  production  of  the  muscle-sound,  and 
shows  that   we  cannot    from  the   pitch   of  the   muscle-sound  alone 

*  In  order  that  a  muscular  sound  may  he  produced  there  must  be  a 
certain  abruptness  in  the  contraction.  Thus,  the  slowly  contracting 
smooth  muscles  do  not  produce  a  sound,  nor  the  slowly-contracting 
heart-muscle  of  cold-blooded  animals. 


MUSCl  E 


deduce  the  rate  .it  which  the  muscle-substance  is  vibrating,i1  do*  i 
nut  invalidate  Helmholtz's  objective  observations  with  the  <>scil- 
lating  reeds. 

And  several  observers  (Schafer,  Horsley,  v.  Kries)  have  noticed 
periodic  oscillations,  a1  the  rate  ol  to  or  12  per  second,  in  the 


/I 


Fig.    248. — Vibrations   of  Contracted   Arm    Muscles   (Griffiths). 
The  arm  was  stretched  out,  holding  a  weight  of  about  6  kilos. 

curves  taken  from  muscles  (Fig.  248),  contracted  voluntarily 
against  a  small  resistance.  When  the  resistance  is  greater,  the 
rate  may  be  as  much  as  18  or  20  a  second,  and  in  quick  and 
rapidly  repeated  movements  of  the  fingers  even  40  a  second.  In 
habitual  movements,  such  as  those  employed  by  a  man  in  his 
trade,  the  tremors  are  much  less  coarse  than  in  unaccustomed 
movements.  For 
this  reason  the 
tremors  of  the  left 
hand  are  greater 
than  those  of  the 
right  in  execut- 
ing a  movement 
usually  made 
with  the  latter 
(Eshner).  In 
disease  these 
tremors  are  often 
increased  —  e.g., 
in  the  clonic  con- 
vulsions of  epi- 
lepsy— but  the 
frequency  is  the  same.  Similar  vibrations,  and  at  about  the 
same  rate,  are  seen  in  curves  traced  by  muscles  excited  through 
stimulation  of  the  motor  areas  of  the  surface  of  the  brain.  Since 
this  rate  remains  the  same  whether  the  motor  cortex,  the  corona 
radiata,  or  the  spinal  cord  is  excited,  and,  unlike  the  rate 
of  response  to  excitation  of  peripheral  nerves,  is  independent 


Fig.  240. 


-Contractions  caused    by TStimulatioi 
the  Spinal  Cord. 


662  /    w  ixill    OF  PHYSIOLOGY 

oi  the  frequency  oi  stimulation  (so  long  as  the  rate  ol  stimu- 
lation is  greater  than  io  or  12  a  second),  it  has  been  supposed 
to  represent  the  rhythm  with  which  impulses  an-  discharged 
from  the  motor  cells  of  the  cord  (Fig.  249).  It  is  probable 
that  the  cortical  centres  discharge  at  aboul  the  same  rate,  for 
not  only  is  it  impossible  to  articulate  more  rapidly  than  eleven 
syllables  per  second,  but  it  is  impossible  to  reproduce  the  act 
of  articulation  in  thought  at  a  greater  rate  than  this  (Richet). 
But  while  this  rate  of  10  or  12  a  second  does  seem  to  represent  a 
fundamental  rhythm  of  the  central  discharge, there  are  fa<  ts  which 
indicate  that  upon  this  relatively  slov  rhythm  a  quit  ker  rhythm 
is  superposed.  In  other  words,  each  of  these  discharges  is  itseli 
discontinuous,  and  made  up  of  a  number  of  separate  impulses. 

Thus,  according  to  Piper,  the  total  number  of  simple  discharges, 
each  associated  with  an  electrical  change  in  the  muscle,  is  47  to  50  a 
second.  The  rhythm  of  strychnine  tetanus  in  the  frog  is  about  8  to 
12  per  second.  By  means  of  the  capillary  electrometer  (p.  oj  1 1  large 
electrical  oscillations  at  this  rate  can  be  demonstrated,  each  of 
which  represents  a  short  tetanic  spasm,  as  is  shown  by  the  fa<  t  that 
a  number  of  smaller  electrical  oscillations  arc  superposed  upon 
the   large  ones   (Sanderson).     The   electrical   changes  that 

each  discharge  causes  a  simple  contraction  much  more  prolonged 
than  the  twitch  of  a  directly  stimulated  muscle.  This  removes  the 
difficulty  of  understanding  how  such  a  small  number  as  10  contrac- 
tions per  second  could  be  smoothlv  fused,  and  indii  ates  that  even  the 
shortest  possible  voluntary  movement,  winch  can  be  executed  in 
10  to  .}u  of  a  second,  is  not  caused  by  a  single  impulse,  but  is  a 
tetanus.  For  these  brief  movements  the  frequency  oi  oscillation, 
as  shown  by  the  action  currents,  is  the  same  as  for  sustained  con- 
tractions, 'the  electrical  changes  in  the  voluntarily  contracted 
muscle  seem  to  differ  in  amplitude  or  abruptness  from  those  pro- 
duced in  experimental  tetanus.  For  secondary  tetanus  (p.  730)  is  not 
caused  by  muscle  in  voluntary  contraction.  But  this  is  also  the 
case  with  the  other  prolonged  contractions  caused  by  continuous 
artificial  stimulation  e.g.,  Kilter's  tetanus  (p.  636)  and  the 
contraction  produced  by  sodium  chloride  or  ammonia.  We  need 
not  hesitate  to  emu  hide.  then,  thai  the  voluntary  contraction  is 
discontinuous,  in  the  sense  th.it  it  is  nol  a  perfectly  smooth 
and  uniform  tonic  contraction,  although  we  still  lack  a  decisive 
proof  that  it  is  maintaied  by  a  strictly  intermittent  outflow  of 
nervous  energy,  and  not  by  a  continuous  outflow  causing  a  sus- 
tained contraction,  which,  it  may  be.  remits  and  is  reinforced  at 
intervals.  The  apparent  discrepancies  as  to  the  rate  oi  discharge 
in  the  results  obtained  by  different  observers  and  by  different 
methods,  far  from  exciting  distrust  of  them  all.  really  lend  support 
to  the  idea  of  a  fundamental  and  fairly  constant  rhythm  in  the 
outflow  as  soon  as  it  is  recognised  that  the  higher  rates  are  approxi- 
mately multiples  of  the  lower.  Thus,  the  number  deduced  by  1  lelm- 
holtz  from  the  experiment  of  the  springs  is  twice  the  lowest  rate 
calculated  from  graphic  records  of  the  contraction.  The  rates 
corresponding  to  the  muscle-sound  and  to  the  frequency  of  the 
electrical  oscillations  are  aboul  lour  times  this  number.  Now.  in  a 
vibrating   elastic   body   like   a   contracting    muscle,  a   simple   mathe- 


MUSCLE  663 

maticaJ  relation  of  this  sort   might  be  expected  to  appear  when 
determinations    oi    the    rate    of    oscillation    and    of   accompanying 
periodic   changes  are    made  l>v  methods  varying   in   principle  and 
in  delicacy.     For  instance,  an  arrangement  suited  to  record  an 
count  coarse  vibrations  could  not  be  expected   I  the  same 

result  .'-  an  arrangement  suited  to  record  and  count  fine  vibrations. 
But  it"  both  the  coarse  and  the  fine  vibrations  were  related  to  a 
fundamental  rhythm,  a  simple  proportion  might  be  expected  to  exist 
between  the  two  sets  of  results. 

(3)  Thermal  Phenomena  of  the  Muscular  Contraction.— 
When  a  muscle  contracts  its  temperature  rises;  the  production 
of  heat  in  it  is  increased.  This  is  most  distinct  when  the 
muscle  is  tetanized,  but  has  also  been  proved  for  single  con- 
tractions. The  change  of  temperature  can  be  detected  by  a 
delicate  mercury  or  air  thermometer  ;  and,  indeed,  a  thermometer 
thrust  among  the  thigh-muscles  of  a  dog  may  rise  as  much  as 
i°  to  2°  C.  when  the  muscles  are  thrown  into  tetanus.  In  the 
isolated  muscles  of  cold-blooded  animals  the  increase  of  tem- 
perature is  much  less  ;  and  electrical  methods,  which  are  the 
most  delicate  at  present  known,  have  generally  been  used  for 
its  detection  and  measurement. 

They  depend  either  upon  the  fundamental  fact  of  thermo-elec- 
tricity, that  in  a  circuit  composed  of  two  metals  a  current  is  set  up  if 
the  junctions  of  the  metals  are  at  different  temperatures  ;  or  upon 
the  fact  that  the  electrical  resistance  of  a  metallic  conductor  varies 
with  its  temperature.  On  the  former  principle  the  thermopile  lias 
been  constructed  (Fig.  250),  on  the  latter  the  bolometer,  or  'electrical- 
resistance  thermometer  '  (Fig.  25 1). 

Where  no  very  fine  differences  of  temperature  are  to  be  measured, 
a  single  thermo-j  unction  of  German  silver  and  iron,  or  copper  and 
iron,  is  inserted  into  a  muscle  or  between  two  muscles.  But  the 
electro-motive  force,  and  therefore  the  strength  of  the  thermo- 
electric current,  is  proportional  for  any  given  pair  of  metals  to  the 
number  of  junctions,  and  for  delicate  measurements  it  mav  be 
neeessarv  to  use  several  connected  together  in  series.  A  thermopile 
of  antimony-bismuth  junctions  gives  a  stronger  current  for  a  given 
difference  of  temperature  than  the  same  number  of  German  silver- 
iron  couples,  but  from  its  brittle  nature  is  otherwise  less  convenient. 

The  direction  of  the  current  in  the  circuit  is  such  that  it  passes 
through  the  heated  junction  from  bismuth  to  antimony  and  from 
copper  or  German  silver  to  iron.  Knowing  this  direction,  we  are 
aware  of  the  changes  of  temperature  which  take  place  from  the 
movements  of  the  mirror  of  the  galvanometer  with  which  the  pile 
is  connected.  The  galvanometer  must  be  of  low  resistance,  since 
the  electromotive  force  of  the  thermo-electric  currents  is  small,  and 
a  high  resistance  would  cut  down  their  intensity  too  much. 

The  muscle  which  is  to  be  excited  is  brought  into  close  contact 
with  one  junction  or  set  of  junctions,  the  other  set  being  kept  at 
constant  temperature  by  immersing  them  in  water,  or  covering  them 
with  muscle  that  is  not  to  be  stimulated.  The  image  will  now  come 
to  rest  on  the  scale  ;  and  excitation  of  the  muscle  will  cause  a  move- 
ment indicating  an  increase  of  temperature  in  it,  the  amount  of 
which  can  be  calculated  from  the  deflection. 


,,,, 


A    MANl    ll    OF  I'll)  sionx,  ) 


In  this  way  Helmholtz  observed  a  rise  of  temperature  of 
ni|  to  o*i8  C.  in  excised  frogs'  muscles  when  tetanized  for 
a  couple  of  minutes. 

Heidenhain,  with  a  very  delicate  pile,  found  a  rise  <>t  oooi    to 

0-005°  C.  for  a  single  con- 
1 1  a<  tion  ol  .1  frog'  mus- 
cle. On  the  assumption 
thai  the  pile  had  lime  to 
take  on  the  ti  mpei  ature 
oi  the  must  le  before  there 
was  any  appre<  iable  loss 
nl  heat,  this  would  be 
1  qua]  to  the  production 
by  every  gramme  ol  mus- 
cle of  a  thousandth  to 
five-  thousandths  of  a 
small  calorie  (p.  574)  of 
heat.  From  Fick's  ob- 
servations we  may  take 
about  three-thousandths 
n|  a  small  calorie  as  the 
maximum  production  of 
a  gramme  of  frog's  mus- 
1  le  in  a  single  conti 
1  ion. 

It  is  certain  thai  when  work  is  dune  by  a  muscle  an  equivalent 
amount  is  subtracted  from  its  sum-total  <>t  energy,  and  under 
proper  1  onditions  tins  can  be  actually  demonstrated  by  the  deficit  ru  y 

B        _  B 


Fig.    250. 

A,  a  single  copper -iron  thermo-electric  couple; 
B,  two  pairs,  one  inserted  into  the  tissued,  the 

other  dipping  into  water  in  a  beaker  «.     The 
temperature  oi   the  water  may  be  adjusted  so 
that    the  galvanometer   shows   no  deflection 
The  temperature  ol  the  tissue  is  then  the  same 
.i-  1  li.it  oi  tin   v.  ater. 


As  used  for  in\  estigating  heat- 
production  in  mammalian  turves 
in  situ.  A,  a  piei  e  oi  hard  rubber 
in  the  hook-shaped  pari  ol  w  hit  h 
the  fine  platinum  wire  P  is  fixed, 
and  '  <  '\  ered  with  insulating 
Mish  :  c,  1 .  thick  copper  \\  ires 
connected  with  P,  fastened  in 
grooves,  and  1  o\  ered  with  para  tin  1. 
Above  they  end  in  contact  with 
the  small  binding  posts,  Bj,  Bg. 
B  is  a  hard  rubber  sliding  piece, 
with  a  slut  s.  When  B  is  in 
]n>siti'>ii  the  screw,  a,  projects 
through  the  slot.  By  a  nut  on 
this  si  rew  B  is  fixed  on  A  when 
the  nerve  has  been  arranged  in  the 
groove.  A  similar  larger  arrange- 
ment can  l»-  used  for  muscle. 


"JUL 


B 


IhM 


: 


_j 


: 


Fig.   251. — F.i  i  C  i  R1C  \\  -Ki  SISTANCB 
'I'm  RMOM1  n  R  (NATURAl    Si/i  ). 


in  the  heat-production.     This  is  done  by  means  oi  .1  contrh 
called  a  work-adder.     It  ((insists  of  a  wheel,  the  rotation  of  which 
raises  .1    weigh!    attached  to  a  corcl  wound   round   its  axle.     The 


WUSCL1  665 

muscle  ai  I  1  on  the  periphery  of  the  wheel,  and  l>v  rotating  H  i 
the  weighl   a  little  .it   each  contraction.     At    the  end  oi  the  con 

traction  the  wheel  is  prevented  from  moving  back  by  a  catch. 
lln-  work  done  in  .1  series  of  contractions  is  calculated  from  the 
total  heigh.1  to  which  the  weight  has  been  raised.  Suppose  a  frog's 
gastrocnemius  is  made  to  contract  a  certain  number  01  times  while 
attached  to  the  work-adder,  and  thai  simultaneously  the  heat  pro- 
duction is  measured  by  means  of  a  thermopile.  Let  H  repri 
the  lie.it  actualhj  produced,  and  h  the  beat  equivalent  of  the  work 
done.  Now  let  the  muscle  be  disconnected  from  the  adder  and 
made  to  raise  t  he  same  weight,  due,  tly  .it  1  ached  to  it,  by  a  scries 
of  contractions  elicited  in  precisely  the  same  way  as  the  previous 
ones.  e\(  epl  t  ba1  t  lie  weigh!  is  allowed  lo  tall  with  the  muscle  when 
it  relaxes  alter  e.uh  coid ruction.  Here  heat  corresponding  to  the 
external  work-  disappears  from  the  muscle  during  the  contraction 
just  as  in  the  first,  experiment .  but  1  his  beat  is  returned  to  the  muscle 
during  the  relaxation,  since  on  the  whole  no  external  work  is  done. 
The  heat  produced  in  the  second  experiment  is  found,  as  a  matter 
oi  fact,  allowing  for  unavoidable  errors,  to  be  equal  to  H+  h. 

Here  the  assumption  is  made  that  the  difference  in  the  mechanical 
conditions  during  the  relaxation  (the  muscle  in  the  first  experiment 
relaxing  without  load  but  being  stretched  by  the  weight  as  it  relaxes 
in  the  second)  docs  not  affect  the  heat-production.  This  assumption 
has  been  shown  to  be  correct,  although  it.  was  at  one  time  supposed 
that  changes  in  the  tension  of  the  muscle  produced  during  the 
relaxation  did  cause  changes  in  the  amount  of  heat  produced.  On 
the  other  hand,  it  has  been  clearly  proved  that  the  total  energy 
transformed  during  the  period  of  contraction,  and  the  fraction  of 
it  which  appears  as  external  muscular  work,  are  greatly  influenced 
by  the  mechanical  conditions  under  which  the  contraction  takes 
place.  A  stretched  muscle,  when  caused  to  contract,  produces 
more  heat  than  if  it  had  started  without  tension,  and  still  more 
heat  when  it  is  fixed  so  that  it  cannot  shorten  during  stimulation. 
A  muscle,  starting  without  tension,  produces  more  neat  when  it 
contracts  isometrically  than  when  it  contracts  isotonically.  This 
fact  does  not,  however,  prove  that  the  heat-production  is  greater 
when  no  work  is  clone,  because  the  tension  increases  during  excita- 
tion when  contraction  is  prevented,  and,  as  has  been  said,  increase 
of  tension  alone  causes  more  heat  to  be  given  out  by  an  active  muscle. 

When  a  muscle,  excited  by  maximal  stimuli,  is  made  to  lift 
continuously  increasing  weights,  both  the  work  done  and  the  heat 
given  out  increase  up  to  a  certain  limit.  The  muscle,  as  it  were, 
burns  the  candle  at  both  ends.  This  would  be  of  itself  enough  to 
show  that  there  is  no  fixed  relation  between  the  work  and  the  heat- 
production  ;  although  the  latter  reaches  its  maximum  somewhat 
sooner  than  the  former. 

Although  a  loaded  muscle  kept  in  steady  tetanic  contraction  is  doing 
no  work,  it  produces  heat,  but  far  less  than  would  be  produced  if  the 
muscle  could  fully  contract  and  relax  at  each  excitation.  The  amount 
of  energy  liberated  by  an  excitation  of  given  strength  depends,  there- 
fore, on  the  mechanical  condition  of  the  muscle  into  which  it  falls. 

The  fraction  of   the  total  energy  transformed  which  appears 

as  muscular  work  varies  with  the  conditions  of  the  contraction. 

The  greater  the  resistance,  so  long  as  the  muscle  can  overcome 

it  so  as  to  do  its  utmost  amount  of  external  work,*  the  larger 

*  This  statement,  based  on  experiments  with  excised  frog's  muscles,  is 
not,  of  course,  inconsistent  with  the  fact  mentioned  on  p.  583,  that  in  the 


A   M  \NV  //    OF  PHYSIOLOGY 

is  the  proportion  of  energy  which  appears  as  work,  the  smaller 
the  proportion  which  appears  as  heat.  For  every  muscle, 
under  given  conditions,  i  here  is  a  certain  load  which  can  he  raised 
more  advantageously  than  any  other  ;  but  even  in  the  most 
favourable  case,  an  excised  frog's  muscle  never  does  work  equal 
to  more  than  J  oi  the  heat  given  off.  Generally  the  rati 
much  less,  and  may  sink  as  low  as  ._,'..  In  the  Lnta<  I  mammalian 
body  the  muscles  work  somewhat  more  economically  than  the 
excised  frog's  muscles  at  their  best;  for  both  experiment  and 
calculation  show  (p.  583)  that  in  a  normal  man  under  the  most 
favourable  conditions  as  much  as  one  third  oi  the  energy  is 
converted  into  work.  According  to  Zuntz  and  Katzenstein, 
35  per  cent,  of  the  total  energy  appeared  as  muscular  work  in 
climbing  a  mountain,  and  in  bicycling  only  25  per  cent.  Move- 
ments which  have  been  much  practised  are  more  economically 
performed  than  unaccustomed  ones,  and  this  explains  the 
superior  efficiency  of  the  muscles  concerned  in  climbing,  for 
no  movements  can  possibly  be  more  familiar  than  those  concerned 
in  locomotion.  So  far  as  this  indication  goes,  it  would  seem  that 
in  the  treatment  of  obesity  unfamiliar,  and  therefore  physiologi- 
cally expensive,  forms  of  exercise  should  be  recommended,  in  so 
far,  of  course,  as  they  do  not  injuriously  react  upon  the  general 
condition,  especially  upon  the  circulation. 

As  a  muscle  becomes  fatigued  it  works  more  economically, 
the  heat-production  diminishing  more  rapidly  than  its  working 
power.  This  is  an  illustration  of  the  fact  that  the  heat-pro- 
ducing mechanism  and  the  work-producing  mechanism  of  muscle 
are  in  some  respects  distinct,  and  a  variation  in  the  activity  of 
the  one  is  not  necessarily  associated  with  a  corresponding 
variation  in  the  activity  of  the  other. 

(4)   Chemical  Phenomena  of  the  Muscular  Contraction.     We  know- 
but  little  regarding  the  chemical  composition  of  living  muscle,  since 
most  chemical  operations  cause  the  immediate  death  of  the  tissue. 
The  composition  of  dead  mammalian  musclt    oi   the  striped  variety 
may  be  stated,  in  round  [lumbers,  as  follows,  but  tin-re  arc  consider- 
able variations,  even  within  the  same  species  : 

Water     -----  -  75  per  cent. 

Proteins-         -         -         -         -         -         -         -20 

I  ats,  lecithin,  and  cholesterin  - 
Nitrogenous  f Kreatin  (02 to 04)        - 

metabolites       1  ganthm       -         -       Pur.n 
^Hypoxanthin,  etc.  1     bodies 
Carbo-hydrates  (glycogen,  dextrose,  and malt< 
Lactic  acid        -  . 

Inosit        -------- 

Salts,  chiefly  carbonate  and  phosphate  of  potassium,  less  than 
1  per  cent.    Potassium  is  absent  from  the  nuclei  (Frontispiece). 


intact  body  the  fraction  of  the  energy  transformed  into  heat  is  greater  in 
hard  than  in  moderate  work. 


MUSCLE 

There  is  more  water  in  the  muscles  oi  young  than  oi  old  animals 
Bibra),  and  more  in  tetanized  than  in  rested  muscle  (Ranki 
The  fats  belong  to  a  sm. ill  extent  to  the  ai  tual  mus<  le-fibres.     For 
even  when  the  visible  fat  is  separated  with  the  utmost  care,  nearly 
i  percent,  of  fat  still  remains  (Steil). 

The  glycogen  content  varies  extremely  in  different  muscles  and 
in  the  same  muscle  under  differenl  nutritive  and  functional  con- 
ditions. Thus,  in  one  and  the  same  dog  the  biceps  brachii  contained 
C17  and  the  quadriceps  femoris  053  per  cent.  In  dogs  on  a  diet 
rich  in  carbo-hydrate  and  protein  the  percentage  in  the  whole 
skeletal  musculature  ranged  from  o'j  to  37,  and  in  the  heart  from 
01  to  1  j.  The  average  for  human  muscles  has  been  given  as 
04  per  cent.  In  lean  horse-flesh  Pfliiger  found  o  35  per  cent,  of 
glycogen,  but  no  sugar.  The  total  nitrogen  was  321  per  cent,  of 
the  moist  tissue.  The  lactic  acid  of  muscle  and  other  tissues  is 
the  ^/-lactic  acid,  which  rotates  the  plane  of  polarization  to  the 
right.  By  the  action  of  certain  bacteria  on  cane-sugar  /-lactic 
acid  is  obtained,  which  is  left  rotatory.  The  optically  inactive 
fermentation  lactic  acid  is  obtained  by  the  fermentation  of  lactose. 

Smooth  muscle  is  somewhat  richer  in  water  than  the  striated 
variety  from  the  same  species,  because  skeletal  muscle  is  richer  in 
fat.  Glycogen  is  either  absent  or  present  only  in  traces  in  the 
smooth  muscle  (of  the  stomach  and  bladder).  Lactic  acid,  kreatin, 
and  kreatinin  are  also  found  in  much  smaller  amount  than  in  striped 
muscle  (Mendel  and  Saiki).  As  in  striated  muscle,  hypoxanthin  is 
the  conspicuous  purin  base  occurring  in  the  free  form — i.e.,  obtain- 
able in  muscle  extracts.  The  most  remarkable  difference  in  the 
quantitative  relations  of  the  inorganic  constituents  is  that  in 
striated  muscle  potassium  preponderates  over  sodium  and  mag- 
nesium over  calcium,  whereas  in  the  smooth  variety  this  relation 
is  reversed. 

It  would  be  natural  to  expect  that  the  proteins,  which  bulk 
so  largely  among  the  solids  of  the  dead  muscle,  and  which  are 
so  obviously  important  in  the  living  muscle,  should  be  affected 
by  contraction.  But  up  to  the  present  time  no  quantitative 
difference  in  the  proteins  of  resting  and  exhausted  muscle  has 
ever  been  made  out.  The  quantity  of  kreatin  (and  kreatinin)  is 
said  by  some  authorities  to  be  increased.  The  following  chemical 
changes  have  been  definitely  established.     In  an  active  muscle — 

(a)  More  carbon  dioxide  is  produced. 

(b)  More  oxygen  is  consumed. 

(c)  Lactic  acid  is  formed. 

(d)  Glycogen  is  used  up. 

(e)  The  substances  soluble  in  water  diminish  in  amount  ;  those 

soluble  in  alcohol  increase. 

That  the  carbon  dioxide  is  not  formed  by  direct  oxidation, 
but  by  the  splitting  up  of  a  substance  or  substances  with  which 
the  oxygen  has  previously  combined,  is,  as  has  already  been 
shown  (pp.  261,  263),  highly  probable. 

Formation  of  Lactic  Acid — Reaction  of  Muscle. — To  litmus- 
paper  fresh  muscle  is  amphicroic — that  is,  it  turns  red  litmus  blue 
and  blue  litmus  red.  This  is  due,  partly  at  least,  to  the  phosphates. 
Monophosphate    (tribasic   phosphoric   acid,    H3PQ4,    in    which   one 


A   MA  vr  1/    <>/    PHYSIOLOGY 

hydrogen  atom  is  replaced,  say,  by  sodium  or  potassium  reddens  blue 
litmus,  while  diphosphate  (where  two  hydrogen  atoms  are  replaced) 
turns  nd  litmus  blue.  Litmoid  (lacmoid)  differs  from  litmus  in  not 
being  affected  by  monophosphates.  Diphosphates  turn  red  litmoid 
blue,  and  so  docs  fresh  muscle,  which  has  no  effect  on  blue  litmoid. 
A  cross-section  of  fresh  muscle  is  about  neutral  (sometimes  faintly 
acid)  to  turmeric  paper,  which  is  turned  yellow  by  monophosph 
A  muscle  which  has  entered  into  rigor  or  has  been  fatigued  by  pro- 
longed stimulation  is  distinctly  acid  to  blue  litmus  and  to  brown 
turmeric,  reddening  the  former  and  turning  the  latter  yellow,  but 
does  not  affect  blue  litmoid. 

Perfectly  fresh  resting  muscle  excised  with  avoidance  of  all 
unnecessary  manipulation  contains  very  little  lactic  acid  (as 
little  as  o*02  per  cent,  expressed  as  zinc  lactate).  Mechanical 
injury,  heating,  and  chemical  irritation  cause  a  marked  increase 
in  the  amount.  Under  anaerobic  conditions— in  an  atmosphere 
of  hydrogen,  for  instance — lactic  acid  is  spontaneously  developed 
in  the  resting  muscle  so  long  as  irritability  persists,  but  not 
longer.  In  air,  which  for  even  small  excised  musi  Les  corresponds 
to  a  partial  asphyxia,  there  is  a  small  increase  in  the  lactic  acid, 
but  its  production  is  very  slow  in  comparison  with  that  in  the 
hydrogen  atmosphere.  In  pure  oxygen  not  only  is  there  no 
accumulation  of  lactic  acid  for  a  long  time  after  excision,  bul  a 
portion  of  the  amount  originally  present  in  the  resting  >  \<  ised 
muscle  disappears.  The  same  is  true  of  the  lactic  acid  formed 
in  a  muscle  fatigued  by  stimulation  when  it  is  afterwards  placed 
in  an  atmosphere  of  pure  oxygen.  There  is  no  doubt  that  the 
production  of  lactic  acid  in  functional  activity  and  its  trans- 
formation into  other  substances  are  processes  that  go  on  also 
in  the  muscles  of  the  intact  body.  The  formation  of  the  acid  in 
the  excised  muscle,  far  from  being  a  sign  of  death,  is  an  index  ol 
the  '  survival  '  of  a  process  by  whicli  it  is  normally  formed,  as 
the  accumulation  of  it  is  an  index  ol  the  crippling,  in  the  absence 
of  oxygen,  of  a  mechanism  by  which  it  is  normally  trans- 
formed. 

The  lactic  acid  which  accumulates  in  the  excised  muscle  in 
rigor  and  activity  does  not  remain  free,  since  blue  litmoid  paper 
is  not  reddened  as  it  would  be  by  free  La<  tic  acid.  It  causes  a 
repartition  of  the  bases  at  the  expense  ol  the  sodium  carbonate 
and  disodium  phosphate,  the  latter  being  changed  into  mono- 
phosphate, which,  in  part  at  least,  accounts  for  the  acid  reaction 
to  turmeric  (Rohmann).  It  is  of  great  interest  that  this  oxidative 
transformation  of  lactic  acid  only  occurs  in  muscle  whose  struc- 
ture is  so  far  preserved  that  its  irritability  is  not  lost.  In  mini  ed 
or  triturated  muscle  it  does  not  take  plai  e 

Glycogen  is  the  one  solid  constituent  of  muscle  which  has 
been  definitely  proved  to  diminish  during  activity.  It  accumu- 
lates in  a  resting  muscle,  especially  in  a   muscle   whose  motor 


MUSC1  ' 

nerve  has  been  cul  ;  bul  rapidly  disappears  fi the  mus<  les  ol 

an  animal  made  to  '1"  work  while  food  is  withheld  ;  or  from  the 
muscles  oi  an  animal  poisoned  by  strychnine,  which  causes 
violent  mus<  ular  contractions. 

Wli.it  materia]  is  the  lactic  acid  formed  from?  There 
reasons  for  thinking  that  it  is  an  intermediate  substance  which 
in  metabolism  may  serve  .1-  .1  link  between  the  products  of 
protein  decomposition  and  carbo-hydrates,  and  between  carbo- 
hydrates  and  fat.  From  what  we  know  <>t  the  production  of 
lactic  acid  both  outside  the  body  and  in  the  intestine  from  carbo- 
hydrates,  it  might  seem  a  most  plausible  suggestion  that  in  the 
active  muscle  it  comes  from  glycogen.  But  the  best  evidence 
points  the  other  way— e.g.,  in  rigor  mortis  lactic  acid  is  produced 
just  as  in  muscular  contraction.  Nay,  more,  the  amount  of 
lactic  acid  (as  much  as  05  per  cent,  expressed  as  zinc  lactate) 
produced  in  full  heat  rigor  (at  40°  to  450  C.)  is  constant  for 
similar  excised  muscles.  This  '  acid-maximum  '  is  the  same 
when  fresh  muscle  is  at  once  put  into  rigor  ;  or  when  fatigue  is 
first  induced,  with  formation  of  lactic  acid,  before  rigor;  or, 
finally,  when  the  lactic  acid  of  the  fatigued  muscle  is  caused  to 
disappear  under  the  influence  of  oxygen,  and  heat  rigor  is  then 
brought  about  in  the  muscle  (Fletcher  and  Hopkins).  Yet  in 
rigor  mortis  the  quantity  of  glycogen  is  unaltered  (Boehm). 
Further,  under  certain  conditions  an  excised  muscle  is  capable 
of  producing  a  quantity  of  lactic  acid  much  greater  than  could 
be  derived  from  the  glycogen  contained  in  it.  It  is  very  possible 
that  the  lactic  acid  arises  from  protein  in  the  transformation 
of  the  store  of  material  whose  decomposition  is  associated 
with  the  act  of  contraction.  The  facts  just  mentioned  suggest 
that  it  is  the  same  store  which  yields  the  lactic  acid  developed 
with  the  onset  of  rigor.  But  if  this  be  so  the  transformation 
must  be  more  complete  in  rigor  than  in  the  fatigue  of  excised 
muscles,  since  the  amount  of  acid  produced  by  severe  direct 
stimulation  of  a  muscle  is  not  more  than  about  one-half  of  that 
reached  in  full  heat  rigor. 

Source  of  the  Energy  of  Muscular  Contraction. — The  facts 
just  mentioned  show  that  glycogen  may  be  one  of  the  sources 
of  muscular  energy,  but  it  cannot  be  the  only  source,  for  its 
amount  is  too  small. 

For  example,  the  heart  of  an  average  man,  which  weighs  280 
grammes,  contains  about  60  grammes  of  solids,  and  among  these 
certainly  not  more  than  1  gramme  of  glycogen.  In  twentv-four 
hours  it  produces  1^0  calories  of  heat  (pp.  127,  584),  equivalent  to 
the  complete  combustion,  of  a  little  less  than  30  grammes  of  glycogen 
To  supply  this  amount,  the  whole  store  of  glycogen  in  the  heart 
would  have  to  be  used  and  replaced  every  fifty  minutes.  But  the 
accumulation  of  glycogen  is  immensely  slower  in  the  muscles  of  a 


6;o  A   M  \NUAL  <>/    PHI  SIOLOGY 

rabbit  in. nli  glycogen  free  by  strychnine,  and  therefon  w<  uav<  to 
look  around  for  some  other  source  <>i  energy  to  supplemenl  the 
glycogen,  We  have  already  brought  forward  evidence  (p.  537) 
that,  under  ordinary  circumstances,  not  a  great  deal,  a1  any  rate, 
ni  the  energy  oi  muscular  contraction  comes  from  the  proteins.  01 
carbo-hydrates,  the  only  one  except  glycogen  which  is  at  .ill  adequate 
to  the  task  of  supplying  so  much  energy  is  the  dextrose  oi  the  blood. 
The  quantity  oi  blood  passing  through  the  coronary  circulation  has 
been  estimated  a1  30  c.c.  per  too  grammes  oi  cardial  muscle  per 
minute  (Bohr  and  Henriques),  which  would  be  equivalent  ton  an 
average  man  to  aboul  t20  litres  in  twenty-lour  hours.  This  quan- 
tity  of  blood  will  contain  at  least  i  jo  grammes  oi  dextrose,  and 
about  $2  grammes  will  suffice  to  supply  all  the  heat  produced  by  the 
heart.  Of  proteins  a  little  less  than  30  grammes  would  be  needed, 
of  fat  a  little  more  than  12  grammes.  W<  >ee,  therefore,  how  in- 
tense must  be  the  metabolism  that  goes  on  in  an  actively  con- 
tracting muscle.  On  any  probable  assumption  as  to  the  source  oi 
muscular  energy  a  quantity  of  material  equal  to  half  of  its  solids 
must  be  used  up  by  the  heart  in  twenty-four  hours  <  >r.  to  put  it 
in  another  way.  the  heart  requires  not  less  than  two-fifths  of  its  weight 
of  ordinary  solid  food  in  a  day.  The  body  as  a  whole  requires 
-,'<>  *"  r'o  of  its  weight. 

To  sum  up:  It  is  universally  admitted  thai  carbo-hydrates 
can  yield  energy  for  muscular  work.  It  lias  been  demonstrated 
by  Zuntz  and  his  pupils  and  by  others  that  fat  can  do  so.  The 
experiments  of  Pfliiger,  to  which  we  have  already  alluded  (p.  538), 
have  shown  that  when  an  animal  is  fed  on  lean  meat,  the  mus- 
cular work  done  is  far  too  great  to  have  come  from  non-protein 
substances.  We  must  conclude,  therefore,  that  when  carbo- 
hydrates and  fats  are  plentiful  in  the  food,  the  greater  part  of 
the  energy  of  muscular  contraction  comes  from  them.  It  conn-- 
on  the  other  hand  from  proteins,  when  the.  carbo-hydrates  and 
the  fats  are  restricted,  and  the  proteins  plentifully  supplied. 
Not  only  so,  but  these  three  groups  of  food  substances  yield 
muscular  energy  in  isodynamic  relation.  In  other  words,  a 
given  amount  of  muscular  work  requires  the  expenditure  <>f 
approximately  the  same  quantity  of  chemical  energy,  whether 
it  comes  almost  entirely  from  protein,  or  chiefly  from  carbo- 
hydrates, or  chiefly  from  fat.  Some  observers  have  staled  that 
the  taking  of  even  a  comparatively  small  quantity  oi  sugar 
vastly  increases  the  capacity  for  muscular  work  as  measured 
by  the  ergograph  (p.  649).  The  glycogen  of  the  muscle  is  believed 
to  be  converted  into  dextrose  during  muscular  activity.  D  \- 
trins  and  maltose,  the  intermediate  products  of  this  decom- 
position, have  been  detected  in  muscle,  more  maltose,  indeed, 
than  dextrose  being  present  (Osborne),  since  the  dextrose  is 
rapidly  oxidized.  But  although  it  is  not  to  be  doubted  that 
sugar  is  under  normal  circumstances  one  of  the  most  important 
substances   used   up   in   muscular   contraction,    the   claim    that 


vrsr  /./  671 

sugar  is,  pa?  excellence,  the  food  for  muscular  exertion  has  nol 
\  el  been  made  ou1 . 

Physico-chemical  Conditions  of  Muscular  Contraction.  Foj  ex<  i  i  d 
fresh  muscle  a  (p.  399)  has  been  estimated  at  o'68c  C.  Bu1  this 
is  probably  higher  than  in  the  living  body,  for  after  excision  v. 
products,  with  their  relatively  smaD  and  numerous  molecules,  arc 
still  for  a  time  produced,  and  are  no  lunger  removed  by  the  blood. 
In  salt  solutions  isotonic  with  the  muscle  substance  e.g.,  for  the 
frog's  gastrocnemius  at  room-tcmpei 'ature  a  075  per  cent,  solution 
of  sodium  chloride — the  resting  muscle  neither  gains  nor  loses  v 
for  some  hours.  The  active  muscle  behaves  quite  differently. 
When  a  muscle  immersed  in  isotonic  salt  solution  is  tetanized, 
water  enters  it,  leading  to  an  increase  in  weight  and  a  diminution 
in  specific  gravity  (Ranke,  Loeb,  Barlow).  The  same  occurs  even 
when  blood  is  circulated  through  active  muscles,  the  blood  becoming 
poorer  in  water  (Ranke).  This  may  be  explained  by  the  increase 
of  osmotic  pressure  in  the  muscle  substance  which  must  accompany 
the  decomposition  of  large  molecules  into  small.  As  fatigue  pro- 
ses, a  movement  of  water  in  the  reverse  direction  occurs,  and 
the  muscle  rapidly  loses  water.  Exposure  of  the  fatigued  muscle 
for  a  sufficient  time  to  an  atmosphere  of  oxygen  restores  the  osmotic 
properties  of  the  resting  muscle.  Striking  differences  have  also 
been  demonstrated  in  the  behaviour  of  resting  and  fatigued  muscle 
to  hypotonic  solutions  or  water.  Hales  observed  long  ago  that, 
on  injecting  large  quantities  of  water  into  the  bloodvessels  of  a  dog, 
so  as  to  replace  the  blood,  marked  swelling  of  the  muscles  occurred. 
This  physiological  fact  is  well  known  to  the  pork-butchers  in  China, 
who  have  given  it  a  practical,  if  not  a  very  praiseworthy,  application 
in  sophisticating  their  product  by  increasing  its  weight  (MacGowan). 

So  long  as  the  muscular  fibres  are  uninjured  they  are  permeable 
or  impermeable  for  exactly  the  same  compounds  as  other  animal 
and  vegetable  cells.  All  substances  easily  soluble  in  media  like 
ether  or  olive  oil  readily  penetrate  them  (Overton).  To  most  salts 
they  arc  relatively  impermeable,  as  is  shown  by  the  fibres  retaining 
their  original  volume  in  isotonic  solutions  of  them.  In  particular, 
they  cannot  easily  take  up  or  retain  the  salts  of  the  blood-plasma, 
otherwise  the  observed  qualitative  differences — e.g.,  the  preponder- 
ance of  potassium  in  the  muscle  and  sodium  in  the  plasma — could 
not  be  maintained.  There  are  facts  which  indicate  that  temporary 
changes  in  the  permeability  to  ions,  not  only  of  muscular  fibres,  but 
also  of  nerve  fibres  and  other  excitable  structures,  are  concerned  in 
their  stimulation.  Potassium  salts  after  a  time  seem  to  produce 
an  effect  upon  frog's  muscle,  which  alters  its  permeability  so  that 
it  takes  up  water  from  hypertonic  solutions.  Calcium  salts  have 
the  opposite  effect  (Loeb).  Sodium  (and  in  a  minor  degree  lithium) 
salts  have  a  peculiar  relation  to  the  contraction  of  skeletal  muscle,  for 
which  they  appear  to  be  indispensable.  Yet  sodium  chloride  produces 
a  paralyzing  action  on  the  frog's  motor  nerve-endings,  so  that  after 
perfusion  with  a  solution  of  that  salt  stimulation  of  the  motor  nerve 
causes  no  contraction,  or  with  a  slighter  degree  of  paralysis  con- 
traction only  after  a  long  interval.  The  effect  can  be  counteracted 
by  solutions  containing  calcium  salts  (Locke,  Cushing). 

Rigor  Mortis. — When  a  muscle  is  dying,  its  excitability, 
after  perhaps  a  temporary  rise  at   the  beginning,   diminishes 


67-  I    \r  I  \i    1/    <>/■    /■/! )  SIOLOGY 

more  and  more  until  ii  ultimately  responds  to  no  stimulus 
however  strong.  The  loss  ol  excitability  is  nol  in  itselt  a  sure 
mark  ol  death,  for,  as  we  have  seen,  an  inexcitable  muscle  may 
be  partially  or  completely  restored  :  bul  it  is  followed, 
where  the  death  ot  the  muscle  takes  place  very  rapidly,  perhaps 
accompanied,  by  .1  more  decisive  event,  the  appearance  <>! 
rigor.  The  muscle,  which  was  before  suit  and  at  the  same  time 
elastic  to  the  touch,  becomes  firm;  bul  its  elasticit)  is  gone. 
The  iilnes  .tie  no  longer  translucent,  bul  opaque  and  turbid. 
It  shortening  of  the  muscle  has  nol  been  opposed,  it  may  be 
somewhat  contracted,  although  the  absolute  force  ol  this  con- 
traction is  small  compared  with  that  of  a  living  muscle,  and  a 
slight  resistance  is  enough  to  prevent  it.  The  reaction  is  now 
distinctly  acid  to  litmus.  This  is  rigor  mortis,  the  death- 
stiffening  <it  muscle. 

An  insight  into  the  real  meaning  of  this  singular  and  some- 
times sudden  change  was  first  given  by  the  experiments  oi 
Kiilme.  He  took  living  frog's  muscle,  freed  from  blood,  froze 
it,  and  minced  it  in  the  frozen  state.  The  pieces  were  then 
rubbed  up  in  a  mortar  with  snow  containing  1  pei  cent,  of  common 
salt,  and  a  thick  neutral  or  alkaline  liquid,  the  muscL  plasma 
was  obtained  by  filtration.  This  clotted  into  .1  jelly  when  the 
temperature  was  allowed  to  rise,  bul  at  0  C.  remained  fluid. 
The  clotting  was  accompanied  by  a  change  ot  reaction,  the 
liquid  becoming  acid.  An  equally  good,  or  better,  method  is 
to  use  pressure  to;  the  extraction  of  the  plasma  from  the  frozen 
fragments  of  muscle.  A  low  temperature  is  essential,  otherwise  the 
plasma  will  coagulate  rapidly  within  the  injured  muscle.  Asimilai 
plasma  can  be  expressed  from  the  skeletal  muscles  of  warm- 
blooded animals  (Halliburton),  and  with  greater  difficulty  from 
the  heart. 

When  the  muscle,  alter  exhaustion  with  water,  is  covered  with  a 
solution  of  a  neutral  salt,  a 5  percent,  solution  of  magnesium  sulphate 
or  10  per  cent,  solution  oi  amnion  aim  chloride  being  the  best .  certain 
proteins  are  extracted  which  clot  or  are  precipitated  much  in  the 
same  way  as  the  muscle-plasma  obtained  by  cold  and  pressure  .  and 
the  process  is  hastened  by  keeping  them  at  a  temperature  ot  10    < 

In  the  extracts  oi  mammalian  muscle  three  chiel  proteins  are 
present:  paramyosinogen  (v.  Furth's  myosin),  coagulating  by  heat  at 
470  to  500  C.  ;  myosinogen  (v.  Furth's  myogen),  coagulating  at  55 
to  6o°  C.  (usually  about  56°);  and  serum-albumin,  coagulating 
about  730.  There  is  reason  to  believe  that  the  serum-albumin 
belongs  to  the  blood  and  lymph,  and  is  not  a  constituent  of  the 
muscli   ill"'       In  -I    frog's   muscle   there  1-  in  addition  a 

substance  which  coagulati  >  at  about  \o°.  Both  thi  paramyosinogen 
and  the  myosinogen.  but  particularly  thi  former,  3hov  a  tendency, 
even  at  ordinary  temperatures,  to  pass  into  an  insoluble  form — 
myosin  (v.  Furth's  muscle  fibrin).  But  whereas  paramyosinogen 
passes  directly  into   myosin,   myosinogen    is    first    changed    into   a 


MUSi  l.i 

soluble  modification  (soluble  myosin),  which  coagulates  aA  [O0  C, 
and  seems  to  be  identical  with  the  protein  coagulating  at  that 
temperature  which  can  1)'-  extracted  from  frog's  muscles.  At  body- 
temperature  the  transformation  occurs  more  quickly.  The  myosin 
precipitate,  which  rapidly  tonus  in  muscle-plasma,  is  sometimes 
called  the  muscle-clot,  and  the  Liquid  which  is  left  the  muscle-serum. 
A  similar  myosin  precipitate  or  clol  seems  to  be  formed  in  the 
interim-  of  the  muscular  fibres  in  natural  rigor  and  in  the  rapid 
rigor  produced  by  heating  a  muscle  to  a  little  above  the  body- 
temperature.  But  in  nat  ural  rigor  the  whole  of  the  paramyosin 
and  myosinogen  do  nol  undergo  the  change,  since  a  certain  amount 
of  these  substances  can  as  a  rule  be  extracted  from  dead  muscle  by 
saline  solutions.  Thus,  in  rabbit's  muscles,  before  the  onset  of  rigor 
mortis,  87*3  per  cent,  of  the  total  protein  was  found  to  be  soluble 
in  10  per  cent,  ammonium  chloride  solution,  and  only  127  percent, 
coagulated  ;  while  after  rigor  had  occurred,  715  per  cent,  was 
coagulated,  and  only  28*5  per  cent,  remained  soluble  (Saxl).  It  is  not 
known  whether  in  the  living  muscle  paramyosinogen  and  myosinogen 
exist  as  such.  Certain  facts  suggest  that  muscle  contains  only  one 
protein  (Mellanby).  It  has,  indeed,  been  stated  that  if  a  tracing  is 
taken  from  a  muscle  which  is  gradually  heated,  it  first  shortens  at 
the  temperature  of  coagulation  of  paramyosinogen,  and  then  again 
at  that  of  myosinogen,  and  that  in  frog's  muscle  there  is  an  addi- 
tional shortening  at  40°.  the  temperature  of  coagulation  of  the 
soluble  myosin.  The  conclusion  has  been  drawn  that  these  sub- 
stances must  be  present  as  such  in  the  living  fibres,  and  that  the 
successive  shortenings  are  mechanical  phenomena  due  to  their  heat 
coagulation.  Similar  shortenings  have  been  described  in  nerve 
and  liver  tissue  at  about  the  temperatures  at  which  the  proteins 
in  extracts  of  these  tissues  are  coagulated  by  heat.  But  Meigs  has 
shown  that  the  supposed  correspondence  is  far  from  being  exact, 
and^that  muscles  whose  proteins  have  been  already  coagulated  in 
a  mixture  of  alcohol  and  salt  solution  still  show  the  typical  shortening 
on  being  heated.  The  heat  shortening  is,  therefore,  dependent  on  some 
other  process  than  aggregation  of  the  particles  of  coagulable  protein. 

It  has  been  suggested  that  myosin  (or  its  precursors),  lactic 
acid,  and  carbon  dioxide  are  all  products  of  some  complex  body 
which  breaks  up  both  during  contraction  and  at  or  before  the 
death  of  the  muscle,  and  that,  indeed,  contraction  is  only  a 
transient  and  removable  rigor  (Hermann).  But  it  cannot  be 
admitted  that  there  is  any  fundamental  connection  between 
rigor  and  contraction,  although  there  are  some  superficial  resem- 
blances. In  both  there  is  (1)  shortening  ;  (2)  heat-production  ; 
(3)  formation  of  lactic  acid  and  carbon  dioxide  ;  (4)  electrical 
changes.  Another  analogy  might  be  forced  into  the  list  by  any- 
one who  was  determined  to  see  only  rigor  in  contraction  :  the 
rigor  passes  off  as  the  contraction  passes  off,  although  the  '  reso- 
lution '  of  a  rigid  muscle  takes  days,  the  relaxation  of  an  active 
muscle  a  fraction  of  a  second.  The  disappearance  ofjrigor  is  not 
dependent  on  putrefaction  ;  it  takes  place  when  growth  of  bacteria 
is  prevented'(Hermann).  Possibly  it  is  connected  with  autolytic 
processes 'due  to  intracellular  ferments  (p.  509). 

43 


A    MIMA/.  OF    1'IIYSIOLOGY 

Why  does  coagulation  o\  myosin  occur  al  the  death  of  the 
muscle?  To  this  question  no  cleai  answer  can  be  given.  Some 
have  Looked  on  the  process  as  analogous  to  the  clotting  "l  blood 
when  it  is  shed,  and  it  has  even  been  suggested  thai  jusl  as  a 
fibrin  fermenl  is  developed  when  the  leucocytes  and  blood- 
plates  begin  t<>  die,  a  myosin  ferment,  which  aids  coagulation,  is 
developed  in  dead  or  dying  muscle.  But  no  clear  prooi  has  been 
given  of  the  existence  of  such  a  ferment.  And  it  is  easy  to  make 
too  much  of  the  apparent  analogy  between  the  clotting  of  muscle 
and  the  clotting  of  blood,  for  there  are  differences  as  well  as 
resemblances.  For  instance,  the  addition  of  potassium  oxalate 
does  not  prevent  coagulation  of  muscle  extracts,  as  it  does  of 
blood  and  blood-plasma.  The  development  of  lactic  acid  in  the 
muscle  is  not  the  primary  cause  of  the  coagulation  which  con- 
stitutes the  essential  feature  of  rigor  mortis,  although  after  rigor 
has  occurred  direct  precipitation  of  hitherto  unclotted  muscle 
proteins  may  be  induced  by  the  acid,  or  the  acid  salts  produced 
in  its  presence.  Deficiency  of  oxygen  is  associated  with  the 
occurrence  of  rigor  mortis,  as  it  is  with  the  accumulation  of  La 
acid,  and  a  developing  rigor  can  be  abolished  by  oxygen,  and 
its  onset  long  or  indefinitely  delayed.  Winn  strict  asceptic 
technique  is  observed  an  excised  sartorius  muscle  of  the  I 
may  remain  irritable  in  sterile  Ringer's  solution,  even  without 
oxygenation,  for  as  long  as  three  weeks  (Mines). 

Various  influences  affect  the  onset  of  rigor.  Fatigue  hastens 
it  ;  heat  has  a  similar  effect  ;  the  contact  of  caffeine,  chloroform, 
and  other  drugs  causes  most  pronounced  and  immediate  rigor. 
Blood  applied  to  the  cross-section  of  a  muscle  first  stimulates  the 
fibres  with  which  it  is  in  contact,  and  then  renders  them  rigid. 
But  it  is  to  be  remembered  that  normally  the  blood  does  not 
come  into  direct  contact  even  with  the  sarcolemma,  much  Less 
with  its  contents. 

The  effect  of  heat  is  of  special  interest.  A  skeletal  muscle  of 
a  frog,  like  the  gastrocnemius,  if  dipped  into  physiological  saline 
solution  at  400  or  410  C.  goes  into  rigor  at  once  ;  the  frog's  heart 
requires  a  temperature  30  or  40  higher  ;  the  distended  bulbus 
aorta?  can  withstand  even  a  temperature  of  480  for  a  short  time. 
An  excised  mammalian  muscle  passes  into  immediate  rigor  at 
450  to  500.  In  heat  rigor  the  reaction  of  the  muscle  becomes 
strongly  acid  owing  to  the  format  ion  of  lactic  acid,  and  the 
production  of  carbon  dioxide  is  also  increased.  Heat  rigor 
resembles  in  these  respects  a  greatly  accelerated  rigor  mortis. 
A  small  quantity  of  heat  is  produced,  and  the  temperature  of 
the  muscle  may  be  raised  as  much  as  2V  C.  This  is  probably 
due  chiefly  to  the  increased  chemical  change,  and  only  to  a  slight 
extent  to  the  physical  alteration  in  the  myosin. 


MUSCLE  675 

When  muscle  is  at  once  raised  toa  temperature  0(75°  to  ioo°  C, 
and  all  the  proteins  thus  coagulated  by  heat,  there  is  also  an 
increase  in  the  discharge  of  carbon  dioxide  (Fletcher),  and  the 
reaction  becomes  distinctly  acid  to  blue  litmus,  although  still 

alkaline  to  red.  This  is  the  easiest  way  of  obtaining  a  maximum 
evolution  of  carbon  dioxide  from  an  excised  muscle.  It  is 
highly  improbable  that  a  marked  production  of  carbon  dioxide 

should  take  place  in  heat-coagulated  proteins.  We  must  there- 
fore suppose  that  the  characteristic  decomposition  associated 
with  rigor  mortis  can  complete  itself  in  the  brief  space  that 
elapses  between  the  application  of  the  heat  and  the  heat-coagula- 
tion of  the  proteins.  This  decomposition  is  wanting  in  the 
so-called  rigor  caused  by  water,  which  is  not  a  true  rigor,  and 
causes  no  increase  in  the  carbon  dioxide  given  off.  Chloroform, 
on  the  other  hand,  produces  a  marked  increase  in  the  carbon 
dioxide  production,  and  this  is  evidently  related  to  its  action 
in  hastening  the  onset  of  rigor.  The  process  is  to  some  extent 
influenced  by  the  nervous  system,  for  section  of  its  nerves 
retards  the  onset  of  rigor  in  the  muscles  of  a  limb.  This  and 
other  facts  have  given  rise  to  the  idea  that  the  rigor  is  initiated 
by  something  analogous  to  a  muscular  spasm.  Ante-mortem 
stimulation  of  the  peripheral  ends  of  the  vagi,  even  with  currents 
too  weak  to  cause  a  perceptible  effect  upon  the  heart-beats,  pro- 
longs the  period  of  spontaneous  contraction  and  the  irritability 
of  the  ventricles  after  death,  and  retards  the  onset  of  rigor  (Joseph 
and  Meltzer).  Cold  rigor  is  obtained  when  frog's  muscles  are 
cooled  to  —15°  C.  The  muscles  remain  perfectly  translucent. 
They  do  not  recover  their  irritability  on  thawing,  but  if  cooled 
only  to  —  70  C.  they  recover  (Folin). 

In  a  human  body  rigor  generally  appears  not  earlier  than  an 
hour,  and  not  later  than  four  or  five  hours,  after  death.  In 
exceptional  cases,  however,  it  may  come  on  at  once,  and  the 
annals  of  war  and  crime  contain  instances  where  a  man  has  been 
found  after  death  still  holding  with  a  firm  grip  the  weapon  with 
which  he  had  fought,  or  which  had  been  thrust  into  his  hand 
by  his  murderer.  It  is  related  that  after  one  of  the  battles  of 
the  American  Revolutionary  War  some  of  the  dead  were  found 
with  one  eye  open  and  the  other  closed  as  in  the  act  of  taking 
aim.  A  high  temperature  favours  a  rapid  onset  ;  a  body  wrapped 
up  in  bed  will,  other  things  being  equal,  become  rigid  sooner 
than  a  body  lying  stripped  in  a  field.  Muscular  exhaustion, 
as  we  have  said,  is  another  favouring  condition  :  hunted  animals 
and  the  victims  of  wasting  diseases  go  quickly  into  rigor.  It 
is  a  rule,  but  not  an  invariable  one,  that  rigor,  when  it  comes  on 
quickly,  is  short,  and  lasts  longer  when  it  comes  on  late.  All  the 
muscles  of  the  body  do  not  stiffen  at  the  same  time  ;  the  order 

43—2 


676  A   MANUAL  OF  PHYSIOLOGY 

is  usually  from  above  downwards,  beginning  at  the  jaws  and 
neck,  then  reaching  the  anus,  and  finally  the  legs.     After  two 

or  three  days  the  rigor  disappears  in  the  same  order.  The 
position  of  the  limbs  in  rigor  is  the  same  as  at  death  ;  the  muscles 
stiffen  without  any  marked  contraction.  This  can  be  strikingly 
shown  on  a  newly-killed  animal  by  cutting  the  tendons  of  the 
extensors  of  one  foot  and  the  flexors  of  the  other  ;  when  natural 
rigor  comes  on,  the  feet  remain  just  as  they  were.  If  heat 
rigor,  however,  is  caused,  the  one  foot  becomes  rigid  in  flexion 
and  the  other  in  extension  ;  and  the  contraction-force  is  con- 
siderable, although  not  so  great  as  that  of  an  elect  rind  tetanus 
in  a  living  mucsle. 

The  Removability  of  Rigor. — After  interrupting  the  circula- 
tion in  the  hind-legs  of  rabbits  by  compression  or  ligation  of 
the  abdominal  aorta  (Stenson's  experiment),  and  so  causing 
the  muscles  to  become  rigid,  Brown-Sequard  saw  them  recover 
their  irritability  when  the  blood  was  again  allowed  to  reach  them. 
He  performed  a  similar  experiment  with  artificial  circulation 
through  the  hand  of  an  executed  criminal,  with  a  like  result. 
But  most  writers  have  taken  the  view  that  rigor  is  the  irrevocable 
end  of  excitability,  and  that  the  apparent  recovery  which 
Brown-Sequard  saw  was  due  to  the  muscles  not  having  been 
completely  rigid.  Heubel  has,  however,  stated  that  rhythmical 
contractions  of  the  frog's  heart  can  be  restored  by  filling  its 
cavity  with  blood,  after  rigor  has  been  caused  by  heat  and  in 
other  ways,  and  we  have  already  seen  that  the  same  is  true  of 
the  mammalian  heart  after  the  onset  of  rigor.  Excised  frog's 
muscles  which  have  undergone  rigor  mortis  become  less  stiff 
when  exposed  to  an  atmosphere  of  oxygen.  Both  mammalian 
and  frog's  skeletal  muscles,  after  rigor  mortis  has  come  on,  are 
said  to  regain  their  excitability  in  physiological  salt  solution 
(Mangold). 


CHAPTER  X 

NERVE 

The  voluntary  movements  are  originated  by  efferent  or  outgoing 
impulses  from  the  brain,  which  reach  the  muscles  along  their 
motor  nerves.  The  involuntary  movements  and  the  secretions 
are  in  many  cases  able  to  go  on  in  the  absence  of  central  con- 
nections, but  are  normally  under  central  control.  Afferent 
impulses  are  continually  ascending  to  the  cord  and  brain  from 
the  skin,  joints,  bones,  muscles,  and  organs  of  special  sense  like 
the  eye  and  the  ear.  Everywhere  the  connection  between  the 
nervous  centres  and  the  peripheral  organs,  and  between  different 
parts  of  the  central  nervous  system,  is  made  by  nerve-fibres. 
Those  which  run  outside  the  brain  and  cord  are  called  peripheral 
nerve-fibres  to  distinguish  them  from  the  intracentral  fibres  of 
the  central  nervous  system  itself. 

In  this  chapter  we  propose  to  consider  certain  of  the  general 
properties  of  nerve-fibres.  Most  of  our  knowledge  of  these 
properties  has  been  derived  from  experiments  on  the  peripheral, 
and  particularly  the  peripheral  motor  nerves  ;  but  there  is  every 
reason  to  believe  that  the  main  results  are  true  of  all  nerve- 
fibres,  afferent  and  efferent,  peripheral  and  central. 

What  we  call  nerve-fibres  were  known  and  named,  and  many 
important  facts  in  their  physiology  discovered,  long  before  their 
true  morphological  significance  was  recognised.  The  researches  of 
recent  years  have  shown  that  every  nerve-fibre  is,  as  regards  its 
essential  constituent  the  axis-cylinder,  a  process  of  a  nerve-cell. 
The  nerve-cells,  each  of  which,  including  all  its  processes,  may  be 
conveniently  termed  a  neuron,  are  the  essential  elements  of  the 
nervous  system.  The  cell-bodies  of  most  of  the  neurons  are  situated 
in,  or  in  close  relation  to,  the  spinal  cord  and  the  brain,  and  therefore 
the  detailed  description  of  them  will  be  reserved  till  we  come  to 
treat  of  the  central  nervous  system  (see  p.  748  and  Figs.  3°°  to  311). 
It  is  enough  to  say  here  that  in  general  a  nerve-cell  gives  off  two 
kinds  of  processes  :  (1)  one  or  more  dendrites  or  protoplasmic 
processes,  which  repeatedly  bifurcate  like  the  branches  of  a  tree  into 
thinner  and  thinner  twigs,  and  extend  only  for  a  relatively  short 
distance  from  the  cell-body  ;  (2)  an  axis-cylinder  process  or  axon, 

S77 


A   M  iNr  //.  OF  PHYSIOLOGY 

which  as  .1  rule  runs  for  a  considerable  distance  without  altering 
its  calibre,  and  either  gives  ofl  no  branches  (.is  in  the  peripheral 
nerves)  or  only  a  comparatively  small  number  oi  Lateral  twigs 
(collaterals).  Ultimately  the  axis-cylinder  process  and  its  col- 
laterals, if  it  has  any,  end  by  breaking  up  into  a  brush,  a  plexus  or 
a  feltwork  or  baskctwork  of  fibrils.  The  axons  oi  different  nerve- 
cells  vary  greatly  in  length.  Some  termin  ite  within  the  grey  matter 
of  the  brain  or  spinal  cord  not  far  from  their  origin  ;  others  run  in  the 
white  I  r,u  is  of  the  central  nervous  system  or  in  the  peripher  il  n a 
for  half  the  height  of  a  man.  All  except  the  shortest  axis-cvlind  r 
processes  become  clothed  at  a  Little  distance  from  the  cell-b 
with  a  protective  covering,  which  continues  to  invest  them  (and 
their  collaterals)  throughout  the  rest  of  their  course,  disappearing 
only  when  they  begin  to  break  up  at  their  terminations.  An  axis- 
cylinder  process  (spoken  of  simply  as  the  axis-cylinder,  when  con- 
sidered apart  from  the  nerve-cell)  constitutes,  with  its  covering,  a 
nerve-fibre. 

An  ordinary  peripheral  nerve  like  the  sciatic  is  made  up  of  a 
number  of  bundles  of  nerve-fibres.  Connective  tissue  surround; 
and  separates  the  bundles,  and  also  penetrates  in  fine  septa  within 
them  and  between  the  individual  fibres,  forming  a  framework  for 
their  supp  >rt,  and  carrying  the  bloodvessels  and  Lymph  '.tics. 

The  great  majority  of  the  nerve-fibres  of  the  sciatic  consist  of 
cylinders  covered  by  two  sheaths.  The  axis-cylinders  are  pro  :e 
of  nerve-cells  in  the  anterior  horn  of  the  spinal  cord  in  the 
the  motor  fibres,  and  of  nerve-cells  in  the  spinal  g  inglia  in  the  c  ise 
of  the  sensory.  The  axis-cylinder  is  the  essential  conducting  part 
of  the  fibre,  for  it  is  present  in  every  nerve-fibre,  running  from  end 
to  end  of  it  without  break,  and  towards  the  periphery  it  is  alone 
present.  It  is  made  up  of  fine  longitudinal  fibrils  embedded  in 
interstitial  substance  (Fig.  301,  p.  748)  iuch  .1  fibrillar  structure 
is  best  shown  after  treatment  of  the  nerve-fibres  with  certain 
reagents,  although  it  is  certain  that  it  exists  preformed  in  the  living 
fibres.  The  innermost  (Fig.  236),  and  by  far  the  thickest,  of  the 
sheaths  is  the  medullary  sheath,  or  white  substance  of  Schwann, 
which  is  of  fatty  nature,  and  is  blackened  by  osmic  acid.  It  under- 
goes a  kind  of  coagulation  at  death,  loses  its  homogeneitv,  and  shows 
a  double  contour.  This  sheath  is  not  continuous,  but  is  broken  by 
constrictions  of  the  outer  sheath,  called  nodes  of  Ranvier,  into 
numerous  segments.  The  outer  sheath,  or  neurilemma,  is  a  thin, 
structureless  envelope  immcdiatelv  external  to  the  medulla.  It 
invests  the  nerve-fibre,  as  the  sarcolemm x  does  the  muscle-fibre. 
In  e  ich  intcrnodal  segment  immediatelv  under  the  neurilemma  lies 
a  nucleus  surrounded  by  a  little  protoplasm.  Fibres  with  a  medul- 
lary sheath  such  as  those  described  are  called  medullated  fibres. 
Thc-y  are  by  fir  the  most  numerous  in  the  cercbro-spinal  ner. 
but  thev  arc  mixed  with  a  few  fibres  which  contain  n  1  white  substance 
of  Schwann,  and  are,  therefore,  called  non-medullated.  In  these 
the  axis-cylinder  is  covered  only  by  the  neurilemma.  In  the 
sympathetic  system  the  non-medullated  variety  is  present  in 
greiter  abundance  than  the  medulUtcd.  In  the  central  nervous 
system  the  medullated  fibres  possess  no  neurilemma. 

So  far  as  we  know,  the  only  function  of  nerve-fibres  is  to 
conduct  impulses  from  nerve-centres  to  peripheral  organs,  or 
from   peripheral   organs   to  nerve-centres,   or   from   one   nerve- 


NERVE 

centre  to  another.  And  in  the  normal  body  these  impulses 
never,  or  only  very  rarely,  originate  in  the  course  of  the  nerve- 
fibres  :  they  are  set  up  either  at  their  peripheral  or  at  their  central 
endings.  By  artificial  stimulation,  however,  a  nerve-impulse 
may  be  started  at  any  part  of  a  fibre,  just  as  a  telegram  may 
be  despatched  by  tapping  any  part  of  a  telegraph  wire,  although 
it  is  usually  sent  from  one  fixed  station  to  another. 


The  Nerve-impulse  :  its  Initiation  and  Conduction. 

What  the  nerve-impulse  actually  consists  in  we  do  not  know. 
All  we  know  is  that  a  change  of  some  kind,  of  which  the  only 
external  token  is  an  electrical  change,  passes  over  the  nerve 
with  a  measurable  velocity,  and  gives  tidings  of  itself,  if  it  is 
travelling  along  efferent  fibres — that  is,  out  from  the  central 
nervous  system — by  the  contraction  or  inhibition  of  muscle  or 
by  secretion  ;  if  it  is  travelling  along  afferent  fibres — that  is,  up 
to  the  central  nervous  system — by  sensation,  or  by  reflex  mus- 
cular or  glandular  effects. 

Whether  the  wave  which  passes  along  the  nerve  is  a  wave  of 
chemical  change  (such,  to  take  a  very  crude  example,  as  runs 
along  a  train  of  gunpowder  when  it  is  fired  at  one  end),  or  a  wave 
of  mechanical  change,  a  peculiar  and  most  delicate  molecular 
shiver,  if  we  mav  so  phrase  it,  or  a  shear  in  a  definite  direction 
along  the  colloidal  substance  of  the  axis-cylinder  (Sutherland), 
there  is  no  absolutely  definite  experimental  evidence  to  decide. 
An  electrical  change  accompanies  the  nerve-impulse  travelling 
at  the  same  rate,  and  although  this  is  to  be  distinguished  from 
the  impulse  itself,  there  is  little  doubt  that  the  latter  is  essentially 
connected  with  a  disturbance  of  the  electrical  equilibrium  of  the 
nerve-substance. 

An  attempt  has  been  made  to  settle  the  question  by  determining 
the  temperature  coefficient  of  the  velocity  of  conduction  of  the 
impulse — i.e.,  the  quantity  which  measures  the  change  of  velocity 
for  a  given  change  of  temperature.     For  most  physical  processes 

.,  ..      .    velocity  at  T»+  10      ,  ~ 

the  quotient  - .    -       „       - ,  where   in  is  any  given  tempera- 

ture, is  not  greater  than  12,  while  for  frog's  sciatic  nerve  the  tem- 
perature coefficient  for  the  most  part  lies  between  2  and  3  (Snyder) . 
The  mean  value  of  a  large  number  of  observations  is  i'79,  with 
T»=8°  to  90  C.  (Lucas).  For  the  pedal  nerve  of  the  giant  slug  the 
mean  value  of  the  temperature  coefficient  is  178  (Maxwell).  In 
other  words,  while  for  most  physical  processes  an  increase  of  10°  C. 
increases  the  velocity  of  the  process  by  at  most  one-fifth,  the  same 
increase  of  temperature  increases  the  velocity  of  conduction  of  the 
nerve-impulse  bv  four-fifths,  or  even  more.  While  it  is  true  that  it 
may  not  be  entirely  safe  to  apply  such  a  criterion  to  a  biological 


68o  ./   MANU  II.  OF    I'll)  SIOLOGY 

process  which  need  uol  be  either  entirely  chemical  or  entirely 
physical,  and  very  likely  is  a  complex  one,  the  suggestion,  so  far  as 
it  goes,  is  undoubtedly  in  favour  of  the  chemical  hypothesis. 

Ni.ii  chemical  changes  go  on  in  living  nerve  we  need  no1  hesi- 
tate in  assume  :  and,  indeed,  it'  the  circulation  through  a  Limb  oi  .1 
warm-blooded  animal  be  stopped  for  .1  short  time,  the  nerves  lose 
their  excitability.  But  the  metabolism  is  very  slight  compared 
with  that  in  muscle  or  gland.  Even  in  active  nerve  no  tn<  asurable 
production  of  carbon  dioxide  has  ever  been  observed,  nor,  in  fact, 
lias  any  chemical  difference  between  the  excited  and  the  resting 
state  ever  been  unequivocally  made  out.  Neither  in  cold-blooded 
nor  in  mammalian  nerves  is  there  any  sensible  rise  oi  temperature 
during  stimulation.  It  has  already  been  staled  that,  under  ordinary 
conditions,  nerve-fibres  are  practically  insusceptible  <»1  fatigue,  and 
this  has  been  considered  a  strong  support  of  the  physical  nature  of 
the  conduction  process.  Nevertheless,  it  is  possible  to  show  In- 
special  methods  that  nerve  can  be  temporarily  fatigued,  although 
it  recovers  very  rapidly.  When  a  medullated  nerve  is  stimulated, 
a  brief  period  ensues  during  which  it  refuses  to  respond  to  a  second 
stimulus.  This  refractory  period  is  normally  very  short  not  more 
than  o*oo2  second  for  the  frog's  sciatic.  But  it  can  be  greatly  pro- 
longed by  cold,  asphyxia,  or  anaesthesia,  especially  l'\  the  alkaloid 
yohimbine  (Tait  and  Gunn),  and  when  the  refractory  period  is  thus 
prolonged,  fatigue  phenomena  are  readily  induced  by  stimulation. 

Stimulation  of  Nerve. — With  some  differences,  the  sam< 
stimuli  are  effective  for  nerve  as  for  muscle  (p.  632)  ;  but  chemical 

stimulation  is  not  in  general  so  easily  obtained.  The  so-called 
thermal  stimulation  is  not  a  real  stimulation  due  to  the  sudden 
change  of  temperature.  The  irregular  contractions  of  the 
muscle  caused  by  the  local  application  of  heat  to  the  nerve  are 
dependent  on  desiccation  of  the  nerve. 

Chemical  Stimulation. — When  hyper-  or  hypotonic  solutions  arc 
employed,  the  withdrawal  or  entrance  of  water  may  be  an  important 
factor. 

For  salts  which  penetrate  the  fibres  with  equal  difficulty  this 
factor  can  be  eliminated  by  applying  them  as  isotonic  solutions. 
There  is  evidence  that  chemical  stimulation  proper,  as  distinguished 
from  the  stimulation  produced  by  changes  in  the  water  content  of 
the  fibres  by  osmosis,  is  connected  with  the  electrical  charges  on 
the  dissociated  ions  of  the  salts  (p.  400).  Electrical  stimulation, 
indeed,  may  only  be  a  variety  of  chemical  stimulation  (Loeb, 
Mathews,  etc.). 

Mechanical  stimulation  may  be  applied  to  a  nerve  by  allowing  a 
small  weight  to  fall  on  it  from  a  definite  height  or  permitting  mercury 
to  drop  upon  it  from  a  vessel  with  a  fine  outflow  lube.  A  regular 
tetanus  may  thus  be  obtained.  Tigerstedf  found  that  the  smallest 
amount  of  work  spent  on  a  frog's  nerve  which  would  suffice  to  excite 
if  was  a  little  less  than  a  gramme-millimetre  thai  is.  the  work  done 
by  a  gramme  falling  through  a  distance  of  a  millimetre,  or  (taking 
an  erg  as  equivalent  to  ,,,',,,_,  gramme-centimetre)  about  [00  1 
No  doubt  a  great  part  oi  this  is  wasted,  as  a  much  smaller  quantity 
ni  work  done  by  a  beam  of  light  on  the  retina  or  by  an  electrical 
■  urrent  on  an  isolated  nerve,  both  oi  which  may  be  supposed  to  act 
more  directly  on  the  excitable  constituents,  suffices  to  cause  stimu- 


Nl  RVf.  68i 

Lation.  Thus,  the  work  done  l>v  the  niiuiin.il.  natural  or  specific, 
stimulus  for  the  retina  in  the  form  oJ  green  light  may  be  -is  little  us 

I  erg  (S.  P.  Langley),  or  only  one-ten-thousand-rnillionth  pari  oi 

the  minimum  work  necessary  Eor  mechanical  stimulation.  Again, 
with  electrical  stimulation  (closure  of  a  voltaic  current,  or  condenser 

discharges)  it  has  been  shown  that  an  amount  of  work  equal  to       , 

erg  may  be  enough  to  cause  excitation  of  a  frog's  nerve.  This  is 
ten  thousand  times  as  great  as  the  minimal  luminous  stimulus,  but 
a  million  times  less  than  the  minimal  mechanical  stimulus. 

The  laws  of  electrical  stimulation  for  nerve  arc  essentially  the  same 
as  those  we  have  already  discussed  for  muscle  (p.  636).  The  voltaic 
current  stimulates  a  nerve,  as  it  does  a  muscle,  at  closure  and 
opening.  During  the  flow  of  the  current,  so  long  as  its  intensity 
remains  constant,  there  is.  as  a  rule,  no  excitation,  or  at  least  none 
which  is  propagated  along  the  nerve,  so  that  the  muscles  supplied 
by  it  remain  uncontractcd.  But  under  certain  conditions — for 
example,  when  the  nerve  is  more  excitable  than  usual  (as  is  the  case 
with  nerves  taken  from  frogs  which  have  been  long  kept  in  the  cold) 
— a  closing  tetanus  may  be  seen  while  the  current  continues  to  pass 
through  the  nerve,  and  an  opening  tetanus  after  it  has  ceased  to  flow, 
just  as  when  the  current  is  led  directly  through  the  muscle.  Sensory 
nerve-fibres,  too.  are  stimulated  by  a  voltaic  current  during  the  whole 
time  of  flow.  Induction  shocks  are  relatively  more  powerful  stimuli 
for  nerve  than  the  make  or  break  of  a  voltaic  current.  The  opposite, 
as  we  have  seen,  is  true  of  muscle  ;  and,  upon  the  whole,  we  may 
say  that  muscle  is  more  sluggish  in  its  response  to  stimuli,  and  is 
excited  less  easilv  by  very  brief  currents,  than  nerve  is.  An  apparent 
illustration  of  this  difference  is  the  fact  that  the  nervous  excitation 
has  no  measurable  latent  period,  while  muscular  excitation  has. 
But  it  is  quite  possible  that,  if  the  conditions  of  experiment  were  as 
favourable  in  nerve  as  in  muscle,  a  sensible  latent  period  might  be 
found  here  too. 

In  nerve  as  in  muscle,  strength  of  stimulus  and  intensity  of 
response  correspond  within  a  fairlv  wide  range,  when  we  take  the 
height  of  the  muscular  contraction  or  the  amount  of  the  negative 
variation  (p.  719)  as  the  measure  of  the  nervous  excitation.  Sum- 
mation of  stimuli,  superposition  of  contractions,  and  complete 
tetanus,  are  caused  by  stimulating  a  muscle  through  its  nerve,  just 
as  by  stimulating  the  muscle  itself  (p.  655). 

Excitability  of  Nerve, — It  has  usually  been  stated  that  the 
excitability  of  frog's  nerve,  as  measured  by  the  muscular  response 
to  stimulation,  is  increased  by  rise  of  temperature,  and  diminished 
by  fall  of  temperature.  It  has,  however,  been  shown  that  this 
increase  of  excitability  is  only  apparent,  and  due  to  the  strength- 
ening of  the  current  by  diminution  of  the  resistance,  since  the 
resistance  of  all  animal  tissues,  like  that  of  electrolytic  conductors 
in  general,  diminishes  as  the  temperature  rises  (Gotch).  When 
precautions  are  taken  to  keep  the  current  intensity  the  same  at  the 
various  temperatures  compared,  it  is  found  that  cooling  of  a 
(frog's)  nerve,  even  to  50  C,  increases  the  excitability  for  currents 
of  long  duration  (several  hundredths  of  a  second).   It  has,  indeed. 


./    MANUAL  OF   PHYSIOLOGY 


been  shown  both  for  muscle  and  for  nerve  thai  the  cooler  tissue 
requires  a  smaller  current  strength  for  its  excitation  when  the 
current  is  of  long   duration.     Wit  It  brief  currents  this  effect  is 
masked,  either  partially  of  completely,  by  the  greater  ini 
current  strength  needed  in  the  case  of  the  cooler  tis  om- 

pensate  for  a  given 
decrease  in  duration 
;  as  and 
Mines).  This  is  the 
reason  that  forindn 
shocks  or  voltaic  cur- 
rents of  short  duration, 
the  excitability  of   the 

seems    to    1  i 
creased  by  a  rise  of  tem- 
perature (up    to   about 
in  theca- 
.    and  dimin 
•ling. 
Drying  of  a  nerve  at 
first    increases    it- 
citability  ;  and  the  same 
is  tni'  ration  of 

a  nerve  from  its  centre. 
In  the    latter    case    the 
of    irritability 
-  at   the  proximal 
t    the   nerve,  and 
travels  towards  the  peri- 
phery.     As    time    goes 
on,    the  excitability 
diminishes,      and     ulti- 
mately disappears  in  the 
same  i  litter- Valli 

Law).  .V  i  ■  :•■:: 
it  may  be  found  that  a 
given  stimulus  cau- 
smaller  and  smaller  con- 
traction the  farther  down 
the  nerve-  that  is,  the 
nearer  to  the  muscle— it  is  applied.  On  this  was  based  the  now 
abandoned  '  avalanche  theory,'  according  to  which  the  impulse 
continuallv  unlocked  new  energy  as  it  pas-  the  nerv 

so  gathered  strength  in  its  course  like  an  avalanche.  It  is  now 
known  that  no  material  change  takes  place  in  the  intensitv  of 
the  excitation  while  it  is  being  propagated  along  a  normal  un- 


>ram   <>}■    Changes   of    I. 
ability    and  . ivity    produced    in 

a  Nerve  by  a  Voltaic  Current. 

E,  changes  of  excitability  during  the  flow  of 
the  current,  according  to  Pniit:<-r.  The  ordinates 
drawn  from  the  abscissa  axis  to  cut  the  curve 
represent  the  amount  of  the  change.  C(i), 
changes  of  conductivity  during  the  flow  of  a 
moderately  strong  current.  Conductivity 
greatly  reduced  around  kathode  ;  little  aft' 
at  a:.  .  changes  of  conductivity  <1 

fl<>\\  :.g   current.     Conductivity 

reduced  both  in  anodic  and  kathodic  re- 
but less  in  the  former.  C,  changes  of 
ductivity   just     after    opening    a    moder 

•  lit.  Conductivity  greatly  reduced 
in  region  which  was  formerly  anodic:  little 
affected  in  aerly  kathodic. 


\7  A'I7 


injured  nerve.  Por  instance,  experiments  on  the  phrenic  nerve, 
in  its  natural  position,  and  with  all  its  connections  intact,  ; 
shown  that  with  ;i  given  strength  ol  stimulus  the  amount  of 
contraction  of  the  diaphragm  is  the  same  whether  the  nerve  be 
excited  in  the  upper,  middle,  or  lower  portion  oi  its  course.  In 
the  above  experiment  on  the  isolated,  and  therefore  injured,  nerve, 
the  contraction  varies  in  heighl  with  the  distance  "t  the  point  oi 
stimulation  from  the  muscle,  not  because  the  excitation  grows 
a--  it  travels,  bu1  because  it  is  already  greater  a1  the  moment 
when  it  sets  out  from  a  point  near  the  central  end  oi  the  nerve 
than  at  the  moment  when  it  sets  out  from  a  point  near  tin 
muscle. 

Electrotonus. — Although  the  constant  current  docs  not,  unless 
it  is  very  strong  or  the  nerve  very  irritable,  cause  stimulation 


Fig.    253. — Katelectrotom  s. 

Weak  tetanus  of  muscle  (the 
right-hand  elevation),  greatly  in- 
tensified in  katelectrotonus  of  the 
motor  nerve  (the  left-hand  eleva- 
tion). 


I  I:..    254.  — Anelectrotonus. 

Strong  tetanus  oi  muscle  (left- 
hand  elevation),  lessened  in 
strength  by  anelectrotonic  con- 
dition of  the  motor  nerve  (right- 
hand  elevation). 


during  its  passage,  it  modifies  profoundly  the  excitability  and 
conductivity  of  the  nerve.  In  the  neighbourhood  of  the  kathode 
the  excitability  is  increased  (condition  of  katelectrotonus),  while 
around  the  anode  it  is  diminished  (anelectrotonus).  Immediately 
after  the  opening  of  the  current  these  relations  are  for  a  brief 
time  reversed,  the  excitability  of  the  post-kathodic  area  (area 
which  was  at  the  kathode  during  the  flow)  being  diminished,  and 
that  of  the  post-anodic  increased.  In  the  intrapolar  area  there 
is  one  point  the  excitability  of  which  is  not  altered.  This  in- 
different point,  as  it  is  called,  shifts  its  position  when  the  intensity 
of  the  current  is  varied,  moving  towards  the  kathode  when  the 
current  is  increased,  towards  the  anode  when  it  is  diminished. 

These  statements  have  been  made  on  the  strength  of  experiments 
in  which  the  height  of  the  muscular  contraction  was  taken  as  the 
index    of  the   excitability   of  the   nerve    at    any   given    point.      But 


684  '    MANUAL  OF  PHYSIOLOGY 

alterations  of  conductivity — i.e.,  of  the  power  of  a  portion  of  the 
nerve  to  conduct  an  impulse  set  up  elsewhere  arc  also  produced  by 
the  constant  current,  which  even  outlast  its  flow.     For  all  currents 

except  the  weakest  the  conductivity  at  the  kathode  and  in  its 
neighbourhood  is  diminished,  and  with  currents  still  only  moderately 
strong  the  block  deepens  into  utter  impassability.  The  i  onductivity 
at  the  anode  is.  during  all  this  stage,  but  little  affected,  and  is  at 
any  rate  much  higher  than  at  the  kathode,  so  that  at  the  time  of 
full  kathodic  block  the  nerve-impulse  still  freely  passes  through  the 
region  around  the  positive  pole.  With  still  stronger  currents  the 
conductivity  here,  too,  begins  to  diminish,  until  at  last  the  anode 
is  also  blocked  ;  but  this  is  to  be  looked  upon  as  merely  an  extension 
of  the  defect  of  conductivity  which  has  been  creeping  along  the 
intrapolar  area  from  the  kathode.  Alter  the  opening  of  the  current, 
the  relation  between  kathodic  and  anodic  conductivity  is  reversed, 
for  now  the  post-kathodic  region  conducts  the  nerve-impulse  rela- 
tively better  than  the  post-anodic. 

The  above  facts  serve  to  explain  the  manner  in  which  the  effects 
of  stimulation  of  a  nerve  with  the  constant  current  vary  with  the 
strength  and  direction  of  the  stream.  These  effects,  so  far  as  the 
contraction  of  the  muscles  supplied  by  the  nerve  is  concerned,  have 
been  formulated  in  what  has  been  somewhat  loosely  termed  the 
law  of  contraction.  In  this  formula  the  direction  of  the  current 
in  the  nerve  is  commonly  distinguished  by  a  thoroughly  bad  but 
now  ingrained  phraseology,  as  ascending  when  the  anode  is  next  the 
muscle,  and  descending  when  the  kathode  is  next  the  muscle. 

Law  of  Contraction. 


Ascending 

Descending. 

C  urrent. 

M. 

B. 

M. 

B- 

Weak- 

Medium 
Strong 

c 
c 

c 
c 

c 
c 
c 

c 

Here  M  means  '  make,'  B,  '  break,'  of  the  current  ;  C  means  '  con- 
traction follows.' 

The  explanation  generally  given  of  the  facts  summed  up  in  the 
'  law  of  contraction  '  is  as  follows  :  Wherever  there  is  an  increase 
of  excitabilitv  sufficiently  rapid  and  sufficiently  large,  stimulation 
is  supposed  to  take  place  ;  where  there  is  a  fall  of  excitability. 
stimulation  does  not  occur.  Accordingly,  at  closure  the  kathode 
stimulates — the  anode  does  not  ;  while  at  opening,  the  anode,  at 
which  the  depressed  excitabilitv  jumps  up  to  normal  or  more,  is 
the  stimulating  pole  ;  the  kathode,  at  which  it  declines  to  normal 
or  under  it.  is  inactive. 

With  a  weak  current,  (i)  contraction  only  occurs  at  make,  and 
(2)  the  direction  of  the  current  is  indifferent.  The  explanation  of 
the  first  fact  is  that  the  make  is  a  stronger  stimulus  than  the  break, 
and  when  the  current  is  weak  enough  the  break  is  less  than  a  mini- 


\7  RVE 

ma]  stimulus.     No  sensible  change  of  conductivity  is  caused   by 
weak  currents,  which  suffices  to  explain  (2). 

With  a  '  medium  '  current,  contraction  occurs  at  make  and  break 
with  both  directions.  Here  the  break  excitation  is  effective  as  well 
as  the  make.  With  anode  next  the  muscle  (ascending  current),  there 
is,  of  course,  nothing  to  prevent  the  opening  excitation,  which  starts 
at  the  anode,  from  passing  down  the  nerve  and  causing  contraction  ; 
and  since  there  is  no  block  around  the  anode  or  in  the  intrapolar 
region  with  '  medium  '  currents,  there  is  nothing  to  keep  the  closing 
(kathodic)  excitation  from  reaching  the  muscle  too.  With  the 
kathode  next  the  muscle  (descending  current),  the  closing  excita- 
tion, which  starts  from  the  kathode,  has  no  region  of  diminished  con- 
ductivity to  pass  through,  nor  has  the  opening  (anodic)  excitation, 
for  the  kathodic  block,  caused  by  moderately  strong  currents,  is 
removed  as  soon  as  the  current  is  broken. 

With  '  strong  '  currents  there  arc  only  two  cases  of  contraction 
out  of  the  four,  just  as  with  '  weak,'  but  for  very  different  reasons. 
There  is  a  break-contraction  with  ascending,  and  a  mak'e-contraction 
with  descending  current.  With  ascending  current  the  anode  is  next 
the  muscle,  and  the  break-excitation  starting  there  has  nothing  to 
hinder  its  course.  The  make-excitation,  although  as  strong  or 
stronger,  has  to  pass  through  the  whole  intrapolar  region  and  over 
the  anode,  and  here  the  conductivity  is  depressed  and  the  nerve- 
impulse  blocked.  With  descending  current  the  kathode  is  next  the 
muscle,  and  there  is  no  hindrance  to  the  passage  of  the  make-excita- 
tion. The  break-excitation,  however,  has  to  traverse  the  intrapolar 
region,  and  the  anodic  end  of  this  area  has  a  smaller  conductivity 
immediately  after  opening  than  during  the  flow,  while  the  kathodic 
end  does  not  at  once,  after  a  strong  current,  become  passable.  The 
break-excitation,  accordingly,  cannot  get  through  to  the  muscle. 

In  all  these  cases  of  complete  or  partial  block,  during  or  after  the 
flow  of  a  constant  current,  the  progress  of  the  nerve-impulse,  its 
gradual  weakening,  and  final  extinction  can  be  very  well  shown  by 
means  of  the  action  stream  (p.  719). 

The  above  formula  can  only  be  verified  upon  isolated  nerves,  and, 
even  for  these,  exceptional  results  are  apt  to  be  obtained  as  soon  as 
the  nerves  begin  to  die. 

A  formula  similar  to  the  law  of  contraction  has  been  shown  to 
hold  for  the  inhibitory  fibres  of  the  vagus  (Donders),  '  inhibition  ' 
being  substituted  for  '  contraction.'  There  is  also  some  evidence 
that  a  similar  law  obtains  for  sensory  nerves. 

It  is  not  difficult  to  see  that  with  currents  of  brief  duration  the 
break  follows  so  quickly  on  the  make  that  interference  of  their 
opposed  effects  may  occur.  This  is  the  reason — or,  at  least,  one 
reason — why,  above  a  certain  frequency,  a  muscle  or  nerve  ceases 
to  respond  to  all  of  a  series  of  rapidly  recurring  electrical  stimuli 
(p.  658).  It  is  also  the  reason  why,  with  single  very  brief  stimuli, 
a  greater  current  intensity  must  be  employed  in  order  to  cause 
excitation  than  when  the  duration  of  the  stimulating  current  is 
greater  (Woodworth,  Lucas).  Not  enough  weight  has  been  given 
to  this  circumstance  by  some  of  the  writers,  who,  in  attacking 
du  Bois  -  Reymond's  law  of  the  dependence  of  excitation  upon 
variation  in  current  density  (p.  636),  have  sought  to  establish  a 
relation  between  the  excitatory  effect  and  some  such  factor  as 
current  strength,  the  quantity  of  electricity  passed,  or  the  electrical 
energy  expended. 


686 


/    u  I  \r  \i    OF  PHYSIOLOGY 


The  Law  of  Contraction  for  Nerves  '  in  Situ.'  Win  n  a  nerve  is 
stimulated  without  previous  isolation — in  the  human  body,  for 
instance,  through  electrodes  laid  on  the  skin  the  current  will  not 
enier  .iinl  Leave  \\  through  definite  small  portions  of  its  sheath,  nor 
will  it  be  possible  to  make  the  lines  of  flow  nearly  parallel  to  eat  b 
other  and  to  the  long  axis  of  the  nerve,  as  is  the  case  in  a  slender  strip 
ol  tissue  when  there  is  a  considerable  distance  between  th<  i  lectrodes. 
<  >n  the  contrary,  when,  ;is  is  usually  the  case  in  electro-thera- 
peutical treatment,  a  single  electrode  say.  the  positive  is  placed 
over  the  position  of  the  nerve,  and  the  other  at  a  distance  on  some 
convenient  part  of  the  body,  the  current  will  enter  the  nerve  by  a 
broad  fan  of  stream-lines  cutting  it  more  or  less  obliquely,  and  pass 
out  again  into  the  surrounding  tissues  ;  so  that  both  an  an  cde 
(surface  of  entrance)  and  a  kathode  (still  larger  surface  of  exit)  will 
correspond  to  the  single  positive  pole.  Similarly,  the  single  negal  Lve 
electrode  will  correspond  to  an  anodic  surface  where  the  now  narrow- 
ing sheaf  of  lines  of  flow  enters  the  nerve,  and  a  smaller  kathodic 
surface,  where  they  emerge.     Even  if  the  two  electrodes  were  on  the 

course  of  the  nerve,  the  stream- 
lines would  still  cut  it  in  such 
a  way  that  each  electrode  would 
correspond  both  to  anode  and 
kathode  (Fig.  255). 

It  is  impossible  under  thesi 
circumstances  to  take  account 
of  the  directio)i  of  a  current  in 
a  nerve,  or  to  connect  direction 
with  any  specific  effect.  When 
we  place  one  of  the  electrodes 
over  the  nerve  and  the  other 
at  a  distance,  the  law  of  con- 
traction only  appears  in  a  dis- 
guised form  ;  for  since  a  kathode 
and  an  anode  exist  at  each  pole, 
there  is,  with  a  current  of  suffi- 
cient strength  ('  strong  cur- 
rent '),  excitation  at  each  both 
at  make  and  break.  The  nega- 
tive make  contraction  is,  how- 
ever, stronger  than  the  positive, 
for  the  excitation  corresponding 
to  the  latter  arises  at  the 
secondary  kathodic  surface, 
where  the  sheaf  of  current-lines 
spreading  from  the  positive  electrode  passes  out  of  the  nerve.  Now, 
this  is  much  larger  than  the  primary  kathodic  surface,  through 
which  the  narrow  wedge  of  stream-lines  passes  to  reach  the  nega- 
tive electrode,  and  the  current  density  at  the  latter  is  accordingly 
much  greater.  The  positive  break-contraction  is,  for  a  similar 
reason,  stronger  than  the  negative. 

With  a  '  weak  '  current,  the  only  contraction  is  a  closing  one  at 
the  kathode  ;  with  a  '  medium  '  current  there  arc  both  opening  and 
closing  contractions  at  the  positive  pole,  and  a  closing  but  no  opening 
contraction  at  the  negative  (Practical  Exercises,  p.  743). 

The  conductivity  of  the  nerve,  as  we  have  scon  in  various 
examples,  is  not  necessarily  altered  in  the  same  sense  as  the 


Fig.  055.  -Diagram  of  Lines  of  Flow 
mi  a  Current  passing  through  a 
Nerve. 

A.  .in  isolated  nerve;  B,  a  nerve 
in  situ.  Secondary  anodes  (  +  )  arc 
funned  where  the  current  re  -  enters 
tlic  nerve  below  the  negative  electrode 
after  passing  through  the  tissues  in 
which  it  is  embedded,  and  secondary 
kathodes  (  -  )  where  the  current 
passes  (nit  oi  the  nerve  into  the  sur- 
rounding tissues  below  the  positive 
electrode. 


Nl  AT/ 

excitability.     In  the  neighbourhood  of  the  kathode  it  is  easier 
to  cause  excitation  than  in  the  normal  nerve  (increased  <  \ 

bility),  but  it  is  less  easy  for  an  excitation  set  up  elsewhere  to 
pass  through  (diminished  conductivity).  Change  oi  tempi 
ture  also,  for  certain  kinds  of  stimuli,  at  any  rate,  acts  Ln  the 
opposite  way  on  these  two  properties  of  nerve.  The  excita 
bility  of  frog's  nerve  is  increased  by  cooling  (from  35  C.  to 
2°  C.)  for  mechanical  and  chemical  stimulation,  and  for  stimula- 
tion by  the  opening  or  closure  oi  a  voltaic  current,  unless  of  very 
short  duration  (p.  681),  but  cooling  diminishes  and  heat  increases 
the  conductivity.  Carbon  dioxide  and  monoxide  depress  the 
excitability  without  affecting  the  conductivity.  Alcohol  vapour 
rapidly  impairs  the  conductivity  without  for  a  time  affecting  the 
excitability.  On  ceasing  to  apply  the  vapour  the  conductivity  is 
restored  much  sooner  than  the  excitability  (Gad  and  Sawyer, 
Piotrowski).  Munk  found  that  in  a  dying  sciatic  nerve  certain 
points  may  be  quite  inexcitable  to  the  strongest  stimuli,  while 
weak  stimulation  of  points  lying  nearer  the  central  end  may  cause 
muscular  contraction.  These  facts  indicate  that  the  process  by 
which  the  nerve-impulse  is  propagated  may  not  be  the  same  as  that 
by  which  it  is  originated,  and  therefore  is  not  merely  an  excitation 
of  each  nerve-element  by  the  one  next  it,  as  some  have 
supposed. 

Cocaine  localfy  applied  to  a  nerve  diminishes  or  abolishes  its  con- 
ductivity, according  to  the  dose.  It  exercises  a  selective  action  as 
regards  nerve-fibres  of  different  kinds,  picking  out  and  paralyzing 
sensory  fibres  before  motor  ;  vagus  fibres  conducting  upwards 
before  those  conducting  downwards,  vaso-constrictors  before  vaso- 
dilators, and  broncho-constrictors  before  broncho-dilators  (Dixon). 
Pressure  also  abolishes  the  conductivity  of  sensory  fibres  sooner  than 
that  of  motor  fibres. 

Double  Conduction. — When  a  nerve  (or  muscle)  is  stimu- 
lated artificially,  the  excitation  runs  along  it  in  both  directions 
from  the  point  of  stimulation  ;  so  that  nerve-fibres  which  in  the 
intact  body  are  afferent  can  conduct  impulses  towards  the 
periphery,  and  efferent  fibres  can  conduct  impulses  away  from 
the  periphery.  In  the  normal  state,  however,  double  conduc- 
tion must  seldom  occur,  for  efferent  fibres  are  connected  centrally, 
and  afferent  fibres  peripherally,  with  the  structures  in  which 
their  natural  stimuli  arise.  In  general,  too,  an  impulse,  if  it 
did  pass  centrifugally  along  an  afferent  fibre,  would  not  give 
any  token  of  its  existence,  for  the  peripheral  organ  would  not 
be  able  to  respond  to  it  ;  and  we  have  no  reason  to  believe  that 
the  central  mechanisms  connected  with  afferent  fibres  are  better 
fitted  to  answer  such  foreign  and  unaccustomed  calls  as  impulses 
reaching  them  along  normally  efferent  nerves.     There  is  good 


688  I     MANUAL  OF  PHYSIOLOGY 

evidence  that  muscular  excitation  is  not  carried  over  to  the  motor 
nerve-ribres  ;  in  other  words,  the  wave  of  action  flows  from  the 
nerve  to  the  muscle,  but  cannot  be  got  to  flow  backwards.  Ex- 
citation of  the  central  end  of  an  efferent  (anterior)  spinal  root 
is  not  transferred  to  the  corresponding  afferent  (posterior) 
root,  the  connection  between  the  efferent  and  afferent  neurons 
presenting  the  character  of  a  physiological '  valve,'  which  permits 
impulses  to  pass  only  in  one  direction.  We  have  seen  that 
vaso-dilator  impulses  possibly  pass  out  to  the  limbs  over 
fibres  which,  morphologically  speaking,  are  afferent  fibres  (p.  165). 
And  we  shall  see  that  a  nutritive  influence  is  exerted  over  the 
afferent  fibres  of  the  spinal  nerves  by  the  ganglion  cells  of  the 
posterior  root  ganglia  (p.  693),  an  influence  which  must  spread 
along  these  fibres  in  the  opposite  direction  to  that  of  the  normal 
excitation. 

The  best  proofs  of  double  conduction  in  nerves,  with  artificial 
stimulation,  are  :  (1)  The  propagation  of  the  negative  variation 
or  action  current  in  both  directions.  This  holds  for  sensory  as  well 
as  for  motor  fibres,  as  du  Bois-Reymond  showed  on  the  posterior 
roots  of  the  spinal  nerves  of  the  frog  and  the  optic  nerves  of 
fishes.  (2)  Stimulation  of  the  posterior  free  end  of  the  electrical 
nerve  of  Malapterurus  (p.  737)  causes  discharge  of  the  electric  organ, 
although  the  nerve-impulse  travels  normally  in  the  opposite  direc- 
tion. (3)  If  the  lower  end  of  the  frog's  sartorius  is  split  into  two, 
"entle  stimulation  of  one  of  the  tongues  causes  contraction  of 
individual  fibres  in  the  other.  This  is  supposed  to  be  due  to  con- 
duction of  the  nerve-impulse  up  a  twig  of  a  nerve-fibre  distributed 
to  the  one  tongue,  and  down  another  twig  of  the  same  fibre  going 
to  the  other  tongue.  A  similar  experiment  can  be  done  on  the 
gracilis  of  the  frog.  This  muscle  is  divided  by  a  tendinous  inscription 
into  two  parts,  each  supplied  by  a  branch  of  a  nerve  which  divides 
after  entering  the  muscle.  Stimulation  of  either  twig  is  followed  by 
contraction  of  both  parts  of  the  muscle  (Kiihne). 

Bert's  much-quoted  experiment  on  the  rat  is  valueless  as  a  proof 
of  double  conduction.  He  caused  union  of  the  point  of  the  tail 
with  the  tissues  of  the  back,  then  divided  the  tail  at  the  root,  and 
found  that  stimulation  of  what  was  now  the  distal  end  caused  pain. 
From  this  he  concluded  that  the  sensory  fibres  of  the  '  transposed  ' 
tail  conducted  in  the  direction  from  root  to  tip.  But  the  conclusion 
is  not  warranted,  for  sensation  disappeared  in  the  tail  after  the 
section,  and  did  not  return  till  some  months  later,  when  the  nerve- 
fibres,  after  degenerating,  would  have  been  replaced  by  new  sensory 
fibres' growing  down  from  the  dorsal  nerves  (Ranvier).  For  a  similar 
reason'the  so-called  union  of  the  peripheral  end  of  the  cut  hypo- 
glossal nerve  (motor)  with  the  central  end  of  the  cut  lingual  (sensory) 
proves  nothing  as  to  double  conduction,  nor  as  to  the  possibility  of 
motor  nerves  taking  on  a  sensory  function.  For  while  sensation  is 
after  a  time  restored  in  the  affected  portion  of  the  tongue,  this  is 
due  to  the  growth  of  sensory  fibres  from  the  central  stump  of  the 
lingual  down  through  the  degenerated  hypoglossal,  and  not  to  the 
conduction  upwards  of  sensory  impulses  by  the  motor  fibres  of  the 
latter.  ...  .... 


Uerve  689 

Every  fibre  of  a  nerve  is  physiologically  isolated  from  the 
rest,  so  that  an  impulse  set  up  in  a  fibre  runs  its  course  within 
it,  and  does  not  pass  laterally  into  others  (law  of  isolated  con- 
duction). In  connection  with  this  physiological  fact  there  is 
the  anatomical  fact  that  nerve-fibres  do  not  normally  branch  in 
the  trunk  of  a  peripheral  nerve.  (But  see  p.  697.)  It  has, 
however,  been  shown  that  bifurcation  of  nerve-fibres  may  occur 
in  the  spinal  cord  (Sherrington).  The  axis-cylinder  of  a  peri- 
pheral nerve-fibre  only  begins  to  branch  where  complete  isolation 
of  function  is  no  longer  required,  as  within  a  muscle.  The 
experiment  of  Kiihne  on  double  conduction,  mentioned  above, 
shows  that  an  excitation  set  up  in  one  twig  or  one  fibril  of  an 
axis-cylinder  which  has  branched  can  spread  to  the  rest. 

Velocity  of  the  Nerve-impulse. — We  have  said  that  the 
nerve-impulse  travels  with  a  measurable  velocity.  It  is  now 
time  to  describe  how  this  has  been  ascertained  (p.  713).  For 
motor  fibres  the  simplest  method  is  to  stimulate  a  nerve  suc- 
cessively at  two  points,  one  near  its  muscle,  the  other  as  far 
away  from  it  as  possible,  and  to  record  the  contractions  on  a 
rapidly-moving  surface  (pendulum  or  spring  myograph)  (p.  643) . 
The  apparent  latent  period  of  the  curve  corresponding  to  the 
nearer  point  will  be  less  than  that  of  the  curve  corresponding 
to  the  point  which  is  more  remote,  by  the  time  which  the  impulse 
takes  to  pass  between  the  two  points.  The  distance  between 
these  points  being  measured,  the  velocity  is  known.  Helmholtz 
found  the  velocity  for  frog's  nerves  at  the  ordinary  temperature 
of  the  air  to  be  a  little  under,  and  for  human  nerves,  cooled  so 
as  to  approximate  to  the  ordinary  temperature,  a  little  over 
30  metres  per  second.  For  observations  on  man  the  contrac- 
tion curves  of  the  flexors  of  one  of  the  fingers  or  of  the  thumb 
may  be  recorded,  first  with  stimulation  of  the  brachial  plexus 
at  the  axilla,  and  then  with  stimulation  of  the  median  or  ulnar 
nerve  at  the  elbow.  Probably  at  the  same  temperature  there 
is  little  difference  in  the  rate  of  transmission  in  the  nerves  of 
warm-blooded  and  cold-blooded  animals,  but  temperature  has 
a  considerable  influence  (p.  679). 

By  cooling  a  frog's  nerve  Helmholtz  reduced  the  rate  to  ^  of  its 
value  at  the  ordinary  temperature.  In  the  human  arm  he  found  a 
variation  from  30  to  90  metres  per  second,  according  to  the  tempera- 
ture, 50  metres  being  about  the  normal  rate.  This  is  greater  than 
the  speed  of  the  fastest  train  in  the  world.  According  to  Piper's 
recent  measurements  the  velocity  in  human  medullated  nerve  is  even 
greater  than  Helmholtz  concluded,  about  1 20  metres  a  second  under 
ordinary  conditions.  The  rate  is  independent  of  the  intensity  of  the 
excitation. 

The  velocity  with  which  the  negative  variation  is  propagated 
(p.  723)  is  the  same  as  that  of  the  nerve-impulse. 

44 


690  I    MANl    \1    OF  PUYSIOLOG  V 

In  sensory  nerves  there  is  no  reason  to  believe  thai  the  velocity 
of  tin.-  nerve-impulse  differs  from  that  in  motor  nerves,  but  experi- 
ments on  man  really  lire  from  objection  are  as  yet  wanting. 

The  usual  method  is  to  stimulate  the  skin  first  at  a  point  distanl 
from  the  brain,  and  then  at  a  much  nearer  point.  The  person 
experimented  on,  as  soon  as  he  feels  the  stimulation,  makes  a  signal, 
say,  by  closing  or  opening  with  the  hand  a  current  connected  with 
an  electric  time-marker,  writing  on  a  moving  surface.  There  is,  oi 
course,  a  measurable  interval  between  the  excitation  and  the  signal, 
and  this  being  in  general  longer  the  more  remote  the  point  of  stimu- 
lation is  from  the  brain,  it  is  assumed  that  the  excess  represents  t he 
time  taken  by  the  nerve-impulse  to  pass  over  a  length  of  sensory 
nerve  equal  to  the  difference  in  the  length  of  the  path.  But  thin  is 
this  difficulty,  that  the  propagation  of  the  impulse  from  the  point  of 
stimulation  to  the  brain  is  only  one  link  in  the  chain  of  events  ol 
which  the  signal  marks  the  end.  The  impulse  has  first  to  be  trans- 
formed into  a  sensation,  and  then  the  will  has  to  be  called  into  action, 
and  an  impulse  sent  down  the  motor  nerves  to  the  hand.  And  \\  hi  li- 
the time  taken  by  the  excitation  in  travelling  up  and  down  the 
peripheral  nerve-fibres  is  probably  fairly  constant,  the  time  spent  in 
the  intermediate  psychical  processes  is  very  variable. 

Chemistry  of  Nerve.- — Our  knowledge  of  this  subject  is  still 
scanty  ;  and  most  of  what  we  do  know  lias  been  obtained  from 
analyses,  not  of  the  peripheral  nerves,  but  of  the  white  matter 
of  the  central  nervous  system. 

I  roteins  are  present,  especially  in  the  axis-cylinder.  The  proteins 
of  nervous  tissue  include  two  globulins,  one  coagulated  by  heat  at 
470  C,  the  other  at  700  to  750  C.,  and  a  nucleo-protein  coagulating 
at  560  to  6o°  C. 

The  lipoids  of  nervous  tissue  are  very  important  constituents. 
They  are  substances  soluble  in  organic  solvents,  like  benzol  and 
ether,  and  comprise  cholesterin,  certain  phosphatides  [kephalin  and 
lecithin),  and  certain  cerebrins  or  cerebrosides.  The  cercbrins  arc 
glucosidcs  containing  nitrogen,  but  no  phosphorus,  and  they  yield 
a  reducing  sugar  (galactose)  on  hydrolysis.  In  the  nervous  tissue 
there  is  also  present,  according  to  some  authorities,  a  compound 
called  protagon.  Others  consider  it  a  mere  mixture  of  phos- 
phatides and  cerebrosides.  The  lipoids  of  nerve-fibres  belong 
largely  to  the  medullary  sheath,  but  they  are  not  confined  to  it. 
since  non-mcdullated  nerves  also  yield  a  considerable  quantity  oi 
lipoids  (ll"5  per  cent,  of  the  solids  as  against  46*6  per  cent,  for 
medullated  nerves).  Non-medullated  nerves  (splenic  nerves  of  the 
ox)  are  distinguished  from  medullated  nerves  (human  sciatic)  by 
the  high  proportion  of  their  total  Lipoids  constituted  by  the  phos- 
phatides (kephalin  and  lecithin)  and  cholesterin.  Thus,  in  non- 
medullated  fibres  47  per  cent,  of  the  lipoid  extract  consisted  of 
cholesterin,  and  237  per  cent,  of  kephalin  ;  while  in  the  medullated 
fibres  cholesterin  made  up  only  25  per  cent,  of  the  extract,  and 
kephalin  12-4  per  cent.  On  the  other  hand,  the  cerebrosides  are 
present,  both  relatively  and  absolutely,  in  much  larger  quantity 
in  medullated  than  in  non-medullated  nerves.  In  both  varieties  of 
fibres  kephalin,  and  not  lecithin,  is  the  chief  phosphorus-containing 
body  (balk).  The  medullary  sheath  further  contains  a  kind  of  net- 
work oi  a  peculiar  resistant  substance,  neurokeratin.  The  neurilemma 
consists  of  substances  insoluble  in  dilute  sodium  hydroxide.    Gelatin 


NERVE  691 

is  obtained  from  the  connective  tissue  which  binds  the  nerve- 
fibres  together.  There  may  also  be  ordinary  fat  in  the  meshes 
of  the  epineurium  connecting  the  bundles.  Small  quantities  of 
xanthin,  hypoxanthin,  and  other  extractives,  can  also  be  obtained 
from  aerve.  According  to  Halliburton's  analyses,  the  water  in 
sciatic  nerves  amounts  to  05-1  per  cent.,  and  the  solids  to  349  per 
cent.     The  proteins  make  up  29  per  cent,  of  the  solids. 

For  an  analysis  of  the  white  matter  of  the  brain,  sec  p.  881. 

Nerve-cells  contain  no  potassium,  according  to  Macallum  ;  and 
this  is  true  both  of  the  dendrites  and  the  axons,  fn  medullated 
nerves,  however,  potassium  compounds  are  present  external  to  the 
axons,  chiefly  at  the  nodes  of  Ranvier  (Frontispiece)  and  in  the 
neurokeratin  framework  of  the  sheath. 

The  only  chemical  difference  between  living  and  dead  nervous 
tissue  which  has  been  made  out  with  any  degree  of  certainty  is 
that  the  former  is  neutral  or  faintly  alkaline,  and  the  latter  acid, 
in  reaction  to  such  indicators  as  litmus.  This  is  especially  true  of 
the  grey  matter  of  the  central  nervous  system,  although  the  white 
matter  also  is  often  found  acid.  The  change  of  reaction  is  due  to 
the  accumulation  of  lactic  acid.  Such  a  change  has  not  hitherto 
been  clearly  demonstrated  in  peripheral  nerves,  either  after  death 
or  after  prolonged  stimulation.  The  (non-medullated)  splenic  nerves 
of  the  dog,  even  after  stimulation  for  six  hours,  never  became  acid 
(Halliburton  and  Brodie). 

Degeneration  of  Nerve. — Neive-fibres  are  '  bound  in  the 
bundle  of  life  '  with  the  nerve-cells  from  which  their  axis-cylinders 
arise  ;  the  connection  between  cell  and  axon  once  severed,  the 
nerve-fibre  dies  inevitably.  This  is  an  illustration  of  a  general 
law  that  no  portion  of  a  cell  can  live  once  it  is  separated  from 
the  nucleus.  We  shall  see  later  on  that  changes  also  occur  in 
the  nerve-cell  whose  axon  has  been  divided  from  it,  although 
they  are  of  a  different  nature  (rather  a  slow  atrophy  than  an 
acute  degeneration),  and  do  not  necessarily  lead  to  the  destruc- 
tion of  the  cell.  We  must  regard  the  neuron  not  only  as  a 
morphological  unit,  a  single  cell  from  nucleus  to  remotest  end- 
brush,  but  also  as  a  functional  and  nutritive  unit,  the  fortune 
of  any  portion  of  which  is  not  indifferent  to  the  rest.  Thus, 
when  a  man's  arm  is  amputated  the  arm  fares  worse  than  the 
man,  for  the  arm  dies.  But  the  man  is  not  unaffected.  He 
lives,  but  he  suffers  much  temporary  disturbance  and  some 
permanent  loss.  What  is  left  of  him  is  not  quite  the  same  as 
it  was.  The  acute  changes  that  occur  in  severed  nerve-fibres 
are  most  conveniently  studied  in  the  peripheral  nerves,  although 
essentially  similar  phenomena  take  place  also  in  the  fibres  of 
the  central  nervous  system. 

A  spinal  nerve  is  composed  of  efferent  fibres  whose  cells  of 
origin  are  in  the  grey  matter  of  the  anterior  horn,  and  afferent 
fibres  whose  cells  of  origin  are  in  the  posterior  root  ganglion. 
When  such  a  nerve  is  cut  below  the  junction  of  its  roots,  muscular 
paralysis  and  impairment  of  sensation  at  once  follow  in   the 

44—2 


692 


A    M  INI     II    <>h    I'HYSIUI.OCY 


region  supplied  by  the  nerve  ;  bul  for  a  time  the  nerve  remains 
excitable  to  direct  stimulation.  The  excitability  gradually 
diminishes,  and  in  a  leu  days  is  completely  gone.     It  portions  oi 

the  nerve  distal  to  the  lesion  arc  examined  at  different  periods 
after  section,  a  remarkable  process  of  degeneration  (commonly 

spoken  of  as  Wallerian  de- 
generation) is  seen  to  he  going 
on.  In  the  medullated  fibres 
this  hegins  on  the  second  <>r 
third  day  with  a  swelling  oi 
the  axis-cylinder,  which  breaks 
up  into  detached  pieces  (frag- 
mentation), and  assumes  a 
granular  appearam  e.  The 
medullary  sheath  also  under- 
goes fragmentation  at  the  lines 
of  Lantermann,  and  a  little 
later  separates  into  clumps 
and  droplets  of  myelin.  The 
nuclei  under  the  neurilemma 
increase  in  size,  proliferate  by 
mitosis,  and  insinuate  them- 
selves between  the  fragments 
of  the  medullary  sheath  and 
axis-cylinder,  which  ultimately 
disappear,  leaving  the  nerve- 
fibre  represented  only  by  a 
kind  of  mummy  of  connective 
tissue,  in  which  the  neuri- 
lemma with  its  abnormally 
numerous  nuclei  can  still  be 
recognised.  The  protoplasm 
around  the  nuclei  of  the 
neurilemma  also  increases  in 
amount,  and  undergoes  other 
changes,  which  will  he  more 
particularly  referred  to  in 
describing  the  regeneration 
of  nerve.  The  degenerative 
process  begins  near  the  cut  end,  and  extends  gradually  to 
the  periphery,  and  more'  rapidly  in  warm  than  in  cold- 
blooded  animals.  At  any  rate,  that  is  the  interpretation  generally 
given  to  the  fact  that  at  a  given  period  after  section  the 
1  lunges — especially  the  breaking-up  of  the  myelin — are  more 
pronounced  near  the  proximal  end  of  the  peripheral  stump.  In 
a  mammal  degeneration  is  far  advanced  in  a  fortnight,  although 


Fig.  256. — Degeneration  of  Nerve- 
fibki  s  ai  ri  R  Suction  (Barker,  after 
Thoma). 

I,  normal  fibre;  II,  degenerating  fibre; 
III,  further  stage  of  degeneration; 
S.  neurilemma ;  m.  medullary  sheath  ; 
A,  axis -cylinder ;  I.,  Lantcrmann's  line 
or  cleft ;  R,  node;  mt,  drops  of  myelin ; 
«,  remains  of  axis-cylinder;  w,  prolifera- 
ting cells  "t  neurilemma. 


SERVE 


the  last  remnants  of  the  myelin  may  not  be  absorbed  for 
months.  In  the  degenerated  nerve  (cat's  sciatic)  the  per- 
centage of  phosphorus  undergoes  a  diminution  from  about 
the  third  day.     About  the  eighth  day  the  loss  of  phosphorus 

•i.e.,  of  the  phosphatides  (lecithin,  kephalin)— is  markedly 
accelerated,  coinciding  with  the  appearance  of  a  strong 
Marchi*  staining  reaction.  By  the  twenty-ninth  day  the  de- 
generated nerve  is  practically  devoid  of  phosphorus.  A  pro- 
gressive increase  in  the  water  and  a  diminution  in  the  total  solids 
also  culminate  about  the  same  time  (Mott  and  Halliburton). 
In  the  portion  of  the  nerve-fibre  still  connected  with  the  nerve- 
cell  the  degeneration  only  extends  as  far  back  as  the  next  node 
of  Ranvier,  and  seems  to  be  due  to  the  direct  effect  of  the  injury. 
In  non  -  medullated 
fibres,  such  as  the 
fibres  arising  from 
the  cells  of  the  su- 
perior cervical  gan- 
glion (Tuckett),  the 
degeneration  is  con- 
fined to  the  axis- 
cylinders.  It  begins 
in  about  twenty-four 
hours  after  section, 
and  the  loss  of  ex- 
citability and  con- 
ductivity is  complete 
by  the  fortieth  hour. 

It  follows  from 
what  has  been  said 
as  to  the  position  of  the  cells  of  origin  of  the  root  fibres  of  the 
spinal  nerves  that  section  of  the  anterior  root  causes  degenera- 
tion on  the  peripheral,  but  not  on  the  central  side  of  the  lesion. f 
Only  the  anterior  root  fibres  in  the  mixed  nerve  degenerate. 
Section  of  the  posterior  root  above  the  ganglion  causes  degene- 
ration of  the  central  stump,  but  not  of  the  portion  still  con- 
nected with  the  ganglion,  nor  of  the  posterior  root  fibres  below 
the  ganglion  or  in  the  mixed  nerve.  Section  of  the  posterior 
root  below  the  ganglion  causes  degeneration  of  the  fibres  of 
the  root  below  the  section  and  in  the  mixed  nerve,  but  not 
above  it. 

*  The  chief  constituents  of  Marchi's  solution  are  potassium  bichromate 
and  osmic  acid.  It  stains  medullated  nerve -fibres  black  in  the  earlier 
stages  of  degeneration. 

t  A  few  fibres  in  the  peripheral  stump  of  the  anterior  root  do  not 
degenerate,  and  a  few  fibres  in  the  central  stump  do.  These  are  the 
'  recurrent  fibres,'  whose  course  is  described  on  p.  791. 


Fig.  257-- 


-Degeneration  of  Spinal  Nerves  and 
their  Roots  after   Section. 


The  shading  shows  the  degenerated  portions. 


6o4  A   MANUAL  OF  PHYSIOLOGY 

Regeneration  of  Nerve. — Degeneration  of  nerve  is  followed, 
if  its  divided  ends  are  not  kept  artificially  apart,  by  a  process  of 
regeneration,  already  distinct  under  favourable  conditions  in 
from  three  to  tour  winks  after  the  section,  and  indeed  in  some 
cases  commencing  as  early  as  the  second  week.  This  consists 
in  the  outgrowth  of  new  axis-cylinders,  in  the  form  of  fine  fibres, 
from  the  ends  of  the  divided  axis-cylinders  of  the  central  stum]) 
of  the  nerve.  These  push  their  way  into  and  along  the  de- 
generated fibres,  ultimately  acquire  a  medullary  sheath,  anil 
develop  into  complete  nerve-fibres,  restoring  first  sensation,  and 
later  on  voluntary  motion,  to  the  paralyzed  part.  Or  they  may 
possiblv  unite  with  imperfect  fibres  developed  in  the  peripheral 
stump.  The  process  needs  several  months  for  its  completion, 
even  in  warm-blooded  animals.  It  takes  place  under  the 
influence  of  the  nucleated  portion  of  the  neuron  (the  cell-body), 
and  is  never  completed  if  the  peripheral  and  central  portions  of 
the  nerve  are  permanently  separated  by  a  substance  through 
which  the  new  axis-cylinders  cannot  grow  or  by  a  gap  too  wide 
for  them  to  bridge  over.  When  the  cut  ends  of  the  nerve  are 
carefully  sutured  together,  the  conditions  for  complete  and 
speedy  regeneration  are  rendered  more  favourable — a  fact  which 
finds  its  application  in  the  surgical  treatment  of  injured  nerves. 
The  cycle  of  chemical  changes  described  in  the  degenerating 
nerve  is  retraced  in  the  reverse  order.  In  the  cat's  sciatic  the 
first  sign  of  the  return  of  the  phosphorus  was  seen  with  the 
beginning  of  the  normal  myelin  reaction  about  the  sixtieth  day 
after  section.  At  the  one-hundredth  day  the  phosphorus  content 
was  almost  as  great  as  that  of  the  normal  nerve  (a  little  under 
i  per  cent,  of  the  solids  for  the  regenerated,  as  compared  with 
a  little  over  i  per  cent,  for  the  normal  nerve). 

It  is  not  as  yet  well  understood  how  the  regenerating  fibre? 
are  directed  in  their  growth,  so  that  they  join  their  centres  to 
the  appropriate  end-organs  without  mistake.  That  they  have 
a  high  capacity  for  finding  their  way  is  indicated  by  the  results 
of  cross-suturing  such  nerves  as  the  median  and  ulnar — i.e., 
of  uniting  the  central  end  of  the  one  with  the  peripheral  end  of 
the  other.  Howell  and  Huber  found  that  after  this  operation 
in  the  dog,  both  co-ordinated  voluntary  motion  and  sensation 
returned  in  large  measure  in  the  parts  supplied  by  the  nerves. 
Here  the  motor  fibres  of  the  median  nerve  must,  of  course,  have 
made  connection  with  muscles  previously  supplied  by  the  ulnar, 
being  guided  to  them  along  the  nerve-sheaths  of  the  latter. 
Doubtless  the  old  nerve-sheaths  serve  to  some  extent  as 
mechanical  guides  by  offering  to  the  new  axons  a  path  of  least 
resistance.  And  when  a  nerve-trunk  containing  motor  and 
sensory  fibres  is  simply  crushed  so  as  to  destroy  all  physiological 


NERVE 

continuity,  but  is  not  cut,  no  distortion  of  the  motor  and  sei 
'patterns'  of  the  nerve  in  other  words,  no  '  straying '  ol 
the  fibres  from  their  old  paths  -can  be  detected  on  regeneration. 
When  the  nerve  is  cut  and  then  sutured,  a  certain  amount  of 
distortion  of  the  pattern  is  inevitable.  The  mechanical  apposi- 
tion of  central  and  peripheral  stumps  is,  of  course,  much  more 
nearly  perfect  in  the  crushed  nerve  than  in  the  cut  nerve,  however 
exact  the  suturing  may  be  (Osborne  and  Kilvington).  That, 
however,  the  degenerated  peripheral  stump  directs  the  growth 
of  the  axons  from  the  central  stump  in  sonic  other  than  a  merely 
mechanical  way  is  evident  from  the  experiments  of  Langley  on 
regeneration  of  the  cervical  sympathetic  in  the  cat  after  section 
below  the  superior  cervical  ganglion.  The  nerve  contains  fibres 
of  various  functions  which  reach  it  from  the  upper  thoracic 
nerves.  The  anterior  roots  of  the  first  and  third  thoracic  nerves 
supply  the  cervical  sympathetic  mainly  with  fibres  which  end 
in  the  ganglion  around  cells  that  give  off  dilator  fibres  for  the 
pupil.  The  fibres  connected  with  the  cells  in  the  ganglion 
which  send  vaso-motor  fibres  to  the  vessels  of  the  ear  are  for  the 
most  part  contained  in  the  anterior  roots  of  the  second  and  fifth 
thoracic  nerves  ;  and  the  fibres  connected  with  the  cells  that 
give  origin  to  the  pilo-motor  fibres  for  the  hairs  of  the  face  and 
neck  in  the  anterior  roots  of  the  fourth  to  the  seventh.  Stimula- 
tion of  any  one  of  the  upper  thoracic  roots  accordingly  causes 
a  specific  effect,  which,  according  to  Langley,  is  in  general  the 
same  after  regeneration  as  before  section  of  the  cervical  sym- 
pathetic. We  must  assume,  therefore,  that  each  regenerating 
fibre  seeks  out  either  the  ganglion  cell  with  which  it  was  originallv 
connected,  or  one  belonging  to  the  same  class.  No  mere  mechanical 
guidance  of  the  growing  axons  by  the  old  neurilemmas  will 
suffice  to  explain  this  selective  growth.  It  is  necessary  to 
postulate,  in  addition,  an  attraction  of  a  chemical  or  physico- 
chemical  nature  (chemiotaxis),  dependent  upon  a  specific  rela- 
tion between  the  new  axons  and  the  scaffolding  of  the  peripheral 
stump  or  the  ganglion  cells.  But  it  is  not  possible  at  present 
to  form  any  very  precise  conception  of  the  properties  on  which 
the  chemiotactic  phenomena  depend.  And  the  specificity  is 
not  an  absolute  one.  Under  certain  conditions  these  pre- 
ganglionic nerve-fibres  (that  is  to  say,  nerve-fibres  running  from 
the  spinal  cord  to  end  around  the  sympathetic  ganglion  cells) 
can  form  connections  with  nerve-cells  of  a  different  class — e.g., 
pupillo-dilators  with  cells  whose  axons  end  in  the  erector  musdes 
of  the  hairs.  Further,  after  section  of  the  sympathetic  above 
the  superior  cervical  ganglion,  the  post-ganglionic  nerve-fibres 
(i.e.,  the  fibres  coming  off  from  the  cells  of  the  ganglion)  may 
also,  if  the  opportunity  be  favourable  during  regeneration,  ex- 


A   MANUAL  OF  PHYSIOLOGY 

change  their  old  end-organs  for  new  ones  ;  pilo-motor  fibres,  for 
instance,  finding  their  way  into  the  iris  and  becoming  pupillo- 
dilators.  After  excision  of  the  superior  cervical  ganglion  the 
cervical  sympathetic  does  not  recover  its  function.  Accordingly 
the  pre-ganglionic  fibres  cannot  form  direci  functional  con- 
nection with  the  post-ganglionic  fibres,  but  can  become  connected 
with  them  only  indirectly  through  the  ganglion  cells.  Nor  can 
efferent  post-ganglionic  fibres  achieve  regenerative  union  with 
a  cerebro-spinal  (somatic)  motor  nerve,  although  they  can 
themselves  regenerate,  as  has  been  shown,  e.g.,  in  the  case  of  the 
vaso-constrictors  of  the  limbs.  On  the  other  hand,  union 
easily  takes  place  between  pre-ganglionic  fibres  and  efferent 
somatic  fibres,  and  vice  versa.  For  example,  the  cervical 
sympathetic  can  unite  with  the  phrenic  nerve,  and  cause  con- 
traction of  the  diaphragm,  or  with  the  recurrent  laryngeal 
nerve,  and  cause  movement  of  the  vocal  cords,  or  with  the 
spinal  accessory,  and  cause  contraction  of  the  sterno-mastoid 
muscle.  Conversely,  the  phrenic  nerve,  when  united  with  the  cer- 
vical sympathetic,  can,  when  stimulated,  produce  the  usual  effects 
observed  on  exciting  the  latter  nerve  (Langley  and  Ander- 

Although  the  establishment  of  connection  with  the  central 
end  of  the  cut  nerve  is  necessary  for  complete  regeneration,  it 
must  not  be  supposed  that  no  share  whatever  is  taken  in  the 
process  by  the  peripheral  stump.  Even  while  it  remains  com- 
pletely isolated  from  the  central  nervous  system  changes  occur 
which  are  often  described  as  the  third  or  final  stage  of  degenera- 
tion, but  which  are  more  correctly  interpreted  as  forming  a 
stage  in  the  regenerative  cycle.  Spindle-shaped  cells  or  fibres 
with  elongated  nuclei  make  their  appearance,  produced  by  the 
proliferation  of  the  nuclei  of  the  primitive  sheath  already 
described,  and  the  increase  of  the  protoplasm  in  which  these 
nuclei  are  embedded.  These  so-called  axial  strand  fibres 
or  this  hhrillated  protoplasm  ma}7  appear  long  before  the 
remains  of  the  degenerated  axis-cylinder  and  myelin  sheath 
have  been  completely  removed.  It  is  generally  acknowledged 
that  in  the  adult  they  do  not  develop  beyond  this,  so  I 
as  the  peripheral  portion  of  the  nerve  remains  completely  isolated, 
but  neither  do  they  disappear  even  after  a  very  long  interval. 
When  strict  precautions  against  union  with  other  nerve-trunks 
were  taken  the  radial  nerve  of  an  adult  cat  was  found  in  this 
resting-stage  nearly  a  year  and  a  half  after  division,  and  the  same 
was  true  after  two  years  and  a  half  in  a  nerve  divided  in  a  human 
being.  The  fibres  are  incapable  of  being  excited  or  of  conducting 
nerve  impulses.  The  precise  relation  between  these  axial  strand 
fibres  of  the  peripheral  stump  and  the  myelinated  fibres  found 


NERVl  697 

there  alter  regeneration  lias  been  much  debated.  All  are  agreed 
that  nerve-fibrils  sprout  from  the  central  stump,  and  the  weight 
of  evidence  is  in  favour  of  the  long-accept e<i  view  that  it  is  by 
the  growth  of  these  fibrils  along  the  peripheral  stump  thai  the 

new  axons  are  formed,  and  that  all  the  changes  in  the  distal 
portion  of  the  nerve,  however  important  for  directing  and 
perhaps  sustaining  the  growth  of  the  central  fibrils,  are  subsidiary 

to  this.     But  some  maintain  that  the  outgrowing  central  fibrils 

meet  and  unite  with  corresponding  fibrils  sprouting  from  the 

peripheral  stump,  and  that  the  new  axis-cylinders  arise  from 

the  fibrils  of  the  axial  strand.     It  is  said  that  very  shortly  after 

being  brought  into  connection  with  the  central  portion  of  the 

same  or  of  another  nerve  by  careful  suturing  the  spindle  cells 

begin  to  lengthen,  and  form  non-medullated  fibres,  like  those  of 

the  sympathetic.     Four  weeks  after  union  the  afferent  fibres, 

although  still  non-medullated,  are  capable  of  being  stimulated 

mechanically    and    electrically,    and    of    conducting    impulses 

towards  the  centre.     In  about  eight  weeks  they  become  medul- 

lated,  but  at  first  are  of  small  calibre  (Head  and  Ham).     Bethe, 

the  most  strenuous  defender  of  the  inherent  regenerative  power 

of  the  isolated  peripheral  stump  (autogenetic  theory),  has  even 

stated  that  complete  regeneration  occurs  in  young  animals  in 

nerves  entirely  separated  from  their  centres.     The  controversy 

turns  largely  upon  the  precautions  judged  necessary  to  prevent 

the  ingrowth  of  central  fibres.     And  while  it  is  comparatively 

easy  to  make  sure,  by  removing  a  large  part  of  it,  that  the  central 

end  of  the  nerve  under  observation   shall  remain   completely 

unconnected  with  the  peripheral  end,  it  is  often  a  matter  of  the 

greatest  difficulty  to  prevent  the  union  of  the  distal  stump  with 

central  fibres  from  other  sources — e.g.,  from  the  nerves  cut  in 

the  wound.     There  is  no  doubt  that  many  of  the  results  which 

seemed  to  favour  the  autogenetic  theory  were  due  to  this  cause. 

A  fact  of  great  physiological  interest,  and  also  of  practical  im- 
portance, in  connection  with  the  anastomosis  of  nerves  for  the 
relief  of  certain  forms  of  paralysis,  is  the  bifurcation  of  axons  in 
regeneration,  when  the  conditions  are  such  that  the  axons  of  the 
central  stump  are  offered  more  than  one  path  along  which  to 
regenerate.  If,  for  instance,  a  limb  nerve-trunk  containing  motor 
fibres  is  cut,  and  its  central  end  sutured  both  to  its  own  distal  end 
and  to  the  distal  end  of  an  adjacent  nerve-trunk,  the  sum  of  the 
nerve-fibres  in  the  two  distal  trunks  after  regeneration  has  occurred 
is  greater  than  the  number  of  fibres  in  the  central  stump  (Kilvington) . 
That  this  is  due  to  splitting  of  axons  is  shown  by  the  fact  that  an 
axon  reflex  (p.  809)  can  be  elicited  on  dividing  one  of  the  distal 
trunks  and  stimulating  its  central  end  after  complete  separation 
of  the  proximal  or  parent  stem  from  the  central  nervous  system. 
Even  when  the  second  path  offered  to  the  regenerating  motor  axon 


/    WANUA1    OF  PHYSIOLOGY 

is  a  sensory  path,  bifurcation  of  the  axon  occurs,  one  branch  passing 
down  along  the  pre\  Lous  motor  path  to  its  proper  muscular  termina- 
tion, and  the  other  passing  down  the  sensory  path.  Although  there 
is  no  evidence  thai  efferent  fibres  can  unite  with  afferent  fibres, 
a  degenerated  afferent  path  can  therefore  serve  as  a  chemiotactic 
scaffolding  or  guide  for  the  growth  of  regenerating  motor  axons, 
though  not  such  an  efficient  one  as  a  degenerated  motor  path. 
Sensors-  fibres,  however,  cannol  regenerate  along  motor  pal  lis  or 
make  functional  union  with  the  receptive  substance  of  skeletal 
muscle. 

It  is  a  remarkable  fact  that  regeneration  of  the  fibres  of  t  he  central 
nervous  system  either  does  not  in  general  occur,  or  is  exceedingly 
difficult  to  realize.  This  lends  support  to  the  doctrine  of  the 
importance  of  the  neurilemma  in  regeneration,  since  the  neurilemma 
is  absent  from  the  fibres  of  the  brain  and  cord.  It  has,  however, 
been  shown  that  regeneration  of  the  fibres  which  proceed  from  the 
cells  of  the  spinal  ganglia  along  the  posterior  roots  into  the  cord  may 
take  place  after  the  roots  have  been  cut,  so  that  the  normal  refb 
through  the  respiratory,  cardiac,  and  vaso-motor  centres  may  be 
once  more  obtained. 

Degeneration  of  Muscle. — Experimental  section  or,  in  man, 
traumatic  division  or  compression  of  a  nerve  leads  not  only  to 
its  degeneration,  but  ultimately,  if  regeneration  of  the  nerve 
does  not  take  place,  to  degeneration  of  the  muscles  supplied  by 
it  as  well.  The  muscle-fibres  dwindle  to  a  quarter  of  their  normal 
diameter  ;  the  stripes  disappear  ;  the  longitudinal  fibrillation 
lades  out  ;  and  at  length  only  hyaline  moulds  of  the  fibres  are 
left,  filled,  and  separated  by  fatty  granules  and  globules  and 
surrounded  by  engorged  capillaries.  Amidst  the  general  decay, 
the  muscular  fibres  of  the  terminal  '  spindles  '  with  which  the 
afferent  nerves  of  muscles  are  connected,  alone  remain  un- 
changed •  (Sherrington).  Certain  diseases  of  the  cord  which 
interfere  with  the  cells  of  the  anterior  horn  cause  degeneration 
of  motor  nerves,  and  ultimately  of  muscles.  The  motor  nerve- 
endings  degenerate  sooner  than  the  sensory.  Both  may,  under 
suitable  conditions,  regenerate  (Huber). 

Reaction  of  Degeneration.  —Muscles  whose  motor  nerves  have 
been  separated  from  their  trophic  centres  show,  when  a  cert. on 
stage  in  degeneration  has  been  reached,  a  peculiar  behaviour  to 
electrical  stimulation,  called  the  'reaction  of  degeneration.'  To 
the  constant  current  the  muscles  are  more  excitable,  and  the  con- 
traction slower  and  more  prolonged  than  normal.  When  a  current. 
cither  constant  or  induced,  is  passed  through  a  normal  muscle, 
the  muscular  fibres  may  be  stimulated  either  directly,  or  indirectly 
through  the  intramuscular  nerves.  Under  ordinary  conditions  the 
nerves  respond  more  readily  than  the  muscular  fibres,  especially  to 
momentary  stimuli  like  induction  shocks,  and  therefore  the  so-called 
direct  stimulation  of  uncurarized  muscle  is.  as  a  rule,  an  indirect 
stimulation.  When  the  muscle  is  curarized  and  the  nerves  thus 
eliminated,  the  excitability  to  induced  currents  is  found  to  be 
diminished.     The  same  is  ^he  case  in  a  muscle  which  exhibits  the 


VERV1 

reaction  oJ  degeneration  after  section  of  its  motor  nerve,  only  the 
LOSS  "1  excitability  to  induced  currents  is  greater,  and  may  even  be 
complete.  The  closing  anodic  contraction  is  stronger  than  the 
closing  kathodic  the  opposite  oi  the  ordinary  law.  The  nerves 
are  inexcitable  either  to  constant  or  induced  currents.  The  reaction 
ut  degeneration  is  only  obtained  from  paralyzed  muscles  when  the 
paralyzing  lesion  is  situated  in  the  cells  of  the  anterior  horn  from 
which  the  motor  nerves  take  origin,  or  below  that  level.  Acccfrd- 
ingly,  it  is  sometimes  of  use  in  localizing  the  position  of  a  lesion. 
For  instance,  a  group  of  muscles  might  be  paralyzed  by  a  lesion  in 
the  grey  matter  of  the  brain  or  in  the  nerve-fibres  connecting  this 
with  the  grey  matter  of  the  anterior  horn  of  the  cord,  or  in  the 
grey  matter  of  the  anterior  horn  itself,  or  in  the  peripheral  nerve- 
fibres  leading  from  this  to  the  muscles.  In  the  first  two  cases 
the  reaction  of  degeneration  would  be  absent,  although  the  muscles, 
if  the  lesion  was  of  long  standing,  would  be  atrophied  to  some 
extent  ;  in  the  last  two  there  would  be  acute  atrophy  of  the  muscles. 
and  the  reaction  of  degeneration  would  be  obtained. 

Trophic  Nerves. — There  is  no  question  that  nerves  exert 
a  very  important  influence  upon  the  nutrition  of  the  parts 
supplied  by  them,  in  influencing  the  specific  function  of  those 
parts.  So  that  in  this  sense  all  nerves  are  trophic  nerves.  The 
fact  that  the  proper  nutrition  of  nerve-fibres  and  striated 
muscular  fibres  is  dependent  on  their  connection  with  nerve- 
cells  has  been  by  some  writers  generalized  into  the  doctrine 
that  all  tissues  are  provided  with  '  trophic  '  nerves,  which, 
apart  from  any  influence  of  functional  activity,  regulate  the 
nutrition  of  the  organs  they  supply.  But  the  evidence  for  this 
view,  when  weighed  in  the  balance,  is  found  wanting  ;  and  it  may 
be  said  that  up  to  the  present  no  unequivocal  proof,  experimental 
or  clinical,  has  ever  been  given  of  the  existence  of  specific  trophic 
fibres,  anatomically  distinct  from  other  efferent  or  afferent  nerves. 

It  is  true  that  in  various  diseases  and  injuries  of  the  nervous 
system  nutritive  changes  in  the  skin,  and  sometimes  in  the 
bones  and  joints,  are  apt  to  appear.  But  it  is  very  difficult  in 
such  cases  to  disentangle  the  effects  produced  by  accidental 
injuries  acting  on  structures  whose  normal  sensibility  is  lost  or 
lessened,  or  whose  circulation  is  deranged,  from  true  trophic 
changes.  The  most  that  can  be  said  is  that  there  is  some  evidence 
that  the  power  of  the  skin  to  resist  injury,  and  the  capacity  of 
recovering  from  it,  are  diminished  by  interference  with  its  nerve- 
supply,  so  that  a  large  sore  may  result  from  a  trifling  lesion, 
and  healing  may  be  slow  and  difficult.  Experimentally  it  has 
been  found  that  division  of  the  trigeminus  nerve  within  the  skull 
is  sometimes  followed  by  cloudiness  of  the  cornea,  going  on  to 
ulceration,  and  ultimately  inflammation  and  destruction  of  the 
eyeball.  Ulcers  also  form  on  the  lips  and  on  the  mucous  mem- 
brane of  the  mouth  and  gums  ;  and  the  nasal  mucous  membrane 


;,„,  I    \i  INU  II    OF  PHYSIOLOGY 

on  the  side  corresponding  to  the  divided  nerve  becomes  inflamed. 
But  in  this  case  the  sensibility  of  the  eye  is  lost,  and  reflex 
closure  of  the  eyelids  ceases  to  prevent  the  entrance  oi  foreign 
1  Holies.  The  animal  is  no  longer  aware  of  the  contai  I  oi  particles 
of  dust  or  bits  of  straw  or  accumulated  secretion  with  the  con- 
junct iva,  and  makes  no  effort  to  remove  them.  The  lips,  being 
also  without  sensation,  are  hurt  by  the  teeth,  particularly  as 
the  muscles  of  mastication  on  the  side  of  the  divided  nerve  are 
paralyzed,  and  decomposed  food,  collecting  in  the  mouth,  and 
inhaled  dust  in  the  nose,  will  tend  still  further  to  irritate  the 
mucous  membranes.  There  is  thus  no  more  need  to  assume 
the  loss  of  unknown  trophic  influences  in  order  to  explain  the 
occurrence  of  the  ulcerative  changes  than  their  is  to  explain 
the  production  of  ordinary  bed-sores,  bunions  or  corns  on  parts 
peculiarly  liable  to  pressure.  And,  as  a  matter  of  fact,  if  the 
eye  be  artificially  protected,  after  section  of  the  trigeminal  nerve, 
the  ophthalmia  either  does  not  occur  or  is  much  delayed. 

In  man,  too,  a  case  has  been  recorded  in  which  both  the  huh 
and  the  third  nerves  were  paralyzed.  The  eye  was  still  shielded 
by  the  contraction  of  the  orbicularis  oculi  supplied  by  the 
seventh  nerve,  as  well  as  by  the  drooping  of  the  upper  eyelid 
that  accompanies  paralysis  of  the  third.  It  remained  perfectly 
sound  for  many  months,  till  at  length  the  tumour  at  the  base  ol 
the  brain  which  had  affected  the  other  nerves  invoked  the 
seventh,  too.  The  eye  was  now  no  longer  completely  closed; 
inflammation  came  on,  and  vision  was  soon  permanently  lost 
(Shaw).  In  another  case  a  patient  lived  for  seven  years  with 
complete  paralysis  of  the  fifth  nerve,  vet  the  eye  remained  free 
from  disease  and  sight  was  unimpaired  (Gowers). 

The  so-called  '  trophic  '  effects  following  division  of  both  vagi 
we  have  already  discussed  (p.  236)  so  far  as  they  are  concerned 
with  the  respiratory  system.  The  degenerative  changes  some- 
times seen  in  the  heart  are  perhaps  due  to  its  being  overworked 
in  the  absence  of  nervous  restraint  on  its  functional  activity. 
The  nutritive  alterations  in  muscles  and  salivary  glands  after 
section  of  motor  and  secretory  nerves  seem  to  depend  in  pari 
on  functional  and  vaso-motor  changes.  In  the  paralyzed  muscles 
nutrition  is  not  only  interfered  with  in  consequence  of  their 
inactivity,  as  would  be  the  case  even  if  the  paralysis  wire  due 
to  a  lesion  above  the  level  of  the  anterior  cornual  cells,  buf  the 
already  poorly  nourished  fibres  are  continually  pressed  upon  by 
the  capillaries,  which  are  dilated  owing  to  the  division  oi  the 
vaso-motor  nerves.  The  degeneration  must  also  be  in  part 
ascribed  to  the  loss  of  a  tonic  influence  exerted  on  the  muscles 
by  the  motor  cells  of  the  spinal  cord,  through  the  ordinary  motor 


NERVE  701 

nerves  (p.  813).  When  all  allowance  has  been  made  Eoi  tl 
factors,  the  rapid  and  characteristic  degeneration  of  the  striated 
muscles,  alter  their  connection  with  the  central  nervous  system  i^ 
severed,  1-  -till  inexplicable,  except  on  the  assumption  that  their 
nutrition  is  specially  related  to  the  integrity  of  their  efferent 
nerves.  In  other  words,  it  is  necessary  to  suppose,  not,  indeed, 
that  distinct  trophic  nerves  exist  for  the  muscles,  but  that  an 
influence  or  impulses,  which  can  be  termed  trophic  or  nutritive, 
do  normally  pass  out  to  them  from  the  spinal  cord  along  their 
motor  nerves. 

Section  of  the  cervical  sympathetic  in  young  rabbits  and  dogs 
increases  the  growth  of  the  ear  and  of  the  hair  on  the  same 
side.  But  it  is  impossible  to  separate  these  consequences  from 
the  vaso-motor  paralysis  ;  and  the  same  is  true  of  the  hyper- 
trophy following  section  of  the  vaso-motor  nerves  of  the  cock's 
comb  and  of  the  nerves  of  the  bones.  After  section  of  the  superior 
laryngeal  the  vocal  cord  on  the  side  of  the  section  is  at  once 
rendered  motionless,  and  remains  so,  but  the  muscles,  notwith- 
standing their  inaction,  do  not  degenerate.  And  Mott  and 
Sherrington  have  found  that,  although  section  of  the  posterior 
roots  in  monkeys  is  followed  after  a  time  (three  weeks  to  three 
months)  by  ulceration  over  certain  portions  of  the  foot,  no  corre- 
sponding lesions  occur  in  the  hand.  They  believe,  therefore, 
that  the  lesions  are  not  due  to  the  withdrawal  of  a  reflex  trophic 
tone,  but  are  accidental  injuries  in  positions  specially  exposed 
to  mechanical  or  microbic  insults. 

One  of  the  best  examples  of  interference  with  the  proper 
nutrition  of  a  part  produced  by  a  lesion  in  the  nerves  supplying 
it  is  an  eruption  (herpes  zoster),  limited  to  the  skin  supplied  by 
the  nerve-fibres  coming  from  one  or  more  spinal  ganglia,  and 
'depending  on  an  (infectious)  inflammatory  change  in  the  ganglia. 
It  has  been  suggested  that  the  vesicles  are  formed  either  because 
the  passage  of  afferent  impulses  normally  concerned  in  the 
nutrition  of  the  skin  is  interfered  with,  or  because  the  skin  is 
bombarded  by  antidromic  (p.  165)  impulses  discharged  from  the 
inflamed  ganglia.  But  an  alternative  hypothesis  is  that  a  toxine 
spreads  out  along  the  nerves  from  the  ganglia,  just  as  in  traumatic 
tetanus  the  toxine  is  known  to  pass  in  the  opposite  direction 
along  the  nerves  from  the  seat  of  injury  to  the  central  nervous 
system. 

Omitting  the  group  of  '  trophic  '  nerves,  and  the  even  more 
problematical  '  thermogenic  '  fibres  (which  some  have  sup- 
posed to  preside  over  the  production  of  heat,  and  therefore  to 
assist  in  the  regulation  of  the  temperature  of  the  body,  but  of 
whose  existence  as  distinct   and  specific  nerve-fibres  with  no 


702 


AM  INU  XL  OF  PHYSIOLOGY 


other  function  there  is  not  the  slightest  proof),  peripheral  nerves 
miy  be  classified  as  follows  : 


Centripetal 

or   afferent-^ 

fibres 


I.  Nerves  of  special  sensation 


2.  Nerves  of  general  sensation 


Possibly  nerves  other  than 
those  included  under  i 
and  2,  concerned  in 
reflex  changes  in 


Centrifugal 

or   efferent^ 

fibres 


i.  Motor  nerves  for- 


/Smell. 
I  Taste. 
I  Hearing. 
ISight. 

'Touch  (light  touch). 
Pressure    (perhaps    in- 
cluding the  nerves  of 
musculnr  sense). 
Warmth— Cold. 
Pain. 
rCalibre  of  small  arteries 

(pressor,  depressor). 
Action  of  heart. 
Respiratory    move- 
ments. 
Visceral  movements. 
Glandular  secretion. 
Ordinary  skeletal 
muscles. 
Skelel    1  muscles 
Visceral 


Vascular 


i  Vaso-constrictor 
-!  Cardio 


Erector     muscles 
motor  fibres). 
I  Visceral  muscles 


augmen- 
tor. 
of    hairs 


(pilo- 


2.  Inhibitory  nerves  for-; 

3.  Secretory  nerves 


Vascular 


(  Vaso-dilator. 
-.  Cardio  -  inhi- 
l      bitory. 


*   It  is  not  known  whether  the  afferent  portion  of  a  retiex  arc  is  ah 
composed   of   fibres   included   in   the   first   two   categories,   although   un- 
doubtedly in  some  cases  it  is. 


PRACTICAL  EXERCISES  ON  CHAPTERS    IX.   AM)   X. 

1 .  Difference  of  Make  and  Break  Shocks  from  an  Induction 
Machine. — Connect  a  Daniell  or  other  cell  B  (p.  015)  with  the  two 
upper  binding-screws  of  the  primary  coil  P,  and  interpose  a  spring 
key  K  in  the  circuit.  Connect  a  pair  of  electrodes  with  the  binding- 
screws  of  the  secondary  coil  (Fig.  258). 

Electrodes  can  be  very  simply  made  by  pushing  copper  wires 
through  two  glass  tubes,  filling  the  ends  of  the  tubes  with  sealing- 
wax,  and  binding  them  together  with  waxed  thread.  The  projecting 
points  may  be  filed,  and  the  nerve  laid  directly  on  them,  or  they 
may  be  tipped  .with  small  pieces  of  platinum  wire  soldered  on. 

(a)  Push  the  secondary  away  from  the  primary,  until  no  shock  can 
be  felt  on  the  tongue  when  the  current  from  the  battery  is  made  or 
broken    with   the    key.     Then    bring   the    secondary    gradually    up 


PRA(  I  HAL    EXERi  ISES  703 

towards  the  primary,  testing  at  every  new  position  whethei  thi  shock 
is  perceptible.  It  will  be  felt  first  ;il  break.  If  the  secondary  is 
pushed  still  further  up,  aTshock  will  be  felt  both  at  make  and  at 
break.  h'rom  this  we  learn  that  for  sensory  nerves  the  break  shock 
is  stronger  than  the  make.  The  same  can  easily  be  demonstrated 
for  motor  nerves  and  for  muscle. 

(b)  Smoke  a  drum  and  arrange  a  myograph,  as  shown  in  Fig.  261. 
But  omit  the  brass  piece  F,  and  do  not  connect  the  primary  through 
the  drum,  as  there  shown,  but  connect  it  as  in  Fig.  258.  Pith  a  frog 
(brain  and  cord),  and  make  a  muscle-nerve  preparation. 

To  make  a  Muscle-nerve  Preparation. — Hold  the  frog  by  the  hind 
legs  back  upwards  ;  the  front  part  of  the  body  will  hang  down, 
making  an  angle  with  the  posterior  portion.  With  strong  scissors 
divide  the  backbone  anterior  to  this  angle,  and  cut  away  all  the 
front  portion  of  the  body,  which  will  fall  down  of  its  own  weight. 
.Make  a  circular  incision  at  the  level  of  the  tendo  Achillis,  and  another 
at  the  lower  end  of  the  femur,  through  the  skin.  The  sciatic  nerve 
must  now  be  dissected  out,  as  follows  :  Remove  the  skin  from  the 
thigh,  and,  holding  the  leg  in  the  left  hand,  slit  up  the  fascia  which 


Fig.  258. — Arrangement  of  Coil  for  Single  Shocks. 

connects  the  external  and  internal  groups  of  muscles  on  the  back 
of  the  thigh.  Complete  the  separation  with  the  two  thumbs.  Cut 
through  the  iliac  bone,  taking  care  that  the  blade  of  the  scissors  is 
well  pressed  against  the  bone,  otherwise  there  is  danger  of  severing 
the  sciatic  plexus.  Now  divide  in  the  middle  line  the  part  of  the 
spinal  column  which  remains  above  the  urostyle.  A  piece  of  bone 
is  thus  obtained  by  means  of  which  the  nerve  can  be  manipulated 
without  injury.  Seize  this  piece  of  bone  with  the  forceps,  and 
carefully  free  the  sciatic  plexus  and  nerve  from  their  attachments 
right  down  to  the  gastrocnemius  muscle,  taking  care  not  to  drag 
upon  the  nerve.  The  muscles  of  the  thigh  will  contract,  as  the 
branches  going  to  them  are  cut.  This  is  an  instance  of  mechanical 
stimulation.  Now  pass  a  thread  under  the  tendo  Achillis,  tie  it, 
and  divide  the  tendon  below  it.  Strip  up  the  tube  of  skin  that  covers 
the  gastrocnemius,  as  if  the  finger  of  a  glove  Avere  being  taken  off. 
Tear  through  the  loose  connective  tissue  between  the  muscle  and 
the  bones  of  the  leg,  and  divide  the  latter  with  scissors  just  below 
the  knee.     Cut  across  the  thigh  at  its  middle. 


7<>4  /    1/  INUAL  OF  PHYSIOLOGY 

Fix  the  preparation  on  the  cork  plate  of  the  myograph  by  a  pin 
passed  through  the  cartilaginous  lower  end  of  the  Eemur,  and  attach 
i  in-  t  bread  to  the  upright  arm  of  the  lever  by  one  ot  the  h< >les  in  it. 
I  tang  not  Ear  from  the  axis  by  means  of  a  hook  a  small  leaden  weight 
(5  to  10  grammes)  on  the  arm  of  the  lever  which  carries  the  writing- 
point,  and  move  the  myograph  plate  or  the  muscle-nerve  preparation 
until  this  arm  is  just  horizontal.  Fasten  the  electrodes  from  the 
secondary  coil  on  the  cork  plate  with  an  indiarubber  band  ;  lay  the 
nerve  on  them  ;  and  cover  both  muscle  and  nerve  with  an  arch  oi 
blotting-paper  moistened  with  physiological  salt  solution,  taking  eare 
that  the  blotting-paper  does  not  touch  the  thread.  ( >r  put  the  pre- 
paration in  a  moist  chamber*  (Fig.  204,  p.  730).  Adjust  the  writing- 
point  to  the  drum.  Begin  with  such  a  distance  between  the  coils 
that  a  break  contraction  is  just  obtained  on  opening  the  key  in  the 
primary  circuit,  but  no  make  contraction.  The  lexer  will  trace  a 
vertical  line  on  the  stationary  drum.  Read  off  on  the  scale  of  the 
induction  machine  the  distance  between  the  coils,  and  mark  this  on 
the  drum.  Now  allow  the  drum  to  move  a  little,  still  keeping  the 
writing-point  in  contact  with  it  ;  then  push  up  the  secondary  coil 
1  centimetre  nearer  the  primary,  and  close  the  key.  If  there  is  a 
contraction,  let  the  drum  move  a  little  before  opening  the  key  again, 
so  that  the  lines  corresponding  to  make  and  break  may  be  separated 
from  each  other.  If  there  is  still  no  contraction  at  make,  go  on 
moving  the  secondary  up,  a  centimetre  (or  less)  at  a  time,  till  a  make 
contraction  appears.  When  the  coils  are  still  further  approximated, 
the  make  may  become  equal  in  height  to  the:  break  contraction, 
both  being  maximal — i.e.,  as  great  as  the  muscle  can  give  with  any 
single  shock  (Fig.  259). 

(c)  Attach  a  thin  insulated  copper  wire  to  each  terminal  of  the 
secondary.  Loop  the  bared  end  of  one  of  the  wires  through  the 
tendo  Achillis,  and  coil  the  other  round  the  pin  in  the  femur,  so 
that  the  shocks  will  pass  through  the  whole  length  of  the  muscle. 
Repeat  the  experiment  of  (6),  with  direct  stimulation  of  the  muscle. 

2.  Stimulation  of  Nerve  and  Muscle  by  the  Voltaic  Current. — {a) 
Connect  a  Danicll  cell  through  a  key  with  a  pair  of  electrodes  on 
which  the  nerve  of  a  muscle-nerve  preparation  lies.  Observe  that 
the  muscle  contracts  when  the  current  is  closed  or  broken,  but  not 
during  its  passage. 

Connect  the  cell  with  a  simple  rheocord,  as  shown  in  Fig.  26o,  so 
that  a  twig  of  the  current  of  any  desired  strength  may  be  sent  through 
the  nerve.  As  the  strength  of  the  current  is  decreased  by  moving 
the  slider  S,  it  will  be  found  that  it  first  becomes  impossible  to  obtain 
a  contraction  at  break.  The  current  must  be  still  further  reduced 
before  the  make  contraction  disappears,  for  the  closing  of  a  galvanic 
stream  is  a  stronger  stimulus  than  the  breaking  of  it.  The  break 
or  make  contraction  obtained  by  stimulating  a  nerve  with  an  in- 

t 

*  Porter's  moist  chamber  is  found  in  many  laboratories,  and  is  very 
convenient.    It  consists  of  a  porcelain  plate,  around  which  runs  a  groove. 

\  bell-shaped  glass  Cover,  which  can  he  lilted  ofl  at  will,  rests  in  the  groove. 
The  femur  ol  the  muscle-nerve  preparation  is  fixed  in  a  small  clamp, 
composed  of  a  split  screw  on  which  moves  a  nut.  By  means  oi  the  nut 
the  clamp  is  tightened  en  the  lemur.  The  gastrocnemius  hangs  vertically 
down,  the  thread  on  the  tendo  Achillis  passing  through  a  hole  in  the 
porcelain  plate  to  a  lever  separately  supported  on  the  same  stand  as  the 
moist  chamber.  A  piece  ot  wet  blotting-paper  fixed  inside  the  cover 
keeps  the  air  in  the  chamber  saturated. 


PR  ICTICAL  EXERCISES 


705 


duction-machine  must  no1  be  confused  with  the  break  or  make 
contraction  caused  l>v  the  voltaic  current.  In  the  case  of  the 
induction  machine,  the  break  or  make  applies  merely  to  what  is  done 
in  the  primary  circuit,  no1  to  what  happens  to  the  current  actually 
passing  through  the  nerve.  I  he  current  induced  in  the  se<  ondary  a1 
make  of  the  primary  circuit  is.  of  course,  both  made  and  broken  in 
ill-  nerve     made  when  it  begins  to  flow,  broken  when  the  How  is 


MB      MB       MB 
22        20        J8 


Fig.    259. — Contractions   caused   by   Make   and   Break   Shocks   from  an 
Induction  Machini  . 

M,  make,  B,  break,  contractions.     The  numbers  give  the  distance  between  t..c 
primary  and  secondary  coils  in  centimetres. 

over  ;  the  shock  induced  at  break  of  the  primary  is  also  made  and 
broken  in  the  nerve.  And  although  make  and  break  of  the  actual 
stimulating  current  come  very  close  together,  the  real  make,  here, 
too,  is  a  stronger  stimulus  than  the  real  break. 

(b)  Repeat  (a)  with  the  muscle  directly  connected  to  the  cell  by 
thin  copper  wires,  or.  better,  unpolarizable  electrodes  (p.  625). 

3.  Ciliary  Motion. — Cut  away  the  lower  jaw  of  the  same  frog,  and 


Fig.    260. — Simple    Rheocord   arranged   to   send   a   Twig  of  a   Current 
through  a  Muscle   or   Nerve. 

B,  battery  ;  R,  rheocord  wire  (German  silver)  ;  S,  slider  formed  of  a  short  piece 
of  thick  indiarubber  tubing  filled  with  mercury  ;  K.  spring  key  ;  W,  W,  wires 
connected  with  electrodes. 


place  a  small  piece  of  cork  moistened  with  physiological  salt  solution 
(°'75  Per  cent.)  on  the  ciliated  surface  of  the  mucous  membrane 
covering  the  roof  of  the  mouth.  It  will  be  moved  by  the  cilia  down 
towards  the  gullet.  Lay  a  small  rule,  divided  into  millimetres,  over 
the  mucous  membrane,  and  measure  with  a  stop-watch  the  time  the 
piece  of  cork  takes  to  travel  over  10  millimetres.  Then  pour  salt 
solution  heated  to  300  C.  on  the  ciliary  surface,  rapidly  swab  with 
blotting-paper,  and  repeat  the  observation.     The  piece  of  cork  will 

45 


/     MANl  .//    OF  1'IIYSIOI.OGY 

now  be  moved  more  quickly  than  before,  unless  the  sail  solution  has 
been  so  hoi  as  to  in  jure  I  he  cilia. 

4.  Direct  Excitability  of  Muscle — Action  of  Curara.  Pith  the 
brain  oi  .1  frog,  and  prevent  bleeding  by  inserting  a  piece  <>f  match. 
Expose  the  scial  Lc  nerve  in  the  thigh  on  one  side.  Carefully  separate 
M  .  tor  a  length  of  half  an  inch,  from  the  tissues  in  which  it  lies.  I  'ass 
a  strong  thread  under  the  nerve,  and  tie  il  tightly  round  the  limb, 
excluding  the  nerve.  Now  inject  into  the  dorsal  or  ventral  lymph- 
sa<  a  few  drops  of  a  1  per  cent,  curara  solution.  A.s  soon  as  paralysis 
is  complete,  make  two  muscle-nerve  preparations,  isolating  the 
sciatic  nerves  righ.1  up  to  the  vertebral  column.  Lay  their  upper 
en  1  Is  on  electrodes  and  stimulate  ;  the  muscle  oi  the  ligatured  limb 
will  contract.  This  proves  that  the  nerve-trunks  are  no1  paralyzed 
by  curara,  since  the  poison  has  been  circulating  in  them  above  the 
ligature.  The  muscle  of  the  leg  which  was  not  ligatured  will  contract 
if  it  be  stimulated  directly,  although  stimulation  of  its  nerve  has  no 
effect.  The  ordinary  contractile  substance  of  the  muscular  fibres, 
accordingly,  is  not  paralyzed.  The  seat  of  paralysis  must  therefore 
be  some  structure  or  substance  physiologically  intermediate  between 
the  nerve-trunk  and  the  general  contra  ct  ile  subst  auce  ()|  t  he  muscular 
fibres  (p.  634). 

5.  Graphic  Record  of  a  Single  Muscular  Contraction  or  Twitch. — 
Pith  a  frog  (brain  and  cord),  make  a  muscle-nerve  preparation,  and 
arrange  it  on  the  myograph  plate,  as  in  1  [b).  Lay  the  nerve  on 
electrodes  con  net  ted  with  the  secondary  coil  of  an  induction  machine 
arranged  for  single  shocks.  Introduce  a  short-circuiting  key  (Fig.  2  1  5, 
p.  626)  between  the  electrodes  and  the  secondary  coil,  and  a  spring 
key  in  the  primary  circuit.  (lose  the  short-circuiting  key,  and 
then  press  down  the  spring  key  with  the  finger.  Let  the  drum  off 
(fast  speed)  ;  the  writing-point  will  trace  a  horizontal  abscissa  line. 
Open  the  short-circuiting  key,  and  then  remove  the  finger  from  the 
spring  key.  The  nerve  receives  an  opening  shock,  and  the  muscle 
traces  a  curve.  Now  adjust  the  writing-point  of  an  electrical 
tuning-fork  (Fig.  261),  vibrating,  say,  100  times  a  second,  to  the 
drum,  and  take  a  time-tracing  below  the  muscle-curve.  Stop  the 
drum,  or  take  off  the  writing-point,  the  moment  the  time-tracing  has 
completed  one  circumference  of  the  drum,  so  that  the  trace  may  not 
run  over  on  itself.  Cut  off  the  drum-paper,  write  on  it  a  brief 
description  of  the  experiment,  with  the  time-value  of  each  vibration 
of  the  fork,  the  date,  and  the  name  of  the  maker  of  the  tracing,  and 
then  varnish  it.  An  exactly  similar  tracing  can  be  obtained  by 
directly  stimulating  the  muscle  (curarized  or  not). 

6.  Influence  of  Temperature  on  the  Muscle-curve.  Pith  a  frog 
(brain  and  cord),  make  a  muscle-nerve  preparation,  and  arrange  it 
on  a  myograph.  Lay  the  nerve  on  electrodes  connected  through  a 
short-circuiting  key  with  the  secondary  coil  of  an  induction-machine, 
or  connect  the  muscle  directly  with  the  key  by  thin  copper  wires. 
Take  a  Daniell  cell,  connect  one  pole  through  a  simple  key  with 
one  of  the  upper  binding-screws  of  the  primary  coil,  and  the  othei 
pole  with  the  metal  oi  the  drum.  A  wire,  insulated  from  the 
drum,  but  clamped  on  the  vertical  part  oi  its  support,  and  with  its 
bare  did  projecting  so  as  to  make  contact  with  a  strip  of  brass 
fastened  on  the  spindle,  is  (  onnected  with  the  other  upper  terminal 
of  the  primary  (Fig.  261).  At  each  revolution  of  the  drum  the 
primary  cir<  ml  is  mule  and  broken  once  as  the  strip  of  brass  brushes 
the  projei  tin"  end  of  the  wire.      The  object  of  this  arrangement  is  to 


/'/.'  /C7  IC.11     I  XI  h'CISI  s 


ensure  that  when  the  writing  poini  oi  the  myograph  lever  has  been 
once  adjusted  to  the  drum,  successive  stimuli  will  cause  contra,  lions. 


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the  curves  of  which  all  rise  from  the  same  point.  Close  the  key  in 
the  primary,  set  the  drum  off  (fast  speed),  open  the  short-circuiting 
key,  and  as  soon  as  the  muscle  has  contracted  once,  close  it  again. 

45— 2 


;..s  ./   .1/  I  \ru    OF  PHYSIOLOGY 

Now  stop  the  drum,  mark  with  a  pencil  the  position  of  the  fe<  t  <>\  the 
stand  carrying  the  myograph  plate,  take  the  writing-poin1  ofl  the 
drum,  ami  surround  the  muscle  with  pounded  ice  or  snow.  After  a 
i  ouple  ot  rninutes  brush  away  any  i<  e  which  could  binder  tin-  move- 
ment oi  iln-  muscle, rapidly  replace  the  stand  in  exactly  its  original 
position,  with  the  writing-point  on  the  drum,  and  take  another 
tracing.  Again  take  of]  the  writing-point,  and  remove  all  unmelted 
ice  or  snow.  Willi  a  fine-pointed  pipette  irrigate  the  muscle  with 
physiological  sail  solution  at  300  ('..  and  quickly  take  another 
tracing.  Then  put  on  a  time-tracing  with  tin-  electrii  -I  tuning- 
fork.      Fig.  233,  p.  646,  show  s  a  series  of  <  an  es  1  .lit, lined  in  this  ■ 

7.  Influence  of  Load  on  the  Muscle-curve. — Arrange  everything 
as  in  6.     Take  a  tracing  firsl  with  the  lever  alone,  then  with  a  weight 
of  10  grammes,  then  with  50,  100.  200,  and  500  grammes  (Fig 
p.  046). 

S.  Influence  of  Fatigue  on  the  Muscle-curve.  Arrange  as  in  7. 
but  leave  on  the  same  weight  (say  [o  grammes)  all  the  tune.  Place 
the  nerve  on  the  electrodes.  Leave  the  short-circuiting  key  open. 
The  nerve  will  be  stimulated  ai  ea<  h  revohrl  i<  »n  1  it  t  he  drum,  and  the 


Fig.  262. — Arrangemeni   for  Studying  Voluntary  Muscular  Fatigue. 

writing-point  will  trace  a  series  of  curves,  which  become  lower,  and 
especially  longer,  as  the  preparation  is  fatigued.  Two  or  four 
curves  can  be  taken  at  the  same  time,  if  both  ends  of  one  or  of  two 
brass  slips  be  arranged  so  as  to  make  contact  with  the  projecting 
wire  at  an  interval  of  a  semicircumference  or  quadrant  of  the  drum 
(Fig.  261).     (For  specimen  curve,  see  Fig.  241,  p.  6 

9.  Seat  of  Exhaustion  in  Fatigue  of  the  Muscle-nerve  Preparation 
for  Indirect  Stimulation.  When  the  nerve  of  a  muscle-nerve  prepara- 
tion has  been  stimulated  until  contraction  no  longer  occurs,  tin 
muscle  can,  under  ordinary  conditions,  be  made  to  contract  In- 
direct stimulation.  The  seat  of  exhaustion  is,  therefore,  not  the 
general  contractile  substance  of  the  muscular  fibres  themselves.  To 
determine  whether  it  is  the  nerve-fibres  or  some  structure  or  sub- 
stance intermediate  between  them  and  the  ordinary  contractile 
substance  of  the  muscle,  perform  the  following  experiments  : 

(a)  Pith  a  frog;  make  two  muscle-nerve  |  'reparations  ;  arrange 
them  both  on  a  myograph  plate,  which  has  two  lexers  connected 
w  it  h  it.  Attach  each  of  the  muscles  to  a  lexer  in  the  usual  wax-,  and 
lax-  both  nerves  side  by  side  on  the  same  pair  of  electrodes.  Cover 
with  moist  blotting-paper.      The  electrodes  are  connected  with  the 


PR  (<  in    \i    I  XERC1SI  S  709 

secondary  oi  an  induction  machine  arranged  foi  tetanus.  With  a 
camel's  nair  brush  moisten  one  oi  the  nerves  between  the  ele<  tro 
and  the  muscle  with  a  mixture  oi  equal  parts  of  ether  and  al<  ohol, 
diluted  with  twice  its  volume  of  water,  to  abolish  the  conductivity. 
(  >i  put  the  mixture  in  a  small  bottle,  in  whi<  h  dips  a  piei  e  oi  filter- 
paper.  The  projecting  end  of  the  filter-paper  is  pointed,  and  the 
nerve  is  laid  on  the  point.  As  sunn  as  ri  is  possible  to  stimulate 
the  nerves  withoui  obtaining  contraction  in  this  muscle,  proceed  to 
tetanize  both  nerves  till  the  coni  rad  ing  muscle  is  exhausted.  If  the 
other  muscle  begins  to  twitch  during  the  stimulation,  more  of  the 
etlur  mixture  must  be  painted  on  the  nerve.  As  soon  as  the  stimula- 
tion ee.ises  to  cause  contraction  in  the  non-etherized  preparation, 
wash  off  the  mixture  from  the  other  nerve  with  physiological  salt 
solution,  and  soon  contraction  may  be  seen  to  take  place  in  the 
muscle  of  this  preparation.  This  shows  that  the  nerve-trunk  is 
still  excitable.  Now.  both  nerves  have  been  equally  stimulated, 
and  therefore  the  exhaustion  in  the  non-etherized  preparation  was 
not  due  to  fatigue  of  the  nerve-fibres,  but  of  something  between  them 
and  the  contractile  substance  of  the  muscle. 

10.  Seat  of  Exhaustion  in  Fatigue  for  Voluntary  Muscular  Con- 
traction. —Support  the  arm.  extensor  surface  downwards,  on  a  rest 
such  as  that  shown  in  Fig.  J<>_>.  or  Fig.  _•  |".  p.  650,  and  connect 
the  middle  finger  of  one  hand,  by  means  oi  a,  string  passing  over 
a  pulley  on  the  edge  of  a  table,  with  a,  weigh!  of  ■;  or  |  kilos.  The 
string  is  attached  to  the  linger  by  a.  leather  collar  surrounding  the 
second  phalanx  of  the  finger,  but  allowing  free  movements  of  the 
joints.  The  extent  of  the  vertical  movements  of  the  string  (and 
therefore  the  work  done!  may  be  registered  on  a  drum  by  a  writing- 
point  connected  with  it.  the  whole  arrangement  forming  what  is  called 
an  crgograpli.  Two  collar  electrodes  (strips  of  copper  covered  with 
cotton -wool  soaked  in  salt  solution,  and  bent  to  a  circular  form)  arc 
placed  on  the  forearm,  and  connected  through  a  short-circuiting 
key  with  the  secondary  coil  of  an  induction  machine  arranged  for 
tetanus  (p.  184),  and  having  a  battery  of  two  or  three  good  dry  cells 
or  of  four  or  five  Daniell  cells,  coupled  in  series,*  in  its  primary 
circuit.  The  middle  finger  is  now  made  to  raise  the  weight  re- 
peatedlv  bv  vigorous  contractions  of  the  flexor  muscles  until  at 
length  a  failure  occurs.  At  this  moment  the  short-circuiting  key  is 
opened,  and  the  flexor  muscles  stimulated  electrically.  They  again 
contract,  and  raise  the  weight,  therefore  the  seat  of  exhaustion  in 
voluntary  muscular  effort  is  not  usually  in  the  ordinary  contractile 
substance  of  the  muscles.  That  it  is  not  usually  in  the  nerves 
may  be  shown  by  inducing  fatigue  of  the  finger  for  voluntary 
contraction  in  the  same  way,  and  then  stimulating  the  median  nerve 
at  the  bend  of  the  elbow  by  sponge  electrodes.  The  usual  seat  of 
fatigue  for  voluntary  muscular  contraction  must  therefore  be  in  the 
spinal  cord  or  brain. 

11.  Influence  of  Veratrine  on  Muscular  Contraction. — Arrange  a 
drum  as  in  Fig.  261.  Pith  a  frog  (brain  only),  expose  the  sciatic 
nerve  in  one  thigh,  and  isolate  it  for  \  inch  from  the  surrounding 
tissues.  Pass  under  it  a  strong  thread,  and  ligature  everything 
except  the  nerve.  Now  inject  into  the  dorsal  or  ventral  lymph-sac 
a  few  drops  of  01  per  cent,  solution  of  sulphate  of  veratrine.  In  a 
few  minutes  make  two  muscle-nerve  preparations  from  the  posterior 
limbs.     First  put  the  preparation  from  the  unligatured  limb  on  the 

*  I.e.,  the  copper  of  one  cell  connected  with  the  zinc  of  the  next. 


;io  i  MANUA1    OF  rilYsiOLOGY 

myograph  plate.  Lay  the  nerve  on  elei  trodes  connected  through  a 
sliorl  me  uitin^  \n\  with  the  secondary  <>f  .in  induction  machm>- 
arranged  as  in  Fig.  261.     Put  the  writing-point  on  the  drum  and  set 

it  off  (fast  speed).  Open  the  short-cir<  airing  key  till  the  nerve  has 
been  once  stimulated,  then  close  it  again.  The  curve  obtained 
differs  from  a  normal  curve,  in  that  the  period  of  descent  (relaxation) 
is  exceedingly  prolonged.  Now  connect  the  preparation  from  the 
ligatured  limb  with  the  lever,  and  lake  a  tracing  of  a  single  con- 
traction. Put  on  a  time -tracing  with  the  electrical  tuning-fork 
(see  Figs.  243,  245,  pp.  653,  055). 

i_'.  Measurement  of  the  Latent  Period  of  Muscular  Contraction. — ■ 
(r)  For  this  the  drum  must  travel  at  a  faster  speed  than  usual. 
The  arrangement  for  automatic  stimulation  described  in  Experi- 
ment 6  (p.  70(0  may  be  employed.  Or  an  electro-magnetic  signal 
may  be  connected  in  the  primary  circuit  of  the  induction  cod  so 
that  when  the  primary  is  closed  or  opened  the  writing-point  of 
the  signal  moves.  Arrange  the  writing-point  of  the  signal  on 
tin-  drum  in  the  same  vertical  line  as  the  writing-point  of  the 
muscle  lever,  and  in  the  same  line  place  the  writing-point  of  a 
vibrating  electric  tuning-fork.  The  coil  is  adjusted  for  single  opening 
shocks  as  in  Experiment  5  (p.  706).  Pith  a  frog,  and  make  a  muscle- 
nerve  preparation.  Arrange  it  on  the  myograph  plate.  The  muscle, 
or  the  nerve  very  near  the  muscle,  is  to  be  excited  by  a  single  opening 
shock  while  the  drum  is  moving.  When  the  curve  has  been  traced 
the  latent  period  is  got  by  drawing  a  vertical  line  through  the  point 
at  which  the  curve  just  begins  to  rise  from  the  abscissa  line,  and 
another  through  the  signal  mark.  The  number  of  vibrations  of  the 
tuning-fork  included  between  these  two  verticals  gives  the  latent 
period. 

Or  (2)  use  the  spring  myograph  (Fig.  228,  p.  643),  raising  it  on 
blocks  of  wood.  Smoke  the  glass  plate  over  a.  paraffin  flame,  or  cover 
it  with  paper,  and  smoke  the  paper.  Connect  the  knock-over  key  of 
the  myograph  with  the  primary  circuit  of  an  induction  coil.  Arrange 
a  muscle-nerve  preparation  on  the  myograph  plate.  Place  electrodes 
below  the  nerve  as  near  the  muscle  as  possible,  and  connect  by  a 
short-circuiting  key  with  the  secondary.  Bring  the  writing-point  in 
contact  witli  the  smoked  surface  of  the  spring  myograph,  so  as  to 
get  the  proper  pressure.  Sec  that  the  writing-point  of  the  tuning- 
fork  is  in  the  right  position  for  tracing  time.  Then  push  up  the 
plate  so  as  to  compress  the  spring,  till  the  rod  connected  with  the 
frame  which  carries  the  plate  is  held  by  the  catch. 

W  ith  the  short-circuiting  key  closed,  press  the  release  and  allow 
an  abscissa  line  to  be  traced.  Again  shove  back  the  frame  till  it  is 
caught.  Push  home  the  rod  by  means  of  which  the  prongs  of  the 
tuning-fork  arc  separated,  and  rotate  it  through  900.  Close  the 
knock-over  key,  open  the  short-circuiting  key,  shoot  the  plate  again, 
and  a  muscle-curve  and  time-tracing  will  be  recorded.  Again  close 
the  short-circuiting  key,  withdraw  the  writing-point  of  the  tuning- 
tork,  push  back  the  plate,  close  the  trigger  key,  then  open  the  short- 
circuiting  key,  and  holding  the  travelling  frame  with  the  hand, 
allow  it  just  to  open  the  knock-over  and  stimulate  the  nerve.  The 
writing-point  now  records  a.  vertical  line  (or,  rather,  an  arc  of  a 
circle),  which  marks  on  the  tracing  the  moment  of  stimulation. 
The  latent  period  is  obtained  by  drawing  a  parallel  line  (or  arc) 
through  the  point  of  the  muscle-curve  where  it  just  begins  to 
diverge  from  the  abscissa  line.     The  value  of  the  portion  of  the 


/'/,'  !<   TIC  U.   EXERCISES  7'i 

time-tracing  between  these  two  lines  can   be  readily  determined, 

and  is  t he  I. lit  nt  period. 

i  v  Summation  of  Stimuli.  Arrange  two  knock  over  keys  on  the 
spring  myograph  at  such  .1  distance  from  each  other  thai  the  plate 
travels  From  one  to  the  other  in  a  time  less  than  the  latent  period. 
Connect  each  key  with  the  primary  circuil  oi  a  separate  induction 
coil  having  .1  couple  oi  Daniells  in  it.  Join  two  of  the  binding-screws 
oi  the  secondaries  together  ;  connei  t  the  other  two  through  a  short- 
circuiting  key  with  electrodes,  on  which  the  nerve  of  a  muscle-nerve 
preparation  is  arranged.  Push  up  the  secondaries  till  the  break 
shocks  obtained  on  opening  the  two  knock-over  keys  are  maximal. 
Then  shoot  the  plate  as  described  in  1  2,  first  with  one  trigger  key 
closed,  and  then  with  both.  The  curves  obtained  should  be  of  the 
same  height  in  the  two  cases,  as  a  second  maximal  stimulus  falling 
within  the  latent  period  is  ignored  by  the  nerve  or  muscle.  Repeat 
the  experiment  with  submaximal  stimuli  -i.e.,  with  such  a  distani  e 
of  the  coils  that  opening  of  either  trigger  key  does  not  cause  as  strong 
a  contraction  as  is  caused  when  the  coils  are  closer.  The  curve  will 
now  be  higher  when  the  two  shocks  are  thrown  in  successively  than 
when  the  nerve  is  only  once  stimulated.  This  shows  that  (sub- 
maximal)  stimuli  can  be  summed  in  the  nerve.  The  same  could  be 
demonstrated  for  muscle  (p.  655). 

i|.  Superposition  of  Contractions. — Smoke  a  drum  arranged  for 
automatic  stimulation  as  in  Fig.  261.  Adjust  the  brass  points  with 
a  distance  of.  say.  1  centimetre  between  them,  so  that  a  second 
stimulus  may  be  thrown  into  the  nerve  at  an  interval  greater  than 
the  latent  period  of  muscle.  Put  two  Daniells  in  the  primary 
circuit.  Lay  the  nerve  of  a  muscle-nerve  preparation  on  electrodes 
connected  through  a  short-circuiting  key  with  the  secondary. 
Allow  the  drum  to  revolve  (fast  speed)  ;  open  the  short-circuiting 
key  till  both  brass  points  have  passed  the  projecting  wire,  then  close 
it.  Now  bend  back  the  second  brass  point,  and  take  a  tracing  in 
which  the  first  curve  is  allowed  to  complete  itself.  This  will  not  rise 
as  high  as  the  second  curve  obtained  when  the  two  stimuli  were 
thrown  in.  Repeat  the  experiment  with  varying  intervals  between 
the  brass  points — that  is,  between  the  two  successive  stimuli.  Put 
on  a  time-tracing  with  the  electrical  tuning-fork.  (For  specimen 
curve,  sec  Fig.  246,  p.  656.) 

15.  Composition  of  Tetanus. — (a)  Adjust  a  muscle-nerve  prepara- 
tion on  a  myograph  plate,  the  nerve  being  laid  on  electrodes  con- 
nected through  a  short-circuiting  key  with  the  secondary  of  an 
induction  machine,  the  primary  circuit  of  which  contains  a  Daniell 
cell  and  is  arranged  for  an  interrupted  current  (Fig.  81,  p.  184).  The 
lever  should  be  shorter  than  that  used  for  the  previous  experiments, 
or  the  thread  should  be  tied  in  a  hole  farther  from  the  axis  of  rota- 
tion, so  as  to  give  less  magnification  of  the  contraction.  Set  the 
Xcef's  hammer  going,  let  the  drum  revolve  (slow  speed),  and  open 
the  key  in  the  secondary.  The  writing-point  at  once  rises,  and  traces 
a  horizontal  or  perhaps  slightlv-ascending  line.  Close  the  short- 
circuiting  key,  and  the  lever  sinks  down  again  to  the  abscissa  line. 
If  it  does  not  quite  return,  it  should  be  loaded  with  a  small  weight. 
This  is  an  example  of  complete  tetanus. 

(b)  Connect  the  spring  shown  in  Fig.  263  with  one  of  the  upper 
terminals  of  the  primary  coil,  and  the  mercury  cup  with  the  other. 
Fasten  the  end  of  the  spring  in  one  of  the  notches  in  the  upright 
piece  of  wood  by  means  of  a  wedge,  so  that  its  whole  length  can  be 


7i- 


A     M  IMAL   OF   PHYSIOLOGY 


made  to  vibrate,  lit  the  drum  <>it.  set  the  spring  vibrating  by 
depressing  il  with  the  finger,  then  open  the  key  in  the  secondary 
The^muscle  is  thrown  into  incomplete  tetanus,  and  the  writi 
point  traces  .1  wavy  curve  at  a  higher  level  than  the  abscissa  line. 
Close  the  short-circuiting  key,  and  the  lever  Jails  to  the  horizontal. 
Repeal  the  experiment  with  the  spring  fastened,  so  thai  onlj  \  \.  \. 
I  of  its  length  is  free  to  vibrate.  The  rate  of  interruption  of  the 
primary  circuit  in<  leases  in  proportion  to  the  shortening  oJ  the 
spring,  and  the  tetanus  becomes  more  and  more  complete  till 
ultimately  the  writing-point  marks  an  unbroken  straight  line  Put 
on  a  time-tracing  by  means  of  an  electro-magnetic  marker  <  onm  1  t<  d 
with  a  metronome  beating  seconds  or  half-seconds  (Fig.  70.  p>  170). 
(For  specimen  curves,  see  Fig.  247,  p.  657.) 

[6.   Contraction  of  Smooth  Muscles     (1)  Spontaneous  Rhythmical 
Contractions. — Immerse   in   oxygenated    Ringer's  solution   a   ring   of 

(esophagus  ob- 
tained immediate- 
ly after  death  from 
.1  ( ,11 ,  or.  still  bet- 
ter, from  a  chi<  ken. 
I  Fse  the  arrange- 
ment  described  on 
p.  102 ,.  In  the  1  ase 
of  the  cat's  oeso- 
phagus    the     ring 

should  be  taken 
from  the  lower  half 
oi  the  oesophagus, 
since  the  upper  por- 
tion contains  purely 
striated  muselc. 
Obtain  tracings 
of  the  rhythmical 
contractions  on 
a  slowly  -  moving 
drum  (Fig.  ^64). 

(2)  Fix  one  end 
of  a  piece  of  cat 's 
oesophagus,  2  to  5 
centimetres  long, 
to  .1  muscle-clamp 

in  a  moist  chamber,  and  the  other  end  to  a  lever  writing  on  a  drum. 

Connei  t  thin  1  oppei  wires  from  the  secondary  coil  of  an  inductorium 

with  the  two  ends  ot  the  piece  of  oesophagus.  lake  tracings  to  show 
(a)  the  curve  of  a  single  contraction  caused  by  a  single  make  or  break 
shock,  with  estimation  of  the  latent  period,  as  in  Experiment  1 
p.  710;  (b)  summation,  as  in  Experiment  13,  p.  711;  [c]  genesis  of 
tetanus,  as  in  Experiment  15,  p.  711;  (d)  the  relations  between  strength 
of  stimulus  and  amount  of  contraction.  For  this  last  experiment 
l  he  drum  should  be  stationarv  while  the  contraction  is  being  recorded, 
and  should  be  allowed  to  move  a  little  between  successive  con- 
tractions. Begin  with  the  secondary  at  such  a  distance  from  the 
primary  that  a  contraction  is  just  caused  by  a  break  shock.  Then 
gradually  increase  the  strength  of  the  stimulus  (always  using  the 
break)  till  maximum  contra<  don  is  obtained  1  he  gradual  in<  rease 
in  the  response  is  very  clearly  seen  with  the  oesophageal  preparation 
(Waller) . 


Fig.  263. — Arrangement  for  Tetanus. 
A,  upright  with   notches,  in  which  the  spring 


S  is 


fastened  (shown  in  section) ;  C,  horizontal  board  to  which 
A  is  attached,  and  in  a  groove  in  which  the  mercury-cup 
E  slides.  The  primary  coil  P  is  connected  with  E,  and 
through  a  simple  key.  K.  with  the  battery  B,  the  other 
pole  of  which  is  connected  with  the  end  of  the  spring. 
The  wires  from  the  secondary  coil,  P'.  go  to  a  short- 
circuiting  key,  K',  from  which  the  wires  F  go  oil  to  the 
elei  tn  ides. 


PR  /(/'/<    //     EX1  /.'<  TSES 


7>3 


17.  Velocity  of  the  Nerve-impulse.- I'se  the  spring  myograph 
(Fig.  228,  p.  643)  or  a  very  rapidly  rotating  drum.  Make  a  muscle- 
uerve  preparation  from  .1  large  frog  (preferably  a  bull-frog),  s<>  thai 
the  sciatic  nerve  may  be  as  long  as  possible.  Conned  the  knock-ovei 
key  with  the  primary  cir<  ail  of  an  induction  machine,  whi<  h  should 
contain  a  single  Daniell  cell.  Arrange  two  pairs  of  fine  electrodes 
under  the  nerve  on  the  myograph  plate,  one  near  the  muscle,  the 
other  at  the  central  end.  Connect  the  electrodes  with  a Pohl's  com- 
mutator (without  cross-wires),  the  side-cups  of  which  arc  joined  to 
the  terminals  of  the  secondary  coil,  as  shown  in  Fig.  265.  By 
tilting  the  bridge  of  the  commutator  the  nerve  may  be  stimulated 
at  either  point.  Great  care  must  be  taken  to  keep  the  nerve  in  a 
moist  atmosphere  by  means  of  wet  blotting-paper  or  a  moist 
chamber  ;  but  at  the  same  time  it  must  not  lie  in  a  pool  of  salt 
solution,  as  twigs  of  the  stimulating  current  would'in  this  ease  spread 
down  the  nerve,  and 
we  could  never  be 
sure  that  the  appar- 
ent was  always  the 
real  point  of  stimu- 
lation. The  writing- 
points  of  the  lever 
and  tuning-fork  hav- 
ing been  adjusted  to 
the  smoked  plate,  as 
in  12  (p.  710),  the 
bridge  of  the  Pohl's 
commutator  is  ar- 
ranged for  stimula- 
tion of  the  distal 
point  of  the  nerve, 
the  plate  is  shot 
with  the  short-cir- 
cuiting key  in  the 
secondary  closed, 
and  an  abscissa  line 
and  time -curve 
traced.  Then  the 
writing-point  of  the 
fork  is  removed  and 
the  plate  again  shot  with  the  key  in  the  secondary  open,  and  a  muscle- 
curve  is  obtained.  The  commutator  is  now  arranged  for  stimulation 
of  the  central  end  of  the  nerve,  and  another  muscle-curve  taken. 
Vertical  lines  are  drawn  through  the  points  where  the  two  curves 
just  begin  to  separate  out  from  the  abscissa  line.  The  interval 
between  these  lines  corresponds  to  the  time  taken  by  the  nerve- 
impulse  to  travel  along  the  nerve  from  the  central  to  the  distal  pair 
of  electrodes.  Its  value  in  time  is  given  by  the  tracing  of  the  tuning- 
fork.  The  length  of  the  nerve  between  the  two  pairs  of  electrodes 
is  now  carefullv  measured  with  a  scale  divided  in  millimetres,  and  the 
velocity  calculated  (p.  689). 

18.  Chemistry  of  Muscle. — Mince  up  some  muscle  from  the  hind- 
legs  of  a  dog  or  rabbit  (used  in  some  of  the  other  experiments),  of 
which  the  bloodvessels  have  been  washed  out  by  injecting  oo.  per  cent, 
salt  solution  through  a  cannula  tied  into  the  abdominal  aorta  until 
the  washings  are  no  longer  tinged  with  blood.  To  some  of  the 
minced  muscle  add  twenty  times  its  bulk  of  distilled  water,  to  another 


Fig. 


264. — Rhythmical     Contractions 
phagus  of  Chicken  (Botazzi) 


of     CF.so- 


7'4 


I    M  \NU  \1.  <>!■    PHYSIOLOGY 


portion  ten  times  its  bulk  ol  .1  \  pei  cenl  solution  <<\  magnesium 
sulphate.  Lei  stand,  with  frequenl  stirring,  for  twenty-four  hours. 
I  hen  st  1  ;i in  through  several  Eolds  ol  Linen,  press  out  thi  residue,  and 
filter  through  paper.  (1)  With  the  filtrate  01  the  watery  extract  make 
the  following  observations  : 

[a)   Reaction.   -To  litmus-paper  acid. 

(/))  Determine  the  temperatures,  at  which  coagulation  of  the 
various  proteins  in  the  ex t rat  t  takes  place,  according  to  the  method 
described  on  p.  8.*  Put  some  of  the  watery  extract  in  the  test- 
1  ube,  and  heal  the  bath,  stirring  the  water  in  the  beakers  occasionally 

with   a   leather.       Note  at  what    temperature  a  1  0,1  -iilnni   hrst   tonus. 

It  will  be  about  470  C.  Filter  this  off,  and  again  heal  :  another 
coagulum  will  form  at  560  to  580.  Filter,  and  heat  the  filtrate  ;  a 
third  slight  coagulum  may  be  formed  at  6o°  to  65°  C,  but  this 
represents   merely   a   residue   of   the   myosinogen   which    was   left   in 


Fig.  265.- 


-Arrangement  for  Measuring  the  Velocity  of  thi    Ni  rve- 
impulse  . 


A,  travelling  plate  of  spring  myograph  ;  M,  muscle  lying  on  a  myograph  plate; 

N.  nerve,  lying  mi  tw<>  pairs  of  dec  trodes,  V.  and  V.' ;  (.  Pohl's  commutator 
without  ( ri iss  wires;  K.  (mock-over  key  "t  spring  myograph  (only  the  binding- 
screws  shown)  ;  K',  simple  key  in  primary  circuit  ;  15,  battery  :  P,  primary  coil  ; 
S,  second. if 

solution  at  the  previous  heating.  A  fourth  precipitate  (of  serum- 
albumin)  will  come  down  at  70°  to  73°.  Saturate  some  of  the  watery 
extract  with  magnesium  sulphate  ;  a  large  precipitate  will  be  formed, 
showing  the  presence  of  a  considerable  amount  of  globulin.  Filter 
off  the  precipitate  and  heat  the  filtrate  ;  coagulation  will  again  occur 
at  very  much  the  same  temperatures  as  before,  although  the  total 
amount  of  precipitate  will  be  less.     Note  in  partu  ular  that  there 

*  It  should  be  remembered  that  the  temperature  ol  heat-coagulation  of 

any  substance  is  by  no  means  an  absolute  constant.  It  depends  on  the 
reaction,  the  proportion  and  kind  of  neutral  salts  present,  perhaps  on  the 
strength  of  the  protein  solution  and  the  manner  of  heating.  A  solution 
of  egg-albumin,  e.g.,  can  be  coagulated  at  a  temperature  much  below  700 
when  it  is  heated  tor  a  week.  Small  differences  in  the  temperature  of 
heat-coagulation,  unless  supported  by  well-marked  chemical  reactions, 
arc  not  enough  to  characterize  protein  substances  as  chemical  individuals. 


PRACTIC  1/    EXERCISES  7' 5 

i-  -till  sonic  precipitate  al  \"j  to  500.  Paramyosinogen  possesses 
some  of  the  characters  ol  both  globulins  and  albumins,  for  it  Is 
partially  but  not  entirely  precipitated  by  saturation  with  magnesium 
sulphate,  and  is  not  precipitated  by  sodium  chloride. 

\2)  (a)  Test  the  reaction  of  the  magnesium  sulphate  extract.  It 
will  usually  be  faintly  acid  to  litmus. 

(b)  Heat  some  of  it.  Precipitates  will  be  obtained  at  the  same 
temperatures  as  in  (1)  (b).  but  those  at  470  to  500  and  56°  to  58'  will 
be  more  abundant.  Of  the  two.  that  at  47"  to  500  will  usually  bo 
the  larger  when  time  is  given  for  it  to  come  clown  and  the  heating  is 
gradual. 

(c)  Dilute  some  of  the  magnesium  sulphate  extract  with  three 
times,  another  portion  with  four  times,  and  another  with  five  times, 
its  volume  of  water  in  a  test-tube,  and  put  in  a  bath,  at  400  C. 
Coagulation  or  precipitation  will  occur  in  one  or  all  of  these  test-tubes. 
To  another  test-tube  of  the  extract  diluted  in  the  proportion  which 
has  given  the  best  '  muscle-clot  '  add  a  few  drops  of  a  dilute  solution 
of  potassium  oxalate,  and  place  in  the  bath  at  40°.  Coagulation 
occurs  as  before.  Filter  off  the  clot  from  all  the  test-tubes.  The 
filtrate  is  the  '  muscle-serum,'  and  yields  a  precipitate  of  serum- 
albumin  at  7or  to  730  C. 

(3)  Myosinogen.  like  other  globulins,  is  insoluble  in  distilled  water, 
but  soluble  in  weak  saline  solutions.  Saturation  with  neutral  salts 
like  sodium  chloride  and  magnesium  sulphate  precipitates  myo- 
sinogen.  but  not  albumin,  from  its  solutions  :  saturation  with  ammo- 
nium sulphate  precipitates  both.  Myosinogen  is  said  to  be  dis- 
solved without  change  in  very  weak  acids.  Stronger  acids  precipitate 
it.  Verify  the  following  reactions  of  myosinogen,  using  the  original 
magnesium  sulphate  extract  of  the  muscle. 

(a)  Dropped  into  water,  it  is  precipitated  in  flakes,  which  can  be 
redissolved  bv  a  weak  solution  of  a  neutral  salt  (say  5  per  cent, 
magnesium  sulphate). 

(b)  When  a  solution  of  myosinogen  is  dialyzed,  it  is  precipitated 
on  the  inside  of  the  dialvzer  as  the  salts  pass  out. 

(c)  If  a  piece  of  rock-salt  is  suspended  in  a  solution,  the  myosin 
gradually  gathers  upon  it,  diffusion  of  the  salt  out  through  the  pre- 
cipitated mvosin  alwavs  keeping  a  saturated  layer  around  it. 

(d)  Saturate  a  solution  containing  myosinogen  with  crystals  of 
magnesium  sulphate,  stirring  or  shaking  at  frequent  intervals.  The 
myosinogen  is  precipitated. 

(e)  Without  adding  any  salt,  simply  shake  a  myosinogen  solution 
vigorously  ;  a  certain  amount  of  the  myosinogen  will  be  precipitated, 
and  the  solution  will  become  turbid.  This  reaction  can  also  be  ob- 
tained with  solutions  of  other  proteins,  such  as  albumins (Ramsden). 

Extracts  qualitatively  similar  to  those  obtained  from  the  muscles 
of  a  freshly-killed  animal  can  be  got  from  muscles  that  have  entered 
into  rigor,  but  the  quantity  of  the  various  proteins  going  into  solution 
is  less. 

19.  Reaction  of  Muscle  in  Rest,  Activity,  and  Rigor  Mortis. — 
(a)  Take  a  frog's  muscle,  cut  it  across,  and  press  a  piece  of  red 
litmus-paper  on  the  cut  end  ;  it  is  turned  blue.  Yellow  turmeric 
paper  is  not  affected. 

(b)  Immerse  another  muscle  in  physiological  salt  solution  (o-75 
per  cent,  for  frog's  tissues)  at  40°  to  420  C.  It  becomes  rigid.  The 
reaction  becomes  acid  to  litmus-paper,  and  also  turns  brown  turmeric 
paper  yellow. 


716  A   M  /  \r  1/    OF   PHYSIOLOGl 

(c)  Plunge  another  muscle  into  boiling  physiological  sail  solution. 
It  becomes  harder  than  in  (6),  and  its  reaction  becomes  acid  to  litmus- 
paper. 

(</)  Stimulate   another  muscle  with  an  interrupted  i  urrent  from 
.in  induction  machine  (Fig.  8i,  p.   184),  till  it  no  longer  contracts. 
The  reaction  is  now  acid  to  litmus-paper.      Brown  turmeri<    pi 
may  also  be  turned  yellow. 

(e)  To  demonstrate  the  formation  of  lactic  acid  in  muscle  in  heat 
rigor  or  fatigue,  perform  the  following  experiment  :  Pith  a  frog,  and 
afterwards  leave  it  for  half  an  hour  at  rest,  so  that  the  lactic  a<  id 
produced  in  the  movements  connected  with  the  pithing  operation 
may  disappear  from  the  muscles.  See  that  the  circulation  in  the 
hind-limbs  is  not  interfered  with  by  pressure  or  flexion.  Then 
remove  both  hind-limbs.  Carefully,  but  rapidly,  remove  the  muscles 
of  one  from  the  bones  with  as  little  manipulation  as  possible.  Im- 
mediately place  them  in  a  small  mortar  cooled  in  ice,  and  containing 
sonic  sand  and  20  or  30  c.c.  of  ice-cold  95  per  cent,  alcohol,  and 
quickly  grind  them  up.  Produce  heat  rigor  (p.  (.74)  of  the  muscles  of 
the  other  hind-limb,  or  fatigue  them  with  induction  shocks,  and  then 
grind  them  up  under  alcohol  in  the  same  way.  Filter  the  al<  oholii 
extracts,  and  then  evaporate  them  to  dryness  on  the  water-bath. 
Rub  up  the  residues  with  a  few  c.c.  of  hot  water.  Add  to  ea<  h 
aqueous  extract  a  small  quantity  (say  a  decigramme)  of  finely 
powdered  charcoal.  Then  heat  each  extract  to  boiling  in  a  test- 
tube,  and  filter.     Evaporate  the  filtrates  to  dryness,  and  apply 

Hopkins's  Reaction  for  Lactic  Acid. — The  reagents  required  are 
(1)  a  very  dilute  alcoholic  solution  of  thiophene  (10  to  20  drops  in 
100  c.c.)  ;  (2)  a  saturated  solution  of  copper  sulphate  ;  and  (3)  ordinary 
strong  sulphuric  acid. 

Have  ready  a  glass  beaker  containing  water  briskly  boiling. 
Place  about  5  c.c.  of  strong  sulphuric  acid  in  a  test-tube,  with  1  drop 
of  the  copper  sulphate  solution.*  Add  to  the  mixture  a  few  drops  of 
the  solution  to  be  tested,  and  shake  well.f 

(In  the  case  of  the  muscle  extracts  the  dry  residues  arc  dissolved  in 
the  5  c.c.  of  strong  sulphuric  acid,  the  acid  transferred  to  test-tubes, 
and  the  test  proceeded  with  by  the  addition  of  the  copper  sulphate 
solution,  etc.) 

Now  place  the  test-tube  in  the  boiling  water  for  one  to  two 
minutes.  Then  cool  it  well  under  the  cold-water  tap,  and  add  2  or 
3  drops  of  the  thiophene  solution  from  a  pipette.  Replace  the  lube 
in  the  boiling  water,  and  immediately  observe  the  colour.  If  la<  ti( 
acid  is  present  the  liquid  rapidly  takes  on  a  bright  cherry-red  colour, 
which  is  only  permanent  if  the  test-tube  be  cooled  immediately  after 
its  appearance.  The  tube  should  always  be  cooled,  as  described,  before 
addition  of  the  thiophene,  as  the  gradual  appearance  of  the  colour  en 
re-warming  makes  the  test  more  delicate. 

(The  extract  of  the  resting  limb  generally  gives  a  negative,  that  of 
the  other  a  strongly  positive,  reaction.) 

*  The  copper  sulphate  is  added  to  hasten  the  oxidation  that  follow.-. 

f  For  practice  use  a  1  per  cent,  alcoholic  solution  of  lactic  acid.  The 
test  cannot  be  applied  directly  to  material  which  chars  with  the  strong 
sulphuric  acid  used.  In  this  case  preliminary  extraction  of  the  lactic 
acid  is  necessary.  Alcohol  should  be  used  as  the  solvent,  or  if  ether  is 
employed  it  must  first  In-  well  washed  to  remove  aldehyde-yielding 
products,  since  the  colour  change  is  due  to  an  aldehyde  reaction  with 
thiophene. 


CHAPTER  XI 
ELECTRO-PHYSIOLOGY 

A  little  more  than  a  hundred  years  ago  the  foundation  both  of 
electro-physiology  and  of  the  vast  science  of  voltaic  electricity  was 
laid  by  a  chance  observation  of  a  professor  of  anatomy  in  an  Italian 
garden.  It  is  indeed  true  that  long  before  this  electrical  fishes  were 
not  only  popularly  known,  but  the  shock  of  the  torpedo  had  been  to 
a  certain  extent  scientifically  studied.  But  it  was  with  the  discovery 
of  Galvani  of  Bologna  that  the  epoch  of  fruitful  work  in  electro- 
physiology  began.  Engaged  in  experiments  on  the  effect  of  static 
and  atmospheric  electricity  in  stimulating  animal  tissues,  he  hap- 
pened one  day  to  notice  that  some  frogs'  legs,  suspended  by  copper 
hooks  on  an  iron  railing,  twitched  whenever  the  wind  brought  them 
into  contact  with  one  of  the  bars  (p.  738).  He  concluded  that 
electrical  charges  were  developed  in  the  animal  tissues  themselves, 
and  discharged  when  the  circuit  was  completed.  Volta,  professor  of 
physics  at  Pavia,  fixing  his  attention  on  the  fact  that  in  Galvani's 
experiment  the  metallic  part  of  the  circuit  was  composed  of  two 
metals,  maintained  that  the  contact  of  these  was  the  real  origin  of 
the  current,  and  that  the  tissues  served  merely  as  moist  conductors 
to  complete  the  circuit  ;  and  after  a  controversy  lasting  for  more  than 
a  decade,  he  finally  clinched  his  argument  by  constructing  the 
voltaic  pile,  a  series  of  copper  and  zinc  discs,  every  two  pairs  of  which 
were  separated  by  a  disc  of  wet  cloth,  or  paper  moistened  with  salt 
solution.  The  pile  yielded  a  continuous  current  of  electricity. 
'  So,'  said  Volta,  '  it  is  clear  that  the  tissue  in  Galvani's  experiment 
only  acts  the  part  of  the  cloth.'  Galvani,  however,  had  shown  in 
the  meantime  that  contraction  without  metals  could  be  obtained  by 
dropping  the  nerve  of  a  preparation  on  to  the  muscle  (p.  738)  ;  and 
it  soon  began  to  be  recognised  that  both  Galvani  and  Volta  were  in 
part  right,  that  two  brilliant  discoveries  had  been  made  instead  of 
one  ;  in  short,  that  the  tissues  produce  electricity,  and  that  the 
contact  of  different  metals  does  so  too.  Although  it  is  curious  to 
note  how  completely  the  growth  of  that  science  of  which  Volta's 
discovery  was  the  germ  has  overshadowed  the  parent  tree  planted 
by  the  hand  of  Galvani,  yet  animal  electricity  has  been  deeply 
studied  by  a  large  number  of  observers,  and  many  interesting  and 
important  facts  have  been  brought  to  light. 

Since  it  is  in  muscle  and  nerve  that  the  phenomena  of  electro- 
physiology  are  seen  in  their  simplest  expression,  and  have  been 
chiefly  studied,  we  shall  develop  the  fundamental  laws  with 

717 


718 


A   MANUAL  OF  PHYSIOLOGY 


reference  to  muscle  and  nerve  alone,  and  afterwards  apply  them 
to  other  excitable  tissues. 

i.  All  points  of  an  uninjured  resting  muscle  or  nerve  are  approxi- 
mately at  the  same  potential  (or  iso- electric).  In  other  words,  if 
any  two  points  are  connected  with  a  galvanometer  by  means  of 
unpolarizable  electrodes,  little  or  no  current  is  indicated. 
(Although  it  is  scarcely  possible  to  isolate  a  muscle  without  its 
showing  some  current,  the  more  carefully  the  isolation  is  per- 
formed the  feebler  is  the  current  ;  and  between  two  points  of 
the  inactive,  uninjured  ventricle  of  the  frog's  heart  no  electrical 
difference  has  been  found.  Frogs'  nerves  kept  ten  to  twenty 
hours  after  excision  in  physiological  salt  solution  to  which  a  li tilt- 
calcium  salt  and  frog's  blood  have  been  added,  are  absolutely 
iso-electric.) 

2.  Any  uninjured  point  of  a  resting  muscle  or  nerve  is  at  a 
different  potential  from  any  injured  point.      The  difference  of 


Fig.  266. — A,  uninjured,  B,  in- 
jured, portion  of  nerve  ;  G,  galvano- 
meter. The  large  arrows  show 
direction  of  demarcation  current  or 
current  of  rest,  the  small  arrows 
direction  of  negative  variation  or 
action  current. 


Fig.  267. — Diagram  of  Currents 
of  Rest  in  a  Regular  Muscle, 
or  Muscle  Cylinder. 

E,  equator.  The  dotted  lines 
join  points  at  the  same  potential, 
between  which  there  is  no  current. 


potential  is  such  that  a  current  will  pass  through  the  galvano- 
meter from  uninjured  to  injured  point  and  through  the  tissue 
from  injured  to  uninjured  point  (current  of  rest,  or  demarcation 
current,  or  injury  response)  (Fig.  266). 

3.  Any  unexcited  point  of  a  muscle  or  nerve  is  at  a  different 
potential  from  any  excited  point,  and  any  less  excited  point  is  at 
a  different  potential  from  any  more  excited  point.  The  difference 
of  potential  is  such  that  a  current  will  pass  through  the  galvano- 
meter from  the  excited  to  the  unexcited  or  less  excited  point 
(action  current,  or  negative  variation,  or  excitatory  electrical 
response). 

It  has  been  customary  in  physiological  writings  to  speak  of 
the  electrical  change  in  injured  or  active  tissue  as  a  negative  one, 
because  when  the  tissue  is  led  off  to  a  galvanometer  the  current 
passes  from  the  galvanometer  to  the  injured  or  excited  portion 
of  the  tissue.     It  may  be  called  with  greater  precision  '  galvano- 


/  /  /  CTRO  PHYSIOLOGY 


7i9 


metrically  negal  ive. 
tin-  term. 


It  is  in  this  sense  thai  we  shall  employ 


The  best  object  for  experiments  on  the  demarcation  current  is  a 
straight-fibred  muscle  like  the  frog's  sartorius.  If  this  muscle  be 
taken,  and  the  ends  cut  off  perpendicularly  to  the  surface,  a  muscle- 
prism  or  muscle-cylinder  is  obtained  (Fig.  267).  The  strongest 
current  is  got  when  one  electrode  is  placed  on  the  middle  of  either 
cross-section  and  the  other  on  the  '  equator  ' — that  is,  on  a  line 
passing  round  the  longitudinal  surface  midway  between  the  ends. 
The  direction  of  this  current  is  from  the  cross-section  towards  the 
equator  in  the  muscle.  If  the  electrodes  are  placed  on  symmetrica 
points  on  each  side  of  the  equator,  there  is  no  current. 


Fig.   268. — Diagram  to  illustrate  Propagation  of  the   Electrical 
Change  along  an  Active  Muscle  or  Nerve. 

Suppose  AB  to  be  a  horizontal  bar  representing  the  muscle  or  nerve.  Let  C 
be  a  curved  piece  of  wood  representing  the  curve  of  the  electrical  change  at  any 
point.  Let  W,  W  be  two  glass  cylinders  connected  by  a  flexible  tube,  the  whole 
being  filled  with  water.  Suppose  the  rims  of  the  cylinders  originally  to  touch 
AB  at  the  points  A  and  B,  and  let  them  be  movable  only  in  the  vertical  direction. 
The  level  of  the  water  being  the  same  in  both,  there  is  no  tendency  for  it  to  flow 
from  one  to  the  other.  This  represents  the  resting  state  of  the  tissue  when  A 
and  B  are  symmetrical  points.  Now  let  C  be  moved  along  the  bar  at  a  uniform 
rate.  The  cylinder  W,  being  free  to  move  down,  but  not  horizontally,  will  be 
displaced  by  C,  and,  if  it  is  kept  always  in  contact  with  its  curved  margin,  will, 
after  describing  the  curve  of  the  electrical  variation,  come  again  to  rest  in  its 
old  position  at  A.  B  will  do  the  same  when  C  reaches  it.  But  since  C  reaches 
A  before  B,  the  level  of  the  water  in  B  will  at  first  be  higher  than  that  in  A, 
and  water  will  flow  from  B  to  A  as  the  current  flows  through  the  galvanometer. 
This  will  correspond  to  the  time  during  which  the  point  of  the  tissue  represented 
by  A  would  be  galvanometrically  negative  to  a  point  represented  by  B.  Later 
on,  when  C  has  reached  the  position  shown  by  the  dotted  lines,  the  level  of  the 
water  in  A  will  be  higher  than  that  in  B,  and  a  flow  will  take  place  in  the  opposite 
direction  to  the  first  flow.  This  corresponds  to  a  second  phase  of  the  electrical 
variation. 

Current  of  Action,  or  Negative  Variation. — When  a  muscle 
or  nerve  is  excited,  an  electrical  change  sweeps  over  it  in  the  form 
of  a  wave.     Suppose  two  points,   A  and  B   (Fig.  268),  on  the 


72o  A  MANUA1    OF  PHYSIOLOGY 

longitudinal  surfaced  a  muscle  to  be  connected  with  a  capillary 
electrometer  (p.  621),  the  movements  of  the  mercury  being 
photographed  on  a  travelling  surface,  for  example,  a  pendulum 
carrying  a  sensitive  plate.  Let  the  muscle  be  excited  at  the 
end,  so  that  the  wave  of  excitation  will  be  propagated  in  the 
direction  of  the  arrow.  The  wave  will  reach  A  first,  and  while 
it  has  not  yet  reached  B,  A  will  become  negative  to  B.  It  there 
is  a  resting  difference  of  potential  between  A  and  B,  this  will 
be  altered,  the  new  and  transitory  difference  adding  itself 
algebraically  to  the  old.  When  the  wave  reaches  B,  it  may 
already  have  passed  over  A  altogether,  and  B  now  becoming 
negative  to  A,  there  will  be  a  movement  of  the  meniscus  of 
the  electrometer  in  the  opposite  direction.  This  is  called  the 
diphasic  current  of  action.  If  the  wave  has  not  passed  over  A 
before  it  reaches  B,  as  would  in  general  be  the  ease  in  an  aein.il 
experiment,  there  will  be  first  a  period  during  which  A  is  relatively 


Fig.   269. — Photographic  Electrometer  Curves  from  Sartorius 
Muscle  (Sanderson). 

The  darkly-shaded  curve  represents  the  diphasic  variation  of  the  uninjured 
muscle;  the  lightly-shaded  curve  the  monophasic  variation  of  the  muscle  aftei 
injury  of  one  end.  The  toothed  curve  at  the  top  is  the  time-tracing  registered 
by  photographing  the  prong  of  a  tuning-fork  vibrating  five  hundred  times  a 
second. 

negative  to  B  (first  phase)  ;  this  will  end  as  soon  as  B  has  become 
iso-electric  with  A,  and  will  be  succeeded  by  a  period  during 
which  B  is  relatively  negative  to  A  (second  phase).  Since 
the  wave  takes  time  to  reach  its  maximum,  it  is  evident  that 
a  well-marked  first  phase  will  be  favoured  when  the  interval 
between  its  arrival  at  A  and  at  B  is  long,  for  in  this  case  A  will 
have  a  chance  of  becoming  strongly  negative  while  B  is  still 
normal.  Similarly,  if  A  has  again  become  normal,  or  nearlv 
normal,  before  the  maximum  negative  change  has  passed  over  B, 
a  strong  second  phase  will  be  favoured.  The  heart-muscle, 
accordingly,  where  the  wave  of  contraction,  and  its  accompanying 
electrical  change,  move  with  comparative  slowness,  is  better 
suited  for  showing  a  well-marked  diphasic  variation  than  skeletal 
muscle,  and  still  better  suited  than  nerve.  In  the  gastrocnemius 
muscle  of  the  frog,  when  excited  through  its  nerve,  the  electrical 


ELECT  RO-PH  YSIOLOGY 


721 


response  begins  about  1(,loff  second,  and  the  change  of  form  of 
the  muscle  about  ](yW  second  after  the  stimulation.  It  is 
believed  that  in  a  muscle  directly  excited  the  electrical  change 
begins  in  less  than  ,„',,„  second,  and  the  mechanical  change  in 
,,,',,,,   second  (Burdon  Sanderson,  Figs.  270-274). 


Fig.   270. — '  Spike  '  (Diphasic  Variation)  of  Uninjured  Gastrocnemius 

(Sanderson). 

A  photographed  on  slow,  B  on  fast-moving  plate. 


^^^^^Wvw****** 


Fig.  271. — Variation  of 
Injured  Gastrocnemius 
(Sanderson). 

A  '  spike  '  followed  by  a 
'  hump.' 


Fig.  273. — Variation  of  Unin- 
jured Muscle  excited  Eighty- 
four  Times  a  Second  (Sander- 
son). 


Fig.     272. — Variation     of     Injured 
Gastrocnemius  (Sanderson) 

The    plate    was    moving  ten  times 
faster  than  in  Fig.  271. 


Fig.    274.  —  Curve    of    an    Injured    Muscle    excited 
Sixty  Times  a  Second  (Sanderson). 

46 


722  A  MANUAL  OF  PHYSIOLOGY 

When  one  electrode  is  placed  on  an  injured  part,  the  wave 
of  action  and  of  electrical  change  diminishes  as  it  reaches 
the  injured  tissue  :  and  if  the  tissue  is  killed  at  this  part,  it 
diminishes  to  zero;  so  that  here  the  second  phase  may  be 
greatly  weakened  or  may  disappear  altogether,  and  we  then 
have  what  is  called  a  monophasic  variation. 

In  this  i  ase  the  <  urrcnt  of  a<  tion  ( an  be  demonstrated,  even  for  a 
single  excitation,  but  still  better  for  a  tetanus,  with  the  galvano- 
meter, which  in  general  is  not  quick  enough  to  analyze  a  diphasic 
variation  with  equal  phases,  and  gives,  therefore,  only  their  algebraic 
sum — that   is.    zero.     When  the  muscle  or  nerve   is    I  the 

ac  tion    current   appears,    while   stimulation    is   kept    up,   as   a   per- 
manent defta  tion  representing  the  '  sum  '  of  the  separate  eff< 
It  is  in  the  opposite  direction  to  the  current  of  rest,  sun  <•  the  injured 
tissue   being  less  affected  by  the  exc  itation,  and  therefore  undergoing 
a  smaller  negative  change  than  the  uninjured,  be<  omes  relativi 
the  latter  less  negative.     Appearing  as  a  diminution  or  reversal  of 
the  current  of  rest  it  was  called  the  negative  variation.     The  term 
negative  is  not  used  here  in  its  electrical,  but  in  its  algebraic,  se: 
and  merely  as  indicating  the  direction  of  the  current  with  reference 
to  that  of  the  demarcation  current,      It  is  in  tl  !  i  at '  negative 

variation  '  and  the  converse  term,  '  positive  variation,'  are  used 
(PP-  734-  735)  m  speaking  of  the  electrical  changes  produi  ed  in  glands 
and  in  the  retina  by  stimulation. 

When  the  current  of  rest  is  compensated  by  a  branch  of  an  external 
current  just  sufficient  to  balance  it  and  bring  the  galvanometer  image 
back  to  zero  (Fig.  209,  p.  620),  the  action  current  appears  alone  in  un- 
diminished strength.  This  shows  that  the  latter  is  not  due  to  a  change 
of  electrical  resistance  during  excitation,  since  such  a  change  would 
equally  affect  current  of  rest  and  compensating  current,  and  they 
would  still  balance  each  other.  The  action  current  is  really  di: 
a  change  of  potential,  which  can  be  measured  by  determining  what 
electromotive  force  is  just  required  to  balance  it.  and  which  may 
actually  exceed  that  of  the  current  of  rest.  Thus.  Sanderson  and 
Gotch  obtained  an  average  of  008  of  a  Daniell  cell    I  tromotive 

force  of  the  Daniell  would  be  about  a  volt)  as  the  electromotive  force 
of  the  action  current  due  to  a  single  indirect  excitation  of  a  vigorous 
frog's  gastrocnemius,  and  about  004  Daniell  as  that  of  the  current 
of  rest.  The  electromotive  force  of  the  current  of  rest  in  the  rabbit's 
nerve  was  found  by  du  Bois-Reymond  to  be  0*026 :  (  krtch  and  I  [orsley 
found  the  average  for  the  cat  o"oi.  and  for  the  monkey  only  0005. 

That  the  fusion  of  the  successive  variations  of  a  tetanized  muscle, 
as  seen  with  the  galvanometer,  is  only  apparent  has  been  shown 
by  means  of  the  capillary  electrometer.  Even  with  a  frequency  of 
stimulation  far  beyond  what  is  necessary  for  complete  tetanus,  each 
stimulus  is  answered  by  a  movement  of  the  meniscus  Figs.  273,  - 
In  nerve,  also,  each  of  two  successive  stimuli  cause  its  appropriate 
electrical  change  when  they  are  separated  by  an  interval  longer 
than  a  certain  small  fraction  of  a  second.  The  precise  interval  at 
which  the  second  stimulus  ceases  to  be  effective  depends  on  the 
temperature  of  the  nerve,  being  markedly  increased  by  cold  (Gotch 
and  Burch)." 

Before  Burdon  Sanderson  introduced  the  capillary  electrometer 
for  the  study  of  the  electrical  phenomena  of  living  tissucs.-and  Burch 


I  RO-PHYSIOLOGY 


723 


perfected  a  method  for  the  measurement  of  the  curves,  the  differential 
rheototne,  originally  constructed  by  Bernstein,  was  the  most  valuable 
instrument  we  possessed  for  experiments  <>n  the  time  relations  of 
these  phenomena.  By  its  aid,  tor  instance,  it  was  shown  that  the  rate 
"t  propagation  of  the  electrical  change  in  muscle  is  the  same  as 
that  of  the  mechanical  ch  nge,  and  in  nerve  the  same  as  that  of  the 
nervous  impulse  Observations  on  muscle  made  by  the  capillary 
electrometer  and  the  string  galvanometer  have  confirmed  those 
results.  The  velocity  of  propagation  of  the  diphasic  variation  along 
a  fresh  sartorius  at  140  C.  was  in  one  experiment  2" 8  metres,  in 
another  at  180  C,  35  metres  (Sanderson).  (See  p.  659.)  Lucas 
has  pointed  out  that  in  strict  accuracy  what  is  observed  is  merely 
that  the  time  interval  separating  contraction  at  one  point  of  the 
muscle  from  contraction  at  another  is  equal  to  the  time  interval 
separating  the  electrical  changes  which  occur  at  the  same  points.  The 
facts  observed  do  not  formally  prove  that  either  the  contraction  or  the 
electrical  disturbance  is  pro- 
pagated at  all.  So  far  as  they 
go,  some  other  perfectly  dis- 
tinct change  may  be  pro- 
pagated, which  at  all  points 
of  the  fibre  at  which  it  arrives 
sets  up  both  the  contraction 
and  the  electrical  change. 
Such  direct  evidence,  however, 
as  we  possess  goes  to  show 
that  it  is  the  electrical  disturb- 
ance which  is  the  propagated 
one,  and  that  this  evokes  the 
contractile  disturbance. 

The  differential  rheotome 
(Fig.  275)  consists  essentially 
of  a  stationary  metal  ring, 
the  whole  or  part  of  which  is 
graduated,  and  of  a  portion 
which  can  be  made  to  revolve 
at  a  known  rate.  The  latter 
carries  two  contacts  :  a,  an 
obliquely  -  placed  platinum 
wire  which  touches  at  every 
revolution  a  horizontal  wire  b 
on  the  fixed  ring,  thus  making  and  breaking  the  primary  circuit  P 
of  an  induction  machine,  and  so  causing  stimulation  of  a  muscle 
or  nerve  M  connected  with  the  secondary  'S  ;  and,  c,  a  double 
contact,  either  in  the  form  of  two  platinum  wires,  which  dip  into 
two  mercury  troughs,  or  of  two  wire  brushes  rubbing  on  copper 
blocks  d,  at  a  certain  part  of  the  revolution.  The  troughs  or 
blocks  are  connected  with  a  circuit  containing  a  galvanometer  G, 
and  a  portion  of  the  muscle  or  nerve  arranged  so  as  to  give  a 
strong  action  current.  This  circuit  is  completed  by  the  wires  or 
brushes,  which  are  in  metallic  contact  with  each  other  ;  and  the 
relative  position  of  the  fixed  contact  in  the  primary  circuit  and 
of  the  troughs  or  copper  blocks  can  be  altered  so  as  to  alter  at  will 
the  interval  between  stimulation  and  closure  of  the  galvanometer 
circuit.  The  proportion  of  the  whole  revolution  during  which  this 
circuit  is  closed  can  be  varied  by  changing  the  relative  position  of 

46—2 


Fig, 


-Diagram  of  Differential 
Rheotome. 


724  A    MANUAL  OF  PHYSIOLOGY 

the  two  copper  blocks.  Suppose  the  tissue  is  stimulated  at  one  end 
while  the  leading-ofl  ele<  trodes  are  a1  the  other,  When  the  contact 
a.  b  is  made  at  the  same  time  as  c,  </.  do  deflection  will  be  shown  by 
the  galvanometer  if  the  rheotome  is  revolving  rapidly  (the  demarca- 
tion current  being  accurately  compensated),  because  the  circuit  will 
be  opened  before  the  positive  change  has  time  to  travel  to  the  leading- 
ofl  electrodes.  Bui  .is  the  distant  e  b  twe<  o  b  and  d  is  in<  n  ased,  a 
small  deflection  will  appear,  which,  with  further  increase  ol  the  dis- 
tance, will  become  larger,  reach  ;i  maximum,  and  then  begin  to  fall 
ofl  again.  The  first  small  deflection  corresponds  to  the  position  in 
which  the  positive  change  has  just  had  time  to  reach  the  leadin 
electrodes  before  the  galvanometer  circuit  is  opened.  I  be  maximum 
deflection  corresponds  to  a  period  a  little  later  than  this,  because  tin- 
electrical  variation  does  not  at  once  reach  its  maximum  at  any  point. 

There  is  ample  evidence  that  the  excitatory  electrical  response 
is  a  normal  physiological  phenomenon.  In  human  skeletal 
muscles  the  current  of  action  has  been  demonstrated  by  con- 
necting a  galvanometer  with  ring  electrode-,  passing  round  tin- 
forearm,  and  throwing  the  muscles  into  contraction.  A  diphasic 
variation  is  thus  obtained  ;  and  the  electrical  change  travels 
with  a  velocity  of  as  much  as  twelve  metres  per  second,  which 
is  greater  than  the  velocity  in  frogs'  muscles.  Electromotive 
changes  are  likewise  associated  with  the  beat  of  the  heart. 
Action  currents  have  also  been  detected  in  the  phrenic  nerves 
of  living  animals  accompanying  the  respiratory  discharge  (Reid 
and  Macdonald),  in  the  vagi  accompanying  the  movements  of 
the  lungs,  in  the  oesophagus  during  swallowing,  in  the  cutaneous 
sensory  nerves  in  response  to  the  '  adequate '  stimulus  of  pressure 
(Steinach),  in  the  retina  in  response  to  the  adequate  stimulus 
of  light,  in  glands  during  secretion,  in  the  central  nervous  system 
during  the  passage  of  impulses  along  its  conducting  paths. 
Some  of  these  will  be  further  considered  a  little  later  on. 

As  to  the  interpretation  of  the  facts  we  have  been  describing,  and 
which  are  summed  up  in  the  three  propositions  on  p.  718,  two  chief 
doctrines  long  divided  the  physiological  world  :  (1)  the  theory  of 
du  Bois-Reymond,  the  pioneer  of  electro-physiology,  and  (2)  the 
theory  of  Hermann.  It  was  believed  by  du  Bois-Reymond  that 
the  current  of  rest  seen  in  injured  tissues  is  of  deep  physiological 
import,  and  that  the  electrical  difference  which  gives  rise  to  it  is  not 
developed  by  the  lesion  as  such,  but  only  unmasked  when  the 
electrical  balance  is  upset  by  injury.  He  looked  upon  the  muscle 
or  nerve  as  built  up  of  electromotive  particles,  with  definite  positive 
and  negative  surfaces  arranged  in  a  regular  manner  in  a  sort  of 
ground-substance  which  is  electrically  indifferent.  The  'negative 
variation  '  he  supposed  to  depend  on  an  actual  diminution  of 
previously  existing  electromotive  forces  ;  and  from  this  conception 
arose  its  historic  name.  Hermann  and  his  school  assumed  that 
the  uninjured  muscle  or  nerve  is  '  streamlcss,'  not  because  equal  and 
opposite  electromotive  forces  exactly  balance  each  other  in  the 
substance  of  the  tissue,  but  because  electromotive  forces  are  absent 
until  they  are  called  into  existence  (by  chemical  changes)  at  the 


/  /  I  (   I  UO-PHYSIOLOGY  725 

boundary,  or  plane  of  demarcation,  between  sound  and  injured 
tissue.  For  this  reason  du  Bois-Reymond's  current  of  rest  is 
called  in  the  terminology  oi  Hermann  the  '  demarcation  '  current. 

The  newer  theories,  such  as  Macdonald's,  have  sought  to  take 
account  of  the  recent  developments  of  physical  chemistry,  and  it  is 
unquestionable  thai  it  is  lure  the  real  explanation  is  to  be  found. 
There  is  little  doubt  that  the  electrical  phenomena  of  the  tissues 
are  connected  with  the  existence  in  them  of  membranes,  envelopes, 
or  sheaths,  physiological  if  not  always  anatomical,  which  are  rela- 
tively impermeable  to  certain  ions.  When  such  a  sheath  is  injured, 
these  ions,  carrying  with  them  their  electrical  charges,  may  be 
supposed  to  migrate  with  abnormal  freedom  through  the  injured 
part.  A  new  distribution  of  electricity  is  thus  established  in  the 
tissue,  and  differences  of  potential  depending  upon  differences 
in  the  concentration  of  the  ions  at  different  points  arc  set  up. 
Bernstein  and  Tschermak,  from  an  investigation  of  the  thermo- 
dynamic relations  of  bio-electrical  currents,  have  come  to  the  con- 
clusion that  they  are  analogous  to  the  currents  produced  by  so-called 
concentration  cells — i.e.,  arrangements  of  solutions  of  electrolytes 
of  different  concentration  in  contact  with  each  other.  Since  the 
development  of  the  new  electrical  condition  depends  upon  the 
fundamental  structure  of  the  tissue,  these  modern  views  lead  us 
back  to  du  Bois-Reymond's  doctrine  of  a  pre-existing  electrical 
equilibrium  connected  with  the  essential  physiological  properties 
ot  muscle  or  nerve.  But  instead  of  his  electromotive  elements  and 
their  definite  arrangement,  we  have  the  ions  and  their  definite 
relation  to  the  semi-permeable  membranes. 

Relation  between  the  Action  Current  and  Functional  Activity. — 
Although  the  negative  variation  is  so  general  an  accompaniment 
of  excitation,  and  is  even  within  tolerably  wide  limits,  in  muscle  and 
nerve  at  least,  pretty  nearly  proportional  to  the  strength  of  the 
stimulus,  it  is  at  present  impossible  to  say  definitely  what  the 
chemical  or  physical  changes  are  which  underlie  it.  Unquestionably 
the  electrical  changes  are  closely  related  to  the  excitatory  process 
and  to  the  functional  activity  of  the  tissues. 

Like  the  demarcation  current,  the  action  current  and  the  excita- 
tion which  accompanies  it  may  be  due  to  changes  in  the  permea- 
bility of  membranes  or  changes  in  the  concentration  of  certain  ions. 

Although  the  electromotive  changes  caused  by  excitation  are  much 
more  transient  than  those  caused  by  injury,  everything  suggests  that 
there  must  be  some  deep  analogy  between  the  two  conditions. 
Some  have  supposed  that  what  may  be  called  a  subdued  and  more 
or  less  permanent  excitation  exists  in  the  neighbourhood  of  the 
injured  tissue,  an  excitation  which,  like  some  other  forms,  does  not 
spread,  and  that  this  explains  the  similarity  of  electrical  condition 
in  activity  and  injury. 

It  is,  of  course,  clear  that  energy  must  be  transformed  to  produce 
an  electromotive  force  capable  of  doing  work.  It  may  be  assumed 
that  this  energy  is  ultimately  derived  from  the  stock  of  chemical 
energy  in  the  tissue-substance.  But  whether  in  the  final  trans- 
formation the  electrical  phenomena  are  the  expression  of  chemical 
changes  or  of  physical  (osmotic)  changes,  or  of  both,  we  do  not 
know.  Bernstein  has  supposed  that  in  the  chemical  process,  whose 
visible  outcome  is  a  muscular  contraction,  there  are  three  stages  : 
(1)  The  liberation  of  (intra-molecular)  oxygen  from  the  molecules 
of  the  living  substance,   and   its  appearance  as  active   or  atomic 


726  A   MANUAL  OF  PHYSIOLOGY 

oxygen  (p.  401)  ;  (2)  Oxidation  of  the  contractile  substance  by  this 
oxygen  ;  (3)  The  assimilation  of  oxygen  by  the  contractile  substance 
— i.e.,  its  passage  into  the  molecules  of  this  substance  (p.  264). 
According  to  him,  it  is  the  first  of  these  stages  which  is  asscx  iated 
with  the  abrupt  development  of  the  difference  of  potential  bctw< •<  n 
the  excited  and  unexcited  portions  of  the  muscle  which  we  call  the 
negative  variation.  This  first  stage  he  assumes  to  be  completed 
before  the  visible  contraction  begins  ;  and  he  originally  asserted 
that  the  same  was  true  of  the  negative  variation.  It  is  now  known 
that  the  latter,  although  it  begins  before  the  contraction,  and  very 
rapidly  reaches  its  maximum,  declines  more  gradually,  so  that  it 
overlaps  the  mechanical  change  of  form.  This  is  particularly  well 
seen  in  veratrinized  muscles  (p.  654),  in  which  the  electrical  variation, 
like  the  contraction,  is  greatly  prolonged  (Garten).  Nevertheless, 
Bernstein's  theory,  even  with  this  limitation,  agrees  with  what  is 
known  as  to  the  influence  exerted  on  the  action  current  by  the 
mechanical  conditions  of  the  contraction.  For  the  electrical  change 
is  little,  if  at  all,  affected  by  the  tension  of  the  muscle  or  the  load 
it  has  to  lift  ;  and  this  is  what  we  should  expect  it  if  depends  on  a 
process  which  is  mainly  completed  before  the  contraction  begins. 

Polarization  of  Muscle  and  Nerve. — We  have  already  spoken 
of  electrical  excitation  and  of  the  changes  of  excitability  caused 
by  the  passage  of  a  constant  current  (p.  683).  We  are  now  to 
see  that  these  physiological  effects  are  accompanied  by,  and 
indeed  very  closely  related  to,  more  physical  changes  which  the 
galvanometer  or  electrometer  reveals  to  us.  Since  these  throw 
light  on  the  physical,  and  therefore  ultimately  on  the  physio- 
logical structure  of  the  tissues,  they  have  been  deeply  studied, 
especially  in  nerve.  There  is  no  question  that  they  depend 
upon  the  presence  in  the  tissues  of  membranes  presenting  a 
relatively  great  resistance  to  the  passage  of  ions.  When  a 
current  is  passed  by  means  of  unpolarizable  electrodes  (Fig.  213, 
p.  625)  through  a  muscle  or  nerve  for  several  seconds,  and  the 
tissue  thrown  on  to  the  galvanometer  immediately  after  this 
polarizing  current  is  opened,  a  deflection  is  seen  indicating  a 
current  (negative  polarization  current)  in  the  opposite  direction. 

This  (negative)  polarization,  like  the  polarization  of  the  electrodes 
seen  after  passage  of  a  current  through  any  ordinary  electrolytic 
conductor,  dilute  sulphuric  acid,  e.g.,  depends  on  the  liberation  of 
ions  (p.  401)  at  the  kathode  and  anode.  It  is  seen  not  only  in 
muscle,  nerve,  and  other  animal  tissues,  but  also  in  vegetable 
structures,  and  indeed,  to  a  certain  extent,  in  unorganized  porous 
bodies  soaked  with  electrolytes.  In  muscle  and  nerve,  however,  it 
is  particularly  well  marked  ;  and  although  it  is  not  bound  up  with 
the  life  of  the  tissue,  and  may  be  obtained  when  this  has  become 
quite  inexcitable,  it  is  nevertheless  dependent  on  the  preservation 
of  the  normal  structure,  for  a  boiled  muscle  shows  but  little  negative 
polarization. 

When  the  polarizing  current  is  strong,  and  its  time  of  closure 
short,  we  obtain,  on  connecting  the  tissue  with  the  galvanometer 
after  opening  the  current,  not  a  negative,  but  a  positive  deflection, 


/  /  /  cih'o  niYsior.ocY 


727 


indicating  a  current  in  (he  same  direction  ;is  that  of  the  polarizing 
stream,  ilns  is  really  an  action  stream,  due  to  the  opening  excita- 
tion set  up  at  the  anode  (p.  637).  it  is  only  obtained  when  the  tissue 
is  living,  ami  is  Ear  more  strongly  marked  in  the  anodic  than  in  the 
kathodic  region. 

Suppose  that  the  nerve  in  Fig.  ^76  is  stimulated  by  the  opening 
of  the  battery  B,  and  that,  immediately  after,  the  nerve  is  connected 
with  the  galvanometer  G  by  the  electrodes  E,  E,.  Suppose,  further, 
that  the  shaded  region  near  the  anode  remains  more  excited  for  a 
short  time  than  the  rest  of  the  nerve,  and  we  have  seen  (p.  684)  that 
after  the  opening  of  a  strong  current  there  is  a  defect  of  conductivity, 
especially  in  the  neighbourhood  of  the  anode,  which  would  tend  to 


Fig.  276. — Diagram  to  show 
Distribution  of  '  Positive 
Polarization  '  after  open- 
ing Polarizing  Current. 

B,  battery  ;  G,  galvanometer. 
The  dark  shading  signifies  that 
the  excitation  to  which  the 
current  causing  the  positive 
deflection  after  the  opening  of 
the  polarizing  current  is  due  is 
greatest  in  the  immediate  neigh- 
bourhood of  the  anode,  and 
fades  away  in  the  intrapolar 
region.  +  indicates  the  anode 
and  -  the  kathode  of  the  polar- 
izing current. 


A  strong  voltaic  current  was 
passed  for  some  time  through 
the  nerve  of  a  muscle-nerve 
preparation.  On  opening  the 
circuit,  the  muscle  gave  one 
strong  contraction,  and  then 
entered  into  irregular '[tetanus, 
which  continued  for-  four 
minutes.  (Only  the  first  part 
of  the  tracing  is  reproduced.) 


localize  excitation.  The  portion  of  nerve  at  E  being  galvanometric- 
ally  negative  to  that  at  E1;  an  action  current  will  pass  through  the 
galvanometer  from  E}  to  E,  and  through  the  nerve  in  the  same 
direction  as  the  original  stimulating  stream. 

Under  certain  conditions  a  state  of  continuous  excitation  in  the 
anodic  region  of  a  nerve  is  shown  by  a  tetanus  of  its  muscle  (Ritter's 
tetanus,  p.  636,  and  Fig.  277). 

Grutzner  and  Tigerstedt  have  put  forward  a  different  theory  of 
the  break  contraction.  They  say  it  is  really  a  closing  contraction 
due  to  the  closure  of  the  negative  polarization  current  through  the 
tissue  itself,  as  soon  as  the  polarizing  current  is  opened.  But  while 
stimulation  does  sometimes  take  place  in  this  way,  the  contention 


A   MANUAL  OF  1'IIYSIOLOGY 


of  these  observers  that  there  is  only  one  kind  of  electrical  stimulus. 
the  kathodiCi  or  make,  has  not  been  clearly  established. 

Electrotonic  Currents. — If  a  current  be  passed  from  the 
battery  through  a  medullated  nerve  (Fig.  278)  in  the  direction 
indicated  by  the  arrows,  while  a  galvanometer  is  connected  with 
cither  of  the  extrapolar  areas,  as  shown  in  the  figure,  a  current  will 
pass  through  the  galvanometer,  in  the  same  direction  in  the  nerve 
as  the  polarizing  current,  so  long  as  the  latter  continues  to  flow. 

These  currents  are  called  electrotonic  (in  the  kathodic  region 
katelectrotonic  ;  in  the  anodic,  anelectrotonic) .  The  exact  mode  of 
their  production  is  obscure.  Similar  currents  can  be  detected  in 
artificial  models  consisting  of  a  good  conducting  core,  and  a  badly 

conducting  envelope  ; 


&% 


f*\  £&>, 


Fig.   278. — Diagram    showing   Direction   of  the 
k.xtrapolar  electrotonic  currents. 

+     is    the    anode    and  -  the    kathode    of    the 
polarizing  current. 


for  example,  a   plati- 
num   wire    in    a   glass 
tube  filled  with 
rated      zinc     sulphate 
solution,     or     a     zinc 
wire      covered      with 
cotton-wool  soaked  in 
salt  solution.     In  such 
models    it  appears  to 
be  essential  that  there 
should  be  polarization 
(separation  of  ions)  at  the  boundary  between  the  core  and  the  sheath 
— i.e.,  between   the  wire   and   the  liquid,  where  the  current  passes 
from  the  one  to  the  other. 

A  current  led  into  the  sheath  tries,  so  to  speak,  to  pass  mostly  by 
the  good  conducting  wire.  If  this  is  not  polarizable — if  it  is,  e.g.,  a 
zinc  wire  surrounded  by  saturated  zinc  sulphate  solution — there  is 
little  or  no  spreading  of  the  current  outside  the  electrodes  :  it  passes 
at  once  into  the  core,  and  so  on  to  the  other  electrode.  If.  however, 
there  is  polarization  when  the  current  passes  from  the  liquid  into  the 
wire,  as  is  the  case  in  the  platinum-zinc  sulphate,  or  the  zinc-sodium 
chloride  combinations,  the  stream  spreads  longitudinally  in  the 
sheath  since  the  polarization  introduces  a  virtual  resistance  at  the 
surface  of  the  wire,  in  comparison  with  which  the  difference  in 
resistance  of  an  oblique  and  a  direct  transverse  path  through  the 
liquid  becomes  small.  It  has  been  supposed  that  in  medullated 
nerve  a  similar  polarization  takes  place  at  the  boundary  between 
some  part  of  the  nerve-fibre  which  may  be  called  a  core,  and  another 
part  which  may  be  called  a  sheath — for  instance,  between  the  axis- 
cylinder  and  the  medullary  sheath,  or  between  the  latter  and  the 
neurilemma.  It  is  known  that  the  electrical  resistance  of  nerve  in 
the  transverse  direction  is  much  greater  (five  to  seven  times)*  than 
the  longitudinal  resistance.  Since  a  rapidly-established  polarization 
would,  by  the  ordinary  methods  of  measurement,  appear  as  .1  resist- 
ance, this  has  been  adduced  as  evidence  of  the  great  capacity  of 
nerve  for  polarization  by  a  current  passing  across  the  fibres.  It 
is,   however,   probable,   from   what  we  know  of  the  high  electrical 

*  Since  a  part  of  the  current  is  conducted  by  the  connective  tissue 
and  other  structures  lying  between  the  nerve-fibres,  and  the  longitudinal 
and  transverse  resistance  of  these  tissues  may  be  supposed  equal,  the  dis- 
proportion between  the  longitudinal  and  transverse  resistance  of  the 
nerve-fibres  themselves  is  probably  much  greater  than  tl 


/  RO  PHYSIOLOG  V 


729 


resistance  of  the  physiological  envelopes  of  such  cells  ;is  the  red  blood- 
corpuscles  (p.  25),  that  the  .ureal  transverse  resistance  of  nerve,  and 
indeed  the  electrotonic  currents,  are  due  in  part  ifnoi  wholly  to  the 
true  resistance  of  one  or  more  oi  its  envelopes  (perhaps  the  medullary 
she, ah).  Examples  of  such  differences  of  resistance  even  in  the  fluid 
constituents  of  one  and  the  same  animal  structure  arc  not  wanting. 
For  instance,  the  specific  resisl  ance  of  the  yolk  of  a  hen's  egg  may  be 
three  times  greater  than  that  of  the  white. 

The  electrotonic  currents  cannot  spread  beyond  a  ligature  ;  they 
arc  stopped  by  anything  which  destroys  the  structure  of  the  tissue  ; 
they  are  affected  by  various  reagents.  But  this  does  not  prove  that 
they  arc  other  than  physical  in  origin,  for  what  destroys  the  structure 
of  the  tissue  or  modifies  its  molecular  condition  may  destroy  or 
diminish  its  capacity  for  polarization, or  alter  its  electrical  resistance. 

There  are.  however,  certain  facts 
which  indicate  that  physiological  fac- 
tors, as  well  as  physical,  are  con- 
cerned. While  the  currents  obtained 
from  core-models  show  a  general  re- 
semblance to  the  electrotonic  currents 
of  medullated  nerve,  there  is  one  sig- 
nificant difference  :  in  the  former  the 
katelectrotonic  and  anelectrotonic 
currents  are  of  equal  intensity ;  in 
the  latter  the  anelectrotonic  prepon- 
derates. The  most  probable  explana- 
tion is  that  the  anelectrotonic  current 
of  medullated  nerve  is  made  up  of  two 
distinct  electrical  effects,  one  physio- 
logical in  nature,  the  other  dependent 
merely  on  the  structure  and  physical 
properties  of  the  fibres,  while  the  kat- 
electrotonic current  is  wholly  physi- 
cal. It  is  in  favour  of  this  hypothe- 
sis that  under  the  influence  of  ether, 
which  abolishes  the  physiological 
functions  of  nerve,  the  anelectrotonic 
current  diminishes  till  it  becomes 
equal  to  the    katelectrotonic.      Non- 

medullated  nerves,  in  which  the  conditions  for  physical  electrotonus, 
if  present  at  all,  are  only  feebly  developed,  and  which  exhibit  no  kat- 
electrotonic current,  or  only  a  very  weak  one,  show  an  electrotonic 
current,  which  is  abolished  by  ether,  and  seems  to  represent  the  phy- 
siological portion  of  the  anelectrotonic  current  of  medullated  nerve. 

A  nerve  may  be  stimulated  by  an  electrotonic  current  produced 
in  nerve-fibres  lying  in  contact  with  it.  A  well-known  illustration 
of  this  is  the  experiment  known  as  the  paradoxical  contraction 
(Practical  Exercises,  p.  741). 

The  current  of  action  of  a  nerve  can  also  stimulate  another 
nerve  when  the  excitability  of  both  is  greater  than  normal,  as 
is  the  case  in  the  nerves  of  frogs  kept  in  the  cold.  This  comes 
under  the  head  of  secondary  contraction.  But  the  best-known 
form  of  secondary  contraction  is  where  a  nerve,  placed  on  a 
muscle  so  as  to  touch  it  in  two  points  (Fig.  279),  is  stimulated 


Fig.  279. — Secondary  Contrac- 
tion. 

The  nerve  of  muscle  M  touches 
muscle  M'  at  a  and  b.  Stimula- 
tion of  the  nerve  of  M'  at  S  causes 
contraction  of  M. 


73° 


A    MANUAL  OF  PHYSIOLOGY 


by  the  action-current  of  the  muscle,  and  causes  its  own  muscle 
to  contract.  A  secondary  tetanus  can  be  obtained  in  this  way 
by  dropping  a  nerve  on  an  artificially  tetanized  muscle.  The 
beat  of  the  heart  causes  usually  only  a  single  secondary  con- 
traction when  the  sciatic  nerve  of  a  frog  is  allowed  to  fall  on  it 
(p.  188).  But  when  the  diphasic  variation  is  well  marked,  as 
it  is  in  an  uninjured  heart,  there  may  be  a  secondary  contraction 
for  each  phase — i.e.,  two  for  each  heart-beat.  Excitation  of  one 
muscle  may  in  the  same  way  cause  secondary  contraction  of 
another  with  which  it  is  in  close  contact. 
The  electromotive  phenomena  of  the  heart  and  of  the  central 

nervous    system  are   natu- 


A    A 


\ 


a  r> 


i 


■j 


JLH 

5 


> 


rally  included  under  those 
of  muscle  and  nerve. 

Heart. — Records  of  the 
electrical  changes  obtained 
with  the  capillary  electro- 
meter from  the  exposed 
ventricles  vary  in  certain 
details  with  the  position  of 
the  two  contacts.  They 
indicate  that  in  the  mam- 
malian ventricles  the  rela- 
tive negativity  correspond- 
ing to  the  contraction 
begins  at  the  base,  then 
develops  in  the  region  of 
the  apex,  and  finally  in- 
volves the  portion  of  the 
ventricles  near  the  aorta 
and  pulmonary  artery,  pos- 
sibly extending  even  into 
the  roots  of  these  vessels. 
When  one  contact  is  on 
the  base  of  the  ventricles 
(in  the  rabbit)  near  the 
auriculo- ventricular  groove, 
and  the  other  on  the  apex,  the  record  is  quadriphasic — i.e., 
the  sign  of  the  electrical  disturbance  (as  shown  by  the  change 
of  direction  of  movement  of  the  mercury)  changes  four  times 
Fig.  280).  Foi  each  beat  ol  the  ventricle  the  electrometer  record 
shows  (1)  a  sharp  rise,  indicating  relative  negativity  (activity) 
of  the  base  ;  (2)  an  equally  sharp  fall,  indicating  relative 
negativity  at  the  apex  ;  (3)  a  slower  but  marked  rise,  indi- 
cating an  increase  or  a  fresh  development  of  relative  negativity 
at  the  base  ;    (4)   a  more  rapid  fall,  which  returns  first  slowly, 


Fig.    280. — Electrometer   Record    prom 
Rabbit's  Heart  (Gotch). 

The  heart  was  exposed  and  beating  in  situ. 
Contacts,  "iic  "ii  base  of  right  ventricle,  the 
other  on  right  apex.  The  commencement  oi 
the  beat  is  on  the  left-hand  edge  of  the  dark 
line  V.  The  length  of  the  dark  line  shows  the 
duration  of  the  beat.  Upward  movement 
signifies  relative  negativity  (activity)  of  the 
t  or  near  the  base  contact.  Time-trace 
at  tup,  one-fifth  seconds. 


IRO-PHYSIOLOGY 


73' 


then  quickly,  until  (i)  follows  again  (Gotch).  The  time  between 
the  beginning  and  the  top  of  rise  (i)  is  believed  to  correspond  to 
the  time  of  transmission  of  the  active  state  from  the  base  to  the 
apex.  The  rate  of  propagation  on  the  rabbit's  ventricle  varies 
from  i  to  3  metres  a  second,  according  to  the  rate  of  the  heart- 
beat. The  fourth  phase  is  due  to  the  fact  that  the  effect  in  the 
neighbourhood  of  the  aorta  (and  pulmonary  artery)  is  more 
transient  than  the  apex  effect.  By  altering  the  position  of  the 
contacts  the  record  can  be  made  diphasic,  or  even  triphasic. 

In  the  ventricle  of  the  frog  and  tortoise  the  same  order  of 
development  of  the  negative  change  is  seen,  the  base  first 
becoming  relatively  negative,  then  the  apex,  and  then  the 
neighbourhood  of  the  origin  of  the  aorta  (Fig.  281). 


I 


> 


/    1 


A 


Fig.   2S1. — Electrometer  Record  from  Tortoise  Heart  (Gotch). 

One  contact  upon  the  sinus,  the  other  on  the  apex  of  the  ventricle.  One 
complete  beat  shown.  Upward  movement  signifies  relative  negativity  of  the  sinus 
contact.  The  dark  line  A  shows  the  auricular  effect,  and  the  dark  line  V  the 
ventricular  effect.     Time-trace  at  top,  one-fifth  seconds. 


Under  certain  conditions  the  action  current  of  the  heart  may 
stimulate  the  phrenic  nerves,  causing  the  diaphragm  to  contract 
svnchronouslv  with  the  heart. 

The  Human  Electro-cardiogram. — An  electrical  change  accom- 
panies each  beat  of  the  human  heart.  Waller  first  showed  how 
this  may  be  demonstrated  by  means  cf  ths  capillary  electrometer. 

Einthoven  and  Lint  then  investigated  the  phenomenon  on  a 
large  number  of  persons.  From  the  photographic  records  of  the 
movements  of  the  meniscus   (Fig.   282)  they  constructed   the  true 


732 


I     1/  /  \  /    II.  OF  PHYSIOLOGY 


electrocardiographic  curves*  (Fig.  283),  which  express  the  actual 
changes  to  the  potential  difference  between  thi  two  points  led  off. 
They  distinguished  in  every  one  oJ  these  construe  ted  1  I'  1  tro  1  audio- 
grams five  points  or  cusps,  three  of  which  indicate  relative  negativity 
of  (In-  base  of  the  heart  to  the  apex,  and  two  negativity  of  the  api 
the  base.  The  capillary  electrometer  has  now  been  largely  superseded 
by  the  string  galvanometei  (p.  619)  for  the  investigation  oi  the  human 
ele<  tro  1  ardiogram  ( Figs.  284-287).  Records  arc  obtained  l>v  magnify- 
ing and  photographing  the  movements  of  the  quartz  fibre,  ill'  electro- 
cardiograms arc  distinctly  affected  by  exercise  and  by  the  position 


l;n,  282. — Electro-cardiograms  from  Man 
(Capillary  Electrometer),  (Einthoven 
and  Lint). 

The  image  of  the  capillary  magnified  eight 
hundred  times  was  proje<  ted  on  a  moving  photo- 
graphic plate.     The  figure  is  a  reproduction  of 

the  record  (reduced  to  two-thirds  of  its  original 
size)  obtained  from  the  same  individual  at  rest 
(upper  curve),  and  immediately  after  vigorous 
muscular  exercise  (lower  curve).  The  move- 
ments of  a  tuning-fork,  making  fifty  complete 
vibrations  a  second,  are  shown  below  the  i  ardio- 
grams.  The  sulphuric  acid  pole  of  the  electro- 
meter was  connected  with  the  thoracic  wall  in 
the  neighbourhood  of  the  apex  of  the  heart. 
and  the  mercury  with  the  right  arm.  The 
elevations  A,  C,  D,  indicate  negativity  oi  base 
to  apex  ;  the  notches  li  and  C1;  negativity  oi  apex 
to  base. 


bio.    283.       —      CONS1  R1  I   M  l> 

lectro  -  cardiograms 
from  Man  (Einthoven 
ami   Lint). 

The  curves  are  constructed 
from  the  photographic  records 
shown  m  big.  282.  These  and 
not  the  photographs  are  the 
true  expression  oi  the  actua 
changes  of  potential  during 
the  cardiac  cj  1  le.  lime  is 
laid  oil  along  the  horizontal, 
ami  electromoth e  force  along 

the    vertical     axis,     the    s.uue 
space      being    allotted     to    ten 

millivolts   [i.e.,    1',,,    volt)   as 

to   one    sei  ond. 


ui  the  body,  and  very  markedly  in  disease.  They  .ire  being  more 
and  more  employed  in  clinical  investigations.  The  galvanometer 
may  be  conni  <  ted  with  the  two  hands,  or  better,  with  the  righl  hand 
and  the  hit  foot.  I  in-  two  bid  ,ue  the  nmsi  unfavourable  com- 
bination. 

Central  Nervous  System.  -It  was  discovered  by  du  Bois-Reymond 
that  the  spinal  cord,  like  a  nerve,  shows  a.  current  of  nst  between 

*  In  all  accurate  work  with  the  capillary  elect  n  nuclei  such  curves  must 
be  obtained  by  construction  from  the  direct  photographic  records,  which 
do  not  themselves  give  an  absolutely  true  picture  of  the  variations. 


ELECTRO- PHYSIOLOGY 


733 


longitudinal  surface  and  cross-section,  and  that  a  current  of  action 
is  caused  l>\-  excitation.  Setsi  henow  stated  tli.it  when  the  medulla 
oblongata  of  the  frog  was  connected  with  a  galvanometer,  spon- 
taneous   variations   occurred    which    tie   supposed   due   to   periodic 


Fig.  284.       Human  Electrocardio- 
gram     (String      Galvanometer), 

(Ein  rHOVEN). 

Led  off  from  the  two  hands,      i  mm. 
Af  the    abscissa    corresponds    to    ooi 

second. 


'['■(' 

! :    :  J 

fi 

zttiixttxj 

• -— 

±±& 

i  |..i  .:■. 

| 

fffp 

MM 

H 

a 

1 

Fig.  .,v;v-Hi-.m.\n  Electro-cardio- 
gram (String  Galvanometer), 
(Einthoven). 

Led  off  from  right  hand  and  left 
foot. 


s 


p 

-A. 


T 


Fig.   286. — Schematic   Representation  of  Electro-cardiogram  (String 
Galvanometer),   (Einthoven). 

Five  points  are  lettered  at  which  the  curve  changes  sign.      P.  corresponds  to 
the  auricular  contraction  ;  the  other  four  are  included  in  the  ventricular  cycle. 


Fig.  287. — Electro-cardiogram  from  Man  (String  Galvanometer),  (Lewis). 

From  a  case  of  paroxysmal  tachycardia.     The  heart-rate  was  200  a  minute. 
The  upper  notched  line  is  the  time-trace  in  one-fifth  seconds. 

functional  changes  in  its  grey  matter.  Gotch  and  Horslev  have 
made  elaborate  experiments  on  the  spinal  cords  of  cats  and  mon- 
keys. Leading  off  from  an  isolated  portion  of  the  dorsal  cord  to 
the  capillary  electrometer,  and  stimulating  the  "  motor  "  region  of  the 


A    MANUAL  OF  PHYSIOLOGY 

cortex  cerebri,  they  obtained  a  persistent  negative  variation  followed 
by  a  series  of  intermittent  variations.  This  agrees  remarkably  with 
the  muscular  contractions  in  an  epileptiform  convulsion  started  by 

a  similar  excitation  of  the  cortex,  which  consist  of  a  tonic  spasm 
followed  by  clonic  or  phasic  (interrupted)  contraction-, 

By  means  of  the  galvanometer  the  same  observers  have  made 
investigations  on  the  paths  by  which  impulses  set  up  at  different 
points  travel   along   the  cord.      To  these   we  shall   have  to   i 
again  (p. 

Electrical  Phenomena  of  Glands.  These  have  been  studied  with 
any  care  chiefly  in  the  submaxillary  gland  and  in  the  skin,  although 
the  liver,  kidney,  spleen,  and  other  organs  also  show  currents  when 
injured.  In  the  submaxillary  gland  the  hilus  is  galvanometrically 
positive  to  any  point  on  the  external  surface  of  the  gland  ;  a 
current  passes  from  hilus  to  surface  through  the  galvanometer,  and 
from  surface  to  hilus  through  the  gland  (Fig.  288).  When  the 
chorda    tympani    is   stimulated    with    rapidly-succeeding   shocks   of 

moderate   strength,  there  is  a  positive 
variation      i.e..  the    hilus  becomes  stiH 
more    positive    to    the    surface.      This 
variation  can  be  abolished  by  a   small 
of  atropine. 
Skin  Currents.  —So    far   as   has  been 
investigated,     the    integument     of    all 
animals    shows    a    permanent    current 
passing   in   the  skin  from  the  external 
surface  inwards.     This  is  feebler  in  skin 
which     possesses    no    glands.      In    skin 
Fig.  z88. — Current    of    Sub-     containing  glands  the  current  is  chiefly, 
maxillary  Gland.  but     not     altogether,     secretory.       As 

such,  it  is  affected  by  influences  which 
affect  secretion,  a  positive  variation  being  caused  by  excitation 
of  secretory  nerves — e.g.,  in  the  pad  of  the  cat's  foot  by  stimula- 
tion cf  the  sciatic.  The  deflection  obtained  when  a  finger  of  each 
hand  is  led  off  to  the  galvanometer,  which  was  at  one  time  looked 
upon  as  a  proof  of  the  existence  of  currents  of  rest  in  intact  muscles, 
is  due  to  a  secretion  current. 

'  )f  more  doubtful  origin  is  the  current  of  ciliated  mucous  mem- 
brane, which  has  the  same  direction  as  that  of  the  skin  1  f  the  frog 
and  the  mucous  membrane  of  the  stomach  of  the  frog  and  rabbit — 
viz..  from  ciliated  to  under  surface  through  the  tissue,  or  from 
ciliated  surface  to  cross-section,  if  that  is  the  way  in  which  it  is 
led  off.  The  current  is  strengthened  by  induction  shocks,  by 
heating,  and  in  general  by  influences  which  increase  the  activity  of 
the  cilia.  Some  circumstances  point  to  the  goblet-cells  in  the 
membrane  as  the  source  of  the  current  ;  but.  on  the  whole,  the 
balance  of  evidence  is  in  favour  of  the  cilia  being  the  chief  factor 
(Engelmann),  although  the  mucin-secrcting  cells  may  be  concerned. 
too.  Electrical  changes  associated  with  secretion  have  1 
observed  in  the  frog's  tongue  on  excitation  cf  the  glosso-pharyngeal 
nerve. 

Eye-currents.— If  two  unpolarizable  electrodes  connected  with 
a  galvanometer  are  placed  on  the  excised  eye  of  a  frog  or  rabbit, 
one  on  the  cornea  and  the  other  on  the  cut  optic  nerve,  or  on  the 
posterior  surface  of  the  eyeball,  it  is  found  that  a  current  passes  in 
the  eye  from  optic  nerve  to  cornea,  the  fundus  of  the  eye  being 


ELECTRO-PHYSIOLOGY 


735 


therefore  negative  .1-  regards  the  cornea  (Fig.  289).  The  current 
has  the  same  direction  d  the  anterior  electrode  La  placed  on  the 
anterior  surface  of  the  retina  itself,  the  front  of  the  eyeball  being 
cut  away,  or  if  one  electrode  is  in  contad  with  the  anterior  and  the 
other  with  the  posterior  surface  of  the  isolated  retina.  There  is 
nothing  of  special  interest  in  this  ;  but  the  important  point  is  that 
if    light    be    now    allowed    to    f.i.ll    upon 

the  eye,  or  upon  the   isolated    retina, 

characteristic  electrical  changes  arc 
caused.  These  arc  spoken  of  as  the 
photo-electric  reaction,  and  are  best 
studied  by  means  of  the  string  gal- 
vanometer. The  features  of  the  curve 
representing  the  photo-electric  reaction 
vary  with  the  duration  and  intensity 
of  the  illumination  and  with  the  pre- 
vious condition  of  the  eye  as  regards 
illumination.  A  careful  analysis  of 
the  curves  obtained  under  different 
conditions  supports  the  hypothesis  that 
there  occur  in  the  eye  three  separate 
processes,  which  may  for  convenience 
be  considered  to  depend  upon  the  existence  in  the  retina  of 
three  separate  photo-chemical  substances  (p.  934).  When  light 
of  moderate  intensity  is  allowed  to  act  upon  an  eye  which  has  not 
shortly  before  been  exposed  to  strong  light,  a  form  of  curve  is 
obtained  which  seems  to  represent  the  combined  reaction  of  the 
three  substances  (Einthoven  and  Jolly)   (Fig.  290).     After  a  latent 


Fig.  289. — Eye-current. 


Fig.  290. — Photo-electric  reaction  of  Frog's  Eye  (Einthoven£and 

Jolly). 

The  duration  of  the  flash  (of  green  light)  was  ooi  second.  The  eye  had  been 
previously  in  the  dark,  i  millimetre  of  the  abscissa  corresponds  to  o-5  second, 
1  millimetre  of  the  ordinate  to  10  microvolts.     Curve  to  be  read  from  left  to  right. 


period  a  small  preliminary  negative  deflection  A  is  observed  (down- 
ward movement  of  the  string).  This  is  at  once  followed  by  a  much 
larger  upward  movement  (positive  variation)  in  the  same  direction 
as  the  resting  effect,  the  fundus  becoming  relatively  more  negative 
to  the  cornea  than  before.  After  the  peak  B  has  been  reached,  the 
curve  sinks  first  rapidly,  then  more  gradually,  but  soon  mounts 
again,  and  reaches  a  second  maximum  C,  which  is  higher  than  B 


736 


A    1/  \NUAL  OF  PHYSIOLOGY 


(second  positive  variation).  Finally,  the  curve  descends  to  its 
original  level.*  I  lie  photo-electric  reaction  is  substantially  the 
same  in  all  vertebrate  eyes  hitherto  investigated.  In  the  i  ephalopod 
retina,  too,  the  only  important  electrical  change  on  illumination  is 
in  the  same  dire*  tion  as  the  resting  effect. 

The  reaction  (Upends  upon  the  retina  alone,  and  does  not  occur 
when  it  is  removed.  Bleaching  of  the  visual  purple  does  not  much 
affect  it,  so  that  it  is  not  connected  with  chemical  changes  in  this 


Fig.   291. — Diagram  showing  Direction  of  Shock  in  Gymnotus. 


substance.  Its  seat  must  be  the  layer  of  rods  and  cones,  since  in  the 
ccphalopods  the  structure  called  the  retina  contains  only  this  layer, 
the  other  layers  of  the  vertebrate  retina  being  represented  in  the 
optic  nerve  and  ganglion  (Beck).  Of  the  spectral  colours,  yellow- 
light  causes  the  largest  variation  ;  blue,  the  least  ;  but  white  light 
is  more  powerful  than  either  (Dewar  and  McKendrick).  (For 
'  visual  purple,'  see  p.  934. 

Electric  Fishes. — -Except  lightning,  the  shocks  of  thcse'Jfishes  were 
probably  the  first  manifestations  of  electricity  observed  by  man. 

The  Torpedo,  or  electrical 
ray,  of  the  coasts  of  Europe 
was  known  to  the  Greeks 
and  Romans.  It  is  men- 
tioned in  the  writings  of 
Aristotle  and  Pliny,  and  had 
the  honour  of  being  described 
in  verse  1,500  years  before 
Faraday  made  the  first  really 
exact  investigation  of  the 
shock  of  the  Gymnotus,  or 
electric  eel,  of  South  Amer- 
ica. Another  of  the  electric 
fishes.  Malapterurus  electri- 
CUS,  although  found  in  many 
of  the  African  rivers,  the  Nile  in  particular,  and  known  for  ages, 
was  scarcely  investigated  till  fifty  years  ago. 

In  all  these  fishes  there  is  a  special  bilateral  organ  immediately 
under  the  skin,  called  the  electrical  organ.  It  is  in  this  that  the 
shock  is  developed.  It  consists  of  a  series  of  plates  arranged  parallel 
to  each  other.     To  one  side  of  each  plate  a  branch  of  the  electrical 

*  In  the  figure  the  last  portion  of  the  curve  while  it  is  still  slowly 
descending  has  not  been  reproduced. 


Fig. 


292. — Diagram     showing     DIRECTION 
OF  Shock  in   Malaptervris. 


ELECTRO-PHYSIOLOGY  7n 

nerve  supplying  each  lateral  nail  of  the  organ  is  distributed,  so  thai 
each  hall  oi  the  organ  represents  a  battery  ol  many  cells  arranged 
in  series. 

In  Gymnotus  the  plates  are  vertical,  and  at  right  angles  to  the 
Long  axis  of  the  fish,  and  the  nerves  are  distributed  to  their  posterior 
surface;  the  shock  passes  in  the  animal  from  tail  to  bead.  In 
Malapterurus,  although  the  direction  of  the  plates  is  the  sai 
and  the  nerve-supply  is  also  to  the  posterior  surface,  the  shock 
passes  from  head  to  tail. 

In  Torpedo,  the  plates  or  septa  dividing  the  vertical  hexagonal 
prisms  of  which  each  lateral  half  of  the  organ  consists  are  hori- 
zontal ;  tli"  nerve-supply  is  to  the  lower  or  ventral  surface  ;  and  the 
shock  passes  from  belly  to  back  through  the  organ.  In  all  electric 
fishes  tli-  discharge  is  discontinuous;  an  active  fish  may  give  as 
many  as  200  shocks  per  second. 

The  electrical  nerve  of  Malapterurus  is  very  peculiar.  It  con- 
sists of  a  single  gigantic  nerve-fibre  on  each  side,  arising  from  a 
giant  nerve-cell.  The  fibre  has  an  enormously  thick  sheath,  the 
axis-cylinder  forming  a  relatively  small  part  of  the  whole  ;  and  the 
branches  which  supply  the  plates  of  the  organ  are  divisions  of  this 
single  axis-cylinder. 

The  electromotive  force  of  the  shock  of  the  Gymnotus  may  be 
very  considerable  ;  and  even  Torpedo  and  Malapterurus  are  quite 
able  to  kill  other  fish,  their  ene- 
mies or  their  prey.  Indeed. 
Gotch  has  estimated  the  elec- 
tromotive force  of  1  cm.  of  the 
organ  of  Torpedo  at  5  volts. 
Schonlein  finds  that  the  electro- 
motive force  of  the  whole  organ 
may  be  equal  to  that  of  31 
Danicll  cells,  or  00S  volt  for  Fig.  293.— Diagram  showing  Direc- 
each    plate,    and    it    is    one    of  tiox  of  Shock  in  Torpedo. 

the  most   interesting  questions 

in  the  whole  of  electro-physiology,  how  they  are  protected  from 
their  own  currents.  There  is  no  doubt  that  the  current  density 
inside  the  fish  must  be  at  least  as  great  as  in  any  part  of  the  water 
surrounding  it,  and  probably  much  greater.  The  central  nervous 
svstem  and  the  great  nerves  must  be  struck  by  strong  shocks,  yet 
the  fish  itself  is  not  injured  ;  nay,  more,  the  young  in  the  uterus  of 
the  viviparous  Torpedo  are  unharmed.  The  only  explanation  seems 
to  be  that  the  tissues  of  electric  fishes  are  far  less  excitable  to 
electrical  stimuli  than  the  tissues  of  other  animals  ;  and  this  is  found 
to  be  the  case  when  their  muscles  or  nerves  are  tested  with  galvanic 
or  induction  currents.  It  requires  extremely  strong  currents  to 
stimulate  them  ;  and  the  electrical  nerves  are  more  easily  excited 
mechanically,  as  by  ligaturing  or  pinching,  than  electrically.  In 
general,  too,  the  shock  is  more  readily  called  forth  by  reflex  mechani- 
cal stimulation  of  the  skin  than  by  electrical  stimulation.  But  that 
the  organ  itself  is  excitable  by  electricity  has  been  shown  by  Gotch. 
He  proved  that  in  Torpedo  a  current  passed  in  the  normal  direction 
of  the  shock  is  strengthened,  and  a  current  passed  in  the  opposite 
direction  weakened,  by  the  development  of  an  action  current  in  the 
direction  of  the  shock.  And.  indeed,  a  single  excitation  of  the 
electrical  nerve  is  followed  by  a  series  of  electrical  oscillations  in  the 
organ,   which  gradually  die  away.     The  latent  period  of  a  single 

47 


738  A    V  \NUAL  OF  PHYSIOLOGY 

shock  is  about  ..,',,,  second.  The  skate  must  be  included  in  the  list 
of  electric  fishes.  Although  its  organ  is  relatively  small,  and  its 
electromotive  Eon  e  relatively  feeble,  yet  it  is  in  all  respects  a  com- 
plete electrical  organ.  It  is  situated  on  either  side  of  the  vertebral 
column  in  the  tail.  The  plates  or  discs  are  placed  transversely  and 
in  vertical  planes.  The  nerves  enter  their  anterior  surfaces  ;  the 
shock  passes  in  the  organ  from  anterior  to  posterior  end.  Gotch 
and  Sanderson  have  estimated  the  maximum  electromotive  Eon  e  oi 
a  length  of  i  cm.  of  the  electrical  organ  of  the  skate  at  about  half  a 
volt. 

Wlu-ther  the  electrical  organ  is  the  homologue  of  muscle  or  of 
nerve-ending,  or  whether  it  is  related  to  either,  has  been  much  dis- 
cussed. Our  surest  guide  in  a  question  of  this  sort  is  the  study  of 
development  ;  and  researches  along  this  line  have  shown  that  there 
are  two  kinds  of  electrical  organ,  one  being  modified  muscle  (as  in 
Gymnotus,  Torpedo,  and  the  skate)  ;  the  other  transformed  skin- 
glands  (as  in  MEalapterurus).  The  scanty  blood-supply  of  tin- 
electrical  organs  in  comparison  with  that  of  muscle  is  noteworthy. 
In  no  case  do  bloodvessels  enter  the  substance  of  the  plates. 


PRACTICAL  EXERCISES  OX  CHAPTER   XI. 

i.  Galvani's  Experiment. — Pith  a  frog  (brain  and  cord).  Cut 
through  the  backbone  above  the  urostyle,  and  clear  away  the 
anterior  portion  of  the  body  and  the  viscera.  Lass  a  copper  hook 
beneath  the  two  sciatic  plexuses,  and  hang  the  legs  by  the  hook  on 
an  iron  tripod.  If  the  tripod  has  been  painted,  the  paint  must 
be  scraped  away  where  the  hook  is  in  contact  with  it.  Now  tilt 
the  tripod  so  that  the  legs  come  in  contact  with  one  of  the  iron 
feet.  Whenever  this  happens,  the  circuit  for  the  current  set  up 
by  the  contact  of  the  copper  and  iron  is  completed,  the  nerves  are 
stimulated,  and  the  muscles  contract  (p.  717). 

2.  Make  a  muscle-nerve  preparation  from  the  same  frog,  (rush 
the  muscle  near  the  tendo  Achillis,  so  as  to  cause  a  strong  demarca- 
tion current.  Cut  off  the  end  of  the  sciatic  nerve.  Then  lift  tin- 
nerve  with  a  small  brush  or  thin  glass  rod,  and  let  its  cross-sect  1  mi 
fall  on  or  near  the  injured  part  of  the  muscle.  Every  time  the 
nerve  touches  the  muscle  a  part  of  the  demarcation  current  passes 
through  it,  stimulates  the  nerve,  and  causes  contraction  of  the 
muscle  (p.  717). 

3.  Secondary  Contraction. — Make  two  muscle-nerve  preparations. 
Lay  the  cross-section  of  one  of  the  sciatic  nerves  on  the  muscle  "t 
the  other  preparation  (Fig.  279,  p.  729).  Place  under  the  nerve 
near  its  cut  end  a  small  piece  of  glazed  paper  or  of  f^lass  rod,  and 
let  the  longitudinal  surface  of  the  nerve  come  in  contact  with  tin- 
muscle  beyond  this.  Lay  the  nerve  of  the  other  preparation  on 
electrodes  connectexl  with  an  induction  machine  arranged  for  single 
shocks,  with  a  Danicll  cell  and  a  spring  key  in  the  primary  circuit 
(Fig.  258,  p.  703).  On  closing  or  opening  the  key  both  muscles  con- 
tract. Arrange  the  induction  machine  for  an  interrupted  current. 
When  it  is  thrown  into  one  nerve,  both  muscles  arc  tetanized  ; 
the  nerve  lying  on  the  muscle  whose  nerve  is  directly  stimulated  is 
excited  by  the  action  current  of  the  muscle. 


PRAl  TICAL   EXERCISl  s 


|.  Demarcation  Current  and  Current  of  Action  with  Capillary 
Electrometer,  —(a)  Study  the  construction  <>i  the  capillary  electro- 
meter (Fig.  210,  p.  621).  k.usr  the  glass  reservoir  by  the  rack  and 
pinion  screw,  so  .is  to  bring  the  meniscus  of  the  mercury  into  the 
field.  Place  two  moistened  fingers  on  the  binding-screws  of  the 
electrometer,  open  the  small  key  connecting  them,  and  notice  that 
the  mercury  moves,  .1  difference  of  potential  between  the  two  binding- 
screws  being  caused  by  the  moistened  lingers. 

(b)  Demarcation\Current.  Set  up  a  pair  of  unpolarizable  elec- 
trodes (Fig.  213.  p.  625).  Fill  the  glass  tubes  about  one-third  lull 
Ol  kaolin  mixed  witli  physiological  salt  solution  till  it  can  be  easily 
moulded.  To  do  this,  make  a  piece  of  the  clay  into  a  little  roll,  which 
will  slip  down  the  tube.  Then  with  a  match  push  it  down  until  it 
forms  a  firm  plug.  Next  put  some  saturated  zinc  sulphate  solution 
in  the  tubes,  above 
the  clay,  with  a 
line  -  pointed  pi- 
pette. Fasten  the 
tubes  in  the  holder 
fixed  in  the  moist 
chamber  (Fig.  294) . 
Now  amalgamate 
the  small  pieces  of 
zinc  wire  (p.  182), 
which  ^  are  to  be 
connected  with  the 
binding-screws  of 
the  chamber.  (Or 
use  Porter's  '  boot ' 
electrodes.  These 
are  made  of  un- 
glazed  potter's 
clay.  In  use  the 
leg  of  the  boot  is 
half -filled  with 
saturated  zinc  sul- 
phate solution,  in- 
to which  dips  a 
thick  amalga- 
mated zinc  wire. 
In  the  foot  of  the 
boot  is    a    hollow 

(or  well)  which  is  filled  with  physiological  salt  solution  and  serves 
to  keep  the  feet  well  moistened  with  the  salt  solution.  The  nerve 
is  laid  on  the  feet  of  the  boots.  When  not  in  use  the  boots  should  be 
kept  in  physiological  salt  solution.) 

The  zincs  are  now  placed  in  the  tubes,  dipping  into  the  zinc  sulphate. 
A  piece  of  clay  or  blotting-paper  moistened  with  physiological  salt 
solution  is  laid  across  the  electrodes  to  complete  the  circuit  between 
their  points,  and  they  are  connected  with  the  electrometer  to  test 
whether  they  have  been  properly  set  up.  There  ought  to  be  little, 
if  any,  movement  of  the  mercury  on  opening  the  side-key  of  the 
electrometer.  If  the  movement  is  large,  the  electrodes  are  '  polar- 
ized.' and  must  be  set  up  again.  The  second  pair  of  binding-screws 
in  the  chamber  are  connected  with  a  pair  of  platinum-pointed 
electrodes  on  the  one  side,  and  on  the  other,  through  a  short-cir- 

47—2 


Fig.  294. — Moist  Chamber. 

E,  unpolarizable  electrodes  supported  in  the  cork  C  ; 
M.  muscle  stretched  over  the  electrodes  and^.kept  in 
position  by  the  pins  A,  B,  stuck  in  the  cork  plate  P  ; 
B,  binding-screws  connected  with  galvanometer  or 
capillary  electrometer.  The  other  pair  of  binding- 
screws  serves  to  connect  a  pair  of  stimulating  electn»des 
inside  the  chamber  with  the  secondary  coil  of  an  induc- 
tion machine. 


74"  A   MANl    II    01    PHYSIOLOGY 

cuiting  key,  with  the  second  iry  coil  of  an  induction  mai  nine  arranged 
for  tetanus. 

Next  pith  a  frog  (cord  and  bruin),  and  make  a  muscle-nerve 
preparation.  Injur.'  the  muscle  near  the  tendo  Achillis.  Lay  the 
injured  pari  over  one  unpolarizable  electrode,  and  an  uninjured 
part  over  the  other.  Put  a  wet  sponge  in  the  chamber  to  keep  the 
air  moist,  and  place  the  glass  lid  on  it.  Focus  the  menis<  us  of  the 
mercury,  and  open  the  key  of  the  electrometer;  the  mercury  will 
move,  perhaps  right  out  of  the  field.  Note  the  direction  of  move- 
ment, and  remembering  that  the  real  direction  is  the  opposite  of 
the  apparenl  direction,  and  that  when  the  mercury  in  the  capillary 
tube  is  connected  with  a  part  of  the  muscle  u  tri<  h  is  relatively  positive 
to  that  connected  with  the  sulphuric  acid,  the  movement  is  from 
capillary  to  acid,  determine  which  is  the  galvanometrically  positive 
and  which  the  negal  ive  portion  of  the  muscle 

(c)  Action  ('iinm/.  Now.  without  disturbing  its  position  on  the 
electrode-,,  fasten  the  muscle  to  the  cork  or  paraffin  plate  in  the  i 
chamber  by  pins  thrust  through  the  lower  end  of  the  lemur  and 
the  tendo  Achillis.  Lay  the  nerve  on  the  platinum  electrodes. 
Open  the  key  of  the  electrometer,  and  let  the  meniscus  come  to 
rest.  This  happens  very  quickly,  as  the  capillary  electrometer 
has  but  little  inertia.  If  the  meniscus  has  shot  out  of  the  field,  it 
must  be  brought  back  by  raising  or  lowering  the  reservoir.  Stimu- 
late the  nerve  by  opening  the  key  in  the  secondary  circuit  :  the 
meniscus  moves  in  the  direction  opposite  to  its  former  movement. 

Repeat  (b)  and  (c)  with  the  nerve  alone,  laying  an  injured  part 
■rushed,  cut,  or  overheated)  on  one  electrode,  and  an  uninjured 
part  on  the  other.     <  >f  course,  the  nerve  does  not  need  to  be  pinned. 

(lean  the  unpolarizable  electrodes,  and  be  sure  to  lower  the 
reservoir  of  the  electrometer;  otherwise  the  mercury  may  reach 
the  point  of  the  capillary  tube  and  run  out. 

In  |  a  galvanometer  (p.  017)  may  be  used  with  advantage  by 
students,  if  one  is  available,  instead  of  the  electrometer,  the  un- 
polarizable electrodes  being  connected  to  it  through  a  short- 
uitingkey.  The  spot  of  light  is  brought  to  the  middle  of  the 
scale  by  moving  the  control-magnel  :  or  if  a  telescope-reading 
206,  p.  618)  is  being  used,  the  zero  of  the  scale  is  brought 
by  the  same  means  to  coincide  with  the  vertical  hair-line  of  the 
telescope.     The  short-circuiting  key  is  then  opened. 

5.  Action-current  of  Heart.  -Pith  a  frog  1  brain  and  cord).  Excise 
the  heart,  and  lav  the  base  on  one  unpolarizable  electrode,  and  the 
apex  on  the  other,  having  a  sufficient lv  large  pad  of  clay  on  the  tips 
of  the  el  10  insure  contact  during  the  movements  of  the 
heart,  or  having  little  cups  hollowed  111  the  clay  and  tilled  with 
physiological  salt  solution,  into  which  the  organ  clips.  Connect  the 
electrodes  with  the  capillary  electrometer  and  open  its  key.  V 
each  beat  of  the  heart  the  mercury  will  move  (p.  730). 

6.  Electrotonus.  -Set  up  two  pairs  of  unpolarizable  electrodes  in 
the  moist  chamber.  Connect  two  of  them  with  a  capillary  electro- 
meter (or  galvanometer),  and  two  with  a  batters-  of  three  or  four 
small  Daniell  cells,  as  in  Pig.  J78.  Lay  a  frog's  nerve  on  the  1 
trodes.  When  the  key  in  the  battery  circuit  is  <  losed,  the  mercury 
(or  the.  needle  of  the  galvanometer)  moves  in  such  a  direction  as 
to  indicate  that  in  the  extrapolar  regions  parts  of  the  nerve  nearer 
to  the  anode  are  relatively  positive  to  parts  more  remote,  and  parts 
nearer  to  the  kathode  are  relatively  negative  to  parts  more  remote. 


PRAC7  l<    //.   EXERCISES 


74' 


The  direction  of  movemenl  of  the  mercury  (or  galvanometer  needle) 
must  1>-  made  ou1  &rs1  for  one  direction  of  the  polarizing  current. 
Then  the  latter  musf  be  reversed,  and  the  movemenl  oi  thi  men  ury 
(or  needle)  on  closing  it  again  noted  (p.  728). 

7.  Paradoxical  Contraction.  Pith  a  Erog  (brain  and  cord).  Dis- 
S3d  out  the  sciatic  nerve  down  to  the  point  whore  it  splits  into  two 
divisions,  one  for  the  gastroi  nemius  b,  and  the 
oi  her  for  th  •  p  ir<  mea !  muscles  a.  Divide  the 
peroneal  branch  ;is  low  down  as  possible,  and 
make  a  muscle  nerve  preparation  in  the  usual 
way.  Lay  the  central  end  of  the  peroneal 
n  irveon  electrodes  connected  through  a  simpl  3 
key  with  a  battery  oi  t  wo  I  )ani  II  cells.  W'h  n 
the  peroneal  nerve  is  stimulated  the  gastroc- 
nemius muscle  contracts.  This  result  is  not 
due  to  the  current  of  action,  for  it  is  not 
obtained  with  mechanical  stimulation  of  the 
nerve  ;  but  it  is  not  the  result  of  an  escape  of 
current,  for  if  the  peroneal  nerve  be  ligatured 
between  the  point  of  stimulation  and  the 
bifurcation,  no  contraction  i.s  obtained.  The 
contraction  is  really  due  to  a  part  of  the  electro- 
tonic  current  set  up  in  the  peroneal  nerve 
passing  through  the  fibres  for  the  gastrocne- 
mius, where  they  lie  side  by  side  in  the 
trunk  of  the  sciatic. 

8.  Alterations  in  Excitability  and  Conduc- 
tivity produced  in  Nerve  by  the  Passage  of  a  Voltaic  Current  through 
it. — (a)  Set  up  two  pairs  of  unpolarizable  electrodes  in  the  moist 
chamber.  Connect  a  battery  of  two  or  three  Daniell  cells,  arranged 
in  series  through  a  simple  key  with  the  side-cups  of  a  Pohl's  commu- 
tator with  cross- wires  in.    Connect  the  commutator  to  one  pair  of  the 


Fig.    295.  —  Paradoxi- 
cal Contraction-. 


Fig.  296. — Arrangement  for  showing  Changes  of  Excitability 
produced  by  the  voltaic  current. 
M.  muscle;  N,  nerve;  E,.  K...  electrodes  connected  with  secondary  coil  S;  Es, 
E4.    unpolarizable   electrodes    connected  with    Pohl's  commutator  (with  cross- 
wires)  C  ;   B',  'polarizing'  battery;  B,  'stimulating'   battery  in  primary  circuit 
P;   K,  K",  simple  keys;  K'.  short-circuiting  key. 

unpolarizable  electrodes  ('  the  polarizing  electrodes  '),  as  in  Fig.  296. 
The  other  pair  of  unpolarizable  electrodes  ('the  stimulating  elec- 
trodes ')  are  to  be  connected  through  a  short-circuiting  key  with  the 
secondary  of  an  induction  machine  arranged  for  tetanus.  A  single 
Daniell  is  put  in  the  primary  coil.     Pith  a  frog  (brain  and  cord),  make 


742  .1     XfANUAl    "/■    niYSlOLOCY 

a  mus<  le  aerve  pr<  paration,  pin  the  lowei  end  oi  the  femur  to  the 
cork  plate  iii  the  moist  chamber,  attach  the  thread  on  the  tcndo 
Achillas  to  the  lever  connected  with  the  chamber  through  the  hole 
in  the  glass  provided  Eor  tins  purpose,  and  arrange  the  uerve  on  the 

electrodes  so  thai  the  stimulating  pair  is  between  the  muscle  and 
the  polarizing  pair.  By  moving  the  secondary,  seek  out  such  a 
strength  of  stimulus  as  just  suffices  to  cause  a  weak  tetanus  when 
the  polarizing  current  is  not  closed.  Set  the  drum  oil  (slow  speed), 
and  take  a  tracing  of  the  contraction.  Then  (lose  the  polarizing 
current  with  a  Fold's  commutator  so  arranged  that  the  anode 
is  next  the  stimulating  electrodes  i.e.,  the  current  ascending  in 
the  nerve.  Again  open  the  short-circuiting  key  in  the  secondary  ; 
the  contraction  will  now  be  weaker  than  before,  or  no  contraction 
at  all  may  be  obtained.  Allow  the  preparation  two  minutes  to 
recover,  then  stimulate  again,  as  a  control,  without  closing  the 
polarizing  current.  If  the  contraction  is  of  the  same  height  as  at 
lirst,  close  the  polarizing  current  with  the  bridge  of  the.  commutator 
reversed,  so  that  the  kathode  is  now  next  the  stimulating  electrodes. 
<  >n  stimulating,  the  contraction  will  now  be  increased  in  height. 
(See  Figs  253,  254,  p.  683.) 

(b)  Arrange  everything  as  in  (a),  except  that  one  of  the  polarizing 
electrodes  is  placed  at  each  end.  and  the  two  stimulating  electrodes 
close  together  in  the  middle  of  the  nerve.  A  large  carbon  re- 
sistance (say  500,000  ohms)  is  introduced  into  the  circuit  of  the 
secondary  coil,  to  prevent  more  than  a  very  small  fraction  of  the 
polarizing  current  from  passing  through  the  coil.  Seek  out  the 
strength  of  stimulation  which  just  causes  contraction  when  the 
polarizing  current  is  not  closed.  Now  clcse  the  polarizing  current 
in  such  a  direction  that  the  anode  is  between  the  stimulating  elec- 
trodes and  the  muscle.  If  no  contraction  occurs  on  stimulation. 
push  up  the  secondary  towards  the  primary  till  the  muscle  contracts. 
Then  stop  the  stimulation,  open  the  polarizing  current,  and  allow  an 
interval  of  two  minutes.  Now  pa.ss  the  polarizing  current  through 
the  nerve  in  the  opposite  direction,  so  that  the  kathode  is  between 
the  stimulating  electrodes  and  the  muscles.  No  contraction  will  be 
obtained  on  exciting  with  the  same  strength  of  stimulus  as  caused 
contraction  when  the  anode  was  next  the  muscle.  The  kathode 
has  diminished  the  conductivity  of  the  nerve  ;  and  if  four  or  five 
small  Daniell  cells  are  put  on  in  the  polarizing  circuit,  no  contraction 
may  be  obtained,  even  with  the  (oils  close  together,  while  the 
excitation  will  still  pats  the  anode  and  cause  contraction. 

9.  Pfluger's  Formula  of  Contraction  (p.  684),  To  demonstrate 
this,  connect  two  unpolarizable  electrodes,  through  a.  spring  key 
and  a  commutator,  with  a  simple  rheocord  (Fig.  260,  p.  705),  so  as  to 
lead  oft  a  twig  of  a  current  from  a  Daniell  cell.  The  unpolarizable 
electrodes  are  placed  in  a  moist  chamber.  A  muscle-nerve  prepara- 
tion is  arranged  with  the  nerve  on  the  electrodes  and  the  muscle 
attached  to  a  lever.  The  effects  of  make  and  break  of  a  weak 
current,  ascending  and  descending,  can  be  worked  out  with  the 
simple  rheocord.  The  effects  of  a  medium  current  will  probably 
be  obtained  with  a  single  Daniell  connected  directly  with  the  elec- 
trodes through  a  key.  The  effects  of  a  strong  current  will  be  got 
when  three  or  four  Daniells  are  connected  with  the  electrodes.  Care 
must  be  taken  to  keep  the  preparation  in  a  moist  atmosphere, 
and  more  than  one  preparation  may  be  needed  to  verify  the  whole 
formula. 


PR  !(   IK    \L   EXERCISES  743 

m.  Formula  of  Contraction  for  (Human)  Nerves  in  Situ.  -Connect 
eighl  or  ten  dry  cells  in  scries.  Connect  one  terminal  of  the  battery 
to  a  I  irge  plate  elei  trode,  and  the  other  to  a  small  electrode,  both 
.  mcred  with  cotton,  flannel,  or  sponge,  moistened  with  salt  solution. 
Include  in  the  cir<  nit  ,1  simple  key  for  making  or  breaking  the  current, 
.md  a  commutator  for  changing  its  direction  at  will.  Leave  the 
key  open.  Place  the  Large  electrode  behind  the  shoulder  (or  on  the 
back  of  the  neck),  and  the  small  electrode  over  the  ulnar  nerve  at 
the  elbow  between  the  internal  condyle  and  the  olecranon.  Arrange 
the  commutator  so  that  the  small  electrode  shall  be  the  kathode. 
Close,  and  then  open  the  key.  If  no  contraction  occurs  at  closing, 
the  battery  is  too  weak,  and  more  cells  must  be  added.  If  contraction 
occurs  at  closing,  but  not  at  opening,  reverse  the  commutator, 
making  the  small  electrode  the  anode,  and  observe  whether  con- 
traction now  occurs  at  closing,  at  opening,  or  at  both.  Note  also 
the  relative  strength  of  the  various  contractions.  If  the  current  is 
'  weak  '  the  only  contraction  will  be  a  closing  one  when  the  kathode 
is  over  the  nerve.  If  the  current  is  of  '  medium  '  strength,  a  closing 
kathodic  contraction  and  both  opening  and  closing  anodic  contrac- 
tions will  be  obtained.  With  'strong'  currents  contractions  will 
occur  at  closing  and  at  opening,  whether  the  kathode  or  the  anode  is 
over  the  nerve.  The  contractions  will  vary  in  strength,  as  described 
on  p.  686.  To  work  out  the  different  cases  of  the  formula  summarized 
in  the  table,  the  number  of  cells  must  be  increased  or  diminished. 


Weak  Currents.              Medium  Currents. 

Strong  Currents. 

KCC                                  KCC 

—  ACC 

—  AOC 

KCC 
ACC 
AOC 
KOC 

The  abbreviations  KCC,  ACC,  are  used  respectively  for  kathodic 
closing  contraction  and  anodic  closing  contraction  ;  KOC,  AOC,  for 
kathodic  opening  contraction  and  anodic  opening  contraction. 
KCC  is  stronger  than  KOC,  and  ACC  than  AOC.  KCC  is  stronger 
than  ACC,  and  AOC  than  KOC.  Therefore,  as  the  strength  of  the 
current  is  increased,  in  the  case  of  normal  tissues,  KCC  is  first 
obtained,  then  ACC,  then  AOC,  and  finally  KOC. 

11.  Ritter's  Tetanus. — Lay  the  nerve  of  a  muscle-nerve  prepara- 
tion on  a  pair  of  unpolarizable  electrodes  connected  through  a 
simple  key  with  a  battery  of  three  or  four  small  Daniells.  Connect 
the  muscle  with  a  lever.  Pass  an  ascending  current  (anode  next 
the  muscle)  for  a  few  minutes  through  the  nerve,  and  let  the  writing- 
point  trace  on  a  slowly-moving  drum.  When  the  current  is  closed 
there  may  be  a  single  momentary  twitch,  or  the  muscle  may  remain 
somewhat  contracted  (galvanotonus)  as  long  as  the  current  is  allowed 
to  pass,  or  it  may  continue  to  contract  spasmodically  ('  closing 
tetanus').  When  the  current  is  opened  the  muscle  will  contract 
once,  and  then  immediately  relax,  or  there  may  be  a  more  or  less 
continued  tetanus  (Ritter's  or  '  opening  tetanus  ').  If  opening  tetanus 
is  obtained,  divide  the  nerve  between  the  electrodes  :  the  tetanus  con- 
tinues. Divide  it  between  the  anode  and  the  muscle  :  the  tetanus 
at  once  disappears.  This  shows  that  the  seat  of  the  excitation  which 
causes  the  tetanus  is  in  the  neighbourhood  of  the  anode  (p.  727). 


CHAPTER   XII 

THE  CENTRAL  NERVOUS  SYSTEM 

In  other  divisions  of  our  subject  we  have  been  able  to  follow- 
to  a  greater  or  less  extent  the  processes  which  take  place  in  the 
organs  described.  The  chemistry  and  the  physics  of  these  pro- 
cesses have  bulked  more  largely  in  our  pages  than  the  anatomv 
and  histology  of  the  tissues  themselves.  In  dealing  with  the 
central  nervous  system  we  must  adopt  a  method  the  very  reverse 
of  this.  Its  anatomical  arrangement  is  excessively  intricate. 
The  events  which  take  place  in  that  tangle  of  fibre,  cell,  and 
fibril  are,  on  the  other  hand,  almost  unknown.  So  that  in  the 
description  of  the  physiology  of  the  central  nervous  system  we 
can  as  yet  do  little  more  than  trace  the  paths  by  which  impulses 
7>niy  pass  between  one  portion  of  the  system  and  another,  and 
from  the  anatomical  connections  deduce,  with  more  or  less 
probability,  the  nature  of  the  physiological  nexus  which  its 
parts  form  with  each  other  and  the  rest  of  the  body.  And  here 
it  may  be  well  to  remark  that,  although  for  convenience  of 
treatment  we  have  considered  the  general  properties  of  nerves 
in  a  separate  chapter,  there  is  not  only  no  fundamental  distinc- 
tion between  the  central  nervous  system  and  the  outrunners 
which  connect  it  with  the  periphery,  but  obviously  a  central 
nervous  system  would  be  meaningless  and  useless  without 
afferent  nerves  to  carry  information  to  it  from  the  outside,  and 
efferent  nerves  along  which  its  commands  may  be  conducted  to 
the  peripheral  organs. 

I.  Structure   of  the  Central  Nervous  System. 

In  unravelling  the  complex  structure  of  the  central  nervous 
system,  we  avail  ourselves  of  information  derived  (i)  from  its 
gross  anatomy  ;  (2)  from  its  microscopical  anatomy  ;  (3)  from 
its  development ;  (4)  from  what  we  may  call,  although  the  term 
is  open  to  the  criticism  of  cross-division,  its  physiological  and 
pathological  anatomy. 

744 


////    CENTRA1    M  RVOUS  SYS7  I  M 

Certain  tracts  of  while  or  grey  matter  are  differentiated  from 
each  other  l>v  the  size  oi  their  fibres  or  cells.  For  example,  the 
postero-median  column  of  the  spinal  cord  has  small  fibres,  the  direct 
cerebellar  trad  large  fibres;  the  large  pyramidal  cells  (gianl  cells 
or  tells  oi  l'.et/i.  in  wh.it  we  shall  afterwards  have  to  distinguish 
.is  the  '  motor  area  '  (p.  844)  oi  the  cerebral  cortex,  arc  the  cells 
of  origin  of  fibres  of  the  pyramidal  tract  subserving  the  volitional 
movements  of  the  limbs  and  trunk.  The  pyramidal  cells  oi  th< 
'  face  area  '  arc  comparatively  small.  In  general,  an  efferent  or  motor 
nerve-cell  is  larger  the  longer  its  axon  is — e.g.,  the  largest  of  all  the 
pyramidal  cells  in  the  '  motor  '  region  are  found  in  the  portion  known 
.1^  the  '  leg  ,irea,'  from  which  the  pyramidal  fibres  have  to  pass  all 
the  way  down  the  cord  to  the  segments  from  which  the  spinal  nerves 
going  to  the  lower  limbs  arise. 

The  recent  work  of  Brodman  and  of  Campbell  has  shown  that  the 
cerebral  cortex  may  be  histologically  differentiated  into  regions 
which  correspond  to  a  great  extent  to  the  various  functional  regions 
mapped  out  by  physiological  methods  (p.  851). 

The  study  of  development  enables  us  not  only  to  determine  the 
homology,  the  morphological  rank,  of  the  various  parts  of  the  brain 
and  cord,  but  also,  by  comparison  of  animals  of  different  grades  of 
organization,  sometimes  to  decide  the  probable  function  and  physio- 
logical importance  of  a  strand  of  nerve-fibres  or  a  column  of  nerve- 
cells.  It  is  of  special  value  in  helping  us  to  differentiate  the  various 
areas  of  grey  matter  on  the  surface  of  the  brain,  and  to  trace  the 
various  tracts  or  paths  into  which  the  white  matter  of  the  central 
nervous  system  may  be  divided.  For  the  medullary  sheath  is  not 
developed  at  the  same  time  in  all  the  tracts,  and  a  strand  of  nerve- 
fibres  in  which  it  is  wanting — e.g.,  the  pyramidal  tract  (p.  776), 
which  is  the  last  of  the  spinal  tracts  to  become  myelinated — is 
readily  distinguished  under  the  microscope. 

Then,  again — and  this  is  what  we  propose  to  include  under  the 
fourth  head — experimental  physiology  and  clinical  and  pathological 
observation  throw  light  not  only  on  the  functions,  but  also  on  the 
structure,  of  the  central  nervous  system.  For  instance,  complete 
or  partial  section,  or  destruction  by  disease,  of  the  white  fibres  of 
the  cord  or  brain,  or  of  the  nerve-roots,  or  removal  of  portions  of 
the  grey  matter,  is  followed  by  degeneration  in  definite  tracts. 
And  since,  as  we  have  already  seen,  degeneration  of  a  nerve-fibre 
is  caused  when  it  is  cut  off  from  the  cell  of  which  it  is  a  process, 
the  amount  and  distribution  of  such  degeneration  teaches  us  the 
extent  and  position  of  the  central  connections  of  the  given  tract. 
Conversely,  the  cells  in  which  a  tract  of  nerve-fibres  arises  may  some- 
times be  identified  by  the  alterations  in  the  chromatin  (p.  756)  and 
other  changes  which  occur  in  them  after  section  of  their  axons. 
Particularly  in  young  animals,  removal  of  a  peripheral  organ — an 
eye  or  a  limb — or  section  of  its  nerves,  may  be  followed  by  atrophy 
of  portions  of  the  central  nervous  system  immediately  related  to  it. 

'  Softening  '  of  a  definite  portion  of  the  white  or  grey  matter 
may  also  in  certain  cases  be  caused  by  depriving  it  of  its  blood- 
supply  by  the  injection  of  artificial  emboli,  and  the  resulting 
degenerations  may  then  be  studied.  For  instance,  fine  particles 
like  lycopodium  spores  are  injected  into  the  abdominal  aorta  between 
the  origins  of  the  renal  and  inferior  mesenteric  arteries.  They  are 
prevented  by  clamps  from  entering  these  vessels,  and,  passing 
through  the  lumbar  arteries,  stick  in  the  branches  of  the  anterior 


746 


A   Ml  M    1/    OF    I'll  YSIOLOG  5 


spinal  artery,  and  cause  softening  mainly  of  the  grey  matter  of  the 
lumbar  portion  of  the  cord.  When  the  abdominal  aorta  oi  .1  rabbil 
is  temporarily  compressed  (for  about  an  hour)  below  the  origin  oi 
the  renal  arteries,  the  grey  matter  of  the  corresponding  portion 
oi  the  cord  is  so  seriously  injured  that  it  and  the  fibres  thai  arise 
from  it  degenerate,  while  the  fibres  whose  cells  of  origin  are  not 
situated  in  this  pari  of  the  grey  matter  arc  not  affected,  or  at  least 
completely  recover. 

Certain  tracts  may  also  be  marked  oui  by  means  ol  the  electrical 
^^^^^  variation,  winch  gives   token 


1  the  passage  oi  nervous  im- 
pulses along  them  when  poi 
tions  of  the  central  nervous 
system  or  peripheral  nerves 
are  stimulated  (Horsley  and 
Gotch). 

Development  of  the  Central 
Nervous  System.  Very  early 
in  development  (Fig.  297)  the 
keel  of  the  vertebrate  embryo 
is  laid  down  as  a  groove  or 
gutter  in  the  ectoderm  of 
the  blastodermic  area  (Chap. 
XIV.).  The  walls  of  this  'me- 
dullary '  or  '  neural  '  groove 
grow  inwards,  and  at  length  there  is  formed,  by  their  coalescence, 
the  '  neural  canal  '  (Fig.  298),  which  expands  at  its  anterior  end  to 
form  four  cerebral  vesicles  (Fig.  299).  Thus  there  is  a  continuous 
tunnel  from  end  to  end  of  the  primary  cerebro-spinal  axis  ;  and  this 
persists  as  the  central  canal  of  the  spinal  cord  and  the  ventricles  of 


Fig.  297. — Formation  of  the  Neural 
Canal  at  an  Early  Stage  (after 
Beard). 


0^: 


\ 


CfUMXt 


(r{  SfivnxiZ 
HtuiaJ. COAXAL 


Fig.   298      Neural  Canal  at 
Later  Stage   (after  Beard). 


the  brain,  whose  ciliated   epithe- 
lium   represents    the    ectodermic 


lining  of  the  primitive  neural  <  anal 
In  t  he  adult  portions  ol  I  be  1  anal 
may  become  obliterated   from  an 

overgrowth  of  the  lining  cells,  and 
the  cilia  are.  it  present  at  all.  less 
distinct  than  in  the  child,  and  far 
less  distinct  than  in  the  lower  animals.  From  the  wall  of  this  canal 
is  formed  the  cerebro-spinal  axis,  in  which  developing  nerve-cells 
or  neuroblasts  soon  become  differentiated  from  the  supporting  cells 
or  spongioblasts,  and  wander  outwards  from  the  neighbourhood  oi 
the  central  canal  (Fig.  309)  till  their  further  progress  is  checked  by 
the  harrier  of  the  marginal  veil,  a  closely-WOVen  network  or  thicket, 
into  which  the  processes  of  the  spongioblasts  break  up  at  the  out- 
side of  the  primitive  cerebro-spinal  axis.     Although  the  neuroblasts 


////    CENTRAl    NERVOl  S  SYS1  E  \l 


747 


themselves  are  unable  to  penetrate  the  marginal  veil,  the  axis- 
i  \  Under  processes  of  some  of  them  <1<>  so,  and  form  the  motor  roots 
oi  the  spinal  nerves.  The  neuroblasts  from  which  the  fibres  of  the 
white  columns  of  the  cord  are  developed  are  apparently  unable  to 
send  their  axons  through  the  marginal  veil.     They  are  accordingly 

ed  to  assume  a  longitudinal  direction,  and  in  this  way  the 
central  grey  matter  becomes  covered  with  a  sheath  oi  longitudinal 
white  fibres.  For  a  time  only  motor  nerve-cells  and  the  fibres 
connected  with  them  are  developed  in  the  cerebrospinal  axis.  The 
ganglia  oil  the  posterior  roots  arise  from  a  series  of  ectodermic 
thickenings  or  sprouts  from  the  neural  crest  which  runs  along  the 
dorsal  aspect  of  the  neural  canal.  These  sprouts  contain  the  neuro- 
blasts which  develop  into  the  spinal 
ganglion  cells  with  the  posterior 
root-fibres.  From  each  pole  of 
each  neuroblast  a  process  grows  out , 
one  towards  the  periphery,  which 
forms  a  peripheral  nerve-fibre,  the 
other  centrally  to  connect  the  cell 
with  the  cord.  From  the  after- 
brain  (or  myelencephalon)  is  de- 
veloped the  medulla  oblongata  or 
spinal  bulb,  from  the  hind-brain 
(or  metencephalon)  the  cerebellum 
and  pons,  from  the  mid-brain  (or 
mesencephalon)  the  corpora  quad- 
rigemina  and  crura  cerebri.  The 
fore  -  brain,  or  primary  fore  -  brain 
(thalamencephalon)  gives  rise  of 
itself  only  to  the  third  ventricle 
and  optic  thalamus,  but  a  secondary 
fore-brain  (telencephalon)  buds  off 
from  it  and  soon  divides  into  two 
chambers,  from  the  roof  of  which 
the  cerebral  hemispheres,  and  from 
the  floor  the  corpora  striata,  are 
derived.  Their  cavities  persist  as 
the  lateral  ventricles,  which  com- 
municate with  the  third  ventricle  by 
the  foramen  of  Monro.  The  olfac- 
tory tracts  arc  formed  as  buds  from 
the  secondary  fore-brain. 

To  complete  the  story  of  the  de- 
velopment of  the  brain,  it  may  be 
added  that  the  retina  is  really  an 
expansion  of  its  nervous  substance. 
A  hollow  process,  the  optic  vesicle,  buds  out  on  each  side  from  the 
primary  fore-brain.  A  button  of  ectoderm,  which  afterwards  be- 
comes the  lens,  grows  against  the  vesicle  and  indents  it  so  that  it 
becomes  cup-shaped,  the  inner  concave  surface  of  the  cup  repre- 
senting the  retina  proper,  the  outer  convex  surface  the  choroidal 
epithelium.     The  stalk  becomes  the  optic  nerve. 

Histological  Elements  of  the  Central  Nervous  System. — The  central 
nervous  system  is  built  up  (i)  of  true  nervous  elements,  (2)  of 
supporting  tissue.  The  nervous  elements  have  usually  been  described 
as  consisting  of  nerve-fibres  and   nerve-cells,  but  the  antithesis  of  a 


Fig.  299. — Diagram  to  illustrate 

the  Formation  ok  the  Cerebral 
Vesicles. 

A.  1  indicates  the  cavity  of  the 
secondary  fore-brain,  which  eventu- 
ally becomes  the  lateral  ventricles. 
In  B  the  secondary  fore-brain  has 
grown  backwards  so  as  to  overlap 
the  other  vesicles.  I.  first  cerebral 
vesicle  (primary  fore-brain  or  'tween 
brain)  ;  II.  second  cerebral  vesicle 
(mid-brain)  ;  III,  third  cerebral  vesi- 
cle (hind-brain)  ;  IV,  fourth  cerebral 
vesicle  (after-brain). 


748 


A   MANU  II    OF  PHYSIOLOGY 


time-honoured  distim  tion  must  not  lead  us  to  forget  thai  the  essential 
part  of  .1  nerve-fibre,  the  axis-cylinder,  is  a  process  of  a  nerve-cell, 
and  the  medullary  sin, ah  probably  <i  product  of  the  axis-cylinder.* 
In  strictness,  the  term  'nerve-cell  '  ought  to  include  not  only  the 
cell-body,  but  all  its  processes,  out  to  their  last  ramifications.  But 
the  habit  oJ  speaking  of  the  position  of  the  cell-bodyf  as  that  of  the 
nerve-cell  is  so  ingrained,  that  it  seems  better  to  continue  the  use 
of  the  latter  term  in  its  old  signification,  and  to  speak  of  the  cell 
and  branch.'-  together  as  a  neuron  [also  spelled  neuron 

The  Neurons.    -A  typical  nerve-cell  (Figs,    joo    $02,  304    1-  a  knot 

m!  granular  protoplasm,  1  on- 
,'    '.»  taining   a   large  nucleus,  in- 

side   of    which  lies    a    highly 
refractive  nucleolus.     A  1  en- 
li,       '       '  trosome     and     attraction 

sphere  (p.  5)  have  also  been 

found    in    some    nerve-cells, 

though   not    as    vet   demon- 

__  ■■■.'  st rated  in  all.    Pigment  may 

also    be    present,    especially 


r 


: 


,00. — Anterior    Horn    Cell    from 
Man   showing   Fibrils  (Bethe). 


[oi.  .Mi  mi  lated  Nerve- 
fibre  showing  Fibrils  o* 
Axis-cylinder  (Hi  i 

The  fibrils  arc  seen  pas 
without  interruption,  acros 
node  of  Ranvier. 


m  old  age.  By  certain  methods  of  staining  it  may  be  shown  that 
fibrils  (neuro-fibrils)  run  through  the  protoplasm  ol  the  cell,  forming 
a  felt-work  in  it.  and  entering  the  dendrites  on  the  one  hand  and  the 

*  The  nu(  lei  oJ  the  peripheral  fibres  belong  to  the  neurilemma  and  not 

to  the  medullary  sheath,  and  while  the  medullary  -heath,  like  the  axis- 
cylinder,  1-  as  regards  it-  nutrition  under  the  control  of  the  nerve-cell, 
and  must  therefore  be  looked  upon  as  an  integral  portion  of  the  neuron, 
the  neurilemma  111  respect  both  of  its  nutrition  and  its  development 
appears  to  be  an  independent  structure. 

|   Foster  and  Sherrington  call  the  cell-body  the  perikai 


nil    CENTRAL    XI  RVOUS  SYST1  M  749 

axis-cylinder  process  011  the  other  (Figs,  joo,  [n  the  axis- 

cylinders  of  aerve-fibres  the  fibrils  (Fig.  301)  appear  to  preserve 
their  identity  down  to  the  distribution  oi  the  fibre.  In  the  ground 
substance  between  the  fibrils  lie  round,  angular,  or  spindle-shaped 
bodies  (Nissl's  bodies)  which  stain  with  basic  dyes  (Fig.  311).* 
[*hese  bodies  vary  in  appearance  in  different  kinds  oi  nerve-cells, 
and  in  the  same  nerve-cell  under  different  conditions.  According 
to  Mac. ilium,  they  contain  organically  combined  iron,  in  a  multi- 
polar cell,  like  those  in  the  anterior  horn  oi  the  spinal  cord,  several 
processes — it  may  be  five  or  six.  or  even  more — pass  off  from  the 
cell-body  (Frontispiece).  The  most  complete  pictures  of  them  arc 
given  by  preparations  impregnated  according  to  the  method  oi 
Golgif  (Figs.  302,  305).  One  of  the  processes  of  most  nerve-cells 
is  distinguished  from  the  rest  by  the  tact  that  it  maintains  its 
original  diameter  for  a  comparatively  great  distance  from  the  cell, 
and  gives  off  comparatively  few  branches.  This  process,  which  in 
l.L\ourablc  preparations  can  be  traced  on  till  it  becomes  the  axis- 
cylinder  of  a  nerve-fibre,  is  called  the  axis-cylinder  process,  or  more 
shortly  the  axon.  The  few  slender  branches  that  come  off  from  it, 
usually  at  right  angles,  are  called  collaterals.  The  collaterals  consist 
essentially  of  one  or  more  fibrils  of  the  axon.  Both  the  main 
thread  of  the  axon  and  the  collaterals  end  by  breaking  up  into  an 
arborescent  system  of  fibrils  or  telodendrion.  The  telodendrions 
varv  greatly  in  appearance  from  simple  end-brushes  to  far-branching 
thickets,  or  such  special  end-organs  as  motor  plates  (Fig.  307)  or 
muscular  spindles  (Fig.  433,  p.  983).  The  rest  of  the  processes  of  the 
cell,  which  are  termed  dendrites  or  protoplasmic  processes,  very  rapidly 
diminish  in  diameter,  as  they  pass  away  from  the  cell,  by  breaking 
up  into  fibrils  like  the  branches  of  a  tree.  The  Nissl  bodies  extend 
for  some  distance  into  the  dendrites,  but  not  into  the  axon.  The 
dendrites  of  some  cells,  especially  the  pyramidal  cells  of  the  cerebral, 
and  the  Purkinje's  cells  of  the  cerebellar  cortex,  have  small  swellings, 
the  so-called  lateral  buds  or  gemmules,  on  their  course.  Their  signi- 
ficance is  unknown.  The  dendrites  terminate  at  a  little  distance 
from  the  cell,  where  they  come  into  relation  with  the  end-arboriza- 
tions of  the  axons  of  other  neurons.  In  this  way  two  or  more 
neurons  are  linked  together  to  form  a  nervous  path.  According  to 
the  view  most  commonly  held  (neuron  hypothesis),  the  relation  is 
not  one  of  actual  anatomical  continuity,  but  the  processes  come 
so  close  together  that  nerve  impulses  are  able  to  pass  across  from 
the  terminal  brush  of  the  axon  of  one  nervous  element  to  the 
dendrites  or  cell-body  of  another.  This  kind  of  junction  is  called 
a  synapse. 

It  has  been  suggested  that  the  contact  may  be  rendered  more  or 
less  close  through  amoeboid  movements  of  the  dendrites,  and  that 
in  this  way  the  nervous  impulse  may  be  switched  like  a  railwav- 
train  from  one  path  to  another.  But  there  is  no  experimental  basis 
for  this  somewhat  crude,  if  fascinating,  hypothesis.  Sherrington 
has  suggested  that  the  presence  of  a  '  membrane  '  at  the  synapse 

*  In  Xissl's  method  the  sections  are  stained  in  a  solution  of  methylene 
blue,  and  decolourized  in  anilin-alcohol. 

I  The  method  depends  upon  the  deposition  of  mercury,  or  silver,  in  or 
around  the  cell-bodies  and  their  processes  in  tissues  which  have  been 
hardened  in  bichromate  of  potassium  and  then  soaked  in  a  solution  of 
mercuric  chloride  or  silver  nitrate.  In  Pal's  improvement  of  Golgi's 
method  a  solution  of  sodic  sulphide  follows  the  mercuric  chloride. 


750 


A   MANUAL  OF  PHYSimjH.y 


Fig.   302. — Multipolar  Nerve-cell  :  Golgi    Preparation'  (Barker,  after 

Kolliker). 

n.  axon  :  c,  collaterals. 


Fig.  J03.  Nerve-cells  of  Hirvdo  (Schafer,  after  Apathy). 
A,  unipolar  motor  cell  ;  a.  network  of  neuro-fibrils  near  the  surface  of  the 
( ell  ;  b,  near  the  nucleus  n  ;  c,  afferent :  d,  efferent  neuro-fibril.  B.  bipolar  sensory 
cell  a  with  its  nucleus  n  ;  cu,  cuticle  ;  ep,  epidermis  cells  between  which  a  neuro- 
fibril passes  up  from  its  branched  ending  near  the  surface  of  the  skin  to  the 
nerve-cell,  where  it  forms  a  network,  which  gives  off  a  fibril  passing  towards  the 
central  nervous  system. 


THE  CENTR  U.   Nl  RVOUS  SYS1  I  1/ 


rq  ! 


may  limit  the  conduction  and  determine  its  direction.  Some  mem- 
branes, such  as  frog's  skm.  arc  known  to  possess  a  so-called  irre- 
ciprocal permeability  for  certain  substances,  permitting  them  to 
pass  more  easily  in  one  direction  than  the  other,  and  it  is  con- 
ceivable that  a  membrane  at  the  synapse  might  have  a  similar 
action  in  respect  to  the  movement  of  ions  concerned  in  the  propaga- 
tion of  the  nervous  excitation.  Whatever  the  nature  of  the  relation 
between  two  superposed  neurons  may  be,  it  does  not  permit  the 
conduction  of  nerve-impulses  indiseriminatelv  in  both  directions. 
For  instance,  stimulation  of  the  central  end  of  the  posterior  root  of 
a  spinal  nerve  causes  an  elec- 
trical response  (p.  719)  in  the 
anterior  root  of  the  same  seg- 
ment, while  no  electrical 
change  is  produced  in  the 
posterior  root  by  stimulation 
of  the  anterior.  We  shall 
see  later  on  (p.  770)  that 
some  of  the  fibres  of  the  pos- 
terior root  and  their  collate- 
rals end  by  arborizing  around 
the  dendrites  of  the  cells  of 
the  anterior  horn.  The  ex- 
citation is,  therefore,  able  to 
pass  from  the  telodendrions 
of  the  posterior  root-fibres 
through  the  dendrites  of  the 
anterior  horn  cells  towards 
their  cell-bodies,  but  not  in 
the  opposite  direction,  and 
in  general  the  direction  of 
conduction  is  from  the  den- 
drites towards  the  cell-body. 
Some  investigators  believe 
that  the  fibrils  already 
spoken  of  as  forming  a  felt- 
work  in  the  protoplasm  of 
the  nerve-cell  may  run  right 
through  from  one  cell  to 
another,  thus  constituting  an 
actual  anatomical  connec- 
tion between  the  neurons, 
and  that  such  a  connection 
may  be  established  also  by 
fibrils  which  do  not  enter 
the  cells  at  all,  but  run  in 
the  intercellular  substance  of  the  grey  matter.  Such  a  continuitv 
of  fibrils  from  cell  to  cell  has  been  demonstrated  in  some  of  the 
invertebrates — e.g.,  in  annelids  (Fig.  303) — where  previously  the 
best  examples  of  strictly  isolated  neurons  were  supposed  to  be 
found  (Apathy).  The  supporters  of  the  theory  of  continuity  look 
upon  the  cell-body  as  merely  necessary  for  the  nutrition  of  the 
nerve-net,  but  deny  that  it  is  necessary  for  the  conduction  of 
nerve-impulses.  If  this  is  the  case,  it  is  obvious  that  the  neurons 
can  no  longer  be  considered  as  functional  units  in  which  the  law  of 
isolated  conduction  of  nerve-impulses  (p.  689)  holds  good.     Xor  is 


Fig.  304. — Large  Pyramidal  Cell  of 
Cerebral  Cortex  (Barker,  after  Bech- 
terew). 

a,   axon  ;   b.   dendrite. 


7^ 


.1   MANX    //    OF  PHYSIOLOGY 


it  by  any  means  so  easy  to  understand  as  on  the  neuron  hypothesis 
sucli  tacts  as  the  strict  limitation  oi  Wallerian  degeneration  to  the 


Fig.  305. 
a — e  shows  the  development  of  the  pyramidal  nerve-cells  of  the  cerebral  cortex 
in  a  typical  mammal  :  a,  neuroblast  with  commencing  axon  ;  b,  dendrite  • 
pearing  ;  d,  commencing  collaterals.     A — D  shows  the  different  degree  of  com- 
plexity in  the  fully-developed  pyramidal  cells  in  different  vertebrates  :  A,  frog  ; 
B,  lizard  ;  C,  rat  ;  D,  man  (Donaldson,  after  Ramon  y  Cajal). 

boundaries  of  the  neurons  directly  affected,  or  the  strict  limitation 
of  the  silver  reduction  in  Golgi  preparations  to  single  neurons. 
It  is,  of  course,  true  that  the  simplicity  and  order  introduced  by  the 


Fig.   306. 
Cells  fmm  the  Gasserian  ganglion  of  a  developing  guinea-pig.     The  origin. illy 
bipolar  cells  are  seen  changing  into  cells  apparently  unipolar.     The  same  process 
occurs  in  the  cells  of  the  spinal  ganglia  (Van  Gehuchten). 

neuron  hypothesis  into  our  conceptions  of  the  nervous  conduction 
paths  by  no  means  prove  its  accuracy.  Yet  they  are  reasons  for 
not  lightly  abandoning  it. 


THE  CENTRAL  NERVOUS  SYSTEM 


Varieties  of  Neurons. 
ixly  all  the  nerve- 
cells  <>i  the  cerebro- 
spinal axis  agree  with 
the  cells  of  the  antei  Lor 
horn  in  the  possession  ol 
an  axon  and  one  or  more 
dendrites,  although 
sometimes  the  dendrites 
are  scanty  in  number 
ami  insignificant  in  size 
In  the  cerebral  cortex 
the  typical  cells  are  of 
pyramidal  shape.  From 
the  base  comes  off  the 
axon,  and  from  the  an- 
gles dendritic  processes, 
a  particularly  massive 
dendrite  proceeding 
from  the  apex  of  the 
pyramid  towards  the 
surface  of  the  brain. 

Sometimes  an  axon, 
instead  of  ending  in  an 
arborization  which 
comes  into  relation  with 
the  dendrites  of  another 
nerve-cell,  or,  as  is  more 
frequently  the  case,  with 
the  dendrites  of  more 
than  one  cell,  breaks  up 
into  a  sort  of  basket- 
work  of  fibrils  surround- 
ing the  cell-body.  The 
cells  of  Purkinje,  for 
instance,  in  the  cere- 
bellum are  surrounded 
by  such  pericellular  bas- 
kets (Fig.  308).  The 
cells  of  the  spinal  gan- 
glia have  two  axons, 
which  in  the  embryo 
arise  one  from  each  end 
of  the  bipolar  cell,  but 
in  the  adult,  in  all  verte- 
brates  except  some 
fishes,  are  connected  to 
the  cell  by  a  single  pro- 
cess (Fig.  306).  The 
great  majority  of  them 
have  no  dendrites,  un- 
less, as  some  have  sup- 
posed, the  peripheral 
process  really  represents 
a  dendrite.  Another 
kind  of  cell  which  seems 
undoubtedly    to    be    of 


Fig.  307. — Scheme   of   Lower   Motor   Neuron 
(Barker). 

a,  h,  axon-hillock  (the  portion  of  the  cell  from 
which  the  axon  comes  off),  containing  no  Xissl 
bodies,  and  showing  fibrillation  ;  ax,  axis-cylinder 
or  axon  ;  m,  medullary  sheath,  outside  of  which 
is  the  neurilemma  ;  c,  cell-substance  (cytoplasm), 
showing  Xissl  bodies  in  a  lighter  ground  substance  ; 
d,  protoplasmic  processes  or  dendrites  containing 
Xissl  bodies  ;  n,  nucleus  ;  »',  nucleolus  ;  n,  R, 
node  of  Ranvier  ;  s,  f,  side  fibril  ;  n  of  n,  nucleus 
of  the  neurilemma  ;  tel.,  motor  end  plate  ;  m', 
striped  muscle-fibre  :  s,  L,  incisure. 

48 


754 


A   MANUAL  OF  J'JIYSIOLOGY 


nervous  nature  is  the  granule-cell.'  Granule-cells  are  much  smaller 
than  the  nerve-cells  we  have  been  describing.  Their  processes 
much  less  easily  followed,  but  all  appear  to  give  off  an  axon 
and  several  dendrites.  They  contain  a  relatively  large  nucleus 
(5  to  8  fi  in  diameter),  with  only  a  mere  fringe  of  cell-substance. 
The  nucleus,  unlike  that  of  a  large  nerve-cell,  stains  deeply  with 
hematoxylin.  Some  parts  of  the  grey  matter  are  crowded  with 
these  granule-cells — e.g.,  the  nuclear  layer  of  the  cerebellum  and  the 
substantia  gelatinosa,  or  substance  of  Rolando,  which  caps  the 
posterior  horn  in  the  cord.  In  other  parts  they  are  more  thinly 
scattered,  but  probably  they  are  as  widely  diffused  as  the  large 
nerve-cells  proper,  and  no  extensive  area  of  the  grey  matter  is 
wholly  without  them. 

Although  there  are  several  varieties  of  granules  (Hilli.  they  all 
agree  in  this,  that  their  axons  run  a  comparatively  short  course, 

and  never,  or  rarely,  pass  beyond  the 
grey  matter.  Another  kind  of  neuron 
which  is  also  confined  to  the  grey 
matter,  and  is  typically  seen  in  the 
cortex  of  the  cerebrum  and  cerebellum, 
presents  the  peculiarity  of  an  axon 
which  branches  into  an  intricate  net- 
work immediately  after  coming  off  from 
the  cell  (cell  of  Golgi's  second  type  |.  L'n- 
like  the  long  axon  of  the  typical  large 
nerve-cell,  the  axis-cylinder  process  of 
this  Golgi  cell  remains  unmedullated. 

The  sympathetic  ganglion  cells  are 
developed  from  immature  neuroblasts 
that  migrate,  in  the  course  of  develop- 
ment, from  the  rudiments  of  the  spinal 
ganglia,  and  gathering  in  clumps  form 
the  ganglia  of  the  sympathetic  chain 
(His).  They  agree  in  general  with  the 
cells  of  the  cerebro-spinal  axis  in  pos- 
sessing an  axon  and  one  or  more,  com- 
monly several,  dendrites,  although  a 
few  of  them  are  devoid  of  dendrites. 
The  great  majority  of  the  axons  remain 
unmedullated,  but  a  few  acquire  a  very 
fine  medullary  sheath. 

The  epithelium  lining  the  central 
canal  of  the  cord  and  the  ventricles  of 
the  brain  has  also  been  considered  by 
The  fact  that  the  deep  ends  of  the  cells 
are  continued  into  processes  which  pierce  far  into  the  grey  substance 
has  been  supposed  to  lend  weight  to  this  opinion,  but  there  is  no 
good  ground  for  it. 

Growth  of  Neurons. — The  growth  of  a  neuron  is  a  comparatively 
slow  process.  Early  in  fcetal  life  (about  the  third  or  fourth  week  in 
man)  certain  round  germinal  cells  make  their  appearance  amid  the 
columnar  ectodermic  cells  surrounding  the  neural  canal.  From  their 
division  are  formed,  in  the  first  months  of  embryonic  life,  the  primi- 
tive nerve-cells  or  neuroblasts.  These  soon  elongate  and  push  out 
processes,  first  the  axon  or  axons,  and  then  the  dendrites  (Fig.  305). 
As  development  goes  on.  the  cell-body  grows  larger,  and  thi 


Fig.   308. — Pericellular  Bas- 
kets (Sch'afer,  after  Cajal). 

T\v.>  cells  of  Purkinje  from 
the  cerebellum  are  seen  sur- 
rounded by  end  ramifications 
forming  a  basket-work,  b,  de- 
rived from  the  branching  of 
axons  of  small  nerve-cells  in 
the  molecular  layer  ;  a,  axon. 

some  as  of  nervous  nature. 


/7//    CENTRAL   NERVOUS  SYSTEM 


755 


Longer  and  more  richly  branched.  The  axon  and  its  collaterals,  when 
it  has  any,  in  the  i  ase  oi  bhe  great  majority  of  the  nervous  elements 
mi  the  brain  and  cord,  ultimately  acquire  a  medullary  sheath, 
although,  as  we  have  said,  the  time  at  which  medullation  is  com- 
puted varies  in  different  groups  of  elements,  and  in  some  nervous 
tracts  it  is  even  wanting  at  birth.  At  birth,  too,  the  branches  of 
many  of  the  cells  are  Less  numerous,  and  the  connections  between 
different  nervous  elements  therefore  less  intimate  than  they  will 
afterwards  become.  For  many  years  the  processes,  and  particu- 
larly the  axons,  continue  not  only  to  grow  longer,  but  also  to 
grow  thicker.  The  cell-body  also  enlarges,  and  the  quantity  of 
material    in    it    that    stains    with    basic    dyes    increases.     In    the 


Fig.  309.  —  Section 
through  Half  of 
Neural  Tube  (Bar- 
ker, after  His). 

The  pear -shaped  neuro- 
blasts are  seen  migrating 
outwards.  The  axons  of 
some  of  them  are  seen 
pushing  their  way  out 
through  the  marginal  veil 
as  the  anterior  root  of  a 
spinal  nerve. 


2. 


Fig.   310. 

1,  spinal  ganglion  cells  of  a  still-born  male  child  ; 

2,  of  a  man  ninety-two  years  old  (  x  250) — N,  nuclei ; 

3,  nerve-cells  from  the  antennary  ganglion  of  a 
honey-bee  just  emerged  in  the  perfect  form  ;  4,  of 
an  old  honey-bee.  The  nucleus  is  black  in  the 
figure.  In  3  it  is  very  large,  in  4  it  is  shrunken 
and  the  cell-substance  contains  vacuoles  (Hodge). 


growing  (lumbar)  spinal  ganglia  of  the  white  rat  the  increase 
in  volume  of  the  largest  cell-bodies  is  very  closely  correlated  with 
the  increase  in  area  of  the  cross-section  of  the  nerve-fibres  grow- 
ing out  of  them.  The  cross-section  of  the  axis-cylinder  is,  and 
remains,  almost  exactly  equal  to  the  area  of  the  medullary  sheath 
(Donaldson).  Even  after  puberty  is  reached  the  anatomical 
organization  of  the  nervous  system  may  still  continue  to  advance, 
although  at  an  ever-slackening  rate,  and  the  finishing  touches 
may  only  be  given  to  its  architecture  in  adult  life.  In  old  age 
the  nervous  elements  decay  as  the  body  does.  The  cell-body 
diminishes  in  size  ;  the  stainable  material  lessens  in  amount  ; 
vacuoles   form   in   the   protoplasm    and   pigment   accumulates  ;    the 

48—2 


756 


A   MANUAL  OF  PHYSIOLOGY 


nucleus  shrinks  ;  the  nucleolus  is  obscured  or  may  disappear  alto- 
gether.  At  the  same  time  the  processes  of  the  cell,  and  especially 
the  dendrites,  tend  to  atrophy  (Fig.  310). 

Nutrition  of  the  Neuron.— We  have  already  seen  that  when  an 
axon  is  cut  oh  from  its  cell-body,  it  and  its  medullary  sheath,  when 
it  possesses  one  undergo  a  rapid  degeneration.  It  was  long  sup- 
posed that  no  change  took  place  in  the  nerve-cell.  The  researches 
of  recent  years  have  shown  that  not  only  does  loss  of  the  specific 
function  and  trophic  influence  of  the  cell-body  affect  the  nutrition 
of  the  axon,  but  loss  of  function  of  the  axon  reacts  on  the  cell- 
body.  In  many  cases  at  least,  when  a  nerve-fibre  is  divided  from 
its  cell  characteristic  changes  are  produced  in  the  latter  and  in 
its  dendritic  processes,  and  they  are  scarcely  less  rapid,  although 
usually  less  profound,  and  far  more  transient  than  the  degeneration 
in  the  peripheral  portion  of  the  nerve-fibre.     The  cell-body  and  the 


Fig.  311. — Cells  from  the  Nuclei  of  the  Oculo-motor  Nerves  of  the  Cat 
Thirteen  Days  after  Division  of  the  Root-fibres  on  one  Side  : 
Nissl's  Stain  (Barker,  after  Flatau). 

a,  normal  cell  from  side  on  which  the  roots  were  not  cut  ;  b,  cell  from  side 
operated  upon.  Only  a  few  Nissl  bodies  are  present  in  b,  and  the  nucleus  is 
displaced  to  one  side  of  the  cell. 


nucleus  swell.  .Many  of  the  Nissl  bodies  (Fig.  311)  disintegrate,  and 
are  reduced  to  a  finely  granular  condition.  After  a  time  much  of 
the  disintegrated  chromatic  substance  disappears  altogether.  The 
nucleus  may  be  displaced  to  one  side  of  the  cell.  Certain  changes 
in  the  neurofibrils  of  the  cell  may  accompany  the  changes  in  the 
chromatin.  \n  rabbits  after  division  of  the  facial  nerve  the 
alterations  in  its  nucleus  of  origin  have  been  found  to  reach  a  maxi- 
mum in  about  three  weeks,  after  which  there  is  a  tendency  to  recovery 
on  the  part  of  the  majority  of  the  cells,  even  when  regeneration  of  the 
nerve  has  been  prevented  by  cutting  out  a  portion  of  it.  Some  of 
the  cells  may  completely  atrophy  and  disappear.  Similar  changes 
have  been  found  by  Warrington  in  the  motor  cells  of  the  anterior 
horn  after  section  of  the  posterior  (dorsal)  spinal  roots.  Since  in 
this   case   no   anatomical   injury  has  been   inflicted   on   the   motor 


THE  CENTRA!.   NERVOUS  SYSTEM  757 

neurons,  it  has  been  surmised  that  the  cause  of  the  alterations  is 
the  loss  of  impulses  which  normally  reach  them  along  their  dendrites. 
In  short,  we  may  say  with  Marincsco,  that  the  functional  and 
anatomical  integrity  of  the  neuron  depends  on  the  integrity  of  all 
its  constituent  pails,  and  of  the  neurons  which  carry  to  it  functional 
excitations  i.e.,  excitations  connected  with  its  proper  physiological 
work.  The  neuron,  in  fact,  lives  by  its  function,  or,  in  common 
Language,  by  doing  its  work.  Yet  the  anatomical  tokens  of  mere 
disuse,  as  in  the  motor  cells  of  the  anterior  horn  after  division  of  the 
cord  at  a  higher  level,  are  less  distinct  than  those  which  follow 
section  of  the  axon.  Therefore  it  must  be  concluded  that  the  latter, 
although  not  indispensable  for  the  nutrition  of  the  cell  as  the  cell 
is  for  the  axon,  exerts  an  influence  upon  it.  Similar  changes  in  the 
chromatin  may  also  be  produced  in  nerve-cells  by  a  period  of 
anaemia,  in  extensive  superficial  burns,  in  tetanus  caused  by  the 
injection  of  bacterial  cultures,  in  acute  alcoholic  poisoning,  in 
fatigue,  and  in  other  ways.  According  to  Wright,  the  inhalation 
of  ether  or  chloroform  (in  dogs)  so  alters  the  chromatic  substance, 
that  it  loses  its  affinity  for  aniline  dyes.  In  long-continued  anaes- 
thesia the  nucleus  is  also  affected,  while  the  nucleolus  is  the  last 
part  of  the  cell  to  suffer.  A  greater  alteration  occurs  in  the  cells 
in  the  three  hours  between  the  sixth  and  ninth  hours  of  anaesthesia 
than  in  the  five  hours  between  the  first  and  sixth.  Although  the 
changes  are  transitory,  the  cells,  after  a  narcosis  of  nine  hours,  being 
practically  normal  in  forty-eight  hours,  they  indicate  that  the 
duration  of  safe  surgical  anaesthesia  has  a  limit  measured  by  hours. 

It  is  probable  that  the  alterations  in  the  chromatic  substance 
should  not  be  looked  upon  as  the  token  of  any  specific  lesion  ;  they 
are  the  common  structural  response  of  the  cell  to  injurious  influences 
of  the  most  varied  nature  (p.  873). 

Grey  and  White  Matter. — Nerve-cells  are  the  most  distinctive 
histological  feature  of  the  grey  nervous  substance.  Sown  thickly 
in  the  cerebral  cortex,  the  basal  ganglia,  the  floor  of  the  fourth 
ventricle,  and  the  cervical  and  lumbar  enlargements  of  the  cord, 
they  are  scattered  more  sparingly  wherever  the  grey  matter  extends. 
They  also  occur  in  the  spinal  ganglia  and  their  cerebral  homologues 
(such  as  the  Gasserian  ganglion),  in  the  ganglia  of  the  sympathetic 
system,  and  the  sporadic  ganglia  in  general.  But  wide  as  is  their 
distribution,  and  great  as  is  the  size  of  the  individual  cells,  some  of 
which  have  a  diameter  of  140  n,  or  even  more,  they  yet  make  up 
but  a  small  portion  of  the  whole  of  the  central  nervous  substance, 
the  total  weight  of  the  9,000  millions  of  nerve-cell  bodies  in  the 
human  brain  being  less  than  27  grammes  (Donaldson).  And 
although  it  is  not  to  be  wondered  at  that  objects  so  notable  when 
viewed  under  the  microscope  should  have  struck  the  imagination  of 
physiologists,  it  is  probable  that  the  very  high  powers  which  it  is 
so  common  to  attribute  exclusively  to  them  are,  in  part  at  least, 
shared  with  the  network  or  feltwork  formed  by  their  processes. 

The  grey  matter,  in  addition  to  this  exceedingly  delicate  network 
of  non-medullated  fibres  and  filaments  representing  the  dendrites 
and  such  axons  and  collaterals  as  terminate  within  itself,  contains 
also,  as  may  be  seen  in  preparations  stained  by  Weigert's  method,* 
great  numbers  of  exceedingly  fine  medullated  fibres,  many  of  which 
are  the  collaterals  of  fibres  that  are  passing  out  to  the  white  matter. 

*  Weigert's  is  a  special  method  of  staining  the  medullary  sheath  with 
hematoxylin. 


758 


A  MANUAL  <>/    PHYSIOLOGY 


<>nlv  medullated  nerve-fibres  are  mei  with  in  the  white  matter  of 
the  cerebrospinal   axis.     They   are  devoid   oi   a  neurilemma.     In 
diameter  they  vary  from  -■  /<  to  ju  p.     In  Malapterw 
the  fibre  in  the  <  ord  which  supplies  the  ele<  tri<  al  organ  is  oi  immi 
size  ,  and  in  the  anterior  column  oi  many  fishes  may  also  be 
.1  -ii:  ti<   fibre  on  ea<  h  side  with  a  diameter  o\  nearly  ioi 

It  cannol  I"  said  thai  any  relation  between  the  functions  oi  neurons 
and  the  calibre  ol  their  axons  has  been  definitely  established.  Many 
afferent  fibres,  it  is  true,  are  small  this  is  notably  the  case  with 
the  fibres  of  the  posterior  column,  and  many  motor  libn-s  are  large. 
But  the  distinction  can  by  no  means  be  generalized,  for  the  fib 
of  the  direct  cerebellar  trad  (p.  764),  which  certainly  are  afferent. 
arc  amongst  the  largest  in  the  spinal  cord  ;  and  the  vaso-motor 
fibres,    which    pass    from   the   cord    by   the   anterior    (ventral)    1 

[12)   into  the  sympathetic,  arc  smaller  than  the  fibres  of  the 
posterior  column.     Even  the  motor  nerve-fibres  of  striated  muscles 

vary  considerably  in  diameter,  those  of 
the  tongue,  e.g..  bein^'  smaller  than  I 
of  the  muscles  of  the  limbs.  Further,  the 
medullated  fibres  of  the  brain  are,  without 
reference  to  function,  in  general  finer  than 
the  fibres  of  the  cord.  As  a  rule,  the 
fibres  whose  course  is  the  longest  are  the 
thickest,  but  the  rule  is  often  broken. 
For  example,  the  average  diameter  of  the 
fibres  going  to  the  thigh  of  the  frog  is 
greater  than  that  of  the  fibres  going 
the  lower  part  of  the  limb  (Dunn).  The 
cause  oi  these  differences  in  the  size  of 
nerve  -  fibres  is  quite  unknown.  It  is 
more  likely  to  be  morphological  than 
physiological. 

Supporting  Tissue.  —  The  protective 
membranes  of  the  central  nervous  system 
consist  of  ordinary  connective  tissue  de- 
rived from  the  mesoderm.  The  support- 
ing framework  which  interpenetrates  the 
nervous  substance  consist  >  oi  a  peculiar 
form  of  tissue  derived  from  the  ectoderm, 
and  called  neuroglia.  The  whole  cerebro- 
spinal axis  is  wrapped  in  four  concentric 
sheaths.  Next  the  walls  of  the  bony  hollow  in  which  it  lies  is  the 
dura  mater.  Next  the  nervous  substance  itself,  following  the 
convolutions  of  the  brain  and  the  fissures  of  the  cord,  and  giving 
off  bloodvessels  to  both,  is  the  pia  mater.  Between  the  dura  and 
the  pia,  separated  from  the  latter  by  a  jacket  of  cerebro-spinal 
fluid,  is  the  double  layer  of  the  arachnoid.  The  comparatively 
coarse  septa  that  run  into  the  nervous  substance  as  if  coming  off 
from  the  pia  mater  are  the  main  beams  in  the  scaffolding  of 
non -nervous  material  with  which  that  substance  is  interwoven, 
and  by  which  it  is  supported.  The  interstices  are  tilled  in  by  a 
thick-set  feltwork  of  interlacing  neuroglia  fibres,  which  lie  close 
against  the  small  glia  cells,  but  according  to  some  authorities  are. 
in  the  adult  at  least,  perfectly  distinct  from  them,  although  origi- 
nally formed  from  the  cells.  In  preparations  impregnated  bv  the 
Golgi  method  many  of  the   neuroglia   fibres  appear  to  be   processes 


Fir,.  312.  —  T  R  A  XSVERSE 
Section  of  a  Bundle  of 
Nervi  -FIBRES  FROM  Illl 
Anterior  (Ventral)  Root 
of  the  First  Coccygeal 
Nerve  of  the  Cat  (Dale). 

The  great  difference  in  the 
diameter  oi  the  fibres  is  well 
shown.  The  small  fibres  are 
vaso-motor. 


/■///■  CENTR  ll     VERVOUS   SYST1  V 


750 


running  out  from  the  attenuated  cell-body  like  the  anna  of  a 
microscopic  crab  or  spider.  Hut  according  to  Weigert  this  is  a 
deceptive  appearance,  as  he  has  attempted  to  show  by  means  of 
a  special  method,  in  which  the  neuroglia  fibres  are  alone  stained 
It  this  is  the  cisc.  we  must  assume  thai  in  the  embryo  the 
fibres  .nv  formed  by  the  cells,  and  afterwards  become  detached 
from  them.  The  processes  oi  the  typical  'spider'  glia  cells  are 
unbranched  even  when  of  great  Length  in  proportion  to  the  diameter 
<>i  the  cell-body.  Other  neuroglia  cells  have  branched  processes. 
The  glia  fibres  are  perfectly  distinct  from  the  nervous  substance 
proper,  but  they  are  not  ordinary  connective  tissue.  Indeed,  it 
would  appear  that  no  connective  tissue  of  mesodermic  origin  exists 
within  the  nervous  substance;  even  the  coarse  septa,  and  particu- 
larly the  one  which  constitutes  the  so-called  posterior  fissure,  seem 
to  consist  of  neuroglia,  and  not  to  be  processes  of  pia  mater.  In  the 
white  matter  nearly  every  medullated  nerve-fibre  is  divided  from 
its  neighbours  by  glia  fibres,  which  form  a  wide-meshed  network. 
The  network  is  denser  in  most  parts  of  the  grey  substance,  though 
not  in  all.  The  neuroglia  is  present  in  greatest  abundance  in  the 
grey  matter  immediately  surrounding  the  central  canal  of  the  cord 
and  the  ventricles  of  the  brain  (the  ependyma,  as  it  is  called),  from 
which  long  neuroglia  fibres  pass  out  radially,  giving  off  branches  on 
their  course,  and  ending  in  little  knobs  or  enlargements  attached  to 
the  pia  mater.  Contrary  to  the  common  opinion,  the  substance  of 
Rolando  is  poor  in  neuroglia  (Weigert). 

General  Arrangement  of  the  White  and  Grey  Matter  in 
the  Central  Nervous  System. — (i)  Around  the  central  canal,  as 
we  have  seen,  a  tube  of  grey  matter  sheathed  with  white  fibres  is 
developed.  This  tube,  from  optic  thalamus  to  conus  medullaris, 
may  be  conveniently  referred  to  as  the  central  grey  axis  or  stem, 
which,  in  the  lowest  vertebrates — e.g.,  fishes — is  much  the  most 
important  part  of  the  central  nervous  system. 

(2)  On  the  outer  surface  of  the  anterior  portion  of  the  neural 
axis,  but  not  in  the  part  corresponding  to  the  spinal  cord,  is  laid 
down  a  second  sheet  or  mantle  of  cortical  grey  matter.  Between 
this  and  the  primitive  grey  stem  are  interposed  (a)  the  sheath  of 
white  fibres  that  clothes  the  latter,  and  connects  its  various  parts, 
and  (b)  a  new  development  of  white  matter  (corona  radiata.  cere- 
bellar peduncles),  which  serves  to  bring  the  cortex  into  relation 
with  the  primitive  axis,  and  through  it  with  the  rest  of  the  body. 

Although  there  are  histological  and  developmental  differences 
between  the  cerebral  and  the  cerebellar  cortex,  we  may,  for  some 
purposes,  classify  them  together  as  cortical  formations.  And  we 
may  also  include  under  this  head  the  corpora  striata,  which, 
although  for  descriptive  purposes  generally  grouped  with  the 
optic  thalami  and  the  other  clumps  of  grey  matter  at  the  base 
of  the  brain,  as  the  basal  ganglia,  are  to  be  regarded  as  cortical 
in  character.  As  we  mount  in  the  vertebrate  scale  the  cortex 
formation  of  the  secondary  fore-brain  and  hind-brain  acquires 
prominence. 


760  A   MANUAL  OF  PHYSIOLOGY 

In  other  words,  the  grey  matter  developed  in  the  roof  of  the 
cerebral  vesicles  I.  and  III.  (Fig.  209)  (the  grey  matter  of  the  cerebral 
and  cerebellar  cortex)  comes  to  overshadow  the  superficial  grey 
matter  hitherto  present  only  in  the  roof  of  vesicle  II.  (in  the  corpora 
bigemina).  Ami  lliis  cortex  formation  becomes  larger  in  amount, 
and.  in  the  case  of  the  cerebral  grey  matter,  more  richly  convo- 
luted, the  higher  we  ascend,  until  it  reaches  its  culmination  in  man. 
As  the  anterior  cerebral  vesicles  develop,  they  spread  continually 
backward,  until  at  length  the  cerebral  hemispheres  cover  over,  and 
almost  completely  surround,  the  primary  fore-brain  and  the  mid- 
and  hind-brains,  so  that  the  anterior  portion  of  the  primitive  stem 
comes,  as  it  were,  to  be  invaginated  into  the  second  wider  tube  of 
cortical  grey  matter.  This  development  of  the  cortical  grey  sub- 
stance is  accompanied  with  a  corresponding  development  of  nerve- 
fibres,  for  an  isolated  nerve-cell  (apart,  of  course,  from  possible 
embryonic  rudiments  which  have  not  undergone  complete  develop- 
ment) is  no  more  conceivable  than  a  railway-station  the  track  from 
which  leads  nowhere  in  particular,  or  a  harbour  on  the  top  of  a 
hill. 

But  it  is  to  be  particularly  observed  that  the  new  formation 
does  not  supplant  the  old,  but  works  through  and  directs  it.  The 
neuroblasts  of  the  cortex  do  not  throw  out  their  axons  to  make 
direct  junction  with  muscles  and  sensory  surfaces.  Such  junction 
the  cortex  finds  already  established  between  the  primitive  cerebro- 
spinal axis  and  the  periphery.  It  joins  itself  on  by  nerve-fibres 
to  the  cells  of  the  central  stem  ;  and  we  have  reason  to  believe  that 
no  single  axon  in  an  ordinary  spinal  or  cranial  nerve*  runs  all  the 
way  from  the  periphery  to  the  cortex,  and  no  axon  of  a  cortical 
nerve-cell  all  the  way  from  the  cortex  to  the  periphery,  but  that 
the  connection  is  made  by  a  chain  of  at  least  two  neurons,  the  cell- 
body  of  one  of  which  is  situate  in  this  primitive  grey  tube. 

The  fibres  from  the  cortex  of  each  cerebral  hemisphere  (corona 
radiata),  radiating  out  like  a  fan  below  the  grey  matter,  arc  gathered 
together  into  a  compact  leash  as  they  sweep  down  through  the 
isthmus  of  the  brain  in  the  internal  capsule,  to  join  the  crura  cerebri. 
The  cortex  of  each  cerebellar  hemisphere,  and  the  ribbed  pouch 
of  grey  matter,  known  as  the  corpus  dentatum,  which  is  buried  in 
its  white  core,  arc  also  connected  by  strands  of  fibres  with  the 
central  stem  and  the  cerebral  mantle.  The  restiform  body  or 
inferior  peduncle  brings  the  cerebellum  into  communication  with  the 
spinal  cord.  The  superior  peduncle  by  one  path,  and  the  middle 
peduncle  by  another,  connect  it  with  the  cerebral  cortex.  A  great 
transverse  commissure,  the  corpus  callosum,  unites  the  cerebral 
hemispheres  across  the  middle  line,  while  transverse  fibres  that 
break  through  the  middle  lobe  or  worm,  form  a  similar  though 
far  less  massive  junction  between  the  two  hemispheres  of  the 
cerebellum. 

The  fibres  of  the  nervous  system  may  be  divided  into  (1)  fibres 
connecting  the  peripheral  organs  with  nerve-cells  in  the  central 
grey  axis  ;  (2)  fibres  connecting  nerve-cells  in  this  central  axis 
with  cells  in  the  external  or  cortical  grey  tube  ;  and  (3)  fibres 

*  The  olfactory  and  possibly  to  some  extent  the  optic  nerves  are  ex- 
ceptions to  this  statement.  Their  relation  to  the  cortex,  as  is  easily 
understood  from  the  manner  of  their  development  (p.  7.47),  is  different 
from  that  of  the  other  nerves. 


77//     C/.V/7.'.//.    .V/ ■Ix'l'Oirs   .SV.S7/:.V/ 


761 


linking  cortex  with  cortex,  or  centra]  ganglia  with  each  other. 
In  the  third  group  arc  included  (a)  fibres  which  connect  portions 
of  die  cortex  on  the  same  side  (association  fibres)  ;  (I>)  fibres 
which  connect  portions  on  opposite  sides  of  the  middle  line 
(commissural  fibres)  ;  (c)  fibres  which  connect  the  central  grey 
matter  at  different  levels — f.£.,  the  proprio-spinal  or  endogenous 
fibres  of  the  cord.     Our   first   task   is,   therefore,   to  trace  the 


'                                         

/ 

2       (\ 

1    1 

Ceri/i  r.ctl 
En  largement 

-3--| 

4 

s       1 

&...  1  If 

7           Ii 

1    1 

[j  r" — Si  1 1  It  n  as  Cervical 
micleus 

1   1 

D 

S 

a.... 

1 

| 

H 

Lateral  cell-column 

(column  of  the  inter— 

1  medic-lateral  tract) 

!                                                                          < 

Cells  of  the.  

7...,1 

rjr Stilhna's  dorsal 

nucleus  or  Clarke's 

anterior  Cornu 

9         I 

/0        I'il 

Column. 

L 

Hi 

1 

1 
1 

! Scattered  cell s  of 

1   1    j        -j 

* 

1                mterme  a  to-lateral 

Lumbar 
Enlargement  (~ 

-—  -1*1 
"-  ill 
/— 1: 

tract . 
1    1 

■*— III' 

Mil 

j    /"-"      StiliinaS  Sacral 
1                nucleus 

Fig.  313. — Diagram  of  Grey  Tracts  of  Cord. 

peripheral  nerves  to  their  cells  of  origin  or  centres  of  reception* 
in  the  nervous  stem.  And  although  there  is  reason  to  believe 
that  the  whole  of  the  peripheral  nerves,  cerebral  and  spinal 
(with  the  exception  of  the  olfactory  and  optic,  which  are  rather 
portions  of  the  brain  than  true  peripheral  nerves),  form  a  morpho- 

*  The  centre  or  nucleus  of  reception  of  a  nerve  contains  the  nerve-cells 
around  which  its  axons  terminate  ;  the  nucleus  of  origin  of  a  nerve  con- 
tains the  cells  from  which  its  axons  arise. 


762  A   M  \NUAL  OF  PHYSIOLOGY 

logical  series,  it  will  be  well  to  begin  with  the  spinal  nerves, 
since  their  motor  and  sensory  fibres  are  gathered  into  different 
and  definite  roots,  whose  course  within  the  curd  is,  in  general, 
more  easily  traced  than  the  course  of  the  cerebral  root-bundles 
within  the  brain. 

Arrangement  of  the  Grey  and  White  Matter  in  the  Spinal 
Cord.  The  grey  matter  of  the  spinal  curd  is  arranged  on 
each  side  in  a  great  unbroken  column  of  roughly  crescentic 
section,  joined  with  its  fellow  across  the  middle  line  by  a  grey 
bar  or  bridge,  which  springs  from  the  convexity  of  the  crescent, 
and  is  pierced  from  end  to  end  by  the  central  canal.  The 
anterior  horn  of  the  crescent,  although  it  varies  in  shape  at 
different  levels  of  the  cord,  is,  in  general,  broad  and  massive, 
in  comparison  with  the  slender  and  tapering  posterior  horn.  In 
the  lower  cervical  and  upper  dorsal  region  a  moulding  or  pro- 
jection, forming  a  lateral  horn,  springs  from  the  fluted  outer 
side  of  the  grey  substance.  Within  the  grey  matter  nerve- 
cells  are  found,  sometimes  so  regularly  arranged  that  they  form 
veritable  cellular  or  vesicular  strands.  Of  these  the  best  marked 
are  :  (i)  The  tract  or  tracts  made  up  by  the  cells  of  the  anterior 
horn  (Fig.  313),  which  practically  run  from  end  to  end  of  the  cord, 
swell  out  in  the  cervical  and  lumbar  enlargements,  where  the 
cells  are  very  numerous  and  of  great  size  (70  /i  to  140  /x  in 
diameter),  and  contract  to  a  thin  thread  in  the  thoracic  region, 
where  they  are  relatively  few,  scattered,  and  small.  In  the 
enlargements  there  are  several  groups  of  these  cells  corresponding 
with  the  segments  of  the  limbs,  the  movements  of  the  hand, 
forearm,  and  upper  arm  being  each  represented  by  a  group  in 
the  cervical,  and  those  of  the  foot,  leg,  and  thigh  by  groups  in 
the  lumbar  swelling.  In  the  rest  of  the  cord  only  two  well- 
marked  groups  of  cells  are  present  in  the  anterior  horn,  a  mesial 
and  a  lateral.  (2)  Clarke's  column,  whose  cells,  mostly  of  good 
size  and  somewhat  rounded  in  outline,  are  situated  at  the  inner 
side  of  the  root  of  the  posterior  horn  just  where  it  joins  on  to  the 
grey  cross-bar.  It  gradually  increases  in  size  from  above  down- 
wards, usually  appearing  first  at  the  level  of  the  seventh  or 
eighth  cervical  nerve,  attaining  its  maximum  development  at 
the  eleventh  or  twelfth  dorsal  and  disappearing  altogether,  as  a 
continuous  strand,  at  the  level  of  the  second  or  third  lumbar 
nerves.  Scattered  nerve-cells,  however,  constituting  the  so- 
called  cervical  and  sacral  nuclei  of  Stilling,  are  frequently  found 
occupying  the  same  position  towards  the  upper  and  lower  ends 
of  the  cord,  and  may  be  looked  upon  as  isolated  portions  of 
Clarke's  column.  (3)  A  tract  of  small  cells  called  the  intcrmedio- 
lateral  tract,  lateral  cell  column,  or  lateral  horn,  situated  at  the  outer 
edge  of  the  grey  matter,  about  midway  between  the  anterior  and 


THI    CENTRAL  NERVOUS  SYS  I I   \l  763 

posterior  horns.  It  is  best  marked  in  the  thoracic  region,  up  to 
about  the  second  thoracic  segment,  although  in  the  correspond- 
ing situation  there  arc  scattered  cells  in  the  Lumbar  swelling  ami 
the  cervical  cord.  There  is  reason  to  believe  that  the  axon-,  ol 
cells  of  the  intermedio-lateral  tract,  which  pass  out  as  small 
mednllated  fibres  in  the  anterior  roots,  form  the  preganglionic 
segments  of  the  efferent  vascular  and  visceral  nerves  (p.  169). 
(4)  The  cells  of  the  posterior  horn,  which,  although  numerous,  are 
smaller  than  those  of  the  anterior  horn.  Throughout  the  whole 
cord,  however,  two  small  groups  of  cells  may  be  distinguished, 
one  on  the  lateral  side  of  the  horn,  about  its  middle,  and  the 
other  on  the  mesial  side,  a  little  in  front  of — i.e.,  ventral  to — the 
edges  of  the  substance  of  Rolando.  Both  of  these  groups  are 
broken  up  by  the  passage  through  them  of  bundles  of  fibres 
which  form  a  network,  and  they  are  therefore  called  respectively 
the  group  of  the  lateral  and  the  group  of  the  posterior  reticular 
formation. 

The  white  matter  of  the  cord  is  anatomically  divided  by  the 
position  of  the  nerve-roots  and  the  anterior  and  posterior  fissures 
into  three  columns  on  each  side  :  the  anterior,  lateral,  and 
posterior  columns.  The  first  two,  since  they  are  not  separated 
by  a  perfectly  definite  boundary,  are  often  grouped  together 
as  the  antero-lateral  column.  In  the  cervical  region  it  may  be 
seen  with  the  microscope  that  the  posterior  white  column  is 
almost  bisected  by  a  septum  running  in  from  the  pia  mater 
towards  the  grey  commissure.  The  inner  half  is  called  the 
postero-median  column,  or  column  of  Goll  ;  the  outer  half  the 
postero-external  column,  or  column  of  Burdach  (Fig.  314). 
No  localization  of  any  of  the  other  conducting  paths  in  the  cord 
is  possible  by  gross  anatomical  examination  ;  but  by  means  of  the 
developmental  method  and  the  method  of  degeneration  the 
columns  of  Goll  and  Burdach  can  be  followed  throughout  the 
cord,  and  several  similar  areas  can  be  mapped  out.  We  shall 
only  mention  those  that  are  physiologically  the  most  important. 

When  the  spinal  cord  is  divided,  and  the  animal  allowed  to 
survive  for  a  time,  certain  tracts  are  picked  out  by  the  degenera- 
tion of  their  fibres,  although  in  every  degenerated  tract  some 
fibres  remain  unaffected.  We  may  distinguish  the  tracts  that 
degenerate  above  the  lesion  (ascending  degeneration)  from  those 
that  degenerate  below  the  lesion  (descending  degeneration). 

Ascending  Tracts. — Above  the  lesion  degeneration  is  found 
both  in  the  posterior  and  the  antero-lateral  columns.  Imme- 
diately above  the  section  nearly  the  whole  of  the  posterior 
column  is  involved.  Higher  up  the  degeneration  clears  away 
from  Burdach's  tract,  and,  shifting  inwards,  comes  to  occupy 
a  position  in  the  column  of  Goll.     In  the  antero-lateral  column 


764 


A   MANUAL  OF  /'ffYSIOLOGY 


two  degenerated  regions  are  seen,  both  at  the  surface  of  the  cord, 
one  a  compact,  sickle-shaped  area  extending  forward-  from  the 
Deighbourhood  of  the  line  of  entrance  of  the  posterior  roots, 
and  the  other  an  area  of  scattered  degeneration,  embracing 
many  intact  fibres,  and  completing  the  outer  boundary  of  the 
column  almost  to  the  anterior  median  fissure.  The  compacl  area 
is  called  the  dorsal  or  direct  cerebellar  tract,  or  tract  of  Flechsig,  the 
diffuse  area  the  antero-lateral  ascending  trad,  or  tract  of  Gowers,  or 
ventral  cerebellar  trad*  The  dorsal  cerebellar  tract  is  dis- 
tinguished by  the  large  size  of  its  fibres.     It  is  only  distinct  in  the 


Anlero-lateral 
und-lnindle 
enous  fibres) 


First  Cervicai 


Direct  pyramidal 


Antero-lateral  ascending  (Gowers') 
(and  antero-lateral  descending) 


Crossed  pyramidal 
Direct  or  dorsal  cerebi  llai 


'ostero-external  (Iiurdach's) 
Postero-median  (Coil's) 


Sixth  Cervical. 


Sixth   Dorsal.  Fifth  Lumbar. 


Fig.  314. 


-Diagrammatic  Sections  of  the  Spinal  Cord  to  show  the  Tracts 
of  White  Matter  at  Different  Levels. 


dorsal  and  cervical  regions  of  the  cord.  The  tract  of  Lissauer,  or 
posterior  marginal  zone,  is  another  small  ascending  tract  at  the 
outer  side  of  the  tip  of  the  posterior  horn.  It  is  made  up  of  fine 
fibres  from  the  posterior  roots  which  soon  pass  into  the  posterior 
column. 

Descending  Tracts. — When  the  cord  is  divided,  say  in  the 
upper  dorsal  or  cervical  region,  the  following  tracts  degenerate 
below  the  lesion  : 

(1)  A  -mall  group  of  fibres  close  to  the  antero-median  fissure, 

*  Some  writers  employ  the  more  precise  terms,  dorsal  and  ventral 
s/n'no-cerebellar  tracts. 


/'///     CI  NTH.IL    NLHl'Otrs   SYS1  I   \l 


76t 


D.  C 


which  lias  received   the  name  of  the  direct  pyramidal  trad 
pyramidal,  because  higher  up  in  (he  medulla  oblongata  it  forms 

part  of  the  pyramid  ;  direct,  because  it  does  not  cross  over  at  the 
decussation  of  the  pyramids,  but  continues  down  on  the  same 
side.  The  direct  pyramidal  tract  is  only  present  in  man  and  the 
higher  apes. 

(2)  A  tract  of  degenerated  fibres  in  the  posterior  part  of  the 
lateral  column.  This  is  the  lateral  or  crossed  pyramidal  tract, 
and  is  much  larger  than  the  direct.  In  the  medulla  it  also  lies 
within  the  pyramid,  but,  unlike  the  direct  pyramidal  tract,  it 
crosses  to  the  opposite  side  of  the  cord  at  the  decussation.  The 
pyramidal  tracts  are  also 
called  cortico  -  spinal  to 
indicate  their  origin  and 
termination. 

(3)  A  tract  of  scattered 
degeneration  lying  along 
the  margin  of  the  cord  in 
the  anterior  portion  of 
the  antero-lateral  column, 
and  partly  overlapping 
the  tract  of  Gowers.  It 
is  called  the  antero-lateral 
descending  tract,  or  tract 
of  Loewenthal. 

(4)  The  pre  pyramidal 
(or  rubro  -  spinal)  tract, 
or  Monakow's  tract,  lying 
immediately  in  front  of  the 
crossed  pyramidal  tract. 

(5)  A  small,  comma- 
shaped  island  of  degene- 
ration (comma  tract)  can 
be  followed  downwards  for  a  short  distance  in  the  middle  of 
Burdach's  column.  It  is  only  seen  in  the  cervical  and  upper 
thoracic  regions. 

When  we  have  deducted  the  long  ascending  and  descending 
tracts  which  have  been  described,  there  still  remains  in  the 
antero-lateral  column  a  balance  of  white  matter  unaccounted 
for.  This  white  substance,  which  does  not  degenerate  for  any 
great  distance  either  above  or  below  a  lesion,  is  called  the  antero- 
lateral ground-bundle,  and  lies  chiefly  in  the  form  of  an  incomplete 
ring  around  the  anterior  cornu.  It  is  believed  to  consist  of 
fibres  (endogenous  or  proprio-spinal  fibres)  which  run  only  a 
comparatively  short  course  in  the  cord,  and  serve  to  connect 
nerve-cells  at  different  levels.     Some  of  these  endogenous  fibres 


v.R 


D.P 
Fig.  315. — Scheme      of  Cross-section      of 

Spinal    Cord    (Donaldson,    after    Len- 

hossek). 

On  the  left  side  only  the  afferent  fibres  are 
shown  ;  the  efferent  fibres  and  the  spinal  cells 
on  the  right  side.  D.R.,  posterior  (dorsal)  root ; 
V.R,  anterior  (ventral)  root  ;  C.P,  crossed 
pyramidal  fibres  ;  C,  direct  cerebellar  tract  ; 
A.L,  antero-lateral  tract;  D.C,  posterior 
columns. 


766 


A   MANUAL  OF  PHYSIOLOGY 


are  ascending,  others  descending.     Some  endogenous  fibres  may 
also  be  intermingled  with  the  fibres  of  certain  of  the  long  tracts, 


-^"^tm     ,rtw^K- 


Fig.  316. — Medulla  Oblongata,   Pons 
«and  Corpora  Quadrigemina  (Dorsal 
or  Posterior  View)  (Sappey). 

1,  corpora  quadrigemina  ;  2,  nates  ; 
3,  testes  ;  4,  anterior  brachium  uniting 
the  nates  to  the  lateral  geniculate  body  ; 
5,  posterior  brachium  uniting  the  testes 
to  the  internal  geniculate  body  6  ; 
7,  posterior  commissure  ;  8,  pineal  gland 
pulled  forward  to  show  nates  ;  9,  superior 
peduncle  of  the  cerebellum;  10,  11,  12. 
valve  of  Vieussens  ;  13,  trochlear  nerve  ; 
14,  lateral  sulcus  515,  fillet  ;  16,  superior, 
17,  middle  and  18,  inferior  peduncle  of 
the  cerebellum  ;  19,  floor  of  fourth  ven- 
tricle ;  20,  auditory  nerve  ;  21,  spinal 
cord;    2;  1    -median   colunu 

tinued  in  the  medulla  as  the  funiculus 
gracilis  ;  z},  the  clava,  the  continuation 
of  the  funiculus  gracilis. 


Fig.  317. — Medulla  Oblongata, 
Pons  and  Crura  Cerebri  (Ven- 
tral or  Anterior  View). 

1,  infundibulum  ;  2,  tuber  cine- 
reum  ;  3,  corpus  mammillare ;  4, 
cerebral  peduncle  or  crus  cerebri  ; 
5,  pons  ;  6,  middle  peduncle  of 
cerebellum  ;  7,  pyramid  ;  8,  decus- 
sation of  the  pyramids  ;  9,  olive  ; 
10,  tubercle  of  Rolando;  11,  ex- 
ternal arcuate  fibres  ;  12,  upper  end 
of  spinal  cord  ;  13,  ligamentum  den- 
ticulatum  :  14.  dura  mater  of  spinal 
cord  ;  15,  optic  tract  ;  16,  chiasma  ; 
17,  third  or  oculo-motor  nerve;  18, 
fourth  or  trochlear  nerve  ;  19,  fifth 
<>r  trigeminal  nerve  :  20.  sixth  nerve 
or  abducens ;  21,  seventh  or  facial 
nerve  :  22.  eighth  "r  auditory  nerve  ; 
23.  nerve  of  Wrisberg  (portio  inter- 
media), which  unites  witli  the 
facial  ;  24,  glosso-pharyngeal  nerve  : 
25.  vagus  nerve  ;  26,  spinal  acces- 
nerve  ;  27.  hypoglossal  nerve  ; 
28,  29,  30,  first,  second,  and  third 
pairs  of  cerviral  spinal  nerves. 


THE  CENTRAL   NERVOUS  SYSTEM 


767 


both  in  the  anterolateral  and  posterior  columns,  and  Sherrington 
has  slmwn  (in  the  dog)  ili.it   long  proprio-spinal  fibres  pa- 
down  in  the  lateral  column  connect  the  upper  with  the  lower 
parts  of  the  cord  (p.  804). 

The  next  question  which  arises  is:  How  are  the  long  tracts 
connected  below — i.e.,  with  the  periphery — and  above — i.e.,  with 
the  higher  parts  of  the  central  nervous  system  ?  The  answer  to 
this  question,  partly  derived  from  clinical  records  and  partly 
from  experimental  results,  is  in  the  case  of  some  of  the  tracts 
unexpectedly  full  and  minute,  though  meagre  in  regard  to  others. 
But  to  render  it  in- 
telligible it  is  neces- 
sary, first  of  all,  to 
describe  briefly — 

The  Arrangement  of 

the    Grey   and   White 

Matter    in   the    Upper 

Portion    of    the    Cere- 

bro-spinal    Axis.  —  In 

the  medulla  oblongata 

the    grey    and    white 

matter  of   the    spinal 

cord     is     rearranged, 

and,  in  addition,  new 

strands  of  fibres  and 

new    nuclei    of    grey 

substance  make  their 

appearance.    Of  these 

nuclei  the  most  con- 
spicuous is  the  den- 
tate   nucleus    of    the 

inferior    olive,   which, 

covered  by  a  crust  of 

white   fibres,    appears 

as  a  projection  on  the 

antero-lateral   surface 

of   the   medulla.      In 

front  of  the  olive,  be- 
tween it  and  the  continuation  of  the  anterior  median  fissure,  is 
another  projection,  the  pyramid,  which  looks  like  a  prolongation 
of  the  anterior  column  of  the  cord,  but  is  made  up  of  very 
different  constituents.  Dorsal  to  the  olive  is  the  restiform  body 
or  inferior  peduncle  of  the  cerebellum,  and  behind  the  restiform 
body  lie  two  thin  columns,  the  funiculus  cuneatus,  which  con- 
tinues the  postero-external  column  of  the  cord,  and  the  funiculus 
gracilis,  which  continues  the  postero-internal  column.  In  these 
funiculi  are  contained  collections  of  small  or  medium-sized  nerve- 
cells  termed  respectively  the  nucleus  cuneatus  and  the  nucleus 
gracilis.  The  rearrangement  of  the  constituents  of  the  cord  is 
due  mainly  to  two  causes  :  (1)  The  opening  up  of  the  central 
canal  to  form  the  fourth  ventricle,  and  the  folding  out,  on  either 
side,  of  the  grey  matter  which  lies  posterior  to  it  in  the  cord  ; 
(2)  the  breaking  up  of  the  grey   matter   of   the   anterior   horn   by 


Fig.  318. — Medulla  Oblongata  and  Cerebellum, 
with  Fourth  Ventricle  (Hirschfeld). 

1,  mesial  groove  of  floor  of  ventricle  running  down 
to  the  calamus  scriptorius  ;  2,  striae  acustica?  ;  3, 
inferior  peduncle  of  the  cerebellum  ;  4,  clava  ;  5, 
superior  peduncle  crossing  the  inferior  and  passing 
to  its  internal  side  ;  7,  7,  lateral  sulcus  ;  8,  corpora 
quadrigemina. 


768  A   MANUAL  OF  PHYSIOLOGY 

strands  of  fibres  as  they  sweep  through  it  from  the  lateral  pyra- 
midal tract  to  take  up  a  position  m  the  pyramid  of  the  opposite  side 
(decussation  oi  the  pyramids),  and  a  little  higher  up  by  fibres 
passing  across  the  middle  line  from  the  gracile  and  cuneate  nuclei 
[sensory  decussation  or  decussation  of  the  fillet).  The  mosaic  of 
grey  and  white  matter  formed  in  the  medulla  by  the  interlacing 
of  longitudinal  and  transverse  fibres  with  each  other  and  with  the 
rehes  of  the  anterior  horn,  is  called  the  reticular  formation  [formatio 
reticularis).  It  occupies  the  anterior  and  lateral  portions  of  the 
bulb  behind  the  pyramids  and  olivary  bodies,  and  is  continued 
upwards  in  the  dorsal  portion  of  the  pons  and  crura  cerebri,  and 
downwards  for  a  little  way  into  the  upper  part  of  the  cervical  cord. 

The  cerebro-spinal  axis  passes  up  from  the  medulla  through  the 
pons,  encircled  and  traversed  by  the  transverse  pontine  fibres 
derived  from  the  middle  cerebellar  peduncle  or  commissure,  which 
enclose  everywhere  between  them  numerous  collections  of  nerve- 
cells  {nuclei  pontis).  Enlarged  by  the  accession  of  many  of  these 
fibres  which  come  from  the  cortex  of  the  cerebellum  on  the  opposite 
side,  as  well  as  of  fibres  from  the  nuclei  of  the  cranial  nerves  that 
take  origin  in  this  neighbourhood  (fifth  and  eighth),  the  central 
nervous  stem  bifurcates  above  the  pons  into  the  two  divergent  crura 
cerebri.  From  each  crus  a  great  sheet  of  fibres  passes  up  between 
the  optic  thalamus  and  the  caudate  nucleus  of  the  corpus  striatum 
on  the  one  hand,  and  the  globus  pallidus  of  the  lenticular  nucleus  on 
the  other,  as  the  internal  capsule,  from  which  they  are  dispersed, 
in  the  corona  radiata,  to  the  cerebral  cortex.  Both  in  the  upper 
part  of  the  pons  and  in  the  crus  a  ventral  portion,  or  crusta,  con- 
taining the  fibres  of  the  pyramidal  tract,  and  a  dorsal  portion,  or 
tegmentum,  can  be  distinguished,  the  line  of  separation  being  marked 
in  the  crus  by  a  collection  of  grey  matter,  called  from  its  usual, 
though  not  invariable,  colour  the  substantia  nigra  (Fig.  324).  A 
portion  of  the  tegmentum  is  continued  below  the  optic  thalamus. 

Coming  back  now  to  our  question  as  to  the  connections  of 
the  long  tracts  of  the  cord,  let  us  consider,  first  of  all, 

The  Connections  of  the  Postero-median  and  Postero-external 
Columns. — When  a  single  posterior  root  is  divided,  savin  the 
dorsal  region,  between  the  cord  and  the  ganglion,  its  fibres,  as 
we  have  already  seen  (p.  693),  degenerate  above  the  section. 
Since  the  cell-bodies  of  these  neurons  lie  in  the  ganglion,  if  a 
series  of  microscopic  sections  of  the  spinal  cord  be  made,  well- 
marked  degeneration  will  be  found  at  the  level  of  entrance  of 
the  root  on  the  same  side  of  the  cord,  while  below  that  level 
there  will  be  only  a  few  degenerated  fibres  in  the  comma  tract. 
Immediately  above  the  plane  of  the  divided  root  the  degenera- 
tion will  be  confined  to  Burdach's  column  and  to  its  external 
border.  Higher  up  it  will  be  found  in  the  internal  portion  of 
Burdach's  and  the  external  rim  of  Goll's  column.  Still  higher 
up  the  degenerated  fibres  will  be  confined  to  the  postero-median 
column  ;  the  postero-external  will  be  entirely  free  from  de- 
generation. 

When  a  number  of  consecutive  posterior  roots  are  cut,  the 


/'///.   I  ENTRAL  NERVOUS  SYSTEM 


whole  of  the  posteroexternal  column  in  the  sections  immediately 
above  the  highest  of  the  divided  roots  will  be  found  occupied  by 
degenerated  fibres,  while  Goll's  column  may  be  free  from  de- 
feneration, or  degenerated  only  at  its  outer  border.  Higher  up 
degeneration  will  be  found  to  have  involved  the  whole  of  the 
postero-median  column,  and  to  have  cleared  away  altogether 
from  the  postero-external.  The  degeneration  in  the  column  of 
Goll  may  be  traced  along  the  whole  length  of  the  cord  to  the 
medulla,  although  the  number  of  degenerated  fibres  diminishes 
as  we  pass  upward.     The  explanation  of  these  appearances  is  as 


| 

;  -Mr 


Fig.  319.  —  Posterior  Roots 
entering  spinal  cord  (at  the 
Left  of  the  Figure). 

(From  a  preparation  stained  with 
aniline  blue-black.) 


Fig.  320. — Branching  of  Pos- 
terior Root-fibres  in  Cord 
(Donaldson,  after  Cajal). 

Collaterals,  Col,  are  seen  coming 
off  from  the  two  main  branches  of 
the  root-fibres,  DR,  and  ending 
in  arborizations.  CC,  cells  in  the 
grey  matter  of  the  cord,  whose 
axons  also  give  off  collaterals. 

follows  :  It  may  be  seen  in  preparations  of  the  cord  impregnated 
by  Golgi's  method  that  the  fibres  of  the  posterior  roots  soon  after 
their  entrance  into  the  cord  divide  into  two  processes,  one  of 
which  runs  up  and  the  other  down  in  the  posterior  column,  or 
in  the  adjoining  portion  of  the  posterior  horn.  From  both  of 
these  collaterals  are  given  off  at  intervals  to  the  grey  matter. 
The  descending  branches  run  downwards  only  for  a  short 
distance,  and  the  degeneration  in  the  comma  tract  seen  after 
section  of  the  cord  is  due  to  the  division  of  these  branches. 
Many  of  the  ascending  branches  pass  up  for  a  short  distance  in 

49 


77o  A   MANUAL  OF  PHYSIOLOGY 

the  posteroexternal  column,  sweeping  obliquely  through  it  to 
gain  the  tract  of  Goll.  In  this  tract  some  of  them  run  right 
on  to  the  medulla  oblongata,  to  end  by  arborizing  among  the 
cells  of  the  nucleus  gracilis.  Other  fibres,  both  of  Goll's  and  of 
Burdach's  tract,  end  at  various  levels  in  the  cord,  their  collaterals, 
and  ultimately  the  main  branches  themselves,  coming  into  rela- 
tion with  nerve-cells  in  the  grey  matter.  When  the  cervical 
posterior  roots  are  cut,  many  of  the  degenerated  fibres  remain  in 
Burdach's  column  up  to  the  medulla,  where  they  terminate  in  the 
nucleus  cuneatus.  In  the  posterior  column,  then,  the  numerous 
fibres  of  the  posterior  roots  which  do  not  end  in  the  spinal  cord 
are  arranged  in  layers,  the  fibres  from  the  lower  roots  being 
nearest  the  median  fissure  (in  the  postero-median  column),  and 
those  from  the  higher  roots  farthest  away  from  it  (in  the  postero- 
external column).  Other  collaterals  from  the  posterior  root- 
fibres,  and  many  of  the  main  root-fibres  themselves,  run  into 
the  anterior  horn  and  terminate  in  arborizations  around  its  cells  ; 
some  pass  into  the  posterior  horn,  and  doubtless  come  into  rela- 
tion with  its  scattered  cells  and,  in  the  dorsal  region,  with  the 
cells  of  Clarke's  column.  Some  of  the  posterior  root-fibres  and 
their  collaterals  also  form  synapses  with  the  cells  of  the  inter- 
medio-lateral  tract.  Other  collaterals  and  probably  some  axons 
cross  the  middle  line  in  the  anterior  and  posterior  commissures 
and  end  in  the  grey  matter  of  the  opposite  side. 

Connections  of  the  Direct  or  Dorsal  Cerebellar  Tract. — Since 
the  dorsal  or  direct  cerebellar  tract  does  not  degenerate  after 
section  of  the  posterior  nerve-roots,  but  does  degenerate  above 
the  level  of  the  lesion  after  section  of  the  spinal  cord,  the  nerve- 
cells  from  which  its  axons  arise  must  be  situated  somewhere  or 
other  in  the  cord.  Now,  it  has  been  observed  that  the  vesicular 
column  of  Clarke  first  becomes  prominent  in  the  lower  dorsal 
region,  and  that  in  this  same  region  the  direct  cerebellar  tract 
begins.  Atrophy  of  the  cells  of  Clarke's  column  has  sometimes 
in  disease  been  shown  to  accompany  degeneration  of  the  direct 
cerebellar  fibres.  After  an  experimental  lesion  of  these  fibres 
in  animals,  some  of  the  cells  of  the  vesicular  column  show  the 
changes  in  the  Nissl  bodies  and  the  other  changes  which  we 
have  already  described  as  occurring  in  nerve-cells  whose 
axons  have  been  cut.  After  two  or  three  months  these 
cells  may  be  found  almost  completely  atrophied  (Schafer). 
Finally,  axis-cylinder  processes  have  been  seen  sweeping  out  from 
Clarke's  column  into  the  direct  cerebellar  tract  (Mott).  The 
evidence,  then,  is  complete  that  the  cells  of  origin  of  this  tract 
are  in  Clarke's  column.  Clarke's  cells  are  surrounded  by  arboriza- 
tions, some  of  which,  as  previously  stated,  represent  the  termina- 
tions   of    posterior    root-fibres    and    of    their    collaterals.     The 


THE  CENTRAL   NERVOUS  SYSTEM 


77 1 


neurons  whose  axons  run  in  the  dorsal  cerebellar  tract  are  there- 
fore the  second  link  in  an  afferent  path.  The  direct  cerebellar 
tract  runs  right  up  to  the  cerebellum  through  the  restiform  body, 
without  crossing  and  without  being  further  interrupted  by  nerve- 
cells.     The  restiform  body  ends  partly  in  the  dentate  nucleus  of 


-  -  .  i  -/       ».e 


nX    t 


^  '  :  f 

-ft 

■--;■  ■'  „i 

Jj—  o ' 

'/it 


a.m.f. 

Fig.  321. — Transverse  Section  of  Me- 
dulla Oblongata  at  the  Level  of 
the  Decussation  of  the  Fillet  (Hal- 
liburton,  AFTER   SCHWALBE). 

a.m.f,  anterior,  and  p.m.f,  posterior 
median  fissure  ;  f.a  and  f.a2,  external  arcu- 
ate fibres  ;  f.a',  internal  arcuate  fibres  be- 
coming external  ;  n.a.r,  nuclei  of  arcuate 
fibres  ;  py,  pyramid  ;  0,  0' ,  lower  end  of 
nucleus  of  olive  ;  f.r,  formatio  reticularis  ; 
n.l,  lateral  nucleus  ;  ti.g,  nucleus  gracilis  ; 
f.g,  funiculus  gracilis  ;  n.c,  nucleus  cuneatus  ; 
n.c',  external  cuneate  nucleus  ;  f.c,  funiculus 
cuneatus  ;  g,  substance  of  Rolando  ;  c.c, 
central  canal  surrounded  by  grey  matter  ; 
n.XI,  nucleus  of  spinal  accessory  ;  n.XII, 
of  hypoglossal  ;  a.V,  ascending  root  of  fifth 
nerve  ;  s.d,  the  decussation  of  the  fillet,  or 
superior  decussation. 


nor. 


Fig.  322. — Transverse  Section  of  Me- 
dulla Oblongata  at  about  the 
Middle  of  the  Olive  (Halliburton, 
after  Schwalbe). 

f.l.a,  anterior  median  fissure ;  n.a.r, 
arcuate  nucleus  ;  p.,  pyramid  ;  n.XII,  hypo- 
glossal nucleus  ;  XII,  root  bundle  of  hypo- 
glossal nerve  coming  off  from  the  surface  ; 
at  b  it  runs  between  the  pyramid  and  the 
dentate  nucleus  of  the  olive,  0  ;  f.a.e,  ex- 
ternal arcuate  fibres  ;  n.l,  lateral  nucleus  ; 
a,  arcuate  fibres  going  to  restiform  body 
c.r,  partly  through  the  substantia  gelatinosa 
g,  partly  superficial  to  the  ascending  root 
of  the  fifth  nerve  a.V ;  X,  root-bundle  of 
vagus  ;  n.X,  n.X',  two  portions  of  vagus 
nucleus  ;  f.r,  formatio  reticularis  ;  n.g, 
nucleus  gracilis  ;  n.c,  nucleus  cuneatus  ; 
n.t,  nucleus  of  the  funiculus  teres  ;  n.am, 
nucleus  ambiguus  ;  r,  raphe  ;  o' ,  o" ,  acces- 
sory olivary  nucleus  ;  p.o.l,  peduncle  of  the 
olive. 


the  cerebellum,  partly  in  the  vermis,  and  among  the  fibres  which 
end  in  the  vermis  are  those  of  the  direct  cerebellar  tract.  In  the 
dorsal  cerebellar  tract  there  is  a  definite  stratification  of  the 
fibres  :  the  fibres  from  the  lowest  segments  of  the  cord  lie  outer- 

49—2 


772 


A   MANUAL  OF  PHYSIOLOGY 


most  ;  beneath  these  come  fibres  from  the  lowest  thoracic  seg- 
ments, then  fibres  from  the  higher  thoracic  segments  ;  and, 
internal  to  all,  fibres  from  the  topmost  thoracic  and  lowest 
cervical  segments  (Sherrington  and  Laslett). 

Connections  of  the  Antero-lateral  Ascending  Tract. —According 
to  Schafer,  the  axons  of  this  tract  are  probably  connects]  with  cells 
situated  in  the  middle  and  posterior  parts  of  the  grey  crescent, 
mainly  on  the  opposite  side  of  the  cord,  although  also  on  the  same 
side.  None  of  the  fibres  of  the  tract  can  come  directly  from  the 
posterior  nerve-roots,  since  no  degeneration  is  seen  in  it  on  section 
of  the  roots  alone. 

The  antero-lateral  ascending  tract  passes  up  through  the  medulla, 
where  some  of  its  fibres  perhaps  form  synapses  with  the  cells  of  the 
lateral  nucleus,  a  collection  of  grey  matter  in  the  lateral  portion  of 
the  spinal  bulb.  But  its  main  strand  runs  on  unbroken  through  the 
medulla,  in  front  of  the  restiform  body,  and  behind  the  olive,  and  after 
reaching  the  upper  part  of  the  pons  bends  back  over  and  in  company 

with  the  superior  peduncle  as 
the  ventral  spino -cerebellar 
bundle,  to  end  in  the  worm 
of  the  cerebellum  (Fig.  330). 

A  few  fibres  of  Gowers'  tract 
may  pass  by  the  middle  pe- 
duncle to  the  opposite  cere- 
bellar hemisphere.  Some  of 
its  fibres  do  not  go  to  the 
cerebellum  at  all.  One  group 
can  be  followed  to  the  cor- 
pora quadrigemina  (spino- 
tectal fibres),  and  another  by 
way  of  the  tegmentum  of  the 
crus  cerebri  to  the  optic  thala- 
mus [spino-thalamic  fibres). 

Through  the  relay  of  the 
gracile  and  cuneate  nuclei, 
the  postero-internal  and  pos- 
tero-external  columns  of  the 
cord  are  further  connected 
on  the  one  hand  with  the 
cerebrum,  and  on  the  other 
with  the  cerebellum.  The  cells  of  the  nuclei  give  off  fibres 
(internal  arcuate  fibres)  which,  sweeping  in  wide  arches  across 
the  mesial  raphe  to  the  opposite  side,  take  up  a  position 
behind  the  pyramid  in  the  tract  of  the  fillet,  a.  bundle  of  fibres 
which  becomes  more  compact,  and  therefore  more  distinct  as  it 
passes  brainwards.  Receiving  fibres  from  other  sources  on  its 
way,  and  also  giving  off  fibres,  it  runs  upwards  through  the 
dorsal  or  tegmental  portion  of  the  pons.  In  the  mid-brain  it 
divides  into  two  portions,  the  Intend  fillet,  also  called  the  lower 
fillet  or  fillet  of  Reil,  and  the  intermediate,  also  called  the  upper 


Fig. 


323.  —  Diagram    of 
of  Fillet. 


Decussation 


a,  nucleus  gracilis  ;  b,  nucleus  cuneatus  ; 
c,  internal  arcuate  fibres  crossing  the 
middle  line  from  a  and  b  to  the  fillet  d, 
and  forming  the  decussation  of  the  fillet  ; 
c,  anterior  median  fissure. 


THE  CENTRAL   NERVOUS  SYSTEM 


773 


fillet.  The  lateral  fillet  contains  mainly  fibres  arising  in  the 
cochlear  nucleus  of  the  auditory  nerve,  and  ends  in  grey  matter 
of  the  posterior  corpus  quadrigeminum,  and  partly  in  the  mesial 
geniculate  body.  It  appears  to  be  a  path  for  the  conduction 
of  auditory  impulses.  The  intermediate  fillet  contains  chiefly 
the  fibres  that  come  off  from  the  gracile  and  cuneate  nuclei,  but 
is  enlarged  by  the  accession  of  fibres  from  the  sensory  nuclei  of 
the  cranial  nerves.  It  terminates  in  the  lateral  nucleus  of  the 
optic  thalamus  ^by  forming  synapses  with  nerve-cells,  whose 
axons,  passing  through  the  posterior  limb  of  the  internal  capsule 


Fig.   324. — Diagrammatic  Transverse  Section  of  Crura  Cerebri  and 
Aqueduct  of  Sylvius. 

a,  anterior  corpora  quadrigemiua  ;  b,  aqueduct  ;  c,  red  nucleus  ;  d,  fillet  ; 
e,  substantia  nigra  ;  /,  pyramidal  tract  in  the  crusta  of  the  crura  cerebri  ; 
g,  fibres  from  frontal  lobe  of  cerebrum  ;  h,  fibres  from  temporo-occipital  lobe  ; 
i,  posterior  longitudinal  bundle. 

and  the  corona  radiata,  continue  the  afferent  path  to  the  cerebral 
cortex. 

Besides  the  ascending  fibres,  the  bundle  anatomically  de- 
scribed as  the  tract  of  the  fillet  contains  some  descending  fibres 
which  on  section  of  the  tract  degenerate  below  the  lesion.  They 
lie  to  the  mesial  side  of  the  intermediate  fillet,  and  since  their 
cells  of  origin  seem  to  be  in  the  thalamus  and  their  course  is 
towards  the  bulb,  they  are  spoken  of  as  a  thalamo-bulbar  tract. 

Not.  all  of  the  axons  from  the  cells  of  the  cranial  sensory 
nuclei  run  in  the  fillet.  Many  of  them  occupy  a  position  in  the 
reticular  formation  of  the  tegmentum  dorsal  to  the  fillet  as  they 
pass  through  the  pons  and  mid-brain  to  end  in  the  thalamus  and 
the  region  below  it   (sub-thalamic  region).     From  the  sensory 


774 


I     MANUAL  OF  PHYSIOLOGY 


nucleus  of  the  fifth  nerve  a  separate  bundle  oi  fibres  as<  end  to 
the  thalamus,  Iving  in  the  tegmentum  of  the  mid-brain  lateral 
to  the  posterior  longitudinal  bundle. 

Connections  of  the  Pyramidal  Tracts.  —  When  the  cortex 
in  and  in  front  of  the  fissure  of  Rolando  is  destroyed  by  disease 
in  man,  or  removed  by  operation  in  animals,  it  is  found  that  in  a 
short  time  degeneration  has  taken  place  in  the  fibres  of  the  corona 
radiata  which  pass  off  from  this  area.  The  degeneration  can  be 
followed  down  through  the  genu  and  the  anterior  two-thirds  of 
the  posterior  limb  of  the  internal  capsule  (Fig.  325)  and  the 
crusta  of  the  cerebral  peduncle  of  the  corresponding  side  into 
the  medulla  oblongata.     Below  the  decussation  of  the  pyramids 


INTERNAL      CAPSULC 

.Fillet 


MID.   BRAIN 

Fig.   325. — Pyramidal  Path  (after    Gowers). 
Degeneration  after   destruction   of   the    'motor'   area   of   the   rijlit   cerebral 
hemisphere.     The  degenerated  areas  are  indicated  by  the  shading. 

it  is  found  that  the  degeneration  has  involved  the  two  pyramidal 
tracts,  and  only  these — the  crossed  pyramidal  tract  on  the  side 
opposite  the  cortical  lesion,  the  direct  pyramidal  tract  on  the 
same  side — and  that  the  cross-section  of  the  two  degenerated 
tracts  goes  on  continually  diminishing  as  we  pass  down  the  cord. 
(We  overlook,  for  the  moment,  in  the  interest  of  simplicity 
of  statement,  the  fact  that  some  degenerated  fibres  are  found 
in  the  crossed  pyramidal  tract  on  the  same  side  as  the  lesion.) 
This  is  proof  positive  that  the  cell-bodies  of  the  neurons  whose 
axons  run  in  these  tracts  are  situated  in  the  cerebral  cortex. 
They  have  indeed  been  identified  with  certain  of  the  large 
pyramidal  cells  (the  so-called  giant  cells  or  cells  of  Betz)  in  the 
cortex  of  the  '  motor '  region  in  front  of  the  Rolandic  fissure 
(p.  851).     For  after  division  of  the  motor  pyramidal  fibres  in  the 


THE  CENTRAL   NERVOUS  SYSTEM  775 

upper  cervical  region  of  the  cord  (in  monkeys)  changes  in  the 
chromatin  (so-called  chromatolysis)  and  atrophy  of  these  large 
cells  occur.  The  same  has  been  found  to  be  true  in  man  in  cases 
where  the  cord  was  injured  by  fracture  of  the  spine  in  such  a 
way  as  to  interrupt  the  tract  (as  well  as  other  tracts)  completely 
and  permanently,  without  entailing  death  for  a  considerable 
time  (Holmes  and  May).  The  fact  that  after  destruction  of  the 
cortex  or  the  path  in  its  course  the  degeneration  below  the  lesion 
does  not  spread  to  the  anterior  roots  shows  that  at  least  one  relay 
of  nerve-cells  intervenes  between  the  pyramidal  fibres  and  the 
root-fibres.  The  results  both  of  normal  and  morbid  histology 
enable  us  to  identify  the  cells  of  the  anterior  horn  as  the  cells 
of  origin  of  the  axons  of  the  anterior  root-fibres.     For 

(1)  Axis-cylinder  processes  have  been  actually  observed  passing 
out  from  certain  of  the  so-called  motor  cells  of  the  anterior  horn  to 
become  the  axis-cylinders  of  the  anterior  root. 

(2)  In  the  pathological  condition  known  as  anterior  poliomyelitis, 
the  cells  of  the  anterior  horn  degenerate,  and  so  do  the  anterior 
roots  of  the  affected  region,  the  motor  fibres  of  the  spinal  nerves, 
and  the  muscles  supplied  by  them. 

(3)  As  already  mentioned  (p.  756),  comparatively  transient  but 
decided  changes  occur  in  the  anterior  horn  cells  on  section  of  the 
corresponding  anterior  roots. 

(4)  An  enumeration*  has  been  made  in  a  small  animal  (frog)  of 
the  cells  of  the  anterior  horn  and  of  the  anterior  root-fibres,  and  it 
has  been  found  that  the  numbers  agree  in  a  remarkable  manner. 
From  all  this  it  cannot  be  doubted  that  most,  at  any  rate,  of  the 
cells  of  the  anterior  horn  are  connected  with  fibres  of  the  anterior 
root.  But  since  the  number  of  fibres  in  the  pyramidal  tracts  (about 
80,000  in  each  half  of  the  human  cord)  falls  far  short  of  the  number 
of  fibres  in  the  anterior  roots  (not  less  than  200,000  in  man  on  each 
side),  it  is  necessary  to  suppose  either  that  one  pyramidal  fibre  may 
be  connected  with  several  cells  or  that  all  the  anterior  root-fibres 
are  not  in  functional  connection  with  the  pyramidal  tract. 

There  is  no  reason  to  assume  any  such  connection  in  the  case  of 
the  fine  medullated  root-fibres  arising  in  the  lateral  horn  and  going 
to  the  visceral  and  vascular  muscles. 

While  there  is  no  doubt  that  anterior  root-fibres  and  pyramidal 
fibres  of  the  brain  and  cord  form  segments  of  the  same  nervous 
path,  the  connection  between  the  pyramidal  fibres  and  the  cells 
of  the  anterior  horn  has  not  yet  been  anatomically  demonstrated. 
Many  of  the  pyramidal  fibres  pass  into  the  grey  matter  between 
the  anterior  and  posterior  horns  or  near  the  base  of  the  posterior 
horn.  The  anterior  horn  cells  are  surrounded  by  arborizations. 
Some  of  these  are  probably  the  terminations  of  axons  whose 
cell-bodies  are  situated  in  the  posterior  horn,  others  the  termina- 
tions of  posterior  root-fibres  or  their  collaterals.  Many  of  them 
very  likely  represent  the  end  arborizations  of  pyramidal  fibres 

*  Such  enumerations  can  be  made  with  great  accuracy  from  photographs 
of  sections  of  the  nerves  (Hardesty,  Dale).      (See  Fig.  312,  p.  758.) 


77(>  A    MANUAL  OF  PHYSIOLOGY 

or  their  collaterals.     Some  observers,  however,  suppose  that  the 
pyramidal  fibres  do  not  come  into  immediate  relation  with  the 

anterior   horn   cells,    but   that    another   neuron   is   intercalated 
between  them  and  the  cells. 

The  pyramidal  fibres  are  unquestionably  paths  for  voluntary 
motor  impulses  passing  down  from  the  cortex  to  the  cord.  But 
they  are  not  the  only  cortico-spinal  efferent  paths,  and  in  many 
animals  they  are  not  even  the  most  important  paths  for  voluntary 
movements.  It  is  the  more  skilled  and  delicate  movements 
which  the  pyramidal  tract  subserves  in  man,  and  it  is  these 
movements  which  are  permanently  lost  when  the  tract  is  de- 
stroyed. The  size  of  the  path  is  proportioned  to  the  degree  of 
development  of  the  brain.  Thus,  it  is  larger  in  the  monkey  than 
in  the  dog,  and  larger  in  man  than  in  the  monkey.  In  the  lower 
mammals  it  is  exceedingly  small.  While  in  man  the  pyramidal 
tracts  constitute  nearly  12  per  cent,  of  the  total  cross-section  of 
the  cord,  they  make  up  little  more  than  1  per  cent,  in  the  mouse. 
In  some  mammals,  as  the  rat,  mouse,  guinea-pig,  and  squirrel, 
the  pyramidal  tracts  lie,  not  in  the  antero-lateral,  but  in  the 
posterior  columns.  In  vertebrates  below  the  mammals  the  pyra- 
midal system  does  not  exist  as  a  collection  of  neurons  which 
send  their  axons  without  interruption  down  from  the  cortex  to 
the  cord.  In  birds,  e.g.,  after  the  removal  of  a  hemisphere, 
the  degeneration  does  not  extend  below  the  mid-brain  (Boyce). 

Connections  of  the  Antero-lateral  Descending  Tract. — The  main 
origin  of  these  fibres  is  the  nucleus  of  Deiters,  a  collection  of  large 
multipolar  nerve-cells  in  the  floor  of  the  fourth  ventricle  near  the 
inner  auditory  nucleus.  These  cells  give  off  axons  which  pass  into 
the  posterior  longitudinal  bundle  of  the  bulb  and  pons,  mostly  to  the 
bundle  of  the  same  side,  but  partly  into  that  of  the  opposite  side. 
Here  the  fibres  bifurcate  into  an  ascending  branch,  which  passes 
up  to  the  oculo-motor  nucleus,  and  a  descending  (vestibulospinal) 
branch,  which  passes  downwards  to  the  spinal  cord  and  enters  the 
antero-lateral  descending  tract.  The  fibres  of  this  tract  ultimately 
pass  into  the  anterior  horn,  where  most  of  them  end  by  arborizing 
amongst  the  cells  of  the  horn.  Higher  up  corresponding  fibres  from 
the  posterior  longitudinal  bundle  arborize  in  the  cranial  motor  nuclei. 

Thus  far,  then,  we  have  been  able  to  map  out  two  great 
paths  from  the  cerebral  cortex  to  the  periphery— one  efferent, 
the  other  afferent. 

(1)  The  great  efferent  or  motor  pyramidal  path,  which, 
starting  in  the  cortex  in  front  of  the  fissure  of  Rolando,  where  its 
axons  give  off  numerous  collaterals  to  the  grey  matter  soon  after 
emerging  from  the  cells,  and  sweeping  down  the  broad  tan  ol 
the  corona  radiata,  passes  through  the  narrow  isthmus  of  the 
internal  capsule  into  the  crusta  of  the  crus  cerebri,  and  thence 
into  the  pons  (Figs.  326,  327).  .  At  this  level,  the  fibres  destined 


Illl    CENTUM    XI-.RVOl'S  SYSTEM 


777 


to  make  connection  with  the  motor  nuclei  "I  the  cranial  nerves 
in  the  grey  matter  underlying  the  aqueduct  of  Sylvius  and  the 
fourth  ventricle  terminate.  Mosl  ol  these  fibres  decussate  to 
make  physiological  connection  with  nuclei  on  the  opposite  side, 
but  some  join  nuclei  on  the  same  side.  The  question  whether 
they  arborize  directly  around  the  cells  of  the  motor  nuclei  or 
make  junction  with  them  through  another  intercalated  neuron 
is  precisely  in  the  same  position  as  the  corresponding  question 


Fig.  326. — Paths  from  Cortex  in  Corona  Radiata  (Starr). 

A,  tract  from  frontal  convolutions  to  nuclei  of  pons  and  so  to  cerebellum  ; 
B,  motor  pyramidal  tract  ;  C,  afferent  tract  for  tactile  sensations  (represented 
in  the  diagram  as  separated  from  B  by  an  interval  for  the  sake  of  clearness)  ; 
D,  visual  tract  ;  E,  auditory  tract  :  F,  G,  H,  superior,  middle,  and  inferior  cere- 
bellar peduncles  ;  J,  fibres  from  the  auditory  nucleus  to  the  posterior  corpus 
quadrigeminum  ;  K,  decussation  of  the  pyramids  in  the  bulb  ;  FV,  fourth 
ventricle.     The  Roman  numerals  indicate  the  cranial  nerves. 


for  the  spinal  pyramidal  path  (p.  775).  On  their  way  through 
the  pons  they  send  off  collaterals  to  the  nuclei  pontis,  as  they  do 
higher  up  to  the  grey  matter  of  the  basal  ganglia  of  the  cerebrum 
and  the  substantia  nigra,  and  the  path  may  be  continued  to  the 
motor  nuclei  by  axons  arising  here.  There  is  no  proof,  however, 
that  this  is  the  case.  The  rest  of  the  pyramidal  fibres  run  on  into 
the  pyramid  of  the  bulb,  where  the  greater  part  (usually  about 
90  per  cent.)  of  the  fibres  decussate,  appearing  in  the  cervical 


7  7* 


A    MANUAL  OF  PHYSIOLOG  Y 


cord   as  the  massive  crossed  pyramidal   tract    ol    the  opposite 

side.  A  few  (usually  about  to  per  cent.)  remain  on  the  same 
side  as  the  slender  direct  pyramidal  tract.  The  size  of  this  tract 
varies  much  in  different  individuals,  and  it  is  occasionally  absent. 
Its  breadth  constantly  diminishes  as  it  proceeds  down  the  cord, 
and  it  disappears  before  the  middle  of  the  thoracic  region  is 
reached,  its  fibres  continually  decussating  across  the  anterior 
white  commissure  and  plunging  into  the  opposite  anterior  horn. 

They  either  end  among  its 
cells,  or,  passing  through 
it,  reinforce  the  crossed 
pyramidal  tract.  The 
fibres  of  this  crossed  tract 
are,  in  their  turn,  con- 
tinually passing  off  into 
the  grey  matter  to  make 
connection  (p.  775)  with 
the  cells  of  the  anterior 
horn,  whose  axis-cylinder 
processes  enter  the  an- 
terior roots  of  the  spinal 
nerves.  The  losses  which 
it  suffers  as  it  descends 
the  cord  may  be  in  some 
slight  degree  compensated 
by  the  bifurcation  of  some 
of  its  fibres  (geminal 
fibres),  but  ultimately  the 
whole  tract  forms  synapses 
with  cells  in  the  grey 
matter,  and  dwindles  away 
as  the  lumbar  region  is 
reached  (Fig.  314).  It  has 
been  asserted  that  on  their 
way  down  tin-  cord  the  two 
crossed  pyramidal  tracts  exchange  some  fibres  with  each  other 
(recrossed  fibres)  ;  and  it  was  supposed  that  this  would  explain 
the  escape  in  hemiplegia  (paralysis  0!  one  side  of  the  body)  of 
those  muscles  which  are  accustomed  to  work  with  the  corre- 
sponding muscles  on  the  opposite  side  e.g.,  the  respiratory 
muscles.  Bui  although  there  is  no  doubt  that  such  muscles 
are  innervated  to  some  extent  from  both  cerebral  hemispheres, 
this  is  due  not  to  recrossed,  but  to  uncrossed  (homolateral),  fibres, 
which  in  the  cord  run  down  in  the  lateral  pyramidal  tract,  and 
are  represented  by  the  fibres  that  degenerate  in  that  tract  after 
a  lesion  in  the  '  motor  '  area  of  the  same  side  (p.  774). 


Fig.  327. — Motor  Pyramidal  Tracts   (Dia- 
grammatic) (Halliburton,  after  Gou -i  rs). 

The  convolutions  are  supposed  to  be  cut 
in  vertical  transverse  section,  the  internal 
capsule,  I,  C,  and  the  cms  in  horizontal 
section.  O,  TH,  optic  thalamus  ;  CN,  cau- 
date  nucleus  ;  L2  and  L3,  middle  and  ex- 
ternal portions  of  lenticular  nucleus  ;  /,  a,  I, 
fibres  from  tin-  laic  arm,  and  leg  areas  of  the 
cortex  respectively  ;  E,  S,  Sylvian  fissure.  The 
genu  or  knee  of  the  internal  capsule  is  indi- 
cated by  the  asterisk. 


////    <  EN  TRAL   NERVOUS  SYSTEM 


77'> 


rJ 


(_>)  A  great  afferent  or  sensory  path  by  which  some  ;it  Lea  i 
of  flic  impulses  carried  up  through  the  posterior  roots  <>i  the 
spinal  nerves,  after  passing  through  various  relays  of  nerve-cells, 
reach  the  cortex  of  the  cerebellum  ;  or  the  upper  portions  of 
the  central  grey  tube,  the  corpora  quadrigemina  and  optic 
thalamus  ;  or,  finally  (through  the  tegmentum  and  the  posterior 
limb  of  the  internal 
capsule  behind  the 
motor  fibres),  the  cere- 
bral cortex  itself. 

The  efferent  pyra- 
midal path  from  the 
cortex  to  the  periphery 
is  broken  by  at  most 
two  relays  of  nerve- 
cells  ■ — those  inter- 
calated cells  to  which 
reference  has  already 
been  made  (p.  775),  if 
they  really  exist,  and 
the  motor  cells  of  the 
anterior  horn.  The 
afferent  path  to  the 
cerebral  cortex  is  in- 
terrupted by  at  least 
three  relays  with 
axons  of  considerable 
length.  One  of  the 
cells  is  situated  in  the 
ganglion  on  the  pos- 
terior root,  another 
in  the  medulla  oblon- 
gata,  a   third   in    the 


Fix.  328. — Paths  of  Middle  Cerebellar 
Peduncle  (Mingazzini). 

The  scheme  indicates  the  afferent  and  efferent 
paths  which  run  through  the  middle  cerebellar 
peduncle,  connecting  the  cerebellum  with  the 
opposite  side  of  the  cerebrum,  a,  fibre  coming 
from  a  cell  in  the  nuclei  pontis  and  going  to  the 
cerebellar  cortex  ;  b,  fibre  from  a  cell  in  the 
cortex  of  the  opposite  cerebral  hemisphere 
making  connection  in  the  pons  with  a  (a  and  b 
together  constitute  an  afferent  path  to  the  cere- 
bellum) ;  c,  a  fibre  springing  from  a  Purkinjc's 
cell  in  the  cerebellar  cortex  and  making  connec- 
tion in  the  pons  with  a  cell  d,  which  sends  its 
axon  to  the  cerebral  cortex  of  the  opposite  side. 
c  and  d  constitute  an  efferent  path  from  the  cere- 
bellum to  the  opposite  cerebral  hemisphere  ; 
e,  f,  represent  a  path  coming  from  the  cerebellar 
cortex,  which  crosses  the  middle  line  in  the  pons, 
and  then  ascends  till  it  loses  itself  in  the  formatio 
reticularis. 


optic    thalamus  ;    and 

on  some  of  the  routes  another,  or  even  more  than  one,  is  inter- 
calated between  the  medulla  and  the  cortex. 

Connections  of  the  Grey  Matter  of  the  Cerebellum  with  the 
Periphery  and  other  Parts  of  the  Central  Nervous  System.— 
Numerous  as  are  the  nervous  ties  of  the  cerebral  cortex,  those  of  the 
grey  matter  of  the  cerebellum  are,  in  proportion  to  its  mass,  still 
more  extensive,  particularly  as  regards  afferent  fibres,  and  perhaps 
not  less  important. 

Speaking  broadly,  we  may  say  that  the  restiform  body  or  inferior 
peduncle  connects  chiefly  the  dentate  nucleus  and  the  grey  matter 
of  the  worm  with  the  spinal  cord  and  medulla  oblongata,  and 
through  them  with  the  periphery.  The  fibres  which  it  receives  from 
the  direct  cerebellar  tract  (dorsal  spino-cerebellar  tract)  of  its  own 
side  it  carries  to  the  worm.      These  fibres  occupy  the  outer  portion 


780 


A   MANUAL  OF  I'll  YSloLOGY 


of  the  peduncle.  The  fibres  which  reach  the  rcstiform  body  from  the 
olivary  nucleus  of  the  opposite,  and  also  in  smaller  numbers  From 
that  of  the  same  side,  run  mainly  to  the  hemisphere.  AN  these 
fibres  are  afferent  in  relation  to  the  cerebellum  (cerebello-petal).  An 
uncrossed  afferent  connection  also  exists  between  the  cerebellum 
and  the  vestibular  branch  of  the  auditory  nerve,  through  certain  of 
its  nuclei  of  reception,  and  also  between  it  and  the  nuclei  of  other 
cranial  nerves,  such  as  the  trigeminus  and  the  vagus.  The  fibres 
pass  up  in  the  inner  portion  of  the  inferior  peduncle  (direct  sensory 
cerebellar  path  of  Edinger,  Fig.  329)  to  the  nucleus  of  the  roof 
(nucleus  tecti)  and  nucleus  globosus.  Some  efferent  fibres  (cerebcllo- 
fugal)  also  run  down  from  the  cerebellum  in  the  inferior  peduncle, 
including  fibres  from  the  nucleus  tecti  of  the  opposite  side  which  are 
on  their  way  to  the  medulla  oblongata. 

The  middle  peduncle  is  in  the  main  a  link  between  the  cerebellar 


^  SSfA 


J~  -    /Xje*. 


Fig.  329. — Direct  Sensory  Cere- 
bellar Path  of  Edinger. 

D,  Deiters'  nucleus ;  v,  median 
nucleus  of  auditory  nerve  ;  /,  nucleus 
of  the  roof ;  g,  nucleus  globosus. 


#•<?.  <r 


Fig.  330. — Diagram  of  Dorsal  and  Ventral 
Spino-cerebellar  Tracts  entering  Cere- 
bellum  (Mott). 

P.C.Q.,  posterior  corpora  quadrigemiua  ; 
s.v.,  superior  vermis  (worm)  of  cerebellum; 
d.a.c,  v.a.c,  dorsal  and  ventral  ascending  cere- 
bellar tracts. 


cortex  and  the  cerebral  cortex  of  the  opposite  side,  through  the 
relay  of  the  pontine  grey  matter.  Most  of  the  fibres  in  it  are  afferent 
in  relation  to  the  cerebellum,  their  cells  of  origin  being  situated  in 
t  he  nuclei  of  the  pons,  and  sending  their  axons  across  the  middle  line 
to  end  in  the  cerebellar  cortex. 

The  superior  peduncle  connects  chiefly  the  dentate  nucleus  of  one 
side  with  the  cortex  of  the  opposite  cerebral  hemisphere  through 
the  red  nucleus  of  the  tegmentum  of  the  cms  cerebri  and  the 
optic  thalamus  on  the  opposite  side.  The  great  majority,  or  perhaps 
all,  of  its  fibres  are  efferent  fibres  as  regards  the  cerebellum — i.e., 
their  cells  of  origin  lie  in  the  dentate  nucleus.  Running  upwards 
and  forwards  in  the  superior  peduncle  towards  the  mid-brain  they 


Till    CENTRAL  NERVOUS  SYSTEM 


781 


cross  the  middle  line  below  the  corpora  quadrigemina,  and  then 
bifurcate  into  ascending  and  descending  branches.  The  ascending 
branches  end  mainly  in  connection  with  cells  in  the  red  nucleus. 
but  some  of  them  pass  on  to  the  optic  thalamus,  with  which  cells  of 
the  red  nucleus  are  also  connected.  The  thalamus,  as  we  have  seen, 
is  in  its  turn  extensively  connected  with  the  cerebral  cortex,  and  the 
red  nucleus  (by  the  efferent  trad  of  Monakow)  with  the  grey  matter 
of  the  cord.  The  descending  branches  of  the  fibres  of  the  superior 
peduncle,  entering  the  reticular  formation  of  the  pons,  pass  down. 
it  is  said,  to  make  connection  with  the  motor  nuclei  of  the  cranial 
and  spinal  nerves.  The  tract  of  Gowers,  as  previously  stated, 
comes  into  relation  with  the  superior  peduncle,  passing  backwards 
along    its   mesial   border   to   the   worm.     Since   the   cortex   of  the 


Fig.  331. 


-Diagrammatic  Horizontal  Section  of  Left  Half  of  Brain  to 
show  Internal  Capsule. 


cerebellum  is  linked  to  the  dentate  nucleus,  the  superior  peduncle 
affords  an  indirect  connection  between  it  and  the  cerebral  cortex. 
Through  the  restiform  body  afferent  impulses  pass  up  to  the  cere- 
bellum. From  the  cerebellum  they  may  proceed  to  the  cerebrum. 
So  that  the  path  by  the  restiform  body,  dentate  nucleus,  and 
superior  peduncle  may  form  an  alternative  route  for  afferent 
impressions  ascending  from  the  periphery  to  the  great  brain — a  path 
broken  by  at  least  four  relays  of  nerve-cells.  The  cerebellar  hemi- 
sphere may  be  connected  by  an  efferent  path  through  the  nucleus  of 
Deiters  and  the  descending  antero-lateral  tract  with  the  motor  roots 
of  the  same  side.  Another  efferent  path  (from  the  dentate  nucleus) 
may  be  constituted  by  the  fibres  of  the  superior  peduncle  and 
Monakow's  bundle. 


7S; 


A   MANUAL  OF  PHYSIOLOGY 


The  Internal  Capsule.-  We  have  already  recognised  the 
pyramidal  trad  and  the  afferent  tegmental  path  as  constituents 
of  the  internal  capsule.  The  cranial  fibres  of  the  pyramidal  tract 
occupy  mainly  the  genu  or  knee,  the  spinal  fibres  the  posterior 
limb  as  far  back  as  the  posterior  border  of  the  lenticular  nucleus. 
r  The  fibres  from  the  various  motor  areas  are  to  a  certain  extent 

arranged  in  order  in  the  cap- 
sule, those  for  the  eyes  and 
head  lying  farthesl  forward, 
those  for  the  leg  farthest  back, 
while  the  fibres  going  to  the 
face,  arm  and  trunk  occupy 
intermediate  positions  (Fig. 
331).  The  separation,  how- 
ever, is  far  from  complete,  the 
fibres  of  neighbouring  regions 
being  considerably  intermixed 
(Hoche).  As  the  tracts  pass 
downwards    the     intermingling 


Fig.  332. — Pyramidal  Tract  in- 
Internal  Capsule  (Simpson 
AND  Jolly). 

Horizontal  section  through  right 
cerebral  hemisphere,  cutting  fibres 
ot  internal  capsule  transversely  at 
an  upper  level  a  little  below  the 
upper  surface  of  the  lenticular 
nucleus.  The  extent  of  the  de- 
generation  following  destruction  oJ 
the  whole  of  the  right  'motor' 
cortex,  except  the  'head  and  eyes' 
ana  (in  one  i>f  the  lower  monkeys), 
i^  shown.  Note  overlapping  of 
fibres  from  face,  arm,  and  leg  areas, 
as  shown  by  experiments  in  which 
one  or  other  of  these  areas  was  alone 
removed. 


Fig.  333. — -Pyramidal  Tract  in  Inter- 
nal Capsule  at  Lower  Level  (Simp- 
son and  Jolly). 

CN,  head  of    caudate    nucleus  ;    O.T, 
optic  thalamus  ;  CI,  ilaustruiu. 


becomes  continually  greater  (Simpson  and  Jolly)  (Figs.  332,  333). 
The  afferent  fibres  from  the  thalamus  to  the  cortex,  which  we 
have  described  as  the  last  segment  of  the  afferent  tegmental 
path,  lie  in  the  posterior  part  of  the  posterior  limb.  But  here 
again  there  is  no  absolutely  sharp  line  of  demarcation.  Some 
motor  fibres  are  intermingled  with  the  sensory  in  the  posterior 


I  111    CI  NTR  U    XI  RVOUS  SYS1  I  M 


783 


pari  <>t  the  capsule,  for  lesions  oi  this  region  produce  a  certain 
degree  of  paralysis  a>  well  as  anaesthesia  on  the  opposite  side 
of  the  body.  A.  pure  capsular  hemianesthesia  that  is,  a  Loss  oi 
sensation  on  the  opposite  side  due  to  a  lesion  in  the  internal 
capsule  ami  unaccompanied  by  motor  delect  does  nol  appear 
to  exist.  Accordingly  the  common  statemenl  that  the  efferent 
(motor)  path  occupies  the  anterior  two-thirds,  and  the  afferent 
(sensory)  path  the  posterior  third  of  the  posterior  limb  of  tin- 
internal  capsule,  while  no  doubl  true  in  a  general  sense,  is  nol 
strictly  correct. 

The  destination  of  the  afferent  fibres  of  the  internal  capsule 
has  not  been  definitely  settled.     There  is  no  doubt  that  t  hey  pass 


Fig.  334. — Association  Fibres  (after  Starr). 

Cerebral  hemisphere  seen  from  the  side.  A,  A,  association  fibres  between 
adjacent  convolutions  ;  B,  between  frontal  and  occipital  lobes  ;  C,  cingulum, 
connecting  frontal  and  temporo-sphenoidal  lobes  ;  D,  uncinate  fasciculus  between 
frontal  and  temporal  regions  ;  E,  inferior  longitudinal  bundle  between  occipital 
and  temporo-sphenoidal  lobes  ;  O.T.,  optic  thalamus  ;  C.N.,  caudate  nucleus. 

up  to  the  convolutions  around  the  fissure  of  Rolando  (central 
convolutions),  and  there  is  reason  to  believe  that  some  of  them 
terminate  in  the  '  motor  '  region  in  front  of  that  fissure. 

But  we  have  not  yet  exhausted  the  constituents  of  the  internal 
capsule.  Two  great  cones  of  fibres  sweep  down  into  it,  one 
from  the  frontal,  the  other  from  the  occipital  and  temporal 
portions  of  the  cerebral  cortex.  The  first  passes  through  its 
anterior  limb,  the  second  behind  the  sensory  path  in  its  posterior 
limb.  The  cells  of  origin  of  the  frontal  fibres  are  known,  and 
those  of  the  occipital  and  temporal  fibres  are  supposed,  to  be 
situated  in  the  cortex.  They  are  therefore  efferent  fibres  as 
regards  the  cortex  (cortifugal).  Running  on  through  the  crusta 
of  the  cerebral  peduncle  (Fig.  324),  the  frontal  tract  internal,  the 


784 


A   MANV  II.  OF   PHYSIOLOGY 


ipito-tempora]  external,  they  end  in  the  grey  matter  of  the 
pons,  and  serve  as  one  segment  of  an  extensive  commissural 
connection  between  the  cerebral  and  the  cerebellai  cortex  oi 
the  opposite  side,  the  other  segmenl  being  formed  by  neurons 
whose  cell-bodies  are  situated   in  the  pons,  and  whose  axons, 

crossing  the  middle  line, 
pursue  t  heir  con  rse 
through  the  middle  cere- 
bellar peduncle,  to  termi- 
nate in  the  superficial  grey 
matter  of  the  cerebellum. 
It  is  evident  that  the  junc- 
tion of  the  cerebral  cortex 
with  this  pontine  grey 
matter,  through  and  into 
which  so  many  nerve- 
tracts  pass,  multiplies  the 
number  of  possible  routes 
by  which  impulses  may 
travel  between  one  pari 
of  the  brain  and  another. 
The  corpus  callosum  forms 
a  mighty  link  between  the 
two  cerebral  hemispheres. 
And  intertwined  in  the 
corona  radiata  with  the 
callosal  fibres  are  other 
systems,  of  which  it  is  es- 
pecially necessary  to  men- 
tion the  afferent  {corti- 
petal)  fibres  that  join  the 
optic  thalamus  with  nearly 
every  part  of  the  cerebral 
cortex.  Such  fibres  pass 
from  the  cells  of  the  grey 
matter  of  the  thalamus  to 
the  frontal  and  parietal 
regions  through  the  an- 
terior border  of  the  in- 
ternal capsule  in  front  of 
the     frontal     fibres     pre- 


!'"■•     335- — Fibres     connecting     Frontal 

and       Tfmporo  -  occipital    Lobes    with 
Cerebellum,      etc.     (Diagram)      (after 

GOWERS). 

Fr,  frontal  ;  Oc,  occipital  lobe  ;  the  in- 
terrupted lines  indicate  the  fibres  (TOC)  con- 
the  cerebellum  and  the  temporo- 
occipital  cortex,  and  the  fronto-cerebellar 
abres  (FC).  On  the  left  side  the  position 
"t  these  two  groups  of  fibres  and  of  the  motor 
(pyramidal)  trait,  PY,  in  the  crus,  is  indi- 
cated by  letters.  The  pyramidal  tract  is 
seen  on  tin-  ri«ht  passing  down  from  the 
Rolandic  area  through  the  posterior  limb  of 
tin-  intrni.il  capsule  IC  (the  genu  or  knee  of 
which  is  indicated  by  the  asterisk)  to  de- 
cussate in  the  bulb.  AF,  ascending  frontal 
convolution;  AP,  ascending  parietal  con- 
volution; FR,  fissure  of  Rolando;  IFF.  in- 
traparietal  fissure  ;  PCF,  precentral  fissure  ; 
Ipt,  crossed  pyramidal  tract  ;  apt,  direct 
pvramidal  tract. 


viously  described  as  run- 
ning in  the  anterior  limb  of  the  capsule  to  the  pons  ;  and  from 
the  thalamus  to  the  occipital  region  through  the  extreme  pos- 
terior border  of  the  internal  capsule,  behind  the  occipital  fibres 
that  proceed  to  the  pons.     The  fibres  that  connect  the  thalamus 


////    CI  \  I  R  II    V/  RVOUS  SYS1  I   1/  785 

with  the  oceiiui.il  cortex  are  spoken  oJ  as  the  opti<  radiation. 
Some  "I  the  fibres  oi  the  optic  radiation,  however,  proceed,  not 
from  the  thalamus,  bul  from  the  anterior  corpus  quadrigeminum 
and  the  lateral  geniculate  body.  The  thalamus  is  also  connected 
with  the  cortex  of  the  temporal  lobe,  with  the  cerebellum,  and 
through  the  fillet  with  the  posterior  part  of  the  tegmental 
system,  the  medulla  oblongata  and  the  spinal  cord  (p.  772). 
Fibres  also  pass  from  the  inner  and  deeper  part  of  the  thalamus 
to  the  lenticular  nucleus  of  the  corpus  striatum.  The  thalamus 
must  be  regarded  as  a  great  sensory  centre  through  which 
afferent  impulses  stream  on  their  way  to  all  parts  of  the 
cortex. 

We  have  purposely  omitted  to  enumerate  other  paths  by 
which  the  various  tracts  of  grey  matter  in  the  brain  are  brought 
into  communication  with  each  other,  and  our  knowledge  of 
such  connections  is  constantly  augmenting.  When  we  add 
that  not  only  are  the  cerebral  hemispheres  united  by  many 
ties  to  the  subordinate  portions  of  the  cerebro-spinal  axis  and 
to  each  other,  but  that  cortical  areas  of  one  and  the  same  hemi- 
sphere are  in  communication  by  short  connecting  loops  of 
'  association'  fibres  (Fig.  334),  it  will  be  seen  that  the  linkage 
of  the  various  parts  of  the  central  nervous  system  is  extremely 
complex  ;  that  an  excitation,  blocked  out  from  one  path,  may 
have  the  choice  of  many  alternative  routes  ;  and  that  the  ap- 
parent simplicity  and  isolation  of  the  pyramidal  tracts  must  not 
be  allowed  too  far  to  govern  our  views  of  the  possibilities  open  to 
a  nervous  impulse  once  it  has  been  set  going  in  the  labyrinth 
of  the  nervous  network.  Nor  is  it  only  by  the  main  channel 
of  the  axis-cylinder  that  nervous  impulses  can  be  conducted. 
It  cannot  be  doubted  that  they  can  also  pass  along  the  col- 
laterals. And  the  actual  route  taken  by  a  given  impulse  is, 
in  all  probability,  determined  not  only  by  anatomical  relations, 
but  also  by  molecular  conditions,  particularly  in  the  terminal 
fibrils  of  the  axons,  collaterals  and  dendrites,  and  in  the  sub- 
stance, if  such  a  substance  there  be.  which  intervenes  between 
the  end  arborizations  of  a  neuron  and  the  dendrites  or  cell- 
bodies  of  the  neurons  with  which  they  lie  in  contact.  So  that 
a  road  open  at  one  moment  may  be  closed  at  another.  We  may 
suppose  that  the  greater  the  number  of  connections  between 
the  cells  of  the  central  nervous  system,  the  greater  is  the  com- 
plexity of  the  processes  which  may  be  carried  on  within  it. 
And,  indeed,  comparison  of  the  brains  of  different  animals  shows 
that  it  is  not  so  much  by  excess  in  the  number  of  nerve-cells 
as  by  the  increased  complexity  of  linkage,  that  a  highly-de- 
veloped brain  differs  from  a  brain  of  lower  type  ;  the  higher  the 
brain,    the   more   richly   branched    are    the    dendrites   and    the 

50 


A   MANUAL  OF  PHYSIOLOGY 

terminations  of  the  axons  and  their  collaterals,  and,  therefore, 
the  greater  is  the  number  oi  possible  paths  between  one  nerve- 
cell  and  another. 

II.   Functions  of  the  Central  Nervous  System. 

.Much  of  our  knowledge  of  the  functions  of  the  central  nervous 
system  and  of  its  divisions  has  been  gained  by  the  removal  or 
destruction  of  more  or  less  extensive  tracts  of  nervous  substance, 
or  the  cutting  off  of  connection  between  one  part  and  another. 
But  it  is  well  to  warn  the  reader  at  the  very  outset  that  in  no 
other  part  of  physiology  is  such  caution  required  in  making 
deductions  as  to  the  working  of  the  intact  mechani>m  from  the 
phenomena  which  manifest  themselves  after  such  lesions. 

In  the  first  place,  every  operation  of  any  magnitude  on  the  brain 
or  cord  is  immediately  followed  by  a  depression  of  the  functional 
power  of  the  nervous  tissue  distal  to  the  lesion,  a  depression  which 
may  extend  far  from  the  actual  seat  of  injury  and  manifest  itself 
by  various  phenomena,  which  are  grouped  together  under  the  name 
of  '  shock,'  better  termed  spinal  or  cerebro-spinal  shock,  to  dis- 
tinguish it  from  the  cardiovascular  or  surgical  shock  already  de- 
scribed (p.  175).  Thus,  when  the  spinal  cord  of  a  dog  is  divided. 
e.g.,  in  the  dorsal  region,  all  power,  all  vitality,  one  might  almost 
say,  seems  to  be  for  ever  gone  from  the  portion  of  the  body  below 
the  level  of  the  section.  The  legs  hang  limp  and  useless.  Pinching 
or  tickling  them  calls  forth  no  reflex  movements.  The  vaso-motor 
tone  is  destroyed,  and  the  vessels  gorged  with  blood.  The  urine 
accumulates,  overfills  the  paralyzed  bladder,  and  continually 
dribbles  away  from  it.  The  sphincter  of  the  anus  has  lost  its  tone, 
and  the  faeces  escape  involuntarily.  And  if  we  were  to  continue  our 
observations  only  for  a  short  time,  a  few  hours  or  days,  we  should 
be  apt  to  appraise  at  a  very  low  value  the  functions  of  that  part  of 
the  cord  which  still  remains  in  connection  with  the  paralyzed 
extremities.  But  these  symptoms  are  essentially  temporary.  They 
are  the  immediate  results  of  the  section  ;  they  are  not  permanent 
'  deficiency  '  phenomena.  And  if  we  wait  for  a  time,  we  shall  find 
that  this  torpor  of  the  lower  dorsal  and  lumbar  cord  is  far  from 
giving  a  true  picture  of  its  potentialities  ;  that,  cut  ofi  as  it  is  from 
the  influence  of  the  brain,  it  is  still  endowed  with  marvellous  pow 
If  we  wait  long  enough,  we  shall  see  that,  although  voluntary 
motion  never  returns,  reflex  movements  of  the  hind-limbs,  complex 
and  co-ordinated  to  a  high  degree,  arc  readily  induced.  Vaso-motor 
tone  comes  back.  The  functions  of  defalcation  and  micturition  are 
normally  performed.  Erection  of  the  penis  and  ejaculation  of  the 
semen  take  place  in  a  dog.  A  man  with  complete  paralysis  below  the 
loins  and  destitute  of  all  sensation  in  the  paralyzed  region  has  been 
known  to  become  a  father  (Bracket  | .  1  *regnancy  carried  on  to  labour 
at  full  term  has  been  observed  in  a  bitch  whose  cord  was  completely 
divided  above  the  lumbar  enlargement.  The  severity  and  duration 
of  spinal  shock  are  greater  in  the  monkey  than  in  the  dog.  in  man 
than  in  the  monkey,  and  in  the  whole  mammalian  group  than  in  the 
lower  vertebrates.  The  mechanism  of  its  production  has  been 
much  discussed,  and  will  be  referred  to  on  another  page  (p.  808). 


////    CI  NTRAL   Nl  RVOUS  SYSTEM  7H7 

We  c  annot  doubt  that  the  spinal  curd  takes  an  important  sh 
the  recovery  of  function  after  shock.  But  here  again  it  would  be 
erroneous  to  conclude  that  everything  is  due  to  the  cord.  For  Goltz 
and  Kwald  haw  been  able  to  keep  dogs  alive  for  long  periods  after 
preliminary  section  of  the  cord  in  the  cervical  region  and  subsequent 
removal  of  large  portions  of  it.  They  find  that  even  after  destruction 
of  the  lumbar  and  sacral  regions  of  the  cord  the  external  sphincter  of 
the  anus,  striped  and  even  voluntary  muscle  though  it  be,  regains  its 
tone,  although  it  is  temporarily  lost  after  the  first  cervical  section. 
The  bladder  ultimately  recovers  the  power  of  emptying  itself  spon- 
taneously and  at  regular  intervals.  A  pregnant  bitch  in  which  the 
lumbar  enlargement  and  the  whole  cord  below  it  to  the  cauda  equina 
had  been  removed,  and  therefore  all  the  nerve-roots  supplying 
fibres  to  the  uterus  cut,  whelped  in  a  normal  manner,  and  the 
corresponding  mammary  glands  behaved  exactly  as  the  rest.  Diges- 
tion went  on  as  usual  when  practically  nothing  of  the  cord  except 
its  cervical  portion  was  left.  Certain  vaso-motor  phenomena  were 
also  observed  which  suggest  that  the  sympathetic  system,  inde- 
pendently of  the  cerebro-spinal  system,  is  itself  possessed  of  regula- 
tive powers  (p.  168). 

Secondly,  we  must  not  run  into  the  opposite  error,  and  assume, 
without  proof,  that  all  the  functions  which  the  brain  or  cord  is 
capable  of  manifesting  under  abnormal  circumstances  are  actually 
exercised  by  either  when,  under  ordinary  conditions,  it  is  working 
along  with  and  guiding,  or  being  guided  by,  the  other.  For  example, 
in  many  animals  certain  of  the  reflex  powers  of  the  cord  are,  if  not 
increased,  at  all  events  more  freely  exercised  when  the  controlling 
influence  of  the  higher  centres  has  been  cut  off  than  when  the  central 
nervous  system  is  intact. 

Thirdly,  there  is  another  class  of  phenomena  which  we  must  make 
allowance  for,  and  perhaps  more  frequently  in  the  case  of  patho- 
logical lesions  in  man  than  in  experimental  lesions  in  the  lower 
animals.  This  is  the  class  of  '  irritative  '  phenomena.  The  irrita- 
tion set  up  by  a  blood-clot  or  a  collection  of  pus,  or  in  any  other  way, 
in  a  wound  of  the  grey  or  white  matter,  may  cause  a  stimulation  of 
nervous  tracts  by  which,  for  a  time,  the  '  deficiency  '  effects  of  the 
lesion  may  be  masked. 

In  the  fourth  place,  we  must  not  hastily  conclude  that  when  no 
obvious  deficiency  seems  to  follow  the  removal  of  a  portion  of 
the  central  nervous  system,  the  function  of  that  portion  must 
necessarily  be  of  such  a  nature  as  to  give  rise  to  no  objective 
signs.  For  there  is  reason  to  believe  that,  to  a  certain  extent, 
the  function  of  one  part  may,  in  its  absence,  be  vicariously  per- 
formed by  another. 

Bearing  in  mind  the  cautions  we  have  just  been  emphasizing, 
we  may  broadly  distinguish  between  the  functions  of  the  cord 
(including  the  bulb)  and  those  of  the  brain  proper  by  saying 
that  the  cord  is  essentially  the  seat  of  reflex  actions,  the  brain 
the  seat  of  automatic  actions  and  conscious  processes.  But 
neither  of  these  conceptions  is  entirely  correct.  Both  err  by 
defect  and  by  excess.  The  brain,  it  is  true,  is  pre-eminently 
automatic.  The  movements  which  are  started  in  the  grey 
matter    of    the    cerebral    cortex    are    pre-eminently    voluntary 

50—2 


788  A   MANUAL  OF    I'HYslOLOGY 

(p.  840),  but  we  cannot  deny  to  the  brain  the  possession  of 
reflex  powers  as  well.  The  movements  in  which  the  only  nerve 
centres  concerned  are  those  of  the  spinal  cord  are  above  all  reflex 
(P-  79°) •  But  some  of  its  centres,  and  especially  those  lying  in 
the  medulla  oblongata — e.g.,  the  respiratory  centre — are,  much  as 
they  are  influenced  by  afferent  impulses,  capable  of  discharging 
automatic  impulses  too.  And  while  consciousness  is  certainly 
bound  up  with  integrity  of  the  brain,  and  in  all  the  higher 
mammals  is  probably  associated  with  cerebral  activity  alone, 
it  has  been  plausibly  maintained  that  the  spinal  cord,  even  of 
such  an  animal  as  the  frog,  is  also  endowed  with  something 
which  might  be  called  a  kind  of  hushed  consciousness.  If  this 
is  so  for  the  frog,  with  its  distinct  though  relatively  ill-developed 
cerebral  hemispheres,  it  must  be  still  more  likely  in  the  case  of 
fishes  and  animals  below  them,  which  are  practically  devoid  of 
a  cerebral  cortex  altogether. 

Functions  of  Spinal  Cord  (including  Medulla  Oblongata). 

The  functions  of  the  spinal  cord  may  be  classified  thus  : 

1.  The  conduction  of  impulses  set  up  elsewhere — either  in 

the  brain  or  at  the  periphery. 

2.  The   modification    of    impulses    set    up    elsewhere    (reflex 

action). 

3.  The  origination  of  impulses  (?). 

1.  Conduction  of  Nervous  Impulses  by  the  Cord. — The  old 
controversy  as  to  whether  the  white  fibres  of  the  spinal  cord 
are  directly  excitable  may  be  considered  as  definitely  settled  in 
the  affirmative.  The  inquiry  was  complicated  by  the  presence 
of  the  spinal  roots,  which,  since  the  experiments  of  Charles  Bell, 
have  been  known  to  be  capable  of  excitation  by  artificial  stimuli. 
But  at  length  the  difficulty  was  overcome  in  this  way.  The 
posterior  (dorsal)  portion  of  several  segments  of  the  cord  with 
the  attached  posterior  roots  and  the  grey  matter  was  excised. 
Long  strands  of  the  white  matter  of  the  anterior  (ventral) 
portion  of  the  cord  were  isolated,  and  laid  on  electrodes,  and 
contractions  of  muscles  were  seen  to  follow  stimulation,  even 
when  the  anterior  roots  nearest  the  stimulating  electrodes  had 
been  cut,  and  every  precaution  taken  to  avoid  escape  of  current 
on  to  the  distant  anterior  roots  of  the  nerves  supplying  the 
muscles.  Indeed,  apart  from  direct  experimental  evidence, 
the  fact  that  the  white  fibres  of  the  brain  are  universally  admitted 
to  be  excitable  by  artificial  means  would  be  of  itself  almost 
sufficient  to  decide  the  question,  for  we  know  of  no  essential 
difference  between  the  cerebral  and  the  spinal  fibres.  But  the 
conditions  must  rarely  occur  under  which  direct  stimulation 


THE  CENTRAL   NERVOUS  SYST1  V 


7«o 


of  white  fibres  in  their  course  is  possible  in  the  intact  body  ; 
and  the  only  impulses  with  which  we  need  concern  ourselves 


Cere bral 
Co rte x 


Fihre  for- 
Head 


Po\ns 


De  cussa  tton 

of  Pyramids. 

Fibre  of  Direct 

Pur  am  i  dal  traot. 

Nerise-Ce7lsr .T*d 

of  Ant. Horn  ._J^ — 
Terminal  Arborisation  LVj-.- 

of  a  Pyramidal  Fibre  \ . 

around  Cell  of    — ■*"' 
Ant.  Horn 


SI 


I  Medulla 
Oblongata 

yRtcrcsse  dFib  rt 

/..Uncrossed  Fibre. 

Spinal 
^  Co  rd 


Anterior 

Root 

Fibres- 


1    A         > 

Efferent  Paths. 


pIG    336. — Some  Possible  Paths  of  Efferent  Impulses  in  the  Central 

Nervous  System  (Schematic). 
Details  are  omitted  from  the  scheme.     For  instance,  each  pyramidal  fibre  is 
represented  as  arborizing  around  one  anterior  cornual  cell  only,  and  no  collaterals 
are  shown.     The  hypothetical  intercalated  neurons  between  the  pyramidal  fibres 
and  the  anterior  horn  cells  (p.  776)  are  not  shown. 

here  are  those  that  reach  the  conducting  paths  from  grey  matter 
in  the  cord  itself  or  in  the  brain,  or  from  the  peripheral  organs. 


790  I    i/i  xr  //.  OF  PHYSIOLOGY 

What  sort  of  impulses  do  the  various  tracts  of  the  spinal 
cord  conduct  ?  For  the  dorsal  or  posterior  roots  this  question 
was  first  fully  answered  by  Magendie  ;  for  the  ventral  or 
anterior  roots,  although  with  a  certain  degree  of  ambiguity, 
by  Sir  Charles  Bell.  Bell  observed  that  when,  in  an  animal 
just  killed,  he  mechanically  stimulated  the  anterior  roots, 
muscular  contractions  were  obtained  at  each  touch  of  the 
forceps.  He  concluded  that  the  anterior  roots  are  motor  and 
sensory,  while  the  posterior  roots  are  '  vegetative  ' — i.e.,  con- 
nected with  the  functions  of  the  viscera,  the  so-called  '  vegeta- 
tive' organs.  But  although  he  is  often  credited  with  the 
discovery  of  the  functions  of  the  posterior  roots  as  well,  he 
was  not  the  first  to  make  the  decisive  experiment  necessary 
to  show  that  they  are  the  conductors  of  sensor}'  impulses.  It 
was  after  Magendie's  discovery  that  only  a  portion  of  the  nerves 
are  sensitive,  and  that  there  are  nerves  '  which  are  like  tendons, 
aponeuroses,  or  cartilages  in  insensibility '  that  Bell  formu- 
lated the  law  that  the  anterior  roots  are  purely  motor,  the 
posterior  purely  sensory.  This  law,  often  termed  Bell's  Law, 
is  more  correctly  denominated  the  Bell-Magendie  Law . 

When  the  posterior  roots  are  divided,  loss  of  sensation  occurs 
in  the  region  to  which  they  are  distributed.  If  only  one  root 
is  cut,  the  loss  of  sensation  is  never  complete  in  any  part  of  the 
skin  ;  and  Sherrington  has  found  that  the  cutaneous  areas  of 
distribution  of  consecutive  nerve-roots  are  not  perfectly  inde- 
pendent, but  to  some  extent  overlap.  Stimulation  of  the  peri- 
pheral end  of  the  divided  posterior  root  has  no  effect.  Stimula- 
tion of  the  central  end  gives  rise,  if  the  animal  be  conscious,  to 
evidences  of  pain,  and  other  signs  of  the  passage  of  afferent 
impulses — e.g.,  a  rise  in  blood-pressure.  The  latter  may  also 
be  observed  when  the  animal  is  anaesthetized. 

Referred  Pain. — The  posterior  roots  contain  sensory  fibres  not  only 
for  the  skin,  but  also  for  the  deeper  structures  and  the  viscera.  The 
afferent  fibres  reach  the  viscera  by  the  sympathetic,  the  vagus,  and 
the  pelvic  nerves  or  nervi  erigentes.  Recent  clinical  observations 
have  thrown  much  light  upon  the  distribution  of  the  visceral  fibres 
and  their  relation  to  the  cutaneous  sensory  nerves.  It  has  long 
been  known  that  in  disease  of  an  internal  organ  the  pain  is  often 
referred  to  some  superficial  part.  It  has  now  been  demonstrated 
that  each  organ  is  related  to  a  more  or  less  definite  region,  or  more 
than  one  region,  of  the  skin.  In  disease  of  the  organ  there  is  in  tins 
area  increased  excitability  (hyperalgesia)  or  tenderness  to  slight 
mechanical  stimuli,  and  often  also  increased  excitability  for  heat 
or  cold,  and  the  reflexes  elicited  by  stimulation  are  exaggerated 
(1  lead,  Dana). 

The  bond  of  connection  appears  to  be  the  origin  from  the  same 
spinal  segments  of  the  autonomic*  sensory  fibres  of  any  viscus  and 

*  Langley  uses  the  term  autonomic  nervous  system  to  include  the 
nerve  supply  of  heart  muscle,  all   unstriated   muscle,  and  all  gland   cells- 


////    i  /  \  /  R  //     \'/  RVOUS  SYSTEM  791 

the  sensory  supply  of  the  corresponding  cutaneous  area.     The'  com 
mon  anatomical  origin  seems  to  carry  with  it  a  physiological  1  1 
lation,  either  because  the  irritation  of  the  visceral  fibres  .spreads  in 
the  conl  to  the  somatic  afferent  fibres  which  enter  the  corresponding 

segments,  or  because  Of  some  action  higher  up  in  the  cerebral  centres, 
the  nature  of  which  will  be  best  considered  along  with  the  general 
topic  of  the  localization  of  sensory  impressions  (p.  982). 

Recurrent  Sensibility.-  -Although  muscular  contraction  is 
the  most  conspicuous  event  that  follows  stimulation  of  the 
peripheral  end  of  an  anterior  nerve-root,  it  is  by  no  means  the 
only  one.  It  is  frequently  observed,  though  not  in  all  kinds  of 
animals,  that  here,  too,  pain  is  caused.  That  this  pain  is  not 
due  to  the  muscular  contraction  is  proved  by  the  fact  that  it 
can  still  be  elicited  when  the  nerve-trunk  is  divided  between  the 
junction  of  the  roots  and  the  periphery.  The  real  explanation 
of  the  phenomenon  is  that  certain  fibres  from  the  posterior 
roots  ('  recurrent  fibres,'  see  footnote  on  p.  693)  bend  up  for 
some  distance  into  the  anterior  roots,  and  then  turn  round 
again  and  pursue  their  course  to  their  peripheral  distribution 
in  the  mixed  nerve,  or  run  on  in  the  motor  roots  to  supply  the 
sheath  surrounding  them  (nervi  nervorum),  and  even  the  mem- 
branes of  the  spinal  cord. 

The  afferent  impulses  that  enter  the  cord  along  the  pos- 
terior roots  have  the  choice  of  many  paths  by  which  they  may 
reach  the  brain.  The  following  are  a  few  of  the  routes  which 
they  may  follow  : 

(1)  They  may  pass  directly  up  through  the  postero-median  column. 
If  they  take  this  route,  their  course  will  be  first  interrupted  by  nerve- 
cells  in  the  gracile  or  cuneate  nuclei  in  the  medulla  oblongata. 
Thence  they  may  find  their  way  across  the  middle  line  by  the  arcuate 
fibres  of  the  upper  or  sensory  decussation,  and  sweeping  along  the 
fillet  and  the  sensory  path  in  the  hinder  part  of  the  posterior  limb 
of  the  internal  capsule,  finally  arrive  at  the  cerebral  cortex.  Between 
the  gracile  and  cuneate  nuclei  and  the  cortex  they  pass  through 
nerve-cells  in  the  optic  thalamus. 

(2)  They  may  pass  up  by  the  direct  cerebellar  tract  and  restiform 
body  to  the  grey  matter  of  the  cerebellar  worm.  If  they  take  this 
route  their  course  will  be  interrupted  very  soon  after  their  entrance 
into  the  cord  in  the  cells  of  Clarke's  column.  Since  the  superficial 
grey  matter  of  the  vermis  is  connected  by  association  fibres  with 
the  dentate  nucleus,  and  the  dentate  nucleus  by  the  superior  peduncle 
with  the  opposite  cerebral  hemisphere,  this  is  also  a  possible  path 
to  the  great  brain. 

(3)  They  may  reach  the  antero-lateral  ascending  tract  of  the  same 
side  through  its  cells  of  origin  in  the  spinal  grey  matter,  and  passing 
through  the  medulla  and  pons  to  the  superior  peduncle  of  the  cere- 
bellum, enter  the  grey  matter  of  the  superior  worm. 

in  the  body.  It  embraces,  in  addition  to  the  sympathetic,  cranial  auto- 
nomic fibres  in  several  of  the  cranial  nerves  and  sacral  autonomic  fibres 
in  the  nervi  erigentes  (see  p.  883). 


A   MANU  XL  OF  PHYSIOLOGY 

I     J'hcy  may  cross  the  middle  line,  after  entering  the  cord,  through 

axons  or  collaterals    p.  77"    which  run  in  the  anterior  and  also  in 

the  posterior  commissure,  enter  one  of  the  ascending  tracts  on  the 

other  side     e.g.,  the  tract  of  Gowers     and  continue  without  further 

sation  up  to  their  central  destination. 

i  hey  may  spread  from  neuron  to  neuron  in  the  tangle  of  the 
.   matter  itself,  and  pass  out  again  at  a  different  level  into  one  of 
. lute  tracts  on  the  same  or  on  the  opposite  side  ol  1  he  <  onl. 

Efferent  Impulses  from  the  brain  may  travel  : 

1  Through  the  direct  or  crossed  pyramidal  tract. 

2  From  one  side  of  the  cerebral  cortex  to  the  other,  and  then 
a  the  pyramidal  tracts  corresponding  to  that  side  (?). 

,  From  the  frontal  part  of  the  cerebral  cortex,  through  the 
anterior  limb  of  the  internal  capsule  to  the  grey  matter  in  the  pons, 
and  thence  to  the  cerebellum  by  its  middle  peduncle. 

I  From  the  occipital  or  temporal  cortex,  in  the  hinder  rim  of  the 
internal  capsule,  to  the  pontine  grey  matter  and  through  the  middle- 
peduncle  to  the  cerebellum.  From  the  cerebellum  they  may  possibly 
pass  down  to  the  nucleus  of  Deiters  and  thence  along  the  antero- 
lateral descending  tract  to  the  anterior  horn  of  the  cord,  and 
indirectly  to  the  periphery. 

All  the  paths  enumerated,  as  well  as  other-  to  which  it  would 
be  tedious  to  formally  refer,  and  which  the  ingenuity  of  the 
reader  mav  profitably  be  employed  in  constructing  for  himself, 
from  the  data  already  given,  are  to  be  looked  upon  as  possible 
channels  for  the  passage  of  impulses  between  the  brain  and  the 
periphery.  But  it  must  be  distinctly  pointed  out  that  what  i- 
certain  is  in  this  case  much  more  limited  than  what  is  possible. 
Among  the  efferent  paths  it  is  certain  that  the  pyramidal  ti 
are  conductors  of  voluntary  motor  impulses,  and  that  in  mosl 
individuals  the  great  majority  of  such  impulses  decussate  in 
the  medulla  oblongata,  only  a  -mall  minority  in  the  cord.  For 
a  lesion  involving  the  pyramidal  tract  above  the  decussation 
of  the  pyramids  causes  paralysis  of  the  opposite  side  of  the 
body,  a  lesion  below  the  decussation  paraly-is  of  the  same  side. 
It  is  certain  that  when  one  pyramidal  tract  has  been  destroyed, 
in  many  animals  at  least,  the  resulting  paralysis  is  soon  recovered 
from,  at  anv  rate  to  a  great  extent,  and  it  i>  possible  that  in  tin- 
case  the  motor  cortex  on  the  side  of  the  lesion  has  placed  itself 
again  in  communication  with  the  paralyzed  muscles  through  it- 
commissural  connections  with  the  opposite  hemisphere.  This, 
however,  is  not  the  only  alternative,  for,  as  already  pointed  out, 
the  pyramidal  tracts  are  not  the  only  cortico-spinal  paths  which 
can  subserve  volitional  movements,  and  division  of  the  anterior 
portion  of  the  antero-lateral  column  may  cause  deeper  and  more 
permanent  paralysis  than  division  of  the  pyramidal  tract. 

Decussation    of    the    Sensory   Paths.     On   the   other   hand, 
it   is  certain  that   pathological  or  traumatic    lesions,  apparently 


////    i  I  XI  R  1/     VERVOUS  SYSTE  W  793 

involving  the  destruction  oi  one  Literal  half  of  the  cord  in  man 
and  experimental  semisections  in  some  mammals,  are  followed 
by  symptoms  which  suggest  thai  some  kinds  of  sensory  impul  e 
decussate  chiefly  in  the  spinal  cord  viz.,  diminution  or  loss  <>l 
sensibility  to  pain  and  to  changes  of  temperature  on  the  opposite 
side  below  the  level  of  the  lesion,  with  little  or  n<>  impairment ,  and 
often  increase  of  sensibility  (hyperesthesia)  on  the  same  side. 
Tactile  sensibility  is  lost  on  the  side  of  the  lesion,  and  likewise 
the  muscular  sense. 

The  first  general  description  of  this  symptom-complex  was  given 
by  Brown-Sequard,  although  long  after  he  saw  cause  to  retract  this 
interpretation  of  the  facts.  While  it  may  be  true  that  in  man  it  has 
not  been  rigidly  demonstrated  that  the  symptoms  are  associated  with 
a  clean-cut  lesion  precisely  limited  to  one-half  of  the  cord,  clinical 
observation  has  on  the  whole  tended  to  confirm  the  view  that  an 
important  portion  of  the  sensory  path  decussates  in  the  cord.  But 
it  is  a  curious  circumstance  that  experimental  physiologists  have  for 
the  most  part  obtained  contradictory  results.  Thus  Mott,  working 
with  monkeys,  found  that  the  different  kinds  of  sensation,  far  from 
being  abolished,  are,  as  a  rule,  impaired  in  a  smaller  degree  on  the 
side  opposite  to  the  semisection  than  on  the  same  side,  while  Ferrier 
and  Turner  obtained  on  the  whole  a  contrary  result,  and  one  that 
corresponded  closely  with  Brown-Sequard's  original  description. 
The  discovery  that  no  ascending  degeneration,  or  only  a  trifling 
amount,  is  to  be  found  on  the  opposite  side  of  the  cord,  either 
after  semisection  or  after  division  of  posterior  roots,  does  not  of 
itself  enable  us  to  decide  the  question.  For  while  this  latter  fact 
shows  that  few  or  none  of  the  afferent  fibres  cross  the  middle  line 
to  enter  the  long  conducting  paths  before  being  interrupted  by 
nerve-cells,  it  by  no  means  proves  that  afferent  impulses  do  not 
decussate  in  the  cord.  The  long  paths  of  the  posterior  column,  indeed, 
do  not  decussate  below  the  level  of  the  bulb.  The  dorsal  and  ventral 
spino-cerebellar  tracts  are  also,  in  the  main  at  least,  uncrossed  spinal 
paths.  A  portion  of  the  afferent  impulses  must  therefore  be  carried 
up  to  the  cerebrum  and  cerebellum  without  decussating  in  the  cord. 
But  nobody  can  tell  how  massive  a  link  between  the  two  halves  of 
the  cord  may  be  formed  by  the  grey  matter  and  the  endogenous 
fibres  of  the  white  columns  and  their  collaterals.  We  know  that 
some  afferent  impulses  do  decussate  far  below  the  level  of  the  medulla. 
For,  (1)  A  part  of  the  action  current  (p.  719)  crosses  the  middle  line 
and  ascends  in  the  opposite  half  of  the  cord  when  the  central  end  of 
one  sciatic  is  stimulated  (Gotch  and  Horsley).  (2)  Crossed  reflex 
movements  are  possible  ;  and  when  excitation  of  the  central  end  of 
the  sciatic  is  followed  by  contraction  of  the  muscles  of  the  opposite 
fore-limb,  the  afferent  impulses  must  either  decussate  in  the  lumbar 
cord,  and  then  run  up  on  the  opposite  side  to  the  level  of  the  brachial 
plexus,  or  must  ascend  on  the  same  side  and  cross  over  somewhere 
between  the  plane  of  the  sciatic  and  the  brachial  nerve-roots.  The 
only  other  hypothesis  on  which  crossed  reflex  action  can  be 
explained — but  a  hypothesis  for  which  there  is  not  a  tittle  of  evidence 
— is  that  the  afferent  impulse  always  acts  on  the  few  motor  cells 
whose  axis-cylinder  processes  pass  over  to  the  opposite  side,  and 
there  enter  anterior  nerve-roots.  But  while,  for  these  reasons,  it 
cannot  be  denied  that  some  afferent  impulses  decussate  in  the  cord, 


704  A   M  \NV  \L  OF  PHYSIOLOGY 

it  would  be  an  error  to  conclude  that  all  do  so  in  any  animal,  or  that 
all  animals  are  in  this  respect  alike.  It  is  indeed  extremely  probable 
that  in  different  species  of  animals,  and  even  in  individuals  of  the 
same  spe<  Les,  there  are  considerable  differences  in  the  extent  of  the 
sensory  decussation  in  the  cord,  just  as  there  are  in  the  extent  of  the 
motor  decussation  in  the  bulb.  In  some  animals  the  greater  part  of 
the  sensory  path  may  decussate  in  the  cord  ;  in  others  the  greater 
part  may  decussate  in  the  bulb,  or  higher  up.  The  lack  of 
agreement  in  the  experimental  results  may  be  due  partly  to  this 
cause.  When  it  is  further  remembered  how  difficult  it  sometimes 
is  to  interpret  the  account  which  a  man  gives  of  his  sensations  and 
to  recognise  precisely  the  degree  and  nature  of  sensory  defects 
produced  by  disease  in  the  human  subject,  it  will  not  be  thought 
surprising  that  experiments  on  animals,  from  the  time  of  Galen 
onwards,  should  have  yielded  evidence  which,  although  perhaps  now 
at  length  tending  to  a  definite  result,  is  still  unfinished  and  in  part 
conflicting. 

If,  leaving  them  out  of  account,  not  as  valueless  but  as  still 
difficult  of  interpretation,  we  attempt  to  draw  any  general 
conclusion  from  the  clinical  observations  which,  however  im- 
perfect, are  in  such  questions  our  surest  guide,  it  can  only  be 
this,  that  in  man  some  of  the  sensory  impulses,  and  particularly 
those  connected  with  the  cutaneous  sensations  of  pain  and  tempera- 
ture, decussate,  in  part  at  least,  in  the  cord.  But  there  is  also 
evidence  that  tactile  afferent  impulses,  including  those  coming 
from  the  muscles  and  related  to  the  muscular  sense,  and,  it  may  be, 
some  of  the  impulses  associated  with  pain,  decussate,  not  in  the 
cord,  but  in  the  bulb. 

The  Paths  for  Different  Kinds  of  Sensory  Impressions. — If  this  is 
the  state  of  our  knowledge  where  the  problem  is  merely  to  determine 
the  crossing-place  of  afferent  impulses  which  are  certainly  known 
to  cross,  it  is  only  to  be  expected  that  we  should  be  still  more  in 
the  dark  as  regards  the  routes  by  which  different  kinds  of  afferent 
impulses  thread  their  way  through  the  maze  of  conducting  paths  in 
the  neural  axis  to  reach  their  planes  of  decussation  and  gain  the 
'  sensory  crossway  '  in  the  internal  capsule.  Some  authors  have 
indeed  cut  the  Gordian  knot  by  assuming  that  any  kind  of  sensory 
impression  may  travel  up  any  afferent  path.  Direct  stimulation  ot 
a  naked  nerve-trunk,  it  has  been  argued  in  favour  of  this  view,  gives 
rise  to  a  sensation  of  pain  ;  stimulation  of  the  skin  in  which  the 
end-organs  of  the  nerve  lie  gives  rise  to  a  sensation  of  touch  or  a 
sensation  of  temperature,  according  as  the  stimulus  is  a  mild 
mechanical  or  a  thermal  one,  the  contact  of  a  feather  or  of  a  hot 
test-tube.  Why,  it  has  been  asked,  should  we  imagine  that  the 
difference  in  the  result  of  stimulation  depends  on  a  difference  in 
the  nerve-fibres  excited,  and  not  on  a  difference  in  the  kind  of 
impulses  set  up  in  the  same  nerve-fibres  ?  This  is  a  question  which 
we  shall  have  again  to  discuss  (p.  968).  But  apropos  of  our  present 
problem,  we  may  say  that  there  is  very  clear  proof  from  the  patho- 
logical side  that  a  limited  lesion  in  the  conducting  paths  of  the 
central  nervous  system  may  be  associated  with  defect  or  total  loss 
of  one  kind  of  sensation,  while  all  the  other  kinds  remain  intact. 


THE  CENTRAL   NERVOUS  SYSTEM  795 

And  there  seems  no  other  tenable  hypothesis  than  that  in  such 
cases  the  pathological  change  has  picked  out  a  particular  group  oi 
fibres,  either  collected  into  a  single  strand  or  scattered  among 
unaltered  fibres  of  diflferenl  function.  For  example,  in  syringo- 
myelia,  a  condition  in  which  cavities  are  formed  in  the  grey  matter 
of  the  cord  secondary  to  a  new  growth  of  the  neuroglia  surrounding 
the  central  canal,  a  frequent  symptom  is  the  loss  in  a  certain  region 
of  sensibility  to  pain  and  to  changes  of  temperature,  while  tactile 
sensibility  is  unaffected  (dissociation  of  sensations).  Again,  in  loco- 
motor ataxia,  a  disease  in  which  in  co-ordination  of  movement  and 
derangement  of  the  mechanism  of  equilibration  are  prominent  symp- 
toms, degeneration  in  the  posterior  column  of  the  cord  is  a  most 
constant  lesion.  And  there  is  strong  evidence  that  afferent  impulses 
from  muscles  and  tendons,  which  either  give  rise  to  impressions  be- 
longing to  the  group  of  tactile  sensations,  or  produce  no  effect  in 
consciousness,  and  which,  according  to  the  most  widely  accepted 
doctrine,  serve  as  the  basis  of  the  muscular  sense,  and  play  an  impor- 
tant part  in  the  maintenance  of  equilibrium  (p.  835),  pass  up  in  the 
posterior  column.  It  may  also  conduct  tactile  impressions  from  the 
skin.  A  case  has  been  observed  where  a  man  received  a  stab  which 
divided  the  whole  of  one  side  of  the  cord  and  the  posterior  column  of 
the  other  side.  Sensibility  to  touch  was  lost  on  both  sides  of  the  body 
below  the  level  of  the  injury,  sensibility  to  pain  only  on  the  side 
opposite  to  the  main  lesion.  In  another  case,  in  which  some  small 
syphilitic  tumours  (gummata)  in  the  lateral  column  on  the  left  side 
caused  marked  degeneration  in  the  left  direct  cerebellar  tract,  the 
tract  of  Gowers,  and  the  crossed  pyramidal  tract,  without  affecting 
the  posterior  columns,  tactile  sensibility  was  only  slightly  impaired 
in  the  opposite  leg,  while  the  sensibility  for  pain  and  temperature 
was  much  enfeebled.  In  the  left  leg,  which  was  paralyzed,  there 
was  slight  hyperesthesia.  These  observations  indicate  that  impres- 
sions of  pain  and  temperature  pass  up  in  the  antero-lateral  column, 
either  in  the  tract  of  Gowers,  or  in  the  direct  cerebellar  tract,  or  in 
both  (Dejerine  and  Thomas). 

But  it  does  not  follow  that  they  cannot  ascend  by  other  paths  as 
well.  It  appears  indeed  that  the  grey  matter  of  the  cord,  or,  rather, 
short  endogenous  fibres  arranged  in  series  in  the  antero-lateral  column 
so  as  to  connect  the  grey  matter  at  different  levels,  constitute  such  a 
path,  and  that  impulses  which  give  rise  to  pain  can  be  propagated 
along  a  cord  in  which  hardly  a  vestige  of  white  substance  remains 
uncut.  In  man  the  path  for  pain  and  temperature  impressions  along 
these  short  endogenous  fibres  seems  to  be  mainly  or  entirely  a  crossed 
path.  The  afferent  paths  for  such  vaso-motor  reflexes  as  are  elicited 
by  stimulation  of  the  central  end  of  the  sciatic  ascend  in  the  lateral 
column,  and  the  impulses  largely  cross  the  middle  line  in  the  cord. 
The  posterior  columns  have  nothing  to  do  with  the  conduction  of 
painful  impressions,  for  division  of  them  causes  not  anaesthesia,  but 
rather  hyperesthesia,  while  if  they  are  left  intact,  and  the  rest  of 
the  cord,  including  the  grey  matter,  divided,  the  animal  is  insensitive 
to  pain  below  the  level  of  the  lesion.  Just  as  man  differs  from  lower 
animals  in  the  completeness  with  which  certain  of  the  sensory 
impressions  decussate  in  the  cord,  so  differences  exist  in  the  degree 
of  localization  of  the  different  kinds  of  impressions  in  particular 
tracts.  One  of  the  outstanding  differences  is  that  in  animals  it 
seems  to  be  easier  for  a  still  intact  path  to  be  substituted  for  a 
severed   path  as  a  conductor  of  impulses  which  normally  traverse 


jgh  A    M  INV  XL  OF  PHYSIOLOGY 

the  latter.  The  rapidity  with  which  sensation  i>  restored  below 
the  lesion  after  semisection  of  the  cord  in  animals  is  an  illustration  of 
this.  Another  difference,  which  can  be  explained  in  the  same  way,  is 
that  a  sharply-marked  dissociation  oi  sensations  -retention  ol  tactile 
sensibility,  for  example,  with  loss  of  sensibility  to  pain  or  to  pain  and 
temperature  changes  either  cannot  be  produced  experimentally  in 
animals,  or  is  very  difficult  to  realize. 

The  impulses  which  descend  the  cord  give  token  of  their  arrival 
at  the  periphery  bv  causing  either  contraction  of  voluntary  mus 
or  contraction  of  the  smooth  muscular  fibres  of  arteries,  or  so  retion 
in  glands.  They  all  pass  down  in  the  antero-lateral  column,  but  tin- 
path  of  the  voluntary  impulses  in  the  pyramidal  tracts  is  the  best 
known  and  most  sharply  defined. 

2.  Modification  of  Impulses  set  up  elsewhere  (Reflex 
Action). — The  spinal  cord,  although  it  is  a  conductor  of  nervous 
impulses  originating  elsewhere,  is  by  no  means  a  mere  con- 
ductor. Many  of  the  impulses  which  fall  into  the  cord  are 
interrupted  in  its  grey  matter.  Some  of  the  efferent  impulses 
proceeding  from  the  brain  are  perhaps  modified  in  the  cord, 
and  then  transmitted  to  the  muscles.  Some  of  the  afferent 
impulses  are  modified,  and  then  transmitted  to  the  brain  ; 
some  are  modified,  and  deflected  altogether  into  an  efferent 
path.  These  last  are  the  impulses  which  give  rise  to  reflex 
effects.  A  reflex  action  has  sometimes  been  defined  as  an  action 
carried  out  in  the  absence  of  consciousness  ;  not  necessarily, 
however,  in  the  absence  of  general  consciousness,  but  in  the 
absence  of  consciousness  of  the  particular  act  itself.  But  the 
term  is  now  more  correctly  used  so  as  to  embrace  all  kinds  of 
actions  which  are  not  directly  voluntary,  whether  the  individual  is 
conscious  of  them  or  not.  For  example,  when  the  sole  of  the  foot  is 
tickled,  the  leg  is  irresistibly  and  involuntarily  drawn  up  by  reflex 
contraction  of  its  muscles  ;  yet  the  person  is  perfectly  cognizant 
both  of  the  movement  and  of  the  sensation  which  accompanies 
the  afferent  impulse.  Many  reflex  actions  usually  associated  with 
sensations  proceed  normally  when  consci  lusness  is  entirely  in  abey- 
ance ;  during  sleep  most  of  the  ordinary  reflexes  can  be  elicited. 

Anatomical  Basis  of  Reflex  Action. — Since  the  essence  of  reflex 
action  is  that  the  arrival  of  afferent  impulses  in  the  spinal  cord  or 
brain  causes  the  discharge  of  efferent  impulses,  there  must  be  some 
connection  between  the  incoming  and  the  outgoing  nerve-fibres. 
When  the  nervous  system  is  still  only  a  process  of  an  epithelial 
(sensory)  cell  joining  hands  with  a  muscular  cell,  the  distinction 
between  afferent  and  efferent  fibre  docs  not  exist.  When  develop- 
ment has  gone  a  step  further,  and  the  neuro-muscular  process  is 
interrupted  by  a  second  epithelial  cell  transformed  into  a  nerve-cell, 
the  afferent  fibre  enters  one  pole  and  the  efferent  fibre  leaves  the 
other  pole  of  the  same  cell.  In  a  simple  reflex  action  three  events 
can  be  distinguished  :  stimulation  of  a  receiving  mechanism,  con- 
duction of  the  excitation,  and  the  consequent  reaction  or  end-efl 
The  receiving  mechanism  or  receptor  may  consist  of  ordinarv  sensory 


////    CI  \  /A'  //    NERVOUS  SYSTEM 


797 


nerve-endings  in  the  skin,  or  oi  special  sense-endings,  as  in  the  retina 
or  interna]  ear.  The  conducting  mechanism  or  conductor  is  madi 
up  oi  .it  Leasi  two  neurons,  one  the  afferent  portion  of  the  reflex 
arc  connected  with  the  receptor,  the  other  the  efferent  portion  oi 
the  arc,  connected  with  the  organ,  sometimes  termed  the  effector 
organ — a  muscle,  e.g.,  or  a  gland — which  accomplishes  the  end-effect. 
The  transference  oi  the  excitation  from  tin  afferent  to  the  efferent 
neuron  takes  place  across  the  intervening  synapse.  The  simple 
isolated  reflex  arc,  as  thus  described,  although  a  convenient  abstrac- 
tion, corresponds  but  little  to  anything  which  actually  exists  in  one 
of  the  higher  animals.  With  increasing  complexity  of  organization 
the  nervous  impulse  passing  up  an  afferent  fibre  is  in  general  offered, 
instead  of  a  single  efferent  path,  a  choice  of  many  potential  routes 
when  it  reaches  the  spinal  cord.  We  have  previously  (p.  769)  described 
the  course  taker:  by  the  fibres  of  the  posterior  roots  on  entering  the 
cord.  It  is  obvious  that  through  the  mam  fibres  and  their  collaterals 
an  extensive  connection — partly  direct,  partly  by  the  link  of  inter- 
mediate neurons — is  established  with  the  motor  cells  on  both  sides  of 
the  cord.  But  the  facts  of 
physiology  demonstrate  an 
even  ampler  connection  than 
the  mere  anatomical  study  of 
the  distribution  of  the  root- 
fibres  would  suggest.  Indeed, 
the  phenomena  of  strychnine- 
poisoning  seem  to  show  that 
every  afferent  fibre  is  poten- 
tially connected  with  the 
motor  mechanisms  of  the 
whole  cord,  or  at  least  with 
a  very  large  proportion  of 
them.  For  in  a  frog  under 
the  influence  of  this  drug, 
stimulation     of    the    smallest 

portion  of  the  skin  will  cause  violent  and  general  convulsions,  which 
are  unaffected  by  destruction  of  the  brain,  but  cease  at  once  on 
destruction  of  the  cord  (p.  886). 

It  is  therefore  a  question  of  great  interest  how  the  isolated  con- 
duction of  the  impulses  in  a  given  reflex  arc  is  normally  achieved. 
The  best  answer  which  can  at  present  be  given  is  that  it  is  not 
equally  easy  for  a  reflex  excitation  to  pass  across  all  the  synapses 
which  are  potentially  open  to  it.  Following  the  path  of  least  re- 
sistance, the  excitation  traverses  the  synapse  or  synapses  which  it 
is  easiest  for  it  to  break  through.  What  property  of  the  synapse  is 
associated  with  resistance  to  the  passage  of  the  impulse  is  unknown. 
But  it  is  a  variable  property,  and  when  a  general  reduction  in  the 
resistance  is  produced,  as  by  strychnine  or  tetanus  toxin,  an  excita- 
tion impressed  upon  a  single  afferent  path  may  force  a  great  many 
synapses  normally  impervious  to  it. 

While  it  is  convenient  in  a  preliminary  survey  to  speak  of  the 
resistance  to  spreading  of  the  excitation  in  the  cord  being  diminished 
by  strychnine  or  by  tetanus  toxin,  we  shall  see  presently  that  more 
than  this  is  involved  (p.  801). 

Principle  of  the  Common  Path. — In  considering  the  architecture 
of  the  cerebro-spinal  nervous  system  as  a  basis  of  reflex  action,  one 
feature  is  of  such  importance  as  to  deserve  special  mention.     The 


Fig.  337. — Diagram  of 
Reflex  Arc. 


Simple 


The  arrows  indicate  the  direction  of  the 
afferent  and  efferent  impulses. 


798  A   MANUAL  OF  I'HYSIOLOGY 

afferent  neurons,  running  from  the  receptive  surfaces  to  the  cento ■-,. 
constitute  each  for  its  own  receptive  point  a  '  private  '  path  which 
can  only  be  used  by  impulses  arising  at  that  point,  and  not  by 
impulses  arising  at  any  other  point.  Through  its  central  connections 
an  afferent  neuron  from  a  single  point  may  be  put  into  communica- 
tion with  numerous  efferent  neurons,  and  thus  with  numerous  and 
distant  effector  organs  (muscles  or  glands).  Conversely,  the  efferent 
portion  of  a  single  reflex  arc  can  convey  reflex  excitations  originating 
in  numerous  and  distant  receptive  fields.  It  is  the  sole  path  which 
all  efferent  impulses — let  them  originate  where  they  may — must 
use  to  reach  the  end-organ  in  question.  It  is  therefore  not  a  private 
but  a  public  path,  and  may  be  termed  in  this  relation  the  final 
common  path  (Sherrington). 

The  existence  of  the  common  path  is  of  great  importance  in 
understanding  the  manner  in  which  reflexes  are  compounded 
together,    a    problem    absolutely   fundamental    in    nervous   co- 
ordination.    One  consequence  of  the  existence  of  a  common 
path  is  that  when,  among  the  receptors  which  may  use  it,  two 
are  simultaneously  stimulated  which,  when  separately  excited, 
produce  opposite  effects  upon  the  effector  organ,  only  one  of 
the  effects  is  produced.     In  other  words,  impulses  which  produce 
the   two  opposed   effects    can   be  successively,   but   cannot   be 
simultaneously,  sent  along  the  common  path.     Thus,  '  excitation 
of  the  central  end  of  the  afferent  root  of  the  eighth  or  seventh 
cervical  nerve  of  the  monkey  evokes  reflexly  in  the  same  indi- 
vidual animal  sometimes  flexion  at  the  elbow,  sometimes  ex- 
tension.    If  the   excitation  be  preceded   by  excitation   of  the 
first    thoracic    root,    the    result    is    usually    extension  ;    if    by 
excitation  of  the  sixth  cervical  root,  it  is  usually  flexion.     Yet 
though  the  same  root  may  thus  be  made  to  evoke  reflex  con- 
traction of  the  flexors  or  of  the  extensors,  it  does  not  evoke 
contraction  in  both  flexors    and   extensors  in  the  same  reflex 
response.  .  .  .     The  flexor-reflex,  when  it  occurs,  seems,  therefore, 
to  exclude  the  extensor-reflex,  and  vice  versa.     Either  the  one  or 
the  other  results,  but  not  the  two  together  '  (Sherrington).      It 
is  obvious  that  this  is  an  advantageous  arrangement.     An  alge- 
braical summation  of  the  opposed  effects  by  the  common  path 
would  result  in  a  useless  action  which  was  neither  effective  flexion 
nor  effective  extension,  a  compromise  and  not  a  co-ordination. 
The  role  of  the  receptor  in  the  reflex  arc  is  above  all  to  sift 
out  from  the  various  kinds  of  impressions  impinging  upon  the 
receiving  surface  the  particular  kind  to  which  the  appropriate 
response  is  the  reflex  action  in  question.     As  will  be  pointed 
out  in  greater  detail  in  the  study  of  the  special  senses,  each  kind 
of  afferent  end-organ  has  become  adapted  to  a  special,  or,  as 
it  is  termed,  an  '  adequate  '  stimulus,  so  that  it  is  easily  affected 
by  this,  and  with  difficulty  or  not  at  all  by  other  modes  of  stimula- 
tion.    Thus,  light  is  the  adequate  stimulus  of  the  end-organ  of 


THI    <  I  NTRAL   XI.RVOUS  SYSTI.M  799 

the  optic  nerve,  heat  that  of  the  end-organs  of  the  nerves  by 
which  we  perceive  the  sensation  of  warmth,  mechanical  pressure 
that  of  the  nerves  by  which  we  perceive  the  sensation  of  pressure. 
Other  kinds  of  stimuli  are  either  entirely  inactive  or  much  less 
effective  in  evoking  the  particular  sensory  response.  There  is 
every  reason  to  believe  that  the  receptor  in  the  reflex  arc  occupies 
the  same  position  in  regard  to  adequate  stimuli  as  it  does  when 
it  functions  as  a  sense-organ. 

Sherrington  has  shown  that  the  different  kinds  of  nerve- 
endings  in  one  and  the  same  area  of  the  skin  (in  the  dog) 
must  be  assumed  to  possess  totally  different  spinal  connections, 
since  the  movements  elicited  by  stimuli  suitable  for  one  form  of 
nerve-ending  are  quite  different  from  those  elicited  by  stimuli 
suitable  for  another. 

The  '  extensor- thrust  '  is  a  reflex  obtained  in  the  hind-leg  of 
the  dog,  and  characterized  by  a  brief,  strong  extension  at  the 
hip,  knee,  and  ankle.  It  is  only  elicited  by  a  certain  kind  of 
mechanical  stimulation,  best  in  the  spinal  dog — i.e.,  in  a  dog 
whose  brain  has  been  destroyed  or  severed  from  the  cord — by 
pushing  the  tip  of  the  finger  between  the  plantar  cushion  and 
the  pads  of  the  toes.  It  cannot  be  obtained  by  electrical  stimu- 
lation or  by  any  kind  of  direct  stimulation  of  afferent  nerve 
trunks.  The  same  is  true  of  the  pinna-reflex  in  the  cat — i.e.,  the 
backward  crumpling  of  the  ear  elicited  by  squeezing  or  tickling 
its  tip.  The  scratch-reflex,*  a  scratching  movement  of  the  hind- 
foot,  is  much  more  easily  elicited  in  the  spinal  dog  by  mechanical 
stimulation  (rubbing,  tickling,  or  tapping)  applied  to  the  skin 
of  the  back  behind  the  shoulder  than  by  electrical  stimulation, 
which  often  fails  to  evoke  it  at  all.  The  puzzling  fact  that, 
according  to  surgical  experience,  many  of  the  internal  organs — 
e.g.,  the  ureters  and  bile-ducts — can  be  handled,  cut,  and  sutured 
without  pain,  while  the  passage  of  a  renal  calculus  or  a  gall- 
stone may  cause  excruciating  agon\r,  becomes  explicable  in  view 
of  the  apparently  slight  difference  which  sometimes  distinguishes 
an  adequate  from  an  inadequate  stimulus.  Thus  Sherrington 
has  shown  that  very  distinct  reflex  effects — e.g.,  a  rise  of  blood- 
pressure — can  be  obtained  by  sudden  distension  of  the  bile-duct 
by  the  injection  of  salt  solution  into  its  lumen.  Distension  is 
here  the  adequate  form  of  mechanical  stimulation,  and  it  is  the 
form  induced  by  the  passage  of  a  calculus,  while  nerve-cutting, 
although  a  mechanical  stimulus,  is  not  an  adequate  one. 

Conduction  in  reflex  arcs  shows  certain  peculiarities  when 
compared  with  the  conduction  in  nerve-trunks  already  studied 
(p.  687)  :  (1)  The  direction  of  the  reflex  conduction  cannot  be 

*  The  scratch-reflex  is  very  easily  obtained  in  cats  during  resuscitation 
after  a  period  of  cerebral  anaemia. 


/   MIXTA/    OF   PHYSIOLOGY 

reversed.  (2)  Its  velocity  over  the  whole  reflex  art  is  much 
smaller  than  over  a  nerve-trunk  of  equal  length.  Both  ol  these 
differences  depend  mainly  on  the  fa<  t  thai  the  impulses  must  be 
transmitted  from  one  neuron  to  another,  and  very  likely  on  a 
fundamental  property  of  the  synapse.  (3)  The  reflex  arc  is  easily 
fatigued,  easily  affected  by  deprivation  ol  oxygen  and  bydi 
in  comparison  with  the  nerve-trunk.  .This  difference  is  due  to 
the  portion  of  the  arc  in  the  grey  matter,  including  the  synapse 
or  synapses.  (4)  The  reflex  end-effect  may  much  outlast  the 
stimulus  in  other  words,  a  marked  '  after-discharge  '  is  charai  - 
teristic  ol  reflexes.  The  more  intense  the  stimulus  which 
liberates  the  end-effect,  the  greater  is  the  duration  ol  the  utter- 
discharge.  For  example,  the  '  crossed  extension  reflex  '  (ex- 
tension at  the  knee,  ankle,  and  hip,  produced  in  the  spinal  dog 
by  stimulation  of  the  skin  of  the  opposite  or  contralateral  hind- 
limb),  when  provoked  by  a  stimulus  of  more  than  a  certain 
intensity,  may  outlast  the  stimulation  by  ten  or  fifteen  seconds, 
and  the  after-discharge  may  be  stronger  than  any  other  part  of 
the  reflex  (Sherrington).  (5)  A  succession  of  impulses  may 
easily  pass  along  a  reflex  arc  when  one  of  the  series  would  fail 
to  pass  (temporal  summation).  This  does  not  occur  in  a  nerve- 
trunk.  The  first  stimulus,  though  itself  unable  to  produce  the 
reflex  effect,  facilitates  the  action  of  succeeding  stimuli,  so  that 
summation  of  the  impulses  occurs  in  the  cord  (Stirling).  A 
stimulus — e.g.,  a  make-induction  shock,  far  too  weak  to  produce 
the  scratch-reflex  when  applied  once  only  to  a  point  of  that  area 
of  skin  from  which  the  reflex  is  normally  elicited — has  been 
seen  to  cause  the  reflex  after  more  than  forty  shocks  had  been 
delivered  at  the  rate  of  eighteen  per  second.  (6)  The  rhythm 
and  intensity  of  the  reflex  end-effect  correspond  much  Less 
closely  with  the  rhythm  and  intensity  of  the  stimulus  than  in 
nerve-trunks.  (7)  The  phenomena  of  refractor}'  period  (p.  141), 
inhibition  and  '  shock,'  are  much  more  conspicuous  in  the  reflex 
arc  than  in  nerve-trunks. 

Inhibition  in  Reflex  Action. — Special  emphasis  must  be  laid 
upon  the  part  played  by  inhibition  in  reflex  actions.  For  the 
proper  carrying  out  of  many  reflex  movements  it  is  necessary 
not  only  that  the  appropriate  effector  organ,  the  appropriate 
muscle,  or  group  of  muscles,  should  be  caused  to  contract  at 
the  proper  time,  but  that  their  contraction,  or  that  of  other 
muscles,  should  be  diminished  or  abolished  by  inhibition,  or  even 
rendered  for  a  certain  period  impracticable  by  the  establishment 
somewhere  in  the  reflex  arc  of  a  refractory  state,  which  is  itself 
a  phenomenon  of  inhibition.  There  is  good  evidence  that  this 
is  a  central  inhibition  — i.e.,  it  depends  on  some  process  occurring 
in  the  spinal  portion  of  the  reflex  arc. 


THE  l  I  Y/A'  //     \7  RVOUS    SYST1  M 

As  an  example  of  the  numerous  class  of  reflexes  in  which  the 
excitation  of  certain  muscles  is  accompanied  by  the  inhibition 
of  their  antagonists  (reciprocal  inhibition),  we  may  take  the 
'  flexion  reflex,'  the  flexion  at  the  knee,  hip,  and  ankle  of  the 
hind-limb  readily  elicited  in  the  spinal  dog  by  '  nocuous  '  or 
harmful  stimuli  (such  as  a  prick,  a  strong  squeeze,  chemical 
agents,  or  excessive  heat),  or  by  electrical  stimuli  applied  to  the 
skin  of  the  limb  or  <>!  any  afferent  nerve  of  the  limb. 

Sherrington  has  shown  that  when  the  legs  of  the  animal  are 
so  prepared  that  only  the  flexors  can  ad  <>n  one  knee,  and  only 
the  extensors  on  the  other,  stimulation  of  symmetrical  points  on 
the  two  sides  in  the  area  of  skin  (receptive  held)  from  which  the 
flexion  reflex  can  he  evoked  causes  contraction  (excitation)  of 
the  flexors  and  simultaneous  relaxation  (inhibition)  of  the  tone 
of  the  extensors.  The  same  is  true  when  corresponding  afferent 
nerve-twigs  are  stimulated  on  the  two  sides.  From  this  it  is 
inferred  that  each  of  the  nerve-fibres  from  the  receptive  field  of 
the  reflex  divides  in  the  cord  into  two  sets  of  end-branches 
{e.g.,  collaterals) — a  set  which  produces  excitation  when  it  is 
stimulated,  and  another  set  which  produces  inhibition. 

The  difference  in  action  is  specific  in  the  sense  that  no  mere 
change  in  the  kind  or  intensity  of  stimulation  affects  it.  Yet 
there  are  facts  which  show  that  the  specificity  is  not  absolutely 
immutable,  and  that  a  change  of  conditions  in  the  spinal  cord 
may  permit  excitation  of  a  given  group  of  muscles  to  be  produced 
by  the  stimulation  of  an  afferent  path  which  is  primarily  inhibi- 
tory for  them.  One  of  the  most  striking  illustrations  of  this 
possibility  is  seen  in  the  action  of  strychnine.  Stimulation  of 
the  internal  saphenous  nerve  below  the  knee — say  in  a  dog  after 
removal  of  the  cerebrum — is  known  always  to  produce  inhibition 
of  the  portion  of  the  quadriceps  extensor  whose  contraction 
causes  the  knee-jerk. 

If  now  the  animal  be  poisoned  by  a  small  dose  of  strychnine, 
stimulation  of  the  nerve  causes  no  longer  reflex  relaxation,  but 
reflex  contraction  of  the  muscle.  This  fact  indicates  that  the 
essential  action  of  strychnine  is  something  different  from  a  mere 
reduction  of  the  resistance  to  the  spread  of  impulses  in  the  cord 
(Sherrington).  Tetanus  toxin  produces  a  similar  effect,  though 
more  slowly. 

Not  only  is  the  tone  of  the  extensors  diminished  or  abolished 
during  the  activity  of  the  flexors,  but  the  contraction  of  the 
knee  extensors  evoked  by  striking  the  patellar  tendon,  which  is 
called  the  knee-jerk,  either  fails  to  appear,  or  appears  but  feebly, 
when  the  flexion  reflex  is  simultaneously  elicited,  even  when  the 
mechanical  antagonism  of  the  flexor  contraction  has  been  elim- 
inated by  previously  detaching  the  flexors  from  the  knee. 

51 


802  A    MANUAL  OF  PHYSIOLOGY 

The  Knee-jerk  is  sometimes  termed  a  pseudo-reflex.  For 
certain  authorities  believe  that  the  mechanism  by  which  it  is 
produced  is  different  from  that  concerned  in  the  reflex  blinking 
of  the  eyelid,  or  the  reflex  retraction  of  the  testicle,  or  the 
drawing-up  of  the  foot  when  the  sole  is  tickled.  The  strongest 
objection  to  considering  it  an  ordinary  reflex  is  the  fact  thai  the 
interval  which  elapses  between  the  tap  and  the  jerk  ,,;,,  to  ,,',,, 
second)  is  distinctly  shorter  than  the  reflex  time  of  the  extremely 
rapid  lid  -  reflex,  and  is  not  much  greater  than  the  latent 
period  of  the  quadriceps  muscle  for  direct  electrical  stimula- 
tion, as  measured  under  the  ordinary  conditions  of  its  con- 
traction. The  knee-jerk  is  obtained  in  undiminished  strength 
when  the  nerves  of  the  ligamentum  patellae  have  been  divided. 
It  is  therefore  not  a  reflex  movement  caused  by  stimulation  of 
afferent  nerves  coming  from  the  tendon,  and  the  name  '  tendon- 
reflex  '  is  clearlv  a  misnomer.  But  that  it  is  related  in  some 
way  or  other  to  afferent  impulses  is  certain,  for  division  of 
the  posterior  roots  that  enter  into  the  anterior  crural  nerve 
abolishes  the  knee-jerk.  The  phenomenon,  according  to  some 
authors,  comes  under  the  head  of  what  is  called  myotatic  irrita- 
bility— that  is,  it  depends  on  mechanical  stimulation  of  the 
slightly-stretched  muscle  by  the  pull  of  the  tendon  when  it  is 
struck.  It  is  necessary  for  this  stimulation  that  the  muscle 
should  be  to  a  certain  extent  tonically  contracted.  So  that  when 
the  afferent  fibres  are  interrupted,  or  the  grey  matter  of  the 
cord  disorganized,  and  the  reflex  tone  abolished,  the  knee-jerk 
disappears.  It  is  admitted  by  all  that,  in  addition  to  the  direct 
stimulation  of  the  muscle  on  the  same  side,  the  tendon-tap  may 
cause  also  a  true  reflex  knee-jerk  on  the  opposite  side,  the  interval 
between  tap  and  contraction  being  about  |  second. 

Spread  or  Irradiation  of  Reflex  Action. — As  the  strength 
of  the  stimulus  which  has  been  evoking  a  given  reflex  movement 
is  increased  the  reflex  effect  becomes  more  and  more  extensive, 
spreading  out  or  irradiating  in  various  directions.  If,  for 
example,  the  reflex  in  question  is  the  flexion  reflex  elicited  by 
stimulation  of  the  plantar  surface  of  the  hind-foot  in  the  spinal 
animal,  increase  of  the  stimulus  will  cause,  in  addition  to  flexion 
of  the  same  hind-foot,  extension  of  the  opposite  hind-limb,  then 
in  the  homonymous  fore-limb  [i.e.,  the  limb  on  the  same  side) 
extension  at  the  elbow  and  retraction  at  the  shoulder,  then  certain 
definite  movements,  the  details  of  which  need  not  detain  us  here, 
in  the  opposite  fore-limb,  and  ultimately  also  definite  movements 
of  the  head  and  tail  (Sherrington).  Obviously  there  is  a  certain 
orderliness  in  the  spread  of  the  reflexes  ;  they  follow  a  certain 
regular  march  ;  the  inadiation  in  the  tangle  of  the  spinal  paths 
is  not  an  indiscriminate  one.     The  same  fact  emerges  quite  as 


THE  CENTRAL  NERVOUS  SYSTEM  S03 

clearly  when  other  reflexes  are  studied  in  a  similar  way;  and 
certain  laws  or  rules  which  define  the  spread  of  the  impulses  in 
spinal  reflexes  have  been  deduced.  For  descriptive  purposes, 
in  dealing  with  reflex  action,  it  is  convenient  to  consider  each 
lateral  half  of  the  cord  as  divisible  into  regions  each  related  on 
the  one  hand  to  a  certain  area  of  the  r-ceptive  surface  (skin),  and 
on  the  other  to  certain  muscles.  Such  regions  are  those  of  the 
neck,  including  the  pinna  (cervical),  the  fore-limb  (brachial),  the 
trunk  (thoracic),  the  hind-limb  (crural),  and  the  tail  (caudal). 
According  to  their  relation  to  these  regions  the  spinal  reflexes 
can  be  classified  as  '  short  '  or  '  long.'  The  short  spinal  reflexes 
are  those  in  which  the  muscular  response  takes  place  in  the  same 
region  as  the  application  of  the  stimulus.  The  long  reflexes  are 
those  evoked  when  the  stimulus  is  applied  to  the  receptive  field 
of  one  region,  and  the  response  occurs  in  the  musculature  of 
another  region.  For  the  short  reflexes  Sherrington  has  given 
a  number  of  rules,  which  may  be  stated  as  follows  :  (1)  The  closer 
together  their  spinal  segments,  the  easier  is  it  for  stimulation  of 
a  given  afferent  root  to  excite  reflex  contractions  of  muscles 
supplied  by  a  given  efferent  root.  (2)  For  each  afferent  root 
there  exists  in  its  own  spinal  segment  (of  course,  on  its  own  side 
of  the  cord)  a  reflex  motor  path  of  as  low  a  threshold  (i.e.,  as 
easily  set  into  action)  and  of  as  high  potency  (i.e.,  producing 
as  great  a  reflex  effect)  as  any  open  to  it  anywhere.  It  has  been 
shown  that  the  afferent  nerves  of  a  skeletal  muscle  are  derived 
from  the  spinal  ganglion  corresponding  to  the  segment  of  the 
cord  containing  its  motor  cells.  (3)  Motor  mechanisms  for  the 
skeletal  musculature  lying  in  the  same  region  of  the  cord,  and  in 
the  selfsame  spinal  segment,  show  markedly  unequal  accessibility 
to  the  local  afferent  channels  as  judged  by  the  reflex  contractions 
produced.  For  example,  the  reflex  contraction  of  the  flexors  of 
the  knee  on  the  stimulated  side,  and  of  the  extensors  of  the 
opposite  knee,  is  in  many  animals  much  more  easily  elicited  than 
contraction  of  the  extensors  of  the  homonymous  and  the  flexors 
of  the  contralateral  (i.e.  opposite)  side.  This,  however,  is  not 
because  the  last-named  extensors  and  flexors  are  really  incapable 
of  being  reflexly  affected  through  the  afferent  fibres  of  the 
corresponding  spinal  segments,  but  because  the  reflex  effect 
produced  by  them  is  in  this  case  not  contraction  but  inhibition. 
(4)  The  groups  of  motor  cells  contemporaneously  discharged  by 
spinal  reflex  action  innervate  synergic  muscles  (muscles  which 
act  in  the  same  direction  in  effecting  a  harmonious  movement), 
and  not  antergic  muscles  (which  antagonize  each  other). 

This  disproves  the  old  idea  that  the  movements,  caused  b\- 
excitation  of  an  efferent  spinal  root  are  co-ordinated  synergic 
movements,  since  at  many  joints  the  flexors  and  extensors  both 

51—2 


So4  I    1/  \NUAL  OF  PHYSIOLOGY 

receive  motor  fibres  from  one  and  the  same  root,  and  stimulation 
of  the  root  must  simultaneously  excite  antagonistic  muscles. 
'  The  collection  of  fibres  in  a  motor  spinal  root  does  nol  represent 
a  reflex  figure — i.e.,  a  number  of  simple  reflexes  occurring 
simultaneously — nor  does  the  receptive  field  of  a  reflex  corre- 
spond with  the  distribution  of  an  afferenl  root.' 

(5)  It  follows  from  (1),  (2),  and  (4)  that  the  spinal  reflex 
movement  which  can  be  elicited  in  and  from  any  one  spinal 
region  will  exhibit  much  uniformity  even  when  the  exciting 
stimulus  is  applied  at  different  and  distant  points  within  the 
receptive  held.  The  flexion  reflex  of  the  hind-limb,  e.g.,  will 
have  the  same  general  character — i.e.,  flexion  of  each  of  the 
three  main  joints — whatever  part  of  the  surface  of  the  limb  is 
stimulated.  Yet  the  flexion  movement  will  be  strongest  at  the 
joint  whose  flexors  are  innervated  by  motor  cells  situated  in  a 
spinal  segment  near  the  entrance  of  the  afferent  fibres  from  the 
stimulated  skin  area. 

For  the  long  spinal  reflexes  it  is  less  easy  to  deduce  definite 
rules,  for  they  can  be  less  easily  and  constantly  evoked  than  the 
short  reflexes.  The  so-called  laws  of  spread  formulated  by 
Pfluger  for  the  long  spinal  reflexes,  and  based  mainly  on  observa- 
tions made  in  the  brainless  frog  and  on  clinical  records  in  cases 
of  spinal  lesion  in  man,  need  not  be  stated  here.  For  Sherrington 
has  shown  that  they  require  serious  modification.  Especially 
is  this  true  of  Pfliiger's  fourth  law  that  the  reflex  irradiation 
spreads  always  more  easily  up  in  the  direction  of  the  medulla 
oblongata,  so  that  stimulation  of  a  fore-limb  does  not  cause 
reflex  contraction  of  a  hind-limb,  although  excitation  of  a  hind- 
limb  may  cause  movement  of  one  or  both  fore-limbs.  This  law 
does  not  hold  in  the  mammal.  As  a  rule,  indeed,  irradiation 
takes  place  more  easily  down  than  up  the  cord.  Excitation  of 
the  skin  of  the  pinna  easily  causes  reflex  movements  of  the  limbs, 
while  the  reverse  is  rare.  Reflex  movements  of  the  hind-limb 
in  the  spinal  animal  are  more  easily  evoked  by  stimulation  of  the 
fore-limb  than  movements  of  the  fore-limb  by  stimulation  of  the 
hind.  It  is  easier  for  the  irradiation  to  cross  the  cord  from 
hind-limb  to  hind-limb  than  to  pass  up  from  hind-  to  fore-limb  ; 
but  it  is  often  easier  for  irradiation  to  occur  down  the  cord  from 
fore-  to  hind-limb  than  across  the  cord  from  one  fore-limb  to  the 
othei .  Afferent  channels  from  the  skin  of  the  shoulder,  through 
which  the  scratch-reflex  is  discharged  (in  the  dog),  are  freely  con- 
nected with  efferent  paths  to  the  muscles  of  the  hip,  knee,  and  ankle 
by  an  uncrossed  path  descending  the  lateral  column  (Sherrington). 
In  cats,  after  temporary  occlusion  of  the  cerebral  circulation, 
which  throws  the  brain  out  of  gear,  it  is  easy  to  elicit  movements 
of  the  hind-legs  by  pinching  the  fore-paws  or  the  skin  of  the 


////    CENTRA1     VERVOUS  SYST1  M  805 

upper  part  of  the  body.  The  scratch-reflex  can  also  be  very 
readily  evoked,  and  in  great  intensity,  by  stimulating  the  pinna, 
and  is  not  confined  to  the  side  stimulated.  In  anaemia  of  the  brain 
and  (cervical)  cord  and  subsequent  resuscitation,  homolateral 
reflexes  (i.e.,  on  the  same  side  as  the  stimulus)  are  submerged  later 
and  emerge  sooner  than  contralateral  reflexes  whose  centres  lie  in 
the  area  which  was  rendered  an;emic  (Pike,  Guthrie,  and  Stewart). 

Co-ordination  of  Reflexes.  The  co-ordination  or  orderly 
combination  of  muscular  actions  for  the  production  of  appropriate 
and  harmonious  movements  is  one  of  the  most  important 
functions  of  the  central  nervous  system.  Both  the  brain  and  the 
cord  take  a  share  in  this  co-ordination.  The  role  of  the  brain 
will  be  considered  later  on,  but  it  is  essential  to  recognise  now 
that  many  of  the  movements  which  the  brain  directs  represent 
spinal  reflexes  already  synthesized,  compounded,  or  co-ordinated 
in  a  very  high  degree.  This  is  the  reason  why,  in  the  spinal 
animal,  the  inexperienced  observer  may  sometimes  be  startled 
by  the  apparently  '  purposive  character  '  of  a  reflex  movement — 
the  scratch-reflex  in  the  dog  or  cat,  e.g.,  or  the  extensive  reflex 
movements  of  the  hind-legs  of  a  brainless  frog  when  the  skin  is 
pinched  or  painted  with  dilute  acid,  so  plainly  directed  to  the  seat 
of  irritation.  When  a  drop  of  acid  is  applied  to  the  flank  of  such  a 
frog,  it  will  attempt  to  wipe  it  off  with  the  foot  which  is  situated 
most  conveniently.     If  this  foot  be  held,  it  will  use  the  other. 

In  the  combining  of  reflexes  we  may  distinguish  between 
simultaneous  combination — i.e.,  the  combination  of  reflex 
actions  taking  place  at  the  same  time — and  successive  com- 
bination— i.e.,  the  combination  of  reflexes  in  such  a  way  that 
they  follow  each  other  in  an  orderly  sequence.  The  facts  already 
mentioned  in  speaking  of  irradiation  afford  a  partial  explanation 
of  the  co-ordination  of  reflexes  by  simultaneous  combination. 
The  movements  are  orderly  and  harmonious  because  the  spread 
of  the  reflexes  is  not  indiscriminate,  but  follows  a  definite 
'  march,'  determined  partly  by  the  anatomical  relations  of  afferent 
and  efferent  paths,  partly  by  the  varying  resistance  of  the 
synapses  or  other  structures  whose  properties  fix  the  threshold 
value  of  the  excitation  by  which  an  arc  can  be  forced.  In 
general  it  is  not  enough  that  the  channel  of  the  final  common 
paths  (p.  798)  to  the  muscles  whose  contraction  produces  the 
reflex  movement  should  be  thus  open  to  the  afferent  arcs  that 
elicit  the  movement  ;  they  must  be  closed  to  other  afferent  arcs 
which  might  disturb  the  reflex.  Not  only  so  :  there  is  evidence 
that  very  frequently  the  final  common  paths  are,  so  to  say,  more 
widely  opened  to  the  afferent  arcs  in  question  by  the  '  reinforcing  ' 
or  '  facilitating  '  influence  of  allied,  though  it  may  be  distant, 
afferent  arcs,  which  are  simultaneously  excited  (p.  S07).     Further, 


8o6  A    MANUAL  OF  PHYSIOLOGY 

thf  final  common  paths  to  antagonistic  muscles  musl  also  be 
temporarily  closed.  The  closing  of  these  central  connections, 
or  rather  the  raising  of  their  threshold  sufficiently  to  bar  the 

impulses  from  passing  through  the  door,  is  an  inhibitory  pheno- 
menon. Inhibition  and  excitation  go  hand-in-hand  in  the 
simultaneous  combination  of  reflexes. 

The  successive  combination  of  reflexes  is  well  illustrated  by 
the  contraction  of  the  oesophagus  in  deglutition.  First  one 
portion  of  the  tube  and  then  the  next  below  are  involved  in 
the  reflex  action.  The  combination  consists  in  the  orderly 
sequence.  The  manner  in  which  this  is  secured  in  this  class  of 
reflex  actions  has  been  luminously  discussed  by  Sherrington,* 
but  details  cannot  be  given  here.  While  only  allied  reflexes — 
i.e.,  such  as  mutually  reinforce  and  therefore  harmonize  with  each 
other — -can  be  simultaneously  combined,  and  antagonistic 
reflexes  cannot,  both  allied  and  antagonistic  reflexes  can  be 
successively  combined.  An  example  of  the  successive  com- 
bination of  allied  reflexes  is  the  series  of  scratch-reflexes  caused 
by  a  parasite  travelling  across  the  receptive  field  of  the  reflex. 
An  example  of  the  successive  combination  of  antagonistic 
reflexes  is  afforded  when  either  the  scratch-reflex  or  the  flexion 
reflex  is  induced  and  caused  to  interrupt  the  other  while  it  is 
proceeding.  The  transition — e.g.,  from  flexion  to  scratch  reflex 
— is  made  without  any  period  of  confusion.  The  same  holds 
good  for  other  antagonistic  reflexes.  In  many  cases  the  avoidance 
of  confusion  is  due  to  the  inhibition  of  the  first  reflex,  or  often 
to  inhibition  of  the  set  of  muscles  which  were  active  in  the  first 
reflex  combined  with  excitation  of  their  antagonists  (so-called 
interference).  It  is  obvious  that  this  is  an  adaptation  of  great 
importance. 

Influence  of  the  Brain  on  the  Spinal  Reflexes. — The  spinal  roll' 
can  be  influenced  by  impulses  descending  from  the  higher  centres. 
For  (a)  it  is  a  matter  of  common  experience  that  a  reflex  movement 
may  be  to  a  certain  extent  controlled,  or  prevented  altogether  by  an 
effort  of  the  will,  and  it  is  worthy  of  remark  that  only  movements 
which  can  be  voluntarily  produced  can  be  voluntarily  inhibited. 
A  scratching  reflex  in  the  normal  dog  may  be  seen  to  be  modified 
in  character  or  duration  as  compared  with  the  same  reflex  in  the 
spinal  animal.  (/))  An  animal  like  a  frog  responds  to  stimuli  by 
reflex  movements  more  readily  after  the  medulla  oblongata  has  been 
divided  from  the  spinal  cord,  (c)  Long-continued  muscular  con- 
tractions may  be  caused  in  animals  after  removal  of  the  cerebral 
hemispheres  by  stimulation  of  afferent  nerves — for  example,  by 
scratching  the  mucous  membrane  of  the  mouth  in  a  '  brainless  ' 
frog  or  Necturus.  (d)  By  stimulation  of  certain  of  the  higher 
centres  reflex  movements  which  would  otherwise  be  elicited  may  be 
suppressed   or   greatly   delayed.     If  the   cerebral   hemispheres   are 

*  '  Integrative  Action  of  the  Nervous  System,'  to  which  work  the 
advanced  student  is  referred. 


THI    <  ENTR  U.   M.HVOUS  SYSTEM  807 

removed  from  a  frog,  and  one  leg  of  the  animal  dipped  into  dilute 
acid,  a  certain  interval,  the  (uncorrected)  reflex  time,  will  elapse 
before  the  foot  is  drawn  up  (p.  880).  If,  now,  a  crystal  of  common 
Bait  be  applied  to  the  optic  lobes  or  the  upper  part  of  the  spinal  cord, 
and  the  experiment  repeated,  it  will  be  found  either  that  the  interval 
is  much  lengthened  or  that  the  reflex  disappears  altogether.  Strong 
stimulation  of  an  afferent  nerve  may  abolish  or  delay  a  reflex  move- 
ment which  is  being  elicited  through  other  receptors. 

That  the  brain  exerts  more  than  a  merely  inhibitory  influence  on 
the  production  of  reflex  movements  is  suggested  by  many  facts. 
The  knee-jerk,  for  example,  is  increased  or  '  reinforced  '  if  an  instant 
before  the  tendon  is  struck  the  patient  makes  a  voluntary  movement 
or  is  acted  on  by  a  sensory  stimulus  (Bowditch  and  Warren).  In 
health  it  varies  in  strength  with  many  circumstances  which  affect 
the  activity  of  the  central  nervous  system  as  a  whole  (Lom- 
bard, etc.).  It  often  disappears  in  pathological  lesions,  situated 
high  up  in  the  cord  in  man,  and  is  markedly  impaired  after  high 
section  of  the  cord  in  dogs.  In  hemiplegia  (paralysis  of  one  side  of 
the  body,  caused  by  disease  in  the  brain)  the  cutaneous  reflexes 
on  the  paralyzed  side  may  sometimes  be  absent  for  years.  Some 
observers  have  even  gone  so  far  as  to  say  that,  under  normal  con- 
ditions, the  so-called  spinal  reflexes  are  really  cerebral—in  other 
words,  that  the  afferent  impulses  run  up  to  the  brain  and  there 
discharge  efferent  impulses,  which  pass  down  to  the  motor  cells  of 
the  anterior  horn  and  cause  their  discharge.  It  may  be  admitted 
that  there  is  no  physiological  ground  for  supposing  that  the  afferent 
impulses  which  have  to  do  with  the  reflex  contraction  of  the  muscles 
of  the  leg  when  the  sole  is  tickled,  stop  short  at  the  motor  cells  of 
those  spinal  segments  from  which  the  efferent  nerves  come  off,  while 
the  afferent  impulses  which  have  to  do  with  the  sensation  of  tickling 
pass  up  to  the  brain.  The  probability  is  that  under  ordinary 
circumstances  such  afferent  impulses  pass  up  the  cord  in  long  afferent 
paths,  as  well  as  directly  towards  the  motor  cells  along  those  fibres 
of  the  posterior  roots  and  their  collaterals  which  bend  forward  into 
the  anterior  horn  at  the  level  of  their  entrance  into  the  cord.  And 
the  only  question  is  whether,  as  a  matter  of  fact,  the  spinal  motor 
cells  are  most  easily  discharged  by  the  impulses  that  reach  them 
directly,  or  by  the  impulses  that  come  down  to  them  by  the  round- 
about way  of  the  brain  and  the  efferent  fibres  that  connect  it  with 
the  cord.  It  is  evident  that  the  answer  to  this  question  need  not 
be  the  same  for  all  kinds  of  animals.  It  may  well  be  that  in  the 
higher  animals,  in  which  the  cortex  has  undergone  a  relatively  great 
development,  the  spinal  motor  mechanisms  are  more  easily  dis- 
charged from  above  than  from  below,  while  in  lower  animals  the 
opposite  may  be  the  case.  When  the  cord  is  cut  off  from  the  brain,  the 
afferent  impulses  may  overflow  more  easily  into  the  spinal  motor 
cells  since  their  alternative  path  is  blocked.  In  the  frog,  where 
there  is  already  a  beaten  track  between  the  posterior  root-fibres 
and  the  cells  of  the  anterior  horn,  this  overflow  may  be  established 
immediately  after  section  of  the  cord,  and  may  of  itself  lead  to  an 
exaggeration  of  the  reflexes.  In  animals  like  the  dog  a  longer  time 
may  be  necessary  before  the  unaccustomed  route  from  the  end 
arborizations  of  the  afferent  axons  and  their  collaterals  to  the 
dendrites  or  the  bodies  of  the  motor  cells  becomes  natural  and  easy  ; 
in  man  a  still  longer  interval  may  be  required.  Moore  and  Oertel 
have  made  a  careful  comparative  study  of  reflex  action  after  com- 


./    1/  I  \  i    II.  OF  PHYSIOLOG  J 

plete  section  oi  the  cord  in  the  cervical  ot  upper  dorsal  region,  and 
conclude  that  the  spinal  reflexes  in  the  higher  animals  are  Ear  more 

dependent  on  the  upper  portions  ot  tin    eentral  nervous  svstein  than 
in  the  frog. 

The  phenomena  of  spinal  shock  and  its  varying  severity  in 
different  animals  may  be  accounted  for  by  the  rupture  of  the  paths 
normally  used  in  the  reflexes.  The  theory  that  the  shock  is 
due  to  an  inhibition  set  up  by  the  mechanical  injury  is  untenable. 
For  shock  affects  only  the  portion  of  the  central  nervous  system 
distal  (or  aboral)  to  the  lesion.  When  a  dog  is  allowed  to  live  after 
transection  of  the  cord  in  the  lower  cervical  region  till  shock  has 
been  recovered  from,  a  second  transection  distal  to  the  first  is 
followed  by  only  slight  and  very  transient  depression  of  the  reflex 
power,  although  the  direct  effect  of  the  second  injury  ought,  of 
course,  to  be  as  great  as  that  of  the  first.  Finally,  according  to 
Sherrington,  the  condition  of  the  spinal  reflex  arcs  in  shock  differs 
from  th"  condition  caused  by  inhibition,  and  resembles  rather  a 
general  spinal  fatigue  in  which  conduction  along  the  arc  and  especially 
across  the  synapses  is  difficult  and  uncertain.  This  condition  is 
supposed  to  be  due  to  the  loss  of  a  '  tonic  '  influence  of  higher  centres, 
assumed  to  be  necessary  for  the  maintenance  of  the  normal  con- 
ductivity of  the  arc.  These  cranial  centres,  if  they  exist,  or,  at 
least,  the  most  efficient  of  them,  must  be  assumed  to  be  situated 
distal  to  the  cerebral  cortex,  probably  in  the  pons  or  midbrain. 
For  section  just  behind  the  pons  causes  much  more  severe  shock  than 
removal  of  the  cerebral  hemispheres. 

Peripheral  Reflex  Centres. — The  question  whether  any  reflex 
centres  exist  outside  of  the  spinal  cord  and  brain,  and  especially  in 
the  sympathetic  ganglia,  has  been  the  subject  of  a  lengthy  contro- 
versy. That  the  spinal  ganglia  cannot  act  as  reflex  centres  is 
generally  acknowledged,  and  it  is  not  difficult  to  sec  that,  for  ana- 
tomical reasons,  this  must  be  so.  A  reflex  arc  must,  so  far  as  we 
know,  in  all  highly-organized  animals,  include  at  least  two  neurons. 
There  is  no  proof  that  an  afferent  impulse  can  ascend  an  axon  to  a 
cell-body  and  there  excite  an  efferent  impulse,  which,  descending 
the  same  axon  in  a  separate  set  of  fibrils,  gives  rise  to  a  reflex  con- 
traction, or  a  reflex  secretion.  Now.  the  cells  of  a  spinal  ganglion 
represent  the  original  neuroblasts  from  which  the  posterior  root- 
fibres  grew  out  as  processes  towards  the  cord  on  the  one  side  and 
tin  periphery  on  the  other.  A  sensory  fibre  passing  into  the 
ganglion  makes  connection  with  a  cell  by  a  T-shaped  junction  and 
passes  on  its  course  again.  No  afferent  fibres  run  from  the  nerve- 
trunk  into  the  ganglion,  to  end  in  arborizations  around  the  ganglion 
cells,  and  no  efferent  fibres  arise  from  nerve-cells  in  the  ganglion  to 
pass  out  into  the  trunk.  For  although  a  slightly  greater  number  ol 
medullated  fibres  of  small  calibre  is  found  in  a  spinal  nerve-trunk 
immediately  distal  to  the  junction  of  the  roots  than  in  both  roots 
taken  together,  this  appears  to  be  due  to  the  passage  into  the  nerve 
(from  the  grey  ramus  communicans)  of  medullated  fibres  which  end 
in  the  bloodvessels  or  other  tissue  of  the  ganglion  (Dale).  Her< 
it  is  evident  that  there  is  no  possibility  of  a  complete  reflex  arc. 
Indeed,  it  is  not  certain  that  the  normal  afferent  impulses  pass 
through  the  bodies  of  the  spinal  ganglion  cells  at  all.  For 
negative  variation  can  be  observed  in  the  posterior  roots  above 
the  ganglia  on  stimulation  of  the  trunk  of  a  frog's  sciatic  nerve 
more  than  two  days  after  the  death  of  the  animal,  when  the  ganglion 


////    CI  NTR  \l    NERVOUS  SI  SI  I   \l 

cells  may  be  supposed  to  have  completely  losl  their  vitality,  and 
when  no  reflex  negative  variation  can  be  detected  in  the  central 
stump  of  a  severed  anterior  root  on  excitation  of  the  sciatic  or  the 
corresponding  posterior  root.  Such  a  reflex  action  current  is 
normally  obtainable  From  a  fresh  preparation.  (2)  When  the  blood 
supply  of  the  posterior  root-fibres  and  the  ganglion  is  cut  on"  without 
killing  the  frog,  the  nerve  impulse  is  still  conducted  by  the  fibres, 
as  is  shown  by  the  reflex  movements  elicited  on  stimulation  of  the 
central  end  of  the  sciatic,  at  a  time  when  the  nerve-cells  show 
marked  histological  alterations.  (3)  Prolonged  excitation  of  the 
posterior  roots  or  the  mixed  nerve  causes  no  noticeable  microscopical 
changes  in  the  ganglion  cells  (Steinach).*  (4)  The  application  of 
nicotine  to  a  spinal  ganglion  does  not  hinder  the  passage  of  impulses 
through  the  corresponding  afferent  fibres.  If  it  acts  on  spinal 
ganglion  cells  as  it  does  on  sympathetic  ganglion  cells  (p.  165),  this 
must  be  because  the  impulses  do  not  require  to  traverse  the  ganglion. 
Axon-reflexes. — In  the  ordinary  sympathetic  ganglia,f  also,  it  is 
doubtful  whether  the  anatomical  foundation  for  a  reflex  arc  exists, 
and  the  most  careful  physiological  experiments  have  failed  to  con- 
nect them  with  any  reflex  function.  Sokownin,  indeed,  observed 
that  stimulation  of  the  central  end  of  the  hypogastric  nerve  caused 
contractions  of  the  bladder,  and  he  considered  these  movements 
to  be  reflex,  the  centre  being  the  inferior  mesenteric  ganglion. 
Langley  and  Anderson  have  also  found  that  when  all  the  nervous 
connections  of  the  inferior  mesenteric  ganglion,  except  the  hypo- 
gastric nerves,  are  cut,  stimulation  of  the  central  end  of  one  hypo- 
gastric causes  contraction  of  the  bladder,  the  efferent  path  being 
the  other  hypogastric.  In  addition,  they  have  observed  an  apparent 
reflex  excitation  of  the  nerves  which  supply  the  erector  muscles  of 
the  hairs  (pilo-motor  nerves)  through  other  sympathetic  ganglia. 
They  believe,  however,  that  in  neither  case  is  the  action  truly  reflex, 
but  that  it  is  caused  by  stimulation  of  the  central  ends  of  motor 
fibres,  which  come  off  from  the  spinal  cord,  and  in  passing  through 
the  ganglion  give  off  collateral  branches  to  some  of  its  cells. 
In  the  case  of  the  inferior  mesenteric  ganglion  the  spinal  fibres 
passing  down  in  the  left  hypogastric  would  send  branches  to 
arborize  around  ganglion  cells  which  give  origin  to  fibres  of  the 
right  hypogastric,  and  vice  versa.  When  the  central  end  of  the  left 
hypogastric  is  stimulated  the  excitation  is  conducted  up  the  spinal 
fibres,  and  so  reaches  their  branches,  and,  through  the  ganglion 
cells,  the  sympathetic  fibres  of  the  right  hypogastric,  which  convey 
it  to  the  muscles  of  the  bladder  (see  sartorius  or  gracilis  experiment 
of  Kuhne,  p.  688).     Other  examples  of  such  axon-reflexes  exist. 

Reflex  Time. — When  a  reflex  movement  is  evoked,  a 
measurable  period  elapses  between  the  application  of  the 
stimulus  and  the  commencement  of  the  movement.  This 
interval  may  be  called  the  uncorrected  reflex  time  or  the  latent 

*  Hodge  obtained  changes.  In  such  experiments  it  is  necessary  that 
the  ganglion  should  not  be  directly  excited  by  electrotonic  currents  or 
escape  of  the  stimulating  current. 

t  The  ganglion  cells  of  Auerbach's  and  Meissner's  plexus  in  the  intes- 
tine are  not  of  ordinary  sympathetic  type,  and,  as  has  been  previously 
pointed  out,  it  is  probable  that  they,  or  some  of  them,  are  true  reflex 
centres  for  the  stomach  and  intestines. 


810  A   MANUAL  OF  PHYSIOLOGY 

period  of  the  reflex.  A  part  of  the  interval  is  taken  up  in  the 
transmission  <»i  the  afferent  impulse  to  the  reflex  centre,  a  part 
in  the  transmission  of  the  efferent  impulse  to  the  muscles,  a  part 

represents  the  latent  period  of  muscular  contraction,  and  the 
remainder  is  the  time  spent  in  the  centre,  or  the  true  reflex  time. 
Ordinarily  this  time,  though  absolutely  short,  is  relatively  so 

great  that  the  total  latent  period  of  a  reflex  is  much  longer 
than  when  a  similar  length  of  nerve-trunk  is  interposed  between 
the  point  of  application  of  the  stimulus  and  the  muscle.  When 
the  conjunctiva  or  eyelid  is  stimulated  on  one  side  both  eyelids 
blink.  This  is  a  typical  reflex  action  reduced  to  its  simplest 
expression,  and  the  true  reflex  time  is  correspondingly  short — 
only  about  VV  second  (50  a*).  An  additional  ,^jj  second  (10  <r) 
is  consumed  in  the  passage  of  the  afferent  impulse  along  the  fifth 
nerve  to  the  medulla  oblongata,  of  the  efferent  impulse  from  the 
medulla  to  the  orbicularis  palpebrarum  along  the  seventh  nerve. 
and  in  the  latent  period  of  the  muscle.  When  a  naked  nerve, 
like  the  sciatic,  is  stimulated,  the  true  reflex  time  is  reduced  to 
ion  to  -',,  second.  As  estimated  by  Tiirck's  method  (p.  886). 
the  uncorrected  reflex  time  is  greatly  lengthened,  it  may  be  to 
several,  or  even  many,  seconds.  For  here  it  is  evident  that  the 
time  taken  by  the  acid  to  soak  through  the  skin  and  reach  the 
nerve-endings  in  strength  sufficient  to  stimulate  them  is  included. 
But  even  when  the  peripheral  factors  remain  constant,  the  central 
factor  may  vary.  With  strong  stimulation,  e.g..  the  reflex  time 
is  shorter  than  with  weak  stimulation.  With  weak  stimuli  the 
latent  period  of  the  flexion  reflex  in  the  dog  is  usually  60  a  to 
120  o-.  It  may  even  be  as  long  as  200  a .  With  strong  stimuli 
it  may  be  as  little  as  30  a .  Even  22  a  has  been  seen,  which  is 
little  more  than  for  nerve-trunk  conduction.  Fatigue  of  the 
nerve-centres  delays  the  passage  of  impulses  through  them  ;  and 
strychnine,  while  it  increases  the  excitability  of  the  cord,  also 
lengthens  the  reflex  time. 

Reflexes  in  Disease. — In  order  that  a  reflex  action  may  take  place, 
the  reflex  arc — afferent  nerve,  central  mechanism,  and  efferent 
nerve — must  be  complete  ;  and,  in  fact,  a  whole  series  of  simple 
reflex  movements  exists,  the  suppression,  diminution,  or  exaggera- 
tion of  which  can  be  used  in  diagnosis  as  tests  of  the  condition  of 
the  reflex  arc.  It  is  customary  to  divide  these  into  superficial 
reflexes,  elicited  from  receptive  fields  on  the  surface  of  the  body 
{extero-ceptive  fields),  and  deep  reflexes,  elicited  from  receptors  in 
the  depth  of  the  organism  {proprto-ceptive  fields),  especially  in  the 
muscles  and  the  tendons  and  joints  connected  with  them.  The 
extero-ceptive  reflexes  are  normally  excited  by  extraneous  stimuli 
acting  on  the  surface  from  the  environment.  The  proprio-ceptnr 
reflexes  are  normally  excited  by  changes  (muscular  contractions) 
occurring  in  the  body  itself,  which  changes  arc  in  turn  usually 
initiated  by  excitation  of  surface  receptors  by  the  environment. 
*  ff=o'ooi  second. 


Till    CI  NTR  U     V/  RVOUS  SYS1  I  M 


<V 

2 


Examples  of  superfi*  Lai  reflexes  are  the  plantar  reflex  (the  drav 
up  of  ilir  fool  when  the  sole  is  tickled),  the  cremasterit  reflex  (retra< 
t ion  of  the  testicle  when  the  skin  on  the  inside  of  the  thigh  just 
below  Poupart's  ligamenl  is  stroked,  especially  in  boys),  the  gluteal, 
abdominal,  epigastric,  and  interscapular  reflexes  (contraction  of  the 
muscles  in  those  regions  when  the  skin  covering  them  is  tickled). 
The  behaviour  of  the  toes,  especially  of  the  greal  toe,  is  of  consider- 
able  diagnostic    importance.      Normally,   on   tickling  the    SOle,rjthe 
toes  are  flexed  towards  the  plants  . 
but  when  a  lesion  of  the  pyramidal 
tract    exists,     as    in    hemiplegia, 
there  is  dorsal  instead  of  plantar 
ilexion,  most  marked  in  the  case  of 
the  great  toe,  and  the  toe  moves 
more   slowly   than    in   the  healthy 
person   (Babinski's  sign).      In  chil- 
dren during  the  first  few  months 
of    life    stimulation     of    the    sole 
causes  normally  a  dorsal  flexion  of 
the  big  toe.     Examples  of  dee))  re- 
flexes are  the  knee-jerk  (a  sudden 
extension  of  the  leg  by  the  rectus 
femoris  and  vastus  medialis  com- 
ponents of  the  quadriceps  muscle 
when   the    ligamentum  patellae    is 
sharply   struck),    the    heel-jerk    or 
foot-jerk  (a  movement  of  the  foot 
caused    in   most  healthy  persons, 
though    not    in     all,     by    tapping 
the  tendo  Achillis),  and  the  peri- 
osteal  radial   reflex  (a  movement 
of    flexion     and    slight    pronation 
of  the  forearm   and  hand  elicited 
by  tapping  the  lower  end  of  the 
radius).    The  jaw-jerk  (a  movement 
of  the  lower  jaw  when,  with  the 
mouth   open,  the  chin   is  smartly 
tapped)  and  ankle-clonus   (a  series 
of    spasmodic   movements   of    the 
foot,  brought  about  by  flexing  it 
sharply  on  the  leg)  are  phenomena 
of  the   same  class,  which  can  be 
elicited  only  in  disease.     Any  con- 
dition which  impairs  the  conduct- 
ing power  of  the  afferent  or  effer- 
ent fibres  of  the  reflex  arc^ncces- 
sarily  diminishes  or  abolishes  the 
reflex  movement,  even  if  the  cen- 
tral connections  are  intact.     E.g., 
in  locomotor  ataxia  the  disappearance  of  the  knee-jerk  is  one  ot  the 
most  important  diagnostic  signs.     This  disease  involves  the  posterior 
roots  and  the  fibres  that  continue  them  in  the  posterior  column. 
The  anterior  nerve-roots  are  perfectly  healthy.     The  grey  matter 
of    the    cord— at    least,    in    the    earlier   stages    of    the    disease— is 
unaffected.      The    weak   link    in    the   chain    is   the    afferent    path. 
Where  the   presence   of  the  knee-jerk  is  doubtful,  it   is  necessary 


u: 

12. 

L  h 

2  Cremaster 

3 .-- 

.4. 

S. 

5/    t^esict 
2  facicil''. 


'nterscapult* 


Epigastric 


hbdottt'tttal 


Knee-jerk 


Plantar 


Fig.     338. — Diagram    of    Reflux 
Centres  in  Cord  (after  Hill). 


su  ./   .1/  l.\i    II.  OF  PHYSIOLOGY 

to  search  for  the  most  favourable  position  of  the  limb  for  eliciting 
it  before  determining  that  it  is  absent.  The  patient  may  be 
made  to  clasp  his  hands  tightly  at  the  moment  of  the  tap  to 
reinforce  the  jerk  (p.  807).  In  anterior  poliomyelitis  (p.  775)  the 
.liferent  link  is  intact,  but  the  other  two  arc  broken,  and  the 
reflexes  also  disappear.  Certain  lesions  which  partially  cut  off 
the  spinal  cord  from  the  higher  centres  without  affecting  the 
integrity  of  the  spinal  reflex  arcs  increase  the  strength  of  reflex 
movements  and  the  facility  with  which  they  are  called  forth.  In 
primary  spastic  paraplegia  (a  paralysis  of  the  legs  and  tin-  Lower 
portion  of  the  body),  which  is  associated  witli  degenerative  changes 
in  the  lateral  columns,  the  deep  reflexes  are  all  exaggerated.  But, 
according  to  the  best  authorities,  a  lesion  amounting  to  total  tran- 
section of  the  cord  in  man  abolishes  all  reflexes  below  the  lesion. 
In  the  monkey  the  knee-jerk  may  be  tried  for  in  vain  for  weeks  after 
section  of  the  cord  in  the  middle  of  the  thoracic  region,  whereas  in 
the  rabbit  it  can  be  obtained  ten  to  fifteen  minutes  after  the  tran- 
section. The  position  of  the  centres  in  the  cord  for  the  various 
reflex  movements  is  shown  in  Fig.  338. 

3.  The  Origination  of  Impulses  in  the  Spinal  Cord 
(Autonatism). — A  physiological  action  is  termed  automatic 
when  it  depends  upon  a  nervous  outflow  which  seems  to  be 
spontaneous,  in  the  sense  that  it  is  not  brought  about  by  any 
evident  reflex  mechanism,  or,  in  other  words,  is  not  discharged 
by  afferent  impulses  falling  into  the  centre  where  it  arises, 
although  it  may  be  determined  by  substances  in  the  blood.  An 
action  known  to  be  caused  01  conditioned  by  such  afferent 
impulses  is  called  a  reflex  action.  Automatic  actions  being 
thus  defined  in  a  negative  manner  by  the  defect  of  a  quality, 
there  is  always  a  possibility  that  some  day  or  other  it  may  be 
demonstrated  that  any  given  action  which  at  present  seems 
automatic  in  its  origin  depends  on  afferent  impulses  hitherto 
unnoticed.  As  a  matter  of  fact,  the  supposed  proofs  of  spinal 
automatism  have  in  more  than  one  case  vanished  with  the 
advance  of  knowledge,  and  as  the  domain  of  purely  automatic 
action  has  been  narrowed,  that  of  reflex  action  has  ex- 
tended, until  the  controversy  as  to  the  boundaries  between  the 
two  seems  not  unlikely  to  be  ended  by  the  absorption  of  the 
automatic  in  the  reflex.  And  as  we  seem  almost  driven  to  con- 
clude that  from  the  anatomical  standpoint  the  nervous  system 
is  essentially  a  vast  collection  of  looped  conducting  paths,  each 
with  an  afferent  portion,  an  efferent  portion,  and  connections 
between  them  formed  by  the  end  arborizations  of  the  axons  and 
their  collaterals,  the  dendrites  and  the  cell-bodies,  so  it  may 
be  that  no  strict  physiological  automatism  really  exists  either 
in  cord  or  brain,  that  every  form  of  physiological  activity — 
muscular  movement,  secretion,  intellectual  labour,  conscious- 
ness itself — would  cease  if  all  afferent  impulses  were  cut  ofl 
from    the   nervous   centres.      Assuredly   no    neuron    is   entirely 


THE  CENTR  II     VERVOUS  SYSTE  M  Ri  \ 

isolated  from  other  neurons.  The  more  the  nervous  system  is 
investigated,  the  deeper  grows  the  conviction  of  its  essential 
solidarity,  the  more  clearly  it  displays  itself  as  a  single  mechanism. 
the  most  distanl  parts  of  which  are  intricately  knit  together. 
But  there  are  certain  groups  of  actions  so  widely  separated  from 
the  most  typical  reflex  actions  that,  provisionally  at  least,  they 
may  be  distinguished  as  automatic.  Such  are  the  voluntary 
movements,  and  certain  involuntary  movements,  like  the  beat 
of  the  heart.  And  we  may  proceed  to  inquire  whether  the  spinal 
cord  has  any  power  of  originating  movements  or  other  actions  of 
this  high  degree  of  automatism. 

Muscular  Tone. — So  long  as  a  muscle  is  connected  with 
the  spinal  segment  from  which  its  nerves  arise,  it  is  never  com- 
pletely relaxed  ;  its  fibres  are  in  a  condition  of  slight  tonic  con- 
traction, and  retract  when  cut.  If  a  frog  whose  brain  has 
been  destroyed  is  suspended  so  that  the  legs  hang  down,  and  one 
sciatic  nerve  is  cut,  the  corresponding  limb  may  be  observed 
to  elongate  a  little  as  compared  with  the  other.  At  one  time 
this  tone  of  the  muscles  was  supposed  to  be  due  to  the  con- 
tinual automatic  discharge  of  feeble  impulses  from  the  grey 
matter  of  the  cord  along  the  motor  nerves.  But  it  has  been 
proved  that  if  the  posterior  roots  be  cut,  or  the  skin  removed 
from  the  leg,  its  tone  is  completely  lost,  although  the  anterior 
roots  are  intact.  So  that  the  tone  of  the  skeletal  muscles 
depends  on  the  passage  of  afferent  impulses  to  the  cord,  and 
must  be  removed  from  the  group  of  automatic  actions  and 
included  in  the  reflexes. 

The  '  rigidity  '  of  the  muscles,  often  observed  in  paralysis 
from  lesions  of  the  central  system,  and  denominated  '  early  ' 
or  '  late  '  according  as  it  comes  on  within  a  few  days  or  a  few 
weeks  after  the  occurrence  of  the  lesion,  is  also  probably  in  part, 
at  least,  a  reflex  phenomenon,  although,  perhaps,  possessing 
some  of  the  characters  of  a  tonic  contraction  due  to  automatic 
discharge  from  the  spinal  centres.  For  in  such  cases  '  myotatic 
irritability  '  is  increased  ;  the  knee-jerk  is  exaggerated  ;  a  finger- 
jerk  may  be  elicited  by  tapping  the  wrist,  an  arm-jerk  by  striking 
the  skin  over  the  insertion  of  the  biceps  or  triceps,  ankle-clonus 
by  flexing  the  foot  (Gowers) .  Now,  myotatic  irritability  depends 
on  reflex  muscular  tone  (p.  802). 

It  is  probable  that  the  tone  of  such  visceral  muscles  as  the 
sphincters  of  the  anus  and  bladder  has  also  a  reflex  element, 
and  possible  that  the  same  is  true  of  the  tone  of  the  smooth 
muscular  fibres  of  the  bloodvessels  on  which  the  maintenance 
of  the  mean  blood- pressure  so  largely  depends  (p.  169). 

Trophic  Tone.  —  The  degenerative  changes  that  occur  in 
muscles,  nerves,  and  other  tissues  when  their  connection  with 


8 14  '     W  -1.VUAL  OF  PHYSIOLOGY 

the  central  nervous  system  is  interrupted  have  been  already 
referred  to  (p.  699).  It  is  possible  to  explain  these  changes 
in  some  cases  without  the  assumption  that  tonic  impulses  are 
constantly  passing  out  from  the  brain  and  cord  to  control  the 
nutrition  of  the  peripheral  organs  ;  and  we  have  seen  that  there 
is  no  real  evidence  of  the  existence  of  specific  trophic  fibres. 
But  the  degeneration  of  muscles  after  section  of  their  motor 
nerves  is  difficult  to  understand  except  on  the  hypothesis  that 
impulses  from  the  cells  of  the  anterior  horn  influence  their 
nutrition.  The  only  question  is  whether  these  are  the  impulses 
to  which  muscular  tone  is  due,  and  therefore  reflex,  or  different 
in  nature  and  automatically  discharged.  Now,  degeneration 
of  a  muscle  is  not  usually  caused,  or  at  least  not  for  a  long  time, 
by  interruption  of  its  afferent  nerve-fibres,  as  in  locomotor 
ataxia,  or  after  section  of  the  posterior  nerve-roots  (Mott  and 
Sherrington).  We  can  hardly  suppose  that  in  any  case  the 
trophic  influence  of  the  cells  of  the  spinal  or  sympathetic  ganglia 
to  which  all  other  reflex  powers  have  been  denied,  is  of  reflex 
nature.  And  there  is,  indeed,  more  evidence  in  favour  of  trophic 
tone  being  an  automatic  action  of  the  cord  than  for  any  of  the 
other  tonic  functions  hitherto  considered. 

The  evidence  for  respiratory  automatism  upon  which  the  spinal 
cord  has  been  chiefly  credited  with  true  automatic  action  has 
previously  been  given  (p.  233). 

The  '  Centres '  of  the  Cord  and  Bulb. — We  have  frequently  used 
the  word  '  centre  '  in  describing  the  functions  of  the  spinal  cord, 
but  the  term,  although  a  convenient  one,  is  apt  to  convey  the  idea 
that  our  knowledge  is  far  more  minute  and  precise  than  it  really 
is.  When  we  say  that  a  centre  for  a  given  physiological  action 
exists  in  a  definite  portion  of  the  spinal  cord,  all  that  is  meant  is 
that  the  action  can  be  called  out  experimentally,  or  can  normally 
go  on,  so  long  as  this  portion  of  the  cord  and  the  nerves  coming  to 
it  and  leaving  it  are  intact,  and  that  destruction  of  the  '  centre  ' 
abolishes  the  action.  For  example,  a  part  of  the  medulla  oblongata 
on  each  side  of  the  middle  line  in  the  floor  of  the  fourth  ventricle 
above  the  calamus  scriptorius  is  so  related  to  the  function  of  respira- 
tion that  when  it  is  destroyed  the  animal  ceases  to  breathe.  But 
this  respiratory  centre — the  '  nceud  vital  '  of  Flourens — does  not 
correspond  in  position  with  any  definite  collection  of  grey  matter, 
although  it  includes  the  nuclei  of  origin  of  several  cranial  nerves, 
and  forms  an  important  point  of  departure  for  efferent,  and  of  arrival 
for  afferent,  fibres  connected  with  the  respiratory  act.  Its  destruc- 
tion involves  the  cutting  off  of  the  impulses  constantly  travelling 
up  the  vagus  to  modify  the  respiratory  rhythm,  and  of  the  impulses 
constantly  passing  down  the  cord  to  the  phrenics  and  the  inter- 
costal nerves.  And  just  as  the  traffic  of  a  wide  region  can  be 
paralyzed  at  a  single  blow  by  severing  the  lines  in  the  neighbourhood 
of  a  great  railway  junction,  or  more  laboriously,  though  not  less 
effectually,  by  separate  section  of  the  same  tracks  at  a  radius  of  a 
hundred  miles,  so  destruction  of  the  respiratory  centre  accomplishes 


////    CENTRA1    NERVOUS  SYSTEM  815 

by  a  Single  puncturi'  what  can  be  also  performed  by  section  of  all 
the  respiratory  nerves  at  a  distance  from  the  medulla  oblongata. 
But  while  nobody  speaks  of  the  destruction  of  a  '  centre  '  win  n  a 
reflex  action  is  abolished  by  division  of  the  peripheral  nerves  con- 
cerned in  it,  there  is  ;i  tendency,  when  the  same  effect  is  brought 
about  by  a  lesion  in  the  brain  or  cord,  to  invoke  that  mysterious 
name,  and  to  forget  that  the  cercbro-spinal  axis  is  at  least  as  much 
a  stretch  of  conducting  paths  as  a  collection  of  discharging  nervous 
mechanisms. 

It  is,  perhaps,  a  profitless  task  to  enumerate  all  the  so-called 
centres  in  the  bulb  and  cord  with  which  the  perverse  ingenuity  of 
investigators  and  systematic  writers  has  encumbered  the  archives 
and  text-books  of  physiology.  In  addition  to  the  great  vaso-motor, 
respiratory,  cardio-inhibitory  and  cardio-augmentor  centres  in  the 
bulb,  which,  perhaps,  have  more  right  than  the  rest  to  be  regarded 
as  distinct  physiological  mechanisms,  if  not  as  definitely  bounded 
anatomical  areas,  there  had  been  distinguished  ano-spinal,  vesico- 
spinal, and  genito-spinal  centres  in  the  lumbar  cord,  a  cilio-spinal 
centre  for  dilatation  of  the  pupil  in  the  cervical  cord,  and  in  the 
medulla  centres  for  sneezing,  for  coughing,  for  sweating,  for  sucking, 
for  masticating,  for  swallowing,  for  salivating,  for  vomiting,  for  the 
production  of  general  convulsions,  for  closure  of  the  eyes,  for  the 
secretion  of  tears,  and  even  a  '  diabetes  '  or  '  sugar  '  centre  (p.  518). 
It  would  be  just  as  correct,  and  more  practically  useful  (for  it  would 
perhaps  encourage  the  student  who  has  lost  his  way  amidst  these 
interminable  distinctions),  to  say  that  the  cerebral  cortex  contains 
a  centre  for  learning  sense,  and  another  for  forgetting  nonsense, 
and  that  in  a  healthy  brain  it  is  the  latter  which  is  generally  thrown 
into  activity  in  the  study  of  a  list  like  this. 


The  Cranial  Nerves. 

Unlike  the  spinal  nerves,  which  arise  at  not  very  unequal 
intervals  from  the  cord,  the  nuclei  of  the  cranial  nerves,  with 
the  exception  of  the  olfactory  and  optic,  are  crowded  together 
in  the  inch  or  two  of  grey  matter  of  the  primitive  neural  axis 
in  the  immediate  neighbourhood  of  the  fourth  ventricle  and 
the  Sylvian  aqueduct.  Of  these  nuclei  some  are  the  end  nuclei 
or  '  nuclei  of  reception  '  of  sensory  fibres — that  is  to  say,  collec- 
tions of  nerve-cells  around  which  the  sensory  fibres  break  up 
into  terminal  arborizations.  Such  are  the  sensory  nuclei  of  the 
fifth,  the  nuclei  of  the  eighth,  and  the  sensory  nuclei  of  the 
glossopharyngeal  and  vagus  nerves  (Figs.  339,  340).  The  nuclei 
of  origin  of  the  motor  fibres  lie,  upon  the  whole,  in  two  longi- 
tudinal rows — a  median  row,  which  consists  of  the  nuclei  of 
the  third  and  fourth  nerves  in  the  floor  of  the  aqueduct,  and 
those  of  the  sixth  and  twelfth  nerves  in  the  floor  of  the  fourth 
ventricle  ;  and  a  lateral  row  comprising  the  motor  nuclei  of 
the  fifth,  seventh,  tenth,  and  eleventh  nerves.  The  clumps  of 
grey  matter  which  make  up  these  nuclei  may  be  considered  as 
homologous  with  the  grey  matter  of  the  ventral  or  anterior 


3i6 


/    .1/  INU  U    OF  PHYSTOLOG  I 


(including  the  lateral)  horn  of  the  spinal  cord  ;  and  the  motor 
fibres  of  the  nerves  themselves  as  homologous  with  the  anterior 
spinal  roots.  Without  going  further  into  the  thorny  subject 
of  the  homologies  ol  the  cranial  and  spinal  nerves,  we  may 
point  out  thai  while  all  the  spinal  nerves  contain  both  efferent 
and  afferent  fibres,  some  of  the  cranial  nerves  are  purely 
efferent,  some  purely  afferent,  and  others  mixed.  So  that  il 
we  are  to  look  upon  the  motor  nerves  as  the  homologues  ol  the 
ventral   roots,  the  dorsal   (posterior)   rool  fibres  corresponding 

to  them  musl  be 
represented  in  the 
other  cranial  nerves. 
Thus,  the  sensory 
portion  of  the  mixed 
fifth  nerve,  and  the 
purely  afferent  audi- 
tory nerve,  must  be 
supposed  to  contain 
fibres  corresponding 
to  several  dorsal 
roots. 

The  first  or  olfactory 
nerve  consists  of  fine 
fibres,  each  of  which 
is  a  process  of  an 
olfactory  cell  (Fig. 
341).  The  olfactory 
cells,  which  arc  really 
peripheral  nerve-cells, 
lie  among  the  epithe- 
lial cells  in  the  olfac- 
tory region  of  the 
Schneidcrian  mem- 
brane, the  common 
lining  of  the  nostrils. 
Each  olfactory  cell 
gives  off  two  pro- 
cesses, a  short  one, 
representing  a  dendrite,  which  runs  out  to  the  surface  of  the 
mucous  membrane,  and  a  longer  but  more  slender  process,  repre- 
senting an  axon,  which  as  a  fibre  of  the  olfactory  nerve  pierces  the 
cribriform  plate  of  the  ethmoid  bone,  and  plunges  into  the  olfactory 
bulb. 

In  the  olfactory  bulb  at  least  four  layers  can  be  distinguished  - 
(i)  on  the  surface,  beneath  the  pia  mater,  the  layer  of  entering 
olfactory  nerve-fibres;  (2)  the  layer  of  olfactory  glomeruli,  peculiar 
structures,  each  of  which  is  made  up  of  an  intricate  basket-like 
arborization  formed  by  an  olfactory  nerve-fibre,  or,  it  may  be,  more 
than  one,  and  a  brush-like  arborization  belonging  to  a  dendrite  ol 
one  o!  the  mitral  cells  of  the  next  layer  ;  (3)  the  molecular  or  mitral 
layer,  which  contains  a  number  of  large  nerve-cells  called,  from  their 


Fir..  339.— Nuclei  of  Cranial  Nerves  (Toldt). 
Motor  red,  sensory  blue.     The  numbers  correspond 
to  the  cranial  nerves. 


THE  CENTR  \l     VERVOUS  SYSTEM 


mosl  common  shape,  mitral  cells,  along  with  smaller  nerve-cells 
('granules')  and  neuroglia;  (4)  the  nuclear  layer,  containing 
numerous  small  nerve-cefis  or  'granules'  intermingled  with  white 
fibres.  The  mitral  cells  give  off  axons,  which  pass  through  the 
fourth  layer,  and  then  as  fibres  of  the  olfactory  tract  to  the  grey 
matter  of  the  hippocampal  region  of  the  brain.  The  course  of  the 
impulses  from  the  olfactory  mucous  membrane  to  the  brain  is 
shown  in  Fig.  341.  The  olfactory  tract,  as  it  runs  back,  divides 
into  portions  called  its   '  roots.'     Of  these  the  lateral  is  the  most 


Fig.   340. — Nuclei  and   Roots  of  Cranial  Nerves  (Toldt). 
Lateral  view.     Motor  red,  sensory  blue. 

important,  and  it  terminates  in  the  hippocampal  and  uncinate 
gyri  of  the  same  side.  Fibres  of  the  olfactory  tract  are  also  con- 
nected either  directly  or  through  the  relay  of  another  neuron  with 
the  opposite  side  of  the  brain,  especially  the  opposite  uncinate  gyrus. 
The  anterior  commissure  contains  numerous  fibres,  which  connect 
the  hippocampal  regions  of  the  two  sides.  Other  central  connections 
of  the  olfactory  tract  exist,  but  some  are  imperfectly  known.  The 
name  '  rhinencephalon  '  is  given  to  the  portions  of  the  brain  con- 
cerned with  the  sense  of  smell.    Disturbances  of  smell  sensation  may 

52 


8i8 


A    1/  /  \r  If    OF  PHYSIOLOGY 


be  caused  by  lesions  in  any  pari  of  the  rhinencephalon,  and  also  by 
changes  in  the  olfactory  mucous  membrane  and  olfactory  fibres; 
but  the  symptoms  do  nol  obtrude  themselves,  and  are  doubtless 
often  overlooked.  Excessive  stimulation  of  the  olfactory  nerve  by 
exposure  to  a  strong  odour  has  been  said  to  cause  complete  and 
permanent  loss  of  smell. 

The  second  or  optic  nerve  contains  mainly  afferent  fibres,  which 
arise  from  the  ganglion  cells  of  the  retina,  and  terminate  by  forming 
synapses  with  nerve-eells  in  the  lateral  or  external  geniculate  body, 
the  pulvinar  (or  posterior  portion)  of  the  optic  thalamus,  and  the 
anterior  corpus  quadrigeminum.  In  young  animals  all  these 
structures  undergo  atrophy  after  extirpation  of  the  eyeball.  The 
visual  path  is  continued  from  the  pulvinar  and  the  external  corpus 
geniculatum  by  the  axons  of  these  nerve-cells,   which  proceed   in 


Fie.   341. — Scheme  of  the  Olfactory  Nervous  Apparatus  (Halli- 
burton,   AFTER   C'AJAL). 

A,  olfactory  cells;  B,  glomeruli;  C,  mitral  cells;  I>,  olfactory  granule  cell; 
E,  lateral  root  of  olfactory  tract  ;  F,  cortex  of  brain  in  the  region  of  the  urn  inate 
gyrus  ;  a,  small  cell  of  mitral  layer  ;  b,  brush  of  dendrite  of  a  mitral  cell  ending  in 
a  glomerulus  ;  c,  thorns  or  spines  on  the  processes  of  an  olfactory  granule  ; 
e,  collateral  coming  off  from  the  axon  of  a  mitral  cell  ;  /,  collaterals  ending  in  the 
molecular  layer  of  the  uncinate  gyrus  ;  g,  pyramidal  cells  of  the  cortex  :  '/.  sup- 
porting epithelial  cells  of  the  olfactory  mucous  membrane. 


the  optic  radiation  (p.  785)  to  the  occipital  cortex.  The  fibres  which 
pass  from  the  retina  to  the  anterior  corpus  quadrigeminum  are 
distinguished  by  their  small  size,  and  probably  constitute  the  path 
of  the  impulses  which  cause  contraction  of  the  pupil  when  light 
falls  on  the  retina.  The  reflex  arc  is  schematically  shown  in  Fig.  342, 
where  optic  nerve-fibres  are  represented  as  forming  synapses  with 
cells  in  the  anterior  corpus  quadrigeminum  whose  axons  pass  to 
the  nucleus  of  the  third  nerve  and  arborize  around  some  of  its  cells 
(Figs.  326,  331,  and  355).  At  the  chiasma  the  fibres  of  the  optic 
nerve  decussate,  partially  in  man  and  some  mammals,  as  the  rabbit, 
dog,  cat,  and  monkey,  completely  in  animals  whose  visual  field  is 
entirely  independent  for  the  two  eyes,  as  in  fishes  and  birds.  In 
man  the  fibres  tor  the  nasal  halves  of  both  retinae  cross  the  middle 
line  at  the  chiasma.  those  for  the  temporal  hakes  do  not.  Tins 
does  not  mean,  however,  that  exactly  half  of  the  optic  .nerve-fibres 


I  III    i  I  VTRA1    NERVOUS  SYS7  I  1/ 


decussate.  The  number  <>i  uncrossed  fibres  is  smaller  than  thai  oi 
crossed.  The  chiasma  also  contains  fibres  in  its  posterior  portion, 
which  extend  from  one  optic  trad  to  the  other,  but  arc  not  con- 
nected with  the  retinae  or  the  opti<  nerves.  They  are  commissural 
fibres  which  connect  the  two  mesial  geniculate  bodies  across  the 
middle  line,  and  are  called  Gudden's  commissure.  A  sufficiently 
extensive  lesion  involving  the  occipital  cortex  on  one  side,  or  the 
post  trior  portion  of  the  optic  thalamus,  or  the  optic  tract,  causes 
hemianopia*  or  defect  oi  tin-  visual  field  on  the  side  opposite  to  the 
lesion,  with  blindness  of  the  corresponding  halves  of  the  two  retinae. 
Thus,  a  lesion  equivalent  to  complete  section  of  the  right  optic  tract 
would  cause  blindness  of  the 

nasal  half  of  the  left,  and  of  te  ..      .  -J 

the  temporal  hall  of  the 
right  eye,  and  the  left  half 
of  the  field  of  vision  would 
be  blotted  out — the  patient 
would  be  unable,  with  his 
eyes  directed  forwards,  to 
see  an  object  at  his  left. 
Such  a  complete  hemianopia 
is  much  rarer  in  disease  of 
the  cortex  than  in  disease 
of  the  optic  tract.  A  lesion 
— e.g.,  a  tumour  of  the  pitui- 
tary body  —  involving  the 
whole  of  the  optic  nerve  in 
front  of  the  chiasma,  would 
cause  complete  blindness 
in  the  corresponding  eye. 
Sometimes  in  disease  of  the 
optic  nerve  vision  is  not 
totally  destroyed  in  the  eye 
to  which  it  belongs,  but  the 
field  is  narrowed  by  a  cir- 
cumference of  blindness.  In 
this  case  the  pathological 
change  involves  the  cir- 
cumferential fibres  of  the 
nerve.  When  the  chiasma 
is  affected  by  disease,  a  very 
frequent  symptom  is  bitem- 
poral hemianopia,  blindness 
of  the  nasal  halves  of  the 
retinae,  with  loss  of  the  outer  or  temporal  half  of  each  field  of 
vision.  The  optic  nerve  and  tract  contain  a  few  efferent  fibres  for 
the  retina,  whose  cell-bodies  have  not  yet  been  certainly  located. 

The  third  nerve,  or  oculo-motor,  arises  from  an  elongated  nucleus, 
or  a  series  of  nuclei,  containing  large  nerve-cells  in  the  floor  of  the 
Sylvian  aqueduct  below  the  anterior  corpora  quadrigemina.  The 
root-bundles  coming  off  from  the  most  anterior  of  the  nuclei  carrv 
fibres  that  innervate  the  ciliary  muscle,  and  thus  have  to  do  with 

*  The  terms  '  hemiopia,'  '  hemianopia,'  '  hemianopsia,'  are  used  with 
reference  sometimes  to  the  blind  side  of  the  retinae,  but  ordinarily  to  the 
half  of  the  visual  field  which  is  deficient.  We  shall  always  use  the  word 
'  hemianopia  '  in  the  latter  sense. 

52—2 


III  Nerve 


Fig.  342. — Scheme  of  the  Visual  Path 
(Halliburton,  after  Schafer). 


820  /    v  /  vr  \l    OF  PHYSIOLOGY 

the  mechanism  ol  accommodation,  and  also  fibres  thai  innervate 
the  sphincter  muscle  of  the  iris,  and  thus  cause  contraction  of  the 
pupil  when  light  falls  on  the  retina.  Both  groups  of  fibres  ter- 
minate by  arborescing  around  sympathetic  cells  in  the  ciliary 
ganglion,  from  which  the  path  to  the  (unstriated)  ciliary  and 
sphincter  muscles  is  continued  by  post-ganglionic  fibres.  Further 
back  in  the  oculo-motor  nucleus  arise  the  motor  fibres  for  four  of  the 
extrinsic  muscles  of  the  eyeball  and  the  elevator  of  the  upper  eyelid. 
In  the  dog  these  fibres  come  off  in  the  following  order,  from  before 
backwards  :  internal  rectus,  superior  rectus,  levator  palpebral 
SUperioris,  inferior  rectus,  inferior  oblique.  Most  of  the  fibres  of  the 
third  nerve  arise  from  nerve-cells  on  their  own  side  of  the  middle  line, 
but  a  certain  number  decussate  to  enter  the  nerve  of  the  opposite 
side.  Complete  paralysis  of  the  third  nerve  causes  loss  of  the  power 
of  accommodation  of  the  corresponding  eye,  dilatation  of  the  pupil 
by  the  unopposed  action  of  the  sympathetic  fibres,  diminution  of  the 
power  of  moving  the  eyeball,  ptosis,  or  drooping  of  the  upper  lid. 
external  squint,  and  consequent  diplopia,  or  double  vision. 

The  fourth  or  trochlear  nerve  arises  from  the  posterior  part  of  the 
same  tract  of  grey  matter  which  gives  origin  to  the  third  nerve. 
It  supplies  the  superior  oblique  muscle.  Paralysis  of  the  nerve  causes 
internal  squint  when  an  object  below  the  horizontal  plane  is  looked 
at,  owing  to  the  unopposed  action  of  the  inferior  rectus.  There  is 
also  diplopia  on  looking  down.  Unlike  the  other  cranial  nerves,  the 
two  trochlear  nerves  decussate  completely  after  they  emerge  from 
their  nuclei  of  origin. 

The  fifth  or  trigeminus  nerve  appears  on  the  surface  of  the  pons 
as  a  large  sensory  root  and  a  smaller  motor  root.  Its  deep  origin 
is  more  extensive  than  that  of  any  of  the  other  cerebral  nerves, 
stretching  as  it  does  from  the  level  of  the  anterior  corpus  quadri- 
geminum  above  to  the  upper  part  of  the  spinal  cord  below.  Its 
sensory  root,  in  fact,  seems  to  include  the  sensory  divisions  of  several 
motor  cranial  nerves. 

The  motor  root  arises  partly  from  a  nucleus  (principal  motor 
nucleus)  in  the  floor  of  the  fourth  ventricle  below  the  pons,  partly 
from  large  round  nerve-cells  lying  at  the  side  of  the  grey  matter 
bounding  the  aqueduct  of  Sylvius  all  the  way  from  the  anterior 
quadrigeminate  body  to  the  point  at  which  the  motor  root  is  given 
off  (accessory  or  superior  motor  nucleus). 

The  fibres  of  the  sensory  root  have  their  cells  of  origin  in  the  Gas- 
serian  ganglion,  whence  they  pass  into  the  pons.  Here  they 
bifurcate  into  ascending  and  descending  branches.  The  ascending 
branches  end  in  the  principal  sensory  nucleus,  a  collection  of  grcv 
matter  at  the  side  of  the  principal  motor  nucleus.  The  descending 
branches,  turning  downwards  into  the  medulla  oblongata,  terminate 
in  a  long  tract  of  scattered  cells,  constituting  with  the  fibres  the 
so-called  spinal  root,  and  extending  from  the  level  of  the  second 
cervical  nerve  through  the  medulla  oblongata  and  the  pons,  where 
it  is  continued  into  the  principal  sensory  nucleus.  The  afferent 
path  is  continued  by  the  axons  of  cells  of  the  sensory  nuclei  (or 
nuclei  of  reception)  of  the  nerve,  many  of  which  cross  the  middle 
line  and  enter  the  intermediate  fillet  of  the  opposite  side,  and  also 
the  special  ascending  bundle  going  to  the  thalamus.  Some  of  the 
axons  do  not  decussate,  but  ascend  in  the  fillet  of  the  same  side. 

The  motor  fibres  of  the  fifth  nerve  supply  the  muscles  of  mastica- 
tion and  the  tensor  tympani.     The^sensory  fibres  confer  common 


THE  CI  \  //.'//    Sl-liVOUS  SYST1-M 


821 


Bensation  on  the  face,  conjunctiva,  the  mucous  membranes  of  the 
mouth  and  nose,  and  the  structures  contained  111  them,  and,  accord- 
ing t<>  Gowers,  special  sensation,  through  branches  given  off  to  the 
facial  and  glosso-pharyngeal  aerves,  on  the  organs  of  taste.*  Com- 
plete  paralysis  of  the  nerve  causes  loss  of  movement  in  the  muscles 
of  mastication,  sometimes  impaired  hearing,  and  loss  of  common 
sensation  in  the  area,  supplied  by  it.  Loss 
or  impairment  of  taste  in  the  correspond- 
ing half  of  the  tongue  is  also  often  seen 
m  disease  involving  the  sensory  root, 
although  not  in  affections  of  the  trunk 
of  the  nerve,  since  the  taste  fibres  leave 
it  near  its  origin  (Gowers) .  Both  taste  and 
touch  are  lost  in   the  monkey  in  the  an- 


Nu.m.pr.n.V. 


TV.  sp.  n.  V. 


Fig.  343. — Scheme  of  Motor  and  Sensory  Neurons  of  Trigeminus 
(Gehuchten). 

G.  s.  G.,  Gasserian  ganglion  ;  Nu.  m.  m.  n.  V.,  nucleus  of  the  descending  rout  ; 
\u.  m.  pr.  n.  V.,  chief  motor  nucleus  of  the  fifth  nerve;  Rod.  desc.  mes.  n.  V., 
accessory  motor  nucleus,  sometimes  called  the  descending  root  ;  Tr.  s/>.  n.  V., 
tractus  spinalis,  or  spinal  root  of  the  fifth. 

terior   two-thirds  of  the  tongue  after  intracranial  section  of  the 
trigeminus  (Sherrington). 

Vaso-motor  changes  are  occasionally,  and  '  trophic  '  changes 
frequently,   observed   in   disease   of  the  fifth  nerve.     The  trophic 

*  It  should  be  stated  that  some  physiologists  believe  that  the  glosso- 
pharyngeal is  the  nerve  of  taste,  and  that  none  of  the  taste  fibres  go  to 
the  sensory  nuclei  of  the  fifth  nerve.  The  majority  hold  that  the  glosso- 
pharyngeal supplies  the  posterior  third,  and  the  chorda  tympani  and 
lingual  the  anterior  two-thirds  of  the  tongue  with  gustatory  fibres.  The 
removal  of  the  Gasserian  ganglion  and  the  adjacent  portion  of  the  fifth 
nerve  for  severe  and  persistent  neuralgia,  has  afforded  opportunities  to 
test  this  question.  But,  unfortunately,  the  results  described  by  various 
observers  do  not  agree,  some  finding  that  taste  is  unimpaired,  others  that  it 
is  abolished.  Gowers  states  that  the  gustatory  sensations  may  persist  for 
some  time  after  the  operation,  although  ultimately  (in  two  or  three  weeks) 
they  disappear.  It  may  be,  however,  that  this  disappearance  is  due  to  secon- 
dary changes  produced  in  the  end-organs  of  the  true  taste  fibres,  the  taste 
buds,  by  degeneration  of  the  supporting  cells  consequent  on  section  of  the 


/   M  !  '•  I    //.  OF   PHYSIOLOGY 

disturbance  is  mo  I  conspicuous  in  the  eyeball  (ulceration  of  the 
<  orn  on,  it  may  be,  to  i  omplete  disorganization  of  the  eye). 

The-  ire  partly  du  ■  to  the  loss  of  sensation  in  the  i  ye,  and  the 

•  <  I  in  nt  risk  of  damage  from  without,  and  the  unregarded  pres 
of  foreign  bodies  and  accumulation  of  a  ivithin  the  lid 

The  sixth  or  abducens  nerve  takes  origin  from  a  nucleus  in  the 
floor  of  the  fourth  ventricle  at  the  level  of  the  posterior  portion  of 
the  pons.     It  is  a  purely  efferent  aerve,  and  supplies  the  external 

is  muscle  of  the  eyeball.  Paralysis  of  it  causes  internal  squint. 
The  motor  fibres  of  the  seventh  or  facial  nerve  arise  from  a  nucleus 
in  the  reticular  formation  of  th<  medulla  oblongata,  and  running  up 
some  distance  into  t  he  pons.  They  supply  the  muscles  of  the  face  ;  and 
when  these  are  greatly  developed,  as  in  the  trunk  of  the  elephant, 
very  large  proportions.  Since  the  fibres  which 
conned  the  cerebral  cortex  with  the  nucleus  decussate  about  the 
middle  of  the  pons,  a  lesion  above  this  level  which  causes  hemiplegia 
paralyzes  the  face  on  the  same  side  as  the  rest  of  the  body  u ..  on 
the  side  opposite  the  lesion.  But  the  paralysis  is  confined  to  the 
muscles  of  the  lower  portion  of  the  face,  and  aft'  ially  the 

muscles  about  the  mouth.  Sometimes  the  pyramidal  tract  and  the 
facial  nerve,  or  nucleus,  are  involved  in  a  common  lesion.  In  this 
paralysis  of  the  face  is  on  the  side  of  the  lesion,  and  is  total, 
while  the  rest  of  the  body  is  paralyzed  on  the  opposite  side.  Paralysis 
of  the  seventh  nerve  is  more  common  than  that  of  any  other  n 
in  the  bod  v.  It  is  often  caused  by  an  inflammatory  process  in  the 
nerve  itself  (neuritis).     Thi  >ms  of  complete  facial  palsy  are 

very  characteristic.  The  face  and  forehead  on  the  paralyzed  side 
are  smooth,  motionless,  and  devoid  of  expression.  The  eye  re- 
mains open  even  in  sleep,  owing  to  paralysis  of  the  orbicularis 
palpebrarum.  A  smile  becomes  a  grimace.  An  attempt  to  wink 
with  both  eyes  results  in  a  grotesque  contortion.  The  mouth 
appears  like  a  diagonal  slit  in  the  face,  its  angle  being  drawn  up  on 
the  sound  side,  and  the  patient  cannot  bring  the  lips  sufficiently 
i  lose  togel  her  to  be  able  to  blow  out  a  candle  or  to  whistle.     Liquids 

pe  from  the  mouth,  and  food  collects  between  the  paralyzed 
bue<  inator  and  the  teeth.  The  labial  consonants  are  not  properly 
pronounced.  I   in  the  anterior  two-thirds  01  the 

tongue  when  the  nerve  is  injured  above  the  exit  of  the  gustatory 
fibres  in  the  chorda  tympani,  but  not  when  the  lesion  is  in  the 
nucleus  of  origin,  or  anywhere  above  it  I  baring  is  sometimes 
impaired  because  the  auditory  and  facial  nerves.  King  close  together 
for  part  of  their  course,  are  apt  to  suffer  together,  but  perhaps  also 
because  the  stapedius  muscle  is  supplied  by  the  seventh. 

nth  nerve  i->  not  purely  motor,  from  the  cells  of  a  ganglion 
on  it  corresponding  to  a  spinal  ganglion  (the  geniculate  ganglion) 
afferent  fibres  arise,  which  pass  in  the  pars  intermedia  or  nerve  of 
Wrisberg  into  the  pons  between  the  seventh  and  eighth  nerves,  and 
there  bifurcate  into  ascending  and  descending  branches,  like  other 
afferent  fibres  originating  in  ganglia  of  the  spinal  type.  The  descending 
bran'  hes  enter  the  fast  ic  ulus  solitarius,  and  end  by  arborizing  around 

trigeminus,  or  to  degeneration  and  swelling  of  the  trigeminal  fibres  n)  the 
ungual  nerve  and  consequenl  interference  with  the  conductivity  ol 
intermingled  chorda  tympani  fibres.  Gushing  believes  that  the  fifth  nerve 
supplies  no  taste  fibres,  but  that  the  taste  fibre-,  for  the  anterior  two- 
thirds  of  the  tongue  have  their  cells  of  origin  in  the  geniculate  ganglion 
ol  the  pars  intermedia  ol  the  seventh  nerve,  an'l  those  for  the  posterior 
third  in  the  ganglion  petrosum  of  the  ninth  nerve. 


THE  CENTRAL  NERVOUS  SYSTEM 


823 


nerve-cells  in  the  upper  part  of  that  bundle  The  peripheral  axons 
oi  the  nerve-cells  in  the  geniculate  ganglion  enter  the  large  super- 
ficial petrosal  nerve  and  the  chorda  tympani,  in  which  they,  or 
some  of  them,  perhaps  represent  taste  fibres. 

The  eighth  or  auditory  nerve  enters  the  medulla  oblongata  by  two 
roots  (a  dorsal  and  a  ventral),  one  of  which  passes  in  on  each  side 
of  the  restiform  body.  The  cells  of  origin,  both  of  the  dorsal  and 
of  the  ventral  root,  arc  situated  in  the  internal  car,  the  former  in 
the  ganglion  spirale,  or  ganglion  of  Corti,  which  is  embedded  in  the 
bony  spiral  of  the  cochlea,  the  latter  in  the  ganglion  vestibulare, 
or  ganglion  of  Scarpa,  which  lies  in  the  vestibule.  These  cells 
correspond   to  the  ganglion  cells  on  the  posterior  root  of  a  spinal 


V1I1 


Fig.   344. — Scheme  of  Path  of  Auditory  Impulses  (Lewandowsky), 

Sp.  ganglion  spirale  ;  G,  accessory  nucleus  ;  T,  acoustic  tubercle  ;  Tr,  trapezium  ; 
H,  Hold's  fibres  ;  St,  striae  acustica?  ;  tr,  trapezoid  nucleus  ;  Os,  upper  olive  ; 
LI,  lateral  fillet,  with  its  nucleus,  11L ;  P,  commissure  of  the  lateral  fillets  :  Qp,  pos- 
terior corpora  quadrigemina  ;  with  Cq,  their  commissure,  and  Bq,  the  brachia  ; 
Gm,  mesial  or  internal  geniculate  body  ;   R,  cerebral  cortex. 


nerve,  but,  unlike  them,  they  remain,  even  in  mammals,  bipolar 
throughout  life.  Their  central  processes  form  the  axons  of  the 
eighth  nerve.  Their  peripheral  processes  are  distributed  in  the  case 
of  the  dorsal  root  to  the  organ  of  Corti,  in  the  case  of  the  ventral 
root  to  the  semicircular  canals  and  the  vestibule.  For  this  reason 
the  dorsal  root  is  often  called  the  cochlear  division,  and  the  ventral 
root  the  vestibular  division  of  the  auditory  nerve.  And  the  cochlear 
and  vestibular  roots  are  physiologically  as  well  as  anatomically 
distinct.  For  (p.  958)  the  cochlea  subserves  the  function  of 
hearing,  the  semicircular  canals  and  vestibule  the  function  of 
equilibration.  As  they  enter  the  medulla  oblongata,  the  fibres  of 
the  dorsal  root  bifurcate.     Of  the  two  branches,  one  is  considerably 


824  A   MANUAL  OF  PHYSIOLOGY 

thicker  than  the  other.  Many  of  the  thicker  branches  terminate 
by  arborizing  around  the  cells  of  the  accessory  auditory  nucleus, 
whose  position  is  indicated  by  a  swelling  on  the  ventral  surface  of 
the  restiform  body  at  the  junction  of  the  dorsal  and  ventral  roots  ; 
but  some  pass  over  the  restiform  body  to  end  in  another  nucleus 
(lateral  nucleus),  alsc  indicated  by  a  swelling  (tuberculum  acusticum) 
lying  over  the  restiform  body.  The  nerve-cells  of  the  accessory 
nucleus  and  the  acoustic  tubercle,  therefore,  constitute  nuclei  of 
rei  eption  for  the  dorsal  root-fibres.  The  more  slender  branches 
of  the  cochlear  root-fibres  run  downwards  for  some  distance  before 
breaking  up  into  fibrils. 

The  path  to  the  high  parts  of  the  brain  is  continued  by  the  axons 
of  nerve-cells  in  the  accessory  nucleus  and  the  acoustic  tubercle. 
The  fibres  from  the  accessory  nucleus  pass  into  the  trapezium,  a 
mass  of  transverse  fibres  lying  in  the  pons  behind  the  pyramidal 
fibres.  In  their  course  through  the  trapezium  some  of  the  fibres 
terminate  around  the  cells  of  the  nucleus  of  the  trapezium,  others 
run  into  the  superior  olive  of  the  same  side,  and  end  there  ;  but 
most  of  them  cross  the  middle  line,  and  enter  the  trapezoid  nucleus 
and  superior  olive  of  the  opposite  side,  where  many  of  them  ter- 
minate. Others,  however,  run  through  those  nuclei  and  pass  into 
the  lateral  fillet,  to  end  in  its  nucleus  or  in  the  posterior  corpora 
quadrigemina.  The  path  of  the  fibres  which  terminate  in  the  nuclei 
of  the  trapezium,  superior  olive,  and  lateral  fillet,  is  continued  by 
another  relay  of  fibres,  which  link  them  also  to  the  posterior  corpora 
quadrigemina.  The  axons  of  the  cells  of  the  acoustic  tubercle 
enter  for  the  most  part  the  strice  acusticce,  a  series  of  prominent 
strands  that  run  transversely  across  the  floor  of  the  fourth  ventricle. 
Passing  across  the  raphe,  they  join  the  fibres  from  the  accessory 
nucleus  on  their  way  to  the  superior  olive,  and  accompany  them  into 
the  lateral  fillet,  which  terminates  in  the  grey  matter  of  the  posterior 
corpus  quadrigeminum.  We  must  assume,  from  clinical  and 
experimental  data,  that  the  dorsal  root  is  ultimately  connected  with 
the  first,  or  first  and  second  temporo-sphenoidal  convolutions  on 
the  opposite  side.  From  the  posterior  corpora  quadrigemina  the 
auditory  path  to  the  convolutions  seems  to  run  in  the  brachium  to 
the  internal  or  mesial  geniculate  body,  whence  it  is  continued  in 
the  posterior  extremity  of  the  internal  capsule. 

The  fibres  of  the  ventral  root  of  the  eighth  nerve,  better  termed  the 
vestibular  nerve,  after  entering  the  medulla  oblongata,  pass  to  a 
nucleus  called  the  principal  nucleus  of  the  vestibular  division. 
Here  each  bifurcates  into  a  descending  and  an  ascending  branch. 
The  descending  branches  running  down  in  the  medulla  terminate 
at  different  levels  around  cells  in  the  principal  nucleus,  and  the  grey 
matter  continued  down  from  it  {descending  vestibular  nucleus). 
The  ascending  branches  run  up  on  the  inner  side  of  the  restiform 
body  towards  the  nucleus  of  the  roof  {nucleus  tecti)  in  the  cerebellar 
worm.  On  their  course  they  enter  into  relation  through  their  col- 
laterals with  the  nuclei  of  Deiters  and  Bechterew.  The  nucleus 
of  Deiters,  as  already  stated,  sends  fibres  into  the  posterior  longi- 
tudinal bundles.  Through  ascending  branches  of  these  fibres  a 
communication  is  established  with  the  nuclei  of  the  third  and  sixth 
nerves,  and  through  descending  branches  that  pass  into  the  antero- 
lateral descending  tract  of  the  cord  with  the  anterior  horn  cells. 
It  is  obvious  that  through  these  connections  which  link  the  vestibule 
with  the  cerebellum,  the  nuclei  of  the  motor  nerves  of  the  eyeball 
and   the   motor   cells  of  the   cord,  the  nucleus  of   Deiters   has  an 


THE  CENTRAL  NERVOUS  SYSTI   \1  K25 

important  relation  to  the  co-ordination  of  those  movements  mainly 
concerned  in  equilibration.  Nothing  is  known  of  the  connections 
of  the  vestibular  nerve  with  the  cerebrum.  Two  prominent  symp- 
toms may  be  associated  with  disease  of  the  auditory  nerve — (a)  dis- 
turban.ee  or  loss  of  hearing  ;  (/;)  loss  or  impairment  of  equilibration. 

The  ninth  or  glosso-pharyngeal  nerve  comprises  both  sensory  and 
motor  fibres — sensory  for  the  posterior  third  of  the  tongue  and  the 
mucous  membrane  of  the  back  of  the  mouth,  motor  for  the  middle 
constrictor  of  the  pharynx  and  the  stylo-pharyngeus.  It  also 
contains  the  nerves  of  taste  for  the  posterior  third  of  the  tongue. 
The  efferent  fibres  arise  from  a  nucleus  (motor  nucleus  of  the  glosso- 
pharyngeal) a  little  posterior  to  the  facial  nucleus.  The  afferent 
fibres  take  origin  from  unipolar  cells  in  ganglia  of  spinal  type  con- 
nected with  the  nerve  (ganglion  petrosum  and  ganglion  superius). 
Entering  the  medulla  oblongata,  the  central  processes  of  these  cells 
bifurcate  into  ascending  and  descending  branches.  Their  peripheral 
processes  pursue  their  course  as  the  axons  of  sensory  fibres  to  the 
structures  to  which  the  nerve  is  distributed.  The  ascending 
branches  terminate  in  a  nucleus  {principal  nucleus  of  the  glosso- 
pharyngeal) beneath  the  floor  of  the  fourth  ventricle.  The  descend- 
ing branches,  as  well  as  similar  branches  from  the  pars  intermedia 
of  the  seventh  nerve  and  from  the  afferent  fibres  of  the  vagus,  form 
a  bundle  called  the  fasciculus  solitarius  (sometimes  termed  the 
descending  root  of  the  facial,  vagus,  and  glosso-pharyngeal) .  It  can 
be  traced  to  the  lower  boundary  of  the  spinal  bulb.  Along  the 
mesial  border  of  the  fasciculus  solitarius  are  strung  out  the  some- 
what scattered  fierve-cells  (descending  nucleus  of  facial,  vagus,  and 
glosso-pharyngeal),  around  which  the  descending  branches  arborize. 
At  its  upper  end  the  grey  matter  of  the  fasciculus  solitarius  is  con- 
tinuous with  the  principal  nuclei  of  the  glosso-pharyngeal  and  vagus. 

The  tenth  nerve,  or  vagus,  also  contains  both  motor  and  sensory 
fibres.  The  efferent  fibres  arise  partly  from  the  nucleus  ambiguus 
or  ventral  nucleus  of  the  vagus,  a  collection  of  large  nerve-cells 
situated  in  the  reticular  formation,  and  extending  from  a  point 
a  little  below  the  facial  nucleus  to  a  point  a  little  above  the  lower 
limit  of  the  medulla  oblongata,  where  it  becomes  continuous  with 
the  column  of  cells  from  which  the  spinal  fibres  of  the  eleventh  nerve 
take  origin.  A  second  nucleus  of  origin  for  efferent  vagus  fibres  is 
constituted  by  the  upper  part  of  the  dorsal  accessory-vagus  nucleus, 
a  collection  of  rather  small  cells  extending  from  a  little  below  the 
lower  margin  of  the  pons  to  nearly  the  level  of  the  first  cervical  nerve. 

The  afferent  fibres  of  the  vagus  arise  from  unipolar  cells  in  ganglia 
connected  with  the  nerve  (ganglion  jugulare,  ganglion  nodosum). 
In  the  medulla  oblongata  they  bifurcate,  like  other  fibres  coming 
off  from  the  cells  of  ganglia  of  spinal  type.  The  ascending  branches, 
winch  are  short,  terminate  in  the  upper  sensory  or  principal  nucleus, 
and  the  descending  branches,  which  are  long,  in  the  cells  of  the 
fasciculus  solitarius,  just  as  in  the  case  of  the  glosso-pharyngeus. 

The  motor  fibres  of  the  vagus  are  partly  derived  from  the  accessory, 
whose  internal  branch  joins  the  vagus  not  far  from  its  origin.  The 
distribution  of  the  nerve  is  more  extensive  than  that  of  any  other  in 
the  body.  The  oesophagus  receives  both  motor  and  sensory  branches 
from  the  oesophageal  plexus.  The  pharyngeal  branch  of  the  vagus 
is  the  chief  motor  nerve  of  the  pharynx  and  soft  palate  (including 
the  tensor  palati).  The  superior  laryngeal  branch  is  the  nerve  of 
common  sensation  for  the  larynx  above  the  vocal  cords,  and  the 
motor  nerve  of  the  crico-thyriod  muscle.     The  inferior  or  recurrent 


826  A   MANUAL  OF  PHYSIOLOGY 

laryngeal  supplies  the  rest  of  the  laryngeal  muscles,  and  the  sensory 
fibres  for  the  mucous  membrane  of  the  trachea  and  the  larynx  below 
the  glottis.      The  superior  laryngeal  contains  afferent  fibres,  stimula- 
tion of  which  gives  rise  to  coughing,  slows  respiration,  or  stops  it 
in    expiration.      Reflex   movements  of  deglutition   are  also  caused. 
I  he  vagus  supplies  the  lung  both  with  motor  and  sensory  filaments 
through  the  pulmonary  plexus.     The  motor  fibres  when  stimulated 
cause  constriction  of  the  bronchi  ;  excitation  of  the  afferent  fibres 
causes    reflex   changes   in   the   rate    or    depth    of    respiration.     The 
cardiac  branches  contain   inhibitory  fibres  probably  derived   from 
the  spinal  accessory,  and  depressor  fibres  which  pass  up  in  the  vagus 
trunk  (dog),  or  as  a  separate  nerve  to  join  the  vagus  or  its  superior 
laryngeal    branch    or    both    (rabbit).     The    gastric    and    intestinal 
branches  contain  both  motor  and  sensory  nerves  for  the  stomach 
and  intestines.     The  sensory  are  probably  large  medullated  fibres 
(7  /1  to  0  /<).     The  afferent  vagus  fibres  from  the  stomach  carry  up 
impulses  which  excite  the  action  of  vomiting.     Lesions  of  the  vagus, 
its    nuclei    of   origin,    or    its   branches,    are    associated    with    many 
interesting  forms  of  paralysis  and  other  symptoms.     Paralysis  of 
the  pharynx  is  generally  caused  by  disease  of  the  nucleus  in  the 
medulla.     From  its  anatomical  relation  to  the  nuclei  of  the  glosso- 
pharyngeal and  hypoglossal,  it  will  be  easily  understood  that  these 
nerves  are  often  involved  in  localized  central  lesions  along  with  the 
vagus.     But  the  fact  that  in  progressive  bulbar  palsy  (glosso-labio- 
laryngeal     paralysis) — a     condition     characterized     by     progressive 
paralysis  and  atrophy  of  the  muscles  of  the  tongue",   lips,  larynx, 
and  pharynx — the  orbicularis  oris  and  other  muscles  of  the  mouth 
and  chin  are  paralyzed,  while  the  rest  of  the  muscles  supplied  by 
the   facial   remain   intact,   might  seem  to   indicate  that   in   system 
diseases  it  is  not  so  much  anatomical  groups  of  nerve-cells  which  are 
liable   to   simultaneous   degeneration    and    failure,    as   physiological 
groups  normally  associated  in  particular  functions.     Such  functional 
groups  of  cells,  occupied  with  the  same  kinds  of  labour  at  the  same 
times  and  under  the  same  conditions,  might  be  supposed  to  take  on 
a  similar  bias  or  tendency  to  degeneration — a  tendency  not  indi- 
cated, it  may  be,  by  any  structural  peculiarity,  but  traced  deep  in 
the  molecular  activity  of  the  cells.     There  is  no  foundation  for  the 
view  that  the  lips  arc  involved  in  progressive  bulbar  palsy  because 
the  fibres  of  the  facial  which  supply  them  arise  from  the  hypo- 
glossal nucleus,  any  more  than  for  the  idea  that   the   upper   part 
of  the   face   escapes   because    its    motor    fibres,    while   reaching   it 
in    the   seventh   nerve,    really   arise   from   the   oculo-motor  nucleus 
(Bruce).     Difficulty  in  swallowing  is  the  chief  symptom  of  pharyn- 
geal  paralysis.     The   symptoms   of  laryngeal  paralysis   have   been 
already    described    under    '  Voice  '     (p.    286).     Tachycardia,    or    a 
permanent  increase  in  the  rate  of  the  heart,  has  been  stated  to  occur 
in   certain   cases   of  paralysis  of  the   vagus,   caused   by   disease  or 
accidental  interference  ;  and  a  persistent  slowing  of  the  respiration 
has    been    occasionally   attributed   to   the   same    cause.     But    it    is 
difficult  to  reconcile  many  of  these  cases  with  experimental  results, 
for  in  most  of  them  the  lesion  only  involved  one  vagus  ;  and  in 
animals  section  of  one  vagus  has  no  permanent  effect  on  the  rate 
of  the  heart  or  of  the  respiratory  movements. 

Destruction  of  the  nerve  near  its  origin  has  been  sometimes  found 
associated  with  disappearance  of  the  food-appetites,  hunger  and 
thirst,  and  it  has  been  assumed  that  this  was  due  to  loss  of  afferent 


////    CENTRAL  NERVOUS  SYSTEM  827 

impulses  from  the  stomach.  But  clinical  testimony  is  by  no  means 
unanimous  on  this  point,  and  experiments  on  animals  show  that 
other  factors  arc  involved  in  these  sensations. 

The  eleventh  or  spinal-accessory  nerve  contains  only  efferent 
fibres.  The  cells  of  origin  of  its  spinal  portion  lie  in  the  lateral 
horn  of  the  cord,  from  about  the  level  of  the  first  to  the  fifth  or 
sixth  cervical  nerves.  The  bulbar  portion,  sometimes  called  the 
bulbar  accessory,  arises  from  the  lower  two-thirds  of  the  dorsal 
accessory-vagus  nucleus,  from  about  the  level  of  the  first  cervical 
nerve  up  to  the  level  of  the  tip  of  the  calamus  scriptorius.  The 
accessory  portion  of  the  nucleus  lies  behind  and  to  the  side  of — i.e., 
dorso-lateral  to — the  central  canal  ;  the  upper  or  vagus  portion  is 
more  laterally  placed  in  the  floor  of  the  fourth  ventricle.  Soon  after 
the  junction  of  its  bulbar  and  spinal  portions,  the  nerve  divides  into 
two  branches,  an  internal  and  an  external.  The  external  branch, 
containing  the  spinal  fibres,  passes  out  to  supply  the  trapezius  and 
sterno-mastoid  muscles  with  motor  fibres.  The  internal  branch, 
containing  the  bulbar  fibres,  passes  bodily  into  the  vagus. 

The  twelfth  or  hypoglossal  nerve  is  exclusively  an  efferent  nerve. 
Its  nucleus  of  origin  is  an  elongated  collection  of  large  nerve-cells 
extending  throughout  approximately  the  lower  two-thirds  of  the  bulb 
close  to  the  median  line  and  parallel  to  it.  It  contains  the  motor 
supply  of  the  intrinsic  and  extrinsic  muscles  of  the  tongue  and  of  the 
thyro-  and  genio-hyoid.  Paralysis  of  it  causes  deficient  movement 
of  the  corresponding  half  of  the  tongue.  When  the  tongue  is  put 
out,  it  deviates  towards  the  paralyzed  side,  being  pushed  over  by 
the  unparalyzed  genio-hyoglossus  of  the  opposite  side,  which  is 
thrown  into  action  in  protruding  the  tongue. 


The  Functions  of  the  Brain. 

The  paths  by  which  the  various  parts  of  the  central  nervous 
system  are  connected  with  each  other  and  with  the  periphery 
have  been  already  described,  and  we  have  completed  the  ex- 
amination of  the  functions  of  the  spinal  cord  and  medulla 
oblongata.  The  events  that  take  place  in  the  upper  part  of 
the  central  nervous  stem  and  in  the  cortex  of  the  cerebellum 
and  cerebrum  now  claim  our  attention. 

From  very  early  times  the  brain  has  been  popularly  believed  to 
be  the  seat  of  all  that  we  mean  by  consciousness — sensation,  ideation, 
emotion,  volition.  And  he  who  loves  to  trace  the  roots  of  things 
back  into  the  past  may  see,  if  he  choose,  running  through  the  whole 
texture  of  the  older  speculations  a  belief  that  the  brain  does  not 
act  as  a  whole,  but  is  divided  into  mechanisms,  each  with  its  special 
work — a  foreshadowing,  often  in  grotesque  outlines,  of  the  doctrine 
of  localization  so  widely  held  to-day.  But  until  comparatively 
recent  times,  cerebral  physiology  remained  a  kind  of  scientific 
terra  incognita  ;  and  no  notable  additions  were  made  for  a  thousand 
years  to  the  doctrines  of  Galen.  Even  to-day  the  utmost  limit  of 
our  knowledge  is  reached  when  in  certain  cases  we  have  connected 
a  particular  movement  or  sensation  with  a  more  or  less  sharply- 
defined  anatomical  area.  How  the  cerebral  processes  that  lead  to 
sensations  and  movements,  to  emotions  and  intellectual  acts,  arise 


/    MANUAL  OF  PHYSIOLOGY 


and  die  out  ;  what  molecular  changes  are  associated  with  them  ; 
above  all,  how  the  molecular  changes  are  translated  into  conscious- 
ness— how,  for  example,  it  is  that  a  series  of  nerve-impulses  from 
the  optic  radiation  flickering  across  the  labyrinth  of  the  occipital 
cortex  should  lighi  up  there  a  visual  sensation — these  are  questions 
to  which  we  can  as  yet  give  no  answer,  and  the  answers  to  some  of 
which  must  for  ever  remain  hidden  from  us. 

Functions  of  the  Upper  Part  of  the  Central  Stem  and  Basal 
Ganglia. — The  function  of  the  pons  is  sufficiently  indicated  by  its 
name.  The  grey  matter  so  plentifully  scattered,  especially  in  its 
ventral  portion,  may  exercise  a  not  unimportant  influence  on  the 
impulses  that  traverse  it.  But  on  the  whole  its  main  office  is  to 
provide  a  bridge  along  which  impulses  may  travel  between  other 
portions  of  the  nervous  system.  We  have  already  seen  that  many 
of  its  transverse  fibres  arising  from  the  cells  of  the  pontine  grey 


Corpus  striatum 

Anterior  pillar  of 
the  fornix 

Optic  thalamus 

-■  Third  ventricle 


Fig.  345- 


-Horizontal  Section  through  Brain  to  show  the  Basal  Ganglia 
and  Third  Ventricle  (Human). 


matter,  and  then  crossing  the  middle  line  to  the  opposite  middle 
peduncle,  are  the  cerebellar  segments  of  commissural  arcs  connecting 
the  cerebral  with  the  opposite  cerebellar  hemispheres.  The  cerebral 
segments  of  these  arcs  are  the  cortico-pontine  fibres  originating 
in  the  prefrontal,  temporal,  and  occipital  portions  of  the  cerebral 
cortex,  and  passing  through  the  corona  radiata,  internal  capsule, 
and  crura  cerebri,  to  end  in  the  nuclei  pontis.  Many  fibres  and 
collaterals  of  the  pyramidal  tract  also  terminate  here.  On  the  dorsal 
aspect  of  the  pons  in  the  floor  of  the  fourth  ventricle  are  the  nuclei 
of  origin  (or  reception)  of  the  fifth,  sixth,  and  seventh  cranial 
nerves.  Various  reflex  centres  arc  situated  in  this  region — e.g.,  that 
for  the  closure  of  the  eyelids,  when  the  conjunctiva  is  stimulated. 

The  posterior  corpora  quadrigemina  and  internal  geniculate  bodies 
are  connected  with  the  cochlear  division  of  the  auditory  nerves,  and 
form  important  stations  on  the  auditory  path  to  the  cortex. 


I  III    CENTRAl    NERVOUS  SYSTEM  829 

The  anterior  corpora  quadrigemina  and  the  lateral  corpora  genii  ulata 
are  connected  with  the  optic  tracts.  Their  development  is  arrested 
after  extirpation  of  the  eyeball  in  young  animals,  and  they  may 
therefore  be  assumed  to  be  concerned  in  vision,  although  the  size 
of  their  homologies,  the  optic  lobes  or  corpora  bigemina,  in  animals 
below  the  rank  of  mammals  (birds,  reptiles,  amphibians),  does  not  seem 
to  be  related  to  the  development  of  the  organs  of  sight.  Proteus 
and  the  Hag-fish,  e.g.,  have  large  optic  lobes,  rudimentary  eyes  and 
optic  tracts.  The  optic  nerve,  the  anterior  corpus  quadrigeminum,  the 
nucleus  of  the  oculo-motor  nerve  in  the  wall  of  the  Sylvian  aqueduct, 
and  the  fibres  which  it  carries  to  the  iris,  form  a  reflex  arc  for  the 
contraction  of  the  pupil  to  light,  as  represented  in  Fig.  342,  p.  819. 

The  functions  of  the  optic  thalami  have  not  been  fully  defined 
either  by  experiment  or  pathological  observation,  except  so  far  as 
they  can  be  deduced  from  their  connections.  Lying  as  they  do  in 
the  isthmus  of  the  brain,  begirt  by  the  great  motor  and  sensory 
paths,  it  is  to  be  expected  that  lesions  of  the  thalami  should  affect 
also  the  internal  capsule,  and  give  rise  to  the  symptoms  of  motor 
and  sensory  paralysis.  But  it  is  questionable  whether  any  definite 
defect  of  motor  power  or  common  sensation  has  ever  been  unequivo- 
cally associated  with  a  lesion  restricted  to  the  thalami.  The  most 
constant  features  of  the  so-called  thalamic  syndrome  (or  symptom - 
complex)  are  partial  loss  of  sensibility,  especially  to  tactile  impres- 
sions, and  of  the  muscular  sense  on  the  opposite  side,  with  some  degree 
of  inco-ordination  and  disorder,  though  little,  if  any,  actual  paralysis 
of  voluntary  movements.  These  phenomena  are  accounted  for  by 
the  extensive  connections  of  the  thalami.  Each  of  the  thalamic 
nuclei  is  linked  with  a  definite  cortical  region  in  such  a  way  that 
destruction  of  the  cortical  area  in  young  animals  or  human  beings 
leads  to  degeneration  of  the  corresponding  nucleus.  Some  of  the 
fibres  connecting  the  cortex  (and  the  corpus  striatum)  with  the 
thalamus  end  in  the  thalamic  grey  matter,  and  are  therefore  efferent 
with  respect  to  the  cortex  (corticofugal) .  It  is,  however,  the  afferent 
paths  to  the  cortex  with  which  the  thalami  are  specially  related 
as  centres  of  relay.  The  fibres  of  the  upper  fillet  carrying  afferent 
impulses  up  from  the  opposite  posterior  column  of  the  cord  to  the 
cerebrum  end  in  the  grey  matter  of  the  thalamus,  as  does  the 
central  path  of  the  afferent  fibres  of  the  opposite  fifth  nerve.  The 
posterior  portion  of  the  thalamus,  or  pulvinar,  forms  part  of  the 
central  visual  apparatus  ;  for  (a)  it  is  found  to  be  undeveloped  in 
animals  from  which  the  eyeballs  have  been  removed  soon  after 
birth  ;  (b)  a  portion  of  the  optic  tract  is  certainly  connected  with  it  ; 
(c)  in  some  cases  of  atrophy  of  the  occipital  cortex,  which,  as  we 
shall  see,  is  undoubtedly  a  central  area  for  visual  sensations,  atrophy 
of  the  pulvinar  has  also  been  noticed  ;  (d)  a  lesion  of  the  pulvinar 
may  give  rise  to  hemianopia  (p.  819). 

Haemorrhage  into  the  caudate  or  lenticular  nucleus  of  the  corpus 
striatum  often  causes  hemiplegia,  but  this  is  frequently  due  to  implica- 
tion of  the  internal  capsule.  It  is  said,  however,  that  lesions  presumably 
confined  to  the  lenticular  nucleus  cause  paralysis  or  paresis  of  the 
limbs  or  face,  which  is  less  severe  than  that  produced  by  lesions  in 
the  internal  capsule.  Experimental  lesions  in  dogs  and  rabbits 
are  stated  to  be  followed  by  disturbances  of  the  heat-regulating 
mechanism  and  rise  of  temperature. 

Certain  structures  belonging  to  the  primary  fore-brain  which  have 
now  lost  some  or  all  of  their  functional  importance,  may  neverthe- 


3  JO 


A    MANUAL  OF  PHYSIOLOGY 


less  be  mentioned  as  milestones  in  the  march  of  development.  The 
pineal  body  is  made  up  of  the  vestiges  of  the  unpaired  mesial  eye  of 
such  animals  as  the  ancient  labyrinthodonts.  which  resembled  the 
eye  of  invertebrates  in  having  the  retinal  rods  directed  towards 
the  cavity  instead  of  towards  the  circumference  of  the  eyeball.  In 
many  living  forms,  especially  in  certain  lizards,  this  pineal  or 
parietal  eye  is  found  in  a  more  perfect  condition,  though  covered 
bv  a  thin  membrane.  The  ganglia  habennlce,  two  small  collections 
of  nerve-cells,  one  of  which  is  situated  at  the  posterior  part  of  each 
thalamus,  are  supposed  by  some  authorities  to  represent  the  optic 

ganglia  of  this  cyclopcan  eye. 
They  are  less  prominent  in 
man  than  in  many  of  the 
lower  animals.  The  infundi- 
balnm  is  probably  what  re- 
mains of  the  gullet  of  the 
ancestors  of  the  vertebrates. 
The  pituitary  body  is  in  a 
different  category.  It  is  now 
known  that,  far  from  being 
a  useless  vestigial  remnant, 
it  has  a  highly  important 
function  (p.  566).  It  con- 
sists of  two  portions,  the 
anterior  lobe,  or  hypophysis, 
derived  from  the  buccal 
cavity,  the  posterior  lobe, 
or  infundibular  body,  from 
the  primary  fore-brain. 

Functions  of  the  Cere- 
bellum. —  The     elaborate 
pattern  of  the  arbor  vitae, 
the   appearance   given    by 
the  branched  laminae  in  a 
section  of  the  cerebellum, 
excited  the  speculation  of 
the     old    anatomists.      A 
so     marvellous 
matched,    they 
with     functions 
At    a    time 


structure 
must     be 
thought, 
as     unique 


Fig.   346. — Cerebellar    Cortex  :    Section 
in  Direction  of  Lamina  (Cajal). 

a,  Purkinje's  cell  ;  b,  granule  cell  in  inner 
layer  ;  c,  dendrite  of  a  granule  cell  ;  d,  axon 
of  a  granule  passing  into  the  molecular 
layer,  where  it  bifurcates  into  two  fine 
longitudinal  branches  (Golgi's  method). 

when  the  discoveries  of 
Galvani  and  Yolta  were  fresh,  and  the  world  ran  mad  on 
electricity,  the  hypothesis  of  Rolando,  that  '  nerve-force  ' 
was  generated  by  the  lamellae  of  the  cerebellum  as  electrical 
energy  is  generated  by  the  plates  of  the  voltaic  pile,  ridiculous 
as  it  now  appears,  was  not  unnatural.  The  speculation  of  Gall, 
who  connected  the  cerebellum  with  the  development  of  sexual 
emotions  and  the  action  of  the  generative  mechanisms,  was 
based  on  no  fact.  It  has  been  definitely  disproved  by  the 
observations   of    Luciani,  who  found  that  a  bitch  deprived  of 


////    CI  XI  R  II    NERVOUS  SYS1  I  M 


831 


its  cerebellum  showed  all  the  phenomena  of  heat  or  '  rut,'  was 
impregnated,  whelped  at  lull  term  in  an  entirely  normal  manner, 
and  manifested  the  maternal  instincts  in  their  full  intensity. 
Flourens  put  forward  the  doctrine  that  the  cerebellum  is  an 
organ  concerned  in  the  co-ordination  of  movements  and 
especially  the  maintenance  of  equilibrium,  supporting  his  con- 
clusions by  an  elaborate  series  of  experiments.  Notwith- 
standing the  very  large  amount  of  experimental  and  clinical 
study  which  has  been  devoted  to  the  cerebellum  since  the  time 
of  Flourens,  our  actual  knowledge  of 
its  functions  has  not  greatly  ad- 
vanced beyond  the  point  then  reached. 
Some  of  the  more  modern  authorities 
restrict  its  influence  entirely  to  the 
actions  on  which  equilibration  de- 
pends ;  others  extend  it  to  all  voli- 
tional movements.  Luciani  looks 
upon  it  as  '  an  organ  which  by 
processes  that  do  not  awaken  con- 
sciousness exerts  a  continual  strength- 
ening (reinforcing)  action  upon  the 
activity  of  all  other  nerve-centres.' 
Sherrington  conceives  of  the  cere- 
bellum as  the  head  ganglion  of  the 
proprio-ceptive  system — i-c,  of  the 
system  of  neurons  whose  receptors 
lie  not  on  the  surface,  but  in  the 
deeper  parts  of  the  body  (labyrinth 
of  ear,  muscles,  tendons,  joints,  vis- 
cera, etc.)  (p.  810).  After  removal  of 
the  whole  cerebellum  (in  the  dog  or 
monkey),  there  is  at  first  rigidity  and 
tonic  spasm  of  certain  muscles,  which 
contribute  to  the  difficult}'  of  co- 
ordinating their  movements.  When 
this  stage  has  passed,  the  muscles  all 
over  the  body,  but  especially  those  of 
the  loins  and  hind-limbs,  and  those  which  fix  the  head,  are 
weaker  than  normal,  are  deficient  in  tone,  and  contract  with  a 
peculiar  want  of  steadiness  (Luciani).  When  one  lateral  half 
of  the  cerebellum  is  removed,  the  symptoms  affect  especially  the 
muscles  on  the  same  side.  In  extensive  lesions  of  the  cere- 
bellum in  man  what  has  been  noticed  is  a  marked  inability  to 
maintain  the  upright  posture,  giddiness,  a  staggering  gait, 
twitching  movements  of  the  eyes  (nystagmus),  tremor  accom- 
panying voluntary  movements — in  a  word,  a  general  breakdown 


Fig.  347. — Cerebellar  Cor- 
tex :  Section  across  a 
Lamina  (Cajal). 

a,  Purkinje's  cell ;  the  nu- 
merous dots  in  the  molecular 
layer  represent  cross-sections 
of  the  bifurcated  axons  of  the 
granule  cells  (Golgi's  method). 


332  A   M  \NUAl    OF  PHYSIOLOGY 

ill  the  co-ordinating  machinery,  and  especially  oi  the  part  of 

it  concerned  in  the  movements  necessary  for  locomotion,  and 
for  the  maintenance  of  the  equilibrium  of  the  body — the  so-called 
cerebellar  ataxia.  There  is  no  sensory  paralysis  and  none  of 
voluntary  movement,  such  as  lesions  of  the  cerebral  cortex 
produce,  nor  is  there  any  psychical  disturbance.  In  cases  of 
congenital  defect  of  the  cerebellum,  the  power  of  walking,  and 
even  of  standing,  may  be  late  in  being  acquired,  and  imperfect. 
But  it  is  remarkable  what  great  deficiencies  in  the  cerebellar 
substance  are  often  compensated  for  when  established  earlv  in 
life,  so  that  even  cases  of  marked  atrophy  or  lack  of  develop- 
ment have  sometimes  been  recognised  for  the  first  time  at  the 
autopsy. 

The  connections  of  the  cerebellum  with  other  parts  of  the 
central  nervous  system  and  with  the  periphery  corroborate 
the  direct  results  of  experiment.  For,  in  addition  to  the  visual 
impressions,  the  most  important  afferent  impulses  concerned  in 
equilibration  are  those  from  the  semicircular  canals  and  vestibule 
of  the  internal  ear,  the  muscles,  tendons,  joints,  etc.,  and  certain 
portions  of  the  skin,  such  as  that  of  the  soles  of  the  feet.  And  the 
cerebellum,  as  we  have  seen  (p.  779),  is  linked  with  all  of  these, 
and  has  besides  an  extensive  crossed  connection  through  the 
middle  and  superior  peduncles  with  the  opposite  cerebral 
hemisphere.  The  importance  and  extent  of  this  crossed  connec- 
tion with  the  great  brain  is  illustrated  by  the  facts  that  in 
disease  atrophy  or  deficient  development  of  one  cerebellar 
hemisphere  is  associated  with  a  similar  condition  of  the  opposite 
cerebral  hemisphere,  and  that  a  lesion  in  one-half  of  the  cere- 
bellum affects  chiefly  the  co-ordination  of  the  movements  of 
the  same  side  of  the  body — that  is  to  say,  of  the  side  connected 
with  the  opposite  cerebral  hemisphere. 

Wc  do  not  as  yet  know  the  full  significance  of  this  extraordinarily 
free  communicaticn  of  the  grey  matter  of  the  cerebellum  with  every 
part  of  the  central  nervous  system.  But  it  is  evident  that  by  the 
broad  highway  of  the  restiform  body,  or  the  cross-country  routes 
from  cerebral  cortex  to  cerebellum,  impulses  may  reach  it  from 
every  quarter  ;  while  impulses  passing  out  from  it  along  its  peduncles 
may  influence  the  motor  discharge  either  indirectlv  through  the 
Rolandic  cortex  and  the  pyramidal  tract,  or  more  directly  through 
the  antero-lateral  descending  spinal  path  that  brings  it  into  relation 
with  the  nuclei  of  origin  of  the  motor  nerves.  It  is  an  organ  so 
connected  that  is  suited  to  take  cognizance  of  the  multitudes  of 
afferent  impressions  concerned  in  the  co-ordination  of  movements 
and  the  maintenance  of  equilibrium,  and  to  regulate  the  outflow 
of  efferent  impulses  in  correspondence  with  the  inflow  of  afferent. 

Sherrington  points  out  that  all  the  modern  theories  of  cerebellar 
function  harmonize  with  his  conception  of  the  cerebellum  as  the  head 
ganglion  of  the  proprio-ceptive  system  (p.  831).     The  most  influential 


////■   CI  v/  /,'  II.   NERVOUS  SYST1  M 


*33 


"t  the  proprio  ceptive  organs  being  the  Labyrinth,  the  central  organ 
of  the  whole  proprio-ceptive  mechanism  is  built  up  over  the  central 
connections  of  the  labyrinth.  Thither  converge  connecting  (inter- 
nuncial)  paths  from  the  central  endings  of  proprio-ceptive  neurons 
in  .ill  segments  of  the  body  (from  joints,  muscles,  tendons,  ligaments. 
viscera,  etc.).  Tims  a  centra]  organ  is* developed, which  varies  in 
si/e  and  complexity  in  different  kinds  of  animals  according  to  the 
complexity  of  their  habitual  movements.  This  is  a  convenient 
place  to  consider  a  little  more  in  detail  the  nature  and  peripheral 
s<  >urces  of  some  of  the  most  important  afferent  impressions  concerned 
in  equilibration. 

(i)  Afferent  Impulses  from  the  Semicircular  Canals. — The  semi- 
circular canals  are  three  in  number,  and  lie  nearly  in  three  mutually 
rectangular  planes  :  the  external  canal  in  the  horizontal  plane,  the 
superior  canal  in  a  vertical  longitudinal  plane,  and  the  posterior 
canal  in  a  vertical  transverse  plane.  Each  canal  bulges  out  at  one 
end  into  a  swelling,  or  ampulla,  which  opens  into  the  utricular 
division  of  the 
vestibule  (Figs. 
348,  421).  The 
other  extremi- 
ties of  the  su- 
perior and  pos- 
terior  canals 
join  together, 
and  have  a 
common  aper- 
ture into  the 
utricle,  but  the 
undilated  end 
of  the  external 
or  horizontal 
canal  opens 
separately.  The 
utricle  and  the 
semicircular 
canals  are  thus 
connected      by 

five  distinct  orifices.  The  greater  part  of  the  internal  surface  of 
the  membranous  canals,  utricle  and  saccule,  is  lined  by  a  single 
layer  of  flattened  epithelium.  But  at  one  part  of  each  ampulla 
projects  a  transverse  ridge,  the  crista  acustica,  covered  not  with 
squamous,  but  with  long  columnar  epithelium.  Hair-like  processes 
(auditory  hairs)  are  borne  by  some  of  the  columnar  cells,  between 
which  lie  more  elongated  fibre-like  supporting  cells.  The  hairs 
project  into  a  mucus-like  mass,  sometimes  containing  otoconia, 
or  crystals  of  calcium  carbonate.  The  ampullae,  like  the  rest  of  the 
membranous  labyrinth,  is  filled  with  a  watery  fluid  called  endolymph. 
The  utricle  and  saccule  have  each  a  somewhat  similar  but  broader 
elevation,  the  macula  acustica,  covered  with  epithelium  and  hair- 
cells  of  the  same  character,  and  the  hairs  project  into  a  similar  mass 
in  which  otoconia  are  constantly  present.  In  some  animals,  as  fishes, 
the  calcareous  matter  in  the  utricle  and  saccule  forms  masses  of 
considerable  size  (otoliths).  Fibres  of  the  auditory  nerve  end  in 
arborizations  around  the  bodies  of  the  hair-cells  of  the  maculae 
and  cristae  acusticae.     We  have  already  seen  that  it  is  the  ventral  or 

53 


Fig.    348. — The    Semicircular    Canals    (Diagrammatic) 

(after  Ewald). 

H,  horizontal  or  external  ;  S,  superior ;  P,  posterior. 
The  two  horizontal  canals  lie  in  the  same  plane.  The 
plane  of  the  superior  vertical  canal  of  one  side  is  parallel 
to  the  plane  of  the  posterior  vertical  canal  of  the  opposite 
side. 


S34  A  MANUAL  OB   PHYSIOLOGY 

vestibular  division  of  the  nerve  which  is  especially  related  to  the 
vestibule  (p.  iS j  s  |. 

I  In  re  is  very  strong  evidence  that  the  semicircular  canals  are  con- 
cerned, not  in  hearing,  but  in  equilibration.  A  pigeon  from  which 
the  membranous  canals  have  been  removed  still  hears  perfectly 
well  so  long  as  the  cochlea  is  intact,  but  exhibits  the  most  profound 
disturbance  of  equilibrium.  If  the  horizontal  canal  is  destroyed 
or  divided  the  pigeon  moves  its  head  continually  from  side  to 
side  around  a  vertical  axis  ;  if  the  superior  canal  is  divided,  the 
head  moves  up  and  down  around  a  horizontal  axis.  The  power 
of  co-ordination  of  movements  is  diminished,  but  not  to  the  same 
extent  in  all  kinds  of  animals.  Thrown  into  the  air,  the  pigeon  is 
helpless  ;  it  cannot  fly  ;  but  a  goose  with  divided  semicircular  canals 
can  still  swim.  The  condition  is  only  temporary,  even  when  the 
injury  involves  the  three  canals  on  one  side  ;  but  if  the  canals  on 
both  sides  are  destroyed,  recovery  is  tardy,  and  often  incomplete. 
In  mammals  the  loss  of  co-ordination  is  much  less  than  in  birds  ; 
and  movements  of  the  eyes,  the  direction  of  which  depends  on  th< 
canal  destroyed,  take  to  a  large  extent  the  place  of  movements  of 
the  head.  The  effects  of  destructive  lesions  have  their  counterpart 
in  the  phenomena  caused  by  stimulation  ;  excitation  of  a  posterior 
canal,  for  example,  in  the  pigeon  causes  movements  of  the  head  from 
side  to  side. 

Lee's  results  in  fishes  are,  on  the  whole,  of  similar  tenor. 
Mechanical  stimulation  of  the  ampullae  in  the  dogfish,  by  pressing 
on  them  with  a  blunt  needle,  calls  forth  characteristic  movements 
of  the  eyes  and  fins,  and  electrical  stimulation  of  the  auditory  nerve 
causes  movements  compounded  of  the  separate  movements  obtained 
by  stimulation  of  the  ampulla?  one  by  one.  Lee  concludes  that  the 
semicircular  canals  are  the  sense-organs  for  dynamical  equilibrium 
{i.e.,  equilibrium  of  an  animal  m  motion),  and  the  utricle  and  saccule 
for  statical  equilibrium  (i.e.,  equilibrium  of  an  animal  at  rest). 

The  evidence  from  all  sources  points  strongly  to  the  (jonclusion 
that  afferent  impulses  are  actually  set  up  in  the  fibres  of  the  auditory 
nerve,  through  the  hair-cells,  by  alterations  of  pressure  or  by  stream- 
ing movements  of  the  endolymph  when  the  position  of  the  head  is 
changed.  Rotation  of  the  head  to  the  right  may  be  supposed  to 
cause  the  endolymph  in  the  right  external  canal,  in  virtue  of  its 
inertia,  to  lag  behind  the  movement,  and  to  press  upon  the  anterior 
surface  of  the  ampulla.  The  disorders  of  movement  after  lesions  of 
the  canals  may  be  explained  as  the  result  of  the  withdrawal  of 
certain  of  these  afferent  impulses,  and  the  consequent  overthrow  of 
that  equipoise  of  excitation  necessary  for  the  maintenance  of  equi- 
librium. Even  in  man  there  is  evidence  of  the  existence  of  some 
mechanism  not  depending  on  the  muscular  sense  or  on  impressions 
passing  up  the  channels  of  ordinary  or  special  sensation,  by  which 
orientation  (the  determination  of  the  position  of  the  body  in  space) 
is  rendered  possible.  For  a  man  lying  perfectly  still,  with  eyes  shut, 
on  a  horizontal  table  which  is  made  to  rotate  uniformly,  can  not 
only  judge  whether,  but  also  in  what  direction,  and  approximately 
through  what  angle,  he  is  moved  (Crum  Brown).  The  phenomena 
of  pathology  afford  weight)-  additional  testimony  in  favour  of  the 
equilibratory  function  of  the  semicircular  canals.  For  many  cases 
oi  vertigo  are  associated  with  changes  in  the  internal  ear  (Meniere's 
disease).  And  while  nearly  every  normal  individual  becomes  dizzy 
when  rapidly  rotated,  35  per  cent,  of  deaf-mutes  arc  entirely  un- 


nil    (  /  VTRAL   NERVOUS  SYSTEM  835 

affected  (James),  and  the  proportion  seems  to  be  much  higher  among 
congenital  deaf-mutes.  Kreidl  and  Bruck,  too,  have  found  that 
abnormalities  of  locomotion  anil  equilibration  arc  much  more 
common  in  deaf-and-dumb  children  than  in  others.  Now,  in  t 
cases  the  delect  is  usually  in  the  internal  ear.  We  must  concludi  . 
then,  that  the  co-ordination  of  muscular  movements  necessary  for 
equilibrium  is  achieved  in  some  centre,  to  which  afferent  impulses 
pass  from  the  internal  ear  by  the  vestibular  branch  of  the  auditory 
nerve,  and  from  which  efferent  impulses  pass  out  to  the  muscles.  If,  as 
there  is  strong  reason  to  believe,  tins  cent  re  is  situated  in  the  cerebellum, 
the  efferent  path  is,  as  already  suggested  (p.  832),  partly  an  indirect 
one  (perhaps  by  commissural  fibres  to  the  Rolandic  area,  and  then 
out  along  the  pyramidal  tract),  or  more  probably  to  lower  centres, 
perhaps  in  the  posterior  portion  of  the  optic  thalamus,  which  control 
such  massive  co-ordinated  movements  as  those  concerned  in  walking 
and  the  maintenance  of  the  normal  attitude,  and  thence  out  along 
certain  tracts  that  connect  the  thalamus  to  the  spinal  cord  (p.  781). 

Ewald  has  made  an  observation  which  illustrates  the  peculiar 
relation  of  the  semicircular  canals  to  the  muscular  system — namely, 
that  the  labyrinth  (in  rabbits)  influences  the  course  of  rigor  mortis 
in  the  striped  muscles.  Rigor  does  not  come  on  so  soon  on  the  side 
from  which  the  labyrinth  has  been  removed  (p.  675).  He  attributes 
to  the  labyrinth,  as  one  of  its  functions,  the  maintenance  of  a  certain 
tonus  in  the  entire  skeletal  musculature. 

(2)  Afferent  Impressions  from  the  Muscles. — Muscles  are  richly 
supplied  with  afferent  fibres,  for  about  half  of  the  fibres  in  the  nerves 
of  skeletal  muscles  degenerate  after  section  of  the  posterior  roots 
beyond  the  ganglia  (Sherrington).  Various  kinds  of  impressions 
may  pass  up  these  nerves  :  (a)  Impressions  giving  rise  to  pain, 
as  in  muscular  cramp  and  in  experimental  excitation  of  even  the 
finest  muscular  nerve-filament  ;  (b)  impulses  causing  a  rise  of  blood- 
pressure  ;  (c)  impulses  which  arc  not  associated  with  a  distinct  im- 
pression in  consciousness,  but  which  enable  us  to  localize  the  position 
of  the  limbs,  head,  eyes,  and  other  parts  of  the  body  ;  (d)  impulses 
which  inform  us  as  to  the  extent  and  force  of  muscular  contraction, 
and  seem  to  underlie  the  so-called  muscular  sense.  It  is  the  last 
two  kinds — if,  indeed,  they  are  distinct — which  must  be  concerned 
in  equilibration.  In  locomotor  ataxia  such  impressions  are  blocked 
by  degeneration  in  a  part  of  the  afferent  path  (p.  811),  and  disorders 
of  equilibrium  are  the  result. 

(3)  Afferent  Impressions  from  the  Skin.— Of  the  various  kinds  of 
impulses  that  arise  in  the  nerve-endings  of  the  skin,  only  those 
of  touch  and  pressure  seem  to  be  concerned  in  the  maintenance  of 
equilibrium.  When  the  soles  of  the  feet  are  rendered  insensitive  by 
local  anaesthesia  or  by  cold,  and  the  person  is  directed  to  close  his  eyes, 
he  staggers  and  sways  from  side  to  side.  The  disturbance  of  equili- 
brium in  locomotor  ataxia  must  be  partly  attributed  to  the  loss  of 
these  tactile  sensations,  for  numbness  of  the  feet  is  a  frequent 
symptom,  and  the  patient  asserts  that  he  does  not  feel  the  ground. 
An  interesting  illustration  of  the  importance  of  afferent  impulses 
from  the  skin  in  the  maintenance  of  equilibrium  is  afforded  by  the 
behaviour  of  a  frog  deprived  of  its  cerebral  hemispheres.  Such  a 
frog  will  balance  itself  on  the  edge  of  a  board  like  a  normal  animal, 
but  if  the  skin  be  removed  from  the  hind-legs,  it  will  fall  like  a  log. 

In  birds  and  lower  vertebrates  the  cerebellum  is  only  represented 
by  the  worm.     Yet  in  many  of  these  animals  the  same  characteristic 

53—2 


836  A   MANUA1    OF  PHYSIOLOGY 

disturbances  follow  its  removal  as  in  the  higher  animals  where  the 
ccrcbfll.tr  hemispheres  hav<  become  so  prominent,  [ndeed,  it  was 
mainly  on  the  pigeon  that  Flourens  made  his  classical  experiments. 

At  first  the  pigeon  can  neither  fly  nor  feed  itself.  Winn  {{  attempts 
to  walk  extensor  spasms  of  the  legs  come  on,  and  it  falls,  wildly 
struggling  and  apparently  panic-stricken,  to  the  ground.  '1  he  power 
of  flight  is  soon  regained,  but  for  a  long  time  the  animal  is  unable  to 
perch,  the  legs  and  talons  stiffening  in  rigid  extension  as  it  attempts 
to  alight. 

In  the  higher  animals  stimulation  of  certain  parts  of  the  worm  and 
lateral  lobe  causes  conjugate  movements  of  the  eyes  towards  tin 
same  side,  both  eyes  being  turned  to  the  right,  e.g.,  when  the 
cerebellum  is  stimulated  to  the  right  of  the  middle  line.  Inhibition 
of  movement  can  also  be  elicited  from  the  organ.  Excitation  of 
the  cerebellar  cortex  for  some  distance  outwards  from  the  line  oi 
junction  of  the  superior  worm  with  the  lateral  lobe  in  animals 
which  exhibit  tonic  contraction  of  extensor  muscles  after  excision 
of  the  cerebral  hemispheres  (decerebrate  rigidity  or  acerebral  tonus, 
as  it  is  called)  causes  immediate  relaxation  of  the  rigid  muscles  oi 
the  neck,  tail,  and  especially  the  anterior  limb,  particularly  on  the 
same  side.  The  relaxation  of  the  extensors  may  be  accompanied 
by  contraction  of  the  antagonistic  flexors — for  example,  relaxation 
of  the  triceps  and  contraction  of  the  biceps  (Horsley  and  Lowenthal). 
But  this  can  scarcely  be  considered  a  reaction  specific  to  the  cere- 
bellum. For  Sherrington,  who  finds  that  the  tonus  or  spasm  is 
largely  due  to  centripetal  impulses  coming  from  the  rigid  limb,  has 
been  able  to  inhibit  it  by  stimulation  of  various  other  regions, 
including  the  portion  of  the  cerebral  cortex  in  front  of  the  fissure  of 
Rolando  (p.  847). 

Forced  Movements. — -We  have  incidentally  mentioned  that  in 
fishes  injuries  to  the  semicircular  canals  may  give  rise  to  movements 
which  seem  to  be  beyond  the  control  of  the  animal,  and  which  have 
consequently  received  the  name  of  '  forced  movements.'  It  may  be 
added  that  when  the  internal  ear  of  a  Nccturus  (one  of  the  tailed 
amphibia)  is  destroyed  on  one  side,  rapid  movements  of  rotation 
around  a  longitudinal  axis  arc  observed.  The  animal  spins  round 
and  round  apparently  without  voluntary  control,  purpose,  or 
fatigue.  The  direction  of  rotation  is  towards  the  side  of  the  lesion, 
the  observer  being  supposed  to  look  down  upon  the  animal  as  it  lies 
in  its  normal  position.  After  a  time  it  becomes  quiescent  :  but  the 
forced  movements  can  be  again  produced  by  pinching  or  exciting  it 
in  other  ways.*  In  man,  too,  during  the  passage  of  a  galvanic  current 
through  the  head  by  electrodes  applied  just  behind  the  ears,  a 
tendency  to  move  the  head  towards  the  anode  is  experienced.  The 
person  may  resist  the  tendency,  but  if  the  current  be  strong  enough 
his  resistance  will  be  overcome  ;  he  will  execute  a  forced  movement. 
When  the  head  turns  towards  the  anode  the  eyes  move  in  the  same 
direction,  and  then  undergo  jerking  movements  towards  the  kathode. 
There  is  at  the  same  time  a  feeling  of  vertigo.  Complex  as  such  an 
experiment  is,  involving  as  it  docs  stimulation  of  so  many  structures 
within  the  cranium,  there  is  reason  to  believe  that  it  is  the  excitation 
of  the  semicircular  canals,  or  their  cerebellar  connections,  that  is 
responsible  for  these  forced  movements.  For  when  the  experiment 
is  performed  on  a  pigeon,  forced  movements  are  caused  so  long  as 
the  membranous  canals  arc  intact,  but  not  after  they  have  been 
*  Personal  observation. 


I  ill    (  I  v/A'  II.  WERVOUS  SYSTEM  837 

destroyed  (Ewald),  The  observation  of  Etawitz,  Hud  the  peculiar 
rotatory  movements  oi  the  so-called  Japanese  dancing  mice  arc 
associated  with  marked  anatomical  peculiarities  in  the  labyrinth,  is 
another  fad    in   favour  oi   the  connection  of  the  canals  with  the 

maintenance  of  i< ] u i I i I >ii u n  1  .i.nd  the  sense  of  rotation.  So  is  the 
relation  between  the  degree  of  developmenl  of  the  canals  in  different 
species  of  birds  and  the  degree  of  agility  in  the  co-ordination  of 
their  movements  (Laudenbach). 

But  forced  movements  may  also  follow  injuries  (especially  uni- 
lateral) to  many  portions  of  the  brain — e.g.,  the  pons,  crus  cerebri, 
posterior  corpora  quadrigemina,  corpus  striatum,  even  the  cerebral 
cortex,  and  above  all  the  cerebellum.  The  movements  are  of  the 
most  various  kinds.  The  animal  may  run  round  and  round  in  a  circle 
(circus  movement)  ;  or,  with  the  tip  of  its  tail  as  centre  and  the 
length  of  its  body  as  radius,  it  may  describe  a  circle  with  its  head,  as 
the  hand  of  a  clock  docs  (clock-hand  movement)  ;  or  it  may  rush 
forward,  turning  endless  somersaults  as  it  goes.  Intervals  of  rest 
alternate  with  paroxysms  of  excitement,  and  the  latter  may  be 
brought  on  by  stimulation.  In  man  forced  movements  associated 
with  vertigo  have  been  sometimes  seen  in  cases  of  tumour  of  the 
cerebellum — e.g.,  involuntary  rotation  of  the  body  in  tumour  cf  the 
middle  peduncle.  No  entirely  satisfactory  explanation  of  these 
forced  movements  has  been  given.  They  are  evidently  connected 
with  disturbance  of  the  mechanism  of  co-ordination,  leading  to  a 
loss  of  proportion  in  the  amount  of  the  motor  discharge  to  muscles 
or  groups  of  muscles  accustomed  to  act  together  in  executing  definite 
movements.  For  instance,  in  circus  movements  the  muscles  of  the 
outer  sides  of  the  body  contract  more  powerfully  than  those  of  the 
inner  side,  and  the  animal  is  therefore  constrained  to  trace  a  circle 
instead  of  a  straight  line,  the  excess  cf  contraction  on  the  outer  side 
being  analogous  to  the  acceleration  along  the  radius  in  the  case  of  a 
point  moving  in  a  circle. 

Co-ordination  of  Movements. — The  capacity  of  executing  some 
co-ordinated  movements,  occasionally  of  considerable  complexity, 
seems  to  be  inborn  in  man,  and  to  a  still  greater  extent  in  many  of 
the  lower  animals.  The  new-born  child  brings  with  it  into  the  world 
a  certain  endowment  of  co-ordinative  powers  ;  it  has  inherited,  for 
example,  from  a  long  line  of  mammalian  ancestors  the  power  of 
performing  those  movements  of  the  cheeks,  lips,  and  tongue,  on 
which  sucking  depends  ;  perhaps  from  a  long,  though  somewhat 
shadowy,  race  of  arboreal  ancestors  the  power  of  clinging  with  hands 
and  feet,  and  thus  suspending  itself  in  the  air.  Many  movements, 
such  as  walking  and  the  co-ordinated  muscular  contractions  involved 
in  standing,  and  even  in  sitting,  which,  once  acquired,  appear  so 
natural  and  spontaneous,  have  to  be  learnt  by  painful  effort  in  the 
hard  school  of  (infantile)  experience.  Most  people  learn,  and  are 
willing  to  confess  that  they  have  learnt,  to  execute  a  considerable 
number  of  co-ordinated  movements  with  the  arms,  and  especially 
with  the  fingers  ;  but  few  have  considered  that  the  extreme  dexterity 
of  jaws,  tongue,  and  teeth  displayed  by  a  hungry  mouse  or  school- 
boy is  the  result  of  the  much  practice  which  maketh  perfect.  The 
exquisite  co-ordination  of  the  muscles  of  the  eyeball,  which  we 
shall  afterwards  have  to  speak  of,  and  the  no  less  wonderful  balance 
of  effort  and  resistance,  of  power  put  forth  and  work  to  be  done,  of 
which  we  have  already  had  glimpses  in  studying  the  mechanism 
of  voice  and  speech,  become  to  a  great  extent  the  common  property 


838  /    MANV  \l    OF  PHYSIOLOGY 

of  all  fully-developed  persons.  But  the  technique  of  the  finished 
singer  or  musician,  of  the  swordsman  or  acrobat,  and  even  the 
operative  skill  of  the  surgeon,  are  in  large  part  the  outcome  of  a 
special  and  acquired  agility  of  mind  or  body,  in  virtue  of  which 
highly-complicated  co-ordinated  movements  are  promptly  deter- 
mined on  and  immediately  executed. 

With  such  special  and  elaborate  movements  it  is  impossible  to 
occupy  ourselves  in  a  book  like  this.  Their  number  may  be  almost 
indefinitely  extended,  and  their  nature  almost  infinitely  varied,  by 
the  needs  and  training  of  special  trades  and  professions.  It  will 
be  sufficient  for  our  purpose  to  sketch  in  a  few  words  the  mechanism 
of  one  or  two  of  the  most  common  and  fundamental  co-ordinations 
of  muscular  effort,  passing  over  the  rest  with  the  general  statement 
that  the  more  refined  and  complex  movements  are  in  general  brought 
about  not  by  the  abrupt  contraction  of  crude  anatomical  groups  of 
muscles,  but  by  the  contraction  of  portions  of  muscles,  perhaps  even 
single  fibres  or  small  bundles  of  fibres,  while  the  rest  remain  relaxed. 
The  excitation  may  gradually  wax  and  wane  as  the  different  stages 
of  the  movement  require.  Antagonistic  muscles  may  be  called  into 
play  to  balance  and  tone  down  a  contraction  which  might  otherwise 
be  too  abrupt. 

Many  interesting  illustrations  of  this  process  of  '  give  and  take  ' 
between  opposing  muscles  have  been  reported,  especially  by  Sherring- 
ton. Some  have  been  already  alluded  to  in  discussing  reflex  move- 
ments (p  80 1) .  One  or  two  additional  observations  may  be  given  here. 
In  the  cortex  cerebri,  as  we  shall  see  (pp.  845,  859),  there  is  an  area 
in  the  frontal  region,  and  another  in  the  occipital  region,  stimulation  of 
which  gives  rise  to  conjugate  deviation  of  the  eyes — that  is,  rotation 
of  both  eyes — to  the  opposite  side.  Sherrington  divided  the  third 
and  fourth  cranial  nerves  in  monkeys — say,  on  the  left  side.  The 
external  rectus,  which  is  supplied  by  the  sixth  nerve,  caused  now 
by  its  unopposed  contraction  external  squint  of  the  left  eye.  When 
either  of  the  cortical  areas  referred  to,  or  even  the  subjacent  portion 
of  the  corona  radiata,  was  stimulated  on  the  left  side,  both  eyes 
moved  towards  the  right,  the  left  eye,  however,  only  reaching  the 
middle  line — that  is,  the  position  in  which  it  looked  straight  forward. 
The  same  thing  was  observed  when  the  animal,  after  complete 
recovery  from  the  operation,  was  caused  to  voluntarily  turn  its 
eyes  to  the  right  by  the  sight  of  food.  Here  an  inhibitory  influence 
must  have  descended  the  fibres  of  the  abducens.  the  only  nervous 
path  connected  with  the  extrinsic  muscles  of  the  left  eye,  and 
the  relaxation  of  the  left  external  rectus  must  have  kept  accurate 
step  with  the  contraction  of  the  right  internal  rectus.  Hering  has 
made  an  exhaustive  analysis  of  the  co-ordinated  movements  con- 
cerned in  opening  and  closing  the  hand  in  monkeys.  These  move- 
ments can  be  produced  by  stimulation  of  the  cortex  or  the  internal 
capsule,  but  not  by  stimulation  of  the  anterior  spinal  roots.  When 
the  hand  is  opened  the  muscles  that  open  it  are  excited,  and  those 
which  close  it  are  inhibited  from  the  cortex. 

Standing. — In  the  upright  posture  the  body  is  supported  chiefly 
by  non-muscular  structures,  the  bones  and  ligaments.  But  muscles 
also  play  an  essential  part,  for  it  is  only  peculiarly-gifted  individuals, 
like  some  of  the  fishermen  of  the  North  Sea,  who  can  go  to  sleep  on 
their  feet,  and  a  dead  body  cannot  be  made  to  stand  erect.  The 
condition  of  equilibrium  is  that  the  perpendicular  dropped  from  the 
centre  of  gravity  to  the  ground  should  fall  within  the  base  of  support 


THE  (I  NTRAL    VEVROUS  SYSTEM  830 

— that  is,  within  the  area  enclosed  by  the  outer  borders  of  the  feet 
ami  linrs  joining  the  toes  and  heels  respectively.  The  centre  oi 
gravity  alters  its  position  with  the  position  of  the  body,  which  tends 
to  fall  whenever  the  perpendicular  cuts  the  ground  beyond  the  base 
of  support. 

In  the  comfortable  and  natural  erect  position  the  centre  of  gravity 
6i  the  head  is  a  little  in  front  of  the  vertical  plane  passing  through  the 
occipital  condyles,  and  as  much  as  4  centimetres  in  front  of  the 
vertical  plane  passing  through  the  ankle-joints.  A  certain  degree  of 
contraction  of  the  muscles  of  the  nape  of  the  neck  is  required  to 
balance  it.  When  these  muscles  are  relaxed,  as  in  sleep,  the  land 
must  fall  forward,  and  this  is  the  reason  why  Homer  or  any  lesser 
individual  nods.  In  animals  which  go  upon  all-fours  none  of  the 
weight  of  the  head  bears  directly  upon  the  occipito-atloid  articula- 
tion ;  its  support  by  muscular  action  alone  would  be  an  intolerable 
fatigue,  and  the  ligamentum  nuchae  is  specially  strengthened  to  hold 
it  up. 

The  vertebral  column  is  kept  erect  by  the  ligaments  and  muscles 
of  the  back.  The  centre  of  gravity  of  the  trunk  lies  almost  vertically 
over  the  horizontal  line  joining  the  two  acetabula,  but  the  centre  of 
gravity  of  the  whole  body  is  about  the  level  of  the  third  sacral 
vertebra,  and  a  little  more  than  4  centimetres  in  front  of  the  vertical 
plane  passing  through  the  ankle-joints.  Equilibrium  is  maintained 
by  contraction  of  the  muscles  of  the  back  and  of  the  legs.  By 
means  of  the  muscular  sense,  and  the  tactile  sensations  set  up  by  the 
pressure  of  the  soles  on  the  ground,  alterations  in  the  position  of  the 
centre  of  gravity,  and  consequent  deviations  of  the  perpendicular 
passing  through  it,  are  detected,  and  adjustment  of  the  amount 
of  contraction  of  this  or  the  other  muscular  group  is  promptly  made. 

In  standing  at  '  attention  '  the  heels  are  close  together,  the  legs 
and  back  straightened  to  the  utmost,  and  the  head  erect  ;  the  weight 
falls  equally  upon  both  legs,  but  the  advantage  may  be  more  than 
counterbalanced  by  the  muscular  exertion  associated  with  this  more 
ornamental  than  useful  position.  In  '  standing  at  ease,'  practically 
the  whole  weight  is  supported  by  one  leg,  the  perpendicular  from  the 
centre  of  gravity  passing  through  the  knee  and  ankle-joints.  The 
centre  of  gravity  is  brought  over  the  supporting  leg  by  flexure  of 
the  body  to  the  corresponding  side,  and  comparatively  little  muscular 
effort  is  required.  The  other  foot  rests  lightly  on  the  ground,  the 
weight  of  the  leg  itself  being  almost  balanced  by  the  atmospheric 
pressure  acting  upon  the  air-tight  and  air-free  cavity  of  the  hip- 
joint.  The  light  touch  of  this  foot  varies  slightly  from  time  to  time, 
so  as  to  maintain  equilibrium. 

When  the  head  or  arms  are  moved,  or  the  body  swayed,  the 
centre  of  gravity  is  correspondingly  displaced,  and  it  is  by  such 
movements  that  tight-rope  dancers  continue  to  keep  the  perpen- 
dicular passing  through  it  always  within  the  narrow  base  of  support. 

In  sitting,  the  base  of  support  is  larger  than  in  standing,  and  the 
equilibrium  therefore  more  stable.  The  easiest  posture  in  sitting 
without  support  to  the  back  or  feet  is  that  in  which  the  perpendicular 
from  the  centre  of  gravity  passes  through  the  horizontal  line  joining 
the  two  tubera  ischii. 

Locomotion. —In  walking,  the  legs  are  alternately  swung  forward 
and  rested  on  the  ground.  In  military  marching,  it  is  directed  that 
toe  and  heel  be  simultaneously  set  down.  But  with  most  persons 
the  swinging  foot  first  strikes  the  ground  by  the  heel  ;  then  the  sole 


840  A    MANUAL  OF  PHYSIOLOGY 

comes  down,  the  heel  rises,  the  leg  is  extended,  and,  with  a  parting 
push  from  the  toe,  the  leg  again  swings  free.  By  this  manoeuvre  the 
body  is  raised  vertically,  tilted  to  the  opposite  side,  and  also  pushed 
in  advance. 

The  forward  swing  of  the  leg  is  only  slightly,  if  at  all.  due  to 
muscular  action  ;  it  is  more  like  the  oscillation  of  a  pendulum  dis- 
placed behind  its  position  of  equilibrium,  and  swinging  through  that 
position,  and  in  front  of  it,  under  the  influence  of  gravity.  For  this 
reason  the  natural  pace  of  a  tall  man  is  longer  and  slower  than  that 
of  a  short  man  ;  but  it  may  be  modified  by  voluntary  effort,  as  when 
a  rank  of  soldiers  of  different  height  keeps  step. 

The  lateral  swing  of  the  body  is  illustrated  by  the  everyday 
experience  that  two  persons  knock  against  each  other  when  they 
try  to  walk  close  together  without  keeping  step.  In  step  botli  swing 
their  bodies  to  the  same  side  at  the  same  moment,  and  there  is  no 
jarring. 

Even  in  the  fastest  walking  on  level  ground  there  is  a  short  time 
during  which  both  feet  touch  the  ground  together,  the  one  leg  not 
beginning  its  swing  until  the  other  foot  has  begun  to  be  set  down. 
In  running,  on  the  other  hand,  there  is  an  interval  during  which 
the  body  is  completely  in  the  air.  while  in  walking  uphill  or  in  carry- 
ing a  load  the  one  foot  is  not  raised  until  the  other  has  been  firmly 
planted. 

Functions  of  the  Cerebral  Cortex. — When  an  animal,  like 
a  frog,  is  deprived  of  its  cerebral  hemispheres,  the  power  of 
automatic  voluntary  movement  appears  to  be  definitively  and 
entirely  lost.  The  animal,  as  soon  as  the  effects  of  the  anaes- 
thetic and  the  shock  of  the  operation  have  passed  away,  draws 
up  its  legs,  erects  its  head,  and  assumes  the  characteristic 
position  of  the  normal  frog  at  rest.  So  close  may  be  the  re- 
semblance, that  if  all  external  signs  of  the  operation  have  been 
concealed,  it  may  not  be  possible  for  a  casual  observer  to  tell 
merely  by  inspection  which  is  the  intact  and  which  the  '  brain- 
less '  frog.  The  latter  will  jump  if  it  be  touched  or  otherwise 
stimulated.  It  will  croak  if  its  flanks  be  stroked  or  gently 
squeezed  together.  It  will  swim  if  thrown  into  water.  If 
placed  on  its  back,  it  will  promptly  recover  its  normal  position. 
But  it  will  do  all  these  things  as  a  machine  would  do  them, 
without  purpose,  without  regard  to  its  environment,  with  a  kind 
of  '  fatal '  regularity.  Every  time  it  is  stimulated  it  will  jump, 
every  time  its  flanks  are  squeezed  it  will  croak,  and,  in  the 
absence  of  all  stimulation,  it  will  sit  -till  till  it  withers  to  a 
mummy,  even  by  the  side  of  the  water  that  might  for  a  while 
preserve  it. 

A  Nectunis,  without  its  cerebral  hemispheres,  will,  like  the 
frog,  refuse  to  lie  on  its  back.  On  stimulation  it  moves  its 
feet  or  tail,  or  its  whole  body  ;  but  if  not  interfered  with,  it 
lies  for  an  indefinite  time  in  the  same  position.  Its  gills  are 
seen  to  execute  rhythmic  movements,  which  never  stop,  and 
rarely  slacken,  except  for  an  instant,  when  some  part  of  the 


THE  CENTRAL  NERVOUS  SYSTEM  841 

skin,  particularly  in  the  region  of  the  head,  is  mechanically  or 
electrically  stimulated.  The  normal  Necturus,  on  the  other 
hand,  lies  for  long  periods  with  its  gills  at  perfect  rest,  and  when 
stimulated,  moves  for  a  considerable  distance.*  After  a  time, 
— two  months  or  more— it  is  true  the  brainless  frog,  if  it  be 
kept  alive,  as  may  be  done  by  careful  attention,  will  recover 
a  certain  portion  of  the  powers  which  it  has  lost  by  removal  of 
the  cerebral  hemispheres  ;  and,  indeed,  the  longer  it  lives,  the 
nearer  it  approximates  to  the  condition  of  a  normal  frog.  A 
brainless  frog  has  been  seen  to  catch  flies  and  to  bury  itself  as 
winter  drew  on.  A  fish  even  three  days  after  the  destruction  of 
its  cerebrum  has  been  seen  to  dart  upon  a  worm,  seize  it  before 
it  had  time  to  sink  to  the  bottom  of  the  aquarium,  and  swallow 
it.  Even  in  the  pigeon  the  loss  of  the  hemispheres,  which  at 
first  induces  a  state  of  profound  and  seemingly  permanent 
lethargy,  is  to  a  great  extent  compensated  for,  as  time  passes 
on,  by  the  unfolding  in  the  lower  centres  of  capabilities  pre- 
viously  dormant  or  suppressed.  A  brainless  pigeon  has  been 
known  to  come  at  the  whistle  of  the  attendant  and  follow  him 
through  the  whole  house. 

In  the  mammal  the  removal  of  the  whole  or  the  greater  part  of 
the  cerebral  hemispheres  at  a  single  operation  is  uniformly  and 
speedily  fatal ;  even  rabbits  or  rats,  which  bear  the  operation 
best,  survive  but  a  few  hours.  During  those  hours  they  manifest 
phenomena  similar  to  those  observed  in  the  bird  and  the  frog. 
In  the  dog  the  entire  cortex  has  been  removed  piecemeal  by 
successive  operations.  In  this  case,  of  course,  the  change  in 
the  condition  of  the  animal  is  more  gradually  produced,  and  an 
opportunity  is  afforded  for  a  certain  recovery  of  function  in  the 
intervals  between  the  operations.  On  the  whole,  however, 
as  might  be  expected  from  its  greater  intellectual  development, 
recovery  is  more  imperfect  in  the  dog  than  in  the  bird,  much 
more  imperfect  than  in  the  frog.  But  even  in  the  dog  wonderful 
resources  lie  hidden  in  the  grey  matter  of  the  central  neural 
axis,  and  are  called  forth  by  degrees  to  replace  the  lost  powers 
of  the  cerebral  cortex.  It  is  true  that  a  brainless  dog  is  a 
less  efficient  animal  than  a  brainless  fish,  or  even  than  a  brain- 
less frog  ;  but  in  favourable  cases,  even  in  the  dog,  the  move- 
ments of  walking  may  still  be  carried  out  with  tolerable  pre- 
cision in  the  absence  of  the  cerebral  hemispheres.  The  animal 
can  swallow  food  pushed  well  back  into  the  mouth,  although 
it  cannot  feed  itself.  Stupid  and  listless  as  it  is  compared  with 
the  normal  dog,  it  seems  to  be  by  no  means  devoid  of  the  power 
of  experiencing  sensations  as  the  result  of  impressions  from 
without,  nor  of  carrying  on  mental  operations  of  a  low  intel- 
*  Personal  observations. 


842  A   MANUAL  ()/■'  PHYSIOLOGY 

lectual  grade.  Goltz  had  a  dog  which  lived  more  than  a  year 
and  a  half  practically  without  its  cerebral  hemispheres,  and 
another  which  lived  thirteen  weeks.  He  believes  that  they 
had  lost  understanding,  reflection,  and  memory,  but  not  sen- 
sation, special  or  general,  nor  emotions  and  voluntary  power. 
Their  condition  may  be  best  described  as  one  of  general  im- 
becility. Hunger  and  thirst  are  present.  They  experience 
satisfaction  when  fed,  become  angry  when  attacked,  see  a  very 
bright  light,  avoid  obstacles,  hear  loud  sounds,  such  as  those 
produced  by  a  fog-horn,  and  can  be  awakened  by  them.  They 
are  not  completely  deprived  of  sensations  of  taste  and  touch. 
But  it  ought  to  be  remembered  that  the  interpretation  of  the 
objective  signs  of  sensation  in  animals  is  beset  with  difficulties  ; 
and  although  everybody  admits  the  accuracy  of  Goltz's  descrip- 
tion of  what  is  to  be  seen,  his  interpretation  of  the  facts  has  been 
severely  criticised,  particularly  by  H.  Munk. 

To  the  monkey  there  can  be  no  doubt  that  the  loss  of  the 
cerebral  hemispheres  would  be  a  still  heavier  and  more  irremedi- 
able blow  than  to  the  dog.  But  nobody  has  yet  succeeded  in 
keeping  a  monkey  alive  after  complete  removal  of  even  one 
hemisphere. 

In  man  the  destruction  of  considerable  masses  of  brain-sub- 
stance, particularly  if  gradual,  is  not  necessarily  fatal.  How 
great  a  loss  is  compatible  with  life  cannot  be  exactly  stated.  It 
depends  to  a  large  extent  on  the  position  of  the  lesion.  But  it 
is  possible  that  one  cerebral  hemisphere  may  be  rendered  func- 
tionally.useless  without  immediately  putting  a  term  to  existence. 
In  the  foetus,  however,  no  portion  of  the  great  brain  is  absolutely 
indispensable  for  life  and  movement.  An  anencephalous  foetus 
(in  which  the  brain  has  remained  undeveloped)  may  be  born 
alive,  and  live  for  a  short  time. 

We  see,  then,  that  homologous  organs  are  not  necessarily, 
nor  indeed  usually,  of  the  same  physiological  value  in  different 
kinds  of  animals.  A  loss  which  perhaps  hardly  narrows  the 
range  of  the  psychical,  and  certainly  restricts  only  to  a  slight 
extent  the  physical  powers  of  a  fish,  impairs  in  a  marked  degree 
the  voluntary  movements  of  a  dog,  in  addition  to  cutting  off 
from  it  a  great  part  of  its  intellectual  life,  and  is  in  man  incom- 
patible with  life  altogether. 

The  results  of  the  removal  of  the  entire  cerebral  hemispheres 
help  us  to  fix  their  position  as  a  whole  in  the  physiological 
hierarchy.  A  more  minute  analysis  shows  us  that  the  cerebral 
cortex  itself  is  not  homogeneous  in  function,  that  certain  regions 
of  it  have  been  set  aside  for  special  labours.  Our  knowledge  of 
this  localization  of  function  in  the  cerebral  cortex  has  been 
derived  partly  from  clinical,  coupled  with  pathological  observa- 


THE  CBNTR  1/    NERVOUS  SYSTEM 


«43 


tions  on  man,  and  partly  from  the  results  of  the  removal  or 
stimulation  of  definite  areas  in  animals.  And  so  varied  and 
extensive  have  been  the  contributions  from  both  of  these 
sources,  that  it  is  difficult  to  decide  to  which  we  owe  most. 
In  addition,  the  study  of  the  development  of  the  myelin  sheath, 
and  especially  in  recent  years  the  minute  study  of  the  histology 
of  the  various  regions,  have  aided  materially  in  mapping  out 
the  cortex. 

It  is  a  fact  which  might  appear  strange  and  almost  inexplicable 
did  the  history  of  science  not  constantly  present  us  with  the  like, 
that  forty  years  ago  the 
universal  opinion  among 
physiologists,  pathologists, 
and  physicians  was  that 
the  cerebral  cortex  is  in- 
excitable  to  artificial 
stimuli,  that  no  visible 
response  can  be  obtained 
from  it.  The  great  names 
of  Flourens  and  Magendie 
stood  sponsors  for  this 
error,  and  repressed  re- 
search. In  1870,  however, 
Hitzig  and  Fritsch  showed 
that  not  only  was  it  pos- 
sible to  elicit  muscular 
contractions  by  stimula- 
tion of  the  cortex  of  the 
brain  in  the  dog  with  vol- 
taic currents,  but  that  the 
excitable  area  occupied  a 
definite  region  in  the  neigh- 
bourhood of  the  crucial 
sulcus  or  sulcus  centralis, 
which  runs  out  over  the 
convexity  of  the  hemi- 
spheres nearly  at  right 
angles  to  the  longitudinal 
fissure.  In  this  region 
they  were  further  able  to 
isolate  several  distinct 
areas,  stimulation  of  which  was  followed  by  movements  respectively 
of  the  head,  face,  neck,  hind-leg,  and  fore-leg  (Fig.  349).  This  was 
the  starting-point  of  a  long  series  of  researches  by  Ferrier,  Munk, 
Horsley,  Schafer,  Heidenhain,  and  many  others,  on  the  brains  of 
monkeys  as  well  as  dogs — researches  which  have  formed  the  basis 
of  an  exact  cortical  localization  in  the  brain  of  man,  and  have 
enriched  surgery  with  a  new  province.  In  these  later  experiments 
the  interrupted  current  from  an  induction  machine  has  been  found 
the  most  suitable  form  of  stimulus  (see  Practical  Exercises,  p.  889), 
especially  when  one  electrode  only  is  placed  on  the  cortex  and 
the  other  on  some  indifferent  part  of  the  body — e.g.,  in  the  rectum, 
(unipolar  stimulation),  a  procedure  which  permits  of  finer  localiza- 
tion  than  when  both  electrodes  are  applied  to  the  brain  (bipolar 


Fig.  349. — Motor  Areas  of  Dog's  Brain. 
n,  neck;  /./.,  fore  -  limb  ;  h.l.,  hind  -  limb  ; 
/,  tail;  /,  face;  c.s.,  crucial  sulcus;  e.m.,  eye 
movements;  p,  dilatation  of  the  pupil  in  both 
eyes,  but  especially  in  the  opposite  eye.  All 
the  areas  are  marked  in  the  figure  only  on  the 
left  side  except  the  eye  areas,  whose  position, 
to  avoid  confusion,  is  indicated  on  the  right 
hemisphere. 


Ml 


a  m,\ni>.\l~op  physiology 


stimulation).  For  certain  purposes  the  method  of  Ewald  has 
advantages.  I  [e  fixes  to  a  trephine  hole  in  the  skull  an  ivory  plug, 
through  which  pass  the  electrodes.  When  the  animal  has  recovered 
from  the  operation,  the  region  of  the  brain  in  contact  with  the 
electrodes  can  be  stimulated  without  fastening  the  animal. 

'Motor'  Areas.*  These  have  been  recently  localized  with 
great  care  (both  by  stimulation  and  by  removal  of  portions  of 
the  cortex)  in  the  brains  of  the  higher  apes  (gorilla,  orang,  and 

chimpanzee)    by    Sher- 
ji  rington  and  Griinbaum, 

and  there  can  be  no 
'  doubt  that  the  results, 
in  their  general  outlines 
tn>  at  least,  can  be  applied 
to  the  human  brain. 
These  observers  em- 
ployed the  so-called  uni- 
polar method  of  stimu- 
lation. 

The  '  motor  '  region 
includes  the  whole 
length  of  and  the  whole 
of  the  free  width  of  the 
precentral  or  ascending 
frontal  convolution,  and 
dips  down  to  the  bottom 
of  the  central  sulcus  (fis- 
sure of  Rolando  in 
man),  but  does  not  ex- 
tend behind  the  sulcus. 
It  extends  also  into  the 
depth  of  the  fissures,  so 
that  the  hidden  part  of 
the  excitable  area  prob- 
ably equals,  perhaps  ex- 
ceeds, the  part  which 
is  free  on  the  surface  of 
the  hemisphere.  The  anterior  limit  of  the  '  motor  '  field  is  not 
quite  sharp,  but  shades  off  somewhat  gradually  into  inexcitable 
cortex.     The  sulci  in  this  region  cannot  be  considered  to  repre- 

*  Since  the  so-called  'motor'  area,  as  is  now  well  known,  is  really 
sensori-motor,  and  a  region  having  to  do  purely  with  the  discharge  of 
motor  impulses  does  not  exist,  it  would  be  better  to  call  it  the  sensori- 
motor, or,  following  Bastian's  suggestion,  the  kinesthetic  area.  Probably, 
however,  the  alteration  of  a  term  so  long  sanctioned  by  custom  in  physio- 
logical writings  would  lead  to  confusion.  Accordingly,  in  what  follows 
the  word  '  motor '  will  be  retained,  bul  to  show  thai  it  is  used  in  a  special 
sense  it  will  be  enclosed  in  quotation  marks. 


Fir,.  350. — Dog's  Brain  with  Lesion. 

A  portion  of  the  cortex  indicated  by  the  shaded 
area  was  destroyed  by  cauterization.  The  symp- 
toms were  complete  blindness  of  the  opposite 
eye  (in  this  case  the  right)  ;  weakness  of  the 
muscles  of  the  limbs  and  of  the  neck  on  the  right 
side  ;  slight  weakness  of  the  limbs  on  the  Left 
side.  When  the  animal  walked,  there  was  a 
tendency  to  turn  to  the  left  in  a  circle.  In 
eating  or  drinking,  the  head  was  turned  t<>  the 
left,  SO  that  the  mouth  was  oblique,  and  the  right 
angle  of  the  mouth  was  lower  than  the  left. 
The  tail  movements  were  normal,  and  there  was 
no  deviation  of  the  tail  to  one  side. 


THE  CENTRAL  NERVOUS  SYSTEM 


845 


sent  physiological  boundaries,  and  they  vary  so  much  in  these 
higher  brains,  that  they  can  easily  prove  fallacious  landmarks. 
On  the  mesial  surface  of  the  hemisphere  the  '  motor  '  area 
does  not  extend  quite  to  the  calloso-marginal  fissure. 

Within  this  area  are  localized  movements  of  the  leg  and 
arm  and  their  various  joints,  of  the  head,  face,  mouth,  tongue, 
ear,  nostril,  and  vocal  cords,  of  the  neck,  chest,  and  abdominal 
wall,  of  the  pelvic  floor,  and  the  anal  and  vaginal  orifices. 

The  arrangement  of  the  various  regions  follows  very  closely 
the  order  of  the  cranio-spinal  nerves,  which  supply  them,  but 


Anus  if  vagina.. 


Abdomen 

Cheat 


Fingers 

d,  thumb t_ 


Ear-''  S 


Opening 

OfjcLW. 


Sulcus  centralis. 

Voca.L  \ 

cords.     Mastication 


CSSU1. 


Fig.   351. — 'Motor'  Area  of  Cortex  of  Chimpanzee  (Grunbaum  and 
Sherrington). 

Lateral  aspect  of  the  hemisphere. 


the  organs  whose  nerves  come  off  lowest  down  are  represented 
highest  up  in  the  '  motor  '  area.  Figs.  351,  352  will  make  this 
clear.  In  the  frontal  region,  isolated  from  the  motor  area  by 
a  strait  of  inexcitable  cortex,  lies  an  area  the  stimulation  of 
which  causes  conjugate  deviation  of  the  eyes.  But  the  reaction 
differs  from  that  obtained  on  excitation  of  the  '  motor  '  area 
proper  in  front  of  the  Rolandic  fissure. 

It  is  to  be  particularly  noted  (1)  that  within  the  larger  areas, 
such  as  those  of  the  arm  and  leg,  smaller  foci  can  be  mapped 
off  which  are  related  to  movements  of  the  separate  joints — thus, 


^4" 


A    MANUAL  OF    1'IIYSIOLOGY 


in  the  leg  area,  the  hip,  knee,  and  ankle  joints,  and  the  great 
toe,  are  represented  by  separate  and  special  centres ;  (2)  that 
stimulation  of  any  one  of  these  areas  leads,  not  to  contraction 
of  individual  muscles,  but  to  contraction  of  muscular  groups 
which  have  to  do  with  the  execution  of  definite  movements. 
Inhibition  from  the  Cortex. — Contraction  is  not  the  only  effect 


Side  calloso 
marg 

Sulc.parUto 
uccip 


Sulc  Central      An,Jf  A  VcL2ind 

Sulc  precenCr.  marg 


Subcealcarin 


CSS  .itl. 


Fig.  352. — 'Motor'  Area  on  Mesial  Surface  of  Hemisphere:  Brain  op 
a  Chimpanzee  (Troglodytes  Niger)  (Grunbaum  and  Sherrington). 

Left  hemisphere  :  mesial  surface. 

The  extent  of  the  '  motor  '  area  on  the  free  surface  of  the  hemisphere  is  indicated 
by  the  black  stippling.  On  the  stippled  area  '  LEG  '  indicates  that  the  movements 
of  the  lower  limb  are  represented  in  all  the  regions  of  the  '  motor  '  area  visible  from 
this  aspect.  The  minuter  subdivisions  in  this  area  overlap  each  other  so  much 
that  no  attempt  is  made  to  distinguish  them  in  the  diagram.  '  Anus  and  \  agina  ' 
indicates  the  position  from  which  perineal  movements  can  be  primarily  elicited. 
Suli.  central. =  central  fissure;  Sulc.  calcarin.  =  calcarine  fissure;  Sulc.  paricto 
occ»y>.=parie to-occipital  fissure;  Sulc.  calloso  «!«>•£.  =  calloso-marginal  fissure; 
Sulc.  precentr.  marg.  =  precentral  marginal  fissure.  The  single  italic  letters 
mark  spots  whence,  occasionally  and  irregularly,  movements  of  the  foot  and  leg 
(ff),  of  the  shoulder  and  chest  (s),  and  of  the  thumb  and  fingers  {h)  have  been 
evoked  by  strong  faradization.  The  shaded  area  marked  'EYES'  indicates 
a  field  of  free  surface  of  cortex  which,  under  faradization,  yields  conjugate  move- 
ments of  the  eyeballs.  The  conditions  under  which  these  reactions  are  obtained 
separates  them  from  those  characterizing  the  '  motor  '  area. 

on  the  muscles  which  can  be  elicited  by  stimulating  the  cortex. 
Cortical  inhibition  of  tonus  and  of  active  contraction  is  just  as 
characteristic,  though  not  so  obvious  a  result.  There  is  abundant 
evidence,  some  of  which  has  previously  been  alluded  to  (p.  838), 
of   reciprocal    innervation    of    volitional   movements   from   the 


TH1    <  ENTR  II  NERVOUS  SYSTEM  847 

cortex.  When,  e.g.,  the  part  of  the  arm  area  which  presides 
over  extension  of  the  elbow  is  stimulated  (in  the  monkey; ,  it 
can  be  shown  that  the  biceps  relaxes  as  the  triceps  contracts. 
In  like  manner,  stimulation  of  the  appropriate  part  of  the  leg 
area  will  cause  along  with  contraction  of  the  extensors  of  the  hip 
relaxation  of  such  flexors  as  the  psoas-iliacus  and  the  tensor 
fascicB  femoris.  Such  observations  are  most  easily  made  when, 
in  a  certain  stage  of  narcosis,  the  limbs,  instead  of  hanging  limp, 
assume  a  position  of  tonic  flexion,  especially  at  the  elbow  and 
hip.  Under  other  conditions  the  position  of  tonic  extension 
of  a  joint  may  be  assumed,  and  then  it  can  be  shown  that 
excitation  of  the  appropriate  focus  for  flexion  of  that  joint  will 
cause  simultaneous  contraction  of  the  flexors  and  relaxation 
of  the  extensors. 

The  observer  cannot  fail  to  be  struck  with  the  general  resem- 
blance between  these  cortical  reactions  and  their  co-ordination 
and  the  co-ordinated  bulbo-spinal  reflex  movements  previously 
studied.  There  are,  however,  certain  differences  which  place  the 
cortical  reactions  upon  a  higher  level.  One  of  the  most  important 
is  the  part  played  by  visual,  auditory,  and  pure  '  touch '  stimuli 
in  eliciting  cortical  motor  responses — e.g.,  '  the  closure  of  the 
hand,  pricking  of  the  ear,  opening  of  the  eyes,  and  turning  of  the 
head  in  the  direction  of  the  gaze  '  (Sherrington).  The  facility  of 
response  to  stimuli  acting  from  a  distance  through  the  distance- 
receptors,  such  as  those  of  the  retina  and  the  labyrinth,  is  one  of 
the  great  characteristics  of  the  cerebrum  as  an  organ  concerned  in 
movements,  and  helps  to  place  the  '  motor  '  cortex  at  the  helm, 
since  these  distance-receptors  control  more  than  others  the 
skeletal  musculature  as  a  whole.  Spinal  reflex  movements  are 
mainly  such  as  are  elicited  by  harmful  (nocuous)  stimuli  (pro- 
tective reflexes),  or  through  the  sexual  skin  nerves,  or  from  the 
visceral  afferent  fibres,  or  such  as  are  concerned  in  the  chief 
movements  of  locomotion. 

Decerebrate  Rigidity  is  a  phenomenon  closely  related  to  the 
inhibitory  function  of  the  cerebral  cortex.  It  is  a  condition  of 
prolonged  spasm  of  certain  groups  of  skeletal  muscles  (especially 
the  retractor  muscles  of  the  head  and  neck,  the  elevators  of  the 
jaw  and  tail,  and  the  extensors  of  the  elbow,  knee,  shoulder, 
and  hip),  supervening  on  removal  of  the  cerebral  hemispheres 
by  transection  anywhere  in  the  mid-brain  or  in  the  posterior 
part  of  the  thalamus,  and  favoured  by  suspending  the  animal 
in  the  vertical  posture.  If  the  afferent  roots  belonging  to  one  of 
the  rigid  limbs  are  severed,  it  at  once  becomes  flaccid,  while  the 
other  limbs  remain  rigid.  The  tonus  is  therefore  reflex  through 
the  local  afferent  nerves,  and,  to  be  more  precise,  through  those 
that  supply  the  deep  structures   (joints,  muscles,  etc.).     The 


848  A   MANUAL  OF  PHYSIOLOGY 

centre  must  be  situated  somewhere  between  cerebrum  and  spinal 
bulb,  since  section  of  the  bulb  abolishes  the  rigidity.  It  is  not 
apparently  in  the  cerebellum.  It  is  noteworthy  that  the  muscles 
mainly  involved  in  decerebrate  rigidity  are  those  which  are 
much  more  easily  inhibited  than  excited  from  the  '  motor  '  cortex, 
and  also  in  the  local  spinal  reflexes.  After  removal  of  the 
cerebrum,  the  mechanism  which  maintains  their  tonic  contrac- 
tion has  free  play.  Sherrington  points  out  that  this  mechanism 
sustains  the  steady  muscular  tension  necessary  to  preserve 
against  the  force  of  gravity  the  attitude  or  posture  of  the  body. 
When  the  transient  spinal  reflex  or  the  transient  cortical 
effect  breaks  in  upon  this  tonic  contraction — e.g.,  in  locomotion 
—inhibition  of  the  contracted  extensors  accompanies  contraction 
of  the  flexors  (see  also  p.  836). 

Removal  of  a  single  '  motor  '  region  leads  to  paralysis  of  the 
corresponding  limb,  or  part  of  a  limb,  on  the  opposite  side. 
For  example,  after  extirpation  of  the  hand  area  the  hand  is  for 
a  few  days  practically  useless  and  apparently  powerless.  In  a 
few  weeks,  however,  it  recovers  remarkably,  so  that  it  is  once 
more  used  in  climbing  or  in  conveying  food  to  the  mouth.  It 
is  an  important  question  in  what  way  this  recovery  is  brought 
about.  If  the  whole  of  the  corresponding  area  in  the  opposite 
hemisphere  is  now  removed,  a  similar  paralysis  occurs  in  the 
other  hand,  but  the  hand  whose  motor  area  was  first  extirpated 
remains  entirely  unaffected  by  the  second  lesion.  On  the  con- 
trary, the  first  hand  is  used  more  freely  and  more  adroitly  than 
before  the  second  operation,  probably  because  the  animal  needs 
to  use  it  more.  The  second  hand  recovers  eventually,  like  the 
first.  If  when  this  has  taken  place  the  remaining  part  of  the 
arm  area  from  which  the  hand  area  was  first  excised  be  removed, 
neither  hand  is  apparently  affected,  although  there  is  severe 
paralysis  of  the  shoulder  and  slighter  paralysis  of  the  elbow 
on  the  side  opposite  to  the  lesion,  which  is  again  largely  re- 
covered from.  The  recovery  of  the  hand  movement  cannot 
therefore  be  attributed  to  the  taking  on  of  the  function  of  the 
corresponding  motor  area  either  by  the  opposite  hand  area  or 
by  the  adjacent  '  motor  '  cortex  of  the  same  hemisphere.  Accord- 
ing to  some  authorities,  the  recovery  is  due  to  the  representa- 
tion of  the  upper  limb  in  the  post-central  gyrus  (ascending 
parietal  convolution  in  man)  acting  through  fibres  that  descend 
from  this  gyrus  to  the  optic  thalamus,  and  thence  through  the 
rubro-spinal  tract,  which  runs  to  the  spinal  cord  (p.  765). 

Removal  of  the  whole  of  the  '  motor  '  cortex  of  one  hemi- 
sphere, in  such  animals  as  this  operation  has  been  performed  on, 
causes  paralysis  of  movement  on  the  opposite  side  of  the  body. 
The  paralysis  is  less  marked  in  the  case  of  bilateral  muscles  that 


THE  CENTRAL   NERVOUS  SYSTEM 


849 


habitually  act  together  t  han  in  the  case  of  those  which  ordinarily 
act  alone.  Thus  the  muscles  of  respiration  and  the  muscles 
of  the  trunk  in  general  are,  although  perhaps  weakened,  never 
completely  paralyzed.  This  is  an  indication  that  each  member 
of  such  functional  pairs  of  muscles  is  innervated  from  both 
hemispheres ;  and  this  physiological  deduction  is  supported 
by  the  anatomical  fact  already  referred  to,  that  after  removal 


Fig.  353. — Brain  of  Macaque  Monkey  (Beevor  and  Horsley). 
The  upper  figure  shows  the  lateral  aspect  of  the  left  hemisphere,  and  the  lower 
figure  its  upper  (or  dorsal)  surface.  The  '  motor  '  and  sensory  areas  are.  indicated. 
It  is  questionable  whether  the  '  motor  '  region  is  as  extensive  as  represented. 
Some  observers  do  not  admit  that  it  extends  behind  the  central  sulcus  in  these 
lower  monkeys  an}-  more  than  in  the  higher  apes. 

of  the  '  motor  '  cortex,  or  injury  to  the  pyramidal  tracts  in  the 
internal  capsule  or  crus,  some  degenerated  fibres  (homolateral 
fibres)  are  found  in  the  crossed  pyramidal  tract  on  the  side  of 
the  lesion  (p.  Jj8). 

In  the  dog  after  a  time  the  paralysis  may  more  or  less  com- 
pletely disappear.    In  the  monkey  restoration  is  less  complete. 

54 


8^o 


.1    MANUAL  OF    rilYSIOLOGY 


Some  interesting  observations  have  been  made  on  a  monkey, 
which  was  carefully  watched  for  eleven  years  after  the  removal 


PoR 


Fig.  354. — Mesial  Surface  of  Left  Hemisphere  of  Macaque  Monkey 

(Horsley). 

by  two  operations  of  the  cortex  of  the  greater  portion  of  the 
frontal  and  parietal  lobes  on  the  left  side.  The  character  of 
the   animal,    which    had   been   studied   for   months   before    the 


Fig.  355. — Cerebral  Cortex  :   Man  (seen  from  Above). 
The  front  of  the  brain  is  towards  the  right.     The  dotted  line  shows  the  position 
of  the  fissure  of  R<  ilandi  >',  as  fixed  by  Thane's  rule  (p..  856). 

operations,  was  entirely  unaffected.     All  its  traits- remained  un- 
altered.    There  was  no  loss  of  memory  or  intelligence.     On  the 


Ill/    <  ENTR  \L  NERVOUS  SYSTEM  8si 

other  hand,  disturbances  oJ  movemeni  on  the  right  side  were 
very  noticeable  up  till  its  death.  It  learned  again  to  use  the 
right  limbs  in  locomotion  ;  but,  although  they  were  not  markedly 

weaker  than  those  of  the  Idl  side,  their  movements  had  a  certain 
clumsiness,  which  was  associated  with  a  permanent  diminution 
in  the  sensibility  of  the  skin  of  these  limbs.  Muscular  sensibility 
was  also  lessened.  In  aets  requiring  the  use  only  of  one  hand, 
the  right  was  never  willingly  employed,  and  it  evidently  cost 
the  animal  a  great  effort  to  use  it  in  such  movements,  but  by 
special  training  it  learnt  again  to  give  the  right  hand  when 
asked  for  it,  and  to  make  use  of  it  for  other  purposes.  The 
movements  with  which  the  motor  areas  are  concerned  are  essen- 
tially skilled  movements,  and  we  may  suppose  that  it  is  more 
difficult  for  a  monkey  to  educate  again  a  centre  for  such  complex 
and  elaborate  manoeuvres  as  are  performed  by  its  hand  than 
for  a  dog  to  regain  normal  control  of  the  comparatively  simple 
movements  of  its  paw.  In  man  in  cases  of  hemiplegia,  when 
the  patient  lives  for  some  time,  a  certain  amount  of  recovery 
usually  takes  place,  especially  in  young  persons,  in  the  paralyzed 
leg,  but  much  less  in  the  paralyzed  arm. 

In  the  lower  monkeys  the  'motor'  area  was  formerly 
stated  to  extend  behind  the  sulcus  centralis  into  what  in  man 
would  be  called  the  ascending  parietal  convolution  (postcentral 
gyrus),  and  also  to  be  more  extensively  represented  on  the 
mesial  surface  of  the  hemisphere  than  in  the  higher  apes 
(Figs.  353,  354).  Such  observations,  however,  require  to  be 
reinterpreted  in  view  of  the  results  of  Sherrington  and  Grun- 
baum,  especially  as  they  were  carried  out  by  the  bipolar  method 
of  stimulation,  with  both  electrodes  on  the  cortex.  This  method 
does  not  admit  of  such  strict  localization  of  the  stimulus  as  the 
unipolar  method.  The  most  recent  work  with  the  unipolar 
method  has  indicated  that  in  the  lower  apes  also  excitation  of  the 
gyrus  postcentralis  does  not  cause  movements  (C.  and  O.  Vogt). 

It  is  in  the  light  of  the  results  obtained  in  monkeys,  and  by 
the  aid  of  histological,  embryological,  clinical,  and  pathological 
observations,  that  the  'motor'  areas  in  man  have  to  a  great 
extent  been  mapped  out. 

The  histological  differentiation  of  the  various  cortical  regions  recently 
demonstrated  by  Brodmann  and  by  Campbell  arc  of  especial  interesl 
(Figs.  356-360).  It  has  long  been  customary  to  divide  the  cortex 
into  layers,  although  the  number  and  the  boundaries  of  these  layers 
are  somewhat  arbitrarily  fixed.  Brodmann  distinguishes  six  lay 
(1)  A  zonal  or  peripheral  layer,  containing  many  nerve-fibres  and 
neuroglia  cells,  but  few  nerve-cells  ;  (2)  a  layer  containing  '  granules  ' 
and  small  pyramidal  cells  (external  granular  layer)  ;  (3)  a  layer  of 
medium  and  large  pyramidal  cells  (pyramidal  layer)  ;  (4)  a  layer  of 
small    irregular    cells    (internal    granular    or  -  stellate    layer);     (5)     a 

i,  54—2 


852 

>' 

a! 

3 

4 


I    U  ivr  !/.  OF  PHYSIOLOG  V 


6./!   ■.  :  :-i|  •  a,  : 


Fig.  356. — Cell-lamination  of  Gyrus  Post- 
centralis  (campbell). 

A,  just  behind  upper  end   of  fissure  of  Ro- 
lando ;  />',  from  the  posterior  edge  of  the  gyrus 

(intermediate  postcentral  area  of  Campbell). 


'  ganglioni<  '  layer,  con- 
taining the  largest  pyra- 
midal cells  {deep  large 
pyramids)  ;  (6)  a  layer 
(lamina  multiform  is)  of 
spindle-shaped  or  polymor- 
phous cells.  These  layers 
vary  in  their  structural 
details,  and  especially  in 
their  relative  development 
in  animals  of  different  rank 
m  the  mammalian  scale  In 
one  and  the  same  animal 
at  diffei  enl  pei  iods  in  its 
embryonic  and  extra-uter- 
ine growth,  and  also  in 
different  parts  of  the  cortex 
m  ,in  adult  animal  of  given 
species.  The  region  in 
fronl  of  the  central  sulcus 
(fissure  of  Rolando),  e.g.,  is 
characterized  by  the  pres- 
ence of  the  giant  pyramids 
of  Betz,  which  give  origin 
to  the  pyramidal  fibres 
going  to  the  trunk  and 
limbs  (Fig.  357). 


V 


f 


Fir,.       357. — Cell-i  AMI  NATION'       OF 
Gyrus  Precentralis  (Campbell). 

From  the  portion  of  the  gyrus  im- 
mediately in  fronl  of  the  cent]  il 
sulcus  (Campbell's  precentral  area 
in  Figs.  359,  360). 


•     '     •  *  C 

■ 

K. 

4 


Fig.      358.  —  Cell  -  lamination      OF 
GYRUS  Precentralis  (Campbell). 
From  anteriorpart  of  thegyrus{<  amp- 

bell's   intermediate    pn  -  entral    area  in 

Figs.  359.  360). 


Although  the  results  arc  less  definite,  the  work  of  Flecbsig  on 
the  time  of  development  of  the  medullary  sheath  of  the  fibres  in  the 
various  cerebral  convolutions  has  also  contributed  to  our  knowledge 


THE  CENTR  \L   .VHHVOUS  SYSTl  V 


Viruo -psychic 


u*r 


Fig.    359. — Structurally  Differentiated  Cortical  Areas  (Campbell). 
External  surface  of  hemisphere  (human  brain). 


Vuuo- 
ternary 


,<.<? 


/"termed,^. 


Fig.   360. — Structurally  Differentiated  Cortical  Areas  (Campbell). 
Mesial  surface  of  hemisphere  (human  brain). 


354 


A    U  INU  II    OF  PHYSIOLOGY 


of  Localization  in  the  cort<  k.     tn  the  development  of  a  neuron  four 
stages  can   be  distinguished      (i)   Cells  withoul    proc<  the 

appearan<  e  of  pro  first  the  axon   and   I  hen   the  dendi  i1 


Fig     |6i      Flechsig's  Developmentai    Zones  (after  Flechsig). 
Outer  surface  of  human  cerebral   hemisphere.     Primary  zones  (i-io),  darkly 
led  ;  intermediate  zones  (u    |i),  les    deeply  shaded ;    terminal  zon 
unshaded. 

(3)  the  formation  of  collaterals  ;  (4)  myeUhation  or  the  formation  of 
the  medullary  sheath  (Fig.  305,  p.  752). 

Myelination  occurs  in  the  cerebral  convolutions  in  a  regular  order. 
In   si  as  the  fibres  may  be  medullated  three  months  bei 


Fig.    562.— Flechsig's  Developmentai   Zones  (after  Flechsig). 
Inner  surface  of  human  cerebral  hemisphere. 

birth,  in  others  not  till  six  months  later.  For  instance  the  Rolandic 
and  olfactory  regions,  the  calcarine  portion  of  the  occipital  lobe 
associ.it<-<l  with  vision,  and  the  portion  of  the  temporal  Lobe  associated 
with  hearing,  are  plentifully  provided  with  medullated  fibres  a  short 
time  after  birth.  a1  any  rate  before  the  first  month,  whereas  the 
remaining  regions  of  the  cortex  are  completely,  or  almosl  completely, 


THE  CENTR  \L  NERVOUS  SYSTEM 

free  from  such  fibres.  In  this  way  Flechsig  has  distinguished  thirty-si? 
cortical  fields  (Figs  j6i,  $62),  which  he  divides  a<  cording  to  the  time 
of  myelination  into  three  groups  : 

i.  Primary  fields,  ten  in  number,  which  are  well  provided  with 
myelinated  fibres  .it  birth.  They  include  the  cortical  centre  for 
the  various  sensations  and  also  the'  motor '  area.  They  are  conne<  ted 
especially  with  the  so  called  projection  fibres.  Tims,  the  cutaneous 
and  muscular  scum-  is  assumed  to  be  represented  in  field  t,  the  sense 
of  smell  in  field  j.  oJ  vision  in  4,  and  of  hearing  in  5.  From  field  1 
arise  the  fibres  of  the  pyramidal  tract,  chiefly  from  the  ascending 
frontal  convolution,  while  the  sensory  fibres  from  the  skin  and 
muscles  end  mainly  in  the  ascending  parietal.  This  is  an  illustra- 
tion of  what  Flechsig  considers  a  general  rule  for  these  primary 
tklds — viz.,  that  each  primordial  sensory  region  is  connected  both 
with  an  afferent  (cortici-petal)  and  with  an  efferent  (cortici-fugal) 
tract.  From  the  visual  area  (4),  e.g.,  arises  a  tract  which  proceeds 
mainly  to  the  anterior  corpus  quadrigeminum. 

_'.  Terminal  fields  ($2  to  36  in  the  figures]  which  become  myelinated 
late,  the  process  not  beginning  until  at  least  a  month  after  birth. 

3.  Intermediate  fields  (11  to  31)  which  become  myelinated  earlier 
than  the  terminal,  but  later  than  the  primary.  They  and  the  ter- 
minal fields  constitute  par  excellence  association  centres,  which 
furnish  fibres  (association  fibres)  connecting  the  centres  represented 
in  the  primary  fields — e.g.,  such  fibres  as  must  be  continually  con- 
veying  impressions  from  the  visual  centre  to  the  motor  cortex 
when  the  hand  is  sketching  a  landscape.  It  may  also  be  con- 
sidered a  function  of  these  association  centres  to  store  up  the 
memories  of  previous  sense  impressions.  Flechsig  divides  the 
association  centres  represented  in  the  terminal  fields  into  :  (1)  The 
great  anterior  association  centre  in  the  frontal  lobe  in  front  of  the 
'  motor  '  area  ;  (2)  the  great  posterior  association  centre  in  the  parieto- 
temporal region  ;  (3)  the  smaller  middle  or  insular  association  centre 
which  coincides  with  the  island  of  Reil,  an  area  which,  according  to 
Sherrington  and  Griinbaum,  is  totally  '  inexcitable  '  as  regards  the 
production  of  movement  in  the  anthropoid  apes.  These  association 
centres  are  foci,  from  which  issue  and  to  which  come  the  long 
association  paths.  The  reader  must  bear  in  mind  that  Flechsig's  con- 
clusions as  to  the  functions  of  his  very  numerous  areas  are  in  many 
cases  hvpothetical,  and  can  only  be  accepted  when  corroborated  by 
other  methods.  We  are  far  from  being  able  at  present  to  subdivide 
the  functions  of  the  cortex  so  minutely  as  is  suggested  by  his  map. 

Clinical  and  Pathological  Observations  in  man  agree,  upon  the 
whole,  with  wonderful  precision  with  the  results  of  experiments  on 
animals  ;  and,  indeed,  before  any  experimental  proof  of  the 
minute  and  elaborate  subdivision  of  the  cortex  had  been  obtained. 
Broca  had  already,  from  the  phenomena  of  the  sick-bed  and  the 
post-mortem  room,  located  a  centre  for  speech  in  the  left  inferior 
frontal  convolution  (but  see  p.  863),  and  Hughlings  Jackson  had 
associated  pathological  lesions  of  the  Rolandic  area  with  certain 
cases  of  epileptiform  convulsions. 

An  extensive  haemorrhage  involving  the  Rolandic  area  of  the 
cerebral  cortex  or  an  embolus  blocking  the  middle  cerebral 
artery,  causes  paralysis  of  the  opposite  side  of  the  body.  An 
embolus  of  a  branch  of  the  middle  cerebral  artery  causes  para- 


Bs6  A   MANUAL  OF  PHYSIOLOGY 

lysis  of  the  muscles,  or  rather  movements,  represented  in  the 
area  supplied  by  it.  A  tumour  causes  symptoms  of  irritation, 
motor  or  sensory — convulsions  beginning  in,  or  sensations 
referred  to,  the  parts  represented  in  the  regions  on  which  it 
presses.  In  connection  with  the  localization  of  lesions  in  the 
'  motor'  area  of  the  cortex,  and  operative  interference  for  their 
cure,  the  cortex  has  been  frequently  stimulated  in  man.  There 
is  no  doubt  that  the  '  motor  '  region  corresponds  closely  in 
position  to  that  of  the  higher  apes.  It  does  not  include  the  post- 
central gyrus,  for  stimulation  of  this  convolution  with  such 
strengths  of  current  as  are  permissible  evokes  no  movements, 
while  movements  are  readily  elicited  from  the  precentral  gyrus 
(Horsley,  etc.).  In  exposing  the  '  motor  '  region,  or  any  particular 
part  of  it,  the  exact  position  of  the  fissure  of  Rolando  becomes 
important  ;  and  Thane  has  given  the  following  simple  method 
for  fixing  it  :  The  point  midway  between  the  point  of  the  nose 
and  the  occipital  protuberance  is  fixed  by  measuring  the  distance 
with  a  tape.  The  upper  end  of  the  fissure  of  Rolando  lies  half 
an  inch  behind  this  middle  point.  The  fissure  makes  an  angle  of 
6y°  with  the  longitudinal  fissure  (Fig.  355).  The  minor  fissures 
are  so  inconstant  as  to  afford  no  safe  guidance  in  the  localization 
of  a  given  area.     This  must  be  delimited  by  stimulation. 

Sensory  Functions  of  the  Rolandic  Area. — There  are  many 
proofs  that  the  '  motor  '  region  is  not  a  purely  motor,  but  a 
st')isoyi-motor,  or  kincesthetic,  area.  Histological  and  embryo- 
logical  studies  on  the  course  of  the  sensory  paths,  as  already 
pointed  out,  support  this  conclusion.  It  has  also  been  mentioned 
that,  according  to  Goltz's  observations  (p.  850),  removal  of  the 
Rolandic  cortex  causes  defects  of  sensation  as  well  as  of  move- 
ment. In  man,  in  connection  with  operations  on  the  brain,  still 
better  evidence  has  been  obtained.  In  two  cases  Cushing  was 
able  to  elicit  tactile  sensations  by  electrical  stimulation  of  the 
gyrus  postcentralis  (ascending  parietal  convolution),  and  the 
sense  of  muscular  movement  by  electrical  stimulation  of  the 
gyrus  precentralis.  In  a  very  careful  study  of  a  case  in  which 
he  removed  the  upper  limb  area  of  the  right  hemisphere  in  a  boy 
for  violent  convulsive  movements  of  the  whole  of  the  left  aim, 
Horsley  came  to  the  conclusion  that  the  precentral  gyrus  in  man 
is  the  seat  of  representation  of  (1)  slight  tactile  sensation  (after 
the  operation  appreciation  of  the  lightest  tactile  stimuli  was  lost)  ; 
(2)  topognosis — i.e.,  appreciation  of  the  localization  in  space  of  the 
point  touched  ;  (3)  muscular  sense  ;  (4)  stereognosis,  or  the  power 
of  recognising  the  form  of  objects  touched  and  handled  ;  (5)  pain 
— e.g.,  that  caused  by  a  pin- prick  ;  (6)  volitional  movement. 
The  postcentral  gyrus  in  man  appears  to  be  the  seat  of  a  similar 
sensory  representation,  but  as  its  relation  to  the  efferent  impulses 


THE  CENTR  I/.   NERVOUS  SYSTEM 


857 


concerned  in  volitional  movements  is  less  decided  than  thai  o! 
the  precentral  gyrus,  so  its  relation  to  afferent  impulses,  both 
from  the  skin  and  the  deeper  structures,  is  better  marked.  From 
the  tield  of  experiment  further  evidence  of  the  sensori-motor 
nature  of  the  '  motor  '  region  is  forthcoming. 

(1)  It  has  been  found  that  if  the  posterior  roots  of  the  nerves 
supplying  one  of  the  limits  be  cut  in  a  monkey,  all  the  most  deli- 
1  tic  and  ^killed  movements  of  the  limit  are  either  greatly  impaired 
or  totally  abolished 
(Mott  and  Sherring- 
ton). The  limb  is  not 
used  for  progression  or 
for  climbing,  but  hangs 
limp,  and  apparently 
helpless,  by  the  side  of 
the  animal.  That  this 
condition  is  not  due  to 
any  loss  of  function;  1 
power  by  the  peripheral 
portion  of  the  motor 
path  may  be  assumed, 
since  the  anterior  roots 
remain  intact.  That  it 
is  not  due  to  any  want 
of  capacity  on  the  part 
of  the  '  motor '  centres 
to  discharge  impulses 
when  stimulated  may 
be  shown  by  exciting 
the  cortical  area  of  the 
limb — either  electri- 
cally or  by  inducing 
epileptic  convulsions  by 
intravenous  injection 
of  absinthe  —  w  hen' 
movements  of  the 
affected  limb  take  place 
just  as  readily  as  move- 
ments of  the  sound 
limb.  The  cause  of 
the  impairment  of  vol- 
untary motion,  then, 
can  only  be  the  loss  of  the  afferent  impulses  which  normally,  pass 
up  to  the  brain,  and  presumably  to  the  '  motor  '  cortex.  When 
only  one  sensory  nerve-root  is  cut,  no  defect  of  movement  can  be 
seen  ;  andthisisevidentlv  in  accordance  with  the  fact  previously 


Fig.    363. — Diagram    of    Relations    of    Occi 
tital  Cortex  to  the  Retjxf. 

RO,  LO,  right  and  left  occipital  cortex;  RE, 
LE,  right  and  left  retina ;  C,  optic  chiasma ;  RF, 
LF,  right  and  left  visual  fields.  The  continuous 
lines  passing  back  from  the  retinae  to  the  occipital 
cortex  represent  the  crossed,  the  broken  lines  the 
uncrossed,  fibres  of  the  optic  nerves  and  tracts. 
For  the  sake  of  simplicity  the  intermediate  stations 
on  the  visual  path  in  the  anterior  corpora  quad 
rigemina,  lateral  geniculate  bodies,  and  pulvinar 
are  not  represented  in  the  diagram.  For  these 
connections  see  Fig.  342,  p.  810. 


3s8  /    1/  INUA1    OF  PHYSIOLOGY 

mentioned  (p.  700),  that  complete  anaesthesia  of  even  the  smallest 
patch  of  skin  is  never  caused  by  section  of  a  single  posterior  root. 
Ami  thai  ii  is  the  loss  ol  impulses  from  the  skin  which  plays  the 
chiei  pari  is  shown  by  the  fact  that  after  division  ol  the  posterior 
roots  supplying  the  muscles  of  the  hand  or  foot,  which  only  par- 
tially interferes  with  the  sensory  supply  of  the  skin,  joints, 
sheaths  of  tendons,  etc.,  movement  is  unimpaired  ;  while  section 
"t  i  he  nerve  roots  supplying  the  skin,  those  of  the  musi  les  being 
left  intact,  causes  extreme  loss  of  motor  power. 

(2)  If  a  strength  of  stimulus  be  sought  which  will  just  fail  to 
cause  contraction  of  the  muscular  group  related  to  a  given  motor 
area,  and  a  sensory  nerve,  or,  better,  a  sensory  surface  (best  of  all, 
the  skin  over  the  corresponding  muscles),  be  now  stimulated, 
contraction  may  occur — that  is  to  say,  the  excitability  of  the 
motor  centres  may  be  increased.  This  shows  that  the  '  motor ' 
region  is  en  rapport  not  only  with  efferent,  but  also  with  afferent 
fibres,  that  it  receives  impulses  as  well  as  discharges  them. 

The  same  experiment  is  a  proof  that  the  results  of  excitation  of 
the  motor  cortex  are  due  to  stimulation  of  the  grey  matter,  and  not, 
as  might  be  objected,  of  the  white  fibres  of  the  corona  radiata.  It 
is  undoubtedly  possible  to  excite  these  fibres  by  electrodes  directly 
applied  to  the  motor  cortex,  but  in  the  latter,  case  the  current  has 
to  be  made  stronger  than  is  sufficient  to  excite  the  grey  matter 
alone.  Further  evidence  is  afforded  by  the  following  facts  :  (a)  The 
'  period  of  delay  ' — that  is,  the  period  which  elapses  between  stimula- 
tion and  contraction — is  greater  by  nearly  50  per  cent,  when  the 
cortex  is  stimulated  than  when  the  white  fibres  are  directly  excited. 
[/<)  Morphine  greatly  increases  the  period  of  delay  for  stimulation  of 
the  cortex,  and  at  the  same  time  renders  the  resulting  contractions 
more  prolonged  than  normal,  while  the  results  of  direct  stimulation 
of  the  w-hite  fibres  are  much  less,  if  at  all,  affected,  (c)  Stimula- 
tion of  the  grey  matter,  when  separated  from  the  subjacent 
white  matter  by  the  knife,  but  left  in  position,  is  without 
effect  unless  the  strength  of  stimulus  be  increased,  although  twigs 
of  the  current  ought,  of  course,  to  pass  into  the  corona  radiata  as 
easily  as  before.  Perfectly  definite  movements  can,  however,  be 
excited  or  inhibited  by  stimulating  definite  spots  in  the  corona 
radiata,  and  even  in  the  internal  capsule.  This  simply  means  that 
in  these  positions  the  fibres  representing  these  movements  are  not 
yet  intermingled  with  fibres  representing  other  movements. 

Sensory  Areas  -Visual  Centres. — In  the  occipital  lobe  in 
animals  an  area  of  considerable  extent  has  been  found,  destruc- 
tion of  which  causes  hemianopia  (p.  819).  Thus,  if  the  right 
occipital  cortex  is  destroyed,  the  right  halves  of  the  two  retina 
are  paralyzed,  and  the  left  half  of  the  field  of  vision  is  a  blank. 
There  is  conjugate  deviation  of  the  head  and  eyes  to  the  same  side 
as  the  lesion — in  other  words,  the  animal  turns  its  head  and  eyes 
to  the  right.  Destruction  of  this  region  on  both  sides  causes 
complete  blindness.     When  the  same  region  is  stimulated,  the 


THE  CENT.  R  II     \' I  RVOUS  SYSTE  1/ 

eyes  and  head  are  turned  to  the  left  thai  is.  there  is  conjugate 
deviation  to  the  opposite  side.  In  the  higher  monkeys  the  eye 
movements  can  be  elicited  only  from  the  extreme  posterioi  apex 
nt  tlu-  occipital  Lobe  and  from  its  calcarine  region,  and  then  no1 
easily.  The  movements  differ  from  those  produced  by  stimula 
tion  of  the  area  for  eye  movements  in  the  frontal  lobe.  They 
are  not  so  certain,  their  latent  period  is  longer,  and  a  strongei 
stimulus  is  required  to  evoke  them.  It  cannot  be  doubted  that 
the  occipital  region  is  concerned  in  vision,  and  it  is  a  very  natural 
suggestion  that  the  movements  are  the  result  of  visual  sensations 
in  the  excited  occipital  cortex.  The  right  occipital  lobe  is  con- 
cerned with  vision  in  the  right  halves  of  the  two  retinae  (Figs.  342 
and  363).  Now,  under  normal  conditions,  a  visual  image  would 
be  cast  on  the  two  right  retinal  halves  by  an  object  placed 
towards  the  left  of  the  field.  The  movements  of  the  head  and 
eyes  to  the  left  may  therefore  be  plausibly  explained  as  an 
attempt  to  look  at,  and  a  rotation  towards,  the  supposed  object. 

The  pathological  evidence  is  very  clear  that  disease  of  the  occipital 
lobe,  especially  of  the  cuneus,  a  triangular  area  on  its  mesial  surface, 
causes  hemianopia  in  man.  A  limited  lesion  may  even  be  associated 
with  an  incomplete  hemianopia,  and  cases  have  been  recorded  in 
which  colour  hemianopia  (blindness  of  the  corresponding  halves  of 
the  two  retina?  for  coloured  objects)  co-existed  with  normal  vision  for 
white  light.  The  precise  limits  of  the  occipital  visual  area  are  still 
disputed.  It  probably  occupies,  in  addition  to  the  cuneus,  the 
lingual  lobule  and  a  portion  of  the  external  aspect  of  the  occipital 
lobe.  The  question  of  the  projection  of  the  retina  upon  the  visual 
cortex — i.e.,  the  question  whether  each  retinal  area  is  represented 
in  a  definite  cortical  area — has  given  rise  to  much  debate.  The 
representation  of  the  fovea  centralis,  the  area  of  most  distinct 
vision,  has  aroused  especial  interest.  It  has  been  asserted  that  a 
circumscribed  area  in  the  region  of  the  calcarine  fissure  is  the  centre 
for  the  fovea  (Henschen).  But  it  is  totally  opposed  to  this  view 
that  extensive  lesions  of  the  occipital  cortex,  even  on  both  sides,  do 
not,  except  in  rare  cases,  cause  total  blindness  in  the  foveal  region, 
although  peripheral  vision  is  destroyed.  On  the  other  hand,  in  no 
case  has  a  purely  cortical  lesion  been  found  associated  with  blindness 
confined  to  the  fovea  (Monakow) .  The  fibres  of  the  optic  radiation 
which  are  on  the  path  from  the  fovea  are  accordingly  distributed 
diffusely  to  the  visual  cortex.  Sometimes  dimness  of  vision  in  the 
whole  of  the  opposite  eye  (crossed  amblyopia),  and  not  hemianopia, 
is  caused  bv  a  lesion  of  the  occipital  cortex.  It  seems  impossible 
to  explain  this  and  other  facts  without  postulating  the  existence  of 
more  than  one  visual  centre  ;  and  it  has  been  supposed  that  in  the 
angular  gyrus  and  the  neighbouring  region  a  higher  visual  centre 
exists  which  is  connected  with  the  lower  occipital  centres  for  the 
two  halves  of  the  opposite  eye.  Thus,  the  right  angular  gyrus 
would  be  in  connection  with  the  part  of  the  right  occipital  cortex 
which  has  to  do  with  vision  in  the  nasal  half  of  the  left  eye,  and  with 
the  part  of  the  left  occipital  cortex  which  has  to  do  with  vision  in 
the  temporal  half  of  that  eye.  This  higher  centre,  which  perhaps 
functions  as  a  storehouse  of  visual  memories,  probably  corresponds 


86o 


4    U  •/  vr  1/    m/-  PHYSIOLOGY 


to  the  structurally  differentiated  area  (visuo-psychic  area  of  Camp- 
bell), as  the  lower  centre  corresponds  to  his  structurally  differentiated 
visuo-sensory  area  (Figs.  359,  360). 

Auditory  Centre. — On  the  outer  surface  of  the  temporo- 
sphenoidal  lobe,  mainly  in  the  first  temporal  convolution,  lies 
an  area  associated  with  the  sense  of  hearing.  Stimulation  in  the 
region  of  the  first  temporal  convolution  may  cause  the  animal  to 


Fig.  364. — Lateral  View  ok  Left  Hemisphere  with  Sensorv  Areas  .  Man. 
The  front  of  the  brain  is  towards  the  left. 

prick  up  its  ear  on  the  opposite  side.  Destruction  of  this  area 
on  both  sides  is  followed  by  complete  and  irremediable  loss  of 
hearing.  If  it  is  destroyed  only  on  one  side,  there  is  partial  deaf- 
riess  of  the  opposite  car,  and  also  to  some  extent  of  the  ear  on 
the  same  side.  This  is  gradually  recovered  from.  If  it  is  de- 
stroyed on  the  left  side  there  is  also  the  peculiar  condition  called 
'  word-deafness/  which  will  be  referred  to  directly  (p.  864).  In 
deaf-mutes  the  first   temporal  convolution  may  be  atrophied. 


THE  i  I  \l  RAL    \i  JiVOVS  SYST.  I  \l 


S61 


There  is  evidence  thai  the  posterior  corpora  quadrigemina  and 
the  mesial  geniculate  body  form  an  inferior  relay  on  the  route 
between  the  fibres  oi  the  audit  on  nerve  and  the  temporal  cortex. 
There  are  indications  that   within  the  auditory  area  so-called 

'  musical  centres  '  exist— that  is,  an  orderly  arrangement  of  the 
cell-bodies  of  the  neurons  that  have  to  do  with  the  perception  of 
pitch,  so  that  a  limited  lesion  may  cause  deafness  to  note-  oi 
a  particular  pitch  when  it  is  situated  on  one  part  of  the  area, 
and  deafness  to  notes  of  a  different  pitch  when  it  is  situated  else- 
where (Larionnw  . 

Centre  for  Smell.  As  to  the  position  of  the  i  entre  for  smell, 
direct  experiment  on  animal-  cannot  teach  us  much,  for  if  the 
outward  tokens  of  visual  and  auditory  sensations  are  dubious 
and  fluctuating,  still  more  is  this  the  case  with  the  signs  of 
sensations  of  smell.     A  further  source  of  fallacy  is  the  fad  that 


FIG.   365. — Sensory  Areas  of  .Mesial  Surface  of  Human  Brain. 
The  front  of  the  brain  is  towards  the  right. 


other  sensations  than  those  of  smell  are  caused  by  stimulation 
of  the  mucous  membrane  of  the  nose.  Substances  like  ammonia, 
for  example,  affect  entirely  the  endings  of  the  trigeminus,  which 
is  the  nerve  of  common  sensation  for  the  nostrils.  Pathological 
and  clinical  evidence  would  be  of  great  value,  but  it  is  as  yet 
scanty,  and  of  itself  indecisive.  Some  cases  of  epilepsy  have 
been  reported  in  which  the  attack  was  heralded  by  smells  for 
which  there  was  no  objective  cause.  At  autopsy  the  uncinate 
gyrus  was  found  diseased.  So  far  as  it  goes,  such  evidence 
supports  the  view  derived  from  the  anatomical  connections 
of  the  olfactory  tracts,  that  the  centre  for  smell  is  situated 
in  the  uncinate  gyrus  on  the  mesial  aspect  of  the  temporal  lobe, 
for  the  olfactory  tract  may  be  traced  into  this  region.  In  animals 
with  a  very  acute  sense  of  smell,  this  gyrus  is  magnified  into  a 


I    1/  i. mil  OP  PHYStOLOGl 

veritable  lobe,  called  from  its  shape  the  pyriform  lobe  ;  from  its 
supposed  function,  the  rhinencephalon.  The  centre  for  taste  is 
supposed  to  be  situated  in  the  same  region  as  the  centre  for  smell 
(in  the hippocampal  convolution  posterior  to  the  un<  inati  gyrus  . 
Ordinary  and  Tactile  Sensations,  including  the  muscular  sense, 
have  been  Located  in  the  Rolandic  area  (p.  856)  ;  and  there  are 
good  grounds  for  believing  that  afferent  fibres  from  the  joint-,, 
the  muscles  and  their  accessory  structures  and  the  skin  ter- 
minate here  in  arborizations  which  come  into  contact  either 
with  the  motor  pyramidal  cells,  or  with  intermediate  cells  which 
link  them  to  the  pyramidal  cells. 

Aphasia.  Words  are,  at  bottom,  arbitrary  signs  bj'  which  certain 
ideas  are  expressed.  The  power  of  intelligent  communication  by 
spoken  or  written  language  may  be  lost:  (1)  by  paralysis  of  the 
muscles  of  articulation  or  the  muscles  which  guide  the  pen  ;  (2)  by 
inability  to  hear  or  see  the  spoken  or  written  word  i.e.,  by  deafness 
or  blindness  ;  (3)  by  inability  to  comprehend  the  meaning  of  spoken 
or  written  language,  although  sensations  of  hearing  and  sight  may 
not  be  abolished — that  is  to  say,  by  inability  to  interpret  the  auditory 
or  visual  symbols  by  which  ideas  are  conveyed  ;  (4)  by  inability  to 
clothe  ideas  in  words,  although  the  words  may  be  present  in  the 
patient's  consciousness,  and  the  ideas  conveyed  bv  speech  or  writing 
may  be  comprehended.  Neither  (1)  nor  (2)  is  considered  to  consti- 
tute the  condition  of  aphasia  :  (3)  represents  what  is  called  amnesia, 
or  sensory  aphasia  ;  (4)  is  aphasia  in  the  ordinary  restricted  sense,  or 
1    iphasia. 

Motor  aphasia  may  be  divided  into  two  varieties— subcortical 
or  pure  motor  aphasia,  and  cortical,  or  Broca's  aphasia.  In 
tin  subcortical  type  the  patient  understands  speech  and  writing 
perfectly,  and  is  able  to  write  normally  ;  but  lie  cannot  speak  spon- 
taneously or  read  aloud,  or  repeat  words  when  requested  to  do 
tit'  may  know  quite  well  what  to  reply  m  answer  to  a  question,  but 
the  words  necessary  to  express  his  meaning  do  not  come  to  him. 
In  Broca's  type  of  aphasia,  which  is  the  most  common  form,  the 
patient  may  understand  spoken  and  written  words  —  often  imper- 
fectly, it  is  true — but  he  is  unable  to  speak  spontaneously,  to  repeat 
words  spoken  to  him,  and  to  read  aloud.  Unlike  the  subcortical 
type  oi  motor  aphasic,  he  has  difficulty  in  reading  by  the  eye  with- 
out articulation,  and  in  writing  spontaneously  or  to  dictation. 
I  here  is  often  or  always  a  certain  amount  of  intellectual  deficiency. 
Tin  gradations  in  the  loss  of  the  expri  ssive  factor  in  speech  may  be 
infinite.  A  patient  may  sometimes  sing  a  song  without  a  single 
slip  in  words  or  measure,  and  yet  be  unable  to  speak  or  write  it.  In 
a  case  recorded  bv  Larionow  an  apha.sic  could  speak  only  one 
syllable.  '  tan,'  but  could  sing  the  '  .Marseillaise.'  Jn  certain  I 
the  change  is  confined  to  loss  of  the  power  of  spontaneous  speech, 
and  the  patient  may  be  able  to  read  intelligently.  Sometimes  In- 
can  express  his  ideas  in  speech,  but  not  in  writing  [agraphia).  Some- 
times tli''  Loss  is  restricted  to  certain  sets  of  ideas.  For  cxampi' 
boy  was  injured  by  falling  on  his  head.  Typical  symptoms  of  motor 
aphasia  developed,  but  the  power  of  dealing  with  ideas  of  number 
was  not  interfered  with,  and  the  boy  continued  to  learn  arithmetic 
as  if  nothing  had  happened.     Proper  names  and  nouns  are  more 


////■   CENTRA1    \  i  RVOUS  SI  Si  I  w 

easily  lost  than  adjectives  and   verbs.     Motor  aphasia  erally 

accompanied  In   paralysis,  frequently  transient,  oi  voluntary  trn 
menl  on  the  right  side,  sometimes  amounting  to  complete  hemipl 

but  more  often  involving  the  right  arm  alone.  This  association  is 
generally  explained  by  the  proximity  oi  the  inferior  frontal  convo- 
lution to  the  motor  area  of  the  arm.  and  their  common  blood-supply. 
It  lias  already  been  stated  thai  sun,-  Broca  it  has  been  generally 
assumed  that  in  most  persons  the  inferior  frontal  convolution  on  the 
lett  side  is  concerned  in  the  expression  of  ideas  in  spoken  or  written 
language.  It  is  even  said  that  oratorical  powers  have  been  found 
associated  with  marked  development  oi  this  convolution  (as  in  the 
case  of  (iambetta,  the  French  statesman).  It  is  the  cortical  or 
Broca's  type  of  motor  aphasia,  which  has  been  supposed  to  be 
associated  with  a  lesion  in  the  left  inferior  frontal  convolution.  The 
portion  of  the  convolution  concerned  is  the  posterior  extremity, 
where  it  borders  on  the  fissure  of  Sylvius,  and  it  either  completely 
coincides  with  or  largely  overlaps  the  centre  for  the  movements  of 
the  tongue,  lips,  and  larynx  concerned  in  articulation.  The  failure, 
however,  does  not  lie  in  the  articulatory  mechanism.  The  patient 
uses  the  same  muscles  of  articulation,  without  any  marked  impairment 
of  function,  for  chewing  and  swallowing  his  food.  It  is  only  when  the 
corresponding  area  in  the  right  inferior  frontal  convolution,  or  the 
path  from  it  to  the  internal  capsule,  is  also  destroyed,  that  articula- 
tion is  greatly  and  permanently  interfered  with. 

The  question  obviously  presents  itself  why  it  is  that  motor  aphasia 
is  commonly  due  to  a  lesion  in  the  left  hemisphere  alone.  The 
answer  to  this  question  is  supposed  to  be  partly  supplied  by  the 
important  and  curious  observation  that  in  left-handed  individuals 
damage  to  the  right  inferior  frontal  convolution  may  cause  aphasia. 
In  the  right-handed  man  the  motor  areas  of  the  left  hemisphere 
may  be  supposed  to  be  more  highly  educated  than  those  of  the  right 
hemisphere.  The  movements  of  the  right  side  which  they  initiate 
or  control  are  stronger  and  more  delicate  and  precise  than  those 
of  the  left  side.  It  is  only  necessary  to  assume  that  this  process  of 
specialization,  of  selective  training,  has  been  carried  on  to  a  still 
greater  extent  in  the  left  frontal  convolution,  that  in  most  men  the 
speech-centre  there  has  taken  upon  itself  the  whole,  or  the  greater 
part,  of  the  labour  of  clothing  ideas  in  words,  leaving  to  the  right 
centre  only  its  primitive  but  undeveloped  powers.  In  left-handed 
persons  the  speech-centre  on  the  right  side  may  be  supposed  to  share 
in  the  general  functional  development  of  the  right  hemisphere.  That 
great  capabilities  are  lying  dormant  in  the  right  speech-centre  of  the 
ordinary  right-handed  individual  is  indicated  by  the  fact  that  after 
complete  destruction  of  the  left  inferior  frontal  convolution  the 
power  of  speech  may  be  to  a  considerable  extent,  though  slowly  and 
laboriously,  regained  ;  and  it  is  said  that  this  second  accumulation 
may  be  swept  away,  anil  without  remedy,  by  a  second  lesion  in  the 
right  inferior  frontal  convolution.  But  frail  is  the  tenure  of  life  in 
a  person  who  has  twice  suffered  from  such  a  lesion  ;  and  we  do  not 
know  whether  recovery  might  not  take  place  to  some  extent  even 
after  destruction  of  both  inferior  frontal  convolutions,  if  the  patient 
only  lived  long  enough. 

Recently  Marie  has  reopened  the  whole  question  of  the  relation  of 
aphasia  to  lesions  of  the  inferior  frontal  convolution.  He  believes 
that  the  so-called  Broca's  area  has  nothing  to  do  with  aphasia  in 
the  proper  sense  of  the  term — i.e.,  it  is  not  a  cortical  area  concerned 


864  I    \1.\\  i    ;/.  OF    I'll  YSIOLOG  I 

in   'internal'  speech   ,  .   or  in    which   motor  or  kinesthetic 

'  speech  memories  '  are  stored — but  simply  a  '  motor  '  area  for  the 
movements  oi  articulation.  He  maintains  that  there  is  but  one 
form  oi  tru<  aphasia — the  aphasia  of  Wernicke  -which  has  for  its 
basis  a  lesion  oi  the  so-called  zone  oi  Wernicke  'the-  supramarginal 
and  angular  gyri,  and  the  posterior  portions  of  the-  first  and  second 
temporal  convolutions  This,  according  to  him,  is  t  lie  true  speech- 
centre.  The  symptom-complex  known  as  Broca's  aphasia,  which 
everybody  admits  to  exist  as  a  distinctly  characterized  clinical 
condition,  is  due.  he  says,  to  a  double  lesion.  One  lesion  causes 
aphemia  (loss  oi  the  power  of  co-ordinating  the  movements  needed  in 
the  articulation  oi  words  without  actual  paralysis  of  the  muscles),  and 
the  other  the  disturbance  of  internal  speech,  and  the  difficulty  of 
reading  and  of  writing,  which  constitute  the  true  aphasia.  Accord- 
ing to  Mane,  the  lesion  which  causes  the  aphemia  is  nr>t  even  situ- 
ated in  Broca's  convolution,  but  somewhere  in  a  rather  badly  defined 
region,  which  he  denominates  the  lenticular  zone,  since  it  includes 
the  lenticular  as  well  as  the  caudate  nucleus,  in  addition  to  the 
rnal  and  internal  capsules  and  the  cortex  of  the  island  of  Reil. 
It  would  be  out  of  place  to  enter  more  minutely  here  upon  such 
controversial  matters.  The  conclusion  which  emerges  most  defi- 
nitely from  the  discussion  is  that  Broca's  localization  was  based 
upon  a  very  narrow  foundation,  and  must  probably  be  modified. 

A  so-called  temporary  aphasia  may  occur  without  any  structural 
change  in  the  speech-centre — for  example,  during  an  attack  of 
migraine.  In  children  it  may  even  be  caused  by  some  comparatively 
slight  irritation  in  the  digestive  tract,  such  as  that  due  to  the  presence 
of  a  tape- worm. 

In  the  anthropoid  apes  no  evidence  of  the  existence  of  any  '  speech- 
centre,'  even  distantly  foreshadowing  the  human,  has  been  obtained 
by  stimulating  the  inferior  frontal  convolution  on  either  side.  No 
movements,  and  particularly  no  movements  connected  with  vocali- 
zation, are  elicited. 

Sensory  Aphasia. — In  typical  motor  aphasia  spoken  and  written 
words  convey  to  the  patient  their  ordinary  meaning.  They  call  up 
in  his  mind  the  usual  sequence  of  ideas,  but  the  chain  is  broken  at  the 
speech-centre,  and  the  outgoing  ideas  cannot  be  clothed  in  words.  The 
expressive  factor  in  speech  is  deranged .  J  n  sensory  aphasia  the  percep- 
tive factor  in  speech  is  deranged.  In  ordinary  sensory  aphasia  {Wer- 
nicke's, or  cortical  sensory  aphasia)  the  patient  cannot  understand 
spoken  or  written  language,  but,  far  from  being  unable  to  speak,  he 
often  babbles  incessantly.  He  may  string  together  a  series  of  words, 
each  correctly  articulated,  but  having  no  meaning,  or  may  utter  a 
jargon  not  composed  of  known  words  at  all.  Instead  of  the  words 
which  he  desires  to  use  to  express  his  meaning, he  may  use  others 
having  a  similar  sound  [paraphasia).  Damage  to  two  regions  of  the 
left  hemisphere  oi  the  brain  has  been  found  associated  with  this 
strange  condition  i  the  upper  portion  of  the  temporo-sphenoidal 
lobe,  (21  the  angular  gyrus  and  the  occipital  lobe.  When  the 
temporal  region  is  alone  affected,  it  is  the  spoken  word  that  is  missed, 
the  written  that  is  understood  (word-deafness).  When,  as  occa- 
sionally happens,  the  lesion  is  confined  to  the  occipital  region, 
spoken  language  is  perfectly  understood,  written  language  not  at 
all  (word-blindness).  Sensory,  like  motor  aphasia,  may  exist  in 
any  f  completeness,  from  absolute  word-deafness  or  word- 

blindness,  in  which  no  spoken  or  printed  word  calls  up  any  mental 


111!    CENTRAL  NERVOUS  SYSTEM 

image,  to  a  condition  not  amounting  to  much  more  than  a  marked 
absence  of  mind  or  unusual  obtuseness.  Motor  and  sensory  aphasia 
may  be  present  together.  In  well-marked  cortical  word-deafness 
speech  is  always  interfered  with  to  some  extent.  In  so-called  pure 
word-deafness  (subcortical  sensory  aphasia)  the  patient  may  be  per- 
fectly capable  of  rational  speech.  He  may  talk  to  himself  or  on  a 
set  topic  with  fluency  and  sense,  may  write  intelligently,  and  under- 
stand what  he  reads  ;  but  he  may  be  unable  to  understand  a  single 
word  spoken  to  him,  or  to  repeat  words  when  asked  to  do  so. 

Cortical  Epilepsy. — While  it  was  still  believed  that  the  cortex  was 
incxcitable.  epilepsy  was  supposed  to  be  exclusively  due  to  morbid 
conditions,  structural  or  functional,  of  the  medulla  oblongata 
(Kussmaul  and  Tenner).  Some  more  recent  writers  have  put 
forward  precisely  the  opposite  opinion,  that  the  disease  is  always 
cortical  in  origin  (Unverricht,  etc.).  What  we  know  for  certain  is 
that  some  cases  of  epilepsy,  but  only  a  minority,  are  associated 
with  cortical  lesions.  Among  these  are  the  cases  of  so-called  Jack- 
son ian  epilepsy — a  condition  characterized  by  the  fact  that  the 
seizure  does  not  begin  by  general,  but  by  local,  convulsions.  They 
may  remain  confined  to  a  single  limb,  or  to  one  side  of  the  face,  or 
to  one  side  of  the  body.  So  long  as  the  convulsions  are  not  general, 
consciousness  need  not  be  lost.  Or  a  seizure  beginning  as  Jack- 
scnian  may  spread  so  as  to  involve  the  whole  body,  in  which  case 
the  symptoms  become  identical  with  those  of  ordinary  epilepsy, 
including  the  loss  of  consciousness.  It  has  been  found  possible  in 
some  cases  to  localize  the  position  of  the  lesion  from  the  part  of  the 
body  in  which  the  fit,  or  the  aura  (the  sensation  or  group  of  sensations 
peculiar  to  each  case,  which  precedes  and  announces  the  attack)  begins. 
For  example,  if  the  convulsions  commence  with  a  twitching  of  the 
right  thumb  and  extend  over  the  arm,  or  if  the  aura  consists  of  sen- 
sations beginning  in  the  thumb,  there  is  a  strong  presumption  that 
the  seat  of  the  lesion  is  the  part  of  the  arm-area  known  as  the 
'  thumb-centre  '  in  the  left  cerebral  hemisphere.  It  is  the  seat  of 
the  convulsion  at  its  commencement,  not  the  regions  to  which  it  may 
afterwards  spread,  that  is  important  in  diagnosing  the  position  of 
the  lesion.  For  just  as  strong  or  long-continued  electrical  stimula- 
tion of  a  given  '  centre  '  of  the  '  motor  '  cortex  may  give  rise  to  con- 
tractions of  muscles  associated  with  other  '  centres,'  so  the  excitation 
set  up  by  localized  disease  may  spread  far  and  wide  from  its  original 
focus,  involving  area  after  area  of  the  '  motor  '  region  first  in  the 
one  hemisphere  and  then  in  the  other.  The  part  of  the  body  to 
which  a  sensory  aura  is  referred  is  as  significant  an  indication  of  the 
seat  of  the  discharging  lesion  as  is  the  part  of  the  body  which  first 
begins  to  twitch.  This  is  one  of  the  proofs  that  the  '  motor  '  region 
is  not  a  purely  motor  area. 

Seat  of  Intellectual  Processes. — When  we  have  deducted 
from  the  cortex  of  the  hemisphere  the  whole  Rolandic  region 
and  the  sensory  centres,  there  still  remains  a  large  territory  un- 
accounted for.  Considerable  portions  of  the  occipital,  parietal, 
and  temporal  lobes,  nearly  the  whole  of  the  island  of  Reil  and 
the  greater  part  of  the  frontal  lobe  anterior  to  the  ascending 
frontal  convolution  are  '  silent  areas/  and  respond  to  stimulation 
by  neither  motor  nor  sensory  sign.  They  correspond  to  the 
association   centres    previously   referred   to.     By   a   process   of 

55 


A  MANUAL  OB   PHVSIOLOCi 

exclusion  it  has  been  supposed  that,  in  addition  to,  <>i  partly 
in  virtue  of,  their  associative  function,  the)  are  the  seal  ol  intel- 
lectual .mil  psychical  operations.  The  intellectual  function 
has  been  more  particularly  assigned  to  the  frontal  lobes,  and 
with  great  probability,  although  we  have  little  real  knowli 
to  guide  ii>  i"  a  decision.  Extensive  destruction  and  loss  ol 
substance  ol  the  pre-frontal  region  may  sometimes  occur  with- 
out any  marked  symptoms.  But  usually  then  is  restriction 
ol  mental  power  or  it  may  be  loss  of  moral  restraint.  Thus  in 
the  famous  'American  crowbar  case,'  an  iron  bai  completely 
transfixed  the  left  frontal  lobe  of  a  man  engaged  in  blasting. 
Although  stunned  lor  the  moment,  lie  was  aide  in  an  hour  to 
climb  a  long  flight  of  stalls,  and  to  answer  the  inquiries  of  the 
surgeon.  Finally,  he  recovered,  and  lived  lor  nearly  thirteen 
years  without  either  sensory  or  motor  deficiency,  except  that 
lie  suffered  occasionally  from  epileptic  convulsions.  But  his 
intellect  was  impaired  ;  he  became  fitful  and  vacillating,  profane 
in  his  language  and  inefficient  in  his  work,  although  previously 
decent  in  conversation  and  a  diligent  and  capable  workman. 

Flechsig  supposes  that  his  great  anterior  association  centre  in 
the  frontal  lobe  is  concerned  in  the  retention  of  the  memory  of  all 
conscious  bodily  experiences,  especially  those  connected  with  volun- 
tary acts.  The  great  posterior  association  centre  he  imagines  to  be 
engaged  in  the  formation  and  coliection  of  ideas  of  external  obj 
and  of  the  'word  pictures'  which  represent  them,  and  with  t he- 
preparation  of  speech  in  respect  of  the  thoughts  to  be  expressed  and 
the  form  of  expression,  the  office  of  the  Broca's  area  (but  see  p.  864) 
being  to  execute  the  mechanical  part  of  the  process  by  transforming 
these  thoughts  into  actual  spoken  words.  This  posterior  association 
centre  may  be  looked  upon  as  the  seat  of  intellect  in  the  narrower 
sense,  as  the  anterior  is  of  will  and  feeling. 

The  experiments  of  Franz  on  the  relation  ol  the  cerebral  associa- 
tion areas,  and  especially  the  frontal  area,  to  certain  acquired  habits 
are  1  >1  interest.  Cats  were  allowed  to  acquire  certain  habits  involv- 
ing simple  mental  processes,  and  then  it  was  seen  how  these  were 
aflected  by  cortical  lesions.  After  bilateral  extirpation  of  the  frontal 
lobes  (the  area  anterior  to  the  crucial  sulcus)  newly-formed,  but  not 
long-standing,  habits  are  lost.  This  cannot  be  due  to  shock,  since 
other  brain  lesions  are  not  foflowed  by  loss  of  the  habits.  Extirpa- 
tion of  one  frontal  area  usuafly  causes  a  partial  loss  of  newly-acquired 
habits.  1  ir,  rather,  a  slowing  of  the  association  process  leading  to 
unusual  delay  in  the  execution  of  the  movements  connected  with 
the  habit.  Habits  once  lost  alter  removal  oi  the  frontals  may  be 
ref  earned. 

The  influence  of  psychical  events  upon  bodily  functions  is  well 
known,  and  has  been  more  than  once  illustrated  in  preceding  pages. 
The  converse  question  of  the  influence  1  it  bodily  states  upon  psy<  hical 
events  has  also  been  raised,  especially  in  connection  with  t1 
of  emotions.  Some  psychologists  assume  that  the  buddy  change 
associated  with  such  emotions  as  grief,  fear,  rage,  or  love,  are  not 
evoked  as  a  consequence  of  the  emotions,  but  that  the  bodily  changes 
follow  directly  the  perception  of  the  exciting  fact — e.g.,  a  spectacle 


////    CENTRA1     \  /  Rl  OUS  SYS7  I  M  867 

which  causes  fear  or  rage,  '  and  that  our  feeling  oi  the  same  changes 
.is  they  occur  is  the  emotion  '  ( fames).  Sherrington,  however,  has 
shown  tli.it  in  dogs  in  which,  by  transection  of  the  vagi  and  the 
spina]  conl.  all  sensation  oi  viscera,  skin,  and  muscles  Behind  the 
level  of  the  shoulder  was  eliminated,  no  obvious  emotional  defect 
was  caused.  Notwithstanding  the  immense  abridgment  of  the  field 
oi  sensation,  anger,  joy,  Eear,  disgust  (as  on  being  offered  dog's  flesh, 
which  most  dogs  refuse  to  eat),  were  as  marked  as  ever,  and  were  evoked 
by  the  same  objects  as  before  the  operation.  When  the  afferent 
field  is  still  more  restricted,  as  in  the  head  of  a  dog  grafted  on  the 
circulation  of  .mother  dog  by  anastomosis  oi  the  bloodvessels,  with 
precautions  to  avoid  interruption  of  the  blood-flow,  not  only  does  the 
respiratory  centre  continue  to  discharge  it  sell  with  a  regular  rhythm, 
but  cortical  volitional  movemeni  s persist  (Guthrie,  Pike  and  Stewart), 
and,  so  far  as  can  be  judged,  sense  perception,  emotional,  and  ev<  n 
intellectual,  processes  continue.  In  one  case  the  picture  presented 
by  the  engrafted  head  was  essentially  the  same  as  that  presented  by 
the  he.id  of  the  'host'  for  over  two  hours.  In  a  transplanted  head 
from  a  younger  dog  in  which  the  circulation  had  been  interrupted 
for  twenty-nine  minutes,  a  remarkable  return  of  cerebral  function 
was  observed  (Guthrie). 

Localization  of  Function  in  the  Central  Nervous  System. 
— Let  us  now  consider  a  little  more  closely  the  real  meaning  of 
this  localization  of  function.  Scattered  all  over  the  grey  matter 
of  the  primitive  neural  axis,  and,  as  we  have  seen,  over  the  grey 
mantle  of  the  brain  as  well,  are  numerous  '  centres  '  which  seem 
to  be  related  in  a  special  way  to  special  mechanisms,  sensory, 
secretory,  or  motor.  The  question  may  fitly  be  asked  whether 
those  centres  are  really  distinct  from  each  other  in  quality  of 
structure  or  action,  or  whether  they  owe  their  peculiar  properties 
solely  to  differences  in  situation  and  anatomical  connection.  It 
is  clear  at  the  outset  that  the  nature  of  the  work  in  which  a  centre 
is  engaged  must  be  largely  determined  by  its  connections.  The 
kind  of  activity  which  goes  on  in  the  vaso-motor  centre  in  the 
bulb,  for  example,  may  in  no  essential  respect  differ  from  that 
which  goes  on  in  the  respiratory  centre.  The  calibre  of  the 
bloodvessels  will  alter  in  response  to  a  change  of  activity  in  the 
one  because  it  is  anatomically  connected  with  the  muscular  coat 
of  the  bloodvessels.  The  rate  or  depth  of  the  respiratory  move- 
ments will  alter  in  response  to  a  change  of  activity  in  the  other 
because  it  is  connected  with  muscles  which  can  act  upon  the 
chest-walls. 

Recent  experiments  afford  a  very  interesting  illustration  of 
the  determining  influence  of  their  peripheral  connections  on 
the  function  of  nerve-fibres.  It  has,  in  fact,  been  shown  that 
the  central  end  of  any  efferent  somatic  fibre — i.e.,  any  fibre 
running  from  the  central  nervous  system  and  ending  in  striated 
muscle — can  make  functional  connection  with  the  peripheral 
end  of  any  other  efferent  fibre  of  the  same  class,  whatever  be 
the  normal  actions  produced  by  the  two  fibres.     Advantage  has 

55—2 


868  A    MANX  AL  OF    PHYSIOLOGY 

been  taken  of  this  in  surgery.  For  instance,  in  a  case 
facial  (motor)  tic  the  fa<  ial  nerve  was  divided  and  its  peripheral 
end  united  with  a  portion  of  the  fibres  of  the:  spinal  accessory. 
The  voluntary  movements  of  the  face,  after  regeneration  had 
a ,  urred,  were  normally  carried  out  through  impulses  descending 
the  spinal  a<  i  essory.  In  cases  of  local  paralysis,  due  to  destruc- 
tion  of  anterior  horn-cells  (anterior  poliomyelitis),  restoration  of 
movement  has  also  been  obtained  by  connecting  the  motor  nerve 
of  the  paralyzed  muscles  to  a  portion  of  a  nerve  coming  off  from 
an  uninjured  region  of  the  cord. 

The  central  end  of  any  efferent  somatic  fibre  can  also  make 
functional  union  with  the  peripheral  end  of  any  of  the  efferent 
fibres  which  run  from  the  central  nervous  system  and  end  in 
ganglion  cells  (pre-ganglionic  fibres),  and  the  central  end  of 
any  pre-ganglionic  fibre  can  do  the  same  with  the  peripheral 
end  of  any  efferent  somatic  fibre  (Langley  and  Anderson).  For 
instance,  Langley  divided  (in  cats)  the  vagus  nerve  and  the 
cervical  sympathetic.  The  peripheral  end  of  the  former  de- 
generated, of  course,  below  the  section,  and  the  peripheral 
(cephalic)  end  of  the  latter  degenerated  above  the  section,  up  to 
the  terminations  of  its  axons  in  the  superior  cervical  ganglion. 
The  central  end  of  the  cut  vagus  was  subsequently  sutured  to 
the  peripheral  end  of  the  cut  sympathetic.  After  a  time  the 
vagus-fibres  grew  along  the  course  of  the  degenerated  sympa- 
thetic up  to  the  ganglion,  where  some  of  them  formed  arboriza- 
tions around  the  ganglion  cells.  It  was  now  found  that  stimula- 
tion of  the  vagus  produced  the  effects  usually  caused  by 
stimulation  of  the  cervical  sympathetic — for  example,  dilatation 
of  the  pupil  and  constriction  of  the  bloodvessels  of  the  head  and 
neck.  From  these  experiments  it  follows  that  the  functions 
of  the  various  groups  of  fibres  in  the  cervical  sympathetic  do  not 
depend  on  anything  peculiar  to  the  fibres  ;  any  fibre  which  can 
make  connection  with  one  of  the  ganglion-cells  that  send  axons 
to  the  dilator  muscle  of  the  iri>  will,  when  stimulated,  act  as  a 
pupillo-dilator  fibre,  just  as  well  as  a  cervical  sympathetic  fibre. 
Other  instances  of  the  same  law  have  already  been  given  in 
connection  with  the  regeneration  of  nerves  (p.  6 

Functional  union  does  not  take  place  between  efferent  somatic 
fibres  (or  pre-ganglionic  fibres)  and  post-ganglionic  fibres — i.e., 
fibres  arising  in  peripheral  ganglia,  and  ending  in  smooth  mus<  le 
and  glandular  tissue  ;  e.g.,  the  cervical  sympathetic  after  excision 
of  the  superior  cervical  ganglion  does  not  unite  with  the  fibres 
leaving  the  anterior  end  of  the  ganglion  in  such  a  way  that 
stimulation  of  it  can  produce  any  of  the  effects  normally  produced 
through  these  fibres.  No  proof  has  been  given  that  afferent  fibres 
can  unite  with  efferent  fibres  or  efferent  with  afferent 


I  III    CI  NTR  II.   NERVOUS  SYSTEM  869 

Afferent  fibres  of  one  nerve  can  unite  with  afferent  fibres  of 
another  nerve,  but  there  is  not  sufficient  evidence  to  show 
whether  fibres  concerned  in  one  sensation  can  unite  with  fibres 
concerned  in  another. 

The  localization  of  function  in  the  cerebral  cortex  has  been 
likened  to  the  localization  of  industries  in  the  multiplex  commercial 
life  of  the  modern  world.  The  barbarian  household  in  which  cloth 
is  woven  and  worked  into  garments  ;  sandals,  or  moccasins  cobbled 
together  ;  rough  pottery  baked  in  the  kitchen  fire,  and  all  the  rude 
furniture  of  the  lodge  fashioned  by  the  hands  which  built  it,  and 
which  rest  beneath  its  roof  at  night — this  state  of  things  where 
centralization  has  not  yet  begun,  it  has  been  said,  is  a  picture  of 
what  goes  on  in  the  undeveloped  brains  of  the  frog,  the  pigeon, 
and  the  rabbit.  The  '  diffusion  '  of  industries  which  is  character- 
istic of  a  primitive  state  has  given  place  among  the  most  highly 
civilized  men  to  extreme  centralization  and  concentration.  Man- 
chester spins  cotton  and  Liverpool  ships  it.  Chicago  handles 
wheat  and  pork  that  have  been  produced  on  the  prairies  of  Minnesota 
and  Illinois.  Amsterdam  cuts  diamonds.  Munich  brews  beer. 
Lyons  weaves  silk.  Xew  York  and  London  are  centres  of  finance. 
This,  it  is  said,  is  the  picture  of  the  highly  specialized  brain  of  a 
monkey  or  a  man.  But  ingenious  and  alluring  though  such  analogies 
are,  they  do  not  rest  upon  a  sufficient  basis  of  fact.  Indeed,  the 
more  deeply  the  structure  and  function  of  the  central  nervous  system 
are  studied,  the  more  clearly  does  its  essential  solidarity  appear, 
the  more  clearly  does  it  emerge  as  an  organized  co-ordinated  system, 
not  an  aggregate  of  separate  mechanisms  jumbled  together  for 
convenience  of  storage  in  the  protected  cranio-spinal  cavity. 

It  has  never  been  shown — nor  is  it  likely  that  the  proof  will  soon 
be  forthcoming — that  there  is  any  difference  whatever  in  the 
physical,  chemical,  or  psychical  processes  which  go  on  in  the  various 
centres  of  the  '  motor  '  cortex.  It  may  be  supposed,  indeed,  that 
the  so-called  sensory  areas  of  the  cortex  differ  more  widely  in  their 
internal  activity  from  the  '  motor '  areas  than  the  latter  do  among 
themselves,  and  that  the  activity  of  the  anterior  portion  of  the 
brain,  the  portion  which  has  been  credited  par  excellence  with 
psychical  functions,  differs  in  kind,  not  merely  in  degree,  from  that 
of  all  the  rest.  But,  as  we  have  just  seen,  even  the  '  motor  '  areas 
have  sensory  functions.  A  cast-iron  physiology  may  explain  this 
by  the  assumption  of  '  sensory  '  as  well  as  '  motor  '  cells  in  the 
Rolandic  area,  and  may  find  support  for  such  an  assumption  in  the 
well-known  fact  that  the  large  pyramidal  cells  whose  axons  form  the 
pyramidal  tract  make  up  but  a  small  proportion  of  the  total  number 
of  pyramidal  cells  in  this  region,  which,  besides,  contains  numerous 
cells  of  Golgi's  second  type  (p.  754).  Yet  there  is  absolutely  nothing 
to  contradict  the  supposition  that  the  discharge  of  energy  from 
the  most  circumscribed  motor  area  or  element  may  be  accompanied 
not  only  with  consciousness,  but  with  a  high  degree  of  psychical 
activity.  And,  indeed,  some  writers  have  supposed  that  such  a  con- 
sciousness of,  or"even  conscious  measurement  of,  the  discharge  from 
the  '  motor  '  areas  is  the  basis  of  the  muscular  sense  (Bain,  Wundt). 
So  far,  at  least,  as  the  '  motor  '  region  and  the  grey  matter  imme- 
diately around  the  neural  canal  are  concerned,  the  analogy  of  an 
electrical  switch-board  connected  with  machines  of  various  kinds 
might  be  more  correct.     Touch  one  key  or  another,  and  an  engine 


870  ./   MANUAL  OF  PHYSIOLOGY 

i3  sol  in  motion  to  grind  corn,  or  to  saw  wood,  or  to  light  a  town. 
The  difference  in  result  lies  not  in  any  difference  of  material  or 
workmanship  in  the  switches,  but  solely  in  the  difference  in  their 
connections. 

Grey  matter  in  the  upper  part  of  the  precentral  convolution  is 
excited,  and  the  muscles  of  the  leg  contract.  Grey  matter  on  the 
lower  part  of  the  convolution  is  excited,  and  there  are  movements  of 
the  face  and  mouth.  Grey  matter  in  the  medulla  oblongata  is 
excited,  and  the  salivary  glands  pour  forth  a  thin,  watery  fluid,  poor 
in  proteins,  and  containing  an  amylolytic  ferment.  Another  portion 
of  grey  (?)  matter  in  the  medulla  is  thrown  into  activity,  and  the 
pancreatic  ducts  become  flushed  with  a  thicker  secretion,  relatively 
rich  in  plot*  ins  and  in  ferments  which  act  on  proteins,  starch,  and 
fat.  1  Uri'.  too.  there  is  a  variety  in  result  according  as  one  or 
another  nervous  switch  is  closed  ;  here,  too,  the  variety  is  due,  not  to 
essential  differences  in  the  structure  or  the  activity  of  the  nervous 
centres,  but  to  their  connection,  by  nervous  paths,  with  peripheral 
organs  of  different  kinds.  There  is,  indeed,  a  specialization,  a 
localization,  of  function,  but  the  localization  is  at  the  periphery,  the 
specialization  is  in  the  peripheral  organs. 

It  may  be  asked  whether,  if  this  is  the  case  for  the  peripheral 
organs  of  efferent  nerves,  the  converse  does  not  hold  true  for  the 
afferent  nerves — in  other  words,  whether  the  localization  here  is 
not  at  the  centre.  And  that  there  is  in  some  degree  a  central 
localization  of  sensation  may  be  considered  proved  bv  the  well- 
known  clinical  fact,  already  referred  to.  that  sensations  of  various 
kinds  may  be  produced  by  pathological  changes  in  the  cortex.  For 
example,  a  tumour  involving  the  upper  part  of  the  temporal  lobe 
may  give  rise  to  epileptiform  convulsions  preceded  by  an  auditory 
aura,  a  sound,  it  may  be,  resembling  the.  ringing  of  bells  ;  a  tumour 
involving  the  occipital  region  may  cause  a  visual  aura,  and  so  on. 
Central  sensory  localization  is  the  fundamental  idea  of  the  old 
doctrine  of  the  specific  energy  of  nerves,  which,  in  modern  phrase- 
ology, expresses  the  fact  that  excitation  of  the  central  end  ol  a 
sensory  nerve  by  various  kinds  of  stimuli  causes  always — or  at  least 
very  often-  the  particular  kind  of  sensation  appropriate  to  the  nerve. 
The  observation  so  frequently  made  in  surgery  before  the  days  of 
anaesthetics,  that  when  the  optic  nerve  was  cut  in  removing"  the 
eyeball  the  patient  experienced  the  sensation  of  a  flash  of  light.* 
was  long  looked  upon  as  the  strongest  prop  oi  the  law  of  specific 
energy,  and  well  illustrates  the  meaning  of  the  term.  Here  a 
mechanical  excitation  of  the  optic  fibres  111  their  course  gives  rise 
to  the  same  sensation  as  excitation  of  the  retina  by  the  natural 
or  homologous  or  adequate  stimulus  of  light.  Since  a  similar  mechanical 
stimulus  applied  to  the  auditory  nerve  gives  rise  to  a  sensation  of 
sound,  and,  applied  to  the  trigeminal  nerve,  to  a  sensation  of  pain, 
many  physiologists  have  assumed  that  the  impulses  set  up  in  the 
auditory  nerve  when  sound  impinges  on  the  tympanic  membrane 
do  not  differ  essentially  from  those  set  up  in  the' optic  nerve  whin  a 
ray  of  light  falls  upon  the  retina,  or  from  those  set  up  in  the  fifth 
nerve  by  the  irritation  of  a  carious  tooth,  or  from  those  set  up  in 
certain  fibres  of  the  cutaneous  nerves  when  a  warm  bodv  comes  in 
contact  with  the  skin.  Since  the  results  in  consciousness  are  very 
different,  this  assumption  has  necessitated  the  further  conclusion 
that  somewhere  or  other  in  the  central  nervous  system  there  exist 

*   It  is  said  that  this  is  not  always  the  case. 


THE  CENTRA  1     VERVOUS  SYSTEM  871 

organs  thai  are  differently  affected  by  the  same  kinds  of  afferent 
impulses  in  other  words,  thai  sensory  localization  is  at  the  centre. 
On  this  view,  the  visual  are. is  in  the  cortex  respond  to  all  kinds  01 
stimuli  by  visual  sensations;  the  auditory  areas  by  sensations  ol 
sound,  and  so  on. 

But  while  it  cannot  be  doubted  that  special  sensory  regions  exist 
in  the  grey  matter  of  the  brain,  where  the  afferent  paths  concerned 
in  the  different  kinds  of  sensation  end,  there  is  no  reason  to  suppose 
that  the  nerve-impulses  which  travel  up  the  various  paths  arc 
absolutely  similar  until  they  have  reached  the  centres,  and  there 
suddenly  become,  or  produces  sensations  absolutely  different.  There 
is,  indeed,  evidence  of  a  certain  amount  of  sensory  specialization  at 
the  periphery.  For  example,  when  an  ordinary  nerve-trunk  is 
touched,  the  resultant  sensation  is  not  one  of  touch.  If  there  is  any 
sensation  at  all,  it  is  one  of  pain.  Heating  or  cooling  a  naked  nerve- 
trunk  gives  rise  to  no  sensations  of  temperature.  When  the  ulnar 
nerve  is  artificially  cooled  at  the  elbow,  the  first  effect  is  severe  pain 
in  the  parts  of  the  hand  supplied  by  the  nerve.  The  pain  disappears 
si  miewhat  abruptly  as  cooling  goes  on,  and  is  succeeded  by  gradual  loss 
of  all  sensation  in  the  ulnar  area  of  the  hand  ;  but  the  cooling  of  the 
nerve-trunk  does  not  give  rise  to  any  sensation  of  cold  (Weir  Mitchell) . 
Stimulation  of  the  receptors  or  end-organs  is  normally  essential  in 
order  that  sensations  of  touch  and  temperature  should  be  experienced 
(but  see  p.  980).  Although,  as  previously  stated,  one  great  function  of 
the  receptor  is  to  lower  the  threshold  of  the  adequate  stimulus,  and 
thus  to  render  the  afferent  neuron  more  easily  excited  by  an  adequate 
stimulus  than  by  any  other,  it  may  also  serve  to  impress  a  particular 
rhythm  or  other  character  upon  the  nerve  impulse,  so  that  the 
afferent  impulses  may  be  to  some  extent  differentiated  before  they 
reach  their  centres.  One  reason,  then,  why  excitation  of  the 
temporal  cortex  by  impulses  falling  into  it  along  the  auditory  neive- 
fibres  causes  a  sensation  different  from  that  caused  by  impulses 
reaching  the  occipital  cortex  through  the  fibres  of  the  optic  nerve 
may  be  a  difference  in  the  nature  of  the  impulses.  If  this  were  the 
only  reason,  it  would  follow  that  were  it  possible  to  physiologically 
connect  the  fibres  of  the  optic  radiation  with  the  temporal  cortex, 
and  those  of  the  temporal  radiation  with  the  occipital  cortex, 
sights  and  sounds  would  still  be  perceived  and  discriminated  in  a 
normal  manner,  although  now  the  integrity  of  the  occipital  lobe 
would  be  bound  up  with  the  perception  of  sound,  the  integrity  of 
the  temporal  lobe  with  visual  sensation.  This  state  of  affairs 
would  correspond  to  complete  specialization  for  sensation  in  the 
peripheral  organs,  complete  absence  of  specialization  in  the  centres. 
On  the  other  hand,  it  is  conceivable  that,  after  such  an  ideal  experi- 
ment, sound-waves  falling  on  the  auditory  apparatus  might  cause 
visual  sensations,  and  luminous  impressions  falling  on  the  retina 
sensations  of  sound.  This  would  correspond  to  complete  specializa- 
tion of  sensation  in  the  centres,  complete  absence  of  specialization 
at  the  periphery.  A  third  possibility  would  be  that  the  '  transposed  ' 
centres,  responding  at  first  feebly  or  not  at  all  to  the  new  impulses, 
might,  by  slow  degrees,  become  more  and  more  excitable  to  them. 
This  would  correspond  to  a  peripheral  specialization,  combined 
with  a  tendency  to  development  of  central  specialization.  And, 
indeed,  it  is  not  easy  to  conceive  in  what  way,  except  as  the  result 
of  differences  in  the  nature  of  impulses  coming  from  the  periphery, 
specialization  of  sensory  areas  in  the  central  nervous  system  could 
have  at  first  arisen. 


872  A   MANUAL  OF  PHYSIOLOGY 

Degree  of  Localization  in  Different  Animals.  —  Before 
Leaving  this  subject,  two  points  oughl  to  be  made  clear  :  (1)  The 
degree  of  localization  of  function  in  the  cortex  goes  hand  in  hand 
with  the  general  development  of  the  brain.  In  man  and  the 
monkey,  the  motor  localization  is  more  elaborate  than  in  the 
dog  thai  is  to  say,  a  greater  number  of  movements  can  be 
associated  with  definite  cortical  areas.  In  the  rabbit,  whose 
'motor'  centres  have  been  particularly  studied  in  recent  years 
by  Mann  and  Mills,  localization  is  still  less  advanced  than  in 
the  dog.  Towards  the  bottom  of  the  mammalian  group  certain 
'  motor  '  areas  can  still  be  demonstrated,  though  they  are  rather 
ill-defined,  for  instance  in  the  hedgehog  (Mann),  opossum 
(Cunningham),  and  ornithorhynchus  (Martin).  In  general  the 
movements  of  the  anterior  limb  are  easier  to  obtain  than  those 
oi  the  posterior.  In  birds  Mills  found  no  evidence  of  the  existence 
of  any  '  motor  '  centres. 

(2)  Areas  of  the  same  name  (homologous  areas)  in  different 
groups  of  animals  do  not  necessarily  have  the  same  function — 
that  is,  in  the  case  of  the  '  motor  '  areas,  are  not  necessarily  asso- 
ciated with  the  same  movements.  Taking  the  position  of  the 
centre  for  the  orbicularis  oculi  as  a  test,  Ziehen  has  come  to  the 
conclusion  that  in  the  anthropoid  apes  and  in  man,  this  centre 
has  been  pushed  forward  by  the  encroachment  of  the  centre- 
behind  it,  and  especially  of  the  visual  centre,  the  arm  centre, 
and  the  speech  centre,  which  have  undergone  a  great  functional 
development. 

Reaction  Time. — Just  as  in  a  reflex  act  a  certain  measure- 
able  time  {reflex  tunc)  is  taken  up  by  the  changes  that  occur  in 
the  lower  nervous  centres,  so  we  may  assume  that  in  all  psychical 
processes  the  element  of  time  is  involved.  And,  indeed,  when 
the  interval  that  elapses  between  the  application  of  a  stimulus 
and  the  signal  which  announces  that  it  has  been  felt  (reaction 
time)  is  measured,  it  is  found  that  for  the  cerebral  processes  associ- 
ated with  the  perception  of  the  simplest  sensation  and  the  pro 
duction  of  the  simplest  voluntary  contraction  it  is  longer  than  the 
time  which  the  spinal  centres  require  for  the  elaboration  of  even 
complex  and  co-ordinated  reflex  movements.  Suppose,  e.g., 
that  the  stimulus  is  an  induction  shock  applied  to  a  given  poinl 
of  the  skin,  and  that  the  signal  is  the  closing  of  the  circuit  oi 
an  electro-magnet,  then,  if  both  events  are  automatically  re- 
corded on  a  revolving  drum,  the  interval  can  be  readily  deter- 
mined. It  is  evident  that  this  includes,  not  only  the  time 
actually  consumed  in  the  central  processes,  but  also  the  time 
required  for  the  afferent  impulse  to  reach  the  brain,  and  the 
efferent  impulse  the  hand,  along  with  the  latent  period  of  the 
muscles.     The   time   taken   up   in   these   three   events   can   be 


THE  CENTRAL   NERVOUS  SYSTEM 

approximately  calculated,  and  when  it  is  subtracted,  the  re- 
mainder represents  the  reduced  or  corrected  reaction  time — 
that  is,  the  interval  actually  spent  in  the  centres  themselves. 
This  is  by  no  means  a  constant.  It  is  influenced  not  only  by 
the  degree  of  complexity  of  the  psychical  acts  involved,  and 
the  mental  attitude  of  the  person  (whether  he  expects  the 
stimulus  or  is  taken  by  surprise,  whether  he  has  to  choose 
between  several  possible  kinds  of  stimuli  and  respond  to  only 
one,  etc.).  but  it  varies  also  for  different  kinds  of  sensation, 
for  the  same  sensation  at  different  times,  and  as  is  recognised 
in  the  personal  equation  of  astronomers,  in  different  individual-. 
For  sensations  of  touch  and  pain  it  may  be  taken  as  one-ninth 
to  one-fifth,  for  hearing  one-eighth  to  one-sixth,  and  for  sight 
one-eighth  to  one-fifth  of  a  second.  So  that  the  proverbial 
quickness  of  thought  is  by  no  means  great,  even  in  comparison 
with  that  of  such  a  gross  process  as  the  contraction  of  a  muscle 
(one-tenth  of  a  second).  Nor  is  it  the  case  that  the  man  '  of 
quick  apprehension  '  has  always  a  short  reaction  time,  or  the 
dullard  always  a  long  one,  although  in  all  kinds  of  persons  practice 
will  reduce  it. 

Sleep  and  Fatigue. — Certain  gland-cells,  certain  muscular 
fibres,  and  the  epithelial  cells  of  ciliated  membranes,  never  rest, 
and  perhaps  hardly  ever  even  slacken  their  activity.  But  in 
most  organs  periods  of  action  alternate  at  more  or  less  frequent 
intervals  with  periods  of  relative  repose.  In  all  the  higher 
animals  the  central  nervous  system  enters  once  at  least  in  the 
twenty-four  hours  into  the  condition  of  rest  which  we  call  sleep. 
What  the  cause  of  this  regular  periodicity  is  we  do  not  know. 
It  is  accompanied  by  changes  in  the  microscopical  appearance 
of  the  nerve-cells.  Thus,  Hodge  found  differences  between  the 
cells  of  certain  portions  of  the  cerebral  cortex  in  birds,  and  of 
certain  ganglia  in  the  honey-bee  after  a  long  day  of  work  and 
after  a  night's  rest.  Mann,  Lugaro,  and  other  observers,  found 
similar  differences  in  the  cells  of  the  cerebral  cortex  and  the 
anterior  horn,  and  Dollev  in  the  Purkinje's  cells  of  the  cerebellum 
in  dogs  fatigued  by  muscular  exercise  as  compared  with  rested 
dogs  (Fig.  366). 

According  to  Dolley,  who  has  made  the  most  recent  observations 
on  this  subject,  there  is,  as  a  result  of  continued  activity,  at  first  a 
steady  increase  of  the  basic  chromatic  material.  This  increase 
affects  first  the  extra-nuclear  chromatin,  the  Xissl  substance,  which, 
according  to  the  most  modern  view,  is  really  nuclear  substance 
distributed  through  the  cvtoplasm,  and  functions  as  such  (Gold- 
schmidt).  The  size  and  number  of  the  granules  are  increased,  and 
some  of  the  chromatic  material  is  diffused  throughout  the  cytoplasm, 
as  indicated  by  diffuse  staining.  Then  the  intranuclear  chromatin 
also  undergoes  an  increase,  and  the  size  of  the  cell  is  increased  too. 


«74 


/    M  I  V  l/.  OF  PHYSIOLOGY 


In  moderate  activitj  the  change  Kr,,('s  n"  farther.  At  this  stage  the 
cell  is  hypercbromatic — i.e.,  as  compared  with  a  normal  resting 
cell  it  contains  an  excess  of  chromatin.  The  production  of  chro- 
matin having  rea<  bed  the  maximum  of  which  the  nucleus  is  capable, 
and  functional  activity,  which  entails  the  using  up  of  tl 
nuclear  chromatin  still  continuing,  the  total  chromatin  content 
begins  to  diminish,  first  in  the  nucleus,  through  the  passage  of  its 
<  hi  i.iii.it  m  into  the  cytoplasm  to  recruit  the  Nissl  substance,  then 
m  the  cytoplasm  as  well.  Accompanying  the  disappearance  of  the 
chromatic    material    there   is   diminution    in    the    size   of    both    cell 

and   nucleus,   but    especially 
i  of   the    inn  li  us.   mi    1  hat    the 

normal  propoi  i  ion  be1  ween 
volume  hi  cell  and  volume 
of  nucleus  (nucleus  -  plasma 
relation  of  I  fertwig)  is  dis- 
turbed in  favour  of  the  cyto- 
plasm. Both  cell  and  nucleus 
become  irregular  in  outline 
or  crenated.  Later  on,  and, 
it  would  seem,  rather  ab- 
ruptly, swelling  of  the  nucleus 
and.  .illcr  some  time,  of  the 
cytoplasm  occurs.  This  is 
due  to  oedema,  and  may  be 
taken  to  indicate  an  upset 
of  their  normal  osmotic  rela- 
tions. The  earlier  occurrence 
ot  oedema  in  the  nucleus  leads 
to  another  change  in  the  nu- 
cleus-plasma relation,  which 
is  now  disturbed  in  favour 
of  the  nucleus.  I  n  t  he 
measure  in  which  fatigue 
progresses  the  extranuclear 
chromatic  material  continues 
to  be  used  up,  and.  in  spite 
of  its  replenishment  from  the 
nucleus,  it  almost  or  entirely 
vanishes  from  tin-  cytoplasm. 
Then  follows  what  is  perhaps 
a  '  last  effort  '  on  the  pari  ol 
the  nucleus  to  supply  the 
cytoplasm,  in  the  form  of  a 
dis<  harge  of  chromal  ic  sub- 
stance, which  first  masse-, 
itself  around  the  outside  of  the  nuclear  membrane;  and  tli>  i 
gradually  diffuses  into  the  cytoplasm.  With  the  using  up  oJ 
this  supply  all  the  basic  chromatic  material  of  the  cell,  except  that 
in  the  karyosome  (nucleolus),  is  exhausted  Finally,  this  too  is 
yielded  up  to  the  cytoplasm,  and  with  its  consumption  there 
remains  a  totally  exhausted  cell,  devoid  of  basic  chromatin  and 
incapable  of  recuperation. 

According  to  Pugnet,  even  in  extreme  fatigue,  as  when  dogs 
were  caused  to  run  forty  to  nearly  si\t  v  miles  in  a.  special  apparai  us. 
the  changes  varied  greatly  in  degree  iii  different  cortical  cells,  from 


Fig.  366. — Effect  of  Fatigue  on  Nerve- 
cells  (Barker,  after  Mann). 
Two  motor  cells  from  lumbar  curd  of  dog 
fixed  in  sublimate  and  stained  with  toluidill 
blue.  a.  from  rested  dog;  1,  pale  nucleus; 
2,  dark  Nissl  spindles;  3,  bundles  of  nerve 
fibrils.  b,  from  the  fatigued  dog;  |.  dark 
shrivelled  nucleus  :   5.  pale  spindles. 


THE  CENTR  U    N)  RVOUS  SYST1  M  875 

mere  diminution  of  the  chromatic  substance  to  complete  dis- 
appearance of  it.  and  such  disintegration  of  the  cell  as  must 
precluded  its  recovery  had  the  animal  been  allowed  to  live.  Many, 
and  indeed  most,  of  the  cortical  cells  were  quite  unaffected.  ETi 
logical  alterations  may  also  be  caused  in  sympathetic  ganglion  cells 
bv  prolonged  artificial  stimulation  of  the  nerves  connected  with 
iii.  ganglia.  Experiments  on  fatigue  changes  in  the  cells  ol  bhe 
spinal  ganglia  after  electrical  excitation  oi  the  posterior  root-fibres 
are  less  decisive,  some  observers  having  obtained  positive,  others 
negative,  results  (p.  809). 

Theories  of  the  Causation  of  Sleep.  — (1)  Some  have  suggested  that 
sleep  is  induced  by  the  using  up  of  substances  necessary  for  the 
functional  activity  oi  the  neurons  e.g.,  the  stored-up  or  intra- 
molecular oxygen — or  by  the  action  oi  the  waste  products  of  the 
tissues,  and  especially  lactic  acid,  when  they  accumulate  beyond  a 
certain  amount  in  the  blood,  or  in  the  nervous  elements  themselves. 

(2)  Others  have  looked  for  an  explanation  to  vascular  changes  in 
the  brain,  but  so  far  are  the  possible  causes  of  such  changes  from 
being  understood,  that  it  is  even  yet  a  question  whether  in  sleep  the 
brain  is  congested  or  anaemic.  Certain  writers  have  settled  this 
question  by  the  summary  statement  that  when  the  brain  rests  the 
quantity  of  blood  in  it  must  be  supposed  to  be  diminished,  as  in 
other  resting  organs.  But  this  is  a  fallacious  argument.  For  when 
the  whole  body  rests,  as  it  does  in  sleep,  it  has  as  much  blood  in  it 
as  when  it  works  ;  in  sleep,  therefore,  if  some  resting  organs  have 
less  blood  than  in  waking  life,  other  resting  organs  must  have  more  ; 
and  it  is  the  province  of  experiment  to  decide  which  are  congested 
and  which  anaemic.  In  coma,  a  pathological  condition  which  in 
some  respects  has  analogies  to  profound  and  long-continued  sleep, 
the  brain  is  congested,  and  the  proper  elements  of  the  nervous  tissue 
presumably  compressed.  And  artificial  pressing  (applied  by  means 
of  a  distensible  bag  introduced  through  a  trephine  hole  into  the 
cranial  cavity)  ma}'  cause  not  only  unconsciousness,  but  absolute 
anaesthesia.  But  it  is  possible  that  this  artificial  increase  of  intra- 
cranial pressure  may  produce  its  effects  bv  rendering  the  brain 
anaemic,  and  it  has  been  actually  observed  that  the  retinal  vessels, 
as  seen  with  the  ophthalmoscope,  and  the  vessels  of  the  pia  mater 
exposed  to  direct  observation  in  man  by  disease  of  the  bones  of  the 
skull,  or  in  animals  by  operation,  shrink  during  sleep.  Statements 
to  the  contrary  may  be  due  to  neglecting  the  influence  of  difference 
of  position  in  the  sleeping  and  waking  states.  In  sleeping  children 
the  fontanelle  sinks  in,  an  indication  that  the  intracranial  pressure 
is  reduced.  Observations  with  the  plethysmography  have  shown 
that  the  arm  swells  in  sleep,  and  shrinks  when  the  sleeper  awakes. 
or  even  when  he  is  subjected  to  sensory  stimuli  not  sufficient  to 
arouse  him — e.g.,  a  tune  played  by  a  musical-box  (Howell).  The 
tone  of  the  vaso-motor  centre  is  therefore  diminished,  and  the 
arterial  pressure  falls  during  sleep.  But  a  fall  of  general  arterial 
pressure  is  usually  accompanied  by  a  diminution  of  the  quantity  of 
blood  passing  through  the  brain.  So  that  the  balance  of  evidence 
is  in  favour  of  the  view  that  sleep  is  associated  with  a  certain  degree 
of  cerebral  ancemia. 

As  to  the  nature  of  the  relation  between  the  two  conditions,  it 
has  been  suggested  that  the  anaemia  is  produced  by  fatigue  of  the 
vaso-motor  centre,  which  causes  it  to  relax  its  grip  upon  the  peri- 
pheral bloodvessels,   and  that  the  condition  of  the  cortical  nerve- 


H7r,  I     U  INUAL  OF  PHYSIOLOGY 

cells  which  we  call  sleep  is  directly  produced  by  the  lack  of  blood. 
But  there  does  no1  appear  to  be  any  good  reason  for  believing  that 
the  vaso-motnr  centre  is  more  susceptible  of  fatigue  than  the  higher 
cerebral  centres.  On  the  contrary,  it  is  probable  that  the  bulbar 
centres  are  less  delicately  organized  and  more  resistant  than  the 
higher  centres.  In  any  case,  if  the  cerebral  nerve-cells  '  go  to  slei  p 
because  their  blood-supply  is  diminished,  ought  we  not  to  look  for  a 
similar  cause  for  diminished  activity  of  the  vaso-motor  centre  ?  Or 
it  the  answer  is  made  that  the  activity  of  the  vaso-motor  cells  is 
directly  lessened  by  fatigue,  or  by  the  cessation  ol  external  stimuli, 
why  should  not  this  be  the  case  also  for  the  cortical  ceils  ?  It  can 
be  shown  by  means  of  the  sphygmomanometer  (p.  106)  that  the  tail 
of  arterial  pressure  is  not  essentially  connected  with  sleep,  but  is 
produced  by  the  bodily  rest  and  warmth  which  accompany  it. 
Further,  even  a  great  diminution  in  the  supply  of  blood  going  to  the 
brain  is  not  necessarily  followed  by  sleep.  For  example,  both 
carotids  and  both  vertebral  arLeries  may  frequently  be  tied  in  dogs 
at  the  same  time  without  producing  any  symptoms,  the  anastomosis 
of  the  superior  intercostal  arteries  with  the  anterior  spinal  artery 
providing  a  sufficient  channel  for  the  blood  absolutely  required  by 
the  brain.  Monkeys  after  ligation  of  both  carotids  may  be  most 
alert  and  active.  To  produce  sopor  in  animals  the  cortical  circula- 
tion must  be  reduced  almost  to  the  vanishing-point,  and  to  a  far 
greater  degree  than  ever  occurs  in  sleep  (Hill).  We  must,  there- 
fore, conclude  that  although  sleep  is  normally  associated  with  some 
ancemia  of  the  brain,  it  is  not  directly  caused  by  it.  The  cortical 
centres  go  to  sleep  because  they  are  '  tired,'  or  because  the  stimuli 
which  usually  excite  them  have  ceased,  and  not  because  their  blood- 
supply  is  diminished. 

(3)  The  idea  that  the" dendrites  are  contractile,  and  by  pulling 
themselves  in,  and  thus  breaking  certain  nervous  chains,  cause 
sleep,  is  a  mere  theory,  unsupported  by  any  real  evidence.  The 
same  is  true  of  the  notion  that  the  fibrils  of  the  neuroglia  insinuate 
themselves  into  the  '  joints,'  by  which  one  neuron  comes  into  contact 
with  another,  and  acting  as  insulating  material,  block  the  nerve- 
impulses. 

In  general,  the  depth  of  sleep,  as  measured  by  the  intensity  of 
sound  needed  to  awaken  the  sleeper,  increases  rapidly  in  the  first 
hour,  falls  abruptly  in  the  second,  and  then  slowly  creeps  down  to 
its  minimum,  which  it  reaches  just  before  the  person  awakens.  As 
to  the  amount  of  sleep  required,  no  precise  rules  can  be  laid  down. 
It  varies  with  age,  occupation,  and  perhaps  climate.  An  infant, 
whose  main  business  is  to  grow,  spends,  or  ought  to  spend,  if  mothers 
were  wise  and  feeding-bottles  clean,  the  greater  part  of  its  time  in 
sleep.  The  man,  whose  main  business  it  is  to  work  with  his  hands 
or  brain,  requires  his  full  tale  of  eight  hours'  sleep,  but  not  usually 
more.  The  dry  and  exhilarating  air  of  some  of  the  inland  portions 
of  North  America,  and  perhaps  the  plains  of  Victoria  and  New 
South  Wales,  incites,  and  possibly  enables  a  new-comer  to  live  for 
a  considerable  period  with  less  than  his  ordinary  amount  ol  sleep 
Idiosyncrasv.  and  perhaps  to  a.  still  greater  extent  habit,  have  also 
a  marked  influence.  The  great  Napoleon,  in  his  heyday,  never 
slept  more  than  four  or  five  hours  in  the  twentv-four.  Five  or  six 
hours  or  less  was  the  usual  allowance  of  Frederick  of  Prussia  through- 
out the  greater  part  of  his  long  and  active  life. 

Hypnosis  is  a  condition  in  some  respects  allied  to  natural  slumber  ; 


////    CENTRA1     XI  RVOUS  SYS1  I  \l  877 

but  instead  oi  the  ai  th  ity  oi  the  whole  brain  or  perhaps  we  should 
rather  say,  the  whole  activity  of  the  brain  being  in  abeyance,  th( 
susceptibility  to  external  impressions  remains  as  great  as  in  waking 
life,  Or  mix  be  even  increased,  while  the  critical  faculty,  which 
normally  sits  in  judgmenl  on  them,  is  lulled  to  sleep.  The  con 
dition  can  be  induced  in  nninv  ways  l>v  asking  the  subject  to  Look 
fixedly  a1  .1  bright  object,  by  closing  Ins  eyes,  by  occupying  Ins 
attention,  by  a  sudden  loud  sound  or  a  flash  oi  light,  etc.  Th< 
essentia]  condition  is  thai  the  person  should  have  the  idea  of  going 
to  sleep,  and  that  he  should  surrender  his  will  to  the  operator.  In 
the  hypnotic  condition  the  subject  is  extremely  open  to  suggestions 
made  by  the  operator  with  whom  he  is  en  rapport,  lie  adopts  and 
acts  upon  them  without  criticism.  If,  for  example,  the  hypno- 
ti/er  raises  the  subject's  .0111  .i.bove  Ins  head,  and  suggests  that  he 
cannot  bring  it  down  again,  it  stays  fixed  in  that  position  for  a  long 
time  without  any  appearance  of  fatigue  ;  or  the  whole  body  may  be 
thrown,  on  a  mere  hint,  into  some  unnatural  pose,  in  which  it  remains 
rigid  as  a  statue.  Suggested  hemiplegia  or  hemianesthesia,  or 
paralysis  of  motion  and  sensation  together  or  apart  in  limited  areas, 
can  also  be  realized  ;  and  surgical  operations  have  been  actually 
performed  on  hypnotized  persons  without  any  appearance  of 
suffering.  If,  on  the  other  hand,  the  operator  suggests  that  the 
subject  is  undergoing  intense  pain,  he  will  instantly  take  his  cue, 
writhing  his  body,  pressing  his  hands  upon  his  head  or  breast,  and 
in  all  respects  behaving  as  if  the  suggestion  were  in  accord  with  the 
facts.  If  he  is  told  that  he  is  blind  or  deaf,  he  will  act  as  if  this 
were  the  case.  If  it  is  suggested  that  a  person  actually  present  is 
in  Timbuctoo,  the  subject  will  entirely  ignore  him,  will  leave  him 
out  if  told  to  count  the  persons  in  the  room,  or  try  to  walk  through 
him  if  asked  to  move  in  that  direction.  What  is  even  more  curious 
is  that  the  organic  functions  of  the  body  are  also  liable  to  be  in- 
fluenced by  suggestion.  A  postage-stamp  Avas  placed  on  the  skin 
of  a  hypnotized  person,  and  it  was  suggested  that  it  would  raise  a 
blister.  Next  day  a  blister  was  actually  found  beneath  it.  The 
letter  K,  embroidered  on  a  piece  of  cloth,  was  suggested  to  be  red- 
hot.  The  left  shoulder  was  then  '  branded  '  with  it,  and  on  the 
right  shoulder  appeared  a  facsimile  of  the  K  as  if  burnt  with  a  hot 
iron.  The  secretions  can  be  increased  or  diminished,  subcutaneous 
haemorrhages,  veritable  stigmata,*  can  be  caused,  and  many  of  the 
'  miracles  '  of  Lourdes  and  other  shrines,  ancient  and  modern, 
repeated  or  surpassed  by  the  aid  of  hypnotic  suggestion.  Hyp- 
notism has  also  been  practically  employed  in  the  treatment  of 
various  diseases,  and  particularly  in  functional  derangements  of 
the  nervous  system.  But  care  and  judgment  are  necessary  on  the 
part  of  the  operator,  and  although  as  a  rule  there  is  no  difficulty 
in  putting  an  end  to  the  condition  by  a  suitable  suggestion,  it  is 
said  that  in  rare  instances  grave  mischances  have  occurred.  There 
seems  to  be  no  ground  for  the  opinion  that  women  are  more  easily 
hypnotized  than  men.  Out  of  more  than  a  thousand  persons, 
Liebault  found  only  seventeen  absolutely  refractory. 

*  I.e.,  bleeding  spots  on  the  skin  generally  corresponding  to  the  wounds 
of  Christ.  In  the  well-known  case  of  Louise  Latour,  which  excited  great 
interest  in  France  in  186S,  blisters  first  appeared  ;  they  burst  and  then 
there  was  bleeding  from  the  true  skin.  The  probable  explanation  is  that 
she  concentrated  her  attention  on  these  parts  of  her  body  and  so  influenced 
them,  perhaps  by  causing  congestion  through  the  vaso-motor  centre. 


I  MANUAL  OF   PHYSIOLOGY 

Relation  of  Size  of  Brain  to  Intelligence.  While  it  is  the 
(  ase  thai  iome  nun  ol  greal  ability  have  had  remarkably  heavy 
and  richly  convoluted  brains,  it  would  seem  thai  in  general 
neithei  greal  size  nor  any  other  obvious  anatomical  peculiarity 
of  the  cerebrum  is  constantly  associated  with  exceptional 
intellectual  power.  In  the  animal  kingdom,  as  a  whole,  there  is 
undoubted!)  some  relation  between  the  status  ol  a  group  and 
the  average  brain  development  within  the  group.  But  that 
tin,  is  a  relation  which  is  complicated  by  other  circumstances 
than  the  men  degree  ol  intelligenci  is  5um<  iently  shown  by  the 
t,i<  t  thai  .1  mouse  ha«  more  brain,  in  proportion  to  its  size, 
than  a  man,  and  thirteen  times  more  than  .1  horse  :  while  both 
in  the  rabbil  and  sheep  the  ratio  of  brain-weight  to  body- 
weight  is  nearly  twice  as  great  as  in  the  horse,  in  the  dog  only 
hall  as  greal  as  in  the  cat,  and  not  very  much  more  than  in 
the  donkey.  The  following  tables,  too,  which  illustrate  the 
weight  ot  the  brain  in  man  at  different  ages,  show  that,  although 
we  might  give  '  the  infant  phenomenon  '  an  anatomical  basis, 
we  should  greatly  overrate  the  intellectual  acuteness  of  the 
average  baby  ii  we  were  to  measure  it  by  the  ratio  of  brain  to 
body-weight  alone. 


i    year 

in-weight. 

885  grm. 

S  years     . . 

1  rain-weight. 
1,045    grm- 

_•   \  ear  • 

909     ,, 

i<  > 

.. 

1,315            M 

3 

1,071 

1 1 

1,168           ,, 

.1 

[,099     .. 

12 

1,286           ., 

5 

0       ., 

1,033     .. 
1, 147     .. 

1  1 
1  1 

•■ 

1,505            .. 

r,336     ., 

7 

1  -"J 

15 

•• 

1,414     ., 

BlSCHOFF. 

Brain-weight  - 
Men. 

l',i  ain-weighl 
w   imen. 

Age. 

Brain-weight 

Men. 

—        Brain-weight- 

Women. 

I'     1 1 . 

2<>     29, 

.1   1 1  1  grm. 

.  1. I [9 

.  .  [,219  grm. 

,  .    1    26o      ,, 

5°-59 • 
60-69 . 

.  I 
.  I 

,389  grm.  .  .  1,239  grn 

,2>l^            ..             .    .       I.JIM 

30  39. 

40     |0 

.1,424      .. 
,. 1,406 

.  .    I  .272 
.  .    1  ,  -'  7  2 

7"   79- 
80  90 . 

.  I 
.  I 

,254            ,. 

,3°  3     ,, 

.  .  1,129 

.  .        898       ,, 
— HUSCHKE. 

In  some  small  birds  the  ratio  is  as  high  as  1  :  12,  in  large 
bird-  ,1-  low  as  1  :  1,200  ;  in  certain  fishes  a  gramme  of  brain 
has  to  serve  for  over  5  kilos  of  body.  As  a  rule,  especially 
within  a  given  species,  the  brain  is  proportionally  of  greater 
size  in  small  than  in  large  animals.  It  1- to  be  supposed  that 
quality  as  well  as  quantity  of  brain  substance  is  a  potent  factor 
in  determining  the  degree  ol  mental  capacity. 

The    Cerebral    Circulation.      I  h<  '     oi    the    cerebral 

bloo  '    peculiarities  winch  it  is  ot  importance  to 

remember  in  connect  ion  with  the  study  oi  the  diseases  of  the  brain, 
-  d  by  lesions  in  the  vascular  system — haemor- 
rhage or  embolism.     Four  great  arterial  trunks  carry  blood  to  the 


I  ill    CENTRA1     \i  RVOUS  S5  STl  \l 

brain,  two  internal  carotids  and  two  vertebrals  The  vertcb 
unite  .it  the  base  oi  the  skull  to  form  the  single  mesial  basilar  art<  ry, 
which,  running  foi  ward  in  .1  groov<  in  the  occipital  bone,  splits  into 
the  two  posterior  cerebral  arteries  Eacb  carotid,  passing  in 
through  tin-  carotid  foramen,  divides  into  a  middle  and  an  anterior 
bral  artery;  the  latter  runs  forward  in  the  greal  longitudinal 
fissure,  the  former  lies  in  the  fissun  <>t  Sylvius.  A  communicating 
branch  joins  the  middle  and  posterior  cerebrals  on  each  side,  and  a 
short  loop  connects  the  two  anterior  cerebrals  in  front.  In  this 
way  a  hexagon  is  formed  a1  thi  base  oi  the  brain,  the  so-called 
circle  oi  Willis.  While  the  anastomosis  between  the  large  arteries 
is  thus  very  Eree,  the  opposite  is  true  oi  their  branches.  All  the 
arteries  in  the  substance  oi  the  brain  and  cord  an  '  end-arteri 
— that  is  to  say.  each  terminates  within  its  area  of  distribution 
without  sending  communicating  branches  to  make  junction  with 
its  neighbours.  I  be  i  onsequem  e  of  these  two  anatomical  facts  is  : 
(M  that  interference  with  the  blood-supply  of  the  brain  between 
the  heart  and  the  circle  of  Willis  does  not  readily  produce 
symptoms  of  cerebral  anaemia  ;  (2)  that  the  blocking  oi  any  of  the 
arteries  which  arise  from  the  circle  or  any  of  their  branches  leads 
to  destruction  of  the  area  supplied  by  it.  Nearly  all  dogs  recover 
after  ligation  in  one  operation  oi  both  carotids  and  both  vertebral 
arteries.  In  monkeys  both  carotids  may,  as  a  rule,  be  safely  tied, 
and  one  carotid  in  man.  If.  in  addition  to  the  two  carotids,  one 
vertebral  be  ligated  at  the  same  time  in  the  monkey,  sopor  results, 
and  this  is  generally  followed  by  extensor  rigidity,  coma,  and  death 
in  twenty-four  hours.  In  one  case  a  monkey  survived  this  triple 
ligation,  but  became  demented.  The  motor  paralysis  and  rigidity 
were  much  greater  than  in  the  dog.  In  the  condition  of  partial 
anaemia  the  cortex  is  more  excitable  than  normal,  but  the  excit- 
ability disappears  at  once  when  the  anaemia  is  rendered  complete  (Hill) . 
The  basal  ganglia  are  fed  by  twigs  from  the  circle  of  Willis  and 
the  beginning  of  the  posterior,  middle,  and  anterior  cerebral  arteries. 
Of  these  the  most  important  are  the  lenticulo-striate  and  lenticulo- 
optic  branches  of  the  middle  cerebral,  which  are  given  off  near  its 
origin,  and  run  through  the  lenticular  nucleus  into  the  internal 
capsule,  and  thence  to  the  caudate  nucleus  and  optic  thalamus 
respectively.  the  chief  part  of  the  blood  from  the  circle  of  Willis 
is  carried  by  the  three  great  cerebral  arteries  over  the  cortex  of  the 
brain.  The  white  matter,  with  the  exception  of  that  in  the  imme- 
diate neighbourhood  of  the  basal  ganglia,  is  nourished  by  straight 
arteries  which  penetrate  the  cortex.  The  middle  cerebral  supplies 
the  whole  of  the  parietal  as  well  as  that  portion  of  the  frontal  lobe 
which  lies  immediately  in  front  of  the  fissure  of  Rolando  and  the 
upper  part  of  the  temporal  lobe.  The  rest  of  the  fiontal  lobe  is 
supplied  by  the  anterior  cerebral,  and  the  occipital  lobe,  with  the 
lower  part  of  the  temporal  lobe,  by  the  posterior  cerebral.  The 
medulla  oblongata,  cerebellum,  and  pons  arc  fed  from  the  ver- 
tebrals and  the  basilar  artery  before  the  circle  of  Willis  has  been 
formed. 

Resuscitation  of  the  Central  Nervous  System  after  Total 
Anaemia.— Complete  temporary  anaemia  of  the  brain  and  upper 
cervical  cord  can  be  produced  in  most  cats  by  passing  temporary 
ligatures  around  the  innominate  artery  and  left  subclavian 
proximal  to  the  origin  of  the  vertebral  artery.     Artificial  respira- 


88o  1    MANUAL  OF  PHYSIOLOGY 

tion  is  maintained  through  a  tube  passed  through  the  glottis, 
rhe  eye  reflexes  disappear  very  quickly,  and  a  period  of  high 
blood-pressure  immediately  follows  the  occlusion.  A  fall  of 
pressure  succeeds,  due  to  vagus  inhibition  of  the  heart,  and  this 
i-  followed  by  a  second  rise  after  the  vagus  centre  succumbs  to 
the  anaemia.  Iv--pnati<>n  stops  temporarily  (in  twenty  to  sixty 
seconds)  alter  occlusion  ;  then  follows  a  series  of  strong  gasps, 
and  finally  cessation  of  all  respiratory  movements.  The  blood- 
pressure  slowly  falls  to  a  level  which  is  then  maintained  approxi- 
mately constant  for  the  remainder  of  the  occlusion  period.  The 
anterior  part  of  the  cord  and  the  encephalon  lose  all  function  ; 
no  reflexes  can  be  elicited  from  this  part  of  the  central  nervous 
system.  The  intra-ocular  tension  is  much  reduced,  and  the  cornea 
is  characteristically  wrinkled. 

When  the  cerebral  circulation  is  restored  by  releasing  the 
vessels,  the  general  arterial  pressure  soon  begins  to  rise  if  the 
period  of  occlusion  has  not  overstepped  the  limit  of  successful 
cardio-vascular  resuscitation.  The  respiration  returns  suddenly, 
the  time  of  return  depending  on  the  length  of  the  occlusion  and 
on  other  factors.  The  respiratory  rate,  at  first  slow,  soon  becomes 
normal,  and  then  more  rapid  than  normal.  The  eye-reflexes 
reappear  more  gradually  ;  the  intra-ocular  tension  increases,  and 
the  shrunken  cornea  becomes  smooth  and  hard.  The  anterior 
part  of  the  cord  recovers  its  functions  gradually  ;  the  reflexes  con- 
nected with  it  return,  first  the  homonymous,  then  the  crossed.  A 
short  period  of  quiet  follows  ;  then  spasms  of  the  skeletal  muscles 
appear,  gradually  increase  in  severity  and  extent,  and  termi- 
nate in  (a)  death,  (b)  partial,  or  (c)  complete  recovery.  In  partial 
recovery,  disturbances  of  locomotion,  such  as  walking  in  a  circle, 
paralysis,  apparent  dementia  or  loss  of  intelligence,  and  loss  of 
sight  or  hearing,  may  be  observed.  Voluntary  movements  of 
the  head,  neck,  shoulders,  and  fore-limbs  have  been  seen  eight 
minutes  after  release  from  an  occlusion  of  six  minutes.  Blindness 
has  been  observed  without  loss  of  the  pupillary  light  reflex.  In 
this  case  the  visual  cortex  would  seem  to  have  suffered  more 
than  the  lower  centres,  an  illustration  of  a  general  rule. 
Complete  recovery  is  rare  after  total  anaemia  lasting  as  much 
as  fifteen  minutes,  and  has  not  been  observed  after  an  an.emia 
of  twenty  minutes.  Ten  to  fifteen  minutes  of  total  anaemia 
represent  the  limit  beyond  which  recovery  of  the  brain,  and 
therefore  successful  resuscitation  of  the  animal,  cannot  be 
expected. 

Chemistry  of  Nervous  Activity. — Of  this  we  are  practically 
ignorant.  The  percentage  composition  of  the  solids  and  the 
percentage  of  water  in  the  brains  of  three  persons  of  different  ages 
are  exhibited  in  the  following  table  (W.  Koch)  : 


////    <  F.NTR  II    NERVOUS   SYSTI  M 


Child- 

Child  a  V< 

A.I 

uii  19  \ 

(Brain  640  <  >rms.). 

(Brain  1,100  0 

mi-..). 

(Brail 

Grey. 

White. 

Whole  Brain. 

•  >rev. 

While. 

Whole 

Brain.* 

Brain. 1 

Proteins 

•  6  6 

P    I 

,1  9 

1"    ' 

471 

J"    1 

37*1 

I-.xi ra<  tives  .  . 

1  _■  -  > 

59 

8  0 

39 

"7 

Ash 

1     i 

-  1 

1   ' 

1  a  ithins     and 

kephalins  .  . 

24  7 

273 

Cerebrins 

69 

8-6 

I  2   <i 

8-8 

166 

127 

Lipoid  S  as  S04) 

01 

01 

o\5 

0'3 

01 

°"5 

Cholestcrin| 

1  9 

24 
84-49 

7645 

8-7 

8047 

4  9 
8317 

II7 

Water 

8878 

7642 

The  next  table  shows  the  variations  in  the  content  of  water, 
solids,  and  protein  in  different  parts  of  the  nervous  r-vstem 
(Halliburton)  : 


Cerebral  grey  matter 
Cerebral  white  matter 
Cerebellum 

Spinal  cord  as  a  whole 
Cervical  cord 
Dorsal  cord 
Lumbar  cord 
Sciatic  nerves     .  . 


Water. 


83 
69 

71 

7^ 
69 
7- 
6.5 


Solids. 


J 

[6 

•9 

30  1 

•8 

20  2 

•6 

284 

'5 

275 

■8 

30-2 

•b 

-74 

1 

349 

Percentage  of  Pro- 
teins in  solids. 


I 

4^ 
31 
31 


33 
29 


The  grey  matter  of  the  cerebrum  in  the  adult  contains  Si  to 
86  per  cent,  of  water,  the  white  matter  68  to  72  per  cent.,  the 
brain  as  a  whole  81  per  cent.,  the  spinal  cord  68  to  76  per  cent., 
and  the  peripheral  nerves  57  to  64  per  cent.  In  the  foetus  more 
water  is  present  (92  per  cent,  in  the  grey  and  87  per  cent,  in  the 
white  matter). 

The  superior  richness  of  the  grey  matter  in  proteins  and  the 
preponderance  of  water  in  it,  are  the  chief  chemical  peculiarities 
which  distinguish  it  from  the  white  matter.  That  it  should 
have  a  high  protein  content  is  easily  understood,  for  the  proto- 
plasmic structures,  the  nerve-cells,  are  situated  in  the  grey 
matter.  But  that  the  most  important  functions  should  have 
their  seat  in  a  tissue  containing  only  14  to  19  per  cent,  of  solids 
is  surprising,  and  should  warn  us  that  the  water  is  no  less  signifL 
*  Calculated.  f   Calculated  by  difference. 

56 


882  A   MANUAL  OF  PHYSIOLOGY 

cant  a  constituent  of  Living  matter  than  the  solids,  and  that  it 
is  not  the  mass  oi  the  solid  substances  in  a  tissue  which  is  the 
essential  tiling,  but  the  whole  colloid  complex,  which  cannot  be 
constituted  without  the  water. 

Fresh  nervous  tissues  are  alkaline  to  litmus,  but  become 
acid  soon  alter  death.  No  change  of  reaction  has  been  detected 
during  activity. 

That  oxygen  is  used  up  during  cerebral  activity  is  certain, 
and  when  the  brain  is  coloured  with  methylene  blue,  by  injecting 
it  into  the  circulation,  any  spot  of  it  which  is  stimulated 
the  blue  colour,  the  pigment  being  reduced.  But  if  the  animal 
is  so  deeply  narcotized  that  it  does  not  respond  to  stimulation, 
the  change  of  colour  does  not  occur. 

Cholin,  a  substance  which  can  be  derived  from  lecithin,  is 
believed  to  represent  one  of  the  waste  products  of  nervous 
activity.  Exceedingly  small  traces  of  it  are  present  in  normal 
cerebro-spinal  fluid,  and  in  certain  diseased  conditions  of  the 
brain,  as  in  general  paralysis,  the  quantity  is  said  to  be  notably 
increased.  Some  writers  assert  that  this  increase  in  the  cholin 
can  be  used  as  a  test  to  distinguish  organic  nervous  disease  from 
that  which  is  purely  functional.     But  the  matter  is  in  dispute. 

Cerebro-spinal  Fluid. — The  cerebro-spinal  fluid,  which  Alls 
the  ventricles  of  the  brain  and  the  central  canal  of  the  cord,  is 
continuous  with  that  contained  in  the  subarachnoid  space 
through  the  foramen  of  Magendie,  an  opening  in  the  piece  of  pia 
mater  that  helps  to  roof  in  the  fourth  ventricle.  It  is  secreted  in 
part  by  the  cubical  cells  covering  the  choroid  plexus,  a  fold  of  pia 
mater  which  projects  into  each  lateral  ventricle.  Extracts  of 
choroid  plexus  increase  the  rate  of  secretion.  Cerebro-spinal 
fluid  can  easily  be  obtained  in  man  by  lumbar  puncture  with  a 
hvpodermic  needle  sufficiently  long  to  enter  the  subarachnoid 
space  in  the  spinal  canal.  The  point  usually  selected  for  the 
puncture  is  between  the  fourth  and  fifth  lumbar  vertebrae. 
The  normal  pressure  of  the  fluid  is  such  that  it  trickles  out  by 
drops,  but  in  disease  it  is  sometimes  so  high  that  it  spurts  out  in 
a  steady  stream.  An  examination  of  the  thud,  especially  for  leuco- 
cytes or  bacteria,  is  of  great  diagnostic  value  in  certain  conditions. 
Normally  it  is  a  thin,  clear,  watery  fluid,  faintly  alkaline  in 
reaction  to  litmus,  and  with  a  specific  gravity  of  about  1004  to 
1007.  It  contains  the  ordinary  salts,  but  more  potassium  than 
sodium,  unlike  other  body  fluids  ;  a  very  small  amount  of  protein 
(globulin) — usually  about  01  per  cent. — and  a  little  dextrose 
(Nawratzki).  Its  composition  is  evidently  different  from  that  oJ 
ordinary  lymph.  Only  a  few  lymphocytes  are  present  in  health, 
but  in  some  diseases  (as  in  general  paralysis  of  the  insane,  tabes, 
and  cerebro-spinal  syphilis)  a  marked  increase  occurs.     In  acute 


////    CENTR  II.   NERVOUS  SYS1  I  M 


883 


cerebro-spinal  meningitis  numerous   polymorphonuclear  leuco- 
cytes arc  found,  win.  h  are  absent  from  the  normal  fluid. 

The  depression  <>i  the  freezing-point  (A)  usually  lies  between 
-o-oo  ando-65°C.  [n  a  case  of  hydrocephalus  it  was  -0*65°  C. 
Normally,  cerebro-spinal  fluid  i^  somewhat 
hypertonic  to  the  blood  serum.  In  injury 
of  the  cribriform  plate  <>|  the  ethmoid  bone 
and  also  in  some  cases  where  there  is  no 
traumatic  injury,  the  fluid  escapes  from  the 
nose,  and  the  rate  of  its  formation  can  thus 
be  ascertained.  In  one  case  it  was  found  to 
be  as  much  as  2  c.c.  t.»  nearly  |  c.c.  in  ten 
minutes. 


The  Autonomic  Nervous  System  (the  Sym- 
pathetic and  Allied  Nerves).  -The  efferent  fibres 
of  the  body  can  be  divided  into  two  classes: 
(1)  Those  which  supply  multinuclear  striated 
muscle  (skeletal  muscle)  ;  (z)  those  which  supply 
other  structures  (smooth  muscle,  heart  muscle, 
glands).  The  second  group  is  called  '  auto- 
nomic,' to  indicate  that  it  possesses  a  certain 
independence  of  the  central  nervous  system, 
although  this  independence  is  far  from  abso- 
lute. The  autonomic  fibres  arise  from  four 
regions  of  the  central  nervous  system  :  (i)  The 
mid-brain  ;  (2)  the  bulb  ;  (3)  the  thoracic  and 
upper  lumbar  cord  ;  (4)  the  sacral  portion  of 
the  cord.  All  autonomic  fibres  after  issuing 
from  the  central  nervous  system  end  sooner  or 
later  by  forming  synapses  around  nerve-cells  of 
sympathetic  type,  by  whose  axons  the  path  is 
continued  to  the  peripheral  distribution.  The 
autonomic  path  accordingly  comprises  two 
neurons,  the  fibre  which  arises  from  the  brain 
or  cord  being  termed  the  '  preganglionic,'  and 
that  which  arises  from  the  sympathetic  gan- 
glion the  '  postganglionic  fibre.' 

The  autonomic  fibres  originating  in  the  mid- 
brain emerge  in  the  oculo-motor  nerve,  and  form 
synapses  with  cells  in  the  ciliary  ganglion,  winch 
in  turn  send  fibres  to  the  ciliary  muscle  and  the 
constrictor  muscle  of  the  iris  (pp.  819,  909) .  The 
bulbar  autonomic  fibres  emerge  in  the  seventh, 
ninth,  and  tenth  cranial  nerves.  Those  in  the 
vagus  include  inhibitory  fibres  for  the  heart 
muscle,  motor  and  inhibitory  fibres  for  the 
smooth  muscle  of  the  alimentary  canal  from 
the  oesophagus  to  the  descending  colon,  and  for  the  muscles  of  the 
trachea  and  lungs,  and  secretory  fibres  for  the  gastric  glands  and 
the  pancreas.  The  sympathetic  ganglion  cells  with  which  these 
preganglionic  fibres  form  synapses  have  not  always  been  definitely 
located,  but  lie  near  or  in  the  tissue  supplied  (p.  165).  The  auto- 
nomic fibres  in   the  seventh  and  ninth  nerves  supply  the  mucous 

56—2 


•Sacrai 


Fig.  367. — Diagram 
showing  thh  cen- 
tral origin  of  the 
Autonomic  Fibres 
(Langley). 


A   MANUA1    OF  PHYSIOLOGY 

membranes  of  the  mouth  and  nose  with  vaso-dilator  and  secretory 
fibres.     The  preganglionic  portion  of  the  path  terminates  in  such 

ganglia  as  the  submaxillary  and  sublingual  (p.  302)  and  the  spheno- 
palatine and  otic  ganglia. 

The  part  of  the  autonomic  system  which  originates  in  the  middle 
region  of  the  spinal  cord  (in  the  cat  from  the  first  thoracic  to  the 
fourth  or  fifth  lumbar  nerves)  is  the  sympathetic  proper.  The 
course  of  the  fibres  has  already  been  described  in  connection  with 
the  vasomotor  nerves  (p.  165).  Among  the  fibres  may  be  men- 
tioned the  dilators  of  the  pupil,  the  aujjmenters  of  the  heart,  motor 
(viscero  -  motor),  and  inhibitory  fibres  for  the  smooth  muscle  of 
the  alimentary  canal,  sweat-secretory,  pile-motor  and  vasocon- 
strictor 6bres.  The  preganglionic  fibres  issue-  from  the  cord  in  the 
.interior  roots,  and  leave  the  corresponding  spinal  nerve  in  the 
white  ramus  communicans,  which  connects  it  with  the  corresponding 
ganglion  of  the  lateral  sympathetic  chain.  A  fibre  may  either  end 
in  this  ganglion  by  forming  a  synapse,  or  it  may  run  up  or  down 
in  the  chain  for  some  distance  before  terminating.  Some  of  the 
preganglionic  fibres,  particularly  the  vaso-constrictors  for  the 
abelominal  and  pelvic  viscera,  do  not  end  in  the  lateral  chain  at  all, 
but  issuing  from  it  still  as  medullatcd  fibres,  terminate  in  one  of  the 
prevertebral  ganglia — e.g.,  cceliac  ganglion,  inferior  mesenteric 
ganglion — from  which  postganglionic  fibres  proceed  to  the  viscera, 
as  previously  described  (p.  310).  The  postganglionic  fibres  arising 
from  cells  of  the  lateral  ganglia  return  as  non-medullated  fibres  in 
grey  rami  communicantes  to  the  spinal  nerves,  and  are  distributed 
with  them  to  the  head,  limbs,  and  the  superficial  parts  of  the  trunk. 

The  autonomic  fibres  arising  from  the-  sacral  region  of  the  cord 
emerge  as  preganglionic  fibres  in  the  anterior  roots  of  the  second 
to  the  fourth  sacral  nerves,  from  which  they  pass  to  the  pelvic  nerve 
(nervus  erigens)  (pp.  163,  310).  They  comprise  vaso-dilator  fibres  for 
the  rectum,  anus,  and  external  ge-nitals.  motor  (viscero-motor)  fibres 
for  the  smooth  muscle  of  the  descending  colon,  rectum,  and  anus. 
inhibitory  fibres  for  the  smooth  muscle  of  the  anus,  and  the 
muscles  of  the  external  genitals,  motor  fibres  for  the  bladder, 
etc.  The  preganglionic  fibres  terminate  by  forming  synapses  with 
sympathetic  ganglion  cells  in  the  pelvic  plexus,  or  in  the  neighbour- 
hood of  the  organs  which  they  supply.  From  these  ganglion  cells 
the  postganglionic  fibres  arise. 


PRACTICAL  EXERCISES  OX  CHAPTER   XII. 

1.  Section  and  Stimulation  of  the  Spinal  Nerve-roots  in  the  Frog. 
— (a)  Select  a  large  frog  (a  bull-frog,  if  possible).  Pith  the  brain. 
Fasten  the  frog,  belly  down,  em  a  plate  of  cork.  Make  an  incision 
in  the  middle  line  over  the  spinous  processes  of  the  lowest  three 
or  four  vertebrae,  separate  the  muscles  from  the  vertebral  arches, 
and  with  strong  scissors  open  the  spinal  canal,  taking  care  not  to 
injure  the  cord  by  passing  the  blade  of  the  scissors  too  deeply. 
Extend  the  opening  upwards  till  two  or  three  posterior  roots  come 
into  view.  Pass  fine  silk  ligatures  under  two  of  them.  tie.  and 
divide  one  root  central  to  the  ligature,  the  other  peripheral  to  it. 
Stimulate  the  central  end.  and  reflex  movements  will  occur.  Stimu- 
late the  peripheral  end  :  no  effe<  t  is  produced.  Now  cut  away  the 
exposed  posterior  roots  and  isolate  and  ligature  two  of  the  anterior 


pr  k  i  n  u  i  \i  nasi  s 

roots,  which  are  smaller  than  the  posterior.  Stimulate  the  central 
end  oi  one:  there  is  no  effect.  Stimulation  ol  the  peripheral  end 
of  the  other  causes  contractions  oi  the  corresponding  muse  i> 

(b)  Stimulation  oi  the  roots  may  be  repeated  on  the  mammal, 
using  the  dog  employed  lor  the  experiment  on  the  motor  areas 
(p.  889).  Place  the  animal,  belly  down,  and  insert  a  good-sized  block 
of  wood  between  it  and  the  board  at  the  level  ol  the  lumbar  vertebrae 
of  the  spine.  Divide  the  skin  and  muscles  on  either  side  of  this  region 
till  the  lamina?  of  the  vertebrae  are  exposed.  Snip  through  them 
with  strong  forceps,  and  open  the  spinal  canal,  exposing  a  length  of 
cord  corresponding  to  three  or  tour  vertebrae.  Ligate  and  stimulate 
the  roots  as  in 

2.  Reflex  Action  in  the  '  Spinal  '  Frog.  -Pith  the  brain  of  a  frog, 
destroying  it  down  to  the  posterior  third  of  the  medulla  oblongata. 
1  Note  the  position  of  the  limbs  immediately  after  the  operation, 
and  again  thirty  to  forty  minutes  later.  Its  hind-legs  possess 
tone,  and  are  drawn  up  against  the  flanks.  The  animal  can  still 
1  xecute  certain  co-ordinated  movements — e.g.,  pulling  away  its 
leg  if  a  toe  is  pinched.  The  power  of  maintaining  equilibrium  is 
lost.  If  placed  on  its  back,  it  lies  there.  When  thrown  into  water 
it  sinks  usually  without  any  attempt  at  swimming.  Verify  the 
following  facts,  using  mechanical  stimulation  (pinching  the  toes 
or  skin  of  the  leg)  :  (a)  It  the  stimulus  provokes  muscular  move- 
ments only  on  one  side  of  the  body,  this  is  usually  on  the  same  side 
as  the  stimulated  point.  (b)  When  the  stimulus  causes  reflex 
movements  on  both  sides  of  the  body,  the  stronger  contractions 
are  on  the  side  to  which  the  stimulus  was  applied. 

Determine  whether  it  is  easier  to  obtain  movement  of  a  portion 
of  the  bodv  innervated  from  a  region  of  the  cord  above  the  level 
of  the  stimulated  nerves  or  below  that  level. 

With  electrical  stimuli  (using  a  coil  arranged  for  single  shocks) 
determine  whether  reflex  movements  are  elicited  bv  a  single  induced 
shock  applied  to  the  skin.  Verify  the  fact  that  a  series  of  shocks  is 
more  efficient,  the  effects  of  the  separate  stimuli  being  summated 
in  the  reflex  centres. 

(3)  To  test  the  effect  of  thermal  stimuli,  dip  the  leg  into  a  beaker  of 
warm  water.  Vary  the  temperature  of  the  water,  using  a  series  of 
beakers  with  water  at  io°  C,  200  C,  etc.,  above  the  temperature  of 
the  room.  Place  the  leg  for  a  moment  in  each,  and  determine 
which  is  the  most  efficient  stimulus.  Immediately  on  withdrawing 
the  leg  from  each  of  the  hot-water  beakers  immerse  it  in  a  beaker 
of  water  at  room  temperature.  Finally,  dip  the  leg  into  a  beaker 
of  cold  water,  and  heat  it  gradually  to  a  temperature  at  which  a 
reflex  was  previously  obtained.  Probably  it  will  not  be  elicited 
by  the  gradual  warming. 

(4)  '  Purposive  '  Movements. — -Touch  the  skin  of  one  thigh  with 
blotting-paper  soaked  in  strong  acetic  acid.  The  leg  is  drawn  up, 
and  the  foot  moved  as  if  to  get  rid  of  the  irritant.  If  the  leg  is 
held,  the  other  is  brought  into  action.  Immerse  the  frog  in  water 
to  wash  away  the  acid. 

(5)  Spread  (Irradiation)  of  Reflexes. — Gently  stimulate  a  toe  or 
a  small  spot  on  the  flank  with  weak  induction  shocks  or  weak 
mechanical  stimuli,  and  note  the  reflex  effect  obtained.  Then  go 
on  gradually  increasing  the  strength  of  stimulation  without  in- 
creasing the  area  of  the  field  stimulated,  and  observe  the  extent 
and  order  of  spread  of  the  reflex  movements. 


886  I    M  INI    //.  OF    I'll  YSIOLOG  Y 

3.  Reflex  Time.  Pass  .1  tiook  through  the  jaws.  Holding  the 
frog  by  the  hook,  dip  one  leg  into  .1  dilute  solution  ol  sulphuric 
acid  (o'2  to  o'5  per  cent.),  and  note  with  the  stop-watch  the  interval 
which  elapses  before  the  Erog  draws  up  its  Leg  (Turck's  method  ol 
determining  the  reflex  time).     Wash  the  acid  ofl  with  water. 

Determine  how  the  reflex  time  varies  with  the  strength  of  the 
stimulus.  This  can  be  done  by  using  various  strengths  of  acid. 
The  reflex  time  will  be  shorter  the  stronger  the  stimulus  up  to  a 
certain  point.  Compare  the  reflex  time  of  movements  on  the  same 
side  of  the  body  as  the  point  ot  application  of  the  stimulus  and  on 
the  opposite  side. 

4.  Inhibition  of  the  Reflexes. — (r)  Destroy  the  cerebrum  of  a 
frog.  Dip  one  leg  into  dilute  sulphuric  acid  as  in  3,  and  estimate 
the  reflex  time.  Then  apply  a  crystal  of  common  salt  to  the 
upper  part  of  the  spinal  cord.  If  the  opening  made  for  pithing 
the  frog  is  not  large  enough  to  enable  the  cord  to  be  clearly  seen, 
enlarge  it.  Again  dip  the  leg  in  the  dilute  acid.  It  will  either  not 
be  drawn  up  at  all,  or  the  interval  will  be  distinctly  longer  than  before. 

(2)  Expose  the  viscera,  including  the  heart .  taking  care  not  to 
injure  the  cardiac  nerves.  Tap  the  intestines  sharply  with  tin- 
handle  of  a  scalpel  many  times  in  succession.     The  heart  is  inhibited. 

(3)  Tie  strings  tightly  around  both  fore-legs  of  a  normal  frog. 
Place  the  animal  on  its  back;  it  does  not  turn  over.  The  hind- 
legs  may  be  pulled  about  in  various  ways  without  the  frog  turning 
over  into  its  normal  position.  The  reactions  concerned  in  the 
maintenance  of  equilibrium  arc  inhibited.  Remove  the  strings. 
The  animal  cannot  be  made  to  lie  on  its  back  except  by  force. 

5.  Spinal  Cord  and  Muscular  Tonus. — Destroy  the  brain  of  a  frog. 
Isolate  the  gastrocnemius,  and  cut  away  the  bone  below  the  knee. 
Isolate  the  sciatic  nerve  without  injuring  it.  Remove  the  muscles 
from  the  femur,  cut  the  bone  and  fix  it  in  a  clamp  for  graphic 
recording.  Connect  the  tendon  with  a  lever,  weighted  with  5  to 
10  grammes.  Take  a  base  line.  Destroy  the  spinal  cord,  or  cut 
the  sciatic  and  again  take  a  base  line.  The  length  of  the  muscle  is 
slightly  altered. 

6.  Spinal  Cord  and  Tonus  of  the  Bloodvessels. — Destroy  the  brain 
of  a  frog.  Arrange  the  web  of  the  foot  on  the  stage  of  a  micro- 
scope, and  note  the  calibre  of  the  bloodvessels  in  the  field.  Destroy 
the  cord,  and  observe  the  change  in  their  calibre.    They  will  dilate. 

7.  Action  of  Strychnine. — Pith  a  frog  (brain  only).  Inject  into 
one  of  the  lymph-sacs  three  or  four  drops  of  a  01  per  cent,  solution 
of  strychnine.  In  a  few  minutes  general  spasms  come  on,  which 
have  intermissions,  but  are  excited  by  the  slightest  stimulus.  The  ex- 
tensor muscles  of  the  trunk  and  limbs  overcome  the  flexi  >rs.  Destroy 
the  spinal  cord  ;  the  spasms  at  once  cease,  and  cannot  again  be  excited. 

S.  Mammalian  Spinal  Preparation  (Sherrington).*  —  Deeply 
anaesthetize  a  cat  with  ether.  Insert  a  cannula  into  the  trachea 
(p.  186),  and  continue  the  anaesthesia  through  this.  Expose  and 
ligate  both  common  carotids.  Make  a  transverse  incision  through 
the  skin  over  the  occiput,  and  extend  it  laterally  behind  the  ears. 
Pull  back  the  skin  so  as  to  expose  the  neck  muscles  at  the  level  of 
the  axis  vertebra.     Feel  for  the  ends  of  the  transverse  processes  of 

*  A  similar  preparation  can  lie  used  tor  certain  experiments  on  the 
circulation  (Crile,  Guthrie).  For  these,  as  well  as  [or  the  study  of  many 
reflexes,  a  good  preparation  is  obtained  by  occlusion  ol  the  cerebral  blood- 
supply  in  cats  /without  decapitation). 


/'/,'  /(//('  //.    /  XI  /,•('/.  S7-.S-  :ss7 

i  in-  atlas,  and  divide  the  muscles  down  to  the  bone  just  behind  these 
processes.  Now  start  artificial  respiration  (p.  187),  or  sooner  if 
in ■<  essary.  Notch  the  spinous  process  of  the  axis  with  bone  for<  eps, 
Pass  a  strong  thick  ligal  lire  by  .1  sharp-ended  aneurism  needle  1  lo  •■ 
under  the  body  of  the  axis  and  tie  it  tightly  in  the  groove  left  by  the 
incision  behind  the  transverse  processes  oi  the  atlas  and  the  notch 
made  in  the  spinous  process  of  the  axis.  This  compresses  the 
vertebral  arteries  where  they  pass  From  transverse  process  of  axis 
to  transverse  process  of  atlas.  Pass  a  second  strong  ligature  undei 
the  trachea  at  the  level  of  the  cricoid  cartilage  and  include  in  it  the 
whole  neck,  except  the  trachea,  but  at  present  only  tie  a  single 
loop  on  it.  Now  decapitate  the  animal  with  a  large  knife  (an 
amputating  knife)  passed  from  the  ventral  aspect  of  the  neck 
through  the  occipito-atlantal  space,  severing  the  cord  just  behind 
its  junction  with  the  bulb.  At  the  moment  of  decapitation  tighten 
the  ligature  round  the  neck,  and  complete  the  knot.  Destroy  the 
head.  If  there  is  oozing  of  blood  from  the  vertebral  canal,  arrest  it: 
by  raising  the  neck  somewhat  above  the  level  of  the  body.  The 
carcass  must  be  kept  warm  by  placing  it  on  a  metal  box  or  table 
containing  hot  water,  and  the  air  used  for  artificial  respiration  must 
also  be  warmed,  as  by  passing  it  through  a  coil  of  rubber-tubing 
immersed  in  a  water-bath  which  is  kept  hot.  Stitch  the  skin-flaps 
together  so  as  to  cover  the  cut  end  of  the  spinal  cord  and  the  other 
structures  cut  in  decapitation.  By  this  procedure  the  spinal  cord 
is  usually  severed  about  4  millimetres  behind  the  point  of  the 
calamus  scriptorius.  Although  the  blood-pressure  remains  low, 
reflexes  employing  the  skeletal  muscles  can  be  fairly  well  elicited  for 
hours.  Study  on  the  preparation  the  reflexes  described  in  the  text 
(pp.  799,  801) — e.g.,  the  flexion  reflex  of  the  hind  and  fore  limb, 
as  elicited  from  the  skin,  or  one  of  the  afferent  nerves  of  the  limb — 
the  crossed  extension  reflex  of  hind  and  fore  limb,  the  scratch  reflex. 

(1)  Scratch  Reflex. — (a)  Evoke  the  reflex  by  rubbing  the  skin  of 
the  neck  behind  the  pinna.  The  scratching  movements  are  in  the 
hind-leg  of  the  same  side.  Record  them  on  a  drum,  on  which  is 
also  written  a  time-tracing  in  seconds.  The  record  can  be  obtained 
by  tying  a  piece  of  tape,  not  too  tightly,  round  the  foot,  leg,  or 
thigh,  and  connecting  this  by  a  thread  with  a  lever.  The  thread 
is  passed  over  a  pulley  below  the  lever,  so  that  its  pull  may  be 
exerted  at  right  angles  to  the  axis  of  rotation  of  the  lever.  The 
lever  is  attached  to  a  light  spring  or  a  rubber  band,  which  is  stretched 
when  it  moves  in  one  direction,  and  in  recoiling  brings  it  back  again 
to  its  position  of  rest  at  the  end  of  the  contraction.  If  the  reflex 
is  not  easilv  evoked,  it  can  be  facilitated  by  producing  a  slight  degree  of 
asphyxia,  by  temporarily  clamping  the  respiration  tube.  Some  time 
must  elapse  after  the  decapitation  before  a  fair  scratch  reflex  can 
be  expected.     It  is  usually  sufficiently  well  marked  within  an  hour. 

(b)  While  the  reflex  is  occurring,  stimulate  with  an  interrupted 
current  the  central  stump  of  the  popliteal  nerve  of  the  opposite  hind- 
limb.  The  scratch  reflex  may  be  cut  short  by  inhibition.  Also,  during 
the  stimulation  of  this  nerve  the  reflex  may  be  incapable  of  being 
elicited  till  the  excitation  of  the  inhibitory  afferent  nerve  is  stopped. 

(2)  Flexion  Reflex. — (a)  Stimulate  with  a  weak  interrupted  current 
the  skin  of  some  part  of  the  hind-limb — say  one  of  the  toes.  The 
flexion  reflex  of  the  hind-limb  on  the  same  side  may  be  evoked — 
i.e.,  a  flexion  movement  at  the  knee,  hip,  and  ankle.  Record  the 
movements  of  one  of  the  joints  or  of  flexor  muscles  after  severing 
them  from  their  insertion. 


/    w  INI    //.  OF   PHYSIOLOG  Y 


stimulate  with  a  weak  interrupt*  d  (faradic)  currenl  the  central 
stump  "i  on<  "i  the  n<  rves  oi  a  hind-limb  say,  the  peroneal  n<  i 
The  flexion  reflex  oi  the  same  limb  may  be  elicited  Record  the 
movements.  Now  produce  temporary  asphyxia  by  clamping  the 
respiration  tube,  and  repeat  the  stimulation  at  half-minute  intervals. 
I  In  reflex  will  be  Ln<  reased  by  the  asphyxia.  Do  not  interrupt  the 
respiral  ion  for  more  than  two  or  three  minutes,  and  immediately  start 
it  if  the  heart,  which  can  be  felt  through  the  chest,  begins  to  weaken. 

(3)  Elicit  the  knee-jerk,  as  described  in  the 
text  (p.  802).     It  is  generally  exaggerated. 

(4)  By  the  unipolar  method  (p.  843)  stimu- 
late with  a  point  electrode  one  lateral  half  oi 
iir  <  ross  se<  1  ion  of  the  <  ervical  cord  exposed 
in  decapitation.  The  large  electrode  is  plai  1  d 
on  a  shaved  part  of  a  forearm.  Various  eft 
may  be  elicited  according  to  the  point  of  the 
<  ross  section  stimulated  e.g.,  stepping  and 
scratch  movements  of  the  hind  limbs.  <  >ther 
facts  mentioned  in  the  text  in  regard  to  spinal 
reflexes  can  be  verified  on  this  preparation. 

9.  Reflexes  in  Man. — Study  systematically 
on  a  fellow -student  and  on  yourself  the  chief 
reflexes  described  in  the  text  (p.  8io). 

10.  Excision  of  Cerebral  Hemispheres  in  the 
Frog  (lig.  368). —  Anaesthetize  a  frog  lightly 
by  putting  it  under  a  bell-jar  or  tumbler  with 
a  small  piece  of  cotton-wool  soaked  in  ether. 
Put  very  little  ether  on  the  cotton,  and  leave 
the  frog  only  a  very  short  time  under  the  bell- 
jar.  Then,  holding  it  in  a  cloth,  make  an 
incision  through  the  skin  over  the  skull  in 
the  mesial  line.  With  scissors  open  the 
cranium  about  the  position  of  a  line  drawn 
at  a  tangent  to  the  posterior  borders  of  the 
two  tympanic  membranes.  Remove  the  roof 
of  the  skull  in  front  of  this  line  with  forceps, 

p  out  the  cerebral  hemispheres,  and 
up  the  wound.  As  soon  as  the  animal  has 
recovered  from  the  ether,  the  phenomena 
described  at  p.  840  should  be  verified.  The 
frog  will  swim  when  thrown  into  water,  will 
refuse  to  lie  on  its  back,  and  will  not  fall  if 
the  board  on  which  it  lies  be  gradually  slanted. 
Let  the  frog  live  for  a  day,  keeping  it  in  a  moist 
atmosphere  ;  then  expose  the  brain  again, 
nnine  the  reflex  time  by  Tiirck's  method  ;  apply  a  crystal  of 
common  salt  to  the  optic  lobes,  and  repeal  the  observation.  The 
reflex  movements  will  be  completely  inhibited  or  delayed.  Remove 
tin'  salt,  wash  with  physiological  salt  solution,  excise  the  optic  lobes, 
ami  see  whether  the  frog  will  now  swim. 

11.  Excision  of  the  Cerebral  Hemispheres  in  a  Pigeon. — Feed  a 
pigeon  for  two  or  three  days  on  dry  food,  etherize  it  by  holding 
a  piece  of  cotton-wool  sprinkled  with  ether  over  its  beak,  or  inject 
into  the  rectum  i  gramme  chloral  hydrate.  The  pigeon  being 
wrapped  up  in  a  cloth,  and  the  head  held  steady  by  an  assistant, 
the  feathers  are  clipped  ofl  the  head,  an  incision  made  in  the  middle 
line   through   the   skin,   and    the   flaps   reflected   SO  as  to  expose  the 


1  1       368.  ■ 

I     R   u  G 

Steiner). 

a,       cerebral       hemi- 
-pin  res  ;    b,    position    of 

optic     thai, inn  ;    < .    optic 

1  l"  -  :     <i.     (  erebellum  ; 

medulla     obi 
.1,   uppi  r  end   "l   spinal 
cord. 


PRAi  I  K    \L   I  XI  RCIS1  S 

skull.     Cut  through  tin-  bones  with  s<  issors,  and  mak<   a  suffi<  iently 
Large  opening  to  bring  the  cerebral  hemispheres  into  view.     The) 
n«>w  rapidly  divided  from  the  corpora  bigemina  and  lifted  out  with 
the  handle  oi  a   scalpel       The  bleeding  is  very  tree,  but   may  be 
partially  controlled  by  stuffing  the  cavity  with  th<  ble  libre 

known   .is    Peng  Djambi,    which  should   be  removed   in  a  few 

minutes,  the  wound  cleansed  with  iodoform  gauze,  wrung  out  of 
physiological  salt  solution  .it  500  C,  and  sewed  up.  Study  the 
phenomena  described  on  p.  8  |  I 

1  j.  Stimulation  of  the  Motor  Areas  in  the  Dog. — (a)  Study  a 
hardened  brain  oi  a  dog,  noting  especially  the  crucial  sulcus  (Fig.  349, 
p.  843).  the  convolutions  in  relation  to  it.  and  the  areas  mapped  out 
around  it  byHitzigand  Fritsch  and  others,  [b)  Inject  morphine  under 
the  skin  of  a  dog.  Set  up  an  induction-coil  arranged  for  tetanus, 
with  a  single  Daniel]  in  the  primary  circuit.  Connect  a  pair  of 
fine  but  not  sharp-pointed  electrodes  through  a  short-circuiting  key 
with  the  secondary.  1'asten  the  dog  on  the  holder,  belly  down, 
and  put  a  large  pad  under  the  neck  to  support  the  head.  Clip  the 
hair  over  the  scalp.  Feel  for  the  condyles  of  the  lower  jaw.  and 
join  them  by  a  string  across  the  top  of  the  head.  Connect  the 
outer  canthi  of  the  eyes  by  another  thread.  The  crucial  sulcus 
lies  a  little  behind  the  mid-point  between  these  two  lines.  Now 
give  the  dog  ether,  make  a  mesial  incision  through  the  skin  down 
to  the  bone,  and  reflect  the  flaps  on  either  side.  Detach  as  much 
of  the  temporal  muscle  from  the  bone  as  is  necessary  to  get  room  for 
two  trephine  holes,  the  internal  borders  of  which  must  be  not  less 
than  I  inch  from  the  middle  line,  so  as  to  avoid  wounding  the  longi- 
tudinal sinus.  Carefully  work  the  trephine  through  the  skull,  taking 
care  not  to  press  heavily  on  it  at  the  last.  Raise  up  the  two  piece? 
of  bone  with  forceps,  connect  the  holes  with  bone  forceps,  and 
enlarge  the  opening  as  much  as  may  be  necessary  to  reach  all  the 
'  motor  '  areas.  At  this  stage  only  enough  ether  should  be  given  to 
prevent  suffering.  Now  unbind  the  hind  and  fore  limbs  on  the  side 
opposite  to  that  on  which  the  brain  has  been  exposed,  apply  blunt 
electrodes  successivelv  to  the  areas  for  the  fore  and  hind  limbs, 
and  stimulate.*  The*  '  unipolar  '  method  of  stimulation  (p. 
may  also  be  emploved.  Contraction  of  the  corresponding  groups 
of  muscles  will  be  seen  if  the  narcosis  is  not  too  deep.  Movements 
of  the  head.  neck,  and  eyelids  may  also  Ire  called  forth  by  stimulating 
the  'motor'  areas  for'thesc  regions.  Stimulation  in  front  of  the 
crucial  sulcus  may  also  cause  great  dilatation  of  the  pupil,  the  iris 
almost  disappearing.  The  dilatation  takes  place  most  promptlv. 
and  is  greatest  on  the  opposite  side,  but  the  pupil  on  the  same  side 
is  also  widened.  Even  after  section  of  both  vago-sympathetic 
nerves  in  the  neck,  a  slow  and  slight  dilatation,  greatest  perhaps 
on  the  same  side,  may  be  caused  by  cortical  stimulation.  Repeat 
the  whole  experiment  on  the  opposite  side  of  the  brain.  In  the 
course  of  his  observations  the  student  will  perhaps  have  the  oppor- 
tunity of  seeing  general  epileptiform  convulsions  set  up  by  a  localized 
excitation.  They  begin  in  the  group  of  muscles  represented  in  the 
portion  of  the  cortex  directly  stimulated.  After  the  convulsions 
have  been  suff.cientlv  studied,  they  should  be  again  induced,  and 
the  stimulated  '  motor  '  area  rapidly  excised  during  their  course.  In 
some  cases  this  will  be  followed  by  immediate  cessation  of  the 
spasms,  (c)  The  same  animal  can  be  used  for  stimulation  of  the 
spinal  nerve-roots,  as  described  in  Experiment  1  (p.  SS5). 
*   It  is  not  necessarv  to  remove  the  dura  mater. 


CHAPTER  XIII 
THE  SENSES 

Hitherto  \vc  have  been  considering  from  a  purely  objective  stand- 
point the  organs  that  compose  the  body,  and  their  work.  I  In- 
student  has  been  assumed  to  be  in  the  little  world — the  '  microcosm  ' 
— of  organization  which  he  has  been  studying,  but  not  of  it.  He 
has  listened  to  the  sounds  of  the  heart,  seen  its  contraction,  felt  it 
hardening  under  his  fingers  ;  but  we  have  not  inquired  as  tc  the 
meaning  or  the  mechanism  of  this  hearing,  seeing,  and  feeling.  We 
have  now  to  recognise  that  all  our  knowledge  of  external  things 
comes  to  us  by  the  channels  of  the  senses,  and.  like  the  light  that 
falls  through  coloured  windows  on  the  floor  of  a  church,  is  tinged, 
and  perhaps  distorted,  in  the  act  of  reaching  us. 

The  Senses  in  General. — The  old  and  orthodox  enumeration 
of  '  the  five  senses  '  of  sight,  hearing,  touch,  taste,  and  smell, 
must  be  augmented  by  at  least  two  more,  the  senses  of  pressure 
and  temperature.  The  so-called  temperature  sensations  are 
themselves  divisible  into  two  groups  of  quite  distinctive  quality, 
sensations  of  warmth  and  sensations  of  cold.  The  power  of  appre- 
ciating the  amount  of  a  muscular  effort  ;  the  power  of  localizing 
the  various  portions  of  the  body  in  space  ;  the  sensations  of  pain, 
tickling,  itching,  hunger,  and  thirst  ;  the  sensations  accompanying 
the  generative  act,  etc.,  can  certainly  be  no  longer  lumped 
together  in  the  omnium  gatherum  of '  common  sensibility.'  They 
are  more  appropriately  regarded  as  separate  senses  subserved  by 
special  nerves,  and  perhaps  connected  with  definite  centres.  In 
the  development  of  a  simple  sensation  we  may  distinguish  three 
stage-  :  the  stimulation  of  a  peripheral  end-organ,  the  propaga- 
tion of  the  impulses  thus  set  up  along  an  afferent  nerve,  and  their 
reception  and  elaboration  in  a  central  organ. 

We  do  not  know  in  what  manner  a  scries  of  transverse  vibrations 
in  the  ether  when  it  falls  upon  the  eye,  or  a  series  of  longitudinal 
vibrations  in  the  air  when  it  strikes  the  ear.  excites  a  sensation  of 
light  or  sound.  We  can  trace  the  ray  of  light  through  the  refractive 
media  of  the  eyeball,  see  it  focussed  on  the  retina,  lead  off  the 
current  of  action  set  up  in  that  membrane,  which,  doubtless,  gives 
token  of  the  passage  of  nervous  impulses  into  and  up  the  optic  nerve. 
We  can  even  follow  the  nervous  impulses  to  a  definite  portion  of  the 
cortex  of  the  occipital  lobe,  and  determine  that  if  this  is  removed 
no  sensation  of  sight  will  result  from  any  excitation  of  retina  or  optic 

890 


THE   SENSES  891 

nerve.  And  it  is  fair  to  conclude  thai  In  some  manner  this  pari  of 
the  cerebral  cortex  is  csscnti.il  to  the  production  of  visual  sensations. 
But  in  what  way  the  chemical  or  physical  processes  in  the  axis- 
cylinders  or  nerve-cells  are  related  to  the  psychical  change,  the  inter- 
ruption oi  the  smooth  and  unregarded  flow  of  consciousness  which 
we  (.ill. 1  sensation  of  light,  we  do  not  know.  To  our  reasoning,  and 
even  to  our  imagination,  there  is  a  great  gulf  fixed  between  the 
physical  stimulus  and  its  psychii  al  consequence  ;  they  seem  incom- 
mensurable quantities  :  the  transition  From  light  to  sensation  of  light 
is  certain,  but  unthinkable. 

Each  kind  of  peripheral  end-organ  is  peculiarly  suited  to 
respond  to  a  certain  kind  of  stimulus.  The  law  of  '  adequate  ' 
or  '  homologous  '  stimuli  is  an  expression  of  this  fact.  The 
'  adequate  '  stimuli  of  the  organs  of  special  sense  may  be  divided 
into  (1)  vibrations  set  up  at  a  distance  without  the  actual  con- 
tact of  the  object — e.g.,  light,  sound,  radiant  heat  ;  (2)  changes 
produced  by  the  contact  of  the  object — e.g.,  in  the  production 
of  sensations  of  taste,  touch,  pressure,  alteration  of  temperature 
(by  conduction).  Midway  between  (1)  and  (2)  lies  the 
adequate  stimulus  of  the  olfactory  end-organs,  which  are  excited 
by  material  particles  given  off  from  the  odoriferous  body  and 
borne  by  the  air  into  the  upper  part  of  the  nostrils. 

The  end-organs  of  the  special  senses  all  agree  in  consisting  essen- 
tially of  modified  ectodermic  cells,  but  they  occupy  areas  by  no  means 
proportioned  to  their  importance  and  to  the  amount  of  information 
we  acquire  through  them.  The  extent  of  surface  which  can  be 
affected  by  light  in  a  man  is  not  more  than  20  sq.  cm.  ;  the  endings 
of  both  nerves  of  hearing  taken  together  do  not  at  most  expand  to 
more  than  5  sq.  cm.  ;  the  olfactory  portion  of  the  mucous  mem- 
brane of  the  nose  has  an  area  of  not  more  than  10  sq.  cm.  ;  the 
sensations  of  taste  are  ministered  to  by  an  area  of  less  than 
50  sq.  cm.  ;  the  end-organs  of  the  senses  of  pressure,  touch,  and 
temperature*  are  distributed  over  a  surface  reckoned  by  square 
metres.  As  the  physiological  status  of  the  sensory  end-organs 
rises,  their  anatomical  distribution  tends  to  shrink.  The  organs  of 
comparatively  coarse  and  common  sensations  are  widely  spread, 
intermingled  with  each  other,  and  seated  in  tissues  whose  primary 
function  mav  not  be  sensory  at  all.  Even  the  nerve-endings  of  the 
sense  of  taste  are  not  confined  to  one  definite  and  circumscribed 
patch,  but  scattered  over  the  tongue  and  palate  ;  and  both  tongue 
and  palate  are  at  least  as  much  concerned  in  mastication  and 
deglutition  as  in  taste.  The  olfactory  portion  of  the  nasal  mucous 
membrane,  although  a  continuous  area  with  fairly  distinct  boun- 
daries, is  still  a  part  of  the  general  lining  of  the  nostril.  The 
epithelial  surfaces  which  minister  to  the  supreme  sensations  of  sight 
and  hearing — the  retina  and  the  sensitive  structures  of  the  cochlea — 
are  the  most  sequestered  of  all  the  sensory  areas,  as  the  organs  of 
which  they  form  a  part  are,  of  all  the  organs  of  sense,  the  most 
highly  specialized  in  function,  and  anatomically  the  most  limited. 
But  although  hidden  in  protected  hollows,  they  are  endowed,  either 
in  virtue  of  their  own  movements  or  of  those  of  the  head,  with  the 
power  of  receiving  impressions  from  every  side,  and  their  actual  size 
is  thus  indefinitely  multiplied. 


A   MANUAL  OF  PHYSIOLOGY 

VISION. 

Physical  Introduction. — Physically,  a  ray  of  light  is  a  series  oi 
disturbances  or  vibrations  in  the  luminiferous  ether,  which  radiates 
nut  from  a  luminous  body  in  what  is  practically  a  straight  line.  The 
ether  is  supposed  to  fill  all  space,  including  the  interstices  between 
the  molecules  of  matter  and  the  atoms  of  which  those  molecules  are 
composed.  Suppose  a  bar  of  iron  to  be  gradually  heated  in  a  dark 
room.  In  the  cold  iron  the  molecules  are  moving  on  the  average 
at  a  relatively  slow  rate,  and  the  waves  set  up  in  the  ether  by  their 
vibrations  are  comparatively  long.  Now,  the  long  ethereal  vibra- 
tions do  not  excite  the  retina,  because  it  is  only  fitted  to  respond  to 
the  impact  oi  the  shorter  waves;  and,  indeed,  the  long  waves  arc 
largely  absorbed  by  the  watery  media  of  the  eye.  As  the  tempera- 
ture of  the  iron  bar  is  increased,  the  molecules  begin  to  move  more 
quickly,  and  waves  of  smaller  and  smaller  length,  of  greater  and 
greater  frequency,  are  set  up,  until  at  last  some  of  them  are  just  able 
to  stimulate  the  retina,  and  the  iron  begins  to  glow  a  dull  red.  As 
the  heating  goes  on  the  molecules  move  more  quickly  still,  and,  in 

addition  to  waves  which  cause  the  sen- 
sation of  red,  shorter  waves  that  give 
Bthc  sensation  of  yellow  appear.  Finally, 
when  a  high  temperature  has  been 
reached,  the  very  shortest  vibrations 
which  can  affect  the  eye  at  all  mingle 
with  the  medium  and  long  waves,  and 
the  sensation  is  one  of  intense  white 
light 
We  have  said  that  a  ray  of  light 
travels  in  a.  straight  line,  and  the 
direction  of  the  straight  line  does  not 
change  as  long  as  the  medium  is  homo- 
geneous. But  when  a  ray  reaches  the 
li  .  369.  Reflf.ction  from  boundary  of  the  medium  through  which 
a  Plane  Mirror.  it   is  passing,  a  part  of  it  is  in  general 

turned  back  or  reflected.  If  the  second 
medium  is  transparent  (water  or  glass,  e.g.),  the  greater  part  of  the 
ray  passes  on  through  it.  a  smaller  portion  is  reflected.  If  the  second 
medium  is  opaque,  the  ray  docs  not  penetrate  it  for  any  great  dis- 
e  :  if  it  is  a  piece  of  polished  metal,  e.g.,  nearly  the  whole  of  t he- 
light  i-  reflei  ted  ;  if  it  is  a  liver  of  lampblack,  very  little  of  the  light 
is  reflected,  most  of  it  is  absorbed. 

Reflection.  -The-  first  law  of  reflection  is  that  the  reflected  ray,  the 
ray  which  fails  upon  the  reflecting  surface  {incident  ray),  and  the 
normal  to  the  surface,  arc  in  one  plane.  The  second  law  is  that  the 
led  ray  makes  with  the  perpendicular  (norma/)  to  the  reflecting 
surface  the  same  angle  as  the  incident  ray.  A  corollary  to  this  is 
that  a  ray  perpendicular  to  the  surface  is  reflected  along  its  own 
path. 

Reflection  from  a  Plane  Mirror. — Let  a  ray  of  light  coming  from 
the  point  P  (Fig.  369)  meet  the  surface  DE'at  B.  making  an  angle 
PBA  with  the  normal  to  the  surface.  The  reflected  ray  BC  will 
make  an  equal  in  T  \1-X"  with  the  normal  ;  and  the  eye  at  C  will  see 
the  image  oi  P  as  it  it  were  placed  at  1",  the  point  where  the  pro- 
longaton  of  BC  cuts  the  straight  line  drawn  from  P  perpendicular 
to  DL\      This  is  the  position  of  an  ordinary  looking-glass  image. 


THE  SENSES 


Reflection  from  a  Concave  Spherical  Minor.  -A  spherical  surface 
may  be  supposed  to  be  made  up  ol  an  infinite  number  oi  infinitely 
small  plane  surfaces.  The  normal  to  each  of  these  plane  surf; 
is  the  radius  of  the  sphere,  and  the  relic;  ted  ray  m  ikes  with  the 
radius  at  the  point  of  incidence  the  same  angle  as  the  incidenl  rav. 
Let  D  (Fig.  370)  be  the  middle  poinl  of  the  mirror,  and  C  its  1  enl  re 


Fig.  370. — Reflection  from  a  Concave    Fig.    371.  —  Formation    of    Real    In- 
Spherical  Mirror.  verted      Image      by      a       Concave 

Spherical  Mirror. 


of  curvature — i.e.,  the  centre  of  the  sphere  of  which  it  is  a  segment. 
Then  CD  is  the  principal  axis,  and  any  other  line  through  C  which 
cuts  the  mirror  is  a  secondary  axis.  When  the  mirror  is  a  small 
portion  of  a  sphere,  rays  parallel  to  the  principal  axis  are  focussed 
at  the  principal  focus  F  midway  between  C  and  D  ;  rays  parallel  to 
any  secondary  axis  are  focussed  in  a  point  lying  on  that  axis  ;  and 
rays  diverging  from 
a  point  on  any  axis 
are  focussed  in  a  point 
on  the  same  axis. 

These  facts  afford  a 
simple  construction 
for  finding  the  posi- 
tion of  the  image  of  an 
object  formed  by  a 
concave  mirror.  Let 
AB  be  the  object 
(Fig.  371).  Then  the 
image  of  A  is  the 
point  in  which  all 
rays  proceeding  from 
A  and  falling  on  the 
mirror,  including  rays 
parallel  to  the  princi- 
pal axis,  are  focussed. 
But     the     ray     AE, 

parallel  to  the  principal  axis,  passes  after  reflection  through  the 
principal  focus  F,  therefore  the  image  of  A  must  lie  on  the  straight 
line  EF.  If  any  secondary  axis  ACD  be  drawn,  the  image  of  A  must 
lie  on  ACD.  It  must  therefore  be  the  point  of  intersection,  a,  of  EF 
and  ACD.  Similarly,  the  image  of  B  must  be  the  point  of  intersec- 
tion, b,  of    GF  and    BCH.     The  image  ab  of   an  object  AB  farther 


Fig. 


572. — Formation  of  Image  by  a   Convex 
Mirror. 


894 


A   MANUAL  OF  PHYSIOLOGY 


from  the  mirror  than  the  principal  focus  is  real  and  inverted.  The 
Purkinje-Sanson  image  reflected  from  the  concave  anterior  surface 
of  the  vitreous  humour  (Fig.  387)  is  an  example. 

After  reflation  from  a  convex  mirror,  rays  of  light  always  diverge, 
and  only  erect,  virtual  images  are  formed — i.e.,  images  which  do  not 
really  exist  in  space,  but  which,  from  the  direction  of  the  rays  of 
light,  we  judge  to  exist.     The  position  of  the  image  of  an  object  AB 
!  J72)  may  be  found  by  a  construction  similar  to  that  for  reflec- 

tion from  a  concave  mirror.  The  image  of  a  flame  reflected  from 
the  anterior  surface  of  the  cornea  or  lens  is  erect  and  virtual.  It 
diminishes  in  size  with  increase  in  the  curvature  or  convexity  of  the 
reflecting  surface  (Fig.  387). 

Refraction.  A  ray  of  light  passing  from  one  medium  into  another 
has  its  velocity,  and  consequently  its  direction,  altered.  It  is  said  to 
be  refracted.     The  first  lrr.v  of  refraction  is  that  the  refracted  ray  is 


51 


_ '                     .       -         J 

Ml  " I    ftm±J 

B4h^^^mV 

Hsjfl 

B 

fij 

Fig.  374. — Refraction*  by  a  Medium 
hounded   by    parallel    planes, 

P    AND    P'. 

The  ray  ABDE  issues  parallel  to  its 
original  direction  :  CB,  FD,  normals 
to  P  and  P' ;  «,  angle  of  incidence ; 
j3,  y,  angles  of  refraction. 


Fig.   373. — Refraction  at  a  Plane 
Surface. 

AB  is  the  incident  :  BD,  the  refracted 
ray  ;  CB,  the  normal  to  the  surface. 
When  the  ray  passes  from  air  into  another 
medium,  the  refractive  index  of  the  latter 

is  the  fraction • 

sinp 

in  the  same  plane  as  the  incident  ray  and  the  normal  to  the  surface. 
The  second  law  is  that  the  sine  of  the  angle  of  incidence  has  a  constant 
ratio  (for  any  given  pair  of  media)  to  the  sine  of  the  angle  of  refraction. 
The  angle  of  incidence  is  the  angle  which  the  ray  makes  with  the 
normal  to  the  surface,  separating  the  two  media  ;  the  angle  of  refrac- 
tion is  the  angle  made  with  the  normal  in  the  second  medium.  This 
ratio  is  called  the  index  of  refraction  between  the  two  media.  For 
purposes  of  comparison,  the  refractive  index  of  a  substance  is  usually 
taken  as  the  ratio  of  the  sine  of  the  angle  of  incidence  to  the  sine  of 
the  angle  of  refraction  of  a  ray  passing  from  air  into  the  substance. 

When  a  ray  strikes  a  surface  at  right  angles,  it  passes  through 
without  suffering  refraction.  When  a  ray  passes  from  a  less  dense 
to  a  denser  medium  {e.g.,  from  air  to  water),  it  is  bent  towards  the 
perpendicular.  When  it  passes  from  a  more  dense  to  a  less  dense 
medium  (as  from  water  to  air),  it  is  bent  away  from  the  perpen- 
dicular. 

When  a  ray  passes  across  a  medium  bounded  by  parallel  planes,  it 


THE  SENSES 


895 


issues  parallel  to  itself  ;  in  other  words,  it  undergoes  no  refraction 
(Fig.  374). 

Refraction  and  Dispersion  by  a  Prism. — The  beam  of  light  is  bent 
towards  the  normal  N  as  it  passes  across  BA  and  away  from  the 
normal  N'  as  it  passes  across  BC  (Fig.  375)  ;  at  both  surfaces  it  is 
bent  towards  the  b.ise  of  the  prism  AC.  At  the  same  time  the  light 
surfers  dispersion — that  is,  the  rays  of  shorter  wave-length  are  more 
refracted  than 
those  of  greater 
wave-length.  The 
deviation  of  any 
given  ray  is 
measured  by  the 
angle  which  the 
refracted  ray 
makes  with  its 
original  direction. 
The  amount  of 
dispersion  pro- 
duced by  a  prism 
is  measured  by 
the  difference  in 
the  deviation  of 
the  extreme  rays 
of  the  spectrum. 

The  dispersion  produced  by  a  given  substance  is  proportional    to 
the  difference  of  its  refractive  indices  for  the  extreme  rays. 

Refraction  by  a  Biconvex  Lens. — A  straight  line  ACB  passing 
through  the  centres  of  curvature  of  the  two  surfaces  of  the  lens  is 
called  the  principal  axis.  A  point  C  lying  on  the  principal  axis 
between  the  two  centres  of  curvature,  and  possessing  the  property 


Fig.  375. — Refraction  and  Dispersion  by  a  Prism. 


Fig. 


376.  —  Refraction    by 
Biconvex  Lens. 


Fig.   377. — Formation  of  Image   by 
Biconvex  Lens. 


that  rays  passing  through  it  do  not  suffer  refraction,  is  called  the 
optical  centre  of  the  lens.  Any  straight  line,  DCE,  passing  through 
the  optical  centre  is  a  secondary  axis.  Rays  of  light  proceeding  from 
a  point  in  the  principal  axis  are  focussed  in  a  point  on  that  axis. 
When  the  rays  proceed  from  an  infinitely  distant  point  in  the 
principal  axis — i.e.,  when  they  are  parallel  to  it — -they  are  focussed 
in  F,  the  principal  focus.  Similarly,  rays  parallel  to,  or  proceeding 
from,  a  point  in  a  secondary  axis  are  focussed  in  a  point  on  that  axis  ; 


.Sg6 


A   MANUAL  OF  PHYSIOLOGY 


but  if  the  focus  is  to  be  sharp,  the  angle  between  the  secondary  and 
the  principal  axis  must  not  be  so  large  as  is  indicated  in   Pig.    $76, 

Formation  of  Image  by  Biconvex  Lens  (Fig.  ^77). — Let  AB  be  the 
object  ;  then  if  Alll>  be  the  path  of  a  ray  from  A  parallel  to  the 
principal  axis,  the  image  of  A  will  be  the  intersection  of  the  straight 
line  DF  and  the  secondary  axis  passing  through  A.  Similarly,  the 
image  oi  B  will  be  the  intersection  of  GF  and  the  secondary  axis  BC. 
Where  AH  is  farther  from  the  lens  than  the  principal  fo(  US,  I  he  image 
ab  is  real  and   inverted.     This  is  the  case  with  the  t   an 

external  object  formed  on  the  retina.  When  the  object  is  nearer 
than  the  prini  ipal  focus,  the  image  is  virtual  and  erect.  The  image 
formed  by  the  objective  of  a  microscope  when  the  object  is  in  focus 
is  real  and  inverted  ;  the  ocular  forms  a  virtual  erect  image  of  this 
real  image. 

Refraction  by  a  Biconcave  Lens  (Fig.  378). — Parallel  rays  are 
rendered  divergent  by  the  lens  ;  there  is  no  real  focus  :  but  if  the  rays 
are  prolonged  backwards  they  meet  in  the  virtual  focus  F,  from 
which  they  appear  to  come  when  received  by  the  eye  through  the 
lens. 

Formation  of  Image  by  Biconcave  Lens  (Fig.  379). — Let  AB  be 
the  object.     Let  AHDI  be  the  path  of  a  ray  from  any  point  A  of 


Fir,.  378.  —  Refraction' 
by  a  Biconcave  Lens. 


Fig.  379. — Formation  op  Image  by  Biconcave 
Lens. 


the  object  parallel  to  the  principal  axis.  Produce  DI  backwards 
(dotted  line)  ;  it  will  pass  through  the  principal  focus  F.  Through  A 
draw  the  secondary  axis  AC.  The  image  of  A  must  lie  both  on 
AC  and  on  IDF — i.e.,  it  must  be  the  intersection,  a,  of  these  straight 
lines.  Similarly,  the  image  of  B  is  b,  the  intersection  of  KGF  and 
BC.     The  image  is  virtual  and  erect. 

Absorption. — Xo  substance  is  perfectly  transparent  ;  in  addition 
to  what  is  reflected,  some  light  is  always  absorbed.  In  other  words, 
in  passing  through  a  body  some  of  the  light  is  transformed  into  heat, 
a  portion  of  the  energy  of  the  short,  luminous  waves  going  to  increase 
the  vibrations  of  the  molecules  of  the  medium,  just  as  a  wave 
passing  under  a  row  of  barges  or  fishing-boats  sets  them  swinging  and 
pitching,  and  so  imparts  to  them  a  certain  amount  of  energy,  which 
is  ultimately  changed  into  heat  by  friction  against  the  water,  and 
against  each  other,  and  by  the  straining  and  rubbing  of  the  chains 
at  their  points  of  attachment.  Some  bodies  absorb  all  the  rays  in 
the  proportion  in  which  they  occur  in  white  light  ;  whether  looked 
at  or  looked  through,  they  appear  colourless  or  white.  Other 
substances  absorb  certain  rays  by  preference,  and  the  amount  of 
absorption  is  proportional  to  the  thickness  of  the  layer.  The 
colours  of  most  natural  bodies  are  due  to  this  selective  absorption. 


THE  SENSES 


897 


^  <£  s* 


V  MM 


Even  when  looked  at  in  reflected  Light,  they  are  seen  by  rays  that 
have  penetrated  a  certain  way  into  the  substance  and  have  then  been 
reflected  ;  and,  oi  course,  .1  smaller  number  of  the  rays  which  the 
body  specially  absorbs  are  reflected  than  of  the  rays  which  it  readily 
transmits,  for  more  of  the  latter  than  of  the  former  reach  any  given 
depth.  This  is  called  '  body  colour  '  ;  and  such  substances  have  tin- 
same  colour  when  seen  by  reflected  and  by  transmitted  Light.  The 
colour  of  haemoglobin  is  due  to  the  absorption  of  the  violet  and  many 
of  the  yellow  and  green  rays,  as  is  shown  by  the  position  of  the 
absorption  bands  in  its  spectrum  (p.  44).  In  Fig.  380  the  violet  rays 
are  represented  as  being  totally  absorbed  before  passing  through  the 
substance.  Some  of  the  green  rays  are  reflected,  some  transmitted, 
some  absorbed.  The  red  rays  are  supposed  to  be  mostly  reflected 
and  transmitted,  only  to  a  slight  extent  absorbed.  The  colour  of 
such  a  substance,  both  when  looked  at  and  when  looked  through, 
would  therefore  be  that  due  to  a  mixture  of  red  light  with  a  smaller 
quantity  of  green.  Then  there  is  another 
class  of  substances  which  owe  their  colour 
to  selective  reflection.  Certain  rays  only 
are  reflected  from  their  surface,  and  the 
light  transmitted  through  a  thin  layer  is 
complementary  to  the  reflected  light — 
that  is,  the  reflected  and  transmitted 
rays  together  would  make  up  white  light. 
These  bodies  have  what  is  called  '  surface 
colour,'  and  include  metals,  various  aniline 
dyes,  and  other  substances. 

Comparative. — Many  invertebrate  ani- 
mals possess  rudimentary  sense-organs, 
by  means  of  wliich  they  may  receive 
certain  luminous  impressions  It  is  true 
that  the  mere  sensation  of  light  is  not  in 
itself  sufficient  for  the  exact  appreciation 
of  the  form  and  situation  of  surrounding 
objects.  But  even  the  closure  of  the  eye- 
lids docs  not  prevent  a  person  of  normal 
eyesight  from  distinguishing  differences 
in  the  intensity  of  illumination.  And  it 
is  possible  that  many  of  the  humbler  ani- 
mals may,  through  the  pigment  spot  \ 
which  are  often  called  eves,  or  perhaps,  as  in  the  earthworm,  by  means 
of  end-organs  more  generallv  diffused  in  the  skin,  attain  to  some  such 
dim  consciousness  of  light  and  shadow  as  will  enable  them  to  avoid 
an  obstacle  or  an  enemy,  to  seek  the  sunny  side  of  a  boulder  or  the 
obscurity  of  an  overhanging  ledge  of  rock.  But  the  indispens  ible 
condition  of  distinct  vision  is  that  an  image  of  each  part  of  an  object 
should  be  formed  upon  a  separate  portion  of  the  receiving  or  sensitive 
surface.  This  condition  is,  to  a  certain  extent,  fulfilled  by  the  com- 
pound eves  of  some  of  the  higher  invertebrates  (insects,  e.g.).  Here 
rays  from  one  point  of  the  object  pass  through  one  of  the  funnel- 
shaped  elements  of  the  compound  eye,  and  rays  from  another  point 
through  another.  Ravs  striking  obliquely  on  the  facets  are  stopped 
by  the  opaque  partitions  between  them.  In  the  Cephalopods  we 
find  that  this  compound  type  of  eye  has  already  been  abandoned  ; 
the  single  svstem  of  curved  refracting  surfaces  so  characteristic  of  the 
vertebrate  eye   has  made  its  appeai'ance  ;   and  the  formation  of  a 

57 


Fig.  3S0. — Diagram  to  show 
Connection  of  Body 
Colour  with  Selective 
Absorption. 


898 


A   MANUAL  OF  PHYSIOLOGY 


clean-cut  image  of  the  object  on  the  retina,  with  the  excitation  of 
a  sharplv-boiinded  area  of  that  membrane,  follows  as  a  geometrical 
consequence  from  the  theory  of  lenses. 

We  have  to  consider  (i)  the  mechanism  by  which  an  image 
is  formed  on  the  retina,  and  (2)  the  events  that  follow  the  for- 
mation of  such  an  image  and  their  relations  to  the  stimulus  that 
calls  them  forth. 

Structure  of  the  Eye.— The  eye  may  be  described  with  sufficient 
accuracy  as  a  spherical  shell,  transparent  in  front,  but  opaque  over 
the  posterior  five-sixths  of  its  surface,  and  filled  up  with  a  series  of 


( 6  t  n  e  a 


Vf  1  ,   <  0 


X 1  litirij  Arfu-sctr 
. '  . ?>s.-  S 11  siit Kscrt/ 

NX  \        r       I  /' 

X       j>  Li tfciuiBnt 
\-\     Choroid 


I.  7  Si /erotic 


R.g!  I  11  'I 


•ai't   -        /',  i\//is  \\\\  ' 


Fig.  381. — Diagrammatic  Horizontal  Section  or  the  Left  Eye. 

..rent  liquids  and  solids.  The  shell  consists  of  three  layers 
concentricallv  arranged,  like  the  coats  of  an  onion  :  (1)  An  external 
tough,  fibrou'3  coat,  the  sclerotic,  the  anterior  portion  of  which  appears 
as  the  white  of  the  eve.  In  front  this  external  layer  is  completed  by 
the  transparent  cornea.  (2)  A  vascular  layer,  the  choroid,  which, 
in  the  restricted  sense  of  the  term,  ends  in  front  in  a  series  of  folds 
or  plaits,  the  ciliary  processes.  The  choroid  contains  a  greater  or 
smaller  quantitv  of  the  black  pigment  melanin.  The  ciliary  processes 
abut  on  the  outer  boundary  of  the  iris,  which  may  be  looked  upon  as 
an  anterior  continuation  of 'the  choroidal  or  middle  coat  of  the  eyeball. 
Between  the  corneo-sclerotic  junction  and  the  anterior  portion  of 
the  choroid  is  interposed  a  ring  of  unstriped  muscular  ribres.  the 
ciliary  muscle.     {$)  The  inner  or  sensitive  coat,  termed  the  retina 


run  senses 


(Figs.  38-',  -\S\).  This  covers  the  choroid  as  a  delicate  membrane, 
extendw  Lli  iry  processes,  where  it  ends  in  a  tool  lied  margin, 

the  ora  serrata.  The  optic  nerve  forms  a  kind  of  stalk  to  which  the 
eyeball  is  attached.  Its  point  of  entrance  at  the  optic  disc  is  a  little 
nearer  the  median  line  than  the  antero-posterior  axis,  which  nearly 
passes  through  the  centre  of  a  small  depression,  the  fovea  centralis, 
situated  in  the  middle  of  the  macula  lutea,  or  vellow  spot.  From 
the  optic  disc  (sometimes  called  the  optic  papiila)  the  optic  nerve 


Cones. 


Fig.   382. — The  Retina. 


Fig.     383. — Diagram     of     Structure     of 
Retina  (after  Cajal). 

Tigs.  3S2,  383. — 1,  internal  limiting  mem- 
brane ;  2,  H,  layer  of  nerve-fibres ;  3,  (7, 
layer  of  ganglion  cells  ;  4,  F,  internal 
molecular  layer  ;  5,  E,  internal  nuclear 
layer  ;  6,  C,  external  molecular  layer  ;  7,  B, 
external  nuclear  layer  ;  8,  external  limiting 
membrane  ;  9,  A,  layer  of  rods  and  cones  ; 
10,  pigmented  epithelium. 


spreads  over  the  retina  as  a  layer  of  non-medullated  fibres,  separated 
from  the  interior  of  the  eyeball  only  by  the  internal  limiting  mem- 
brane. This  so-called  membrane  is  formed  by  the  expanded  feet 
of  the  fibres  of  Midler,  which  run  like  a  scaffolding  or  framework 
through  nearly  the  whole  thickness  of  the  retina,  terminating  at  the 
outer  limiting"  membrane.  External  to  the  layer  of  nerve-fibres  is 
the  stratum  of  large  ganglion  cells,  whose  axons  they  are  ;  next  to 
this  the  inner  molecular  layer,  or  inner  svnapse  layer,  made  up  largely 
of  the  branching  dendrites  of  these  cells.     The  fifth  layer  is  the  inner 

57— 2 


goo 


A   MANUAL  OF  PHYSIOLOGY 


granular  or  nuclear  layer,  containing  many  fusiform  (bipolar) 
'  granule  '  cells  which  send  out  axons  into  the  fourth,  and  dendrites  into 
the  sixth,  or  outer  molecular  layer,  and  are  thus  connected  with  the 
ganglion  cells  of  the  third  layer  on  the  one  hand,  and  with  the  termi- 
nations of  the  rod  and  cone  fibres  of  the  seventh  or  outer  nuclear  layer 
on  the  other.  The  arborizations  of  the  axons  of  these  bipolar  cells 
are  situate  at  different  levels  in  the  internal  molecular  layer.  The 
bipolar  cells  connected  with  the  rod  fibres  send  their  axons  right 
through  the  internal  molecular  layer  to  arborize  around  the  bodies 
of  the  ganglion  cells,  whereas  the  axons  of  the  bipolar  cells  con- 
nected with  the  cone  fibres  ramify  about  the  middle  of  the  layer 
(Fig.  383).  The  seventh  stratum  receives  its  name  from  the  large 
number  of  nuclei  which  it  contains.  These  belong  to  structures 
continuous  with  the  rods  and  cones  of  the  ninth  layer,  which   is 

divided  from  the  seventh  by  the 
external  limiting  membrane. 
Each  rod  is  prolonged  into  the 
external  nuclear  layer  as  a  fine 
fibre,  which  has  on  its  course  a 
swelling  containing  a  nucleus, 
and  terminates  (in  mammals) 
in  a  fine  knob  in  the  external 
molecular  layer  among  the  den- 
drites of  the  bipolar  cells.  Each 
cone  of  the  rod  and  cone  layer 
is  directly  prolonged  into  a 
nucleated  enlargement  in  the 
external  nuclear  layer.  From 
this  enlargement  a  fibre  (cone 
fibre),  of  considerably  greater 
calibre  (in  mammals)  than  the 
rod  fibre,  passes  into  the  ex- 
ternal molecular  layer,  where 
it  forms  an  arborization,  which 
comes  into  relation  with  the 
arborization  of  the  dendrites  of 
a  bipolar  cell.  At  the  fovea 
centralis  the  rods  are  entirely 
absent,  and  the  other  layers  of 
the  retina  greatly  thinned  ; 
over  the  optic  disc  neither  rods 
The  disc  is  pierced  by  the  retinal  blood- 


Fig.  384. — Retinal  Bloodvessels 
(Henle). 

The  arteria  centralis  is  seen  issuing 
from  the  optic  disc  and  branching  over 
the  retina.  The  shaded  area  in  the 
middle  of  the  figure  represents  the 
yellow  spot  with  the  fovea  centralis  in  its 
centre. 


nor  cones  are  present, 
vessels  (Fig.  384). 

External  to  the  rods  and  cones  is  a  sheet  of  pigmented  epithelial 
cells  of  hexagonal  shape,  belonging  to  the  choroid,  but  remaining 
attached  to  the  retina  when  the  latter  is  separated,  and  therefore 
often  reckoned  as  its  most  external  layer. 

A  little  behind  the  cornea  and  anterior  to  the  retina  is  the  lens, 
enclosed  in  a  capsule,  and  attached  to  the  choroid  by  the  suspensory 
ligament,  or  zonule  of  Zinn.  The  iris  hangs  down  in  front  of  the 
lens  like  a  diaphragm,  with  a  central  hole,  the  pupil.  Incorporated 
in  the  stroma  or  framework  of  the  iris  are  two  arrangements  of 
smooth  muscular  fibres,  which  confer  on  it  the  power  of  adjusting 
the  size  of  the  pupil.  One  of  these — the  sphincter  pupillse — con- 
sists of  a  well-defined  band  of  concentric  fibres  surrounding  the 
margin  of  the  pupil.     The  other— the  dilator  pupilkc — is  less  sharply 


THE  SENSES  901 

differentiated.  It  is  represented  l>\-  radial  bundles  oi  elongated, 
spindle-shaped  cells  running  in  from  the  ciliary  border  oi  the  iris 
towards  the  pupil.  Between  the  iris  and  the  posterior  Burfao 
the  cornea  is  the  anterior  chamber  of  the  eye,  filled  with  the  aqueous 
humour.  Between  the  iris  and  the  .interior  surface  of  the  lens  lies 
the  posterior  chamber,  which  is  rather  a  potential  than  an  actual 
cavity.  The  space  between  the  lens  and  the  retina  is  accurately 
occupied  by  an  almost  structureless  semi-fluid  mass,  the  vitreous 
humour,  enclosed  by  the  delicate  hyaloid  membrane,  which  in  front 
is  reflected  over  the  folds  of  the  ciliary  processes,  and  blends  with 
the  suspensory  ligament  of  the  lens.  The  attachment  of  the  sus- 
pensory ligament  is  rendered  firmer  by  the  connection  of  this  part 
of  the  hyaloid  membrane  to  a  circular  fibrous  portion  of  the 
vitreous.  Around  the  edge  of  the  lens  is  left  a  space,  the  canal  of 
Petit. 

Chemistry  of  the  Refractive  Media. — The  aqueous  humour  is  a 
perfectly  colourless,  watery  liquid,  of  slightly  alkaline  reaction  to 
litmus.  The  specific  gravity  is  about  1008,  and  the  total  solids  about 
1  per  cent.  Of  the  solids  the  inorganic  salts  (mainly  sodium 
chloride)  constitute  much  the  largest  portion.  A  very  small  amount 
of  protein  (001  to  004  per  cent.)  is  present,  also  a  little  dextrose 
(0-05  per  cent.),  and  minute  traces  of  urea  and  other  substances. 
The  liquid  of  the  vitreous  humour  has  a  very  similar  composition, 
except  that  it  contains  a  mucin-like  body,  hyalomucoid,  to  the 
amount  of  006  to  01  per  cent.  A  similar  mucin-like  substance  is 
present  in  the  cornea.  The  freezing-point  of  both  liquids  is  a  little 
lower  than  that  of  blood-serum.  A  being  about  o-6°. 

The  lens  is  far  richer  in  solids  than  the  aqueous  and  vitreous 
humours  with  which  it  is  in  contact  (30  to  35  per  cent,  of  solids, 
60  to  65  per  cent,  of  water).  The  salts,  with  small  quantities  of 
lecithin  and  cholesterin.  make  up  about  1  per  cent.  ;  the  balance  of 
the  solids  consists  of  proteins.  The  physical  alterations,  with 
production  of  turbidity,  which  occur  in  the  lens,  and  presumably  in 
its  proteins,  when  water  enters  or  leaves  it  in  too  great  amount 
through  imbibition  or  osmosis,  are  of  importance  in  connection 
with  the  etiology  of  cataract.  The  anatomical  and  physiological 
integrity  of  its  capsule  is  a  prime  factor  in  the  maintenance  of  that 
high  degree  of  transparency  which  is  necessary  for  the  function  of 
the  lens.  Cataract  can  be  experimentally  induced  by  injuring  the 
capsule.  In  like  manner  the  cornea  is  protected  against  injurious 
changes  in  its  water-content  (normally  about  80  per  cent.)  and 
consequent  turbidity  by  the  epithelium,  which  separates  it  from 
the  tears,  and  the  endothelium,  which  separates  it  from  the  aqueous 
humour. 

Secretion  of  the  Intra-ocular  Liquids. — The  aqueous  humour  is 
secreted  by  the  uveal  epithelium  covering  the  ciliary  processes,  and 
to  some  extent  by  that  covering  the  iris.  As  it  is  continually  secreted, 
so  it  is  continually  absorbed,  the  absorbed  constituents  finding  their 
way  eventually  into  the  vein  or  venous  sinus  "called  the  canal  of 
Schlemm  and  the  bloodvessels  of  the  iris  and  ciliary  processes.  The 
source  of  the  liquid  of  the  vitreous  body  is  also  the  uvea.  While  the 
intra-ocular  liquids  differ  from  ordinary  lymph,  there  is  no  reason 
to  doubt  that  they  are  secretions  which  contribute  to  the  nutrition 
of  those  transparent  structures  of  the  eye  which  are  not,  and,  on 
account  of  their  function,  cannot  be  supplied  with  bloodvessels. 
Their  most  obvious  use  is  to  maintain  the  proper  intra-ocular  pressure 


902  /    1/  INUAL  OF  PHYSIOLOGY 

on  which  the  geometrical  figure  of  the  eyeball,  and  therefore  its 
efficiency  as  an  optical  instrument,  depend.     The  balance  betwe<  a 

secretion  and  absorption  is  accurately  adjusted  in  health,  but  in 
disease  it  may  be  upset .  as  in  glaucoma,  where  the  intra-ocular  tension 
is  so  much  im  ls  to  interfere  with  the  circulation,  and  injuri- 

ously affeel  the  nutrition  and  function  of  the  retina.  Experimentally, 
occlusion  of  all  the  arteries  supplying  the  head  causes  ;i  rapid  fall  oi 
tension,  and  the  cornea  becomes  wrinkled  and  slack  to  the  touch. 
<  >n  restoring  the  circulation  after  not  too  long  an  interval,  the  tension 
gradually  returns  to  normal,  and  then  becomes  markedly  hyper- 
normal,  even  when  the  general  arterial  pressure  is  still  low.  This 
is  probably  due  to  the  crippling  of  the  elements  which  secrete  and 
absorb  the  intra-ocular  fluids,  or  of  the  capillary  walls,  so  that  ;i 
propei-  adjustment  can  no  longer  be  attained,  as  happens  in  a  tissue 
rendered  (edematous  by  temporary  anaemia.  Where  asphyxia  oi 
the  eyeball  is  avoided  or  is  brief  the  intra-ocular  pressure  varies 
directly  as  the  blood-pressure  in  the  ocular  vessels  within  a  wide 
range  (Henderson  and  Starling). 

Refraction  in  the  Eye  Formation  of  the  Retinal  Image. 
— The  amount  of  refraction  which  a  ray  of  light  undergoes  at 
a  curved  surface  depends  upon  two  factors — the  radius  of  cur- 
vature of  the  surface,  and  the  difference  between  the  refractive 
indices  of  the  media  from  which  the  ray  comes  and  into  which 
it  passes.  The  smaller  the  radius  of  curvature,  and  the  greater 
the  difference  of  refractive  index,  the  more  is  the  ray  bent  from 
its  original  direction.  A  ray  of  light  passing  into  the  eye  meets 
first  the  approximately  spherical  anterior  surface  of  the  cornea, 
covered  with  a  thin  layer  of  tears.  Since  the  refractive  index 
of  the  tears  is  much  greater  than  that  of  air,  the  ray  is  strongly 
refracted  here.  The  anterior  and  posterior  surfaces  of  the 
cornea  being  practically  parallel,  and  the  refractive  indices  ol 
the  tears  and  aqueous  humour  being  nearly  equal,  but  little 
refraction  takes  place  in  the  cornea  itself.  At  the  anterior  and 
posterior  surfaces  of  the  lens  the  ray  is  again  refracted,  since  the 
refractive  index  of  the  aqueous  and  vitreous  humours  is  less  than 
that  of  the  lens.  The  following  tables  show  the  radii  of  curva- 
ture of  the  refracting  surfaces  and  the  refractive  indices  of  tin 
dioptric  media,  as  well  as  some  other  data  which  are  of  use  in 
studying  the  problems  of  refraction  in  the  eye  : 

In  accommodation  for 
Far  Vision.       Neai  \  isii  in, 

["Cornea                              -  7*8  mm.  7  N  nun. 
Radius  of  curvature  of -!  Anterior  surface  of  lens  to-o  ..  6*o  ,, 
I  Posterior  surf  ace  of  lens  6-o  ..  5*5  .. 
Anterior    surface    of   cornea    and    an- 
terior surface  ol   lens      -                      -  3'6  ,,  .}'-!  •• 
Distance  I  Anterior  surface  of  cornea  and   pos- 
between    |      tcrior  surface  of  lens     -  70  ..  70  ,, 
Anterior  and  posterior  surface  of  lens  [~o  ..  .\-\  „ 
\ Posterior  surface  of  lens  and  retina    -  1  po  ..  14-6  „ 
Anterc-posterior  diameter  of  eye  along  the  axis  jj'j  ..  22*2  „ 


I  III     SI  SSI  S 


Refractive  Indices 

Air  ..........  iooo 

Cornea    --------  1*377 

Aqueous  humour    -  -         -  1 

Yii reous  humour     -  -        -  -  i"3 $65 

I. ens  (total  refractive  index)    -  -  -  1 

Water      -  -         -         -         -         -         -1*335 

It  will  be  seen  that  the  refractive  indices  of  the  aqueous  and 
vitreous  humours  are  nearly  the  same  as  that  of  water.  That 
of  the  lens  differs  for  its  various  layers,  the  central  core  having 
a  higher  refractive  index  (1*411)  than  the  more  superficial  por- 
tions (1-388).  Although  such  calculations  are  open  to  error,  it 
has  been  computed  that  the  Km  is  acts 
as  a  homogeneous  lens  of  the  same 
curvatures,  and  with  a  refractive 
index  of  1-437  would  do.  This  is 
called  the  total  refractive  index  of 
the  lens.  The  apparent  paradox  that 
it  is  greater  than  the  refractive  index 
even  of  the  core  is  explained  by  the 
consideration  that  the  core  taken  by 
itself  has  a  greater  curvature  than 
the  entire  lens,  and  therefore  causes 
a  greater  amount  of  refraction  in 
proportion  to  its  refractive  index. 

The  optical  problems  connected 
with  the  formation  of  the  retinal 
image  are  complicated  by  the  exis- 
tence in  the  eye  of  several  media, 
with  different  refractive  indices, 
bounded  by  surfaces  of  different  and, 
in  certain  cases,  of  variable  curva- 
ture. For  many  purposes,  however, 
the  matter  can  be  greatly  simplified,  and  a  close  enough  approxi- 
mation yet  arrived  at,  by  considering  a  single  homogeneous 
medium,  of  definite  refractive  index,  and  bounded  in  front  by  a 
spherical  surface  of  definite  curvature,  to  replace  the  transparent 
solids  and  liquids  of  the  eye.  The  principal  focus  being  supposed 
to  lie  on  the  retina,  the  position  of  the  nodal  point — i.e.,  the  point 
through  which  rays  pass  without  refraction — of  such  a  '  reduced  ' 
or  'schematic'  or  'simplified'  eye,  and  other  constants,  are  shown 
in  the  following  table.  The  single  refracting  surface  would  be 
situated  behind  the  cornea  and  in  front  of  the  lens,  at  a  rather 
smaller  distance  from  the  anterior  surface  of  the  latter  than 
from  the  anterior  surface  of  the  former.  The  nodal  point  would 
be  less  than  half  a  millimetre  in  front  of  the  posterior  surface 
of  the  lens  (Fig.  385).  The  refractive  index  of  the  single  trans- 
parent medium  would  be  a  little  greater  than  that  of  water. 


Fig.  385.— The  Reduced  Eye. 

S,  the  single  spherical  refract- 
ing surface,  2"2  mm.  behind  the 
anterior  surface  of  the  cornea  ; 
N,  the  nodal  point,  5  mm.  be- 
hind S  ;  F,  the  principal  focus 
(nil  the  retina).  20  mm.  behind  S. 
The  cornea  and  lens  are  put  in  in 
dotted  lines  in  the  position  which 
they  occupy  in  the  normal  eye. 


904 


A  MANUAL  (>/■   )'liYsioi.(H,\ 


Reduced  Eye — 
Radius  of  curvature  of  the  single  refracting  surface     -       51      mm. 
Index  of  refraction  of  the  single  refracting  medium     -       i'.-n* 
Antero-posterior  diameter  oi  reduced  eye  (distance  of 

principal  focus  from  the  single  refracting  surface)  -  20'0 
Distance  of  the  single  refracting  surface  behind  the 

anterior  surface  of  the  cornea  -  -  -  -2*2 
Distance  of  the  nodal  point  of  the  reduced  eye  from 

its  anterior  surface         -         -         -         -         -         -5'° 

Distance  of  the  nodal  point  from  the  principal  focus 

(retina)  .---.___     j^-Q 

Knowing  the  position  of  the  centre  of  curvature  of  the  single 
ideal  refracting  surface — i.e.,  the  nodal  point  of  the  reduced 
eye — all  that  is  necessary  in  order  to  determine  the  position  of 
the  image  of  an  object  on  the  retina  is  to  draw  straight  lines 
from  its  circumference  through  the  nodal  point.  Each  of  these 
lines  cuts  the  refracting  surface  at  right  angles,  and  therefore 
passes  through  without  any  deviation.  The  retinal  image  is 
accordingly  inverted  and  its  size  is  proportional  to  the  solid 
angle  contained  between  the  lines  drawn  from  the  boundary 
of  the  object  to  the  nodal  point,  or  the  equal  angle  contained 
by  the  prolongations  of  the  same  lines  towards  the  retina. 
This  angle  is  called  the  visual  angle,  and  evidently  varies  directlv 
as  the  size  of  the  object,  and  inversely  as  its  distance.  Thus 
the  visual  angle  under  which  the  moon  is  seen  is  much  larger 
than  that  under  which  we  view  any  of  the  fixed  stars,  because 

the  compara- 
tive nearness  of 
the  earth's 
satellite  more 
than  makes  up 
for  its  relatively 
small  size. 

The  d  i  m  e  n  - 
sions  of  the  reti- 
nal image  of  an 
object  are  easily 
calculated  when 
the  size  of  the 
object  and  its 
dista n  c  e  are 
known.     For  let 

AB  in  Fig.  386  represent  one  diameter  of  an  object,  A'B'  the 
image  of  this  diameter,  and  let  AB',  BA',  be  straight  lines  passing 
through  the  nodal  point.  Then  AB  and  A'B'  may  be  1  onsidered 
as  parallel  lines,  and  the  triangles  of  which  they  form  the  bases, 
and  the  nodal  point  the  common  apex,  as  similar  triangles. 
Accordingly,  if  D  is  the  distance  of  the  nodal  point  from   A.   and 

*  Or  a  little  more  than  thai  of  the  aqueous  humour. 


Fig.  386. — Figure  ro  show  how  the  Visual  Angle 
and  Size  of  Retinal  Image  varies  with  the  Ins- 
tance of  an  Object  oe  Given  Size. 

For  the  distant  position  of  AB  the  visual  angle  is  a,  for 
the  near  position  (dotted  lines)  /3. 


////    SENSES 

(I  its  distance  from   I'/,  we  have         —l  Now,  d  may  approxi- 

mately be  taken  .is  13  nun.  Suppose,  then,  that  the  size  <»i  the 
moon's  image  on  tin:  retina  is  required.  Here  D —  238,000  miles, 
and  AB  (the  diameter  of  the  moon)    =2,160  miles.      Thus  we  get 

j.  [60       A'B'  .       .      1       A'B'    ,  .  .  ,     Krai  ,.,       ..         . 

=        -,  or  (say)    — = —      ,  from   winch  A'B    (the  diameter 
238,000       15  *     •"   no       15 

of  the  retinal  image)  =  — ^-.  or  about  1  mm. 
1 10 

A  ship's  mast  120  feet  high,  seen  at  a  distance  of  25  miles,  will 
throw  on  the  retina  an  image  whose  height  is -. —  x  15  nun., 

120  feet  1  .  , 

i.e.,  E -. — -XKmm.,or   -    — x  15  mm.,  equal  to  001^5  mm., 

5,280  x  25  feet       J  1,100       J  n 

or  13  /<  in  size.     This  is  not  much  larger  than  a  red  blood-corpuscle, 

and  only  four  times  the  diameter  of  a  cone  in  the  fovea  centralis, 

where  the  cones  are  most  slender.     In  this  calculation  the  effect 

of  aberration  (p.  912)   in  enlarging  the  image  has  been  neglected. 

This   effect   is,    of   course,    proportionately   greater   for   small   and 

distant  than  for  large  and  near  objects  ;  and  it  is  doubtful  whether 

the  smallest  possible  image  can  be  confined  to  an  area  of  the  retina 

of  the  size  of  a  single  cone. 

Accommodation. — A  lens  adjusted  to  focus  upon  a  screen 
the  rays  coming  from  a  luminous  point  at  a  given  distance  will 
not  be  in  the  proper  position  for  focussing  rays  from  a  point 
which  is  nearer  or  more  remote.  Now,  it  is  evident  that  a 
normal  eye  possesses  a  great  range  of  vision.  The  image  of  a 
mountain  at  a  distance  of  30  miles,  and  of  a  printed  page  at 
a  distance  of  30  cm.,  can  be  focussed  with  equal  sharpness  upon 
the  retina.  In  an  opera-glass  or  a  telescope  accommodation 
is  brought  about  by  altering  the  relative  position  of  the  lenses  ; 
in  a  photographic  camera  and  in  the  eyes  of  fishes  and  cepha- 
lopods,  by  altering  the  distance  between  lens  and  sensitive 
surface  ;  in  the  eye  of  man,'  by  altering  the  curvature,  and  there- 
fore the  refractive  power  of  the  lens.  That  the  cornea  is  not 
alone  concerned  in  accommodation,  as  was  at  one  time  widely 
held,  is  shown  by  the  fact  that  under  water  the  power  of  accom- 
modation is  not  wholly  lost.  Now,  the  refractive  index  of  the 
cornea  being  practically  the  same  as  that  of  water,  no  changes 
of  curvature  in  it  could  affect  refraction  under  these  circum- 
stances. That  the  sole  effective  change  is  in  the  lens  can  be 
most  easily  and  decisively  shown  by  studying  the  behaviour  of 
the  mirror  images  of  a  luminous  object  reflected  from  the 
bounding  surfaces  of  the  various  refractive  media  when  the 
degree  of  accommodation  of  the  eye  is  altered.  Three  images 
are  clearly  recognised  :  the  brightest  an  erect  virtual  image, 
from  the  anterior  (convex)  surface  of  the  cornea  ;  an  erect  virtual 
image,  larger,  but  less  bright,  from  the  anterior  (convex)  surface 


1    M  INI    II.  OF  PHYSIOLOGY 


of  the  Lens  :  and  a  small  inverted  real  image  from  the  (concave) 
posterior  boundary  of  the  lens  (Purkinje-Sanson  images).  The 
second  image  is  intermediate  in  position  between  the  other  two. 

It  is  possible  with  special  care  to  make  out  a  fourth  image; 
but  since  it  is  reflected  from  the  posterior  surface  of  the  cornea, 
at  which  only  a  slight  change  in  the  refractive  index  occurs,  it 
is  less  brilliant  than  the  first  three.  When  the  eye  is  accom- 
modated for  near  vision,  as  in  focussing  the  ivory  point  of  the 
phakoscope  (Fig.  434),  the  corneal  image  is  entirely  unchanged 
in  si/e.  brightness,  and  position.  The  middle  image  diminishes 
in  size,  comes  forward,  and  moves  nearer  to  the  corneal  image. 

This  shows  that  the  curvature 
of  the  anterior  sin  face  of  the 
lens  has  been  increased — that 
is  to  say,  its  radius  of  cur- 
vature diminished — for  tin- 
size  of  the  image  oi  an  object 
reflected  from  a  convex  mirror 
varies  directly  as  the  radius 
of  curvature.  A  slight  change 
takes  place  in  the  image  from 
the  posterior  surface  of  the 
lens,  indicating  a  small  in- 
crease of  its  curvature  too. 
Bymeans  of  a  methodfounded 
on  the  observation  of  the 
changes  in  these  images,  and 
a  special  instrument  called  an 
ophthalmometer  which  allows 
of  their  measurement,  Helm- 
holtz  has  calculated  that, 
during  maximum  accommo- 
dation, the  radius  of  curva- 
ture of  the  anterior  surface 
of  the  lens  is  only  6  mm.,  as 
compared  with  10  mm.  when 


!  1       187.     Purkinje-Sanson   i  m 

A,  in  the  absenci   oi  a<  c elation  ; 

1'..  during  accommodation  for  a  near 
object.  The  upper  pair  of  circles  en- 
close the  images  as  seen  when  the  Light 

falls  mi  the  eye  through  .1  double  sin  mi 
a    pair    of    prisms;    the    lower    pair   show 

the.  images  seen  when  the  slit  is  single 
ami  triangular  in  shape. 


the  eye  is  directed  to  a  distant 
object  and  there  is  no  accommodation.  When  the  lens  has  been 
removed  for  cataract,  Eairly  distincl  vision  may  still  be  obtained 
by  compensating  for  its  loss  by  convex  spectacles  <»t  suitable 
m  fractive  power  (10  diopters*  tor  distant  vision,  and  [5  diopters 
*  A  diopter  (1  I>.)  is  the  unit  of  refractive  power  generally  adopted  in 

urine    the   strength    oi    lenses,   ami   corresponds   to  a    lens  of    l    m 
focal  Length.      A   lens  oi   -'  diopters  (2   D.)  has  a  local  length  oi   \   metre,  a 

lens  of  4  diopters  (4  D.)  a  focal  length  oi  1  metre,  ami  so  on.  The  diverging 
power  of  concave  Lenses  is  similarly  expressed  111  diopters  with  the  negative 
sign  prefixed.  Thus,  a  concave  lens  oi  1  metre  focal  length  has  a  strength 
oi  —  t  D.,  and  will  just  neutralize  a  convex  lens  of  i  D. 


////      s7   VS7  S  007 

[or  the  distance  at  which  a  book  is  usually  held),  but  no  power  of 
accommodation  remains.  The  person  does  indeed  contrad  the 
pupil  in  regarding  .1  near  object,  just  as  happens  in  the  intact 
eye  ;  the  most  divergent  rays  are  thus  cut  oft  and  the  image 
made  somewhat  sharper,  and  there  may  appear  to  be  some 
faculty  of  accommodation  left.  But  the  loss  of  the  whole  iris 
by  operation  does  not  affect  accommodation  in  the  least  ;  the 
iris,  therefore,  takes  no  part  in  it.  That  no  change  in  the 
antero-posterior  diameter  of  the  eyeball,  caused  by  its  deforma- 
tion by  the  contraction  oi  the  extrinsic  muscles,  can  have  any 
share  in  accommodation,  as  has  been  suggested,  is  clearly  proved 
by  the  fact  that  atropine,  which  does  not  affect  the  action  of 
these  muscles,  paralyses  the  mechanism  of  accommodation.  To 
the  consideration  of  that  mechanism  we  now  turn. 

The  Mechanism  of  Accommodation. — While  everybody  is 
agreed  that  the  main  factor  in  accommodation  is  the  alteration 
in  the  curvature  of  the  lens,  there  is  by  no  means  the  same 
unanimity  as  to  the  manner  in  which  this  is  brought  about. 
Helmholtz's  explanation,  which  has  long  been  the  most  popular, 
is  as  follows  :  In  the  unaccommodated  eye  the  suspensory 
ligament  and  the  capsule  of  the  lens  are  tense  and  taut,  the 
anterior  surface  of  the  lens  is  flattened  by  their  pressure,  and 
parallel  rays  (or.  what  is  the  same  thing,  rays  from  a  distant 
object)  are  focussed  on  the  retina  without  any  sense  of  effort. 
In  accommodation  for  a  near  object,  the  meridional  or  antero- 
posterior fibres  of  the  ciliary  muscle  by  their  contraction  pull 
forward  the  choroid  and  relax  the  suspensory  ligament.  The 
elasticitv  of  the  lens  at  once  causes  it  to  bulge  forwards  till  it 
is  again  checked  by  the  tension  of  the  capsule. 

The  explanation  of  Helmholtz,  although  widely  adopted  in  the 
text-books,  has  not  escaped  question  in  the  archives.  Tscherning 
has  put  forward  the  view  that  when  the  ciliary  muscle  contracts,  the 
suspensorv  ligament  is  pulled  backwards  and  outwards.  Its  tension 
is  thus  increased,  and  the  soft  external  layers  of  the  lens  are  in 
consequence  moulded  upon  the  harder  nucleus,  so  as  to  increase  the 
curvature  especially  around  the  anterior  pole.  And  Schoen,  reviving 
a  similar  theorv  originated  fifty  years  ago  by  Mannhardt,  believes 
that  the  ciliary  muscle,  in  contracting,  exerts  pressure  on  the 
anterior  portion  of  the  lens,  and  so  increases  its  curvature.  He 
likens  the  process  to  the  bulging  of  an  indiarubber  ball  when  it  is 
held  in  both  hands  and  compressed  by  the  fingers  a  little  behind  one 
of  the  poles.  It  will  be  observed  that  in  both  of  these  theories  the 
suspensory  ligament  is  supposed  to  be  stretched  during  accommo- 
dation, not  relaxed  as  Helmholtz  supposed.  While  they  have 
certain  advantages  over  the  theory  of  Helmholtz,  particularly  in 
taking  account  of  the  presence  of  radial  and  circular  as  well  as 
meridional  fibres  in  the  ciliary  muscle,  they  do  not  agree  so  well 
with  such  experimental  tests  "as  have  been  applied,  and  therefore 
Helmholtz's  explanation  must  still  be  regarded  as  the  best. 

It  is  supported  by  the  observation  of  Hess  that  when  the  ciliary 


I    MANX)  II.   OF   /'HYSIOLOGY 

muscle  lias  been  very  strongly  i  ontra<  ted  by  eserine  the  lens  <  an  be 
observed  to  mi  tve  about  with  each  slight  movement  of  the  eve.  I  In- 
suspensory  ligament  must  therefore  be  slackened  by  the  contraction 
of  the  ciliary  muscle.  When  atropine  is  applied  the  movability  of 
the  lens  soon  disappears,  owing  to  paralysis  of  the  ciliary  muscle. 
These  facts  were  first  established  in  patients  after  iridectomy,  but 
have  also  been  demonstrated  in  the  normal  eve.  Even  under  the 
influence  of  gravity  alone,  without  any  movements  of  the  eye,  the 
lens  sinks  about  £  to  £  mm.  in  strong  accommodation.  An 
additional  proof  that  the  suspensory  ligament  is  perfectly  slack 
during  accommodation  is  derived  from  the  result  of  simultaneous 
measurements  in  animals  of  the  pressure  in  the  anterior  chamber 
and  in  the  vitreous.  Even  in  strong  accommodation  no  alteration 
occurs,  although  even  slight  contact  with  the  outer  surface  of  the 
eyeball  or  contraction  of  the  external  eye  muscles  causes  a  distinct 
t .  In  two  cavities  separated  by  a  slack  membrane  no  differences 
of  pressure  would  be  expected. 

Anderson  Stuart  lays  stress  upon  the  function  of  those  fibres  of 
the  suspensory  ligament  which  are  attached  to  the  vitreous  bodv, 
and  are  put  under  tension  by  the  contraction  of  the  ciliary  muscle, 
in  anchoring  the  lens  during  strong  accommodation.  He  believes 
that  the  liquid  contents  of  the  hyaloid  canal  move  from  its  anterior 
to  its  posterior  end  in  accommodation,  and  in  the  opposite  direction 
when  accommodation  is  relaxed,  and  that  this  movement  tends  to 
prevent  strains  in  the  vitreous. 

In  cephalopods  and  fishes,  which  are  normally  short-sighted, 
accommodation  for  objects  at  a  distance  is  effected  by  a  movement 
of  the  lens  towards  the  retina.  In  the  fish's  eye  this  is  accomplished 
by  the  contraction  of  a  special  muscle,  the  retractor  lentis.  In  am- 
phibia and  most  snakes  the  lens  is  moved  towards  the  cornea  and 
away  from  the  retina  by  changes  of  intra-ocular  pressure  (Beer). 

Innervation  of  the  Ciliary  Muscle  and  the  Muscles  of  the  Iris. —  The 
ciliary  muscle  and  the  sphincter  pupillae  air  supplied  by  autonomic 
fibres  (p.  883),  reaching  them  through  the  short  ciliary  nerves  arising 
from  the  ciliary  ganglion  (Fig.  388).  The  preganglionic  fibres  take 
origin  from  cells  in  the  anterior  part  of  the  oculo-motor  nucleus  in 
the  mid-brain.  Passing  to  the  orbit  in  the  third  nerve,  they  reach 
the  ciliary  ganglion,  and  end  there  by  forming  synapses  with  some 
of  its  cells.  The  axons  of  these  cells  continue  "the  path  as  post- 
ganglionic fibres  in  the  short  ciliary  nerves.  The  dilator  pupillae  is 
supplied  by  the  long  ciliary  nerves  coming  from  the  ophthalmic 
branch  of  the  fifth  nerve. 

The  preganglionic  dilator  fibres  pass  out  by  the  anterior  roots  oi 
the  first  three  thoracic  nerves  (dog,  cat.  rabbit),  accompanied  by 
raso-constrictor  fibres  for  the  iris.  Reaching  the  sympathetic  chain 
through  the  corresponding  rami  communicantes,  they  traverse  the 
first  thoracic  ganglion,  the  annulus  of  Vieussens.  the  interior  cervical 
ganglion,  and  the  cervical  sympathetic.  They  end  by  arborizing 
around  some  oi  the  cells  of  the  superior  cervical  ganglion,  whose 
axons  eventually  arrive  at  the  Gasserian  ganglion,  and  running  along 
the  ophthalmic  division  of  the  trigeminal  to  the  eye,  reach  the  iris  by 
its  long  ciliary  bran> 

The  exact  origin  of  the  dilator  path  in  the  brain  has  not  been 
definitely  settled.  Some  place  it  in  the  mid-brain,  others  in  the  bulb. 
There  must  be  at  least  one  neuron  on  the  path  central  to  the  spinal 
neuron  whose  axon  emerges  from  the  cord  as  a  preganglionic  fibre. 
The  lower  cervical  and  upper  thoracic  portion  of  the  spinal  cord  has 


THE  SENSES 


received  the  name  oJ  the  cilio-spinal  region  from  its  relation  to  the 
pupillo-dilator  fibres.     It  must  not  be  looked  upon  as  a  centre  in  any 

proper  sense  oi  the  term,  but  rather  as  the  pathway  by  which  these 
fibres  pass  down  from  the  bulb,  and  where  they  may  accordingly  be 
tapped  by  stimulation. 

Stimulation  of  certain  areas  on  the  cortex  of  the  frontal  lobe  of  the 
cerebrum  (p.  889)  causes  slight  dilatation  of  the  pupil  even  after  the 
sympathet  ic  has  been  divided.  This  is  due  to  inhibition  of  the  pupillo- 
constrictor  fibres  in  the  third  nerve, 

Changes  in  the  Pupil  during  Accommodation. — It  has  been 
already  mentioned  that  along  with  the  alteration  in  the  curvature 
of  the  lens  a  change  in  the  diameter  <>t  the  pupil  takes  place  in 
accommodation.      When  a  distant  object  is  looked  at,  the  pupil 


Fig.  388. — Scheme  of  Innervation  of  Ciliary 
and  Iris  Muscles  (after  Schultz). 

1,  ciliary  ganglion;  2,  oculo  -  motor  nucleus; 
3,  spinal  cell,  from  which  comes  off  the  pregangli- 
onic fibre  on  the  pupillo-dilator  path,  which  forms 
a  synapse  with  4,  a  cell  in  the  superior  cervical 
ganglion.  The  axon  of  4  is  shown  passing  (as 
an  interrupted  line)  through  the  Gasserian  gan- 
glion into  the  ophthalmic  division  (Oph.)  of  the 
fifth  nerve,  V,  and  thence  in  a  long  ciliary  nerve,  5,  to  the  dilator  of  the  iris,  8. 
From  1  axons  are  shown  passing  by  short  ciliary  nerves  to  the  ciliary  muscle,  6, 
and  the  constrictor  pupilke,  7  ;  9,  cell  of  origin  (in  mid-brain  ?)  of  fibre  which 
constitutes  the  central  neuron  of  the  pupillo-dilator  path  ;  10,  optic  nerve  ;  III, 
third  nerve  ;  V,  fifth  nerve  with  Gasserian  ganglion. 

becomes  larger ;  when  a  near  object  is  looked  at,  it  becomes  smaller. 
Narrowing  of  the  pupil  is  thus  associated  with  contraction  of  the 
ciliary  muscle,  and  widening  of  the  pupil  with  its  relaxation. 

This  physiological  correlation  has  its  anatomical  counterpart  ;  for 
the  third  nerve  supplies  both  the  iris  and  the  ciliary  muscle.  Stimu- 
lation of  the  nerve  within  the  cranium  causes  contraction  of  the  pupil, 
while  stimulation  of  certain  portions  of  its  nucleus  in  the  floor  of  the 
third  ventricle  and  the  Sylvian  aqueduct  or  of  the  short  ciliary 
nerves  (Fig.  388),  which  receive  branches  from  the  third  nerve,  or 
of  the  ganglion  itself,  is  followed  by  that  change  in  the  anterior 
surface  of  the  lens  which  constitutes  accommodation  (Hensen  and 


9io  A    MANUAL  OF  PHYSIOLOGY 

Voelckers).     This  can  be  observed  either  through  a  window  in  the 

sclerotic  in  a  dog  or  by  following  the  movements  of  a  needle  thrusl 
into  the  eyeball.  I  >\  i  .irel'ullv  localized  stimulation  near  the  junc- 
tion oi  the  aqueduct  with  the  third  ventricle,  it  is  possible  to  bring 
about  the  forward  bulging  of  the  lens  without  any  change  in  the 
iris  ;  but  the  normal  and  voluntary  act  of  accommodation  cannot  be 
disjoined  Erom  the  corresponding  alterations  in  the  size  of  the  pupil. 
Inward  rotation  oi  the  eyes  accompanies  contraction  oi  the  pupil 
in  accommodation,  and  the  question  may  be  raised  whether  the 
pupillary  change  is  associated  with  the  action  of  the  extrinsi< 
muscles  of  the  eyeball  which  cause  convergence  or  with  the  action  of 
the  intrinsic  muscles  which  determine  the  changes  in  the  curvature 
of  the  lens.  It  is  usually  considered  to  be  associated  with  both.  In 
any  case,  actual  convergence  is  not  necessary  for  the  reaction,  since 
it  may  still  be  obtained  on  accommodation  when  convergence  is 
impossible  on  account  of  paralysis  of  the  internal  recti. 

Changes  in  the  Pupil  produced  by  Light. — It  is  not  only  by 
accommodation  that  the  size  of  the  pupil  may  be  affected.  In 
the  dark  it  dilates,  at  first  rapidly,  then  gradually,  and  it  main- 
tains the  width  it  has  reached  for  several  hours.  This  lias  been 
shown  by  taking  photographs  of  the  eye  with  the  magnesium 
flashlight.  In  this  way  the  width  of  the  pupil  is  recorded  before 
it  has  time  to  alter.  Or  a  longer  exposure  to  ultra-violet  light, 
which  affects  the  pupil  but  little,  may  be  employed.  When 
ordinary  light  falls  upon  the  retina  the  pupil  contracts,  and  the 
amount  of  contraction  is  roughly  proportional  to  the  intensity 
of  the  light.  Contraction  of  the  pupil  to  light  is  brought  about 
by  a  reflex  mechanism,  of  which  the  optic  nerve  forms  the 
afferent  and  the  oculo-motor  the  efferent  path,  while  the  centre 
is  situated  in  the  floor  of  the  aqueduct  of  Sylvius.  The  relation 
of  this  centre  to  thai  which  controls  the  changes  in  the  pupil 
during  accommodation  has  not  as  yet  been  sufficiently  eluci- 
dated ;  but  this  we  do  know,  that  one  of  the  paths  may  be 
interrupted  by  disease,  while  the  other  is  intact.  For  in  tabes 
(locomotor  ataxia),  and  in  dementia  paralytica  (general  paralysis), 
the  light-reflex  sometimes  disappears,  while  the  constriction  of 
the  pupil  in  accommodation  and  convergence  still  takes  place 
(Argyll- Robertson  pupil).  Artificial  stimulation  of  the  optic 
nerve  has  the  same  effect  on  the  pupil  as  the  'adequate' 
stimulus  of  light  ;  and  in  many  animals  (including  man),  though 
not  in  those  whose  optic  nerves  completely  decussate,  there  is 
a  consensual  light -reflex — i.e.,  both  pupils  contract  when  one 
retina  or  optic  nerve  is  excited.  This  should  be  remembered 
in  using  the  pupil-reaction  as  a'test  of  the  condition  of  the  retina. 
For  although  the  absence  of  contraction  may  show 'that  the 
retina  of  the  eye  on  which  the  light  is  allowed  to  fall  is*insensible 
(unless  there  is  some  physical  hindrance  to  its  passage,  such 
as  opacity  of  the  lens  or  cataract),  the  occurrence  of  contraction 
does  not  exclude  insensibility  of  the  retina  unless  the  other  eye 
has  been  protected  from  the  light. 


THE  SENSES  91 1 

Stimulation  oi  the  cervical  sympathetic  causes  marked  dilata 
tion  of  the  pupil,  even  when  the  third  nerve  is  excited  a1  the 
same  time,  ["he  pupillo  dilatot  fibres  do  not  act  by  constricting 
the  bloodvessels  of  the  iris.  For  dilatation  of  the  pupil  can  be 
caused  in  a  bloodless  animal  !>\  stimulating  the  sympathetic. 
And  even  when  the  circulation  is  going  on,  a  short  stimulation 
of  (lie  sympathetic  causes  dilatation  of  the  pupil  without  \ 
constriction,  while  with  longer  excitation  \\w  dilatation  of  the 
pupil  begins  before  the  narrowing  of  the  bloodvessels.  Nor 
does  it  seem  possible  to  accept  the  view  that  the  sympathetic 
fibres  are  inhibitory  for  the  sphincter  muscle  of  the  iris.  They 
act  directly  upon  dilator  muscular  fibres.  It  has,  indeed,  long 
been  known  that  in  the  iris  of  the  otter  and  of  birds  a  radial 
dilator  muscle  exists  ;  and  it  has  been  shown  by  Langley  and 
Anderson  that  in  the  iris  of  the  rabbit,  cat,  and  dog,  the  presence 
of  radially  arranged  contractile  substance,  different  it  may  be  in 
some  respects  from  ordinary  smooth  muscle,  must  be  assumed. 
Both  the  constrictor  and  the  dilator  muscles  of  the  iris  are 
normally  in  a  condition  of  greater  or  less  tonic  contraction,  so 
that  the  size  of  the  pupil  at  any  given  moment  depends  on  the 
play  of  two  nicely  balanced  forces.  Reflex  dilatation  of  the 
pupil  through  the  sympathetic  fibres  is  caused  in  man  by  painful 
stimulation  of  the  skin,  by  dyspnoea,  by  muscular  exertion,  and 
in  some  individuals  even  by  tickling  of  the  palms.  In  animals 
the  stimulation  of  naked  sensor}7  nerves  has  the  same  effect. 
The  '  starting  of  the  eyeballs  from  their  sockets,'  which  the 
records  of  torture  so  often  note,  is  due  to  a  similar  reflex  excita- 
tion of  the  sympathetic  fibres  supplying  the  smooth  muscle  of 
the  orbits  and  eyelids. 

Action  of  Drugs  on  the  Function  of  the  Intrinsic  Eye  Muscles. — 
The  local  application  of  atropine  causes  temporary  paralysis  of 
accommodation  and  dilatation  of  the  pupil.  When  the  third  nerve 
is  divided,  the  pupil  dilates ;  it  dilates  still  more  when  atropine  is 
administered  after  the  operation.  Dropped  into  one  eye  in  small 
quantity,  atropine  only  produces  a  local  effect  ;  the  pupil  of  the  other 
eye  remains  of  normal  size,  or  somewhat  constricted  on  account  of 
the  greater  reflex  stimulation  of  its  third  nerve  by  the  greater 
quantity  of  light  new  entering  the  widely-dilated  pupil  of  the 
atropinized  eye.  Even  in  the  excised  eye  the  effect  of  the  drug  is 
the  same.  Introduced  into  the  blood  atropine  causes  both  pupils 
to  ddate.  Its  action  is  to  paralyze  the  endings  of  the  oculo-motor 
fibres  to  the  sphincter  pupilla*  and  ciliary  muscle.  Other  mydriatic, 
or  pupil-dilating  drugs,  are  cocaine,  daturine,  and  livoscyamine. 
Physostigmine  or  eserine.  pilocarpine,  and  muscarine  are  the  chief 
miotics,  or  pupil-constricting  substances.  They  also  cause  spasm  of 
the  ciliary  muscle,  and  inability  to  accommodate  for  distant  objects. 
They  act  by  stimulating  the  structures  (nerve-endings)  (see  pp.  166, 
635)  which  atropine  paralyzes.  The  work  of  the  mydriatics  can  be 
undone  by  the  miotics.  Thus  the  dilatation  produced  by  atropine  is  re- 
moved by  pilocarpine.  Adrenalin,  when  injected  intravenously,  causes 


012 


/    1/  INV  U.  OF  PHYSIOLOGY 


a  fleeting  dil.it  at  i<  >n  of  the  pupil,  distinct  in  cats,  less  marked  in  rabbits. 
Subcutaneous  injection  lias  no  effect.  Instillation  of  the  drug  into 
the  conjunctival  sa<  is  withoul  effed  in  tin- normal  rabbit's  eye,  but 
causes  dilatation  Li  the  superior  cervical  ganglion  has  been  removed. 

Functions  of  the  Iris. — In  vision  the  iris  performs  two 
chief  functions:  (i)  It  regulates  the  quantity  of  light  allowed 
to  fall  upon  Hit'  retina.  The  larger  the  aperture  of  a  lens,  the 
greater  is  its  collecting  power,  the  more  light  does  it  gather  in 
its  focus.  In  the  eye,  the  area  of  the  pupil  determines  the 
breadth  oi  the  pencil  of  light  that  falls  upon  the  lens.  If  this 
area  was  invariable,  the  retina  would  either  be  '  dark  from  e.v 
of  lighl  '  in  bright  sunshine,  or  dark  from  defect  of  light  in  dull 
weather  or  at  dusk.  In  order  that  the  iris  may  act  as  an  efficient 
diaphragm  it  must  be  pigmented,  and  it  is  the  pigment  in  it 
which  gives  the  colour  to  the  normal  eye.  The  vision  of  albinos, 
in  whose  eyes  this  pigment  is  wanting,  is  often,  though  not 

invariably,  deficient 
in  sharpness.  There 
is  always  intol- 
erance of  bright 
light ;  and  the  same 
is  true  in  the  con- 
dition known  as 
irideremia,  or  con- 
genital absence  or 
defect  of  the  iris. 

(2)  Another,  and 
perhaps  equally  im- 
portant, function  of 
the  iris  is  to  cut  off 
the  more  divergent 
rays  of  a  pencil  of  light  falling  upon  the  eye,  and  thus  to  increase 
the  sharpness  of  the  image.  This  leads  us  to  the  consideration 
of  certain  defects  in  the  dioptric  arrangements  of  the  eye. 

Defects  of  the  Eye  as  an  Optical  Instrument. — (1)  Spherical  Aberra- 
tion.— It  is  a  property  of  a  spherical  refracting  surface  that  rays  of 
light  passing  through  the  peripheral  portions  are  more  strongly 
refracted  than  rays  passing  near  the  principal  axis.  Hence  a 
luminous  point  is  not  focussed  accurately  in  a  single  point  by  a 
spherical  lens  ;  the  image  is  surrounded  by  fainter  circles  of  light, 
the  so-called  circles  of  diffusion  representing  the  rays  which  have 
not  yet  come  to  a  focus,  or  having  been  already  focussed  have 
crossed  and  are  now  diverging.  In  the  eye  this  spherical  aberration 
is  partly  corrected  by  the  interposition  of  the  iris,  which  cuts  off 
the  more  peripheral  rays,  especially  in  accommodation  for  a  near 
object,  when  they  are  most  divergent.  In  addition,  the  anterior 
surfaces  of  the  cornea  and  lens  are  not  segments  of  spheres,  but  of 
ellipsoids,  so  that  the  curvature  diminishes  somewhat  with  the  dis- 
t  nice  from  the  optic  axis,  and,  therefore,  the  refracting  power  as  we 


Fig 


Aberration. 


389. — Spherical 
Rays  passing  through  the  more  peripheral  parts  of 
a  biconvex  lens  L.are  brought  to  a  focus  F  nearer  the 
lens  than  F',  the  focus  of  rays  passing  through  the 
central  portions  of  the  lens. 


THE  SENSES 


<>i  ] 


pass  away  from  the  axis  does  not  increase  so  rapidly  as  it  would  <1<>  if 
the  surfaces  were  t  ruly  spherical.  Further,  the  refractive  index  of  the 
peripheral  parts  ol  the  lens  is  Less  than  thai  of  its  central  portions. 

(_M  Chromatic  Aberration.  All  the  rays  of  the  spectrum  do  not 
travel  with  the  same  velocity  through  a  lens,  and  are,  therefore, 
unequally  refracted  by  it.  the  short  violet  rays  being  focussed  nearer 
the  lens  than  the  Long  red  rays.  It  was  at  one  time  supposed  that 
this  chromatic  alienation,  as  it  is  called, is  compensated  in  the  eye; 
and  it  is  said  that  this  mistake  gave  the  first  hint  that  Newton's 
dictum  as  to  the  proportionality  between  deviation  and  dispersion 
was  erroneous,  and  led  to  the  discovery  of  achromatic  lenses.  But  in 
reality  the  eye  is  not  an  achromatic  combination  ;  and  the  violet  rays 
are  tocussed  about  .',  mm.  in  front  of  the  red.  Thus,  in  Fig.  390 
the  white  light  passing  through  the  lens  is  broken  up  into  its  con- 
stituents :  the  violet  focus  is  at  V,  and  the  red  at  R,  behind  it.  A 
screen  placed  at  R  would  show  not  a  point  image,  but  a  central 
point  surrounded  by  concentric  circles  of  the  spectral  colours,  with 
violet  outside.     If  the  screen  was  placed  at  V,  the  centre  would  be 


Fig.  390. — Chromatic  Aberration. 
The  violet   rays  are  brought   to  a   focus  V 
nearer  the  lens  than  R,  the  focus  of  the  red 
ravs. 


Fig.  391. — To  Show  Disper- 
sion- in  Eye  (v.  Bezold). 
View  the  figure  from  a  dis- 
tance too  small  for  accommoda- 
tion. Approach  the  eye  to- 
wards it ;  the  white  rings  appear 
bluish  owing  to  circles  of  dis- 
persion falling  on  them — i.e., 
circles  of  light  of  different 
colours  due  to  the  decomposi- 
tion of  white  light  into  its 
spectral  constituents  by  the 
media  of  the  eye.  A  little 
closer,  and  the  black  rings  be- 
come white  or  Yellowish -white. 


violet  and  the  red  would  be  external. 
For  this  reason  it  is  impossible  to  focus 
at  the  same  time  and  with  perfect 
sharpness  objects  of  different  colours  : 
a  red  light  on  a  railway  track  appears 

nearer  than  a  blue  light,  partly  perhaps  for  the  reason  that  it  is 
necessary  to  accommodate  more  strongly  for  the  red  than  for  the 
blue,  and  we  associate  stronger  accommodation  with  shorter  distance 
of  the  object,  although  other  data  are  also  involved  in  such  a  visua 
judgment.  When  we  look  at  a  white  gas-flame  through  a  cobalt 
glass,  which  allows  only  red  and  violet  to  pass,  we  see  either  a  red 
flame,  surrounded  by  a  violet  ring,  or  a  violet  flame  surrounded  by 
a  red  ring,  according  as  we  focus  for  the  red  or  for  the  violet  rays. 
But  the  dispersive  power  of  the  eye  is  so  small,  and  the  capacitv 
of  rapidly  altering  its  accommodation  so  great,  that  no  practical 
inconvenience  results  from  the  lack  of  achromatism,  which,  how- 
ever, may  be  easilv  demonstrated  by  looking  at  a  pattern  such  as 
that  in  Fig.  391  at  a  distance  too  small  for  exact  accommodation. 

It  is  also  reckoned  among  the  optical  imperfections  of  the  eye 
(3)  that  the  curved  surfaces  of  the  cornea  and  lens  do  not  form  a 
'  centred  '  svstem— that  is  to  say,  their  apices  and  their  centres  of 

58 


914 


A    MANUAL  OF  PHYSIOLOGY 


curvature  do  not  all  lie  in  the  same  straight  line  ;  (4)  that  the  pupil 
is  eccentric,  being  situated  not  exactly  opposite  the  middle  of  the 
lens  and  cornea,  but  nearer  the  nasal  side,  and  that  in  consequence 
the  optic  axis,  or  straight  line  joining  the  centres  of  curvature  of  the 
lens  and  cornea,  does  not  coincide  with  the  visual  axis,  or  straight 
line  joining  the  fovea  centralis  with  the  centre  of  the  pupil,  which  is 
also  the  straight  line  joining  the  centre  of  the  pupil  and  any  point  to 
which  the  eye  is  directed  in  vision.  The  angle  between  the  optic 
and  visual  axis  is  about  50  (Fig.  381).  (5)  Musca;  volitantes,  the 
curious  bead-like  or  fibrillar  forms  that  so  often  flit  in  the  visual  field 
when  one  is  looking  through  a  microscope,  are  the  token  that  the 
refractive  media  of  the  eye  are  not  perfectly  transparent  at  all  parts  : 
they  seem  to  be  due  to  floating  opacities  in  the  vitreous  humour, 
probably  the  remains  of  the  embryonic  cells  from  which  the  vitreous 
body  was  developed.  (6)  Lastly,  it  may  be  mentioned  that  slight 
irregularities  in  the  curvature  of  the  lens  exist  in  all  eyes,  so  that  a 
point  of  light,  like  a  star  or  a  distant  street-lamp,  is  not  seen  as  a 
point,  but  ag  a  point  surrounded  by  rays  (irregular  astigmatism).  In 
bringing  this  review  of  the  imperfections  of  the  dioptric  media  of  the 


Fig.   39Z. — Refraction  in  the  (Normal)  Emmetropic  Eye. 

The  image  P'  of  a  distant  point  P  falls  on  the  retina  when  the  eye  is  not  accommo- 
dated.    To  save  space,  P  is  placed  much  too  near  the  eye  in  Figs.  392,  393. 

normal  eye  to  a  close,  it  may  be  well  to  explain  that  what  are  defects 
from  the  point  of  view  of  the  student  of  pure  optics  are  not  neces- 
sarily defects  from  the  freer  standpoint  of  the  physiologist,  who 
surveys  the  mechanism  of  vision  as  a  whole,  the  relations  of  its 
various  parts  to  one  another  and  to  the  needs  of  the  organism  it  has 
to  serve,  the  long  series  of  developmental  changes  through  which  it 
has  come  to  be  what  it  is,  and  the  possibilities,  so  far  as  we  can  limit 
them,  that  were  open  to  evolution  in  the  making  of  an  eye.  The 
optician  may  perhaps  assert,  and  with  justice,  that  he  could  easily 
have  made  a  better  lens  than  Nature  has  furnished,  but  the  physio- 
logist will  not  readily  admit  that  he  could  have  made  as  good  an  eye. 

While  the  defects  hitherto  mentioned  are  shared  in  greater 
or  less  degree  by  every  normal  eye,  there  are  certain  other 
defects  which  either  occur  in  such  a  comparatively  small  number 
of  eyes,  or  leal  to  such  grave  disturbances  of  vision  when  they 
do  occur,  that  they  must  be  reckoned  as  abnormal  conditions. 
In  the  normal  or  emmetropic  eye,  parallel  rays — and  for  this 


TIIF.  SENSES 


91? 


purpose  all  rays  coming  from  an  object  at  a  distance  greater 
than  65  metres  may  be  considered  parallel — are  brought  to  a 
focus  on  the  retina  without  any  effort  of  accommodation.  The 
distance  at  which  objects  can  be  distinctly  seen  is  only  limited 
by  their  si/.e.  the  clearness  of  the  atmosphere,  and  the  curvature 
of  the  earth  ;  in  other  words,  the  punclum  rcmotum,  or  far-point 
of  vision,  the  most  distant  point  at  which  it  is  possible  to  see 
with  distinctness,  is  practically  at  an  infinite  distance.  When 
accommodation  is  paralyzed  by  atropine,  only  remote  objects 
can  be  clearly  seen.  On  the  other  hand,  the  normal  eye,  or,  to 
be  more  precise,  the  normal  eye  of  a  middle-aged  adult,  can  be 
adjusted  for  an  object  at  a  distance  of  not  more  than  12  cm. 
(or  5  inches).  Nearer  than  this  it  is  not  possible  to  see  dis- 
tinctly ;  this  point  is  accordingly  called  the  punctum  proximum 


Fig.    393. — Myoric  Eye. 

The  image  P'  of  a  distant  point  P  falls  in  front  of  the  retina,  even  without  accom- 
modation. By  means  of  a  concave  lens  L  the  image  may  be  made  to  fall  on  the 
retina  (dotted  lines). 


or  near- point.     The  range  of  accommodation  for  distinct  vision 
in  the  emmetropic  eye  is  from  12  cm.  to  infinity. 

Myopia,  or  short-sightedness,  is  generally  due  to  the  excessive 
length  of  the  antero-posterior  diameter  of  the  eyeball  in  relation 
to  the  converging  power  of  the  cornea  and  the  lens.  Even  in 
the  absence  of  accommodation,  parallel  rays  are  not  focussed 
on  the  retina,  but  in  front  of  it  ;  and  in  order  that  a  sharp  image 
may  be  formed  on  the  retina  the  object  must  be  so  near  that  the 
rays  proceeding  from  it  to  the  eye  are  sensibly  divergent — that 
is  to  say,  it  must  be  at  least  nearer  than  65  metres — but  as  a 
rule  an  object  at  a  distance  of  more  than  2  to  3  metres  cannot 
be  distinctly  seen.  With  the  strongest  accommodation  the 
near  point  may  be  as  little  as  3  cm.  from  the  eye.  The  range 
of  vision  in  the  myopic  eve  is  therefore  very  small.     The  defect 

58-2 


9i6 


A   MANUAL  OF  I'HYSIOI.OGY 


may  be  corrected  by  concave  glasses,  which  render  the  rays 
more  divergent.  It  is  to  be  noted  that  many  cases  of  internal 
squint  in  children  are  connected  with  myopia,  the  eyes  neces- 
sarily rotating  inwards  as  they  are  made  to  fix  an  abnormally 
near  object.  The  treatment  both  of  the  squint  and  the  myopia 
in  these  cases  is  the  use  of  concave  spectacles  (Fig.  393).  Myopia, 
although  a  condition  that  shows  a  distinct  hereditary  tendency, 
is  rarely  present  at  birth  ;  the  elongation  of  the  antero- 
posterior diameter  of  the  eyeball  develops  gradually  as  the 
child  grows. 

In  hypermetropia,  or  long-sightedness,  the  eye  is,  as  a  rule, 
too  short  in  relation  to  its  converging  power  ;  and  with  the  lens 
in  the  position  of  rest,  parallel  rays  would  be  focussed  behind 
the  retina.  Accordingly,  the  hypermetropic  eye  must  accommo- 
date even  for  distant  objects,  while  even  with  maximum  accom- 


Fig.   394. — Hypermetropic   Eye. 

The  image  F  of  a  point  P  falls  behind  the  retina  in  the  unaccommodated  eye. 
By  means  of  a  convex  lens  L  it  may  be  focussed  on  the  retina  without  accom- 
modation (dotted  lines). 

modation  an  object  cannot  be  distinctly  seen  unless  it  is  farther 
away  than  the  near-point  of  the  emmetropic  eye.  The  far- 
point  of  distinct  vision  is  at  the  same  distance  as  in  the  emme- 
tropic eye — viz.,  at  infinity — the  near- point  is  farther  from  the 
eye.  The  defect  is  corrected  by  convex  glasses  (Fig.  394). 
Hypermetropia,  unlike  myopia,  is  present  at  birth. 

Presbyopia,  or  the  long-sightedness  of  old  age,  is  not  to  be 
confounded  with  hypermetropia.  It  is  essentially  due  to 
failure  in  the  power  of  accommodation,  chiefly  through  weakness 
of  the  ciliary  muscle,  but  partly  owing  to  increased  rigidity 
and  loss  of  elasticity  of  the  lens.  Images  of  distant  objec  s  are 
still  formed  on  the  retina  of  the  unaccommodated  eye  with 
perfect  sharpness — i.e.,  the  far-point  of  v  sion  is  not  affected. 
But  the  eye  is  unable  to  accommodate  sufficiently  for  the  rays 
diverging  from  an  object  at  the  ordinary  near-point  ;  in  other 


THE  SENSES  9»7 

words,  the  near-point  is  farther  away  than  normal.      Convex 
glasses  are  again  the  remedy. 

The  near-point  of  distinct  vision  can  be  fixed  in  various  ways 
— among  others,  by  means  of  Scheiner's  experiment  (Practical 
Exercises,  p.  987).  Two  pin-holes  are  pricked  in  a  card  at  a 
distance  less  than  the  diameter  of  the  pupil.  A  needle  viewed 
through  the  holes  appears  single  when  it  is  accommodated  for, 
double  if  it  is  out  of  focus.  The  near- point  of  vision  is  the 
nearest  point  at  which  the  needle  can  still,  by  the  strongest 
effort  of  accommodation,  be  seen  single. 

Astigmatism. — It  has  been  mentioned  that  slight  differences 
of  curvature  along  different  meridians  of  the  refracting  surfaces 
exist  in  all  eyes.  But  in  some  cases  the  difference  in  two 
meridians  at  right  angles  to  each  other  is  so  great  as  to  amount 
to  a  serious  defect  of  vision.  To  this  condition  the  name  of 
'  astigmatism  '  or  '  regular  astigmatism  '  has  been  given.  It  is 
usually  due  to  an  excess  of  curvature  in  the  vertical  meridians 
of  the  cornea,  le^s  fre- 
quently in  the  horizontal 
meridians  ;  occasionally 
the  defect  is  in  the  lens. 
Rays  proceeding  from  a 
point  are  not  focussed 
in  a  point,  but  along 
two  lines,  a  horizontal 
and  a  vertical,  the  hori- 
zontal linear  focus  being 
in    front    of    the    other  Fig.  395. 

when  the  vertical  curva- 
ture is  too  great,  behind  it  when  the  horizontal  curvature  is 
excessive.  The  two  limbs  of  a  cross  or  the  two  hands  of  a 
clock  when  they  are  at  right  angles  to  each  other  cannot  be 
seen  distinctly  at  the  same  time,  although  they  can  be  succes- 
sively focussed.  The  condition  may  be  corrected  by  glasses 
which  are  segments  of  cylinders  cut  parallel  to  the  axis 
(Practical  Exercises,  p.  989). 

The  Ophthalmoscope. — The  pupil  of  the  normal  eye  is  dark, 
and  the  interior  of  the  eye  invisible,  without  special  means  of 
illuminating  it.  But  this  is  not  because  all  the  light  that  falls 
upon  the  fundus  is  absorbed  by  the  pigment  of  the  choroid,  for 
even  the  pupil  of  an  albino  appears  dark  when  the  eye  is  covered 
by  a  piece  of  black  cloth  with  a  hole  in  frcnt  of  the  pupil.  The 
explanation  is  as  follows  : 

Let  the  rays  from  a  luminous  point,  P,  be  focussed  by  the  lent;, 
L,  at  P'  (Eig.  395).  It  is  plain  that  rays  proceeding  from  P' 
will  exactly  retrace  the  path  of  those  from  P  and  be  focussed  at 


9iR 


,!  MANUAL  OF  PHYSIOLOGY 


P.  Now,  the  eve  receives  rays  from  all  directions,  and,  when 
it  is  sufficiently  well  illuminated,  sends  rays  out  in  all  direc- 
tions. The  moment,  however,  that  the  observing  eye  is  placed 
in  front  of  the  observed  eye,  the  latter  ceases  to  receive  light 
from  the  part  of  the  field  occupie  1  by  the  pupil  of  the  former, 
and  therefore  ceases  to  reflect  light  into  it. 

This  difficulty  is  avoided  by  the  use  of  an  ophthalmoscopic 
mirror.  The  original,  and  theoretically  the  most  perfect,  form 
of  such  a  mirror  is  a  plate,  or  several  superposed  plates,  of  glass, 
from  which  a  beam  of  light  from  a  laterally  placed  candle  or 
lamp  is  reflected  into  the  observed  eye,  and  through  which  the 
eye  of  the  observer  looks  (Fig.  3Q'j).  But  the  illumination  thus 
obtained  is  comparatively  faint  :  and  a  concave  mirror  is  now 


pje,    3o".—  Fiai-KF    to   ILLTTSTRATB   THr    Privcipt.-:    OF   TirF    QpHTHAT.MOrCOF-. 

Rays  of  light  from  a  point  P  are  reflected  by  a  glass  plate  M  (several  plates 
together  in  Helmholtz's  original  form)  into  the  observed  eye  E'.  Their  focus 
would  fall,  as  shown  in  the  figure,  at  P',  a  little  behind  the  retina  of  E.  Th* 
portion  of  the  retina  AB  is  therefore  illuminated  by  diffusion  circles  ;  and  the 
rays  from  a  point  of  it  F  will,  if  F/  is  emmetropic  and  unaccommodated,  issue 
parallel  from  E'  and  be  brought  to  a  focus  at  F'  on  the  retina  of  the  (emmetropic 
and  unaccommodated)  observing  eye  E. 

generally  used.  In  the  centre  is  a  small  hole  or  a  small  unsilvered 
portion  of  the  mirror  for  the  observer's  eye.  In  the  direct 
method  of  examination  (Fig.  397),  the  mirror  is  held  close  to 
the  observed  eve,  and  an  erect  virtual  image  of  the  fundus  is 
seen.  When  the  eye  of  the  observer  and  of  the  patient  are  both 
emmetropic,  and  both  eyes  are  unaccommodated,  the  rays  of 
light  proceeding  from  a  point  of  the  retina  of  the  observed  eye 
are  rendered  parallel  by  its  dioptric  media,  and  are  again  brought 
to  a  focus  on  the  observer's  retina. 

If  the  observed  eye  is  myopic,  the  rays  of  light  coming  from 
a  point  of  the  retina  leave  the  eye,  even  when  it  is  unaccommo- 
dated, as  a  convergent  pencil  :  and  the  emmetropic  non- 
accommodated  eye  of  the  observer  must  have  a  concave  lens 


///.'  Senses  919 

placed  before   it    in  ordei    that  the  fundus  may  be  distinctly 
seen. 

When  the  observed  eye  is  hypermetropic,  the  rays  emerging 
from   the  unaccommodated  eye  are  divergent,  and  a  convex 


Fig.  337- — DircrcT  Method  or  it.int,  the  Ophthalmoscope. 

Light  falling  on  the  perforated  concave  mirror  M  passes  into  the  observed  eye 
E'  ;  and,  both  E'  and  the  observing  eye  E  being  supposed  emmetropic  and  unac- 
commodated, an  erect  virtual  imase  of  the  illuminated  retina  of  E'  is  seen  by  E. 

lens,  the  strength  of  which  is  proportional  to  the  amount  of 
hypermetropia,  must  be  placed  before  the  observer's  unaccom- 
modated eve  if  he  is  to  see  the  fundus  distinctlv.     Bv  accommo- 


Fie.  398. — Use  of  the  Ophthalmoscopy  (Direct  Method)  fop.  testing  Errors 
of  Refraction  in  Myopic  Eye. 

Rays  issuing  from  a  point  of  the  retina  of  E',  the  observed  (myopic  and  un- 
accommodated) eye,  pass  out,  not  parallel,  but  convergent.  They  will  therefore 
be  focussed  in  front  of  the  retina  of  the  observing  (unaccommodated)  eye  E  if 
the  latter  is  emmetropic.  By  introducing  a  concave  lens  L  of  suitable  strength, 
however,  a  clear  view  of  the  retina  of  E'  will  be  obtained,  and  the  strength  of  this 
lens  is  the  measure  of  the  amount  of  myopia. 

dating,  the  observer  can  see  the  fundus  clearly  without  a  convex- 
lens. 

By  this  method  errors  of  refraction  in  the  eye  may  be  detected 


920  A    MANUAL  OF  PHYSIOLOGY 

and  measured.  The  observer  must  always  keep  his  eye  un- 
accommodated, and  if  it  is  not  emmetropic,  he  must  know  the 
amount  of  his  short-  or  long-sightedness — i.e.,  the  strength  and 
sign  of  the  lens  needed  to  correct  his  defect  of  refraction,  and 
must  allow  for  this  in  calculating  the  defect  of  his  patient. 
Non-accommodation  of  the  eye  of  the  latter  can  always  be 
secured  by  the  use  of  atropine. 

By  the  direct  method  of  ophthalmoscopic  examination,  only 
a  small  portion  of  the  retina  can  be  seen  at  a  time,  and  this  is 
highly  magnified.  A  larger,  though  less  magnified,  view  can 
be  got  by  the  indirect  method.  The  observed  eye  is  illuminated 
as  before,  but  the  mirror  and  the  observer's  eye  are  at  a  greater 
distance  (Fig.  400).  Here  the  rays  from  a  considerable  portion 
of  the  retina  are  brought  to  a  focus  by  a  convex  lens  held  near 


Fig.  399- — Testing  Errors  of  Refraciiox  is-  Hypermetropic  Eye. 

Kays  from  a  point  of  the  retina  of  E  ,  the-  observed  eye,  issue  divergent,  and  are 
focussed  behind  the  retina  of  the  observing  (unaccommodated  and  emmetropic) 
eye  E.  The  strength  of  the  convex  lens  L,  which  must  be  introduced  in  front  of 
E  to  give  clear  vision  of  the  retina  of  E',  measures  the  degree  of  hypermetropia. 

the  eye  of  the  patient,  so  as  to  form  a  real  and  inverted  aerial 
image  of  the  retina.  This  image  is  viewed  by  the  observer  at 
his  ordinary  visual  distance.  It  is  not  necessary  in  this  method 
that  the  observed  eye  should  be  non-accommodated,  although 
it  is  convenient  as  in  the  direct  method  to  cause  dilatation  of 
the  pupil  by  atropine,  which  also  relaxes  the  accommodation 
(Practical  Exercises,  p.  994). 

Skiascopy. — To  a  great  extent  the  ophthalmoscopic  method 
of  measuring  errors  of  refraction  has  been  replaced  by  the  more 
modern  method  of  skiascopy  (shadow  test).  It  depends  upon 
the  following  observation  :  When  one  throws  light  from  a  little 
distance  with  a  concave  mirror  into  an  observed  eye  and  then 
rotates  the  mirror  slowly  around  the  long  axis  of  the  handle, 
one  sees  that  the  pupil,  which  at  first  was  completely  illuminated. 


THE  SENSES 


g.n 


become-  dark  from  one  side  as  if  covered  by  a  shadow.  This 
shadow  will  move  in  the  same  direction  in.  which  the  mirror  is 
rotated  or  in  the  opposite  direction,  according  to  whether  the 
observer  is  farther  from  the  observed  eye  than  its  far-point,  or 
between  the  eye  and  the  far-point.  If  the  observer  is  exactly 
at  the  far-point,  no  direction  of  movement  of  the  shadow  can  be 
made  out,  but  the  pupil  in  its  whole  extent  is  either  illuminated 
or  altogether  dark.  In  this  way  the  distance  of  the  far-point  of 
a  myopic  eye  can  be  easily  determined  by  a  metre  rule,  and 
from  this  the  degree  of  myopia.  If  the  far- point  is  either  too 
near,  as  in  strong  myopia,  or  too  distant,  as  in  weak  myopia 


Fig.  401. — Indirect  Method  of  vsixg  the  Ophthalmoscope. 
The  rays  of  light  issuing  from  E',  the  observed  eye,  are  focussed  by  the  biconvex 
lens  L,  and  a  real  inverted  image  of  a  portion  of  the  retina  of  E',  magnified  four 
or  five  times,  is  formed  in  the  air  between  the  lens  and  the  observing  eye  E.  This 
image  is  viewed  by  E  at  the  ordinary  distance  of  distinct  vision  (10  to  12  inches). 
(The  exaggeration  of  the  size  of  the  mirror  makes  it  appear  as  if  some  of  the  rays 
from  the  lamp  passed  through  the  lens  before  being  reflected  from  the  mirror. 
This  would  not  be  the  case  in  an  actual  observation.) 

and  emmetropia,  or  behind  the  observed  eye,  as  in  hypermetropia, 
it  can  be  brought  to  a  convenient  distance  by  interposing  suit- 
able lenses.  The  observer  then  determines  the  far-point  exactly 
by  moving  his  eye  nearer  to  or  farther  from  the  observed  eye, 
or,  keeping  his  own  eye  fixed,  by  bringing  the  far-point  of  the 
observed  eye  to  coincide  with  it  by  inserting  lenses  (Practical 
Exercises,  pp.  994,  995). 

The  phenomenon  depends  upon  the  interruption  which  the  light 
proceeding  from  the  observed  retina  experiences  first  at  the  margin 
of  the  pupil  of  the  observed  eye,  and  then  at  the  margin  of  the  hole 


922  ,|   MANUAL  OF  PHYSIOLOGY 

in  the  mirror  or  of  the  observer's  pupil.    When  the  minor  is  rotated, 
an  illuminated  poinl  of  the  observed  retina  will  move  in  the  opposite 

direction  over  the  retina.*  The  light  proceeding  from  this  point 
when  the  observed  eye  is  emmetropic  is  so  refracted  by  the  lens  and 
cornea  that  it  leaves  the  eye  as  a  bundle  of  parallel  rays  in  the 
direction  ot  the  image  of  the  source  of  light  (!.')  (Fig.  |  »i).  If  the 
image  of  the  flame  reflected  by  the  mirror  is  situated  on  the  principal 
axis  of  the  observer's  eye,  and  if  the  pupils  of  observed  and  observer 
are  of  equal  size,  all  the  rays  coming  from  the  observed  retina  will 
fall  on  the  observer's  retina,  and  therefore  the  whole  pupil  of  the 
observed  eye  will  appear  light.  If  the  mirror  is  now  rotated  so  that 
the  image  of  the  source  of  light  moves  away  from  the  principal  axis 
and  the  illuminating  rays  are  no  longer  in  that  axis,  the  illuminated 
point  will  move  in  the  opposite  direction  from  the  principal  axis 
and  the  light  returning  from  the  pupil  of  the  observed  eye  will  again 
issue  in  the  direction  of  the  im  xge  of  the  source  of  light.  It  can 
then  happen  that  none  of  the  rays  hit  the  observer's  pupil,  and  the 
observed  pupil  win  appear  entirelv  dark.     Or  the  direction  of  the 


Fig.   401. — Path  of  Rays  in  Skiascopy  (Snellen). 

U,  observed  eye  :  Be,  eye  of  observer  ;  Sp,  mirror  ;  L,  source  of  light  ;  U,  image 
of  the  source  of  light  ;  A,  A',  principal  axis  ;  P,  P',  pupils. 

rays  mav  be  such  that  a  portion  of  them  enters  the  observer's  pupil. 
the  rest  being  interrupted  by  its  border.  In  this  case  the  part  of 
the  observed  pupil  from  which  rays  enter  the  observer's  pupil  will 
appear  light,  while  the  rest  is  dark.  From  Fig.  401  it  can  be  seen 
that  the  light  part  of  the  observed  pupil  is  on  the  opposite  side  of 
the  principal  axis  from  the  image  of  the  source  of  light.  If,  therefore. 
the  image  of  the  source  of  light  moves  to  the  right  (by  rotation  of 
a  concave  mirror  to  the  right,  or  rotation  of  a  plane  mirror  to  the 
left)  the  skiascopic  appearance  in  the  observed  pupil  moves  to  the 
left — i.e.,  in  the  opposite  direction  to  the  image  of  the  source  of  light. 
If  the  observed  pupil  is  myopic — i.e.,  if  its  far-point  is  between 
the  observer  and  the  observed  eye,  rotation  of  the  mirror  so  far  from 
the  principal  axis  that  only  a  part  of  the  rays  issuing  from  the 
observed  pupil  enter  the  observer's  eye,  will  cause  the  pupil  to  appear 

*  When  a  concave  mirror  is  rotated  to  the  right,  the  inverted  real  mirror 
image  also  moves  to  the  right,  and  the  illuminated  point  to  the  left. 
When  a  plane  mirror  is  rotated  to  the  right,  the  virtual  mirror  image 
moves  to  the  left,  and  the  illuminated  point  on  the  retina  therefore  to  the 
right. 


nil    SENSES 


light  only  on  one  side,  and  on  accounl  oi  the  crossing  ol  the  rays  tliis 
illuminated  portion  will  be  on  the  same  side  oi  the  principal  axis 
as  the  image  of  th  2).     Whenth  ifthe 

source  ol  light  is  moved  to  the  right  the  light  area  of  the  observed 
pupil  will  also  move  to  the  right     i.e.,  with  rotation  of  ;i  com 
mirror  in  the  same  dire<  tion  .i->  tin-  image  oi  the  source  of  light,  and 
with  rotation  of  a  plane  mirror  in  tin-  opposite  direction  (Snellen). 

U 


A  — 


Fig.  402. — Path  of   Kan-  i\   Skiascopy  (Myopic  Eve)  (Snellen). 
PR,  far-point  of  observed  eye.     The  other  references  are  as  in  Fig.  401. 

A  method  of  photographing  the  retina  in  the  living  eye  which  has 
recently  been  employed  with  success  bids  fair  to  become  an  important 
supplementary  means  of  investigating  the  fundus  (Dogiel). 

Single  Vision  with  Both  Eyes — Diplopia. — Scheiner's  experiment 
shows  that  it  is  possible  to  have  double  vision,  or  diplopia,  with  a 
single  eye  when  two  separate  images  of  the  same  object  fall  upon 
different  parts  of  the  retina.  In  vision  with  both  eyes,  or  binocular 
vision,  an  image  of  every  object  looked  at  is,  of  course,  formed  on 
each  retina,  and  we  have  to  inquire  how  it  is  that  as  a  rule  these 
images  are  blended  in  consciousness  so  as  to  produce  the  perception 
of  a  single  object  ;  and  how  it  is  that  under  certain  conditions  this 
blending  does  not  take  place,  and  diplopia  results.  Two  chief 
theories  have  been  invoked  in  the  attempt  to  answer  these  questions  : 
(1)  the  theory  of  identical  points,  (2)  the  theory  of  projection. 

In  regard  to  the  second  theory,  we  shall  merely  sav  that  it  assumes 
that  in  some  way  or  other  the  retina,  or,  rather,  the  retino-cerebral 
apparatus,  has  the  power  of  appreciating  not  only  the  shape  and  size 
of  an  image,  but  also  the  direction  of  the  rays  of  light  which  form  it, 
and  that  the  position  of  the  object  is  arrived  at  by  a  process  of 
mental  projection  of  the  image  into  space  along  these  directive  lines. 
Where  the  directive  lines  of  the  two  eyes  cut  each  other  the  two 
images  coincide,  and  the  object  is  seen  single  in  the  position  of  the 
point  of  intersection.  The  first  theory  we  shall  examine  in  some 
detail. 

The  Theory  of  Identical  Points. — This  theory  assumes  that  every 
point  of  one  retina  '  corresponds  '  to  a  definite  point  of  the  other 
retina,  and  that  in  virtue  of  this  correspondence,  either  by  an  inborn 
necessity  or  from  experience,  the  mind  refers  simultaneous  impres- 
sions upon  two  corresponding  or  identical  points  to  a  single  point  in 
external  space.  If  we  imagine  the  two  retinae  in  the  position  which 
the  eyes  occupy  when  fixing  an  infinitely  distant  object — that  is, 
with  the  visual  axes  parallel — to  be  superposed,   with  fovea  over 


924  I   MA  M    \i    m    PRYStOLOG  , 

lovi-.i,  ivcrv  point  oi  the  one  retina  will  be  covered  by  the  corre- 
sponding point  o!  tin  other  retina,  so  that  identical  points  could  be 
pricked  through  with  a  needle.  But  since  the  actual  centre  of  the 
retina  dot's  not  correspond  with  the  fovea  centralis  (Fig.  381),  but 
lies  nearer  the  nasal  side,  the  nasal  edge  of  the  left  retma  will  overlap 
the  temporal  edge  oi  the  light,  and  the  nasal  r.p,-  oi  the  right  will 
overlap  the  temporal  edge  of  the  left  ;  so  that  a  part  of  each  retina 
has  no  corresponding  points  in  the  other. 

The  adherents  of  this  theory  claim,  and  with  justice,  that  a  small 
object  so  situated  that  its  image  must  be  formed  on  corresponding 
points  of  the  two  retinae  does,  as  a  rule,  appear  single,  and,  what  is 
even  more  striking,  that  a  phosphene,  or  luminous  ring  produced 
by  pressing  the  blunt  end  of  a  pencil  or  the  finger-nail  on  a  point  of 
the  globe  of  one  eye  (which  Newton  compared  to  the  circles  on  a 
peacock's  tail),  is  not  doubled  by  pressure  over  the  corresponding 
point  of  the  other  eye,  although  two  circles  are  seen  when  pressure  is 
made  upon  points  which  do  not  correspond.  If  in  rotating  the  eyes 
one  eve  is  prevented  by  pressure  with  the  finger  from  following  the 
movement  of  the  other,  there  is  double  vision .  When  strabismus  or 
squinting  is  produced  by  paralysis  of  the  third  (p.  819)  or  the  sixth 
cranial  nerve  (p.  822),  it  is  accompanied  by  diplopia,  until  in  course 
of  time  the  mind  learns  to  disregard  one  of  the  images.  In  some 
cases  of  squint  the  double  images  are  never  completely  suppressed, 
but  a  new  abnormal  form  of  visual  localization  is  developed,  which, 
however,  vcrv  seldom  permits  any  accurate  judgment  of  depth.  In 
strabismus  it  is  obvious  that  the  two  images  of  an  object  cannot  tall 
on  corresponding  points. 

But  it  is  also  a  fact  that,  under  certain  conditions,  images  sit 
on  corresponding  points  may  not,  and  that  images  not  situated  on 
corresponding  points  may,  give  rise  to  a  single  impression.  For 
example,  if  one  of  the  closed  eyes  be  held  slightly  out  of  its  ordinary 
position  by  the  finger,  pressure  on  identical  points  of  the  two  eyes 
gives  rise  to  two  separate  phosphenes.  And  some  of  the  phenomena 
of  stereoscopic  vision  (p.  925)  show  clearly  that  images  falling  on 
points  not  strictly  corresponding  may  give  a  single  impression  ; 
while  we  do  not  habitually  see  double,  although  it  is  certain  that  the 
images  of  multitudes  of  objects  are  constantly  falling  on  points  of 
the  retinas  not  anatomically  '  identical.'* 

The  question  therefore  arises,  How  is  it  that  we  do  not  see  these 
double  images  ?  This  is  one  of  the  difficulties  of  the  theory  of 
identical  points.  The  following  is  a  partial  explanation  :  (1)  The 
images  of  objects  in  the  portion  of  the  field  most  distinctly  seen — 
that  is,  the  portion  in  the  immediate  neighbourhood  of  the  inter- 
section of  the  visual  lines,  or  the  part  to  which  the  gaze  is  directed — 

*  In  every  fixe  1  position  of  the  eyes,  the  objects  whose  images  fall  on 
corresponding  points  will  be  arranged  on  certain  definite  lines  or  surfaces 
which  vary  with  the  direction  of  the  visual  axis  and  to  which  the  name 
of  horopter,  or  point-horopter,  has  been  given.  For  most  eyes  when 
directed  to  the  horizon — that  is,  with  the  visual  axes  parallel — the  hor- 
opter is  practically  the  horizontal  plane  of  the  ground,  so  that  all  objects 
within  the  held  of  vision,  and  resting  on  the  ground,  fall  upon  corresponding 
points,  and  are  seen  single.  When  the  eyes  are  directed  to  a  point  at 
such  a  distance  that  the  lines  of  vision  are  sensibly  convergent,  the  horopter 
consists  (1)  of  a  straight  line  drawn  through  the  fixing-point  and  at  right 
angles  to  a  plane  passing  through  the  fixing-point  and  the  two  visual  lines 
(visual  plane)  ;  (2)  of  a  circle  passing  through  the  fixing-point  and  the 
nodal  points  of  the  two  eyes  (the  famous  horopteric  circle  of  Midler). 


THE  SENSES 


925 


arc  formed  on  identical  points;  and  by  rapid  movements  the  eyes 
fix  successively  different  parts  oi  the  field  ol  view.  (2)  Vision  grows 
less  distinct  as  we  pass  out  from  the  centre  of  the  retina,  and  we  are 
accustomed  to  neglect  the  blurred  peripheral  images  in  comparison 
with  those  formed  on  the  fovea.  (3)  When  the  images  of  an  object 
do  not  fall  on  identical  points,  one  of  the  points  on  which  they  do  fall 
may  be  occupied  with  the  images  of  other  objects,  some  of  which 
may  be  so  boldly  marked  as  to  enter  into  conflict  with  the  extra 
image  and  to  suppress  it.  (4)  Lastly,  the  physiological  'identical 
point  '  is  not  a  geometrical  point,  but  an  area  which  increases  in  size 
in  the  more  peripheral  zones  of  the  retina  and  can  also  be  increased 
by  practice  ;  and  images  which  lie 
wholly  or  in  chief  part  within  two 
corresponding  areas  practically  co- 
incide. 

Stereoscopic  Vision. — Although  the 
retinal  image  is  a  projection  of  ex- 
ternal objects  on  a  surface,  we  per- 
ceive not  only  the  length  and  breadth, 
but  also  the  depth  or  solidity  of  the 
things  we  look  at.  When  we  look 
directly  at  the  front  of  a  building, 
the  impression  as  to  its  form  is  the 
same  whether  one  or  both  eyes  be 
used,  although  with  a  single  eye  its 
distance  cannot  be  judged  so  accur- 
ately. But  when  we  view  the  build- 
ing from  such  a  position  that  one  of 
the  corners  is  visible,  we  obtain  a 
more  correct  impression  of  its  depth 
with  the  two  eyes.  This  is  partly 
due  to  the  fact  that  to  fix  points  at 
different  distances  from  the  eyes  the 
visual  lines  must  be  made  to  converge 
more  or  less,  and  of  the  amount  of 
this  convergence  we  are  conscious 
through  the  contraction  of  the  mus- 
cles which  regulate  it.  But  there  is 
another  element  involved.  When  the 
two  eyes  look  at  a  uniformly-coloured 
plane  surface,  the  retinal  image  is 
precisely  the  same  in  both.  But 
when  the  two  eyes  are  directed  to 
a  solid  object  (say  a  book  lying  on  a 
table)  the  picture  formed  on  the  left 

retina  differs  slightly  from  that  formed  on  the  right,  for  the  left  eye 
sees  more  of  the  left  side  of  the  book,  and  the  right  eye  more  of  the 
right  side. 

That  there  is  a  close  connection  between  uniformity  of  retinal 
images  and  impression  of  a  plane  surface  on  the  one  hand,  and 
difference  of  retinal  images  and  impression  of  solidity  on  the  other, 
is  proved  bv  the  facts  of  stereoscopy.  It  is  evident  that  if  an  exact 
picture  of  the  solid  object  as  it  is  seen  by  each  eye  can  be  thrown 
on  the  retina,  the  impression  produced  will  be  the  same,  whether 
these  images  are  really  formed  by  the  object  or  not.  Now,  two  such 
pictures  can   be   produced   with    a  near  approach  to  accuracy   by 


Fig.    403. — Brewster's    Stereo- 
scope. 

p  and  it  are  prisms,  with  their  re- 
fracting angles  turned  towards 
each  other.  The  prisms  refract 
the  rays  coming  from  the  points 
c,  y  of  the  pictures  ab  and  a3  so 
that  they  appear  to  come  from  a 
single  point  q.  Similarly,  the 
points  a  and  a  appear  to  be  situ- 
ated at  /,  and  the  points  b  and  /3 
at  <p. 


926  I    MA  \  in    OF    PHYSIOLOGY 

photographing  the  objecl  from  the  point  oi  view  of  each  eye.  It 
only  remains  to  casl  the  image  oi  i  ach  picture  on  the  corresponding 
retma,  while  the  eyes  are  converged  to  the  same  extent  as  would  be 
tin  <  .isc  it  they  were  viewing  the  a<  tual  object.  This  is  accomplished 
by  means  of  a  stereo  cop*   (Fig.  4°3)- 

li  is  found  thai  the  resultant  impression  is  that  (if  the  solid  object. 
1 1  is  impossible  to  reconcile  this  \\  ith  the  doctrine  of  strictly  identical 
geometrical  points.  A  pair  of  identical  pictures  gives  with  the 
Stereoscope  not  the  impression  of  a  solid,  but  of  a  plane  surface. 
It  the  relative  position  of  any  two  points  differs  in  the  two  pictures, 
the  blended  pi<  tun  h.is  ;i  corresponding  point  in  relief.  So  great  is 
the  delicacy  oi  this  test  that  a  good  and  a  bad  banknote  will  not 
blend  under  the  stereoscope  to  a  flat  surface,  and  the  method  may 
be  actually  used  lor  the  detection  of  forgery. 

When  the  pictures  are  interchanged  in  the  stereoscope  so  that  the 
image  which  ought  to  be  formed  on  the  right  retina  falls  on  the  left, 
and  that  which  is  intended  for  the  left  eye  falls  on  the  right,  what 
Were  projections  before  become  hollows,  and  what  were  hollows 
stand  out  in  relief.  The  pseudoscope  of  Wheatstone  is  an  arrange- 
ment by  which  each  eye  sees  an  object  by  reflection,  so  that  the 
images  which  would  be  formed  on  the  two  retinae,  if  the  object  were 
looked  at  directly,  are  interchanged,  with  the  same  reversal  of  our 
judgments  of  relief. 

Visual  Judgments.— We  say  judgments  of  relief  ;  for  what  we  call 
seeing  is  essentially  an  act  that  involves  intellectual  processes.  As 
the  retina  is  anatomically  and  developmentally  a  projection  of  the 
brain  pushed  out  to  catch  the  waves  of  light  which  beat  in  upon 
the  organism  from  every  side,  so,  physiologically,  retina,  optic  nerve, 
and  visual  nervous  centre  are  bound  together  in  an  indissoluble 
chain.  We  cannot  say  that  the  retina  sees,  we  cannot  say  that  the 
optic  nerve  sees— the  optic  nerve  in  itself  is  blind — we  cannot  say 
1  hat  the  visual  centre  sees.  The  ethereal  waves  falling  on  the  retina 
set  up  impulses  in  it  which  ascend  the  optic  nerve  ;  certain  portions 
of  the  brain  are  stirred  to  action,  and  the  resulting  sensations  of  light 
springing  up,  we  know  not  where,  are  elaborated,  we  know  not  how 
(by  processes  of  which  we  have  not  the  faintest  guess),  into  the  per- 
ception of  what  we  call  external  objects — trees,  houses,  men.  parts 
of  our  own  bodies,  and  into  judgments  of  the  relations  of  these  things 
among  themselves,  of  their  distance  and  movements. 

A  child  learns  to  see,  as  it  learns  to  speak,  by  a  process,  often 
unconscious  or  subconscious,  of  '  putting  two  and  two  together.' 
The  musical  sounds  united  and  terminated  by  noises  which  make  up 
the  spoken  word  '  apple  '  are  gradually  associated  in  its  mind  with 
the  visual  sensation  of  a  red  or  green  object,  the  tactile  sensation  of 
a  smooth  and  round  object,  and  the  gustatory  and  olfactory  sensa- 
tions which  we  call  the  taste  or  flavour  of  an  apple.  And  as  it  is  by 
experience  that  the  child  learns  to  label  this  bundle  of  sensations 
with  a  spoken,  and  afterwards  with  a  written,  name,  so  it  is  by 
experience  that  it  learns  to  group  the  single  sensations  together,  and 
to  make  the  induction  that  if  the  hand  be  stretched  out  to  a  certain 
distance  and  in  a  certain  direction — i.e.,  if  various  muscular  move- 
ments, also  associated  with  sensations,  be  made — the  tactile  sensation 
of  grasping  a  smooth  round  body  will  be  felt,  and  that  if  the  further 
muscular  movements  involved  in  conveying  it  to  the  mouth  be 
i  arried  out,  a  sensation  agreeable  to  the  youthful  palate  will  follow. 
At  length  the  child  conus  to  believe,  and.  unless  he  happens  to  be 


////    SI  NSES 


specially  instructed,  carries  his  belie!  with  bim  to  his  grave,  thai 
ulun  in-  looks  .it  .ui  apple  he  sees  a  round,  smooth,  toll  rably  bard 
body,  "i  definite  size  ;m<l  colour  :  while  in  reality  all  that  the  sens*  oi 
sight  can  inform  bim  of  is  the  difference  in  the  intensity  and  colour 
nt  the  light  falling  on  Ins  retina  when  he  turns  his  head  in  a  particular 
directs  n. 

An  interesting  illustration  of  the  role  of  experience  in  shaping 
our  visual  judgments  is  found  in  the  sensations  of  persons  born 
blind  and  relieved  in  after-life  by  operation.  A  boy  'between 
thirteen  and  fourteen  years  of  age,  operated  on  by  Cheselden, 
thought  all  the  objects  he  looked  at  touched  his  eyes.  '  He 
forgot  which  was  the  dog  and  which  the  cat,  but  catching  the 
cat  (which  he  knew  by  feeling),  he  looked  at  her  steadfastly 
and  said,  "  So,  puss,  I  shall  know  you  another  time."  Pictures 
seemed  to  him  only  parti-coloured  planes  ;  but  all  at  once,  two 
months  after  the  operation,  he  discovered  they  represented 
solids.'  Nunnery,  perhaps  remembering  the  dictum  of  Diderot, 
true  as  it  is  in  the  main,  though  tinged  with  the  exaggeration 


Fig.  404. — Illusion  of  Parallel  Lines  (Hering). 

of  the  Encyclopedic,  that  '  to  prepare  and  interrogate  a  person 
born  blind  would  not  have  been  an  occupation  unworthy  of  the 
united  talents  of  Newton,  Des  Cartes,  Locke,  and  Leibnitz,' 
made  an  elaborate  investigation  in  the  case  of  a  boy  nine  years 
old,  on  whom  he  operated  for  congenital  cataract  of  both  eyes, 
and,  what  is  of  special  importance,  instituted  a  set  of  careful 
experiments  and  interrogations  before  the  operation,  so  as  to 
gain  data  for  comparison.  Objects  (cubes  and  spheres)  which 
before  the  operation  he  could  easily  recognise  by  touch  were 
shown  him  afterwards,  but  although  '  he  could  at  once  perceive 
a  difference  in  their  shapes,  he  could  not  in  the  least  say  which 
was  the  cube  and  which  the  sphere.'  It  took  several  days, 
and  the  objects  had  to  be  placed  many  times  in  his  hands  before 
he  could  tell  them  by  the  eye.  '  He  said  everything  touched 
his  eyes,  and  walked  most  carefully  about,  with  his  hands  held 
out  before  him  to  prevent  things  hurting  his  eves  by  touching 
them.' 

Many  other  illustrations  might  be  given  of  the  fact  that 
'  seeing '  is  largely  an  act  of  reasoning  from  data  which  may 
sometimes  mislead.     Thus  in  Figs.  404  and  405  the  long  hori- 


/    VI  \  UA1    OF  1'IIYSTOI.OGY 


zontal  lines  are  hmIK  parallel,  but  do  nol  appear  so  owing  to  the 
confusion  of  judgment  produced  by  the  short  sloping  lines.  In 
Fig.  406  the  spaces  covered  by  A,  B,  and  C  are  equal  squares, 
but  A  appears  taller  than  B,  and  C  smaller  than  either  A  or  B. 
In  the  same  figure  the  lines  I)  and  E  are  of  the  same  length,  but 
E  seems  considerably  longer  than  D. 

Illusions  of  movement  are  among  the  most  interesting  optical 
illusions.     If  two  similar  objects  are  momentarily  shown  to  the 

eye  in  rapid  succes- 
sion and  at  points 
in  space  not  separ- 
ated by  too  great  a 
distance,  the  illu- 
sion is  produced 
that  the  first  object 
has  moved  to  the 
position  of  the 
second.  Such  illu- 
sions are  the  basis 


<u  > 


Fig.   405. — Illusion  ok   Parallel  Lines  (Zollner).     of      the      SO  -  called 

'  moving  pictures  ' 
shown  by  the  cinematograph.  A  series  of  instantaneous  photo- 
graphs of  a  movement  are  taken,  recording  the  successive 
positions  assumed  by  the  moving  body.  When  these  are  thrown 
on  the  retina  in  the  same  order  and  in  rapid  succession,  an 
illusion  of  the  original  movement  is  produced. 

The  apparent  size  and  form  of  an  object  is  intimately  related 
to  the  size,  form,  and  sharpness  of  its  image  on  the  retina.  We 
are,      therefore, 

able   to  discrimi-  ABC 

nate    with    great 
precision  the  un- 
stimulated    from 
the   excited   por- 
tions     of      that 
membrane,    espe- 
cially in  the  fovea 
centralis,  and  also 
the  degree  of  ex- 
citation of  neighbouring  excited  parts.     But  instead  of  localizing 
the  image  on  the  retina  as  we  localize  on  the  skin  the  pressure 
of  an  object  in  contact  with  it,  we  project  the  retinal  image 
into  space,  and  see  everything  outside  the  eye. 

In  vision,  in  fact,  we  have  no  conception  of  the  existence  of  either 
retina  or  retinal  image  ;  and  even  the  shadows  of  objects  within  the 
eye  are  referred  to  points  outside  it.     Thus,  for  instance,  an  opacity 


Fig.  406. — Illusions  of  Space-perception. 


////    SENSES 


or  a  foreign  body  in  any  of  the  refractive  media— -and  no  eye  is 
entirety  free  from  relatively  opaque  spots  -can  be  detected,  and  its 
position  determined  by  the  shadow  which  it  casts  on  the  retina  when 
the  eye  is  examined  by  a  pencil  of  light  proceeding  from  a  very  small 
point.  Let  a  diaphragm  with  a  small  hole  in  it  be  placed  in 
front  of  the  eye  at  such  a  distance  thai  a  pencil  diverging  from  the 
hole  will  pass  through  tire  vitreous  humour  as  a  parallel  beam, 
equal  in  cross  section  to  the  pupil  (Big.  [oj),  and  let  the  aperture  be 
illuminated  by  focussing  on  it.  the  light  of  a  lamp  placed  behind  a 
s<  reen.  The  proper  position  oi  the  hole  will  obviously  be  that  of  the 
.ulterior  principal  locus  of  the  eye — i.e.,  the  point  at  which  parallel 


Fig.  407. — la  A  the  opaque 

1>ih1y  0  is  in  tin-  plane  of  the 
pupil.  The  position  .if  the 
shadow  hi. it  i\  ely  to  the  bright 
field  is  net  altered  when  the 
illuminating  pencil  is  focussed 
at  P'  instead  of  I'.  In  B  Hi.' 
opaque  body  is  in  front  "t  the 
plane  of  tin'  pupil.  When 
P  is  lowered  to  I'',  the  shadow 
moves  towards  the  upper 
edge  "i  the  bright  held,  and 
appears  to  move  downwards 
in  the  visual  field.  When  P 
is  raised,  the  shadow  muxes 
towards  the  lower  edge  of  the 
bright  field,  .md  appears  to 
move  upwards.  In  C  the 
opaque  body  is  behind  the 
plane  of  the  pupil.  When  P 
is  moved  downwards  to  P', 
the  shadow  moves  towards 
the  lower  edge  of  the  bright 
field,  and  appears  to  the 
person  under  observation  to 
move  upwards,  and  vice  versa 
when  P  is  moved  upwards. 
The  farther  the  opaque  body 
is  from  the  pupil,  the  greater 
is  the  apparent  movement, 
or  parallax,  of  its  shadow  for 
a  given  movement  of  the 
source  of  light. 


rays  passing  from  the  vitreous  into  the  lens,  and  then  out  of  the  eye 
would  be  focussed.  This  method  of  examination  of  the  eye  is. 
therefore,  called  focal  illumination.  Opaque  bodies  in  the  vitreous 
humour  will  cast  shadows  on  the  retina  equal  in  area  to  themselves, 
The  shadows  of  opacities  in  the  lens  and  in  front  of  it  will  be  some- 
what larger  them  the  bodies  themselves,  since  the  latter  intercept 
rays  which  are  still  diverging  ;  but  since  the  greater  part  of  the 
refraction  of  the  eye  occurs  at  the  anterior  surface  of  the  cornea,  it 
is  only  the  shadows  of  objects  on  the  front  of  the  cornea,  such  as 
drops  of  mucus,  which  will  be  much  magnified.  Fig.  407  shows 
diagrammatically  how  the  shadows  shift  their  position  within  the 

59 


930 


A    MANUAL  OF   I'll  YSK  >I.0GY 


bright  field  when  the  direction  of  the  illuminating  beam  is  altered. 
Generally  opacities  in  the  vitreous  humour  arc  movable,  in  the  lens 
not 

Purkinje's  Figures. — As  was  first  pointed  out  by  Purkinje, 
the  shadows  of  the  bloodvessels  in  the  retina  itself,  and  even 
of  the  corpuscles  circulating  in  them,  although  neglected  in 
ordinary  vision,  may  be  recognised  under  suitable  conditii 
a  conclusive  proof  that  the  sensitive  layer  must  lie  behind  the 
vessels  (p.  932). 

If  a  beam  of  sunlight  is  concentrated  on  the  sclerotic  as  far  as 
possible  from  the  margin  of  the  cornea,  and  the  eye  directed  to  a 

dark  ground,  the  net- 
work of  retinal  blood- 
vessels will  stand  out 
on  it.  Another  method 
is  Lto  look  at  a  dark 
ground  while  a  lighted 
candle,  held  at  one- 
side  of  the  eye  at  a 
distance  from  the 
visual  line,  is  moved 
slightly  to  and  fro. 
Injthe  first  method, 
a  point  of  the  sclerotic 
behind  the  lens  is  illu- 
minated, and  rays 
passing  from  it  across 
the  interior  of  the 
eyeball  in  every  direc- 
tion cast  shallow  s  ol 
the  vessels  of  the  re- 
tina on  its  sensitive 
layer.  In  the  second 
method,  the  image  oi 
the  flame  formed  on 
the  retina  by  rays  fall- 
ing obliquely  through 
the  pupil  becomes  in 
the  general  darkness 
itself  a  source  oi  light. 
by  interrupting  the  rays  from  which  the  retinal  vessels  form 
shadows.  The  distance  of  the  sensitive  from  the  vascular  layer  may 
be  approximately  calculated  by  measuring  the  amount  by  which  the 
shadows  change  their  position,  when  the  position  of  the  illuminated 
poinl  oi  the  sclerotic  is  altered.  The  nearer  a  vessel  lies  to  the 
sensitive  layer,  the  smaller  must  be  the  angle  through  which  the 
apparent  position  of  its  shadow  moves  for  a  given  movement  of  the 
spot  oi  light.  In  this  way  it  has  been  calculated  that  the  sensitive 
layer  is  about  o"2  to  03  mm.  behind  the  stratum  which  contains  the 
bloodvessels.  This  corresponds  sufficiently  well  with  the  position 
of  the  layer  of  rods  and  cones,  which  all  other  evidence  shows  to  be 
the  portion  of  the  retina  actually  stimulated  by  light.  The  shadows 
of  the  blood-corpuscles  in  the  retina]  vessels  may  be  rendered  visible 
bv  looking  at  a  bright  and  uniformly  illuminated  ground,  like  the 


FlG.     408.  —  Million     Ol-     RENDERING    THE     RETINAL 

Bloodvessels    visible     by    concentrating     a 
Beam  of  Light  on  the  Sclerotic. 

From  the  brightly-illuminated  point  of  the  scle- 
rotic, a,  rays  issue,  and  a  shadow  of  a  vessel,  v,  is 
cast  at  a'.  It  is  referred  to  an  external  point,  a",  in 
the  direction  of  the  straight  line  joining  a'  with  the 
nodal  point.  When  the  light  is  shifted  so  as  to  be 
focussed  at  b,  the  shadow  cast  at  b'  is  referred  to 
b" — i.e.,  it  appears  to  move  in  the  same  direction  as 
the  illuminated  point  of  the  sclerotic. 


THE  SENSES 


93i 


milk  glass  shade  of  .1  Lamp  or  the  blue  sky,  and  moving  the  slightly 
separated  fingers  or  .1  perforated  card  rapidly  before  the  eye.  From 
the  rate  of  their  apparent  movement,  Vierordt  calculated  the  velocity 
of  the  blood  in  the  retinal  capillaries  at  0*5  to  oq  mm.  per  second. 
One  reason  why  the  shadows  oi  these  intra-rctinal  structures  do  not 
appear  in  ordinary  vision  seems  to  be  their  small  size.  The  retinal 
vessels  arc  in  reality  only  vascular  threads  ;  the  thickest  branch  of  the 
central  vein  is  nut  ..'.  mm.  in  diameter.  The  apex  of  the  cone  of 
complete  shadow  (umbra)  cast  by  a  disc  of  this  size,  at  a  distance 
of  jo  nun.  from  a  pupil  |  nun.  wide,  would  lie  only  1  mm.  behind  the 
disc --that  is  to  say,  the  umbra  of  the  retinal  vessels  would  not 
reach  the  layer  of  the  rods  and  cones  at  all,  and  only  the  penumbra, 
or  region  of  relative  darkness,  would  fall  upon  it. 

When  the  eyes,  after  being  closed  for  some  time,  are  suddenly 
opened,  the  branches  of  the 
retinal  vessels  may  be  seen  for 
a  moment.  This  is  especially 
the  case  after  sleep  ;  and  a 
good  view  of  the  phenomenon 
may  be  obtained  by  looking 
at  a  white  pillow  or  the  ceiling 
immediately  on  awaking.  If 
the  eyes  are  kept  open  for 
a  few  seconds,  the  branching 
pattern  fades  away  ;  if  they 
are  only  allowed  to  remain 
open  for  an  instant,  it  may 
be  seen  many  times  in  succes- 
sion. The  main  vessels  appear 
to  radiate  out  from  a  central 
point.  But  their  actual  junc- 
tion there  is  not  seen,  since  it 
lies  in  the  optic  disc  or  blind 
spot . 

The  Blind  Spot. —  The 
fibres  of  the  optic  nerve  are 
insensible  to  light  ;  light 
only  stimulates  them 
through  their  end-organs. 
This  can  be  proved  by  direct- 
ing by  means  of  an  ophthal- 
moscope a  beam  of  light  upon  the  optic  disc,  where  the  true 
retinal  layers  do  not  exist.  The  person  experimented  on  has  no 
sensation  of  light  when  the  beam  falls  entirely  upon  the  disc  ; 
when  its  direction  is  shifted  so  that  it  impinges  upon  any  other 
portion  of  the  retina,  a  sensation  of  light  is  at  once  experienced. 
The  blind  spot  is  not  recognised  in  ordinary  vision,  for  (i)  the 
two  optic  discs  do  not  correspond.  The  left  disc  has  its  corre- 
sponding points  on  a  sensitive  part  of  the  right  retina,  and  the 
right  disc  on  a  sensitive  part  of  the  left  retina  ;  and  the  con- 
sequence is  that  in  binocular  vision  the  objects  whose  images 
are  formed  on  the  corresponding  points  rill  up  the  blind  spots. 

59—2 


Fie..  409. — Method  of  rendering  the 
Bloodvessels  of  the  Retina  visible 
by  Oblique  Illumination  through 
the  Cornea. 

Light  from  a  candle  at  a  illuminates  a', 
and  rays  proceeding  from  a'  cast  a  shadow 
of  the  bloodvessel,  v,  at  a",  which  is  referred 
to  a'".  When  a  is  moved  to  b,  the  shadow 
on  the  retina  moves  to  b" ,  and  the  shadow 
in  the  visual  field  of  the  illuminated  eye 
to  b'". 


93  ^ 


A    MANUAL  OF  PHYSIOLOGY 


(2)  The  optic  disc  does  not  lie  in  the  line  of  direct,  and  therefore 
distinct,  vision.  The  eye  is  constantly  moving  so  as  to  bring 
the  surrounding  objects  successively  on  the  fovea  centralis  ; 
and  the  gap  which  the  blind  spot  makes  in  the  visual  field 
of  a  single  eye  is  thus  more  easily  neglected.  In  any  case  we 
ought  not  to  see  it  as  a  dark  spot,  for  darkm  —  is  only  associated 
with  the  absence  of  excitation  in  parts  of  the  retina  capable  of 
being  excited  by  light.  There  is  no  more  reason  why  the  optic 
discs  sin  mid  appear  dark  than  there  is  for  our  having  a  sensation 
of  darkness  behind  us  when  we  are  looking  straight  in  front. 
And  since  the  experience  of  our  other  senses     th  1  touch, 

for  example  tells  us  that  the  objects  we  look  at  do  not  in  general 
have  a  gap  in  the  position  corresponding  to  the  part  of  the 
image  that  falls  on  the  blind  spot,  we  see,  so  to  speak,  across 
the  spot. 

By  Mariotte's  experiment,  however,  the  existence  of  the  blind 
spot  can  not  only  b;  demonstrated,  but  its  size  determined  and  its 
boundaries  mapped  out.      Let  the  left  eye  be  closed,  and  fix  with  the 


Fig.  410. — Mariotte's  Experiment. 

right  the  small  cross  ;  then,  if  the  eye  be  moved  towards  or  away 
from  the  paper,  keeping  the  cross  fixed  all  the  time,  a  position  will 
be  found  in  which  the  white  disc  disappears  altogether.  In  this 
position  its  image  falls  on  the  blind  spot. 

Relation  of  the  Rods  and  Cones  to  Vision.  We  have  more 
than  once  referred  to  the  rods  and  cones  as  the  sensitive  layer 
of  the  retina.  It  is  now  necessary  to  develop  a  little  more  the 
evidence  in  favour  of  this  statement.  And  at  the  outset,  since 
the  sensitive  layer  has  been  shown  to  lie  behind  the  plane  of 
the  retinal  bloodvessels,  the  only  competitors  of  the  rods  and 
cones  are  the  external  nuclear  layer  and  the  pigmented  epi- 
thelium. The  nuclear  layer  may  be  at  once  excluded  a-  a 
separate  mechanism,  since,  as  we  have  seen  (p.  900),  the  portions 
of  the  rod  and  cone  elements  in  it  are  continuous  with  the 
portions  in  the  layer  of  the  rods  and  cones  proper.  In  the  fovea 
centralis,  where  vision  is  most  distinct,  the  nuclear  layer  becomes 
very  thin  and  inconspicuous. 

The  layer  of  pigmented  hexagonal  cells,  or  at  least  their 
pigment,  cannot  be  essential  to  vision,  for  albino  rats,  rabbits, 


THE  SENSES 

and  men,  in  whose  eyes  pigmenl  is  absent,  can  see.  In  man 
and  most  mammals  there  are  cones,  but  no  rods  in  the  yellow 

spot  and  fovea  centralis  ;  the  relative  proportion  of  rods  in- 
creases as  we  pass  out  fnun  the  fovea  towards  the  ora  serrata. 
lint  this  does  not  enable  us  to  analyze  the  bacillary  layer  into 
sensitive  cones  and  non-sensitive  rods,  for  on  the  rim  oi  the 

retina,  which  is  still  sensitive  to  light,  there  are  only  rods;  in 
the  bat  and  mole  there  art'  said  to  be  no  cones  even  in  the  yellow 
spot,  in  the  rabbit  very  few.  Reptiles  possess  only  cones  over 
the  whole  retinal  surface,  and  birds,  true  to  their  reptilian 
affinities,  have  everywhere  more  cones  than  rods,  as  have  also 
fishes. 

One  of  the  difficulties  in  the  way  of  understanding  how  a 
ray  of  light  can  set  up  an  excitation  in  a  rod  or  cone  is  the 
transparency  of  these  structures.  An  absolutely  transparent 
substance — that  is,  a  substance  which  would  allow  light  to 
traverse  it  without  the  least  absorption  —  would,  after  the 
passage  of  a  ray,  remain  in  precisely  the  same  state  as  before  ; 
its  condition  could  not  be  altered  by  the  passage  of  the  light 
unless  some  of  the  energy  of  the  ethereal  vibrations  was  trans- 
ferred to  it.  But  an  absolutely  transparent  body  does  not 
exist  in  Nature  ;  and  it  is  not  necessary  to  suppose  that  all  the 
energy  required  to  stimulate  the  end-organs  of  the  optic  nerve 
comes  from  the  luminous  vibrations.  These  may,  and  probably 
do,  act  by  setting  free  energy  stored  up  in  the  retina,  just  as  the 
touch  of  a  child's  hand  could  be  made  to  fire  a  mine,  or  launch 
a  ship,  or  flood  a  province.  Some  have  looked  upon  the  trans- 
verse lamellae  into  which  the  outer  members  of  the  rods  and 
cones  can  be  made  to  split  as  an  arrangement  for  reflecting 
back  the  light  to  the  inner  members,  and  have  compared  them 
to  a  pile  of  plates  of  glass,  which,  transparent  as  it  is,  is  a  most 
efficient  reflector.  It  is  even  possible,  although  here  we  are 
already  treading  the  thin  air  of  pure  speculation,  that  the  light 
may  be  polarized  in  the  process  of  reflection,  and  that  the  rods 
and  cones  may  be  less  transparent  to  light  polarized  in  certain 
planes  than  to  unpolarized  light. 

As  to  the  nature  of  the  transformation  undergone  by  the 
ethereal  vibrations  in  the  rods  and  cones,  various  theories  have 
been  formulated.  Some  have  supposed  that  the  absorbed  light- 
waves are  transformed  into  long  heat-waves,  and  that  the 
endings  of  the  optic  nerve  are  thus  excited  by  thermal  stimuli. 
This  hvpothesis  has  so  little  evidence  in  its  favour  that  it  is 
perhaps  an  unjustifiable  waste  of  time  even  to  mention  it.  It 
is  ruled  out  of  court  by  the  mere  fact  that  the  long  radiations 
of  the  ultra  red,  filtered  from  luminous  ravs  by  being  passed 
through  a  solution  of  iodine,  and  focussed  on  the  eye  by  a  lens 


934  A   MANUAL  OF  PHYSIOLOGY 

of  rock-salt,  produce  not  the  slightest  sensation  of  light,  although 
they  are  by  no  means  all  absorbed  in  their  passage  through  the 
dioptric  media.  Again,  it  has  been  suggested  that  the  energy 
of  the  waves  of  light  is  first  transformed  into  electrical  energy, 
and  that  the  visual  stimulus  is  really  electrical.  In  support  of 
this  view  it  has  been  urged  that  the  passage  of  a  voltaic  current 
through  the  eye  causes  sensations  of  light  and  that  light,  un- 
doubtedly, causes  (p.  735)  an  electrical  change  in  the  retina 
and  optic  nerve.  But,  as  has  more  than  once  been  pointed  out, 
an  electrical  change  is  the  token  and  accompaniment  of  the 
activity  of  the  excitable  tissues  in  general  ;  and  all  that  the 
currents  of  action  of  the  retina  show  is  that  light  excites  the 
retina — a  proposition  which  nobody  who  can  see  requires  an 
objective  proof  of,  and  which  does  not  carry  us  very  far  towards 
the  solution  of  the  problem  how  that  excitation  is  brought 
about.  Then  there  is  the  photo-mechanical  theory,  according 
to  which  the  pigmented  epithelial  cells  of  the  retina,  altering 
their  shape  and  volume  under  the  stimulus  of  light,  press  upon 
the  rods  and  cones,  and  thus  mechanically  stimulate  them. 
Lastly,  there  is  the  photo-chemical  theory,  which  supposes  that 
some  chemical  change  produced  in  the  rods  and  cones  under  the 
influence  of  light  sets  up  impulses  in  them  which  ascend  the 
optic  nerve.  This  is  the  most  probable  of  all  the  theories,  not- 
withstanding the  fact  that  the  discovery  by  Boll  of  the  famous 
visual  purple  or  rhodopsin,  which  at  first  seemed  likely  to  place 
it  upon  a  sure  foundation,  has  lost  its  significance  in  this  regard. 
But  although  the  visual  purple  is  not  a  photo-chemical  substance 
through  which  the  retinal  elements  are  excited  by  luminous 
stimuli,  it  seems  to  fulfil  an  important  function  in  adapting 
the  retina — i.e.,  rendering  it  more  sensitive — for  vision  in  dim 
light.  In  any  case,  its  discovery  is  in  itself  so  interesting  and 
so  suggestive  as  a  basis  for  future  work,  that  a  short  account  of 
the  properties  of  the  substance  cannot  be  omitted  here. 

Visual  Purple. — If  the  eye  of  a  frog  or  rabbit,  which  has  been  kept 
in  the  dark,  be  cut  out  in  a  dimly-lighted  chamber  or  in  a  chamber 
illuminated  only  by  red  light,  and  the  retina  removed,  it  is  seen, 
when  viewed  in  ordinary  light,  to  be  of  a  beautiful  red  or  purple 
colour.  Exposed  to  bright  light,  the  colour  soon  fades,  passing 
through  red  and  orange  to  yellow,  and  then  disappearing  altogether. 
The  yellow  colour  is  due  to  the  formation  of  another  pigment,  visual 
yellow  ;  the  preceding  stages  are  due  to  the  intermixture  of  this 
visual  yellow  with  the  unchanged  visual  purple  in  different  propor- 
tions. With  the  microscope  it  may  be  seen  that  the  pigment  is 
entirely  confined  to  the  outer  segment  of  the  rods,  where  it  exists  in 
most  vertebrate  animals.  It  may  be  extracted  by  a  watery  solution 
of  bile-salts,  and  the  properties  of  the  pigment  in  solution  arc  very 
much  the  same  as  its  properties  in  situ  ;  light  bleaches  the  solution 
as  it  does  the  retina.      Examined  with  the" spectroscope,  the  solution 


THE  SENSES 

shows  no  definite  bands,  bu1  only  a  general  absorpl  ion,  which  is  very 
slight  in  the  red,  and  reaches  its  maximum  in  the  yellowish-green. 
In  accordance  with  this,  it  is  Eound  thai  of  all  kinds  of  monochro- 
matic light  the  yellowish-green  rays  bleach  the  purple  most  rapidly, 

the  red  rays  most  slowly. 

M  a  portion  oi  the  retina  is  kepi  dark  while  the  rest  is  exposed  to 
light,  only  t  he  latter  portion  is  bleached.  And  when  the  image  of  an 
object  possessing  well-marked  contrasts  of  light  and  shadow  (e.g.,  a 
glass  plate  with  strips  of  black  paper  pasted  on  it  at  intervals,  or  a 
window  with  dark  bars)  is  allowed  to  fall  on  an  eye  otherwise  pro- 
tected from  light,  the  pal  tern  of  the  object  is  picked  out  on  the  retina 
in  purple  and  white.  A  veritable  photograph  or  'optogram'  may 
thus  be  formed  even  on  the  retina  of  a  living  rabbit  ;  and  if  the  eye 
be  rapidly  excised,  the  picture  may  be 
'  fixed  '  by  a  solution  of  alum,  and  thus 
rendered  permanent. 

These  facts  certainly  suggest  that 
light  falling  on  the  retina  may  cause  in 
some  sensitive  substance  or  substances 
chemical  changes,  the  products  of  which 
stimulate  the  endings  of  the  optic  nerve, 
and  set  up  the  impulses  that  result  in 
visual  sensations. 

The  visual  purple  cannot  itself  be  such        FlG         —Optogram. 
a  substance,  for  it   is   absent  from  the        Part  of  retina^of  rabbit, 
cones   of    all    animals    and    the    rods    of     the  eye  of  which  had  been 
some.        Frogs    and     rabbits     can    un-     directed  to  an  illuminated 
j      ,  .     ■,,  i  -i  _  plate  of  glass  covered  with 

doubtedly  see  at  a  time  when,  by  con-     ^ips  of5black  paper 
tinued  exposure  to  bright  sunlight,  the 

purple  must  have  been  completely  bleached.  And  although  the 
alleged  absence  of  the  pigment  in  the  eye  of  the  bat  might  seem 
to  afford  a  ready  explanation  of  the  proverbial  '  blindness  '  of 
that  animal,  such  a  hasty  deduction  would  be  at  once  corrected 
by  the  fact  that  birds  with  as  sharp  vision  as  the  pigeon  are 
equally  devoid  of  visual  purple,  while  in  other  nocturnal  animals, 
like  the  owl,  it  is  plentifully  found.  The  most  probable  hypo- 
thesis of  the  function  of  the  visual  purple  is  indeed  that  which 
attributes  to  it  the  property,  in  virtue  of  its  capacity  for  regenera- 
tion in  the  dark,  of  adapting  the  eye  for  night  or  twilight  vision — 
in  other  words,  of  increasing  the  sensitiveness  of  the  retinaf  or  faint 
light,  especially  of  the  shorter  wave-lengths.  If  this  is  the  case, 
it  is  preciselv  in  nocturnal  animals  that  we  should  expect  to  find 
it  in  large  amount  ;  and  recently  visual  purple  has  been  obtained 
from  more  than  one  species  of  bat  (Trendelenburg).  The  fact 
that  central  vision  (p.  946)  in  which  the  rodless  fovea  is  con- 
cerned is  but  little,  if  at  all,  susceptible  of  dark- adaptation, 
while  peripheral  vision  shows  a  marked  capacity  of  adaptation, 
agrees  well  with  this  hypothesis.  We  shall  see  later  that  there 
is  some  evidence  that  it  is  the  mere  perception  of  luminous  im- 


936  A   MANUAL  OF  PHYSIOLOGY 

pressions  as  such  and  oi  their  intensity,  without  any  distinction 
of  quality  or  colour,  with  which  the  rods  have  to  do.  They  are, 
then,  on  the  hypothesis  under  discussion,  elements  concerned 
in  achromatic  sensations  under  condition-  oi  feeble  illumination 
(twilight  vision).  The  cones  are  supposed  on  this  theory  to  be 
more  highly  developed  elements  than  the  rods,  their  function 
being  connected  especially  with  the  perception  of  colour,  but 
also  with  the  perception  of  achromatic  sensations  under  daylight 
conditions. 

The  pigmented  retinal  epithelium  is  undoubtedly  sensitive  to  light, 
and  lias  important  relations  to  the  formation  of  the  visual  purple. 
When  the  eve  is  exposed  to  light,  black  pigment  migrates  along  the 
processes  of  the  epithelial  cells  between  the  rods,  even  as  far  as  the 
rnal  limiting  membrane.  In  the  dark  the  pigment  moves  back 
again,  and  gathers  around  the  outer  portions  of  the  rods,  where  the 
visual  purple  is  being  regenerated.  The  precise  meaning  of  the 
changes  in  the  pigmented  cells  is  obscure. 

The  pigmented  epithelium  is  known  to  be  concerned  in  the 
regeneration  of  the  visual  purple.  When  a  frog  is  curarized,  oedema 
occurs  between  the  retina  and  the  choroid,  so  that  the  former  mem- 
brane is  separated  from  the  hexagonal  epithelium.  If  the  frog  is 
now  exposed  to  sunlight  till  the  visual  purple  is  bleached,  and  the 
retina  then  taken  out  and  placed  in  the  dark,  no  regeneration  of  the 
purple  takes  place.  When  the  same  experiment  is  repeated  on  a 
non-curarized  frog,  the  visual  purple  is  restored  in  the  dark,  and 
may  be  seen  under  the  microscope  in  the  rods.  The  only  difference 
in  the  two  experiments  is  that  in  the  latter  the  pigmented  epithelium 
adheres  to  the  retina,  and  it  must  therefore  have  a  hand  in  the 
neration  of  the  pigment.  Even  the  visual  purple  of  a  retina  from 
which  the  epithelium  has  been  detached  will,  after  being  bleached, 
be  restored  if  the  retina  is  simply  laid  again  on  the  epithelial  surface. 
And  it  does  not  seem  to  be  the  black  pigment  of  the  hexagonal  cells 
which  is  the  agent  in  this  restoration,  for  it  takes  place  in  the 
pigment-free  retina^  of  albino  rabbits  or  rats.  Even  a  retina  isolated 
from  the  pigmented  epithelium,  and  then  bleached,  may.  to  a  certain 
extent,  develep  new  visual  purple  in  the  dark.  This  is  even  true 
when  it  has  been  kept  in  the  dark  in  a  saturated  solution  of  sodium 
chloride,  and  is  then,  after  washing  with  physiological  salt  solution, 
bleached  by  light.  Here  the  regeneration  of  the  pigment  cannot  be 
the  result  of  vital  processes,  but  must  be  due  to  chemical  changes 
in  products  formed  from  the  original  pigment  by  the  action  of  light. 
No  such  regeneration  takes  place  in  a  retina  which,  after  having  been 
bleached  in  situ,  is  removed  without  the  pigmented  epithelium  and 
placed  in  the  dark  ;  and  the  only  probable  explanation  of  the  differ- 
ence is  that  in  this  case  the  photo-chemical  substances  from  which 
visual  purple  can  be  formed  have  been  absorbed  into  the  circulation, 
and  have  so  escaped. 

The  inner  segments  of  the  cones  of  certain  animals  (birds,  reptiles, 
amphibia,  and  some  fishes)  contain  globules  of  various  colours, 
ranging  over  almost  the  who]  spectrum,  and  including,  besides,  the 
non-spectral  colour,  purple.  The  globules  are  composed  chiefly  of 
fat  with  the  pigments  (chromophanes,  as  they  have  been  called) 
dissolved  in  it.     The  function  of  these  globules  is  unknown.     They 


THE  SENSES 

cannot  be  concerned  in  colour  vision,  or,  at   least,  they  canm 
atia]  to  it.  for  in  the  human  retina  they  do  not  exis 

The  yellow  pigment  of  the  macula  lu1  3  not  bel(  ng  to  the 

layer  of  rods  and  cones  ;  it  only  exists  in  the  external  molecular  layer 
and  the  layers  in  fronl  of  it  ;   in  the  fovea  centralis  it  is  absent. 

Time  necessary  for  Excitation  of  the  Retina  by  Light  Fusion  of 
Stimuli.  Whatever  the  exact  nature  of  retinal  excitation  may  be, 
it  is  called  forth  by  exceedingly  slight  stimuli.     A  lightning  flash. 

although  it  may  last  only  th  of  a  second,  lasts  long  enough 

3  •    1,000,000  n  b 

to  be  seen.     A  beam  of  light  thrown  from  a  rotating  mirror  on  the 

e\e  stimulates  when  it  onlv  acts  for  - th  of  a  second.     The 

8,000,000 

minimum  stimulus  in  the  form  of  green  light  corresponds,  as  we  have 

already  seen  (p.  681),  to  a  quantity  of  work  equivalent  to  no  more 

than       -   erg — that  is,  about       -.j.  gramme-millimetre,  or    -  =  milli- 
io8      &  io10  6  io7 

gramme-millimetre,  which  is  the  work  done  by  — th  of  a 

•     10,000,000 

milligramme  in  falling  through  a  millimetre  ;  and  it  cannot  be 
doubted  that  a  portion  even  of  this  Lilliputian  bombardment  is 
wasted  as  heat.  So  quickly,  too,  is  the  stimulus  followed  by  the 
response  that  no  latent  period  has  as  yet  ever  been  measured.  It  is 
certain,  however,  that  there  is  a  latent  period,  as  surelv  as  there 
is  a  latent  period  in  the  excitation  of  a  naked  nerve  -  trunk, 
although  this  also  has  never  been  experimentally  detected.  The 
analogies,  in  fact,  between  a  muscular  contraction  and  a  retinal 
excitation  are  numerous  and  close.  Like  the  muscle,  the  retina 
seems  to  possess  a  store  of  explosive  material  which  the  stimulus 
serves  enly  to  fire  off.  The  retina,  like  the  muscle,  is  exhausted  by 
its  activity,  and  recovers  during  rest.  Like  the  muscle  curve,  the 
curve  of  retinal  excitation  rises  not  abruptly,  but  v  ith  a  measurable 
slowness  to  its  height,  and  when  stimulation  is  stopped,  takes  a 
sensible  time  to  fall  again,  the  retinal  impression  outlasting  the 
luminous  stimulus  by  about  one-eighth  of  a  second.  With  compara- 
tively slow  intermittent  stimuli  the  retinal,  like  the  muscle  curve, 
flickers  up  and  down.  "When  the  rate  of  stimulation  is  increased, 
the  steady  contraction  of  the  tetanized  muscle  is  analogous  to  the 
fusion  of  the  individual  stimuli  by  the  tetanized  retina  (or  retino- 
cerebral  apparatus)  into  a  continuous  sensation  of  light,  such,  e.g., 
as  the  bright  '  trail  '  of  a  falling  star,  or  the  fiery  circle  traced  in  the 
air  when  a  firebrand  is  rapidly  whirled  round.  But  the  maximum 
retinal  excitation  which  a  stimulus  of  given  strength  can  call  forth 
depends  much  more  closely  upon  the  time  during  which  the  stimulus 
acts  than  the  maximum  contraction  does  upon  the  length  of  the 
muscular  stimulus. 

As  the  strength  of  the  light  increases  in  geometrical  progression, 
the  time  during  which  it  must  act  in  order  to  produce  its  maximum 
effect  decreases  approximately  in  arithmetical  progression  (Exnen. 
For  light  of  moderate  intensity  this  time  is  about  J  second.  Since 
for  complete  fusion  the  stimuli  must  follow  each  other  at  a  much 
more  rapid  rate  than  four  in  the  second,  the  intensity  of  the  resultant 
sensation  is  always  less  when  a  succession  of  similar  stimuli  are  fused 
than  when  one  of  the  stimuli  is  allowed  to  produce  its  maximum 
effect. 

Jf  the  time  of  each  stimulus  is  equal  to  the  interval  during  which 


938  A    MANUAl    OF  PHYSIOLOGY 

there  is  no  stimulation,  tin-  sensation,  when  complete  fusion  lias  been 
reached,  is  the  same  as  would  be  produced  by  a  constant  light  of 
half  the  strength  employed.  And.  in  general,  if  m  be  the  proportion 
ot  the  time  during  which  the  eye  is  stimulated  by  a  light  of  intensity 
/.  and  //  the  proportion  of  the  time  during  which  it  is  not  stimulated. 
the  resultant  impression  is  the  same  as  that  which  would  be  produced 

by  an  uninterrupted  light  of  intensity   (  V.     This  is  Talbot's 

law,  which  may  be  expressed  without  the  aid  of  symbols  thus  :  When 
a  light  of  given  intensity  is  allowed  to  act  on  the  eye  at  intervals  so  short 
that  the  impressions  are  completely  fused,  the 
resultant  sensation  is  independent  of  the  abso- 
lute length  of  each  flash,  and  is  proportional 
only  to  the  fraction  of  the  whole  time  which  is 
occupied  by  flashes  and  to  the  intensity  of  the 
light.  Talbot's  law  may  be  readily  demon- 
strated by  means  of  a  rotating  disc  with  alter- 
nate white  and  black  sectors  (Fig.  412), 
arranged  that  the  same  proportion  of  the  cir- 
cumference of  each  of  the  three  concentric 
zones  is  black. 

pIG    .I2 Disc  for  de-         When  the  rotation  is  sufficiently  rapid  to 

monstratingTalbot's     give  complete  fusion  (say  20  to  30  times  a 
Law.  second),  the  whole  disc  appears  equally  bright. 

However  much  the  rate  of  rotation  is  now- 
increased,  no  further  change  occurs.  It  has  been  shown  that  even 
for  stimuli  as  short  as  the  KoocnTooth  of  a  second,  repeated  at  intervals 
of  ,:,,th  second,  Talbot's  law  holds  good.  So  that  not  only  does 
a  flash  so  inconceivably  brief  affect  the  retina,  but  it  sets  up  changes 
which  last  for  a  measurable  time.  For  intense  stimuli  Talbot's  law 
ceases  to  be  true  :  the  field  appears  brighter  than  it  should  be 
(Grunbaum) . 

Two  chief  theories  have  been  proposed  to  account  for  the  fusion  of 
intermittent  retinal  stimuli  :  (1)  The  persistence  theory,  according  to 
which  the  excitatory  process  in  the  retina  remains  for  a  short  time 
at  the  maximum  reached  when  the  light  ceases  to  act.  Steady 
fusion  is  supposed  to  be  obtained  when  the  interval  between  succes- 
sive stimuli  does  not  exceed  this  time.  (2)  The  theory  of  Fick,  who 
maintains  that  as  soon  as  the  light  is  withdrawn  the  retinal  excitation 
begins  to  sink,  at  first  rapidly,  then  more  gradually.  As  the  rate  of 
stimulation  is  increased  the  time  allowed  for  the  decline  of  the 
excitation  is,  of  course,  correspondingly  shortened,  and  ultimately 
the  oscillations  become  so  small  that  a  continuous  smooth  sensation 
results.     Fick's  theory  appears  to  explain  the  phenomena  best. 

The  experiments  of  Charpentier  have  shown  that  the  retina  when 
stimulated  has  a  natural  tendency  to  enter  into  oscillations  at  the 
rate  of  about  36  in  the  second,  so  that  the  effect  of  a  flash  of  light 
when  it  falls  on  a  retinal  area  is  not  a  single  excitation  which  rises 
smoothly  to  its  maximum  and  then  declines  fmoothly  to  zero,  but  a 
series  of  swings  which  die  away  like  the  vibrations  of  an  elastic  body. 
This  may  be  demonstrated  bv  slowly  rotating  a  well-illuminated  disc, 
one  quadrant  of  which  is  white  and  the  rest  black,  while  the  eyi 
kept  fixed  on  the  centre.  A  black  band,  or  rather  sector,  running 
out  from  centre  to  circumference,  will  be  seen  in  the  white  quadrant 
a  little  behind  the  border  of  it  which  first  passes  the  eye.  This 
band  may  be  succeeded  by  one  or  more  fainter  black  bands  placed  at 


THE  SENSES  939 

regular  intervals  m  the  white  portion  of  the  disc.     The  explanation  is 

tins.  At  the  moment  when  the  image  of  the  advancing  edge  of  the 
white  quadrant  Calls  upon  the  retina  it  is  excited,  and  we  get  the 
sensation  of  white.  Then  comes  a  swing  in  the  opposite  direction 
which  gives  rise  to  the  first  black  band,  and  succeeding  swings  cause 
the  other  bands.  The  period  of  the  oscillatory  process  can  be 
calculated  from  the  speed  of  the  disc,  and  the  distance  of  the  first 
band  from  the  edge  of  the  white  quadrant.  The  well-known  fact 
that  a  single  flash  of  lightning,  or  other  intense  stimulus,  may  appear 
as  two  flashes,  finds  its  explanation  in  these  retinal  oscillations. 

Colour  Vision. — Besides  differences  in  the  distance,  size, 
shape,  and  brightness  of  objects,  the  eye  recognises  differences 
in  their  colour  ;  and  we  have  now  to  consider  the  physical  and 
physiological  differences  on  which  these  depend. 

Colours  may  differ  from  each  other — (i)  In  tone  or  hue,  e.g.,  red, 
yellow,  green.  (2)  In  degree  of  saturation  or  fulness  or  purity,  i.e., 
in  the  degree  in  which  they  arc  free  from  admixture  with  white  light, 
e.g.,  a  '  pale  '  or  '  light  '  blue  is  a  blue  mixed  with  much  white  light, 
a  '  deep  '  or  '  full  '  blue  with  little  or  none.  (3)  In  brightness  or 
intensity,  i.e.,  in  the  amount  of  the  light  coming  from  unit  area  of 
the  coloured  object.  Thus,  a  '  dark  '  red  cloth  sends  comparatively 
little  light  to  the  eye,  a  '  bright  '  red  cloth  sends  a  great  deal. 

When  a  beam  of  sunlight  falls  into  the  eye,  a  sensation  of 
'  white  light  '  results.  When  a  prism  is  placed  before  the  eye, 
the  sensation  is  entirely  different  ;  we  see  a  spectrum  running 
up  from  red  through  green  to  violet,  with  a  multitude  of  inter- 
mediate shades,  the  eye  being  able  to  distinguish  in  the  solar 
spectrum  at  least  one  thousand  different  hues  (Aubert).  What, 
then,  has  happened  ?  Physically,  nothing  more  has  taken  place 
than  a  rearrangement  of  the  rays  in  the  beam  of  white  light.  A 
few  of  them  may  have  been  lost  by  reflection,  but  upon  the 
whole  the  beam  is  made  up  of  exactly  the  same  constituents  as 
before  ;  only  the  rays  are  now  arranged  in  the  precise  order  of 
their  refrangibility,  the  more  refrangible,  which  are  also  those 
of  shortest  wave-length,  being  displaced  more  towards  the  base 
of  the  prism  than  the  longer  and  less  refrangible  rays.  Instead 
of  the  long  and  short  rays  falling  together  on  the  same  elements 
of  the  retina,  as  they  did  in  the  absence  of  the  prism,  they  now 
fall,  if  proper  precautions  have  been  taken  to  secure  a  pure 
spectrum,  in  regular  order  from  one  side  to  the  other  of  the 
portion  of  retina  on  which  the  image  is  formed.  The  physical 
condition,  then,  of  our  sensations  of  the  prismatic  colours  is, 
that  rays  of  approximately  the  same  wave-length  should  fall 
unmixed  with  other  rays  upon  the  retinal  elements.  Rays  of 
a  wave-length  of  760  fijx*  to  650  /j,/x  give  the  sensation  of  red ; 
from  650  fifM  to  590  /jl/x,  the  sensation  of  orange  ;  from  430  fifi 
to  400  fx/x,  the  sensation  of  violet,  and  so  on.  When  rays  of 
*  ftp  is  a  symbol  representing  one-millionth  of  a  millimetre. 


94°  A   MANUAL  OF  PHYSTOLOGY 

all  these  wave-lengths  fall  together,  in  the  proportion  in  which 
they  are  present  in  sunlight,  upon  the  same  part  of  the  retina, 
the-  resultant  physiological  effect  is  ver}7  different  ;  we  are  no 
longer  able  to  distinguish  red,  blue,  green,  etc.  ;  we  receive 
the  single  sensation  oi  white  light.  The  sensation  is  a  simple 
one  :  in  consciousness  we  have  no  hint  that  it  has  a  multiple 
physical  cause. 

But  we  find  further  that  it  is  not  necessary  for  the  sensation 
of  white  light  that  waves  of  every  length  present  in  the  solar 
spectrum  should  be  mixed.  If  rays  of  wave-lengths  675  ufi 
(which  acting  alone  produce  the  sensation  of  red)  be  mixed  in 
certain  proportions — i.e.,  be  allowed  to  fall  on  the  same  part  of 
the  retina — with  rays  of  wave-length  496  jxy.  (which  give  the 
sensation  of  bluish-green),  the  resultant  sensation  is  also  that 
of  white  light.  And  an  indefinite  number  of  sets  can  be  com- 
bined, two  and  two,  so  as  to  give  the  same  sensation  of  white. 
Such  colours  are  called  complementary.  The  following  are 
pairs  of  complementary  colours  : 

Red  and  bluish-green.  Yellow  and  ultramarine- blue. 

Orange  and  cyan-blue.*  Greenish-yellow  and  violet. 

The  green  of  the  spectrum  has  no  simple  complementary 
colour  ;  purple,  a  colour  not  present  in  the  spectrum,  but  obtained 
by  mixing  light  from  the  two  spectral  extremes — i.e.,  by  mixing 
red  and  violet — may  be  considered  complementary  to  it.  Sup- 
pose now  that  one  of  a  pair  of  complementary  colours  is  added 
to  the  other  in  greater  intensity  than  is  required  to  give  white, 
the  resultant  sensation  is  a  colour  which  has  a  certain  amount 
of  resemblance  both  to  white  and  to  the  colour  present  in  excess. 
Thus,  if  the  two  colours  are  orange  and  blue,  and  the  blue  is 
present  in  greater  intensity  than  is  necessary  to  give  white,  the 
resultant  colour  is  a  whitish  or  pale  blue,  or,  to  use  the  technical 
phrase,  an  unsaturated  blue.  The  more  nearly  the  intensity  of 
the  blue  rays  in  the  mixed  light  approaches  the  proportion 
necessary  to  give  white,  the  less  saturated  is  the  resultant  colour  ; 
the  greater  the  excess  of  blue,  the  more  nearly  does  the  resultant 
sensation  approach  that  of  the  saturated  blue  of  the  spectrum. 
But  any  non-saturated  spectral  colour  produced  by  the  mixture 
of  two  complementary  colours  may  be  equally  well  produced  by 
the  mixture  of  the  corresponding  spectral  colour  with  a  certain 
quantity  of  ordinary  white  light.  And  it  is  found  that  when 
two  spectral  colours  which  are  not  complementary  are  mixed 
together  the  resultant  is  not  white,  but  a  colour  which  may  be 
matched  by  some  spectral  colour  lying  between  the  two  (or  by 
purple),  either  without  addition  or  plus  a  larger  or  smaller 
*  Cyan-blue  is  a  greenish-bhu'. 


/'///    SI  NSES  941 

quantity  of  ordinary  white  light.     Fr all  this  it  follows  thai 

the  retina  maj  be  excited  by  an  infinite  number  oJ  different 
physical  stimuli,  and  yet  the  resultant  sensation  may  be  the 
same.  This  leads  straight  to  the  conclusion  that  somewhere 
or  other  in  the  retino-eerebral  apparatus  simplification,  or  syn- 
thesis, of  impressions  must  take  place  ;  and  we  have  to  inquire 
what  the  simplest  assumptions  arc  which  will  explain  all  the 
phenomena.  Now,  it  is  nol  possible,  from  two  spectral  colours 
alone,  to  produce  a  sensation  corresponding  to  all  the  others. 
By  mixing  three  standard  spectral  colours,  however,  in  various 
proportions,  we  can  produce  not  only  the  sensation  of  white 
light,  but  that  of  every  colour  of  the  spectrum  (and  of  purple). 
These  statements  arc  based  on  demonstrated  facts  obtained  by 
very  numerous  experiments  on  colour  mixtures.  The  hypotheses 
framed  to  explain  the  facts  are  to  be  carefully  discriminated 
from  the  facts  themselves. 

Primary  Colours. — The  simplest  assumption  we  can  make, 
then,  is  that  there  are  three  standard  sensations,  and  that  either 
the  retina  itself  can  respond  by  no  more  than  three  distinct 
modes  of  excitation  to  the  multiplex  stimuli  of  the  luminous 
vibrations,  or  that  complex  impulses  set  up  in  the  retina  are 
reduced  to  simplicity  because  the  central  apparatus  is  capable 
of  responding  by  only  three  distinct  kinds  of  sensation.  Which 
three  sensations  we  select  as  fundamental  or  primary  is,  to  a 
certain  extent,  arbitrary.  Tick  chose  red,  green,  and  blue  ; 
most  commonly  red,  green,  and  violet  are  accepted  as  the 
primary  colours.  Red,  yellow,  and  blue,  although  so  long  con- 
sidered the  primary  colours,  from  data  yielded  by  the  mixture  of 
pigments,  will  not  do  ;  for  no  possible  combination  of  them  will 
produce  either  a  pure  green  or  white  light. 

The  Young-Helmholtz  Theory. — The  theory  which  has  been 
most  widely  accepted  is  that  of  Young,  generally  called,  on  account 
of  its  adoption  and  extension  by  Helmholtz,  the  Young-Helmholtz 
theory.  Red,  green,  and  violet  are  taken  as  the  fundamental  or 
elementary  colour  sensations.  In  its  more  modern  form  it  assumes 
that  in  the  retina,  or  in  the  retino-eerebral  apparatus,  there  are 
three  kinds  of  elements  —  (1)  a  substance  or  a  component 
chiefly  affected  by  light  of  comparatively  long  wave-length 
(red),  to  a  less  extent  by  light  of  medium  wave-length  (green), 
and  to  a  still  less  extent  by  the  shortest  visible  waves  (violet)  ; 
(2)  a  component  mainly  affected  by  medium,  but  also  to  a 
certain  extent  by  long  and  short  waves  ;  (3)  a  component  chiefly 
affected  by  the  short  vibrations,  less  by  the  medium,  and  still 
less  by  the  long  waves.  The  curves  in  Fig.  413  illustrate  these 
relations. 

The  theory  explains   as  follows  the   phenomena   of  colour- 


V(- 


/    MANUAL  OF  PHYSIOL*",) 


mixture  referred  to  above.  When  all  the  rays  oi  the  spectrum 
act  upon  the  retina  together,  the  three  components  are  about 

equally  allected,  and  this  e(]iial  effect  is  supposed  to  be  the 
condition  of  the  sensation  oi  white  light.  When  the  green  of  the 
spectrum  alone  [alls  on  the  retina,  the  '  green  '  component  is 
strongly  excited,  the  other  two  only  slightly  ;  this  is  the  relation 


Fig.  413. — Curves  of  Excitability  of  Primary  Sensations  from  Observa- 
riONS   ON  Colour   Mixtures   (Konig). 

The  numbers  give  wave-lengths  oi  the  spectrum  in  millionths  of  a  millimetre. 

between  the  amount  of  excitation  in  the  three  components 
which  is  associated  with  a  sensation  of  spectral  green.  When 
two  complementary  colours,  such  as  red  and  bluish-green,  fall 
together  on  the  same  portion  of  the  retina,  the  three  components 
are  excited  in  the  relative  proportions  associated  with  the 
sensation  of  white  light. 

The  colour  triangle  is  a.  graphic  method  of  representing  various 
facts  in  colour-mixture  (Fig.  414). 

The  chief  points  to  be  noted  are  the  following  :  (1)  On  the  cur\  e  the 

spectral  colours 
arranged  at  such  dis- 
tances that  the  angle- 
contained  between 
straight  lines  drawn 
from  the  point  marked 
'  white,'  and  inter- 
secting the  curve  at 
the  positions  corre- 
sponding to  any  two 
coloursis  proportional 
to  their  difference  in 
tone.  (2)  The  ihs- 
Umce  of  any  point  of 
the  curve  from  the  point  marked  '  white  '  is  proportional  to  the 
stimulation  intensity  of  the  colour  corresponding  to  it.  (If  the 
stimulation  intensities  of  all  the  colours  be  represented  by  propor- 


Green 
Cyan  Blu  es^       N 

~\^\0ran^e 

/^ 

Vina              Purru 

Fig.  414. — Colour  Triangle. 


Till    SENSES  943 

tional   weights   Lying   at    the   corresponding   points  on   the  cuivc, 
the  point    'white'   will   be  the  centre  of  gravity  oi  the  system 
(3)  The  position  oi  a  colour  produced  by  the  mixture  oi  any  pair 

oi  spectral  colours  is  found  by  joining  the  corresponding  points  by 
.1  straight  line.  The  mixed  "colour  lies  on  this  line  at  distances 
from  the  two  points  inversely  proportional  to  the  stimulation 
intensity  <>i  the  two  colours  i.e.,  it  lies  in  the  centre  of  gravity 
of  the  weights  representing  the  two  colours.  (4)  It  is  a  particular 
case  oi  (3)  that  the  complementary  colours  are  situated  at  the  pomls 
where  straight  lines  drawn  through  '  white  '  intersect  the  curve, 
since  the  point  marked  '  white  '  is  the  centre  of  gravity  corresponding 
to  a  pair  oi  colours  only  when  it  lies  on  the  straight  line  joining  them. 
Thus  the  orange  and  yellow  lying  between  the  red  and  green  are 
mixtures  of  the  red  and  green  sensations  in  different  proportions  ; 
the  cyan-blue  and  indigo-blue  are  mixtures  of  the  green  and  violet 
sensations.  The  purples,  represented  by  a  broken  line,  are  not 
present  in  the  spectrum,  and  are  mixtures  of  red  and  violet. 

It  is  a  point  of  great  theoretical  interest  that  oil  the  Young- 
Helmholtz  theory  the  pure  spectral  colours,  although  physically 
saturated  {i.e.,  due  to  ethereal  vibrations  of  a  definite  wave-length 
for  each  colour),  ought  not  to  be  physiologically  saturated,  since  'they 
all  affect  the  three  components,  although  in  different  degrees.  In 
other  words,  the  red,  let  us  say,  of  the  spectrum  ought  not  to  be  the 
purest  or  fullest  red  which  ii  is  possible  to  perceive.  Now,  it  is 
found  that  this  is  really  the  case.  If,  for  example,  we  look  first  at 
the  bluish-green,  and  then  at  the  red  of  the  spectrum,  the  sensation 
of  red  is  fuller  or  more  saturated  than  if  we  had  looked  at  the  red 
directly.  Similarly,  if  we  look  first  at  a  small  bluish-green  square 
on  a  black  ground,  and  then  at  a  red  ground,  we  see  a  more  fully 
saturated  square  in  the  middle  of  the  latter.  The  explanation,  on 
the  Young-Helmholtz  theory,  is  that  the  '  green  '  component,  being 
fatigued  before  the  eye  is  turned  upon  the  red,  the  latter  colour  no 
longer  affects  it,  or  affects  it  less  than  it  would  otherwise  do,  and 
therefore  the  excitation  is  almost  entirely  confined  to  the  red  com- 
ponent in  the  area  fatigued  for  green.  This  brings  us  to  the  subject 
of  retinal  fatigue,  and  the  related  phenomena  of  after-images  and 
contrast. 

After-images. — We  have  seen  that  the  retinal  excitation  always 
takes  time  to  die  away  after  the  stimulus  is  removed.  If  a  white 
object  is  looked  at,  especially  when  the  eye  is  fresh,  for  a  time  not 
long  enough  to  cause  fatigue,  and  the  eye  is  then  closed,  an  image 
of  the  object  remains  for  a  short  time,  diminishing  in  brightness  at 
first  rapidly,  then  more  slowly.  This  is  a  positive  after-image,  and 
by  careful  observation  it  may,  under  certain  conditions,  be  seen 
that  the  positive  after-image  of  a  white  object,  of  a  slit  illuminated 
by  sunlight,  for  example,  undergoes  changes  of  colour  as  it  fades, 
passing  through  greenish-blue,  indigo,  violet,  or  rose,  to  dirty  orange. 
On  the  Young-IJelmholtz  theory  this  is  explained  by  the  supposition 
that  the  excitation  does  not  decline  with  the  same  rapidity  in  the 
three  hypothetical  components.  If  the  object  is  looked  at  for  a 
longer  time,  or  if  the  eye  is  fatigued,  a  dark  or  negative  image  may 
be  seen  upon  the  faintly-illuminated  ground  of  the  closed  eyes  ; 
but  negative  after-images  may  be  more  easily  obtained  when  the 
eye,  after  being-  made  to  fix  a  small  white  object  on  a  black  ground, 
is  suddenlv  turned  upon  a  white  or  neutral  tint  surface. 

Here  Helmholtz  supposed  the  portion  of  the  retina  on  which  the 


944  I     1/  INV  IL  OF  PHYSIOLOG  J 

image  of  the  objecl  Is  formed  to  be  more  or  less  fatigued.  And  tins 
fatigue  will  extend  to  all  three  kinds  of  fibres;  so  that  white  1  i^fit 
"i  a  given  intensity  will  now  cause  less  excitation  in  this  part  than 
in  the  rest  of  the  retina.  1 1  is  easy  to  understand  thai  the  negative 
after-image  oi  a  coloured  objecl  will  be  seen,  upon  a  white  ground, 
in  the  complementary  colour,  for  the  components  chiefly  excited 
by  the  latter  will  have  been  least  fatigued.  The  negative  after- 
images seen  when  the  eye,  alter  receiving  the  positive  impression,  is 
turned  upon  a  coloured  ground,  vary  with  the  colour  of  the  objecl 
and  ground  in  a  manner  which  has  been  explained  as  due  to  fatigui 
of  one  or  other  component.  It  is  difficult,  however,  to  reconcile  the 
fatigue  hypothesis  of  the  after-image  with  all  the  tacts.  Hering 
supposes  thai  the  retina  is  not  passively  fatigued,  but  that  a  meta- 
bolic change  is  set  up  in  it  which  is  of  the  opposite  kind  to  that 
caused  by  the  original  excitation  (see  p.  945). 

I  he  phenomena  of  negative  after-images  are  often  included 
together  as  examples  of  successive  contrast,  the  name  implying 
mutual  influence  of  the  portions  of  the  retina  (or  retino-cerebral 
apparatus)  successively  stimulated.  We  have  now  to  consider 
simultaneous  contrast,  often  spoken  of  simply  as  contrast. 

Contrast.  -A  small  white  disc  in  a  black  field  appears  whiter,  and 
a  small  black  disc  in  a  white  field  darker,  than  a  large  surface  of 
exactly  the  same  objective  brightness.  A  disc  with  alternate  sectors 
of  white  and  black,  so  arranged  that  the  proportion  of  white  to  black 
increases  in  each  zone  from  centre  to  circumference,  when  set  in 
rotation,  ought,  by  Talbot's  law,  to  show  sharply  marked  and  uni- 
form rings,  of  which  each  is  brighter  than  that  internal  to  it.  But 
1  .eh  /one  appears  brightest  at  its  inner  edge,  where  it  borders  on  a 
/one  darker  than  itself,  and  darkest  at  its  outer  edge,  where  it  borders 
on  a  brighter  zone.  A  plausible  explanation  of  this  is  based  on  the 
assumption  that  in  the  neighbourhood  of  an  excited  area  of  the 
retina,  as  well  as  within  the  area  itself,  the  excitability  is  diminished  ; 
and  the  same  explanation  has  been  extended  to  the  contrast  pheno- 
mena of  coloured  objects.  A  small  piece  of  grey  paper,  e.g.,  is  placed 
on  a  green  sheet.  The  grey  patch  appears  in  the  complementary 
colour  of  the  ground — viz.,  pink  or  rose -red  (Meyer).  The  red  colour 
is  much  stronger  if  the  whole  is  covered  with  translucent  tracing- 
paper.  Here  we  may  suppose  that  the  fatigue  of  the  substance  or 
component  chiefly  affected  by  the  ground  colour  spreads  into  the 
portion  of  the  retina  occupied  by  the  image  of  the  grey  paper  ;  the 
white  light  coming  from  the  latter,  therefore,  affects  mainly  the 
component  connected  with  the  sensation  of  the  complementary  colour. 

The  curious  phenomenon  of  coloured  shadows  is  also  an  illustration 
of  cont  rast  .  They  may  be  produced  in  various  ways.  For  example, 
when  a  lamp  is  lit  in  a  room  in  the  twilight,  before  it  has  yet  grown 
too  dark,  the  shadows  cast  by  opaque  objects  on  a  white  window- 
blind  are  coloured  blue.  The  yellow  light  of  the  lamp  overpowers 
the  feeble  daylighl  which  passes  through  the  blind,  and  the  general 
ground  is  yellowish  ;  but  wherever  a  shadow  is  thrown  it  appears  of 
a  bluish  tint  in  contrast  to  the  yellow  ground.  Here  the  only  illu- 
mination the  eve  receives  from  the  region  occupied  by  the  shadow  is 
the  feeble  daylight.  Falling  upon  an  area  in  which  the  component 
chiefly  affected  by  yellow  rays  is  more  or  less  fatigued,  it  causes  a 
sensation  of  the  complementary  colour.  As  darkness  comes  on,  the 
shadows  become  black,  for  now  practically  no  light  at  all  comes  from 
them. 


THE  si  \si  S  94S 

Helmholtz  looked  upon  simultaneous  contrasl  as  a  resull  oi  falsi 
judgment,  and  no1  of  a  change  of  excitability  in  parts  oi  the  retina 
bordering  on  the  actually  excited  parts.  For  the  sake  of  perspective, 
it  will  he  wort h  while  to  apply  this  t heory  by  way  of  illustrating  it.  to 
the  explanation  of  the  case  oJ  contrasl  we  have  jusl  been  consider- 
ing, from  the  other  point  oi  view,  in  Meyer's  experiment.  Helm- 
holtz's  explanation  oi  this  experiment  is  .is  follows  :  When  a  coloured 
surface  is  covered  with  transluceni  paper,  the  latter  appears  as  a 
coloured  covering  spread  over  the  field.  The  mind  docs  not  recog- 
nise th.it  at  the  grey  patch  there  is  any  breach  of  continuity  in  this 
covering  ;  it  is  therefore  assumed  thai  the  greenish  veil  extends  over 
this  spot  too.  Now,  the  grey  seen  through  the  translucent  white 
paper  is  objectively  white  i.e.,  sends  to  the  eye  the  vibrations 
which  together  would  give  the  sensation  of  white  light.  But  with  a 
green  veil  in  front  of  it.  this  could  only  happen  if  the  really  grey 
patch  was  the  colour  complementary  to  green — that  is,  rose-red. 
The  mind,  therefore,  judges  falsely  that  the  patch  is  red.  Hering 
has  severely  criticised  this  theory  of  Helmholtz  as  to  false  judgments  ; 
and  the  weight  of  evidence  certainly  seems  to  be  in  favour  of  the 
view  that  simultaneous,  like  successive,  contrast  is  due  to  the  influence 
of  one  portion  of  the  retina,  or  rctino-cerebral  apparatus,  on  another. 

Hering's  Theory  of  Colour  Vision. — The  Young-Helmholtz 
theory  of  colour  vision  has  not  met  with  universal  acceptance. 
The  best-known  rival  theory  is  that  of  Hering,  who  takes  his 
stand  upon  the  fact  that  certain  visual  sensations  (red,  yellow, 
green,  blue,  white,  black)  do  appear  to  us  to  be  fundamentally 
distinct  from  each  other,  while  all  the  rest  are  obviously  mixtures 
of  these.  Accepting  these  six  as  primary  sensations,  he  assumes 
the  existence  in  the  visual  nervous  apparatus  of  substances 
of  three  different  kinds,  which  may  be  called  the  black-white, 
the  green-red,  and  the  blue-yellow.  Like  all  other  constituents 
of  the  body,  these  substances  are  broken  down  and  built  up 
again — in  other  words,  undergo  disassimilation  and  assimilation, 
destructive  and  constructive  metabolism.  The  sensations  of 
black,  of  green,  and  of  blue  he  supposes  to  be  associated  with 
the  constructive,  and  the  sensations  of  white,  of  red,  and  of 
yellow  with  the  destructive,  processes  in  the  three  substances. 
The  black-white  substance  is  used  up  under  the  influence  of  all 
the  rays  of  the  spectrum,  but  in  different  degrees  ;  the  smaller 
the  quantity  of  light  falling  on  the  retina,  the  more  rapidly  is  it 
restored,  and  the  more  intense  is  the  sensation  of  black.  The 
green-red  substance  is  built  up  by  green  rays,  broken  down  by 
red.  The  blue-yellow  substance  is  destroyed  by  yellow  rays, 
restored  by  blue.  A  prominent  difference  between  this  and  the 
Young-Helmholtz  theory,  and,  so  far  as  it  goes,  an  advantage, 
is  that  Hering's  theory  attempts  to  assign  a  direct  objective 
cause  for  the  visual  sensations  of  white,  black,  and  yellow,  as 
well  as  for  red,  green,  and  blue,  instead  of  making  the  sensations 
depend  upon  the  magnitude  of  the  stimulation  process.  When 
any  of  the  visual  substances  are  consumed  at  one  part  of  the 

60 


946 


A   MANUAL  OF  PHYSIOLOGY 


retina,  they  are  supposed  to  be  more  rapidly  built  up  in  the  sur- 
rounding parts,  and  in  this  way  many  of  the  phenomena  of 
simultaneous  contrast  receive  an  easy  and  natural  explanation. 
The  same  is  true  of  the  simpler  phenomena  of  after  images  or 
successive  contrast.  But  in  applying  the  theory  to  the  more  com- 
plicated phenomena  difficulties  soon  emerge,  which,  to  say  the 
least,  are  not  less  formidable  than  those  connected  with  the 
Young-Helmholtz  theory.  Neither  theory,  in  short,  can  be 
considered  more  than  a  partially  successful  attempt  to  grapple 
with  a  very  complex  mass  of  facts.  Each,  however,  has  been 
fruitful  in  leading  to  the  discovery  of  new  facts — a  great  merit 
in  a  scientific  hypothesis. 

Sensibility  of  Different  Parts  of  the  Retina — Perimetry.— 

The  perception  of 
colours,  like  the  per- 
ception of  white  light, 
is  not  equally  distinct 
over  the  whole  retina. 
We  have  repeatedly 
had  occasion  to  refer 
to  the  fovea  centralis 
as  the  region  of  most 
distinct  vision  ;  but  it 
would  be  a  mistake  to 
suppose  that  it  is 
therefore  necessarily 
more  sensitive  than 
the  rest  of  the  retina. 
As  a  matter  of  fact, 
when  the  minimum 
intensity  of  white  light 
which  will  cause  an 
impression  at  all  is 
determined  for  each 
portion  of  the  retina, 
it  is  found  that  the 
fovea  centralis  requires  a  somewhat  stronger  stimulus  than  the 
zone  immediately  surrounding  it.  Objects  only  a  little  brighter 
than  the  general  ground  on  which  they  lie — e.g.,  very  faint  stars — 
are  best  seen  when  the  eye  is  directed  a  little  to  one  side.  This 
lias  been  attributed  to  the  absence  of  visual  purple  from  the 
fovea,  in  accordance  with  the  theory  previously  alluded  to  that 
the  visual  purple  acts  as  a  mechanism  which  '  adapts  '  the  retina 
for  the  perception  of  light  of  varying  intensity.  But,  with 
this  exception,  the  sensibility  of  the  retina  diminishes  steadily 
from  centre  to  periphery,  both  for  white  and  for  coloured  light. 


Fig.  415. — Priestley  Smith's  Perimeter. 

A',  rest  for  chin  ;  0,  position  of  eye  ;  Ob,  object, 
white  or  coloured,  which  slides  on  the  graduated 
arc  B  ■.  f,  point  fixed  by  the  eye. 


THE  SENSES 


947 


When  the  eye  is  fixed,  and  the  visual  field — that  is,  the  whole 
space  from  which  lighl  ran  reach  the  retina  in  the  given  position, 
ro,  what  comes  to  the  same  thing,  the  projection  of  the  visual 
field  on  the  retina  by  straight  lines  passing  through  the  nodal 
point — explored  by  means  of  a  perimeter  (Figs.  415,  416),  it  is 
found  that,  under  ordinary  conditions,  a  white  object  is  seen 
over  a  wider  field  than  any  coloured  object,  a  blue  object  over  a 
wider  field  than  a  red,  and  a  red  over  a  wider  field  than  a  green 


xn 


Fig.  416. — Perimetric  Chart  of  Right  Eye  (after  Hirschberg). 
The  numbers  represent  degrees  of  the  visual  field  measured  on  the  graduated  arc 
of  the  perimeter,  w,  boundary  of  field  for  white  object  ;  b,  for  blue  ;  r,  for  red  ; 
g,  for  green  ;  in,  blind  spot  ;  M,  medial,  and  L,  lateral  side  of  the  field  of  vision! 
The  Roman  numbers  represent  twelve  meridians  of  the  retina,  each  making  an 
angle  of  30  with  the  next.  They  fix  the  'longitude'  of  any  point  in  the 
field.  The  concentric  circles  indicated  by  Arabic  numbers  represent  angular 
distances  from  the  fixation  point  in  the  planes  of  these  meridians.  They  give  the 
'  latitude  '  of  any  point. 

object.  The  exact  shape,  as  well  as  size,  of  the  visual  field  also 
differs  somewhat  for  different  colours.  In  disease  of  the  retina, 
or  of  the  visual  path  between  it  and  the  cortex,  or  of  the  visual 
cortex  itself,  the  abridgment  of  the  field  for  white  and  for 
monochromatic  light  as  mapped  out  by  observations  with  the 
perimeter  is  often  of  value  in  diagnosis.  Although  it  has  been 
shown  by  Aubert  and  others  that  monochromatic  light  of  con- 
siderable intensity  can  be  perceived  over  the  whole  retina,  yet 

60 — 2 


948  A   MANUAL  OF  PHYSIOLOGY 

it  may  be  said  that  the  retinal  rim  is  even  then  relatively  and, 
under  ordinary  conditions,  absolutely,  colour-blind.  This  and 
other  facts  have  given  rise  to  the  theory  (p.  935)  that  the  rods, 
which  are  alone  present  at  the  ora  serrata,  are  concerned  in 
achromatic  vision  (under  conditions  of  dark  adaptation),  tin- 
cones  in  colour  vision  as  well  as  in  achromatic  vision  (undei 
daylight  conditions). 

This  brings  us  to  the  subject  of  colour-blindness,  a  pheno- 
menon of  great  interest  in  its  theoretical  as  well  as  in  its  practical 
bearings. 

Colour-blindness. — A  considerable  number  of  persons  (about 
4  per  cent,  of  all  males,  but  only  one-tenth  of  this  proportion 
of  females)  are  deficient  in  the  power  of  distinguishing  between 
certain  colours.  They  are  said  to  be  colour-blind  ;  but  the 
term  must  not  be  taken  to  signify  that  they  are  absolutely 
devoid  of  colour-sensations.  A  very  small  minority  of  the 
colour-blind  appear  to  have  but  one  sensation  of  colour  tone, 
everything  appearing  as  white,  grey,  or  black  (total  colour- 
blindness, sometimes  called  monochromatic  vision).  All  colours 
are  confused  by  them,  but  differences  of  brightness  are  correctly 
appreciated.  Probably  the  totally  colour-blind  person  receives 
somewhat  the  same  impressions  from  a  coloured  picture  as  the 
normal  person  does  from  a  reproduction  of  the  same  picture  in 
black-and-white.  There  are  close  resemblances  between  the 
vision  of  the  totally  colour-blind  eye  and  that  of  the  normal 
eye  adapted  by  resting  in  the  dark  for  twilight  vision.  The 
fovea  is  relatively,  and  in  some  cases  absolutely,  insensitive  to 
light,  while  the  peripheral  portion  of  the  retina  is  normal,  or 
nearly  normal,  in  this  regard.  This  is  the  foundation  of  the  theory 
that  in  total  colour-blindness  the  cones  are  devoid  of  their  normal 
functions,  and  that  the  hypothetical  mechanism  for  twilight 
vision  (the  rods)  is  functioning  alone.  In  another  condition 
(night-blindness,  or  hemeralopia)  it  is  sometimes  assumed  that 
the  other  mechanism  (that  of  the  cones)  which  is  adapted  for 
daylight  vision,  and  has  little  power  of  dark-adaptation,  is  alone 
acting.     But  it  cannot  be  said  that  this  has  been  proved. 

The  rest  of  the  colour-blind  are  dichromatic — i.e.,  their  colour 
reactions  seem  to  correspond  only  to  two  of  the  fundamental 
colour  sensations  of  the  normal  person  and  their  combinations, 
in  addition  to  white.  Of  the  dichromates  a  very  few  confuse 
blue  with  yellow.  The  great  majority  are  unable  to  distinguish 
between  red  and  green.  The  condition  will  be  most  easily 
understood  by  considering  some  of  the  extraordinary  mistakes 
which  may  be  made  by  the  colour-blind,  without  necessarily 
leading  them  to  suspect  that  there  is  anything  abnormal  in  their 
vision.     Thus,  to  quote  the  words  of  a  distinguished  writer  on 


THE  SENSES  949 

tin-  subject,  himseU  .1  suffere]  from  the  deficiency:  'A  naval 
officer  purchases  red  breeches  to  match  his  blue  uniform  ;  a 
tailor  repairs  a  black  article  o\  dress  with  crimson  cloth  ;  a 
painter  colours  trees  red,  the  sky  pink,  and  human  cheeks  blue.' 
The  shoemaker,  Harris,  the  discoverer  of  colour-blinds 
picked  up  a  stocking,  and  was  surprised  to  hear  other  people 
describe  it  as  a  red  stocking  ;  it  seemed  to  him  only  a  stocking. 
The  celebrated  Dalton  was  twenty-six  years  of  age  before  he 
knew  that  he  was  colour-blind.  He  matched  samples  of  red, 
pink,  orange,  and  brown  silk  with  green  of  different  shades  ; 
blue  both  with  pink  and  with  violet  ;  lilac  with  grey. 

When  the  condition  of  vision  in  dichromates  is  tested  by  means  of 
the  spectrum,  it  is  found  that  they  fall  into  two  classes  :  (1)  A  class 
(of  green-blind)  by  whom  the  whole  of  the  spectrum  from  red  to 
yellow  is  described  as  yellow  of  different  degrees  of  brightness  (inten- 
sitvi  ;  the  green  appears  as  a  pale  yellow  with  a  grey  or  white  band 
in  its  midst  ;  while  tin-  violet  end  is  .seen  as  different  shades  of  blue. 
(2)  A  class  (of  red-blind)  whose  whole  spectrum,  from  red  to  green, 
is  seen  as  green  of  different  intensities,  the  extreme  red  being  entirely 
invisible.  The  violet  end  is  blue,  as  in  (1),  and  there  is  a  band  of 
white  or  grey  near  the  blue  end  of  the  green. 

Sir  John  Herschcll  explained  Dalton's  peculiarity  of  vision  on  the 
hypothesis  that  he  only  possessed  two,  instead  of  three,  primary 
sensations. 

On  the  Young-Helmholtz  theory,  the  missing  sensation  is  supposed 
to  be  either  red  or  green.  At  the  intersection  of  the  curves  that 
represent  the  violet  and  green  sensations  (Fig.  413),  the  red-blind 
individual  will  sec  what  he  describes  as  white — viz.,  the  sensation 
produced  by  the  stimulation  of  the  only  two  components  he  pos- 
sesses. Similarly,  at  the  intersection  of  the  red  and  violet  curves 
the  green-blind  person  will  see  what  is  white  to  him. 

Those  who  have  attempted  to  explain  colour-blindness  on  Hering's 
theorv  have  usually  assumed  that  the  colour-blind  possess  the  blue- 
yellow,  but  lack  the  green-red  visual  substance.  So  that  on  this 
theory  there  should  be  no  difference  between  red-blindness  and  green- 
blindness.  But  v.  Krics.  in  a  study  of  twenty  cases  of  congenital 
partial  colour-blindness,  brings  forward  strong  evidence  that  the 
red-green  blind  can  be  divided,  as  regards  the  comparison  of  red 
(lithium)  and  orange  (sodium)  light,  into  two  sharply-separated 
groups — a  residt  which  is,  so  far  as  it  goes,  in  favour  of  the  Young- 
Helmholtz  theory,  and  against  the  theory  of  Hering. 

The  observations  of  Burch  on  temporary  colour-blindness  pro- 
duced by  placing  the  eye  behind  a  transparent  coloured  screen  and 
focussing  a  beam  of  strong  sunlight  on  it,  lend  additional  support 
to  the  former  theory.  Thus,  if  a  spectrum  is  looked  at  after  green- 
blindness  has  been  induced  by  exposure  of  the  eye  to  green  light, 
the  red  portion  of  the  spectrum  seems  to  pass  into  the  blue,  and  no 
intermediate  green  band  is  seen.  If  the  eye  is  exposed  to  yellow- 
light  it  becomes  temporarily  blind  not  only  for  yellow,  but  also  for 
red  and  green.  This  is  in  favour  of  the  assumption  of  the  Young- 
Helmholtz  theory  that  the  sensation  of  yellow  is  caused  when  the 
retinal  elements  concerned  in  the  production  of  the  sensations  of 
red    and    green    are    simultaneously    stimulated.       It    is,    however, 


950  A   MANUAL  OF  PHYSIOLOGY 

equally  difficult  to  reconcile  some  of  the  phenomena  of  colour- 
blindness with  the  Ybung-Helmholtz  theory.  Anomalies  and  defet  1 3 
of  colour-sensation  are  common  accompaniments  of  pathological 
lesions  of  the  visual  apparatus,  and  can  be  produced  by  various  drugs, 
as  by  abuse  of  tobacco.  But  colour-blindness,  in  its  true  sense,  is 
congenital,  often  hereditary  ;  the  colour-blind  are  '  born,  not  made.' 
And  although  the  condition  cannot  be  cured,  it  is  of  great  importance 
that  it  should  be  recognised  in  the  case  of  persons  occupying  posi- 
tions such  as  those  of  engine-drivers,  railway-guards,  and  sailors,  in 
which  coloured  lights  have  to  be  distinguished.  For,  while  it  is  true 
that  the  sensations  which  red  and  green  lights  give  the  colour-blind 
are  far  from  being  identical  (Pole)  under  favourable  conditions,  it  is 
precisely  when  the  conditions  are  unfavourable — as  in  a  fog  or  a 
snow-storm — that  the  capacity  of  distinguishing  them  becomes 
invaluable  (Practical  Exercises,  p.  998). 

Irradiation. — The  phenomenon  known  as  irradiation  was  first 
described  by  Kepler,  who  gave  as  an  example  the  appearance  known 
as  the  '  new  moon  in  the  old  moon's  arms.'  where  the  crescent  of  the 
new  moon  seems  to  overlap  and  embrace  the  unilluminated  portion 
of  the  lunar  disc.  A  white  circle  on  a  black  ground  (Fig.  417)  appears, 
in  a  good  light,  to  be  larger  than  an  exactly  equal  black  circle  on  a 
white  ground.  The  explanation  is  as  follows  :  Owing  to  the  aberra- 
tion of  the  refractive  media  of 
the  eye  (p.  912),  all  the  rays 
proceeding  from  the  luminous 
object  are  not  brought  accu- 
rately to  a  focus  on  the  retina, 
and  the  image  is  surrounded 
by  diffusion  circles  (p.  912) 
which  encroach  upon  the  un- 
illuminated boundary.  Physi- 
Fig.  417.  cally  these  represent  a  weaker 

illumination  than  that  of  the 
image  proper,  and  therefore  the  latter  ought  to  stand  out  in  its  real 
size  as  a  brighter  area  surrounded  by  weaker  haloes.  That  this  is 
not  the  case,  and  that  the  image  is  projected  in  its  full  brightness  for 
a  certain  distance  over  its  dark  boundary,  is  due  to  the  fact  that 
the  eye  does  not  recognise  very  small  differences  of  brightness.  When 
the  accommodation  is  not  perfect,  the  diffusion  circles  are,  of  course, 
much  wider,  and  irradiation  is  better  marked  when  the  object  is  a 
little  out  of  focus. 

Visibility  of  Radium  and  Rontgen  Rays. — It  is  a  question  of  interest 
whether  the  retina  can  be  excited  by  any  other  disturbances  in  the 
ether  than  ordinary  light  waves.  The  Rontgen  rays  seem  to  be 
capable  of  exciting  visual  sensations,  and  it  is  certain  that  this  is  true 
of  the  rays  or  the  emanation  given  off  by  radium.  If  in  the  dark  a 
vessel  containing  a  radium  salt  is  brought  into  the  neighbourhood 
of  the  closed  eyelids  or  the  temple,  a  sensation  of  brightness  is  ex- 
perienced. This,  however,  is  not  due  to  direct  excitation  of  the 
retina  by  the  radium  rays,  but  to  the  phosphorescence  set  up  W 
the  media  of  the  eye  by  the  radium  emanation.  Of  all  the  tissues 
the  lens  is  most  strongly  phosphorescent  after  exposure  to  radium 
In  blindness  due  to  opacity  of  the  media,  where  the  retina  is  still 
sensitive,  the  radium  action  is  perceived,  but  not  where  the  retina 
is  totally  insensitive  to  ordinary  light.  The  radium  rays  do  not 
cause  bleaching  of  the  visual  purple 


THE  SENSES  951 

The  Movements  of  the  Eyes.  That  the  eyes  may  be  efficient 
instruments  of  vision,  it  is  necessary  that  they  should  have  the 
power  of  moving  independently  of  the  head.  An  eye  which 
could  not  move,  though  certainly  better  than  an  eye  which  could 
not  see,  would  yet  be  as  imperfect  after  its  kind  as  a  ship  which 
could  run  before  the  wind,  but  could  not  tack.  The  mere  fact 
that  the  angle  between  the  visual  axes  must  be  adapted  to  the 
distance  of  the  object  looked  at  renders  this  obvious  ;  and  the 
beauty  of  the  intrinsic  mechanism  of  the  eyeball  has  its  fitting 
complement  in  the  precision,  delicacy,  and  range  of  movement 
conferred  upon  it  by  its  extrinsic  muscles. 

Not  only  are  movements  of  convergence  and  divergence  of 
the  eyeballs  necessary  in  accommodating  for  objects  at  different 
distances,  but  without  compensatory  movements  of  the  eyes 
it  would  be  impossible  to  avoid  diplopia  with  every  movement 
of  the  head  ;  for  the  images  of  an  object  fixed  in  one  position  of 
the  head  would  not  continue  to  fall  on  corresponding  points  of 
the  retinae  in  another  position. 

All  the  complicated  movements  of  the  eyeball  may  be  looked 
upon  as  rotations  round  axes  passing  through  a  single  point, 
which  to  a  near  approximation  always  remains  fixed,  and  is 
situated  about  177  mm.  behind  the  centre  of  the  eye. 

The  position  which  the  eyeballs  take  up  when  the  gaze  is  directed 
to  the  horizon,  or  to  any  distant  point  at  the  level  of  the  eyes,  is 
called  the  primary  position.  Here  the  visual  axes  are  parallel,  and 
the  plane  passing  through  them  horizontal.  While  the  head  remains 
fixed  in  this  position,  the  eyeballs  can  rotate  up  or  down  around  a 
horizontal  axis,  or  from  side  to  side  around  a  vertical  axis  ;  or 
upwards  and  inwards,  downwards  and  outwards,  downwards  and 
inwards,  and  upwards  and  outwards  around  oblique  axes,  which 
always  lie  in  the  same  plane  as  the  vertical  and  horizontal  axes  of 
rotation — i.e.,  in  the  vertical  plane  passing  through  the  fixed  centre 
of  rotation.  These  facts,  spoken  of  collectively  as  Listing's  law, 
and  first  deduced  by  him  from  theoretical  considerations,  were 
afterwards  proved  experimentally  by  Helmholtz  and  Donders.  It 
necessarily  follows  from  Listing's  law  (and  this  is,  indeed,  another 
way  of  stating  it)  that  in  moving  from  the  primary  position  into  any 
other,  there  is  no  rotation  of  the  eyeball  round  the  visual  axis — no 
wheel-movement,  as  it  is  called. 

A  true  rotation  of  the  eye  round  the  visual  axis  does,  however, 
occur  when  the  eyes  are  converged  as  in  accommodation  for  a  near 
object,  each  eyeball  rotating  towards  the  temporal  side.  This  is 
especially  the  case  when  the  eyes  are  at  the  same  time  converged 
ami  directed  downwards  ;  and  the  rotation  may  amount  to  as  much 
as  50.  When  the  head  is  rolled  from  side  to  side,  while  the  eyes 
are  kept  fixed  on  an  object,  a  slight  compensatory  rotation  of  the 
eyeballs  takes  place  against  the  direction  of  rotation  of  the  head. 
The  amount  of  rotation  of  the  eyes  is  relatively  greater  for  small 
than  for  large  movements  of  the  head  (eye  50  for  head  200  ;  eye 
to0  for  head  8o° — Krister). 


A   MANUAL  OF  PHYSIOLOGY 


The  Extrinsic  Muscles  of  the  Eyes.     The    eyeball    is    acted 

upon   by  six  muscles  arranged  in  three  pairs,   which  may  be 

idered,  roughly  speaking,  as  antagonistic  sets.     These  are 

the  internal  and  external  recti,  the  superior  and  inferior  recti, 
and  the  superior  and  inferior  obliqui. 

Although  the  movements  of  the  eye  have  been  very  fully 
studied,  and  are,  upon  the  whole,  well  understood,  our  know- 
ledge of  the  manner  in  which  any  given  movement  is  brought 
about,  and  of  i  he  exact  action  of  the  muscles  which  take  part  in 
it,  is  by  no  means  as  copious  and  precise.  And  from  the  nature 
of  the  case,  the  greater  part  of  what  we  do  know  has  been  in- 
ferred from  the  anatomical  relations  of  the  muscles  as  revealed 
by  dissection  in  the  dead  body  rather  than  gained  from  actual 

observation  of  the 
living  eye.  A  plane, 
called  the  plane  of 
traction,  is  supposed 
to  pass  through  the 
middle  points  of  the 
origin  and  insertion  of 
the  muscle  whose  ac- 
tion is  to  be  investi- 
gated, and  through  the 
centre  of  rotation  of 
the  eyeball.  A  straight 
line  drawn  at  right 
angles  to  this  plane 
through  the  centre  of 
rotation  is  evidently 
the  axis  round  which 
the  muscle  when  it  con- 
tracts will  cause  the 
eye  to  rotate,  provided 
that  the  fibres  of  the  muscle  are  symmetrically  distributed  on 
each  side  of  the  plane  of  traction.  The  axes  of  rotation  of  the 
antagonistic  pairs  almost,  but  not  completely,  coincide  with  each 
i  »ther.  The  common  axis  of  the  external  and  internal  recti  practi- 
cally coincides  with  the  vertical  axis  of  the  eyeball  (Fig.  418) 
in  the  primary  position.  The  eye  is  turned  towards  the  temple 
when  the  external  rectus  alone  contracts,  towards  the  nose  when 
the  internal  rectus  alone  contracts.  The  common  axis  of  the 
superior  and  inferior  recti,  /3,  lies  in  the  horizontal  visual  plane 
in  the  primary  position,  but  makes  an  angle  of  about  200  with 
the  tran>vei  its  inner  end   being  tilted  forwards.     The 

consequence  is  that  contraction  of  the  superior  rectus  turns  the 
eye  up,   and  contraction   <>|   the   interior  rectus  turns  it   down, 


l;ii..   4.18.  -Horizonta]   Section  of  I. i:m  Evi 

Arrow?  show  direction  of  pull  of  the  muscles. 
The  axis  of  rotation  of  the  external  and  internal 
recti  would  pass  through  the  intersection  of  a 
and  /3  at  right  angles  to  the  plane  of  the  paper. 


Till    SI  \sl  S  95  3 

but  both  movements  arc  also  combined  with  a  slight  inward 
rotation.  The  common  axis  of  the  oblique  muscles,  a,  makes 
an  angle  of  60  with  the  transverse  axis,  the  outer  end  oi  it 
being  the  most  anterior.  The  direction  of  traction  of  the 
superior  oblique  is,  of  course,  given  not  by  the  line  joining  its 
bony  origin  and  its  insertion,  but  by  the  direction  of  the  portion 
reflected  over  the  pulley.  When  the  superior  oblique  contracts 
alone,  the  eyeball  is  rotated  outwards  and  downwards  ;  the 
interior  oblique  causes  an  outward  and  upward  rotation.  None 
of  the  common  axes  of  rotation  of  the  pairs  of  muscles,  except 
that  of  the  external  and  internal  recti,  lies  in  Listing's  plane. 
Now,  as  we  have  seen  that  every  movement  which  the  eye, 
supposed  to  be  originally  in  the  primary  position,  can  execute 
may  be  considered  as  a  rotation  round  an  axis  in  this  plane,  it 
is  clear  that  every  movement,  except  truly  transverse  rotation, 
must  be  brought  about  by  more  than  one  pair  of  muscles.  For 
vertical  rotation,  the  inward  pull  of  the  superior  rectus  is 
antagonized  by  a  simultaneous  outward  pull  of  the  inferior 
oblique  ;  for  downward  rotation,  the  inferior  rectus  and  superior 
oblique  act  together.  In  oblique  movements,  a  muscle  of  each 
of  the  three  pairs  is  concerned.  The  effect  on  the  eyeball  of 
simultaneous  contraction  of  certain  pairs  of  muscles  may  be 
summarized  thus  : 

External  rectus  (outward)  +  internal  rectus  (inward)  =none. 

Superior  rectus  (upward  and  inward)  +  inferior  oblique  (upward 
and  outward)  =upward. 

Inferior  rectus  (downward  and  inward)  +  superior  oblique  (down- 
ward and  outward)  =  downward. 


HEARING. 

The  transverse  vibrations  of  the  ether  fall  upon  all  parts  of  the 
surface  of  the  body,  but  only  find  nerve-endings  capable  of  giving 
the  sensation  of  light  in  the"  little  discs,  which  we  call  the  retinae. 
ho  the  much  longer  and  slower  longitudinal  waves  of  condensation 
and  rarefaction  which  are  being  constantly  originated  in  the  air 
or  imparted  to  it  by  solid  or  liquid  bodies  that  have  been  themselves 
set  vibrating  fall  upon  all  parts  of  the  surface,  but  only  produce  the 
sensation  of  sound  when  they  strike  upon  the  tiny  mechanism  of  the 
internal  ear. 

But  just  as  the  ethereal  vibrations,  and  especially  those  of  greater 
wave-length,  arc  able  to  excite  certain  end-organs  in  the  skin  which 
have  to  do  with  the  sensation  of  temperature,  so  the  sound-waves, 
when  sufficiently  large,  are  also  capable  of  stimulating  certain 
cutaneous  nerves  and  of  giving  rise  to  a  sensation  of  intermittent 
pressure  or  thrill.  This  is  readily  perceived  when  the  finger  is 
immersed  in  a  vessel  of  water  into  which  dips  a  tube  connected  with 
a  source  of  sound,  or  when  a  vibrating  bell  or  tuning-fork  is  touched. 


954 


A   MANUAL  <>/■'  I'llYSIOLOGY 


f  6  k 


So  far  .is  we  know,  what  takes  place  in  the  cur  is  essentially  simila 
that  is  to  say.  a  mechanical  stimulation  of  the  ends  of  the  auditory 
nerve,  but  a  stimulation  which  acts  through,  and  is  graduated  and 
controlled  by,  a  special  intermediate  mechanism. 

As  the  visual  apparatus  consists  of  a  sensitive  surface,  the 
retina,  which  contains  the  end-organs  of  the  optic  nerve  and  of 
dioptric  arrangements  which  receive  and  focus  the  rays  of  light, 
the  auditory  apparatus  consists  of  the  sensitive  end-organs  of 
the  cochlear  division  of  the  eighth  nerve  and  of  a  mechanism 
which  receives  the  sound-waves  and  communicates  them  to  these. 

Physiological  Anatomy  of  the  Ear.- -At  the  bottom  of  the  external 
auditory  meatus  lies  the  membrana  tvmpani.  a  nearly  circular 
membrane  set  like  a  drum-skin  in  a  ring  of  bone,  and  separating 

the  meatus  from  the  tympa- 
num or  middle  ear.  Its  ex- 
ternal surface  looks  obliquely 
downwards,  and  at  the  same 
time  somewhat  forwards,  so 
that  if  prolonged  the  mem- 
branes of  the  two  ears  would 
cut  each  other  in  front  of, 
and  also  below,  the  hori- 
zontal line  passing  through 
the  centre  of  each  (Figs. 
419,  420). 

The  tympanum  contains  a 
chain  of  little  bones  stretch- 
ing right  across  it  from  outer 
to  inner  wall.  Of  these  the 
malleus,  or  hammer,  is  the 
most  external.  Its  manu- 
brium, or  handle,  is  inserted 
into  the  membrana  tympani, 
which  is  not  stretched  taut 
within  its  bony  ring,  but 
bulges  inwards  at  the  centre, 
where  the  handle  of  the  mal- 
leus is  attached.  The  stapes, 
or  stirrup,  is  the  most  internal 
of  the  chain  of  ossicles,  and 
is  inserted  by  its  foot-plate  into  a  small  oval  opening — the  fora- 
men ovale — -on  the  inner  wall  of  the  tympanic  cavity.  A  mem- 
branous ring — the  orbicular  membrane — surrounds  the  foot  of  the 
stapes,  helping  to  till  up  the  foramen  and  attaching  the  bone  to 
its  edges.  The  inner  surface  of  the  foot  of  the  stapes  is  in  contacl 
with  the  perilymph  of  the  internal  ear.  The  incus,  or  anvil,  forms 
a  link  between  the  malleus  and  the  stapes.  The  auditory  ossicles, 
as  well  as  the  whole  cavity  of  the  tympanum,  are  covered  by  pave- 
ment epithelium. 

The  tympanum  is  not  an  absolutely  closed  chamber  ;  it  lias  one 
channel  of  communication  with  the  external  air — the  Eustachian 
tube — which  opens  into  the  pharynx.  By  the  action  of  the  cilia 
lining  this  tube  the  scanty  secretion  of  the  middle  ear  is  moved 
towards  its  pharyngeal  opening,    which,    usually  closed,    is  opened 


Fig.    419.— The  Ear. 

m,  external  meatus  :  /,  head  of  malleus  : 
0,  short  process  of  malleus  ;  g,  handle  of 
malleus  ;  h,  incus  ;  i,  foot  of  stapes  in  oval 
foramen  ;  e,  tympanic  membrane. 


////    SENSES 


955 


when  ,i  swallowing  movement  occurs.  Us  function  is  to  keep  the 
pressure  in  the  middle  ear  approximately  that  of  the  atmosphere. 
In  a  balloon  ascenl  an  excess  of  pressure  is  established  on  the  internal 
surface  oi  the  tympanic  membrane.  In  the  air-lock  of  a  caisson 
when  the  .hi  is  being  compressed  the  excess  of  pressure  is  on  the 
externa]  surface  oi  the  membrane.  The  feeling  of  uncomfortable 
tension  is  relieved  in  both  eases  by  swallowing  movements  which 
allow  the  pressure  in  the  tympanum  to  adjust  itself  to  that  in  the 
pharynx.  In  catarrh  of  the  naso-pharynx  the  orifice  may  be 
occluded,  and  this  is  accompanied  by  impairment  of  hearing  and  a 
disagreeable  sensation  of  tension  in  the  ear,  owing  to  absorption  and 
consequent  rarefac- 
tion of  the  air  in  the 
tympanum/'ifeThc 
patient  instinctively 
makes  efforts  which 
increase  the  pharyn- 
geal pressure  from 
time  to  time  so  as  to 
open  the  tube. 

The  loosely-jointed 
chain  of  ossicles  is 
steadied  and  its 
movements  directed 
by  ligaments  and  by 
the  tension  of  its  ter- 
minal membranes.  It 
forms  a  kind  of  bent 
lever,  by  which  the 
oscillations  of  the 
membrana  tympani 
are  transferred  to  the 
membrane  covering 
the  oval  foramen,  and 
at  the  same  time  re- 
duced in  size.  Two 
slender  muscles,  the 
tensor  tympani  and 
stapedius,  contained 
in  the  tympanic 
cavity,  are  also  con- 
nected with  and  ma}' 
act  upon  the  ossicles. 
The  former  lies  in  a 
groove  above  the 
Eustachian  tube,  and 

its  tendon,  passing  round  a  kind  of  osseous  pulley  (processus  cochleari- 
formis),  is  inserted  into  the  handle  of  the  malleus  ;  the  stapedius  is 
lodged  in  a  hollow  of  the  inner  bony  wall  of  the  tympanum.  Its 
tendon  is  attached  to  the  neck  of  the  stapes  near  its  articulation  with 
the  incus.  This  inner  wall  is  pierced  not.  only  by  the  oval  foramen, 
but  also  by  a  round  opening,  the  fenestra  rotunda,  which  is  closed 
by  a  membrane  to  which  the  name  of  secondary  membrana  tympani 
is  sometimes  given. 

The  internal  ear  consists  of  the  bony  labyrinth,  a  series  of  curiously 
excavated  and  communicating  spaces  in  the  substance  of  the  petrous 


Fig.   420. 


-Tympanum  of  Left  Ear,   showing  the 
Ossicles  (Morris). 

1,  superior,  and  4,  external,  ligament  of  malleus  ; 
2,  head  ;  7,  short  process,  and  10,  manubrium  or 
handle,  of  malleus  ;  5,  long  process  of  incus,  terminating 
in  9,  the  os  orbiculare  ;  6,  base,  and  8,  head,  of  stapes  ; 
11,  Eustachian  tube;  12,  external  auditory  meatus; 
13,  membrana  tympani  ;  3,  upper,  and  14,  lower,  part  of 
tympanum. 


956 


A    M  /  \'i    U.  <>/■   PHYSIOLOGY 


portion  oi  the  temporal  hour,  filled  with  a  Liquid  called  the  peri- 
lymph, in  which,  anchored  by  strands  of  connective  tissue,  floats  a 
corresponding  scries  oi  membranous  canals  (the  membranous  laby- 
rinth), tilled  with  a  liquid  called  endolymph.     The  Labyrinth  oi  the 

internal  ear  is  divided  into  three  well-marked  parts  :  the  cochlea, 
the  vestibule,  and  the  semicircular  canals  (Fig.  }2i).  The  cochlea, 
the  most  anterior  oi  the  three,  consists  of  a  convoluted  tube  which 
coils  round  a  central  pillar,  the  columella  or  modiolus,  like  a  spiral 
staircase.  The  lamina  spiralis  projects  from  the  modiolus  and  divides 
the  tube  into  an  upper  compartment,  the  scala  vestibuli,  and  a  lower. 
1  he  scala  tympani  (Fig,  422).  The  part  of  the  lamina  next  the  modi- 
olus is  of  bone,  but  it  is  completed  at  its  outer  edge  by  a  membrane, 
the  lamina  spiralis  membranacea,  or  basilar  membrane.  The  scala 
tympani  abuts  on  the  fenestra  rotunda,  and  its  perilymph  is  only 
separated  from  the  air  of  the  tympanic  cavity  by  the  membrane 
which  closes  that  opening.  At  the  apex  of  the  cochlea  the  lamina 
spiralis  is  incomplete  ending  in  a  crescentic  border,  so  that  the  scala 


— y 


Fig.    4-1. — Diagram    of    Right    Membranous    Labyrinth    (after 
Ti  stut). 

1,   utricle;   2.  3,  4,  superior,   posterior,  and  horizontal  semicircular  canals; 
5,  saccule;  6,  ductus  endolymphaticus  arising  by  two  branches,  7.  7'  1 
endolymphaticus  ;  9,  canalis  cochlearis  (canal  of  the  cochlea)  ending  at  9',  and  9*  ; 
io,  canalis  reuniens. 


tympani  and  the  scala  vestibuli  here  communicate  by  a  small 
opening,  the  hclicotrema.  The  scala  vestibuli  communicates  with 
the  vestibule,  and  the  vestibule  with  the  semicircular  canals,  so  that 
the  perilymph  of  the  entire  labyrinth  forms  a  continuous  sheet 
separated  from  the  cavity  of  the  middle  ear  by  the  structures  that 
(ill  up  the  round  and  oval  foramina.  In  the  membranous  labyrinth. 
and  in  it  alone,  are  contained  the  end-organs  oi  the  auditory  nerve. 
The  membranous  portion  of  the  cochlea  is  a  small  canal  of  triangular 
section,  cut  off  from  the  scala  vestibuli  by  the  membrane  of  Reissner, 
which  stretches  from  near  the  edge  of  the  bonv  spiral  lamina  to  the 
outer  wall  (Fig.  4^).  to  which  it  is  attached  by  the  spiral  Ligament. 
The  canal  has  received  the  name  of  the  scala  media,  or  canal  of  the 
cochlea.  The  membrane  of  Reissner  forms  its  roof.  Its  floor  is 
composed  (1)  of  the  projecting  edge  oi  the  spiral  lamina,  called  the 
limbus.  and  (2)  of  the  basilar  membrane.  The  most  conspicuous  con- 
stituent of  the  basilar  membrane  is  .1  Lay*  1  of  stiff,  parallel,  trans- 


/'///'  SENSES 


9S7 


jiarcnt  6brea  arranged  radially  i.e.,  in  the  direction  from  limbus  to 
spiral  ligament.  They  are  embedded  in  ;i  homogeneous  material. 
Below  the  cochlea:  canal  ends  blindly,  but  communicates  by  a 
side-channel  with  the  portion  oi  the  membranous  vestibule  called 
the  saccule,  which  in  its  turn  communicates  with  the  utricle  by 
the  Y-shaped  origin  of  the  ductus  endolymphaticus.  Into  the  utricle 
open^the  thre<    semicircular  canals,  the  endolymph  of  which  has, 


-  str.v, 


9SP 


Fig.  422. — Longitudinal  Section  through  the  Cochlea  of  a  Cat  (Schafer, 
after  sobotta).   x  25. 

tie,  canal  or  duct  of  cochlea  ;  scv,  scala  vestibuli  ;  set,  scala  tympani  ;  w,  bony 
wall  of  cochlea  ;  C,  organ  of  Corti  ;  tnR,  Reissner's  membrane  ;  n,  fibres  of  cochlear 
nerve  ;  gsp,  ganglion  spirale  ;  str.v.,  stria  vascularis. 


therefore,  free  communication  with  that  of  the  vestibule  and  cochlea. 
But  although  the  semicircular  canals  and  vestibule  belong  anatomi- 
cally to  the  internal  ear,  and  are  supplied  by  branches  of  the  auditory 
nerve,  we  have  no  positive  proof  that  in  the  higher  animals,  at  least, 
they  are  in  any  way  concerned  in  hearing  ;  and  since  experiment 
has  assigned  them  a  definite  function  of  another  kind  (p.  834),  we 
shall  not  consider  them  further  in  this  connection.     The  scala  media 


958 


J    1/  /  \r  u    OF  PHYSIOLOGY 


contains  the  organ  oJ  I  orti,  which  (Fig.  424)  consists  of  a  series  of 
□lodified  epithelial  cells  planted  upon  the  basilar  membrane.  The 
epithelial  cells  are  oi  (luce  kinds:  (1)  supporting  epithelial  cells; 
(2)  the  pillars  or  rods  oi  Corti,  in  two  series  (inner  and  outer),  sloped 
againsl  each  other  like  the  rafters  oi  a  runt,  and  covering  in  a  vault 
or  tunnel  which  runs  along  the  w  hole  of  the  sea.  I  a.  media  from  the  base 
to  the  apex  of  the  cochlea;  (3)  the  hair-cells,  around  which  the 
fibres  oi  the  auditory  nerve  arborize.  These  last  are  columnar 
epithelial  cells,  surmounted  by  haiis.  They  are  arranged  in  several 
rows,  one  row  lying  just  internal  to  the  inner  line  of  pillars,  and 
several  rows  external  to  the  outer  line  of  pillars.     Between  the  outer 


Fig.   423. — Vertical  Section   of  the   First  Turn   of  the   Cochlea   (after 

Retzius). 

D.C,  canal  of  cochlea  ;  tC,  tunnel  of  Corti  ;  b.m,  basilar  membrane  j  h.i,  /;.<■, 
internal  and  external  hair-cells;  .1/7,  membrana  tectoria  ;  s.sp,  spiral  groove; 
s/r.r,  stria  vascularis;  sp.l,  spiral  lamina:  n,  fibres  of  the  cochlear  nerve;  /. 
Iimbus  lainime  spiralis  ;  R,  Reissner's  membrane  ;  s.v,  scala  vestibuli  ;  s.t,  scala 
tympani  ;  l.sp,  spiral  ligament. 

hair-cells  are  supporting  cells  (cells  of  Deiters).  A  thin  membrane. 
the  reticular  lamina  or  membrana  reticularis,  composed  of  fiddle- 
shaped  rings  or  phalanges,  covers  the  hair-cells,  and  through  openings 
in  it  the  hairs  project.  A  thicker  membrane,  the  membrana  tectoria, 
springing  from  the  edge  of  the  osseous  spiral  lamina  mar  the  attach- 
ment of  Reissner's  membrane,  forms  a  kind  of  canopy  over  both 
pillars  and  hair-cells.  The  outer  wall  of  the  canal  of  the  cochlea  is 
clad  by  cubical  epithelium  covering  a  membrane  r  hly  supplied 
with  bloodvessels  (stria  vascularis).  The  fact  that  the  hair-cells  of 
Corti's  organ  are  connected  with  the  fibres  of  the  cochlear  division 
of  the  auditory  nerve,  and  its  elaborate  structure,  suggest  that  H 
must    play    a    peculiar    part    in    auditory    sensation.     Comparative 


THE   SI  NS1  S 


959 


anatomy  shows  us  thai  the  cochlea  is  the  most  highly-developed 
portion  ol  the  interna]  ear,  the  lasl  to  appear  in  its  evolution,  and 
the  most  specialized.  It  is  absent  in  fishes,  which  possess  <>nly  a 
vestibule  and  one  to  three  semicircular  canals  It  firsl  acquires 
importance  in  reptiles,  bul  attains  its  highest  development  in 
mammals  ;  and  there  i^  e\  ery  reason  to  believe  that  it  is  the  terminal 
M  usjol  the  sense  oi  heai  ing, 


Fig.  424. — Organ  of  Corti  (Barker,  after  Retzius). 

mb,  basilar  membrane  ;  tb,  its  tympanal  covering  ;  vs,  bloodvessel  (vas  spirale)  ; 
re,  medullated  distal  processes^of  bipolar  nerve-cells  in  the  ganglion  spirale, 
passing  in  to  arborize  around  the  hair-cells  ;  tS,  epithelial  cells  continuous  with 
the  epithelium  oftjthe  sulcus  spiralis  internus  ;  p,  inner  pillar  of  Corti,  with  its 
basal  cell,  b ;  p',  outer  pillar  with  its  basal  cell,  b'  ;  1,  2,  3,  supporting  cells  of 
Deiters,  whose  processes  run  up  to  be  attached  to  the  lamina  reticularis,  r  ;  H, 
Hensen's  supporting  cells  ;  C,  cells  of  Claudius  ;  i,  internal  hair-cell  with  its  hairs, 
i'  (the  upper  part  of  the  hair-cell  is  concealed  by  the  head  of  the  inner  pillar  of 
Corti)  ;  e,  external  hair-cell  ;  e',  hairs  of  three  external  hair-cells  ;  n,  n1,  to  n4, 
cross-sections  of  the  spiral  strand  of  cochlear  nerve-fibres. 

Functions  of  the  Auditory  Ossicles. — The  anatomical 
arrangements  of  the  middle  ear  suggest  that  the  tympanic  mem- 
brane and  the  chain  of  ossicles  have  the  function  of  transmitting 
the  sound-waves  to  the  liquids  of  the  labyrinth  ;  and  observa- 
tion and  experiment  fully  confirm  this  idea.  Tracings  of  the 
movements  0f  the  ossicles  have  been  obtained  by  attaching 
very  small  levers  to  them,  and  their  movements  have  jbeen 
directly  observed  with  the  microscope.  Even  in  man  it  may  be 
shown,  by  viewing  the  membrane  through  a  series  of  slits  in 
a  rapidly-revolving  disc  (stroboscope),  that  it  vibrates  when 
sound-waves  fall  on  it. 

When  the  handle  of  the  malleus  moves  inwards,  rotating 
around  an  axis  which  may  be  supposed  to  pass  through  its  neck, 
its  head  moves  in  the  opposite  direction.  The  joint  between 
that  bone  and  the  incus  is  thus  locked,  on  account  of  the  shape 
of  the  articular  surfaces.     The  long  process  of  the  incus,  consti- 


I    M  INUAL  OF  PHYSIOLOGY 

tilting  the  second  portion  of  the  bent  lever,  passes  inward-, 
carrying  with  it  the  -tape-,  which  is  attached  to  it  by  an  almosl 
rigid  joint,  and  the  stapes  is  pressed  into  the  oval  foramen. 
Since  the  long  process  oi  the  incus  is  about  one-third  shorter 
than  the  handle  of  the  malleus,  the  excursion  of  the  point  of  the 
former  is  correspondingly  smaller  than  that  oi  the  latter,  but  at 
the  same  tune  more  powerful.  When  the  tympanic  membrane 
passes  outwards,  the  handle  of  the  malleus  and  foot  of  the  stapes 
do  the  same.  But  the  joint  now  unlocks,  and  excessive  outward 
movement  of  the  stapes,  which  might  result  in  its  being  torn 
from  it-  orbicular  attachment,  is  prevented.  The  ossicles  vibrate 
en  masse.  It  is  only  to  a  trifling  extent  that  sound  can  be  con- 
ducted through  them  to  the  labyrinth  as  a  molecular  vibration  ; 
for  when  they  are  anchylosed,  and  the  foot  of  the  stapes  fixed 
immovably  in  the  foramen  ovale,  as  sometimes  occurs  in  disease, 
hearing  is  greatly  impaired. 

Of  course,  every  vibration  of  the  tympanic  membrane  must 
cause  a  corresponding  condensation  and  rarefaction  of  the  air 
in  the  middle  ear  ;  and  this  may  act  on  the  membrane  closing  the 
fenestra  rotunda,  and  set  up  oscillations  in  the  perilymph  of 
the  scala  tympani.  That  this  is  a  possible  method  of  conduc- 
tion of  sound  is  shown  by  the  fact  that,  even  after  closure  of  the 
oval  foramen,  a  slight  power  of  hearing  may  remain.  But 
under  ordinary  conditions  by  far  the  most  important  part  of 
the  conduction  takes  place  via  the  ossicles.  And  when  it  is 
remembered  that  the  tympanic  membrane  is  about  thirty  times 
larger  than  that  which  fills  the  oval  foramen,  it  will  be  seen  that 
the  force  acting  on  unit  area  of  the  foot  of  the  stapes  may  be 
much  greater  than  that  acting  on  unit  area  of  the  membrana 
tympani,  and  that  the  mode  of  transmission  by  the  ossicles  is 
a  very  advantageous  method  of  transforming  the  feeble  but 
comparatively  large  excursions  of  the  tympanic  membrane  into 
the  smaller  but  more  powerful  movements  of  the  stapes.  The 
average  excursion  of  the  membrane  of  the  oval  foramen  does 
not  at  most  amount  to  more  than  004  millimetre.  Even  the 
so-called  cranial  conduction  of  sound  when  a  tuning-fork  is 
held  between  the  teeth  or  put  in  contact  with  the  head,  which 
was  at  one  time  supposed  to  be  due  solely  to  direct  transmission 
of  the  vibrations  through  the  bones  of  the  skull  to  the  liquids 
of  the  labyrinth  or  the  end-organs  of  the  auditory  nerve,  has 
been  shown  to  take  place,  in  great  part,  through  the  membrana 
tympani  and  ossicles  ;  the  vibrations  travel  through  the  bones 
to  the  tympanic  membrane,  and  set  it  oscillating.  So  that  this 
test,  when  applied  to  distinguish  deafness  caused  by  disease  of 
the  middle  ear  from  deafness  due  to  disease  of  the  labyrinth  or 
the  central   nervous  system  may  easily  mislead,   although   it 


////    SI  NS1  S  961 

enables  us  to  saj   whethei   the  an« lit  •  n  \   meatus  is  l>Ii»cked — by 

wax,  e.g.      beyond  Ihr  t\  inpanic  m< nil. 1  .inc. 

\  membrane  like  a  drum  bead  has  .1  uote  ol  its  own,  which  it  ;;ives 
.nit  when  stru<  k  and  it  vibrates  more  readily  to  this  note  than  to 
any  other.  It  would  evidently  be  a  serious  disadvantage  if  the 
tympanii  membrane,  whose  office  it  is  to  receive  all  kinds  of  vibra 
tions,  and  respond  to  all,  had  a  marked  fundamental  tone  winch 
would  be  continually  obtruding  Ltseli  among  other  notes.  The 
difficulty  is  obviated  by  the  damping  action  oi  the  ossicles  and  the 
liquids  ol  the  labyrinth  <>n  the  movements  of  the  membrane,  which 
in  addition  is  nol  stretched,  but  lies  slackly  in  its  bony  frame,  so 
thai  when  the  handle  of  the  malleus  is  detached  from  it,  it  retains 
its  shape  ani  I  posil  ion. 

The  tensor  tympani,  when  it  contracts,  pulls  inwards  the  handle 
of  the  malleus,  and  thus  increases  the  tension  of  the  tympanic 
membrane,  The  precise  object  of  this  is  obscure.  It  has  been 
suggested  thai  damping  of  the  movements  of  the  auditory  ossicles 
is  thus  secured.  Another  theory  is  that  the  increased  tension  of 
the  membrane  renders  it  more  capable  of  responding  to  higher 
tones,  and  that  the  muscle  thus  acts  as  a  kind  of  accommodating 
mechanism.  But  llensen  has  observed  that  the  tensor  only  con- 
tracts at  the  beginning  of  a  sound,  and  relaxes  again  when  the 
sound  is  continued  ;  and  this  is  difficult  to  reconcile  with  either  of 
these  hypotheses.  The  muscle  is  normally  excited  reflexly  through 
the  vibrations  of  the  membrana  tympani,  but  some  individuals 
have  the  power  of  throwing  it  into  voluntary  contraction,  which  is 
accompanied  bv  a  feeling  of  pressure  in  the  ear  and  a  harsh  sound. 
The  function  of  the  stapedius  is  unknown.  Its  contraction  would 
tend  to  press  the  posterior  end  of  the  foot-plate  of  the  stapes  deeper 
into  the  foramen  ovale,  and  cause  the  anterior  end  to  move  in  the 
opposite  direction  ;  but  it  is  not  easy  to  see  how  this  would  affect 
the  action  of  the  auditory  mechanism. 

The  tensor  tympani  is  supplied  by  the  fifth  nerve  through  a  branch 
from  the  otic  ganglion  ;  the  stapedius  is  supplied  by  the  seventh. 
Paralysis  of  the  fifth  nerve  may  be  accompanied  with  difficulty 
of  hearing,  especially  for  faint  sounds.  When  the  seventh  nerve 
is  paralyzed,  increased  sensitiveness  to  loud  sounds  has  been 
observed. 

We  have  already  recognised  the  organ  of  Corti,  particularly 
the  hair-cells,  as  a  sensory  epithelium  which  constitutes  the 
terminal  apparatus  of  the  cochlear  nerve.  The  adequate  stimulus 
of  the  auditory  receptors  is  the  periodic  changes  of  pressure  in 
the  endolymph.  But  there  are  various  opinions  as  to  how  these 
vibrations  are  transmitted  to  the  hair-cells,  and  as  to  how  the 
vibrations  of  the  hair-cells  are  translated  into  nerve  impulses  in 
the  auditory  fibres.  The  pillars  of  Corti,  the  basilar  membrane, 
and  the  membrana  tectoria,  have  in  turn  been  regarded  as  the 
structures  immediately  set  into  vibration  by  the  changes  in  the 
endolymph.  The  case  for  the  tectorial  membrane  is  perhaps 
the  most  plausible,  for  its  position  renders  it  most  capable  of 
acting  on  the  hairs.  Others  have  supposed  that  the  hairs  of  the 
hair-cells    are    directly    affected    by    the    endolymph.     Some, 

61 


962  A   MANUAL  OF  PHYSIOLOGY 

despairing  ol  further  analysis,  content  themselves  with  the  con- 
clusion that  the  organ  of  Corti  vibrates  as  a  whole.  Some  of 
these  theories  will  be  again  referred  to  in  considering  what  is  the 
greatest  problem  of  the  physiology  of  hearing,  viz. : 

The  Perception  of  Pitch-  Analysis  of  Complex  Sounds. — 
As  the  eye,  or,  rather,  the  retina  plus  the  brain,  can  perceive 
colour,  so  the  labyrinth  plus  the  brain  can  perceive  pitch.  The 
colour-sensation  produced  by  ethereal  waves  of  definite  fre- 
quency depends  on  that  frequency  ;  and  upon  the  frequency  of 
the  aerial  vibrations  depends  also  the  pitch  of  a  musical  note. 
But  there  is  this  difference  between  the  eye  and  the  ear  :  that 
while  the  sensation  produced  by  a  mixture  of  rays  of  light  of 
different  wave-length  is  always  a  simple  sensation — that  is, 
a  sensation  which  we  do  not  perceive  to  be  built  up  of  a  number 
of  sensations,  which,  in  other  words,  we  do  not  analyze — the 
ear  can  perceive  at  the  same  time,  and  distinguish  from  each 
other,  the  components  of  a  complex  sound.  When  a  number 
of  notes  of  different  pitch  are  sounded  together  at  the  same 
distance  from  the  ear  the  disturbance  which  reaches  the  mem- 
brana  tympani  is  the  physical  resultant  of  all  the  disturbances 
produced  by  the  individual  notes,  and  it  strikes  upon  the  mem- 
brane as  a  single  wave.  '  A  single  curve  describes  all  that  the 
ear  can  possibly  hear  as  the  result  of  the  most  complicated 
musical  performance.  ...  In  the  complicated  sound  the  varia- 
tions of  the  pressure  of  the  air  are  more  abrupt,  more  sudden, 
less  smooth,  and  less  distinctly  periodic  than  they  are  in  softer, 
purer,  and  simpler  sound.  But  the  superposition  of  the  different 
effects  is  really  a  marvel  of  marvels  '  (Kelvin).  The  ear  or 
brain  must,  therefore,  possess  the  power  of  resolving  the  complex 
vibrations  into  their  constituents,  else  we  should  have  a  mixed  or 
blended  sensation,  and  not  a  sensation  in  which  it  is  possible  to 
distinguish  the  constituents  of  which  it  is  made  up.  Several 
hypotheses  have  been  proposed  to  explain  this  physiological 
analysis  of  sound,  on  the  assumption  that  the  analysis  takes  place 
in  the  labyrinth.  The  most  important,  in  spite  of  certain  defects, 
is  still  that  of  Helmholtz. 

Helmholtz  attempted  to  explain  the  perception  of  pitch  on 
the  assumption  that  in  the  internal  ear  there  exists  a  series 
of  resonators,  each  of  which  is  fitted  to  respond  by  sympathetic 
vibration  to  a  particular  note,  while  the  others  are  unaffected  ; 
just  as  when  a  note  is  sung  before  an  open  piano  it  is  taken  up 
by  the  string  which  is  attuned  to  the  same  pitch  and  ignored  by 
the  rest.  Let  us  suppose  that  a  given  fibre  of  the  auditory  nerve 
ends  in  an  organ  which  is  only  set  vibrating  by  waves  impinging 
on  it  at  the  rate  of  ioo  a  second,  and  that  the  end-organ  of  another 
fibre  is  only  influenced  by  waves  with  a  frequency  of  200  a  second. 


THE  SENSES  963 

Then,  on  the  doctrine  ol  '  specific  energy'  (according  to  which 
the  sensation  caused  by  stimulation  of  a  nerve  depends  not  on 
the  particular  kind  ol  stimulus  bul  on  the  anatomical  connection 
of  the  nerve  with  certain  nerve  centres),  in  whatever  way  the 
first  fibre  is  excited,  a  sensation  corresponding  to  a  note  with  a 
pitch  of  100  a  second  will  be  perceived.  Whenever  the  second 
fibre  is  exited,  the  sensation  will  ibe  that  of  a  note  of  200  a 
second,  or  the  octave  ol  the  first.  It  both  fibres  are  excited  at 
the  same  time  the  two  notes  will  be  heard  together.  Now, 
Hensen  actually  observed  that  in  the  auditory  organs  of  some 
crustaceans,  the  hair-like  processes  of  certain  epithelial  cells 
can  be  set  swinging  by  waves  of  sound,  and,  further,  that  they 
do  not  all  vibrate  to  the  same  note  unless  the  sound  is  very 
loud.  In  the  lobster  there  are  between  four  and  five  hundred  of 
these  hairs,  varying  in  length  from  14  /x  to  740  ^  ;  and  in  some 
insects,  such  as  the  locust,  similar  hairs,  also  graduated  in  length, 
exist. 

To  gain  an  anatomical  basis  for  his  theory,  Helmholtz  sup- 
posed first -of  all  that  the  pillars  of  Corti  were  the  vibrating 
structures,  and  that,  directly  or  through  the  hair-cells,  their 
mechanical  \  ibrations  were  translated  into  impulses  in  the 
auditory  nerve-fibres.  But  apart  from  the  fact  that  their 
number  is  too  small  (about  3,000)  to  allow  us  to  assign  one  rod 
to  each  perceptible  difference  of  pitch,  and  their  dimensions  too 
similar  to  permit  of  the  requisite  range  of  vibration  frequency, 
it  was  pointed  out  that  birds  do  not  possess  pillars  of  Corti— 
a  fact  which  was  decisive  against  the  assumption  of  Helmholtz. 
since  nobody  denies  to  singing-birds  the  power  of  appreciating 
pitch.  Helmholtz  accordingly,  choosing  between  the  remain- 
ing possibilities,  gave  up  the  pillars  of  Corti,  and  adopting  a  sug- 
gestion of  Hensen,  substituted  the  radial  fibres  of  the  basilar 
membrane  as  his  hypothetical  resonators.  These  are  more 
adequate  to  the  task  imposed  on  them,  since  their  range  of 
length  is  far  greater  (41  /j,  at  the  base  to  495  /j,  at  the  apex  of 
the  cochlea — Hensen)  ;  and  the  elaborate  structure  of  Corti's 
organ  certainly  suggests  that  some  one  or  other  of  its  elements 
may  be  endowed  with  such  a  function.  Experimentally,  too, 
it  has  been  shown  that  destruction  of  the  apex  of  the  cochlea 
causes  loss  of  appreciation  of  low  notes,  and  destruction  of  the 
base  loss  of  appreciation  of  high  notes,  which  agrees  with  Helm- 
holtz's  view.  But  while  the  theory  of  peripheral  analysis  of 
pitch  tends  upon  the  whole  to  be  strengthened  as  evidence 
gathers,  it  is  possible  that  the  analysis  is  accomplished  in  some 
other  way  than  by  sympathetic  resonance. 

Ewald  has  developed  a  theory  according  to  which  each  note  causes 
the  basilar  membrane  to  vibrate  throughout  its  whole  extent  in 

01—  2 


A    MANUAL  OF  PHYSIOLOGY 


such  a  way  thai  stationary  waves  are  produced  in  it.  like  the  (  hladni's 
figures  seen  on  a  metal  plate  strewed  with  sand  when  it  is  set  into 
vibration.  The  pattern  of  the  movement,  the  '.sound-picture.'  will 
be  different  for  each  tone,  since  the  interval  between  the  waves  will 
be  different.  II ■<■  hair-cells  and  auditory  fibres  of  particular  parts 
<>t  the  organ  ol  Corti  will  therefore  be  stimulated  by  the  pressure  of 
the  membrane,  or  escape  stimulation,  according  to  the  position  of 
rtationary  waves  with  reference  to  them  for  each  note.  In  this 
way  each  sound-picture  will  be  punted,  so  to  speak,  upon  the  sensi- 
tive terminal  apparatus  of  the  auditory  nerve,  as  a  letter  is  printed 
upon  a  piece  ol  paper  by  a  type.  The  corresponding  excitation 
pattern  i.e.,  th<  particular  distribution  of  cochlear  fibres  stimulated 
— is  supposed  to  be  associated  in  consciousness  with  the  appreciation 
of  the  pitch  of  the  particular  note.  Ewald  has  endeavoured  to  sup- 
port his  theory  by  showing  that  fine  membranes  of  the  dimensions 
oi  the  basilar  membrane  do  yield  very  distinct  sound-pictures  for 
different  simple  tones  as  well  as  for  com- 
plex tones.  These  can  be  observed  with 
the  microscope  and  photographed 

The  best-known  theory  of  central  analysis 
may  be  conveniently  labelled  the  '  telephone 
theory,'  in  accordance  with  the  simile  used 
by  Rutherford,  to  whom  we  owe  it  in  its 
present  form,  lie  supposes  that  the  organ 
of  Corti  (or  at  any  rate  the  hair-eel: 
set  into  vibration  as  a  whole  by  all  audible 
sounds,  and  that  its  vibrations  are  trans- 
lated into  impulses  in  the  auditory  nerve, 
which  are  the  phvsiological  counterpart  of 
the  aerial  waves  and  the  waves  of  increased 
and  diminished  pressure  in  the  liquids  of 
the  labyrinth  to  which  they  give  rise. 
Thus,  a  sound  of  ioo  vibrations  a  second 
would  start  ioo  impulses  a  second  in  the 
auditory  nerve  ;  a  loud  sound  would  set  up 
impulses  more  intense  than  a  feeble  sound  ; 
and  a  complex  wave,  which  is  the  resultant 
oi  several  sounds  of  different  vibration-fre- 
quency, would  also  in  some  way  or  other 
stamp  the  impress  of  its  form  <<n  the  auditory  excitation-wave;  just 
as  in  a  telephone  every  wave  in  the  air  causes  a  swing  of  the  vibrating 
plate,  and  thus  sets  up  a  current  of  corresponding  intensity  and  dura- 
tion in  the  wires.  This  theory  evidently  abandons  the  doctrine  of 
specific  energy  for  the  particular  case  of  the  analysis  of  pitch,  for  it 
assumes  that  differences  of  auditory  sensation  are  related  to  differ- 
ences in  the  nature  of  the  impulses  travelling*  up  the  auditory 
nerve,  and  not  merely  to  differences  in  the  anatomical  connections 
ipheral  and  central)  of  the  auditory  nerve-fibres.  It  is  un- 
satisfactory because  it  takes  no  account  of  the  remarkable  and 
suggestive  structure  of  the  telephone  plate — i.e.,  of  the  organ  oi 
Corti — and  gives  no  hint  of  how  the  analysis  is  accomplished  in  the 
central  organ. 

The  range  of  hearing  is  very  great.  The  highest  audible  tone 
corresponds  to  30,000  to  40,000  vibrations  a  second,  the  lowest  to 
about  30.  Between  these  limits  as  many  as  6,000  variations  of 
pitch  can  be  perceived. 


FlG.  4^5. — Photograph  of 
a    Sound- Picture 

(Lwalu). 


////'   SENSES  965 

Ills  elaborately  investigated  the  question  how  rhi 
sitiven<  ss  ol  the  1  ar  varies  for  tones  of  differenl  pitch.  A  tone  of 
^  vibrations  a  second,  in  order  to  be  just  heard,  must  have  an 
intensity  corresponding  to  about  roo  million  times  .is  much  energy 
as  is  ne<  ded  for  a  tone  oi  2,000  vibrations.  It  is  only  on  the  extra- 
ordinary sensibility  of  the  ear  for  the  range  oi  tones  used  in  ordinary 
;>ilitv  <>f  understanding  speech  depends  when 
the  circumstances  are  unfavourable  -e.g.,  at  a  great  distance,  or 
in  the  presence  of  much  stronger  accompanying  noises. 


Smell  and  Taste. 

Smell  was  defined  by  Kant  as  '  taste  at  a  distance';  and  it  is 
obvious  that  these  two  senses  not  only  form  a  natural  group 
when  the  quality  ol  the  sensations  is  considered,  but  are  closely 
•dated  in  their  physiological  action,  especially  in  connection 
with  the  perception  of  the  flavour  of  the  food.  The  olfactory  end- 
organs  in  the  mucous  membrane  of  the  upper  part  of  the  nostrils, 
the  so-called  regio  olfactoria,  have  been  already  described 
(p.  816).  In  cases  of  anosmia,  in  which  the  olfactory  nerve  is 
absent  or  paralyzed,  smell  is  abolished  ;  but  substances  such  as 
ammonia  and  acetic  acid,  which  stimulate  the  ordinary  sensory 
nerves  (nasal  branch  of  fifth)  of  the  olfactory  mucous  mem- 
brane, are  still  perceived,  though  not  distinguished  from  each 
other.  In  fact,  the  so-called  pungent  odour  of  these  substances 
is  no  more  a  true  smell  than  the  sense  of  smarting  they  produce 
when  their  vapour  comes  in  contact  with  a  sensory  surface  like 
the  conjunctiva,  or  a  piece  of  skin  devoid  of  epidermis. 

It  was  at  one  time  believed  that  odoriferous  particles  could  not 
be  appreciated  unless  they  were  borne  by  the  air  into  the  nostrils  ; 
but  this  appears  not  to  be  the  case,  for  the  smell  of  substances 
diss<  lived  in  physiological  salt  solution  is  distinctly  perceived  when 
the  nostrils  are  filled  with  the  liquid  ;  and  fish,  as  every  line- 
fisherman  knows,  have  no  difficulty  in  finding  a  bait  in  the  dark. 

The  substances  which  can  affect  the  olfactory  mucous  membrane 
can  be  divided  into  four  groups  : 

1 .  Those  which  act  only  on  the  olfactory  nerves,  the  odours 

proper. 

2.  Substances  which  act  at  the  same  time  on  olfactory 

nerves,  and  on  nerves  of  common  sensation  (tactile 
nerves) — e.g.,  acetic  acid. 

3.  Substances  which  act  at  the  same  time  on  the  gustatory 

nerves. 

4.  Substances  which  act  only  on  the  nerves  of  common 

sensation  (tactile  nerves) — e.g.,  carbon  dioxide. 
Zwaardemakcr  has  classified  the  pure  odours  as  follows  : 
(1)  Ethereal  odours,  as  those  of  fruits  ;   (2)  aromatic  odours,  as 

of   camphor  or  bitter  almonds  ;   (3)  fragrant  odours,  as  of  flowers  ; 

(4)  ambrosial  odours,  as  of  amber  or  musk  ;   (5)[garlic  odours,  as 


966  I    W  INUAL  OF  PHYSIOLOGY 

of  onion,  garlic,  asafoetida  ;  (6)  empyreumatic,  or  burning  odours,  ;is 
of  burnt  coffee  or  tobacco  smoke  ;   (7)  caprylic  or  goat  odoui 
of  sweat ;  (8)  repulsive  odours,  as  the  odour  of  the  disease  ozaena  ; 
(9)  nauseating  odours,  as  of  faces  or  putrefying  material. 

The  most  interesting  form  of  inadequate  stimulation  is  electrical 
excitation  of  the  olfactory  mucous  membrane,  which  cause 
sensation  like  the  smell  of  phosphorus.  The  sensation  is  experienced 
at  the  kathode  on  closure  and  the  anode  on  opening.  As  to  the 
manner  in  which  the  multitudinous  adequate  stimuli  excite  the 
olfactory  nerves,  we  can  only  suppose  that  they  act  as  chemical 
stimuli.  Smell  and  taste  are  pre-eminently  the  '  chemical  '  senses, 
as  sight  and  hearing  are  pre-eminently  '  physical  '  senses.  But  little 
is  known  of  the  relation  between  the  chemical  constitution  or  physical 
properties  of  substances  and  the  quality  of  the  odoriferous  sensation 
which  they  excite,  although  Haycraft  has  pointed  out  some  inter- 
esting relations  between  the  atomic  weights  of  certain  elements  and 
their  power  of  exciting  odours.  The  number  of  distinct  odours 
which  can  be  perceived  is  so  great  that  it  is  scarcely  conceivable  that 
each  is  subserved  by  special  olfactory  fibres.  Marked  changes 
occur  in  disease,  and  all  odours  need  not  be  affected  to  the  same 
extent.  Some  may  be  almost  normally  perceived,  while  relative  ..r 
complete  loss  of  smell  exists  as  regards  others.  These  and  other  fai  1  s 
have  given  rise  to  the  idea  that  there  are  several  groups  of  olfactory 
fibres,  each  concerned  in  the  appreciation  of  a  particular  odour  or 
group  of  odours.  Yet  it  has  not  proved  possible  to  reduce  them  to 
a  limited  number  of  fundamental  odours  and  their  combinations. 

Acuteness  of  smell  may  be  measured  by  arrangements  called 
olfactometers.  Zwaardemaker's  olfactometer  consists  of  a  piece  of 
indiarubber  tubing  fitted  inside  a  glass  tube,  through  which  air 
is  drawn  into  the  nostrils.  Another  glass  tube  just  fitting  the 
rubber  tube  is  pushed  inside  it,  so  as  to  cover  a  portion  of  it.  The 
minimum  amount  of  surface  of  the  indiarubber  tube  which  must  be 
left  exposed  so  that  the  smell  of  the  rubber  may  be  perceived  is  a 
measure  of  the  acuteness  of  smell.  To  investigate  other  odours 
tubes  of  the  corresponding  odorous  substances  can  be  constructed. 

Taste. — The  sense  of  taste  is  not  so  strictly  localized  as  the 
sense  of  smell.  The  tip  and  sides  of  the  tongue,  its  root,  the 
neighbouring  portions  of  the  soft  palate,  and  a  strip  in  the  centre 
of  the  dorsum,  are  certainly  endowed  with  the  sense  of  taste  ; 
but  the  exact  limits  of  the  sensitive  areas  have  not  been  defined, 
and,  indeed,  vary  in  different  individuals. 

The  nerves  of  taste  are  the  glosso-pharyngcal.  which  innervates 
the  posterior  part  of  the  tongue,  and  the  lingual,  which  supplies 
its  tip  (see  p.  821).  The  end-organs  of  the  gustatory  nerves  are 
the  taste-buds  or  taste-bulbs,  which  stud  the  fungiform  and  cir- 
cumvallate  papillae,  and  are  most  characteristically  seen  in  the 
moats  surrounding  the  latter.  They  arc  barrel-like  bodies,  the 
staves  of  the  barrel  being  represented  by  supporting  cells  ;  each 
bud  encloses  a  number  of  gustatory  cells  with  fine  processes  at  their 
free  ends  projecting  through  the  superficial  end  of  the  barrel.  They 
are  surrounded  by  the  end  arborizations  of  the  fibres  of  the  gustatory 
nerves.  Taste-buds  arc  also  found  on  the  posterior  surface  of  the 
epiglottis  and  in  the  larynx.  It  has  been  suggested  that  these  form 
the  afferent  end-organs  of  a  reflex  apparatus  which  guards  the  glottis 


I  in    si  xsi  s  967 

againsl  the  entrance  oi  food  in  deglutition  (Wilson).  Epithelial 
buds,  different  from  the  olfactory  elements,  also  occur  in  theolfat  tory 
on  oi  the  nasal  mucous  membrane.  It  is  possible  thai  the 
tiled  nasal  taste  e.g.,  the  sweet  t.isie  caused  by  chloroform 
when  aspirated  in  no1  too  small  an  amount  through  the  nose 
depfnds  upon  1  hese  buds. 

Vs  to  the  properties  in  virtue  of  which  sapid  suhstances  are 
enabled  to  stimulate  the  gustatory  nerve-endings,  we  know  that 
they  musl  he  soluble  in  the  liquids  <»t  the  mouth,  and  there  our 
knowledge  ends.  An  attempt  lias  hcen  made  by  various  authors 
to  connect  the  taste  of  such  bodies  with  their  chemical  composi- 
tion, hut  researches  of  this  kind  have  not  hitherto  yielded  much 
fruit.  The  number  of  distinct  qualities  of  taste  sensation  is  con- 
siderable, but  by  no  means  so  great  as  the  number  of  qualities  of 
olfactory  sensations,  and  they  are  more  easily  reduced  to  a  few 
primary  or  fundamental  sensations.  Sapid  substances  have 
generally  been  divided  into  four  classes,  as  regards  the  funda- 
mental sensations  produced  by  them — viz.  :  (1)  Sweet,  (2)  acid, 
(3)  bitter,  (4)  saline.  All  taste  sensations  seem  to  be  combina- 
tions of  these,  or  combinations  of  one  or  more  of  them  with 
olfactory  sensations,  or  with  sensations  due  to  excitation  of  the 
ordinary  sensory  nerves  of  the  tongue. 

Sweet  and  acid  tastes  are  best  appreciated  by  the  tip,  and 
bitter  tastes  by  the  base,  of  the  tongue.  Differences  have  been 
detected  between  individual  papillae  in  their  power  of  reaction 
to  sapid  suhstances  which  produce  one  or  other  of  the  funda- 
mental sensations.  Of  125  fungiform  papillae  tested  with  solu- 
tions of  tartaric  acid,  sugar,  and  quinine,  27  gave  no  sensation 
of  taste.  Tartaric  acid  evoked  its  acid  taste  in  91  of  the  remain- 
ing 98,  sugar  its  sweet  taste  in  79,  and  quinine  its  bitter  taste 
in  71  ;  12  reacted  only  to  tartaric  acid,  and  3  only  to  sugar 
(Ohrwall).  Such  facts  indicate,  although  they  do  not  definitely 
prove,  the  existence  of  specific  receptors  for  each  of  the  funda- 
mental taste  sensations — i.e.,  gustatory  end-organs,  which  are 
easily  excited  by  an  adequate  stimulus  (acid,  e.g.,  in  the  case  of 
an  'acid'  taste-bud),  with  difficulty  or  not  at  all  by  an  in- 
adequate stimulus. 

The  form  of  inadequate  stimulation  most  investigated  is  that 
produced  when  a  constant  current  is  passed  through  the  tongue.  An 
acid  taste  is  experienced  at  the  positive,  and  an  alkaline  or  bitter 
taste  at  the  negative,  pole  ;  and  this  is  the  case  even  when  the  current 
is  conducted  to  and  from  the  tongue  by  unpolarizable  combinations, 
which  prevent  the  deposition  of  electrolytic  products  on  the  mucous 
membrane  (p.  625).  The  sensations  are  due  to  stimulation  of  the 
gustatory  end-organs  and  not  of  the  nerve-trunks. 

Normal  lymph,  which  bathes  these  end-organs,  does  not  excite 
any  sensation  of  taste,  but  when  the  composition  of  the  blood 
is  altered   in   disease  or  by  the  introduction  of  foreign  substances, 


A   MANV  II.  OF  PHYSIOLOGY 


tastes  of  various  kinds  may  be  perceived.  Sometimes  this  may  be 
due  to  the  stimulation  oi  substances  excreted  in  the  saliva  ;  bu1  in 
other  cases  it  seems  that,  vvithoul  passing  beyond  the  blood  and 
lymph,  foreign  substances  may  ex<  ite  the  gustatory  nerves. 

Flavour  embraces  a  group  of  mixed  sensations  in  which  smell  and 
taste  are  both  concerned,  as  is  shown  by  the  common  observation 
thai  a  pei  son  suffering  from  a  cold  in  the  head,  which  bhmts  his  sense 
oi  smell,  loses  the  proper  flavour  of  his  food,  and  that  some  nauseous 
medicines  do  riot  taste  so  badly  when  the  nostrils  are  held. 

In  common  speech,  the  two  sensations  arc  frequently  confounded 
with  each  other  and  with  tactile  sensations.  Thus  the  '  bouquet 
of  wines,  which  most  people  imagine  to  be  a  sensation  of  taste,  is  in 
reality  a  sens.it  ion  of  smell  ;  the  astringent  'taste'  of  tannic  acid  is 
not  a  taste  at  all,  but  a  tactile  sensation  ;  the  '  hot  '  taste  of  mustard 
is  no  more  a  true  sensation  of  taste  than  the  sensation  produced  by 
the  same  substance  when  applied  in  the  form  of  a  mustard  poultice  to 
the  skin. 


Tactile  and  Common  Sensations. 

Under  the  sense  of  touch  it  is  usual  to  include  a  group  of  sensa- 
tions  which  differ  in  quality — and  that  in  some  instances  to  as 
great  an  extent  as  any  of  the  sensations 
which  are  universally  considered  as  separate 
and  distinct — but  agree  in  this,  that  the 
end-organs  by  which  they  are  perceived 
are  all  situated  in  the  skin,  the  mucous 
membranes,  or  the  subcutaneous  tissue. 
Such  are  the  common  tactile  sensations — 
including  pressure,  tickling,  and  itching — 
and  the  sensations  of  temperature,  or, 
more  correctty,  of  change  of  temperature, 
or  of  warmth  and  cold.  The  sensation  oi 
pain,  although  it  cannot  be  absolutely 
separated  from  these,  ought  not  to  be 
grouped  along  with  them.  It  is  called 
forth  by  the  stimulation  of  afferent  nerve- 
fibres  in  their  course  ;  and  it  may  originate, 
under  certain  conditions,  in  internal  organs 
which  are  devoid  of  tactile  sensibility,  and 
the  functional  activity  of  which  in  then 
normal  state  gives  rise  to  no  special  sen- 
sation at  all.  The  peculiar  sensation  asso- 
ciated with  voluntary  muscular  effort,  to 
which  the  name  of  the  muscular  sense 
has  been  given,  also  deserves  a  separate  place  ;  for  although  it 
may  in  part  depend  on  tactile  sensations  set  up  through  the 
medium  of  end-organs  situated  in  muscle,  tendon,  or  the  struc- 
tures which  enter  into  the  formation  of  the  joints,  other  elements 
are,  in  all  probability,  involved. 


Fig.  426. — T  a  c  1  1 1.  E 
Corpuscle  from 
Skin  of  Finger 
(Smirnow). 

(Golgi  preparation.) 
The  winding  and  inter- 
secting black  lines  are 
the  non-medullated 
endings  of  the  one  or 
more  aerve-fibres  that 
enter  the  <  orpusi  le. 


THE  SENSES 

The  simplest  form  ol  tactile  sensation  is  that  of  mere  contact, 
a>  when  t  he  skin  is  lightly  touched  with  the  blunt  end  ol  a  pencil. 
This  soon  deepens  into  the  sensation  ol  pressure  if  the  contact 
i-  made  closer  ;  and  eventually  the  sense  of  pressure  merges  into 
a  feeling  oi  pain.     Most  physiologists  agree  that  in  the  skin  itself 
four  fundamental  qualities  of  sensation  are  represented — touch 
in  the  restricted  sense  (the  sensation  elicited  by  light  contact), 
warmth,  cold,  and  pain.     Pressure  is  mainly  a  sensation  con- 
nected  with  the  stimulation  of  structures  deeper  than  the  skin — ■ 
the  sensation  ol  contact  is  abolished  in  cicatrices  where  the 
true    >kin    has    been    destroyed,  while    sensibility  to    pressure 
persist-    -although  the  sensation  of  light  pressure  may  be  to  some 
extent   represented  in  the  skin  itself  in  association  with  touch. 
In  a  somewhat  diagrammatic  sense  it  may  be  said  that  the  sur- 
face of  the  skin  is  divided  into  a  great  number  of  very  small  areas, 
each  of  which  is  related  especially  to  one  or  other  of  the  four 
fundamental  sensations.     Areas  concerned  in  one  sensation  are 
everywhere    mingled  with  areas  concerned  in  the   others.     By 
appropriate  methods  it  has  been  found  possible  to  determine  the 
existence  on  the  skin  of  the  trunk  and  limbs  of  not  less  than 
30,000  '  warm-spots,'  which  always  react  to  stimulation  by  a 
sensation  of  warmth  ;   250,000  '  cold-spots,'   which  react   by  a 
sensation  of  cold  ;  and  half  a  million  touch-spots,  whose  specific 
reaction  is  a  sensation  of  touch.     It  is  more  difficult  to  localize 
definitely  bounded  '  pain-spots,'  partly  because  of  the  very  rich 
supply  of  pain-fibres  to  the  skin.     Yet  there  is  reason  to  believe 
that  pain,  like  touch,  warmth,  and  cold,  is  subserved  by  separate 
receptors.     The   simplest    assumption   which   will   satisfactorily 
account  for  the  distribution  of  the  four  fundamental  cutaneous 
sensations  is  that  the  skin  is  supplied  with  four  kinds  of  nerve- 
fibres,  anatomically  as  well  as  functionally  distinct.     Some  fibres 
minister  to  the  sensation  of  cold,  others  to  that  of  warmth,  others 
to  that  of  touch,  and  others  still  to  pain.     And  just  as  stimulation 
of  the  optic  nerve  gives  rise  to  a  sensation  of  light,  so  stimulation 
of  any  one  of  the  cutaneous  nerves  gives  rise  to  the  specific  sensa- 
tion proper  to  the  group  to  which  it  belongs.     The  existence  of 
different  forms  of  sensory  end-organs  in  the  skin  and  other  tissues 
(tactile  or  touch-corpuscles,  corpuscles  of  Pacini,  end-bulbs  of 
Krause,  etc.)  points  in  the  same  direction.     The  end-organs  of 
the  touch  sensations  are  believed  to  be  the  ring-like  arrangements 
of  non-medullated  nerve-fibres  encircling  the  hair-follicles,  and 
in  parts  of  the  skin  devoid  of  hairs  the  corpuscles  of  Meissner 
(v.  Freyj. 

Touch-spots  can  easilv  be  demcnstrated  by  touching  the  skin 
lightly  with  some  small  object  such  as  a  hair.  The  most  exact 
quantitative  observations  have  been    made  by  means  of  v.  Frey's 


97° 


I   MANUAL  OF  PHYSIOLOGY 


hair  aesthesiometer.     This  consists  of  a  handle   in   which   hairs  of 
different  diameters  can  be  fixed.  The  area  of  the  en  'iiofeach 

hair  is  measured  under  the  microscope,  and  the  pressure  necessary 
to  bend  it  is  determined  by  pressing  it  upon  the  scale-pan  of  a 
balance.  The  pressure  in  milligrammes,  divided  by  the  i  ross  section 
in  square  millimetres,  gives  the  pressure  per  square  millim< 
which,  according  to  v.  In  y,  permits  hairs  to  be  chosen  so  as  to  give 
a  uniform  intensity  of  stimulation  or  a  variable  intensity,  according 
to  the  object  of  the  investigation.  Many  obsen  e#s,  however.  belie\  e 
that  it  is  more  accurate  to  take  no  account  of  the  pressure  per  unit 
of  area,  but  to  graduate  the  hairs  according  to  the  total  pressure 
needed  to  bend  them.  When  touch-spots  ascertained  in  this  wax- 
are  excited  by  an  inadequate  stimulus — e.g.,  an  alternating  current 
of  minimal  strength,  applied  by  the  unipolar  method  through  the 
head  of  a  pin  as  an  electrode — they  still  respond  by  their  character- 
istic or  specific  reaction — namely,  a  sensation  of  touch — in  the  case 
supposed,  a  vibrating  sensation  like  that  caused  by  a  tuning-fork 
in  contact  with  the  skin.  In  the  spaces  between  the  touch-spots 
the  sensation  produced  by  the  same  strength  of  current,  or  even  by 
a  weaker  current,  is  not  one  of  touch,  but  a  painful  pricking  sensation 
which  has  no  vibratory  character,  but  is  permanent  as  long  as  the 
current  lasts. 

The  spots  most  sensitive  to  touch  lie  close  to  the  hairs  on  their 
'  windward  '  side — i.e.,  on  the  side  away  from  which  they  slope. 
The  minimum  pressure  necessary  to  evoke  a  sensation  of  contact 
is  not  the  same  for  every  portion  of  the  skin.  The  forehead  and  palm 
of  the  hand  are  most  sensitive. 


Number  of  Touch- 
Spots  per  sq.  cm. 

Mean  Threshold  Value 
.     grammes 
sq.  <im. 

Wrist  (ventral  surface) 
Wrist  (dorsal  surface) 
Forearm  - 

Elbow       ...         . 
Upper  arm        ... 
Foot  (dorsal  surface) 
Leg  (ventral  surface) 
Thigh  (ventral  surface) 
Breast 
Back         - 

28 
28 
16 
12 
IO 

23 

5 

2  I 
26 

I    I 
I'2 
12 

i'3 
1*4 

V2 

2"  I 

1  "3 
1*3 

(Kiesow). 

If  two  points  of  the  skin  are  touched  at  the  same  time  there  is 
a  double  sensation  when  the  distance  between  the  points  exceeds 
a  certain  minimum,  which  varies  for  different  parts  of  the  sensitive 
surface. 

Practice  increases  the  acuity  of  touch  for  the  two  points  test.  Even 
in  a  few  hours  it  may  be  temporarily  quadrupled  on  some  parts  of 
the  skin.  Since  at  the  same  time  it  is  increased  in  the  corresponding 
part  of  the  opposite  side  of  the  body,  it  is  argued  that  the  modifica- 
tion takes  place  in  the  central  nervous  system,  not  in  the  end-organs 
themselves. 


////    SENSES 


971 


1  listance  at  which  Two  ! 

vim- 

ran  be  distinctly  fell ,  in 

nun. 

Point  of  tongue  - 

Palmar  surface  of  third 

phalanx  of  finger 

2"2 

Dorsal  surface  of  third 

phalanx  of  finger 

67 

Tip  of  nose  - 

67 

Back  - 

T  I"2 

Eyelids 

II'2 

Skin  over  sacrum 

4°*5 

Upper  arm  - 

67-6 

Few  of  the  internal  organs  are  supplied  with  tactile  nerves.  The 
movements  of  a  tapeworm  in  the  intestines  are  not  recognised  as 
tactile  sensations,  nor  the  movements  of  the  alimentary  canal  during 
digestion,  nor  the  rubbing  of  one  muscle  on  another  during  its 
contraction. 

Pressure  is  only  perceived  when  it  affects  two  neighbouring  areas 
to  a  different  degree.  Thus,  the  atmospheric  pressure,  bearing 
uniformly  on  the  whole  surface  of  the  body,  causes  no  sensation  ;  we 
are  so  entirely  unconscious  of  it  that  it  needed  the  inspiration  of 
genius  to  discover  it,  and  the  persistence  of  genius  to  force  the  dis- 
covery on  the  world.  When  the  finger  is  clipped  in  a  trough  of 
mercury  at  its  own  temperature,  no  sensation  is  perceived  except 
a  feeling  of  constriction  at  the  surface  of  the  liquid.  The  perception 
of  light  pressure  and  of  the  form  and  size  of  objects  in  contact  with 
the  skin  is  believed  to  be  due  to  the  touch-spots.  Deep  pressure, 
however,  is  appreciated,  not  by  the  skin,  but  through  sensory  end- 
organs  in  deeper  structures — probably,  e.g.,  Pacini's  corpuscles  and 
the  muscle-spindles   (Fig.  433,  p.  983). 

Sensations  of  Temperature. — When  a  body  colder  or  hotter 
than  the  skin  is  placed  on  it,  or  when  heat  is  in  any  other  way 
withdrawn  from  or  imparted  to  the  cutaneous  tissues  with  suffi- 
cient abruptness,  a  sensation  of  cold  or  warmth  is  experienced. 
And  when  two  portions  of  the  skin  at  different  temperatures  are 
put  in  contact,  we  feel  that,  relatively  to  one  another,  one  is 
warm  and  the  other  cold.  But  it  is  worthy  of  remark  that  it  is 
only  difference  of  temperature  (or,  perhaps,  rather  the  rate  at 
which  heat  is  being  gained  or  lost  by  the  skin),  and  not  absolute 
height,  which  we  are  able  to  estimate  by  our  sensations.  Thus, 
a  hand  which  has  been  working  in  ice-cold  water  will  feel  water 
at  io°  C.  as  warm  ;  whereas  it  would  appear  cold  to  a  warm  hand. 

Blix,  Goldscheider,  and  others  have  shown  that  the  whole  skin 
is  not  endowed  with  the  capacity  of  distinguishing  temperature, 
but  that  the  temperature  sensations  are  confined  to  minute 
scattered  areas  over  the  cutaneous  surface.  The  great  majority 
of  these  are  '  cold  '  spots — i.e.,  respond  to  stimulation  only  by  a 
sensation  of  cold — while  a  smaller  number  are  '  warm  '  spots,  and 


.1   .1/  I  \r  ;/.  OF  PHYSIOLOGY 


JEIKS 


respond  only  by  a  sensation  of  warmth  (Fig.  427).  These  spots  can 
I  ■■'  mapped  out  by  bringing  into  contact  with  the  skin  small  pieces 
of  wire  at  a  temperature  a  few  degrees  above  or  below  that  of  the 
skin.  With  such  mild  stimuli  a  response  can  generally  be  obtained 
only  from  one  kind  of  spot — that  is,  the  cold  wire  stimulates 
only  the  cold  and  not  the  warm  spots,  and  vice  versa — but  with 

much  more  intense  thermal  stimuli 
— say,  temperatures  of  450  to  500  C. 
— not  only  do  the  warm  spol 
spond  with  the  appropriate  sensa- 
tion, but  the  cold  spots  respond 
with  a  sensation  of  cold.  This  is 
well  seen  when  a  beam  of  sunlight 
is  focussed  successively  on  a  warm 
and  a  cold  spot.  Inadequate  stimuli 
(mechanical  and  electrical)  also  evoke 
the  specific  response  of  warmth  from 
warm  spots,  and  of  cold  from  cold 
spots. 

When  the  hand  is  put  into  water 
at  the  temperature  of  the  skin,  and 
the  water  slowly  heated,  the  warm 
spots  are  at  first  alone  stimulated, 
and  the  sensations  of  lukewarm  and 
then  of  warm  are  experienced. 
When  the  temperature  of  the  water 
reaches  450  C.  the  quality  of  the 
sensation  changes  to  '  hot.'  At  a 
still  higher  temperature  the  sensa- 
tion becomes  painful  or  burning. 
The  most  probable  explanation  of 
these  facts  is  mentioned  below 
(P.  974)- 

It  is  not  only  of  physiological  in- 
terest, but  of  practical  importance, 
that  most  mucous  membranes  are  in 
comparison  with  the  skin  but  slightly 
sensitive  to  changes  of  temperature 
<  tally  towards  the  ends  of  the  alimen- 
tary canal,  in  the  mouth,  pharynx, 
and  rectum,  and  to  some  extent  in 
the  stomach,  does  a  blunted  sensi- 
bility appear.  The  uterus,  too,  is 
quite  insensible  to  moderate  heat ; 
and  hot  liquids  may  be  injected  into  its  cavity  at  a  temperature  higher 
than  thai  which  can  be  borne  by  the  hand,  without  causing  incon- 
venience -a  fact  which  finds  its  application  in  the  practice  of  gynar- 
cology^and  obstetrics.     It  is,  indeed,   obvious  that    in  the  greater 


AND 

Skin- 


Fig.  427.  —  'Warm' 
'  Cold  '  Areas  on 
(Goldscheider). 

The  areas  are  mapped  out  on 
the  palm  of  the  left  hand.  In 
the  upper  figure  the  relative 
sensitiveness  to  warmth  is 
represented  by  the  depth  of  the 
shading,  the  black  areas  being 
nmst  sensitive,  then  the  lined 
an  is,  then  the  dotted,  and 
last  of  all  the  white  areas.  In 
the  lower  figure  the  relative  sen- 
sitiveness to  cold  stimuli  is 
shown  in  the  same  way. 


Till    SI  NSES  973 

number  of  the  internal  organs  the  conditions  necessary  [<  r  stimula- 
tion oi  temperature  nerves,  even  it  sucb  were  present,  could  hardly 
evei  exist, 

It  has  already  been  mentioned  thai  changes  of  external  tempera- 
ture exert  a  remarkable  influence  on  the  intensity  of  metabolism 
(p,  590),  and  it  has  been  supposed  that  this  is  brought  about  by 
afferenl  impulses  travelling  up  the  cutaneous  nerves.  We  have  also 
seen  that  tor  certain  kinds  of  stimuli  the  excitability  of  nerve-fibres 
is  increased  by  cooling  (p.  <><S  1 ) .  It  is  possible  that  this  is  the  case 
lor  the  fibres  in  the-  skin  which  are  concerned  in  the  regulation  of  the 
production  of  heat,  and  it  has  been  suggested  thai  this  fact  may 
have  a  bearing  on  the  reflex  regulation  of  temperature  (Lorrain 
Smith). 

Pain. 

While  the  cold  and  the  warmth  spots  are  irregularly  distributed 
over  the  skin  in  more  or  less  compact  groups,  and  the  touch 
sensations  are  intimately  associated  with  the  hair  follicles,  the 
pain  spots  are  more  uniformly  spread,  and  at  the  same  time  set 
closer  together.  In  parts  of  the  body  where  but  one  of  these 
elementary  forms  of  general  sensibility  is  present,  a?  in  the 
central  parts  of  the  cornea  and  in  the  dentine  and  pulp  of  the 
teeth,  it  is  always  pain. 

In  certain  situations  pain  and  temperature  sensibility  are 
found  together,  but  not  touch — e.g.,  at  the  margin  of  the  cornea 
and  on  the  conjunctiva. 

In  general,  the  skin  is  far  more  sensitive  to  pain  than  the 
deeper  structures.  The  most  painful  part  of  an  operation  is 
generally  the  stitching  of  the  wound.  The  cutting  of  healthy 
muscle  causes  no  pain.  In  an  operation  in  which  an  artificial 
connection  was  established  between  the  stomach  and  the  small 
intestine  (gastroenterostomy),  and  in  which  no  anaesthetic  was 
administered,  the  only  pain  of  which  the  patient  complained 
was  produced  by  the  incision  in  the  skin  (Senn).  This,  however, 
does  not  prove  that  the  abdominal  viscera  are  devoid  of  pain 
nerves,  for  it  has  been  shown  in  animals  that  exposure  of  the 
intestines,  etc.,  as  in  laparotomy,  leads  to  a  rapid  depression 
(exhaustion  ?)  of  the  sensibility  for  pain  (Kast  and  Meltzer). 
In  the  intact  animal  and  human  being  painful  impressions  can 
unquestionably  be  excited  in  the  viscera  by  adequate  stimuli 
(p.  799).  Thus,  the  spasmodic  contraction  of  the  intestines  and 
stomach  causes  the  intense  pain  of  colic  and  gastralgia.  Labour 
is  an  example  of  a  strictly  physiological  function  which  is  the 
occasion  of  severe  pain.  Tissues  normally  insensible,  or,  rather, 
but  slightly  sensible,  to  pain  may  become  acutely  painful  when 
inflamed. 

The  question  has  been  raised  whether  the  sensation  of  pain 
can  be  caused  by  excessive  stimulation  of  the  nerves  of  common 
tactile  sensibilitv,  or  of  the  nerves  that  subserve  the  sensations 


974  I  MANUAL  OF  PHYSIOLOGY 

"t  coolness  and  warmth.  It  is  true  that  when  the  >\^\\\  is  lightly 
touched  in  the  region  of  a  touch-spot  with  a  small  object  at  its 

own  temperature  the  sensation  is  one  of  pure  t<>uch.  As  the 
pressure  is  increased,  a  sensation  of  pressure,  quite  distinct  from 
that  of  contact,  may  he  felt ;  and  if  the  pressure  is  still  further 
increased,  a  sensation  of  pain  may  be  elicited.  It  seem^  t<>  be 
quite  clearly  made  out  that  the  pressure  sensation  in  this  case 
is  due  not  to  excessive  stimulation  of  the  touch-nerves,  but  to 
stimulation  of  the  specific  pressure-nerves  when  the  threshold 
is  reached.  The  most  natural  explanation  of  the  pain  sensation 
is  that  it,  too,  is  due  to  excitation  of  the  nervous  apparatus 
for  pain.  Similarly  (as  was  stated  on  p.  972),  if  the  skm 
is  raised  to  higher  and  higher  temperatures,  the  response 
is  at  first  a  pure  sensation  of  warmth,  increasing  in  intensity 
without  changing  its  quality.  When  a  certain  temperature 
(about  45'  C.)  is  exceeded,  the  sensation  changes  to  '  hot,'  either 
because  a  pain  element  is  now  added  to  the  pure  thermal 
sensation,  or  because  the  cold  spots  are  now  stimulated  as  well 
as  the  warm  spots,  and  mingle  their  specific  response  (cold 
sensation)  with  that  of  the  warm  spots.  Further  increase 
of  the  temperature  will  cause  distinct  pain,  the  sensation 
assuming  a  burning  character.  When  a  cold  spot  is  tested 
with  decreasing  temperatures,  an  analogous  series  of  sensations 
is  run  through,  the  pure  sensation  of  coolness  eventually  giving 
place  to  cold,  intense  cold,  and  finally  pain.  Here,  also,  it  is 
simplest  to  assume  that  the  pain  sensation  is  caused  not  by 
excessive  stimulation  of  warm  or  cold  spots,  but  by  excitation 
of  the  specific  pain-spots.  In  any  case,  there  is  no  doubt  that 
afferent  '  pain  '  fibres  exist  which  are  anatomically  distinct  from 
the  fibres  of  tactile  and  of  temperature  sensations.  For  the 
conducting  paths  in  the  spinal  cord  are  not  the  same  for  tactile 
and  for  painful  impressions.  And  in  certain  cases  of  disease 
sensibility  to  pain  ma}'  be  lost,  while  tactile  sensations  are  still 
perceived  ;  or,  on  the  other  hand,  pain  may  be  felt  in  cases 
where  tactile  sensibility  is  abolished.  Loss  of  temperature 
sensation,  however,  is  usually  accompanied  by  loss  of  sensibility 
to  pain.  When  a  nerve  is  compressed,  the  sensibility  of  the 
tract  supplied  by  it  disappears  for  cold  sooner  than  for 
warmth. 

Pain  has  been  defined  as  '  the  prayer  of  a  nerve  for  pure  blood.' 
The  idea  is  not  only  true  as  poetry,  but,  with  certain  deductions  and 
limitations,  true  as  physiology  ;  that  is  to  saw  pain,  as  a  rule,  is 
a  sign  that  something  has  gone  wrong  with  the  bodily  machinery  ; 
freedom  from  pain  is  the  normal  state  of  the  healthy  body.  Pin 
logically,  pain  acts  as  a  danger-signal.  It  points  out  the  scat  of  the 
mischief,  and  even,  in  certain  cases,  by  compelling  rest,  favours  the 
process  of  repair.     Thus,  the  surgeon  has  sometime*  looked  upon 


THE   SI  NSES  975 

pain  as  'Nature's splint.'  But,  as  a  matter  oi  fact,  a <  ertain  amount 
<it  pain  occurring  at  intervals  is  not  incompatible  with  high  health  ; 
and  probably  nobody,  even  when  accidents  and  indiscretions  of  all 
kinds  are  avoided,  is  entirely  free  from  pain  for  any  considerable 
time.  Sometimes,  indeed,  the  mere  fixing  of  the  attention  on  a 
particular  part  of  the  body  is  sufficient  to  bring  out  or  to  detect  a  slight 
sensation  oi  pain  in  it  ;  and  it  is  matter  of  common  ex  peril  nee  that  a 
ilull  continuous  pain,  like  that  of  some  tonus  of  toothache,  is  aggra- 
vated  by  thinking  of  it.  and  relieved  when  the  attention  is  diverted. 

As  to  the  sensations  oi  tickling  and  itching,  it  is  enough  to 
say  that  physiologists  are  not  agreed  whether  they  represent 
specific  sensibilities  subserved  by  special  nerves  distinct  from 
those  of  touch  and  pain ,  or  merely  modifications  or  mixtures  of 
these  sensations. 

Phenomena  observed  after  Section  of  Cutaneous  Nerves. — 
The  innervation  of  the  skin  can  be  explored  not  only  by  appro- 
priate stimulation  of  the  normal  skin,  but  by  study  of  the  defects 
or  alterations  of  sensibility  which  follow  section  of  a  cutaneous 
nerve,  and  which  may  be  observed  at  different  stages  in  its 
regeneration.  In  recent  years  this  has  proved  a  fruitful  method, 
especially  in  experiments  made  by  skilled  observers  in  whom 
one  or  more  cutaneous  nerves  were  intentionally  divided. 

Quite  recently  a  very  elaborate  investigation  has  been  made 
by  Trotter  and  Davies.  They  divided  at  different  times,  ex- 
tending over  more  than  a  year,  no  fewer  than  seven  of  their  own 
cutaneous  nerves,  including  the  internal  saphenous  at  the  knee, 
the  great  auricular,  three  divisions  or  branches  of  the  internal 
cutaneous  of  the  arm  just  below  the  elbow,  and  a  branch  of  the 
middle  cutaneous  of  the  thigh.  The  operations  were  purposely 
done  at  such  intervals  as  would  allow  the  experience  gained  in 
investigating  one  area  to  be  applied  to  others.  About  a  quarter 
of  an  inch  was  cut  out  of  each  nerve,  and  the  ends  then  sutured 
togethei.  '  In  each  case  the  area  of  skin  supplied  by  the  nerve 
showed  defects  in  seven  distinct  functions  :  four  sensory — namely, 
sensibility  to  touch,  cold.  heat,  pain — and  three  motor — namely, 
vaso-motor.  pilo-motor,  sudo-motor  (sweat-secretory).  The 
sensory  changes  showed  a  central  area  of  profound  loss,  an  area 
of  moderate  extent  surrounding  this  of  partial  loss,  and  a  large 
area  in  which  a  qualitative  change  could  be  alone  detected.' 
The  maximal  extent  of  change,  and  therefore  the  outer  boundary 
of  this  third  area,  can  be  mapped  out  by  getting  the  subject  to 
determine  by  light,  stroking  touches  the  area  which  feels  in  any 
way  unnatural  when  he  touches  it  himself.  The  most  common 
feeling  is  that  the  skin  has  become  smoother  at  the  boundary  as 
the  stroking  finger  crosses  it,  coming  from  the  normal  skin.  This 
area  is  always  much  larger  than  the  area  included  in  it,  in  which 
by  quantitative  methods — e.g.,  the  use  of  a  very  fine  camel's- 


976 


I    1/  /  vr  ;/    OF  PHYSIOLOGY 


hair  l>rush.  01  more  exactly  by  the  v.  Frey  hairs  the  sensi- 
bility tn  touch  can  be  shown  to  be  diminished  (region  ol  hypo- 
sesthesia  to  toui  h)  |  Fig.  428). 

For  a  variable  distance  within   the  'stroking  outline'   the 
hypoaesthesia  for  tactile  stimuli  is  so  slighl   thai   it  cannol   be 


W£Srn£S/A  TO     y 


\ 

iiTflOHIIVG  0(/TillV£- 


I'll,.  ^8.— Areas  01  Altered  Sensibility  produced  by  Section  hi  mi. 
Three  Branches  of  thb  Internal  Cutaneous  Nervi  of  nn  Mm 
Forearm  (Trotter  and  Davies).     (Reduced  by  Two-thirds.) 

The  thick  lines  show  tin-  areas  "t  anaesthesia  t<>  tin'  brush.  The  /link  continuous 
lines  enclose  the  areas  o\  the  anterior  and  posterior  branches.  I'he  thick  broken 
line  and  heavy  shading  mark  tin-  area  oi  the  in.  rease  in  anaesthesia  which  followed 
section  "f  tin-  middle  branch.  The  thin  lines  show  tin-  areas  ,.1  minimal  hypo- 
ssthesia  i.e.,  the  'stroking  outline.'  The  complete  oval  outline  is  the 'stroking 
outline'  which  followed  section  oi  tin-  posterior  branch.  The  large  addition  /<• 
the  oval  on  the  right  of  th,-  diagram  slu.u^  tin-  increase  in  the  'stroking  outline1 
which  followed  --r.ii.in  oi  the  anterior  branch.  The  thin  broken  line  and  fine 
shading  show  the  additions  t"  the  '  stroking  outline  '  produced  by  division  oi  the 
middle  brant  h. 

detected  with  the  brush  or  with  cotton-wool,  or  even  with  the 
v.  Frey  hairs.  Like  those  of  normal  skin,  90  per  cent,  of  its 
hair-bulbs  respond  to  a  hair  exerting  a  pressure  of  70  milli- 
grammes, and  the  remaining  10  per  cent,  to  hairs  exerting  a 
pressure  of  140  or  280  milligrammes.  Inside  this  zone  of  minimal 
hypoaesthesia  the  defect  of  sensibility  rapidly  increases  as  we 


////■  SI  VSES 


<>77 


pass  inwards,  each  line  of  hair-bulbs  requiring  a  heavier  pressure 
than  the  line  external  to  it.  till  at  Lasl  ;l  or  \  grammes'  pressure 
is  needed  to  cause  a  sensation  of  touch,  and  inside  of  this  line  of 
hairs  the  skin  does  nol  respond  at  all.  When  a  bristle  of  this 
pressure  fails  to  elicil  touch  sensation,  no  greater  pressure  will  in 
genera]  do  so  (Fig.  429). 

For   thermal   sensibility   there   is  also  a  region  of  complete 


+     o    \    . 
+  0     o    . 


♦    ♦     «  e 
1  »  ",    o 


lie.  429. — Middle  Cutaneous  :  Left  Thigh  (Trotter  and  Davies) 
(reduced  by  One-third   Linear). 

Twenty-six  days  after  section.  Results  of  examination  with  v.  Frey  hairs. 
Touch  spots  marked  •  responded  to  hair  of  280  milligrammes'  pressure;  those 
marked  o  to  hair  of  Soo  milligrammes  ;  and  those  marked  +  to  hair  of  2,280  milli- 
grammes. The  continuous  line  marks  the  limit  within  which  there  was  anaesthesia 
to  the  camel's-hair  brush. 


anaesthesia  and  a  region  of  partial  anaesthesia.  The  best  way  of 
outlining  these  is  the  use  of  a  temperature  of  o°  C.  as  the  stimulus 
(Fig.  430). 

Outside  the  zone  of  complete  thermal  anaesthesia  there  is  a 
region  in  which  temperature  sensations  are  distinctly  elicited, 
but  do  not  possess  the  normal  intensity,  the  temperature  of 

62 


9;  S 


/   M  I  xr  ii.  OF  PHYSIOLOGY 


0°  C.  for  example,  being  felt  only  ;is  cool,  and  not  as  cold.  The 
outer  limit  of  this  region  is  the  line  at  which  the  temperature 
of  o°  C.  is  first  fell  as  we  work  inwards  from  the  normal  skin  to 
yield  the  sensation  of  cool  instead  of  cold.  Similarly,  the  outer 
limit  of  thermo-hypoaesthesia  can  be  deteimined  by  using  a  high 
temperature  (50  C).  It  is  the  line  at  which  the  sensation  of 
hot  yielded  by  the  normal  skin  gives  place  to  the  sensation  of 


Fig.  430. — Middle  Cutaneous:  Left  Thiih  (Trotter  and  Davies). 
Twenty-one  days  after  section.  Results  of  examination  with  temperature  of 
0°  C.  On  spots  marked  •  stimulus  was  felt  as  cold  ;  on  spots  marked  o  it  was 
felt  as  cool.  The  blank  area  is  that  of  thermal  anaesthesia.  The  continuous 
outline  marks  the  limit  within  which  there  was  anaesthesia  to  the  camel's-hail 
brush. 


warm.  The  two  boundaries  correspond  closely  when  allowance 
is  made  for  the  separate  grouping  of  cold  and  warmth  spots  on  the 
normal  skin. 

The  investigation  of  the  sensibility  of  the  skin  areas  for  painful 
stimuli  is  complicated  by  the  fact  that  during  a  certain  period, 
from  about  the  second  to  the  sixth  week  after  division  of  the 


////    SI  NS1  S 


nerve,  hyperalgesia  (increased  sensitiveness  to  painful  impres- 
sions) may  appear.  This,  however,  does  no1  seem  to  be  a  con- 
sequence of  any  sensory  less,  but  rather  a  complication  due  to 
an  irritative  change.  Winn  this  is  taken  account  of,  it  is  found 
that  the  defecl  of  sensibility  to  pain  alter  nerve  section  resembles 
the  defects  of  sensibility  to  touch  and  temperature,  showing  a 
central   area  of   absolute   aiwesthesia  surrounded    by  a  zone  of 


Fig.   431. — Middle   Cutaneous  (External  Branch)  :   Left  Thigh   (Trotter 

and  davies). 

Twenty-three  days  after  section.  Results  of  examination  with  algometer  (an 
arrangement  by  which  a  needle  is  pressed  against  the  skin  by  a  hair  whose  pres- 
sure value  has  been  determined).  Spots  marked  •  reacted  by  sensation  of  pain 
to  pressure  of  1,860  milligrammes  (normal  threshold)  ;  Spots  marked  o  required 
j.jSo  milligrammes.  The  continuous  line  marks  the  area  within  which  there 
was  anaesthesia  to  the  camel's-hair  brush. 

partial  loss,  which  is  slight   towards  the  outer   boundary,   but 
increases  as  we  pass  inwards  (Fig.  431). 

After  section  of  a  nerve  function  is  recovered  only  as  a  result 
of  regeneration.  This  is  true  of  all  the  sensory  functions  of  the 
skin  and  of  the  pilo-motor  and  sudo-motor  functions.  Vaso- 
motor tone  in  the  affected  area  is  restored  much  sooner  than 
the  other  functions.     This  rapid  recovery  probably  depends  upon 

62 — 2 


980  A   .1/  INUAL  OF  PHYSIOLOGY 

a  local  compensatory  mechanism,  and  not  upon  regeneration  of 
the  vaso-motoi  fibres.  Recovery  of  all  the  functions  dependent 
upon  regeneration  begins  about  the  same  time,  and  this  recovery 
progresses  over  the  area  at  about  the  same  rate  for  all.  although 
the  rate  at  which  they  progress  towards  normal  acuity  is  dif- 
ferent. 

Sensibility  to  touch  probably  appears  a  little  earlier  than  sensi- 
bility to  cold  and  pain.  Yet  the  recovery  of  touch  does  not 
progress  so  fast,  and  for  a  while  a  given  zone  of  the  recovering 
area  remains  hypoaesthetic  (less  sensitive  than  normal)  to  touch, 
while  to  cold  and  pain  it  soon  becomes  even  hypersensitive. 
The  most  remarkable  peculiarities  of  a  recovering  area  are  : 
(i)  This  qualitative  change,  in  virtue  of  which  cold,  pain,  and 
the  pain  element  of  heat  are  intensified,  while  touch  is  little 
altered,  although  more  difficult  to  elicit  ;  (2)  the  reference  of 
sensations,  not  to  the  point  stimulated,  but  to  distant  parts  oi 
the  area. 

'  When  a  spot  which  has  developed  this  peripheral  reference  is 
touched,  one  of  two  possibilities  may  occur  :  either  the  touch  is 
felt  locally,  and  is  referred  as  well,  or  nothing  is  felt  locally,  and 
the  touch  is  felt  in  the  area  of  peripheral  reference.  The  region 
in  which  the  referred  touch  is  felt  is  always  at  the  edge  of  the 
most  peripheral  part  of  the  anaesthesia,'  perhaps  more  than 
a  foot  away  from  the  spot  actually  touched.  The  peripheral 
reference  of  cold  is  even  more  striking,  particularly  in  the  re- 
markable intensity  of  the  referred  sensation. 

Peripheral  reference  occurs  also  with  pain.  '  The  referred 
pain  shows  three  well-marked  qualities  :  it  is,  proportionate!  v 
to  the  stimulus,  very  intense  ;  it  does  not  reproduce  a  normal 
sensation  with  the  exactitude  found  in  the  case  of  touch  or 
cold,  but  has  a  special  quality  of  strangeness  and  unpleasantness, 
such  as  no  pin-prick  on  normal  skin  can  give  ;  finally,  it  produces 
an  almost  irresistible  desire  on  the  part  of  the  subject  to  rub  or 
scratch  the  region  in  which  it  is  felt.'  As  recovery  proceed 
the  local  sensory  response  becomes  more  distinct,  and  the 
abnormal  quality  of  both  local  and  referred  sensations  fades. 
But  '  while  peripheral  reference  is  the  earliest  phenomenon  of 
recovery,  it  persists  until  recovery  is  so  far  advanced  that  hypo- 
aesthesia  is  scarcely  detectable  by  any  quantitative  methods.' 

It  is  a  remarkable  circumstance  that  during  regeneration 
stimulation  of  the  nerve-trunk  itself  below  the  section,  by  the 
application  of  touch,  cold,  or  pain  stimuli  to  the  skin  over  its 
course,  produces  peripherally  referred  sensations  of  the  corre- 
sponding kind.  This  is  the  case  even  when  the  nerve  is  stimu- 
lated outside  the  formerly  anesthetic  area,  and  suggests  that  the 
nerve-trunk  itself  has  acquired  the  specific  sensibility  normally 


THE'Sl   \  s/  s  9*1 

assot  iated  with  the  terminal  organs  of  its  afferenl  fibres  through 
the  loweringoi  the  threshold  for  the  fibres  themselves. 

The  work  ol  Head,  who  was  the  pioneer  in  this  method  ol  investi- 
gation, must  also  be  mentioned.  He  found  that  when  themedian 
nerve  was  divided  in  his  own  arm,  total  loss  of  sensation  was  caused 
over  the  greater  pari  of  the  index  and  middle  fingers,  and  over  a 
portion  oi  the  thumb  in  its  palmar  aspect.  In  addition,  sensation 
was  partialis-  lost  over  .1  larger  area,  where  there  was  complete 
insensibility  to  certain  stimuli,  such  as  light  touch,  moderate  heat 
and  cold,  and  where  the  contact  of  the  two  points  of  a  pair  of  com- 
passes could  not  be  discriminated.  Recovery  of  sensation  after 
complete  division  of  a  peripheral  nerve  began  with  the  restoration 
of  sensibility  to  pain  and  to  extreme  degrees  of  heat  and  cold  ; 
but  the  hand  still  remained  for  a  time  as  insensitive  as  before  to 
such  stimuli  a  slight  touch.  In  the  parts  which  had  regained  their 
s  nsibility  to  severe  stimuli,  like  pricking  and  extremes  of  heat  and 
cold,  the  sensation  radiated  widely,  was  referred  to  remote  parts, 
and  could  not  be  accurately  localized.  This  form  of  sensibility 
Mead  calls  protopathic.  As  the  nerve  recovered  further,  a  second 
form  of  sensibility  appeared,  associated  with  accurate  localization 
ol  cutaneous  stimuli  and  discrimination  of  two  compass  points. 
Light  touch  and  moderate  degrees  of  heat  and  cold  could  now  be 
again  appreciated.  This  form  of  sensibility  he  terms  epicritic.  A 
third  form  of  sensibility  (deep  sensibility)  was  investigated  after 
complete  division  of  the  radial  and  external  cutaneous  nerves  at  the 
elbow.  The  radial  half  of  the  arm  and  back  of  the  hand  became 
totally  insensitive  to  cutaneous  stimuli,  but  retained  their  sensibility 
to  pressure  or  to  any  stimulus  which  deformed  the  subcutaneous 
structures,  as  well  as  their  power  of  localization  of  such  stimuli. 
The  afferent  fibres  upon  which  this  deep  sensibility  depends  must 
run  with  the  motor  nerves.  According  to  Head,  the  other  two  forms 
of  sensibility  (protopathic  and  epicritic)  also  depend  on  two  separate 
systems  of  nerves.  It  is  assumed  that  the  protopathic  fibres  re- 
generate more  easily  and  speedily  than  the  epicritic  or  than  the 
motor  nerves  of  voluntary  muscle.  The  protopathic  fibres  are  sup- 
posed by  Head  to  exert  a  trophic  influence.  A  part  deprived  of  its 
nerve-supply  is  liable  to  injuries,  and  the  sores  so  produced  heal 
slowly.  But  as  soon  as  '  protopathic  '  sensibility  returns  to  the  part, 
they  heal  rapidly,  even  in  the  absence  of  all  epicritic  sensation. 
The  intestine  is  described  as  possessing  '  protopathic,'  but  not 
'  epicritic,'  sensibility — i.e.,  it  reacts  to  extremes  of  heat  and  cold, 
but  not  to  moderate  heat  and  cold  or  light  touch. 

Head's  experimental  results  must  be  sharply  distinguished  from 
his  interpretation  of  them,  and  the  student  is  warned  that  the  dis- 
tinction of  protopathic  and  epicritic  sensibility  has  met  with  adverse 
criticism.  There  does  not  seem  to  be  any  real  necessity  in  the 
observed  facts  for  introducing  so  revolutionary  a  conception  of  the 
nervous  system.  Nor  is  it  possible  to  uphold  the  distinction  in  any 
thoroughgoing  fashion  for  all  structures.  For  instance,  in  abdo- 
minal operations  performed  under  local  anaesthesia  it  has  been  seen 
that  the  parietal  peritoneum  is  quite  insensitive  to  touch,  pressure, 
and  temperature  stimuli,  including  extreme  temperatures  (Ram- 
strom),  while  pain  is  caused  by  traction  on  it.  Its  sensibility  is 
therefore  neither  purely  epicritic  nor  purely  protopathic  in  Head's 
sense.     In  like  manner  the  mucous  membrane  of  the  mouth,   in 


A  M.I  \i    II.  (>/■    IIIYSIOLOGY 

which  sensibility  only  to  touch  and  temperature  is  present,  con- 
forms entirely  to  neither  type.  Its  sensibility  is  not  alone  epicritii  . 
since  i\  responds  to  extreme  temperatures,  nor  is  it  purely  proto- 
pathic,  since  a  pin-prick  produces  no  painful  sensation. 

Localization  of  Cutaneous  Sensations.  -We  not  only  perceive  the 
quality  and  estimate  the  intensity  of  sensations  of  touch,  tempi 
lure,  pain,  etc.,  but  arc  able,  more  or  less  accurately,  to  localize  the 
pari  of  the  body  from  which  the  sensory  impressions  come.  In 
other  words,  two  impressions  from  different  parts  of  the  body. 
although  identical  in  quality  and  intensity,  are  nevertheless  stamped 
with  a  distinctive  something,  which  may  be  called  the  local  sign. 
This  power  of  localization  is  not  equal  for  all  portions  of  the  body 
nor  for  all  kinds  of  sensations.  It  is  best  developed  for  touch  (in 
the  restricted  sense),  and  all  the  varieties  of  common  sensation 
are  better  localized  on  the  skin  than  in  any  of  the  deeper  struct  n 
The  precise  mechanism  of  the  localization  is  unknown.  But  we 
must  suppose  that  each  peripheral  area  is  'represented'  in  the 
brain,  so  that  flu1  arrival  of  afferent  impulses  from  it  affects  par- 
ticularly the  related  cerebral  area.  The  brain,  therefore,  so  to  speak. 
associates  excitation  of  a  given  cerebral  area  with  stimulation  of 
the  corresponding  peripheral  area,  and  thus  not  only  recognises  the 
quality  and  quantity  of  the  resultant  sensation,  but  also  localizes 
it  ;  just  as  a  waiter  who  watches  the  bell-indicator  not  only  learns 
how  a  bell  has  been  rung,  whether  once  or  twice,  peremptorily  or 
languidly,  but  also  in  which  room  it  has  been  rung.  If.  to  pursue 
the  illustration  a  little  farther,  he  is  aware  that  two  rooms  are  con- 
nected with  one  bell,  but  that  one  of  the  rooms  is  scarcely  ever 
occupied,  he  associates  the  ringing  of  the  bell  with  a  summons  from 
the  other  room  even  when  it  happens  to  be  rung  from  the  usually 
vacant  room.  In  like  manner  the  brain  seems  to  connect  the  arrival 
of  sensory  impulses  from  the  internal  organs,  which  have  few  sen- 
sory fibres,  and  these  perhaps  not  often  stimulated,  with  excitation 
in  a  related  cutaneous  region,  from  which  it  is  constantly  receiving 
sensory  impressions.  The  fact  already  mentioned  (p.  790),  that  in 
disease  of  internal  organs  the  pain  is  referred  to  some  portion  of 
the  skin,  may  be  thus  explained. 

It  is  through  the  localization  of  touch  sensations  that  the  size 
and  form  of  objects  in  contact  with  the  skin  are  perceived  in  the 
absence  of  other  than  the  cutaneous  sensations,  and  especially  in 
the  absence  of  visual  and  muscular  sensations  (stereognosis) . 

Muscular  Sensations  (Muscular  Sense),  etc. 

Sometimes,  although  rather  loosely,  grouped  together  as  muscular 
sensations,  area  number  of  formsof  sensation  of  which  our  knowledge 
is  much  less  accurate  than  it  is  in  the  case  of  the  fundamental  skin 
sensations.  Among  these  may  be  mentioned  especially  (1)  the 
sensations  by  which  the  position  in  space  of  the  body  as  a  whole 
or  of  particular  parts  is  recognised  in  the  absence  of  visual  sensa- 
tions ;  (2)  the  sensations  associated  with  movements,  passive  as  well 
as  active;  (3)  the  sensations  associated  with  resistance  to  move- 
ment. In  none  of  these  groups  arc-  we  (haling  with  purely  mus- 
cular sensations  ;  cutaneous  tactile  sensations  and  pressure  sensa- 
tions elicited   from  other  structures  than  muscles  are  also  invoked. 

Voluntary  muscular  movements  are  accompanied  with  a  peculiar 
s  -ns.it  ion  ol  effort,  graduated  according  to  the  strength  of  the  con- 


nil    SENSES 


983 


traction,  and  affording  data  from  which  a  judgment  as  to  its  amount 
.mil  (In  1  ( t  ion  may  l"-  Conned, 

Seme  writers  have  supposed  tli.it  this  so-called  muscular  sense 
does  not  depend  upon  afferent  impulses  at  all,  but  that  the  nervous 
centres  from  winch  the  voluntary  impulses  depart  take  cognizance, 
retain  a  record,  so  to  speak.  >>t  tin-  quantity  of  outgoing  nervous 
force  ;  that  the  effort  which  we  ted  in  ,.  ... 

lifting  a  heavy  weight  is  an  effort  of 
the  cells  of  the  motor  centres  from 
which  the  groups  of  muscles  are  inner- 
vated, and  not  of  the  muscles  them- 
selves. 

But  although  this  feeling  of  central 
effort  or  outflow  (we  can  hardly  say 
oi  central  fatigue)  may  be  a  factor,  it 
cannot  be  doubted  that  the  brain  is 
kept  in  touch  with  the  contracting 
muscle  by  impulses  of  various  kinds 
which  reach  it  by  different  afferent 
channels. 

The  corpuscles  of  Pacini,  which  exist  in  considerable  numbers  in 
the  neighbourhood  of  joints  and  ligaments,  and  in  the  periosteum  of 
bones,  would  seem  well  fitted  to  play  the  part  of  end-organs  for  the 
tactile  sensations  caused  by  the  movements  of  flexion,  extension,  or 
rotation  of  one  bone  on  another,  which  form  so  large  a  portion  of 
all  voluntary  muscular  movements.  And  it  has  been  stated  that 
paralysis  of  these  bodies  in  the  limbs  of  a  cat  by  section  of  the 
nerves  going  to  them  causes  a  characteristic  uncertainty  of  move- 


. 


Fig.  432.  —  Nerve-ending  in 
Tendon  near  the  Inser- 
tion ok  the  Muscular 
Fibres  (Golgi). 


fn  n.h 
Fig.  433. — Muscle  Spindle 


(Halliburton,  after  Ruffini) 


c,  sheath  of  the  spindle  ;  n.tr.,  trunk  of  nerve,  which  sends  fibres  through  the 
sheath  into  the  spindle,  where  they  form  endings  (pr.e.,  s.e.,  pl.e.)  of  various 
kinds  :  m.n.b.,  bundle  of  motor  fibres. 


ment  which  suggests  that  something  necessary  to  normal  co-ordina- 
tion has  been  taken  away.  Tendons  also  possess  afferent  nerve- 
fibres,  which  terminate  by  breaking  up  into  reticulated  end-plates 
(Fig.  432).  We  have  already  seen  that  the  skeletal  muscles  possess 
numerous  afferent  fibres  (p.  835).  Some  of  these  must  be  nerves 
of  ordinary  sensation.  For  although,  when  a  muscle  is  laid  bare  in 
man  and  stimulated  electrically,  the  sensation  does  not  in  general 
amount  to  actual  pain,  it  is  capable,  under  the  influence  of  strong 
stimuli,  of  taking  on  a  painful  character.  And  nobody  who  has  felt 
the  severe  and  sometimes  almost  intolerable  pain  of  muscular  cramp 

would  be  likely  to  deny  the  existence  of  sensory  muscular  nerves. 

But  after  deducting  these,  we  must  assume  that  a  large  proportion 


984  A   M  INV  XL  OF  PHYSIOLOGY 

of  the  afferent  nerves  of  muscle  have  other  functions,  and  among 
them  may  be  the  conveyance  of  impulses  connected  with  the  mus- 
cular sense.  The  muscle-spindles  or  ncuro-muscular  spindles 
(Fig.  433),  peculiar  structures  which  occur  in  large  number  in  must 

of  the  skeletal  muscles,  and  have  been  carefully  studied  by  lluber. 
Sihler,  Ruffini,  and  other  observers,  are  the  terminations  of  many 
of  the  sensory  fibres.  They  are  long  narrow  bodies,  with  a  thi<  I 
sheath  of  connective  tissue  enclosing  fine  striped  muscular  fibres 
Medullated  nerve-fibres  enter  the  spindle,  and  there,  dividing  into 
branches  and  losing  their  medullary  sheath,  form  endings  of  various 
kinds  around  and  between  the  muscular  fibres.  It  is  possible  that 
in  contraction  of  the  muscles  the  nerve-fibres  in  the  spindles  are 
compressed,  and  thus  mechanically  stimulated. 

In  the  spinal  cord  these  impulses  are  conducted  up  through  the 
posterior  column  ;  and,  although  less  is  known  as  to  the  paths 
they  follow  in  the  higher  parts  of  the  central  nervous  system,  it  is 
certain  that  there  is  some  afferent  bond  of  connection  between  the 
cortical  motor  areas  and  the  muscles  which  they  control  (p.  856). 

Tactile  sensations  set  up  in  the  skin  or  mucous  membrane  Lying 
over  contracting  muscles  may  also  help  the  nervous  motor  mechanism 
in  appreciating  and  regulating  the  amount  of  contraction  ;  but  the 
fact  that,  in  anaesthesia  of  the  mucous  membrane  covering  the  vocal 
cords  produced  by  cocaine,  the  voice  is  not  at  all  impaired,  shows 
that  muscular  contractions  of  extreme  nicety  can  be  carried  on 
without  any  such  aid. 

Relation  of  Stimulus  to  Sensation. 

It  is  impossible  to  measure  sensation  in  terms  of  stimulus.  All 
that  we  can  do  is  to  compare  differences  in  the  intensity  of  stimuli 
and  differences  in  the  resultant  sensations,  or,  in  other  words,  to 
compare  stimuli  together  and  to  compare  sensations  together.  And 
when  we  determine  the  amount  by  which  a  given  stimulus  must  be 
increased  or  diminished  in  order  that  there  may  be  a  just  perceptible 
increase  or  diminution  in  the  sensation,  it  is  found  that  (with  certain 
limitations)  the  two  are  connected  by  a  simple  law  :  Whatever  the 
absolute  strength  of  a  stimulus  of  given  kind  may  be,  it  must  be  in- 
creased by  the  same  fraction  of  its  amount  in  order  that  a  difference 
in  the  sensation  may  be  perceived  (sometimes  called  Weber's  law). 
Thus,  a  light  of  the  strength  of  one  standard  candle  must  be  in- 
creased by  r&ffth  candle,  a  light  of  10  candles  by  ^J^ths,  and  a  light 
of  100  candles  by  a  candle,  in  order  that  the  eye  may  perceive  thai 
an  increase  has  taken  place,  just  as  the  weight  necessary  to  turn  a 
balance  increases  with  the  amount  already  in  the  pans.  The  frac- 
tion varies  for  the  different  senses.  It  is  about  ,/,,,  for  light,  I  [01 
sound.  But  it  would  appear  that  Weber's  law  does  not  hold  for 
the  pressure  sense,  nor  for  the  other  senses  above  and  below  certain 
limits.     Fechncr,  making  various  assumptions,  has  thrown  Weber's 

law  into  the  form  y=k      &—,  where  y  is  the  intensity  of  sensation, 

Xq 

x  the  intensity  of  stimulation,  x0  the  smallest  intensity  of  stimulus 
which  can  be  perceived  (liminal  intensity),  and  k,  a  constant.  This 
so-called  psycho-physical  law  of  Fechncr  states  that  the  sensation 
varies  as  the  logarithm  of  the  stimulus.  But  1  ec  liner's  law  has 
been  subjected  to  serious  criticism,  and  the  subject  cannot  be 
further  pursued  here. 


PR  ICTIC  U    EXERCISES  985 

PRACTICAL  EXERCISES  ON  CHAPTER  XIII. 

VISION. 

1.  Dissection  of  the  Eye.  The  student  may  profitably  refresh 
his  memory  on  tin-  anatomy  of  the  eve  by  dissecting  a  fresh  eye — 
t  li.it  dt  .1  large  animal  like  an  ox  is  preferable,  but  the  eye  of  a  sheep 
or  dog  may  also  be  used.  The  eve  is  removed  from  the  orbit  by 
cutting  through  the  conjunctiva  where  it  is  reflected  on  to  the  eye- 
lids, carefully  severing  the  extrinsic  muscles  and  scooping  the 
eyeball  out  of  the  mass  of  loose  connective  tissue  and  fat  in  which 
it  is  embedded,  and  which  serves  as  a  cushion  to  protect  it  from 
injury  during  its  movements.  Observe  the  transparent  cornea  in 
front,  blending  at  its  posterior  border  with  the  opaque  sclerotic, 
which  is  covered  by  a  layer  of  conjunctiva  reflected  from  the  lids. 
On  clearing  the  fat  cautiously  away,  the  tendinous  insertions  of 
the  external  or  extrinsic  muscles  of  the  eyeball  into  the  anterior 
part  of  the  sclerotic  will  be  seen.  Identify  the  various  muscles 
(p.  952). 

Immerse  the  eye  in  water  in  a  small  glas;  dish,  with  the  cornea 
uppermost.  The  interior  can  now  be  seen,  because  the  refractive 
index  of  the  cornea  being  nearly  the  same  as  that  of  water,  the 
light  is  only  very  slightly  refracted  there.  The  same  effect  is  pro- 
duced when  a  cover-slip  is  placed  over  the  cornea  in  the  air  ;  a 
plane  surface  being  substituted  for  the  curved  anterior  surface  of 
the  cornea,  its  refraction  is  abolished.  Observe  in  the  fundus  of 
the  eye  the  optic  disc,  eccentrically  placed  in  the  retina,  and  the 
retinal  vessels  radiating  out  from  it.  A  portion  of  the  fundus  shows 
brilliant  iridescent  colours  in  many  animals  (the  tapetum  lucidum). 
This  portion  is  abruptly  bounded  by  a  line  a  little  above  the  optic 
disc.  The  appearance  is  due  to  a  peculiar  arrangement  of  the  con- 
nective-tissue (including  elastic)  fibres  in  this  part  of  the  choroid. 

Pinch  up  with  forceps  a  small  portion  of  the  sclerotic  a  little 
posterior  to  its  junction  with  the  cornea,  and  clip  it  away  with 
fine,  blunt-pointed  scissors,  being  careful  not  to  penetrate  the 
choroid  layer,  which  lies  immediately  beneath  the  sclerotic.  Extend 
the  incision  through  the  sclerotic  backwards,  and  then  transversely, 
and  peel  off  strips  of  the  sclerotic  from  behind  forwards.  The 
lower  surface  of  the  sclerotic  (the  so-called  lamina  fusca)  is  dark, 
owing  to  the  presence  in  it  of  the  same  pigment  which  is  so  abundant 
in  the  choroid  coat.  Go  on  removing  the  sclerotic  piecemeal  until 
a  considerable  area  of  the  dark  choroid  layer  is  exposed  with  the 
ciliary  nerves  passing  forward  on  its  surface  towards  the  iris.  One 
or  other  of  the  long  ciliary  arteries  may  also  be  seen  coursing  between 
the  sclerotic  and  choroid  if  the  sclerotic  happens  to  have  been 
removed  at  its  position.  On  the  anterior  part  of  the  choroid  may 
be  observed  some  pale  fibres  passing  backwards  from  the  corneo- 
sclerotic  junction.  They  are  the  meridional  fibres  of  the  ciliary 
muscle  (p.  9°7). 

The  eye  being  immersed  in  water,  remove  cautiously  with  the 
forceps  and  scissors  the  portion  of  the  choroid  exposed.  The  retina 
is  now  seen  as  a  pale  membrane,  transparent  when  quite  fresh, 
but  becoming  whitish  soon  after  death.  Cut  through  sclerotic, 
choroid,  and  retina  about  half-way  round  the  eyeball,  a  little  posterior 
to  the  corneo-sclerotic  junction.     The  vitreous  humour  will  bulge 


986  A   M  INUAL  OF  PHYSIOLOGY 

out.  Since  its  refractive  index  is  nearly  the  same  as  that  ol  water, 
it  is  scarcely  observed  when  immersed,  and  the  interior  of  the  eye 
can  be  easily  seen  through  it. 

The  optic  <lise  can  now  be  again  studied,  with  the  stum))  of  the 
optic  nerve  entering  it  and  the  retinal  vessels  piercing  the  disc.  In 
the  centre  of  the  retina  is  the  yellow  spot. 

In  the  .interior  portion  of  the  eyeball  note  the  crystalline  lens, 
and  at  its  circumference  the  radiating  folds  of  the  i  horoid  i  ailed  the 
ciliary  pro<  esses.  Closely  covering  the  ciliary  pro<  esses,  the  anterior 
border  of  the  retina  forms  the  ora  serrata,  a  plaited  arrangement 
like  an  old-t  nne  ruff. 

Now  complete  the  separation  of  the  anterior  and  posterior  por- 
tions of  the  eyeball.  Remove  the  vitreous  humour,  noting  that  it 
is  attached  to  the  i  diary  processes  and  the  posterior  surface  of  the 
capsule  of  the  lens  by  its  enveloping  membrane,  the  hyaloid  mem- 
brane. With  scissors  snip  through  the  corneo-sclerotic  junction  at 
one  point  down  to  the  border  of  the  lens,  and  observe  the  suspensory 
ligament  passing  from  the  ciliary  body  chiefly  towards  the  anterior 
surface  of  the  lens,  where  it  blends  with  the  lens  capsule.  Open 
the  anterior  chamber  of  the  eye  by  an  incision  through  the  cornea 
in  front  of  its  junction  with  the  sclerotic.  It  is  filled  with  the  clei  r, 
watery,  aqueous  humour.  Note  the  pigmented  iris  projecting  in 
front  of  the  lens. 

Remove  the  sclerotic  and  cornea  for  some  distance  along  their 
line  of  junction,  using  gentle  pressure  with  the  edge  of  a  fine  knife 
to  separate  the  junction  from  the  attached  border  of  the  iris.  The 
ciliary  muscle,  forming  a  pale,  narrow  ring  around  the  eye  at  the 
corneo-sclerotic  junction  will  be  thus  exposed.  Its  external  surface 
is  closely  adherent  to  the  sclerotic,  and  its  internal  blends  with  the 
ciliary  body.  The  circumference  of  the  iris  is  attached  at  its  anterior 
border.     Posteriorly  it  passes  into  the  choroid. 

Take  out  the  lens  and  observe  the  curvature  of  its  anterior  and 
posterior  surfaces.  Determine  which  has  the  greater  curvature. 
In  the  excised  eve  the  lens  will,  of  course,  be  in  the  condition  of 
relaxed  p.ccommodation. 

2.  Formation  of  Inverted  Image  on  the  Retina. — Fix  the  eye  of 
an  ox  or  of  a  dog  or  rabbit,  after  careful  removal  of  part  of  the 
posterior  surface  of  the  sclerotic,  in  one  end  of  a  blackened  tube, 
with  the  cornea  in  front.  A  tube  made  by  rolling  up  a  piece  of 
thick  brown  paper  will  do.  Place  a  candle  in  front  of  the  eye. 
Look  through  the  other  end  of  the  tube,  and  observe  the  inverted 
image  of  the  candle  formed  on  the  retina.  Move  the  candle  until 
the  image  is  as  sharp  as  possible.  Now  bring  between  the  candle 
and  the  eye  a  concave  lens.  The  image  becomes  blurred,  the 
candle  must  be  put  farther  away  to  render  it  distinct,  and  perhaps 
no  position  of  the  candle  can  be  found  which  will  urive  a  sharp  mi 

If  the  lens  is  convex,  the  candle  must  be  brought  nearer,  and  a  sharp 
image  can  always  be  formed  by  bringing  it  near  enough.  If  both 
a  convex  and  a  concave  glass  be  plat  ed  in  front  of  the  eve.  they  will 
partially  or  wholly  neutralize  each  other.  Instead  of  the  candle 
a  window  may  be  looked  .it.  If  the  eye  of  an  albino  rabbit  can 
be  obtained,  it  is  not  necessary  to  remove  a  part  of  the  sclerotic. 

3.  Helmholtz's  Phakoscope   (Fig.    434).— This   instrument    is  em- 
ployed in  studying  the  changes  that  take  place  in  the  curvature  of 
the  lens  during  accommodation.      It  is  to  be  used  in  a  dark  room. ' 
A  candle  is  placed  in  front  of  the  two  prisms  P,  P'.     The  observer 


PR  ICTIC  XL  EXERCISl  ! 


9V 


looks  through  the  hole  B  .  the  ob  n  ed  eye  is  placed  at  a  hole  oppo- 
site the  hole  \  ["he  candle  or  the  observed  eye  is  moved  till  the 
observer  sees  three  pairs  ol  images,  one  pair,  the  brightest  of  all, 
reflected  from  the  .interior  surface  ol  the  cornea;  another,  the 
si  ol  the  three,  bul  dim,  refle<  ted  from  the  ariterioi  iurface  oi 
the  lens;  and  a  third  pair,  the  smallesl  ol  all,  reflected  from  the 
posterioi  if  the  lens  (Fig.  387,  p.  906),     Mi'-  last  two  pairs  can, 

"t  course,  only  be  seen  within  the  pupil.  The  observed  eye  is  now 
focussed  firsl  for  .1  distant  object  (it  is  enough  that  the  person  should 
simply  leave  Ins  eye  .it  rest,  or  Imagine  he  is  looking  far  away),  and 
then  lor  a  near  obje<  t  (an  ivory  pin  a1  A).  During  a<  commodation 
for  .1  near  object  no  change  tat  :s  place  in  the  size,  brightness,  or 
position  oi  the  lust  or  third  pair  oi  images;  therefore  the  cornea 
and  tin-  posterior  surface  ol  the  lens  are  not  altered.  The  middle 
mi,!:;.,  become  smaller,  sun -what  brighter,  approach  each  other, 
and  also  come  nearer  to 
the  corneal  images.  This 
pn>\ es  [a]  tli.it  the  anterior 
surface  of  the  lens  under- 
-  a  change  ;  (b)  that 
the  change  is  increase  of 
curvature  (diminution  of 
the  radius  of  curvature), 
for   the   virtual   image   rc- 

from      a      convex 

is       smaller       the 

is  its  radius  of 
(The  third  pair 
really  undergo 


fleeted 
mirror  is 
smaller  is 
curvature. 
of    images 


Fig.  434. — Phaioscop; 


a  slight  change,  such  as 
would  be  caused  by  a  small  increase  in  the  curvature  of  the  posterior 
surface  of  the  lens  ;  but  the  student  need  not  attempt  to  make 
this  out  ) 

4.  Scheiner's  Experiment. — Two  small  holes  are  pricked  with  a 
needle  in  a  card,  the  distance  between  them  being  less  than  the 
diameter  of  the  pupil.  The  card  is  nailed  on  a  wooden  holder,  and 
a  needle  stuck  into  a  piece  of  wood  is  looked  at  with  one  eye  through 
the  holes.  When  the  eye  is  accommodated  for  the  needle,  it  appears 
single  ;  when  it  is  accommodated  for  a  more  distant  object,  or  not 
accommodated  at  all,  the  needle  appears  double.  The  two  images 
approach  each  other  when  the  needle  is  moved  away  from  the  eye, 
and  separate  out  from  each  other  when  it  is  moved  towards  the  eye. 
When  the  eye  is  accommodated  for  a  point  nearer  than  the  needle, 
the  image  is  also  double  ;  the  images  approach  each  other  when  the 
needle  is  brought  closer  to  the  eye,  and  move  away  from  each  other 
when  it  is  moved  away  from  the  eye.  If  while  the  needle  is  in  focus 
one  of  the  holes  be  stopped  by  the  finger,  the  image  is  not  affected. 
When  the  eye  is  focussed  for  a  greater  distance  than  that  of  the 
needle,  stopping  one  of  the  holes  causes  the  image  on  the  other  side 
of  the  field  of  vision  to  disappear  ;  if  the  eye  is  focussed  for  a  smaller 
distance,  the  image  on  the  same  side  as  the  blocked  hole  disappears 
(Fig.  435).  To  determine  the  near-point  ol  distinct  vision  (p.  915) 
the  card  may  be  mounted  vertically  on  a  cork,  and  this  fastened  by 
a  rubber  band  to  the  end  of  a  foot-rule.  Move  a  needle,  also  in- 
serted vertically  into  a  cork,  along  the  rule,  beginning  at  the  end 
farthest  from  the  eye,  until  with  the  strongest  effort  of  accommoda- 


988 


A   MANUAL  OF  PHYSIOLOG  Y 


tion  it  is  seen  double.  Then  push  it  back  slightly  to  the  point  .it 
which,  again  with  maximum  accommodation,  it  is  just  seen  single 
Repeal  the  measurement  with  ;i  needle  mounted  horizontally.  If 
regular  astigmatism  is  present,  the  distances  will  not  be  the  same. 
Mosl  eyes  have  slight  regular  astigmatism. 

In  myopic  persons  the  far-point  of  distinct  vision  can  also  be 
determined  by  Scheiner's  experiment.  The  needle  being  left  on 
a  shelf  at  the  level  of  the  eye.  the  person  walks  away  from  it  back- 
wards, regarding  it  all  the  time  through  the  perforated  card,  till  it 
is  no  longer  seen  single. 

5.  Kuhne's  Artificial  Eye.  This  is  an  elongated  box  provided  with 
a  glass  lens  to  represent  the  crystalline,  and  a  ground-glass  plate  to 
represent  the  retina.  The  box  is  filled  with  water  to  which  a  little 
eosin  has  been  added.  The  water  must  be  perfectly  clear.  If  the 
tap-water  is  turbid  it  should  be  filtered  or  allowed  to  settle,  or  dis- 


Fig.  435. — Scheiner's  Experiment. 
In  the  upper  figure  the  eye  is  focussed  for  a  point  farther  away  than  the  need V. 
in  the  lower  for  a  nearer  point.  The  continuous  lines  represent  rays  from  the 
needle,  the  interrupted  lines  rays  from  the  point  in  focus.  But  the  lines  insidt 
the  eye,  which  by  an  error  in  engraving  are  drawn  as  continuous  lines,  ought  to 
be  interrupted,  and  vice  versa. 

tilled  water  should  be  used.  A  beam  of  sunlight  or  electric  light, 
or,  in  case  these  are  not  available,  a  beam  from  an  oil  stereopticon, 
is  made  to  pass  through  the  box.  Many  of  the  facts  of  vision  can 
be  illustrated  by  means  of  this  piece  of  apparatus.  The  modification 
of  it  introduc  ed  bv  I  .yon  is  very  convenient . 

/  Let  the  rays  oi  light  pass  through  an  arrow-shaped  slit  in  a 
piece  of  cardboard.  An  inverted  image  of  the  arrow  is  formed  on 
the  retina.  Move  the  retina  nearer  to  or  farther  from  the  lens  to 
make  the  image  sharp.  In  the  eye  of  man  and  of  most  animals, 
accommodation  is  not  brought  about  by  a  change  in  the  distance  of 
retina  and  lens,  but  by  a  change  of  curvature  in  the  lens. 

(b)  Remove  the  lens.  The  focus  is  now  far  behind  the  retina. 
This  illustrates  the  state  of  matters  after  the  lens  has  been  removed 
for  cataract.  The  arrow  can  again  be  sharply  focussed  on  the 
retina  bv  putting  a  convex  lens  in  front  oi  the  artificial  eye.     But 


PR  \CTI(    il    I  XI  ff<  / 


this  must  bo  much  weaker  than  th<-  lens  which  has  been  removed, 
for  ii  the  latter  be  placed  in  fronl  oi  the  eye,  the  image  is  formed  a 
little  behind  the  cornea 

■  e  the  Uns.  Move  the  retina  s  i  far  back  that  the  image 
is  focussed  in  front  <>!  it.  This  is  the  condition  in  the  myopic 
Put  a  weak  concave  lens  in  front  of  the  eye  ;  the  image  now  falls 
more  nearly  on  the  retina.  Move  the  retina  forward  ><>  that  the 
focus  is  behind  it  Tins  corresponds  to  the  hypermetropic  eye. 
Put  a  weak  convex  lens  in  front 
of  the  eye  to  <  orrect  the  defei  I 

id)  ( ibserve  that  a  plate  with  a 
hole  in  it.  placed  in  front  of 
the  eye.  renders  an  indistinctly 
focussed  image  somewhat  sharper 
by  cutting  oil  the  more  divergent 
peripheral  rays. 

(e)  Fill  with  water  the  chamber 
in  front  of  the  curved  glass  that 
-■■nts  the  cornea.  The  focus 
is  now  behind  the  back  of  the  eye 
altogether.  Refraction  by  the 
cornea  is  here  abolished,  as  is 
the  case  in  vision  under  water. 
An  additional  lens  inside  the  eye, 
or  a  weaker  one  in  front  of  it, 
corrects  the  defect.  Fishes  have 
a  much  more  nearly  spherical  lens 
than  land  animals,  and  a  flat 
cornea. 

Fill  the  hollow  cylindrical 
lens  with  water,  and  place  it  in 
front  of  the  artificial  eye.  The  eye 
is  now  astigmatic.  A  point  of  light 
is  focussed  on  the  retina,  not  as  a 
point,  but  as  a  line.  The  vertical 
and  horizontal  limbs  of  a  cross 
cut  out  of  a  piece  of  cardboard 
and  placed  in  the  path  of  the 
beam  of  light  cannot  be  both 
focussed  at  the  same  time. 

6.  Astigmatism  Regular).  —  (i) 
Look  at  a  figure  showing  a  number 
of  lines  radiating  horizontally. 
verticaliv.  and  in  intermediate 
directions  from  a  common  centre. 
First    fix    the    figure    at    such    a 


Fk,.  436. — Ophthalmometer,  as  see n" 
from  behind  the   patient. 

B,  blind  for  covering  the  eye  not 
being  examined  ;  H,  chin-rest  :  A.  A. 
graduated  discs  on  which  radii  of 
curvature  of  the  cornea  in  various 
meridians  are  read  off  or  their  equiva- 
lent in  diopters ;  E,  eye-piece  of 
telescope  ;  C,  milled  head  for  raising 
and  lowering  chin-rest  ;  F,  milled  head 
for  adjusting  height  of  the  ophthalmo- 
meter, and  G  for  moving  it  horizon- 
tally back  and  forth  ;  n,  graduated 
disc  for  giving  the  rotation  of  the  outer 
tube  of  the  telescope  and  the  black  disc  w. 
In  it  are  seen  the  two  illuminated  mires. 


distance  that  one  can  comfortably 
accommodate.  If  astigmatism  is  present,  all  the  lines  cannot  be  seen 
with  equal  distinctness  at  the  same  time,  but  they  can  all  be  succes- 
sively accommodated  for.  Next,  bring  the  figure  to  the  near-point 
of  distinct  vision  for  the  horizontal  and  neighbouring  lines.  Probably 
the  vertical  lines  will  be  blurred  and  cannot  be  made  as  distinct 
as  the  horizontal  by  any  effort  of  accommodation.  If  the  eye  is 
distinctly  astigmatic,  the  difference  will  be  marked. 

(2)    Use   the    Ophthalmometer . — A    convenient    form    is    shown    in 
Figs.  436  and  437. 


990 


A    1/  /  \r.\i.  OF  PHYSIOLOGY 


Raise  or  lower  the  chin-resl  till  the  upper  bar  of  the  head-rest 
is  just  above  the  patient's  eyebrows,  ins  head  being  exactly  vertical. 
The  eye  not  to  be  examined  is  covered  with  the  blind.     The  patient 

looks  steadily  into  the  opening  of  the  tube  with  his  eye  wide  open. 
The  height  of  the  instrument  having  been  adjusted,  a  clear  image 
of  the  mires  is  obtained  by  focussing.  The  tube  is  then  turned  hori- 
zontally slightly  to  right  or  left  until  the  two  images  of  the  mires 
are  close  together   and   equally  distinct.     Rotate  the  outer  tube 


Fig.  437. — Vertical  Section  of  Ophthalmometer. 

d,  outer  tube  of  the  telescope  rotating  in  sleeve  or  collar  s  (supported  by 
standard  /,  which  is  swivelled  in  tubular  support,  g)  ;  k,  diaphragm  ;  10.  eye-piece 
with  lenses  a  and  b  ;  n,  a  stationary  disc,  borne  on  collar  s,  graduated  to  indii  ate 
angle  of  rotation  of  it.  a  black  concave  disc  rotating  with  tube  it,  and  having 
fixed  in  it  two  illuminated  figures  (or  mires),  w,  w,  whose  images  reflected  from 
the  cornea  are  observed  ;  i  is  a  pointer  carried  on  the  tube  1/  which  shows  on  the 
graduated  arc  the  amount  of  rotation;  12,  12,  hemispherical  shells  containing 
small  incandescent  lamps  for  illuminating  the  translucent  mires.  The  lamps 
connected  with  wires  running  in  the  hollow  stem  /  .-  /  is  the  inner  tube  oi  the 
telescope  carrying  the  double  prism.  /;,  h.  By  means  of  the  rack  0,  proje< 
through  the  slot  m,  and  engaged  l>v  the  pinion  /\  /  is  moved  back  and  forth 
in  the  outer  tube,  thus  approximating  or  separating  the  corneal  images  ol  the 
mires.  On  the  axis  of  p  is  a  milled  head  for  turning  it.  and  two  dupli<  ate  dia  - 
graduated  with  a  scale  showing  the  radii  of  curvature  of  the  cornea  in  millimetres, 
and  another  scale  showing  their  equivalent  in  diopters. 

(Fig.  437,  d)  until  the  long  meridian  lines  of  the  images  are  exactly 
in  line  with  each  other.  If  there  is  no  astigmatism,  this  will  be 
seen  at  all  axial  positions  ;  if  there  is  astigmatism,  at  only  two 
positions.  An  axis  having  thus  been  obtained,  the  graduated 
disc  (Fig.  436,  A)  on  either  side  of  the  tube  is  rotated  until  the 
shorter  lines  or  spurs  of  the  images  also  unite-,  forming  a  perfect 
cross  with  the  longer  ones  (Fig.  438),  and  the  adjustable  pointer 
on  the  left -handed  isc  is  made  to  coincide  with  the  stationary  one 


PR  ICTICA1    l  XI  RCISES 


<><>l 


and  a  reading  taken.  Nov  rotate  d  through  90  degrees;  the  long 
axial  lines  oi  the  images  will  I"-  Ln  alignmenl  without  further  adjust- 
ment .  I  ''lit  if  the  eye  is  astigmatic,  the  short  lines  will  not  (Fig.  439). 
1  '.\  rotating  A ,  the  shorl  lines  are  made  to  coincide,  so  that  a  perfe<  t 
cross  is  again  formed,  and  the  graduation  is  read.     The  difference 


Fig.  439. 


f/fse*?*~- 


A  \\   i 

TO  \ 


>.  wx- 


^   1! 


jElmdi  \>\*\ 


/  4* 


Fig.  440. — Perimetric  Chart  of  Right  Eye. 

Obtained  with  the  perimeter  shown  in  Fig.  415  (p.  946).     The  numbers  represent 
degrees  of  the  visual  field  measured  on  the  graduated  arc  of  the  perimeter. 

between  this  and  the  previous  reading — i.e.,  the  difference  between 
the   two   pointers — gives  the   difference    in   the   curvature   of  the 
cornea  in  the  two  meridians.     The  images  of  circles  which  form 
the  outer  portion  of  the  mires  are  oval  in  ordinary  astigmatism. 
7.  Spherical  Aberration. — Close  one  eye,  and  bring  a  small  object 


992  ./   MANUAL  OF  PHYSIOLOG  Y 

(a  pin  or  the  point  of  a  pencil)  towards  the  other  eye  till  it  heroines 

blurred.  Interpose  Pet  ween  the  object  and  the  eye  a  card  per- 
forated by  a  small  hole.  The  object  becomes  more  distinct  owing 
to  the  cutting  oil  oi  t  lie  peripheral  rays  (p.  <j  12). 

8.  Chromatic  Aberration. — Look  at  Fig.  391  (p.  913)  from  a  dis- 
tance too  small  for  perfect  accommodation,  and  verify  the  facts 
given  in  the  description  oi  the  figure. 

g.  Measurement  of  the  Extent  of  the  Field  of  Vision.  Use  the 
perimeter  shown  in  Fig.  415  (p.  946). 

(1)  For  White  Light.  Fix  in  the  holder.  1  >l>.  on  the  graduated  arc, 
a  small  piece  of  white  paper,  and  put  on,-  ,,i  the  charts  supplied 
with  the  instrument  at  the  back  of  the  wheel  which  revolves  with 
the  arc.  The  observations  can  be  recorded  on  this  chart.  The 
pat  nut  rests  his  chin  on  K  and  adjusts  one  eye  against  O.  This 
e\  e  is  kept  fixed  on  the  mark  at  /  during  the  whole  period  of  observa- 
tion, and  the  other  eye  is  covered.  The  arc  is  placed  in  a  definite 
position,  and  the  white  object  gradually  moved  from  the  end  ■■! 
the  arc  until  the  person  announces  thai  he  can  just  sec  it.     The 


Fig.  441. — Map  of  Blind  Spot  (reduced  by  One-ham  ). 
Right  eye.     Distance  of  eye  from  paper,  12  inches. 

angle  at  which  this  occurs  is  read  off  and  recorded  on  the  chart. 
The  aic  is  then  rotated  into  a  new  position  and  the  observation 
repeated.  A  line  is  drawn  through  all  the  points  thus  obtained. 
and  this  constitutes  the  boundary  of  the  field  of  vision  (Fig.  440). 

If  the  position  of  each  point  is  inserted  on  the  chart,  a  point  above 
the  horizontal  plane  passing  through  the  visual  axis  being  placed 
below  it,  and  a  point  to  the  right  of  the  vertical  plane  being  moved 
to  the  left,  we  obtain  a  map  of  the  sensitive  portion  of  the  retina. 
Usually  perimeters  are  arranged  to  do  this  automatically. 

(2)  Repeat  the  mapping  of  the  field,  using  coloured  papers  (red, 
green,  and  blue)  instead  of  white. 

10.  Mapping  the  Blind  Spot.  Make  a  black  cross  on  a  pit 
white  paper  attached  to  the  wall,  the  centre  of  the  cross  bein^  at  the 
height  of  the  eye  in  the  erect  position.  Stand  about  12  inches  from 
the  wall,  the  chin  supported  on  a  projecting  piece  of  wood.  Fix  the 
centre  of  the  cross  with  one  eye,  the  other  being  closed,  and  move 
over  the  paper  a  pencil  covered,  except  at  the  point,  with  white 
paper,  until  the  point  just  disappears.  Make  a  mark  on  the  paper 
at  this  point,  and  repeat  the  observation  for  all  diameters  of  the 


PRAi   I  /<    //     /  XI  RCISES 


993 


field       I  lie  blind  spol  is  thus  marked  oul  (Fig.   141).      [ts  shapi 
nol  the  same  in  alf  eyes  (Fig    L42).      Its  size  and  distance  from  the 
fovea  centralis  can   I"-  calculated    from  the  construction  given  in 
Fig,  j86  1  p  91 

1  1 .   The  Macula  Lutea,  or  Yellow  Spot— (1)  After  closing  the  eyes 


Fig.  442. — Composite  Picture  of  Blind  spot  (not  reduced). 

III.  blind  spot  oi  the  right  eye  was  mapped  by  31  men,  the  eye  being  always 
at  a  distance  of  12  inches  from  the  paper.  The  maps  were  then  superposed. 
The  amount  of  white  at  anv  point  of  the  figure  is  intended  to  correspond  to  the 
number  of  maps  which  overlapped  at  that  point.  Although  the  mechanical 
process  ol  reproduction  gives  rather  an  imperfect  view  of  the  composite  map, 
the  area  in  the  centre  of  the  figure  where  the  white  is  most  continuous,  and  which 
represents  the  shape  of  the  majority  of  the  blind  spots,  evidently  bears  a  general 
resemblance  to  the  outline  in  Fig.  441. 

for  a  minute  or  two,  look  with  one  eye  through  a  strong  solution  of 
chrome  alum  in  a  clear  glass  bottle  with  parallel  sides.  Hold  the 
bottle  between  the  eye  and  a  white  screen  or  a  white  cloud.  An 
oval  rose-coloured  spot  will  be  seen  in  a  greenish  field.  The  pig- 
ment of  the  yellow  spot  absorbs  the  blue  and  green  rays. 

63 


A  MANUAL  OF  PHYSIOLOGY 

-  Keep  tin-  eye  closed  for  a  short  time.  Then  direct  it  t<>  .t 
surface  illuminated  by  a  weak  blue  light.  A  dark  blue  or  almost 
black  sput  (Maxwell's  spot),  corresponding  to  the  macula,  is  seen  in 
the  visual  field,  owing  to  the  absorption  oi  the  blue  ra 

12.  Ophthalmoscope  (i)  Human  Eye  (p.  918).  -Let  A  be  the 
observer,  and  I',  tin-  person  whose  eye  is  to  \«  examined.  A  and  B 
arc  seated  facing  each  other.  Suppose  that  the  right  eye  oi  B  is  to 
be  examined,  (lose  to  the  left  ear  of  B  is  a  lamp  on  a  level  with 
his  eyes  :  tie-  room  is  otherwise  dark.  For  a  clinical  examination, 
the  pupil  should  be  dilated  by  putting  into  the  eye  a  drop  of  a 
05  percent,  solution  ol  atropine  sulphate,  but  this  is  not  indispensablt 
]<>r  the  experiment. 

(a)  Direct  Method.  A  takes  the  mirror  in  his  right  hand,  and. 
holding  it  close  to  his  own  eye,  looks  through  the  central  hole,  and 
throws  a  beam  of  light  into  B's  eye.  A  red  glare,  the  so-called 
'  reflex  '  from  the  choroidal  vessels,  is  now  seen.  A  then  brings  the 
mirror  to  within  2  or  3  inches  of  B's  eye.  keeping  his  own  eye  always 
at  the  aperture.  A  and  B  both  relax  their  accommodation,  as  it 
they  were  Looking  away  to  a  distance.  If  both  eyes  are  emmetropic, 
the  retinal  vessels  will  be  seen.  B  should  now  look  away  past  the 
little  finger  ol  As  right  hand.  This  causes  slight  inward  rotation  of 
B's  eye,  and  brings  into  view  the  white  optic  disc  with  the  central 
artery  and  vein  of  the  retina  crossing  it. 

(b)  Indirect  Method. — A  takes  the  mirror  in  his  right  hand  to 
examine  B's  right  eye.  places  his  own  eye  behind  the  aperture  as 
before  at  a  distance  of  about  18  inches  from  B.  and  throws  a  beam 
of  light  into  B's  eye.  Then  A  takes  a  small  biconvex  lens  in  his 
left  hand,  and  places  it  2  or  3  inches  in  front  of  B's  eye,  keeping 
it  steady  by  resting  his  little  finger  on  B's  temple.  A  now  moves 
the  mirror  until  he  sees  the  optic  disc. 

2  Examine  a  rabbit's  eye  by  the  direct  and  indirect  method. 
Ddate  the  pupil  by  a  drop  or  two  of  atropine  solution. 

I  or  pra<  ti(  .  before  doing  (1)  and  (2)  the  student  should  examine 
an  artificial  '  eye  '  by  both  methods,  so  as  to  get  a  clear  view  of  what 
represents  the  retina.  A  substitute  for  the  artificial  eye  may  1>< 
made  by  unscrewing  the  lower  lens  of  the  eyepiece  of  a  microscope. 
and  fastening  in  its  place  a  piece  of  paper  with  some  printed  matter 
on  it.     The  letters  must  be  made  out  with  the  ophthalmoscope. 

The  opportunity  should  also  be  taken  to  observe  the  eye  of  an 
anaesthetized  animal  by  the  simple  iss  method  mentioned 

in  1  (p.  985).     A  round  cover-glass  is  slipped  under  both  eyelids  and 
so  held  in  position  on  the  cornea.     The  fundus  of  the  eve  can  no\ 
clearly  seen,  including  the  optic  disc  and  retinal  vessels.    The  instilla- 
tion of   a  little  cocaine  into  the  eye  < .  t    a  rabbit  will    produce  local 
anaesthesia  sufficient  to  permit  the  experiment. 

13.  Skiascopy  or  Retinoscopy. — The  simplest  method  is  as  follows  : 
The  observer  places  himself  at  a  distance  of  a  metre  from  the 
observed  eye.  which  he  illuminates  by  a  beam  reflected  from  a 
concave  ophthalmoscopic  mirror  held  in  front  of  his  eye.  The 
ommodation  ol  the  observed  eye  is  relaxed.  If,  now.  when  the 
mirror  is  rotated  no  direction  of  movement  of  the  shadow  or  the  light 
area  (p.  920)  tan  be  made  out,  the  pupil  becoming  all  at  once  dark 
throughout  its  whole  extent  when  the  mirror  is  rotated  in  one  direc- 
tion,  and  all  at  once  light  throughout  its  whole  extent  when  the 
mirror  is  rotated  in  the  opposite  direction,  the  observer  is  in  the 
far-point  ol  the  observed  eye      Since  the  far-point  is  at  the  distance 


PR  i,   TIC  II    EXERCISES 


995 


oi  a  metre,  there  is  m  tins  case  myopia  amounting  to  one  diopter. 
Ft.  however,  the  lighl  area  moves  m  the  same  direction  as  the 
rotation  oi  the  concave  mirror,  the  far-point  of  the  observed  eye 


Fig.  443. — Geneva  Retinoscope  and  Ophthalmoscope. 
A.  frame  of  instrument  ;  B,  retinoscope  attachment  ;  C,  ophthalmoscope 
attachment  ;  D,  base  :  1.  mirror  handle  ;  2,  clip  to  hold  the  proper  lens  to  correct 
the  abnormality  of  refraction  of  observer  or  patient  when  viewing  the  retina  with 
the  ophthalmoscope  ;  3.  scale  indicating  the  meridian  of  handle  and  pointer  :  4, 
ring  in  which  mirror  cup  rotates  ;  6,  mirror  ;  7,  mirror  spring  for  reflecting  the  light 
to  a  given  point  :  8,  screws  for  adjusting  mirror  ;  9,  screw  for  holding  light  and 
ring  4  in  position  :  10,  handle  for  swinging  A  from  side  to  side  ;  13,  opening  in  iris 
diaphragm,  controlled  by  handle  14  ;  15,  lamp  hood  ;  17,  knurled  handle  for  rotating 
disc  containing  the  full  diopter  lenses  ;  18,  handle  for  rotating  the  disc  containing 
the  fractional  lenses  (white  numbers  indicate  plus  lenses,  and  red  minus  lenses)  ; 
jo.  opening  through  which  observer  looks  when  adjusting  the  retinoscope  to  the 
patient's  eve  ;  21,  pinion  for  advancing  or  retracting  instrument  ;  24,  bracket 
ring  of  retinoscope  attachment  B,  which  is  slipped  over  ring  25  when  putting 
retinoscope  attachment  into  place  ;  28,  clips  for  'fogging'  lenses  through  which 
the  patient  looks  to  lelax  accommodation  ;  29,  opening  through  which  the  pupil 
is  viewed  in  retinoscopy  :  30.  opening  containing  clip  in  which  extra  lenses  may 
be  inserted  when  required,  or  the  defect  is  over  8  diopters;  32,  patient's  eve- 
cup  :  33.  ring  of  ophthalmoscope  attachment  C,  which  telescopes  over  25  : 
34.  ophthalmoscope  tube  ;  }s.  binding-screw  which  holds  the  instrument  in  a 
tixed  position  when  retinoscope  is  being  used;  37,  rack  to  raise  and  lower  the 
instrument  ;  40,  handle  controlling  height  of  chin-rest  44  ;  46,  forehead-rest. 


lies  between  the  observer  and  the  observed  eye,  so  that  the  myopia 
amounts  to  more  than  one  diopter.  The  precise  degree  of  myopia 
can  be  estimated  by  interposing  biconcave  lenses  of  different  strength 
until  the  far-point  is  made  just  1  metre. 

63—2 


996  A   MANUAL  OF  PHYSIOLOGY 

It  the  light  area  moves  in  the  opposite  direction  to  the  rotation 

of  the  mirror,  the  far-point  is  more  than  a  metre  distant,  and  tl 
fore  the  observed  eye  is  emmetropic  or  hypermetropic,  or  myopic 
to  a  degree  less  than  a  diopter.  The  lens,  convex  or  concave,  can 
now  be  sought  out  which  will  just  bring  the  far-point  to  a  mi 
and  from  the  strength  oi  it.  minus  one  diopter,  the  refraction  can 
be  estimated.  Suppose,  for  instance,  that  a  convex  lens  of  two 
diopters  is  required,  then  hypermetropia  of  one  diopter  exists. 

In  order  to  facilitate  the  introduction  of  the  various  lenses, 
instruments  called  skiascopes  or  retinoscopes  may  be  used,  one  of 
which  is  shown  in  Fig.  443. 

14.  Pupillo-dilator  and  Constrictor  Fibres. — (a)  Set  up  an  induc- 
tion machine  arranged  for  tetanus,  and  connect  a  pair  of  electrodes 
through  a  short-circuiting  key  with  the  secondary.      Etherize  a 

by  putting  it  into  a  large  vessel  with  a  lid.  slipping  into  the  vessel 
a  piece  of  cotton-wool  soaked  with  ether,  and  waiting  till  the  move- 
ments of  the  animal  inside  the  vessel  have  ceased.  Then  quicklv 
put  the  cat  on  a  holder  and  maintain  anaesthesia  with  ether.  H\ 
the  vago-sympathetic  in  the  neck  (pp.  148.  202)  ;  the  carotid  is  taken 
as  the  guide  to  it.  Ligature  the  nerve  and  cut  below  the  ligature. 
On  stimulating  the  upper  (cephalic^  end.  the  pupil  of  the  corre- 
sponding eye  dilates. 

Carefully  separate  the  sympathetic  from  the  vagus,  and  repeat  the 
observation  on  the  former.     The  result  on  the  pupil  is  the  same. 

(b)  Observe  in  the  eye  of  a  fellow-student,  or.  by  means  of  a 
looking-glass,  in  your  own  eye.  that  when  light  falls  on  one  eye  both 
pupils  contract. 

(c)  Observe  that  when  the  eye  is  accommodated  for  a  near  object 
tlie  pupil  contracts,  and  that  it  dilates  when  a  distant  object  is 
looked  at. 

15.  Colour-mixing. — (a)  Arrange  a  red  and  a  bluish-^reen  disc  on 
one  of  the  steel  discs  of  the  colour-mixing  apparatus  shown  in 
Fig.  444,  so  that  a  part  of  each  is  seen.  On  another  arrange  a  violet 
and  a  yellow  disc,  and  on  the  third  an  orange  and  a  blue  disc.  By 
adjustment  of  the  proportions  of  the  two  colours  a  uniform  grey 
can  be  obtained  from  each  of  these  combinations  (complemeir 
colours)  when  the  discs  are  rapidly  rotated. 

Mix  two  colours  that  arc  not  complementary — e.g.,  blue  and 
red — grey  or  white  cannot  be  obtained  by  any  adjustment  of  pro- 
portions ;  the  result  is  always  a  mixed  colour,  the  precise  hue 
depending  on  the  amount  of  each  ingredient. 

(c)  Take  papers  of  any  three  colours  from  widely-separated  parts 
of  the  spectrum — e.g.,  blue,  green,  and  red — and  arrange  them  on  one 
of  the  rotating  discs.  By  varying  the  proportions,  white  (grey)  can 
be  produced,  and  any  other  coloured  paper  fastened  on  another  of  the 
rotating  discs  can  be  matched  by  adding  white  to  the  three  colours. 

10.  After-images— (1)  Positive. — (a)  Rest  the  eyes  tor  two  or  three 
minutes  bv  closing  them,  or  by  going  into  a  dark  room.  Then 
look  tor  an  instant  at  a  bright  object,  a  window  or  an  incandescent 
lamp,  and  at  once  cle.se  the  eyes  again.  A  bright  positive  after- 
image of  the  object  looked  at  will  be  seen. 

(b)  Look  at  an  incandescent  lamp  through  a  coloured  glass  as  in  (a). 
The  positive  after-image  will  appear  in  the  same  colour  as  the  glass. 

(2)  Negative  After-image. — (a)  Look  at  an  incandescent  lamp  for 
thirty  seconds,  and  then  direct  the  eyes  to  a  white  surface.  The 
after-image  of  the  filament  will  appear  dark. 


PR  ICTIC  \L   I  KERCISES  997 

(6)  Look  at  the  lamp  through  a  coloured  glass  for  thirty  or  forty 
seconds,  and  then  <losc  the  eye  or  look  at  a  white  ground.  The 
after-image  of  the  filament  will  appear  in  the  i  omplementary  colour 
of  tlu-  glass.  II  the  glass  was  red,  for  instance,  the  after-image  will 
1"    greenish. 

(c)  Look  .it  .i  while  square  on  a  dark  ground  for  thirty  seconds, 
then  quickly  cover  the  field  with  white  paper.     A  dark  square  will 

be  Men  oil   t  he  w  lute  ground. 


Fig.  444. — Apparatus  for  Colour-mixing. 

(d)  Repeat  (c)  with  coloured  squares.  The  after-image  of  the 
square  will  be  in  the  complementary  colour. 

Contrast. — Perform  .Meyer's  experiment  (p.  944). 

t  7.  Retinal  Fatigue. — Fix  the  eye  steadily  on  a  portion  of  a  printed 
page  a  considerable  distance  away.  Note  that  the  print  soon 
becomes  blurred.  Wink  the  eye  ;  the  short  rest  causes  a  notable 
recovery  of  the  retina. 

18.  Visual  Acuity. — Draw  on  a  white  card  a  series  of  vertical  black 
lines  1  millimetre  thick,  and  separated  from  each  other  by  a  distance 
of  a  millimetre.  Set  the  card  up  in  a  good  light,  and  walk  back- 
wards from  it  till  the  individual  lines  just  fail  to  be  discriminated. 


998  /    MANUAL  OF   PHYSIOLOG  Y 

Measure  the  distance  from  the  c;ir<l  at  which  this  occurs,  and  calcu- 
late the  size  of  the  retinal  image  (p.  904). 

19.  Colour-blindness. — Spread  out  Holmgren's  coloured  wools  on 
a  sheet  of  white  filter-paper  in  a  good  light.  Do  not  mention  the 
colours  of  any  of  the  wools,  but  (1)  ask  the  person  who  is  being 
tested  to  pick  Ou1  all  the  wools  which  seem  to  him  to  match  a  pale  pure 
green  wool  (neither  yellow  green  nor  blue  green),  which  is  handed  to 
him.  I  le  is  not  to  make  an  exact  match,  but  to  pick  out  the  skeins 
which  seem  to  have  the  same  colour.  If  he  makes  any  mistakes, 
by  selecting,  e.g.,  in  addition  to  the  green  skeins  any  of  the  'confusion 
colours,'  such  as  grey,  greyish  yellow,  or  blue  wools,  there  is  some 
defect  of  colour  discrimination.  To  determine  whether  the  person 
is  red  or  green  blind,  tests  (2)  and  (3)  are  then  made.  (2)  Give  him 
a  medium  purple  (magenta)  wool,  and  ask  him  to  pick  out  matches 
for  it.  If  he  is  red-blind,  he  will  select  as  matches  to  it  only  blues 
and  violets,  as  well  as  other  purples.  If  he  is  green-blind,  he  will 
select  only  greens  and  greys.  (3)  The  third  test  is  a  red  wool.  In 
selecting  matches  for  this,  the  red-blind  will  choose  (with  reds)  greens, 
greys,  or  browns  less  bright  than  the  test.  The  green-blind  will 
choose  (with  reds)  greens,  greys,  or  browns  which  are  brighter  than 
the  test. 

It  must  be  remembered  that  the  results  of  tests  with  the  coloured 
wools  need  not  be  precisely  the  same  as  those  with  coloured  lights, 
and  that  when  there  is  a  discrepancy  between  the  two  the  test  with 
the  coloured  lights  should  be  accepted  ;  for  it  is  usually  the  normal 
perception  and  discrimination  of  coloured  lights  which  has  practical 
importance. 

20.  Talbot's  Law. — Rotate  a  disc  one  sector  of  which  is  black  and 
the  rest  white,  or  a  disc  like  that  in  Fig.  412  (p.  938).  A  uniform  shade 
is  produced  as  soon  as  a  speed  of  about  25  revolutions  a  second  has 
been  attained,  and  this  is  not  altered  by  further  increase  in  the 
speed. 

21.  Purkinje's  Figures. — {a)  Concentrate  a  beam  of  sunlight  by 
a  lens  on  the  sclerotic  at  a  point  as  far  as  possible  from  the  corneal 
margin,  passing  the  beam  through  a  parallel-sided  glass  trough  filled 
with  a  solution  of  alum  to  sift  out  the  long  heat-rays.  The  eye  is 
turned  towards  a  dark  ground.  The  field  of  vision  takes  on  a  bronzed 
appearance,  and  the  retinal  bloodvessels  stand  out  on  it  as  a  dark 
network,  which  appears  to  move  in  the  same  direction  as  the  spot 
of  light  on  the  sclerotic.  A  portion  of  the  field  corresponding  to  the 
yellow  spot  is  devoid  of  shadows  (p.  930). 

(b)  Direct  the  eyes  to  a  dark  ground  while  a  flame  held  at  the  side 
of  the  eye,  and  at  a  distance  from  the  visual  line,  is  moved  slightly 
to  and  fro.  A  picture  of  branching  bloodvessels  appears.  This 
experiment  is  performed  in  a  dark  room. 

(c)  Immediately  on  awaking  look  at  a  white  ceiling  for  an  instant; 
a  pattern  of  branched  bloodvessels  is  seen.  If  the  eye  be  at  once 
closed,  and  then  opened  with  a  blinking  movement,  this  may 
be  observed  again  and  again.  Ultimately  the  appearance  fades 
away. 

HEARING,  TASTE,  SMELL,  TOUCH,  ETC. 

22.  Monochord. — Study  by  means  of  the  monochord,  a  stretched 
string  with  a  movable  stop,  the  relation  between  the  pitch  of  the 
note  given  out  by  a  vibrating  string,  and  its  length  and  tension. 


PR  ICTICAL  EXERCISES  099 

23.  Beats.  Cause  two  tuning-forks  oi  nearly  equal  pitch  to 
vibrate  at  the  same  tunc  Make  out  the  beats,  and  counl  their 
number  per  second. 

24.  Sympathetic  Vibration.     Take  three  tuning-forks  mounted  on 
nators.     Let  two  of  them  be  of  the  same  pitch.     Strike  one  of 

these  ;  the  other  is  thrown  into  sympathetic  vibration,  and  continues 
ive  out   a  note  .liter  tin-  lust    is  quickly  stopped  by  touching 
it .      I  he  third  fork  is  unaffected. 

25.  Determine  In-  means  <>t  Galton's  whistle  the  pitch  of  the 
highest  audible  tone. 

j<>.  Cranial  Conduction  of  Sound.  -When  a  tuning-fork  is  held 
between  tlie  teeth,  a  part  of  the  sound  passes  out  of  the  ear  from  the 
vibrating  membrana  tympani  ;  if  one  ear  is  closed,  the  sound  is 
heard  better  in  this  than  in  the  open  ear.  If  the  tuning-fork  is  held 
between  the  teeth,  till,  with  both  ears  open,  it  becomes  inaudible,  it 
will  be  heard  for  a  short  time  if  one  or  both  ears  be  stopped  ;  and 
when  in  this  position  the  sound  again  becomes  inappreciable,  it  can 
still  be  caught  if  the  handle  be  introduced  into  the  auditory  meatus. 

27.  Taste. — (1)  Apply  to  the  tongue  by  means  of  a  camel's-hair 

brush  a  solution  of  quinine  (1  to  1,000),  sodium  chloride  (1  to  200), 

cane-sugar  (1  to  50),  and  sulphuric  acid  (1  to  1,000).     Determine  at 

what  part  of  the  tongue  the  strongest  sensations  are  elicited  by  each. 

(2)  Prepare  a  series  of  solutions  of  sulphuric  acid  of  gradually  in- 

M 
creasing  strength,  beginning  with  a solution  (a  two-thousandth 

gramme-molecular  solution)  (p.  398).  Put  into  the  mouth,  after 
previous  rinsing  with  distilled  water,  4  or  5  c.c.  of  one  of  the  solutions 
of  the  acid,  beginning  with  the  weakest,  and  determine  at  what  con- 
centration of  the  H  ions  the  acid  taste  first  appears,  rinsing  out  the 
mouth  after  each  observation .  Repeat  the  experiment  with  solutions 
of  hydrochloric  acid,  and  determine  whether  the  threshold  value  is 
the  same. 

A  similar  comparison  of  the  necessary  concentration  of  the  OH 
ions  can  be  made  with  solutions  of  sodium  hydroxide  and  potassium 
hydroxide. 

(3)  Connect  two  short  pieces  of  platinum  wire  with  the  copper  wire 
from  the  poles  of  a  Daniell  or  dry  cell.  Apply  one  platinum  wire  to 
the  inner  surface  of  the  lip  and  the  other  to  the  tip  of  the  tongue. 
Reverse  the  poles.  Note  the  difference  in  the  sensation  according  to 
whether  the  anode  or  the  kathode  is  on  the  tongue. 

28.  Smell. — (1)  Pass  a  current  through  the  olfactory  mucous  mem- 
brane by  connecting  one  electrode  with  the  forehead  and  the  other 
by  means  of  a  small  piece  of  sponge  or  cotton-wool  soaked  in  physio- 
logical salt  solution  with  one  nostril.  An  odour  like  that  of  phos- 
phorus will  be  perceived. 

(2)  To  distinguish  between  Taste  and  Smell. — Use  a  solution  of 
clove-oil  in  water  which  can  just  be  distinguished  from  water  when 
it  is  placed  on  the  tongue  by  means  of  a  camel's-hair  brush.  Close 
the  nostrils,  and  determine  whether  the  clove-oil  can  now  be  detected. 

jo.  Touch  and  Pressure. — (1)  Prepare  a  number  of  hair  aesthesio- 
mcters  by  fastening  hairs  of  different  thicknesses  to  small  wooden 
handles  about  3  inches  long  by  means  of  sealing- wrax.  Hairs  as 
straight  as  possible  should  be  chosei  ,  or  straight  portions  of  hairs. 
The  hair  is  to  be  fastened  on  one  end  of  the  piece  of  wood  at  right 
angles  to  the  long  axis  of  the  handle,  so  that  about  an  inch  of  the 
h,ajr  projects  to  one  side.     Determine  the  pressure  value  of  each 


iooo  A   MANUAL  OF  PHYSIOLOGY 

hair  by  pressing  i1  down  upon  the  scale  oi  a  ImI.uh  e  till  it  is  slightly 
bent,  and  observing  the  greatesl  weight  in  the  other  s<  ale  which rl 

will  lilt.  .Mark  tin-  number  in  milligrammes  on  the  handle.  In 
this  way.  when  a  hair  is  placed  at  right  angles  t"  a  poinl  oi  th'-  skin. 
and  pressure  exerted  on  it  till  it  begins  t<i  bend,  tin-  intensity  oi  the 
touch  stimulus  i.e.,  the  pressure  exerted  on  the  skin  is  definitely 
measured,  and  by  using  hairs  oi  different  pressure  values  the  threshold 
value  of  the  stimulus  lor  any  touch  ana  i.e.,  the  pressure  which 
just  gives  the  sensation  of  light  touch — can  be  determined  (p  o, 

(a)  Using  the  back  of  the  hand,  note  how  light  a  touch  oi  the 
aesthesiometer  applied  to  the  end  of  a  hair  suffices  to  elicit  a  sensa- 
tion of  touch,  as  compared  with  a  part  free  from  hairs.  The  hairs 
diminish  the  threshold  of  the  stimulation  by  acting  as  lexers,  whose 
short  arm  presses  against  the  nerve-endings  surrounding  the  hair- 
follicles,  while  the  stimulating  weight  acts  on  the  long  arm.  When 
the  skin  is  shaved  the  threshold  is  always  raised. 

(b)  Shave  an  area  on  the  back  of  the  hand,  and  make  out  the 
relation  of  the  touch-spots  to  the  hair  follicles.  Each  hair  has 
an  especially  sensitive  touch-spot  just  on  the  '  windward  '  side  of 
the  follicle  (p.  970).  Using  aesthesiomcters  of  different  pressure 
values,  determine  the  threshold  value  for  the  shaved  area.  Outline 
an  area  of  a  square  centimetre  on  the  skin,  and  determine  the  number 
of  touch-spots,  using  first  a  hair  of  the  threshold  value,  and  then 
going  over  the  area  again  with  a  hair  of  a  decidedly  higher  pressure 
value.  The  threshold  value  for  many  parts  of  the  hairy  skin  is 
obtained  with  a  hair  which  bends  at  70  milligrammes.  Repeat  the 
determinations  for  other  skin  areas,  such  as  the  back  of  the  upper 
arm,  the  palm  of  the  hand,  the  anterior  surface  of  the  leg,  the  chest. 
the  back,  and  the  cheek,  forehead,  and  lips. 

It  is  well  that  the  subject  should  be  blindfolded  during  the 
examination  of  the  skin  areas.  He  should  understand  by  pre- 
liminary practice  what  the  sensation  of  light  touch  is,  the  percep- 
tion of  which  he  is  to  indicate.  With  strong  aesthesiometer  hairs 
the  pricking  sensation  due  to  stimulation  of  pain-spots  must  be 
discriminated  from  touch  sensation.  When  the  two  sensations  are 
elicited  together,  the  touch  sensation  is  momentary,  and  the  subject 
must  be  alert  to  detect  it  immediately  on  stimulation.  The  pain 
sensation  develops  more  slowly,  but  lasts  longer  and  becomes  much 
more  conspicuous  than  the  touch  sensation,  which  accordingly  is 
apt  to  be  submerged  by  it  in  consciousness. 

(2)  Touch  the  skin  with  a  blunt  point  (at  or  about  skin  tempera- 
ture). With  light  contact  the  sensation  is  th.it  oi  simple  touch. 
On  increasing  the  pressure,  the  quite  distinct  sensation  of  deep 
pressure  is  perceived. 

(3)  Touch  a  portion  of  skin  with  a  camel's-hair  brush  of  ordinary 
size,  pressing  on  it  till  the  hairs  of  the  brush  begin  to  bend.  The 
first  sensation  of  simple  contact  gives  place  to  a  sensation  of  pressure. 
Repeat  with  a  camel's-hair  brush  of  the  finest  hairs  half  a  centimetre 
in  length,  cut  away  till  its  cross  section  is  only  half  a  millimetre  in 
diameter  at  the  base.  Probably  a  pure  sensation  of  touch,  without 
any  pressure  element,  will  be  obtained  when  the  brush  is  applied  so 
as  just  to  bend  the  hairs. 

(4)  Find  the  least  distance  apart  at  which  the  points  oi  the 
aesthesiometer  compasses  can  be  recognised  as  two  when  applied 
to  the  back  of  the  hand,  the  forearm,  upper  arm.  forehead,  finger- 
tips, or  tip  of  the  tongue.     Both  points  oi  the  compasses  must   be 


/'/,'  M  /  re  //    /  XERCISl  s 

placed  on  the  skin  a1  the  same  time,  and  the  same  pressure  applied 
to  both.      I  in-  subject  must  not  see  the  points. 

Tinu  Discrimination  of  Touch.  Touch  the  prong  oi  a 
vibrating  tuning-fork  lightly  with  the  tip  of  the  finger.  The  taps 
of  the  prong  <>n  the  skin  <l<>  not  blend  m t • »  a  continuous  sensation 
even  when  the  fork  vibrates  several  hundred  times  per  second. 

30.  Temperature  Sensations.  For  the  investigation  oi  these, 
pieces  oi  thick  copper  wire,  filed  a1  one  end  to  a  blunt  point,  ;m<l 
fixed  l>\  the  other  in  a  small  wooden  handle,  may  be  used.  They 
can  be  heated  in  a  sand-bath  or  in  a  beaker  of  water  to  the  desired 
temperature,  or  cooled  in  cold  water  or  in  ice.  Or  a  metal  tube 
drawn  out  at  one  end,  through  which  water  at  the  required  tem- 
perature can  be  passed  before  use,  may  be  employed.  Another 
device  is  a  metal  cylinder  ending  in  a  point,  and  filled  with  water 
at  the  given  temperature. 

(i)  On  the  dorsal  side  of  the  hand  outline  an  area  of  skin  with  a 
pen  or  a  coloured  pencil.  Divide  this  into  areas  of  4  square  milli- 
metres. Go  over  the  area  with  a  wire  or  cylinder  at  a  temperature 
of  about  400  C,  and  determine  the  extent  and  position  of  the  spots 
which  on  contact  yield  a  sensation  of  warmth,  marking  them  on  the 
skin  by  ink-dots,  or  mapping  them  on  ruled  paper.  Then  repeat 
the  exploration  with  points  at  a  temperature  of  about  150  C,  and 
map  the  spots  which  yield  a  sensation  of  coolness.  Now  note 
whether  a  warm  spot  touched  with  a  point  at  150  C,  or  a  cold  spot 
touched  with  a  point  at  400  C.  yields  any  temperature  sensation. 

(2)  Touch  the  skin  with  a  test-tube  containing  water  at  500  C, 
and  again  with  a  test-tube  containing  ice.  Do  the  sensations  differ 
in  any  way  from  those  of  pure  warmth  and  coolness  ?  Repeat  (1) 
with  temperatures  of  500  and  o°,  and  note  whether  there  is  any 
difference  in  the  quality  of  the  sensations  yielded  by  the  warm  and 
cold  spots.  When  a  cold  spot  is  touched  with  a  point  at  a  tempera- 
ture of  500,  or  a  warm  spot  with  a  point  at  a  temperature  of  o°,  is 
any  sensation  obtained  ?     If  so,  what  ? 

(3)  Apply  successively  to  one  and  the  same  portion  of  the  skin 
tubes  containing  water  at  500,  450,  400,  350,  300,  250,  200,  150, 

io°,  50,  and  o°  (ice),  and  determine  the  sensations  excited  in  each 
case.  The  contact  should  only  be  momentary,  so  as  not  to  cause 
extensive  and  lasting  change  of  temperature  of  the  skin.  Note 
that  there  is  a  certain  range  of  temperature  above  and  below  that  of 
the  skin  within  which  no  sensation  of  heat  or  cold  is  given. 

(4)  Take  three  beakers  of  water  at  200,  300,  and  40°  C.  respectivelv. 
Place  a  finger  of  one  hand  in  the  coldest  beaker,  a  finger  of  the  other 
hand  in  the  warmest,  until  no  definite  temperature  sensations  are 
felt  by  cither  finger.  Plunge  both  fingers  into  the  beaker  at  300  C, 
and  temperature  sensations  will  be  perceived. 

(5)  Temperature  Discrimination. — Find  the  least  perceptible  differ- 
ence in  temperature  between  two  beakers  of  water  at  about  o°  C. 
Repeat  the  experiment  with  two  beakers  of  water  at  about  300  C, 
and  again  with  two  beakers  of  water  at  about  550  C.  Use  the  same 
hand.     Expose  the  same  amount  of  surface  to  the  water. 

Compare  the  acuteness  of  the  temperature  sensations  of  the 
skin  and  the  mucous  membrane  of  the  mouth,  touching  a  given 
portion  of  skin  and  then  a  portion  of  mucous  membrane  with  tubes 
containing  water  at  various  temperatures. 

31.  Pain. — 1 1 )  Using  a  pin.  explore  a  cutaneous  area  to  determine 
whether   every    point    of  the   skin    yields   the   painful   sensation    of 


roo2  /   M  1X1 '  if   OF  I'll  YSIOLOG  ) 

pricking.  Especially  compare  the  resull  of  stimulating  the  region 
in  (In-  immediate  aeighbourhood  of  the  hairs  with  the  spaces  betwe*  n 
hairs.  Discriminate  the  touch  sensation  given  l>v  the  light  contact 
ol  the  pin  point  from  the  painful  impression  caused  when  the 
pressure  is  increased.  Note  that  the  touch  element  is  more  evanes- 
cent than  the  pain  clement. 

(j)  With  strong  v.  Frey  hairs  determine  the  pressure  at  which 
the  sensation  of  touch  passes  into  that  of  pain. 

( j)  Compare  the  sensibility  to  pin-pricks  of  the  mucous  membrane 
within   the  mouth  with  that  of  the  skin. 


CHAPTER  XIV 

REPRODUCTION 

Regeneration  of  Tissues. — Since  cells  are  constantly  dying  within 
the  body,  they  must  be  constantly  reproduced.  In  some  tissues  the 
process  by  which  this  is  accomplished  is  more  evident,  and  therefore 
better  known,  than  in  others.  The  most  highly-organized  tissues 
are  with  difficulty  repaired,  or  not  at  all.  The  epidermis  is  always 
wearing  away  at  its  surface,  and  is  being  constantly  replaced  by  the 
multiplication  of  the  cells  of  the  stratum  Malpighii.  In  the  corneous 
layer  we  have  only  dead  cells  ;  in  the  Malpighian  layer  we  have  every 
histological  gradation  from  squames  to  columns,  and  every  physio- 
logical gradation  from  cells  which  are  about  to  die  to  cells  that  have 
just  been  born.  The  corpuscles  of  the  blood  undoubtedly  arise  at 
first,  and  are  recruited  throughout  life,  by  the  proliferation  of 
mother-cells.  The  gravid  uterus  grows  by  the  formation  of  new 
fibres  from  the  old,  and  by  the  enlargement  of  both  old  and  new. 
A  severed  muscle  is  generally  united  only  by  connective  or  scar 
tissue,  but  under  favourable  conditions  a  complete  muscular 
'  splice  '  may  be  formed.  A  broken  bone  is  regenerated  by  the 
proliferation  of  cells  of  the  periosteum,  which  become  bone- 
corpuscles.  We  do  not  know  whether  there  is  any  new  formation  of 
nerve-cells  in  the  adult  organism,  but  peripheral  nerve-fibres  which 
have  been  destroyed  by  accident  or  operation  are  readily  regenerated, 
and  the  end-organs  of  efferent  nerves  may  share  in  this  regeneration. 

In  lower  forms  of  animals,  and  in  all  or  most  vegetables,  the  power 
of  regeneration  is  much  greater  than  in  man.  The  starfish  can  not 
only  repair  the  loss  of  an  arm,  but  from  a  severed  arm  a  complete 
animal  can  be  developed.  A  newt  can  reproduce  an  amputated  toe, 
and  every  tissue — skin,  muscle,  nerves,  bone — will  be  in  its  place. 
After  extraction  of  the  crystalline  lens  in  triton  larvae,  a  new  lens 
is  formed  from  the  iris  epithelium.  Artificial  mouths  surrounded 
by  tentacles  can  be  formed  in  Cerianthus,  an  animal  belonging  to 
the  same  group  as  the  sea-anemones,  merely  by  making  a  cut  in 
the  body-wall  and  preventing  it  from  closing.  In  an  Ascidian,  too 
(the  Cynone  intestinalis),  artificial  openings  in  the  branchial  sac, 
surrounded  by  numerous  pigmented  points  similar  to  the  eye-spots 
around  the  natural  mouth  and  anus,  have  been  produced  (Loeb). 

Thus,  in  a  sense,  reproduction  is  constantly  going  on  within  the 
bodies  even  of  the  higher  animals.  But  since  the  whole  organism 
eventually  dies,  as  well  as  its  constituent  cells,  a  reproduction  of  the 
whole,  a  regeneration  en  masse,  is  required. 

A  cell  of  the  stratum  Malpighii  can  only,  so  far  as  we  know, 
reproduce  a  similar  cell,  and  this  is  characteristic  of  cells  that  have 

1003 


A   M  INUAL  OF  PHYSIOLOGY 

undergone  a  certain  amount  oi  differentiation,  especially  in  the 
higher  animals  The  fertilized  ovum,  on  the  other  hand,  lias  the 
power  of  reproducing  not  only  ova  like  itself,  but  the  counterparts 
of  every  cell  in  the  body.  And  this  is  only  the  highesl  development 
oi  a  power  which  is  in  a  smaller  degree  inherent  in  other  cells  in 
lower  forms.  Plants  and  the  lowest  animals  arc  far  less  dependenl 
upon  reproduction  by  means  of  special  cells.  A  piece  of  a  Hydra 
separated  ofl  artificially  or  by  simple  fission  becomes  a  complete 
Hydra,  as  was  shown  by  Trembley  a  century  and  a  half  ago,  \ 
cutting  from  a  branch,  a  root,  a  tuber,  or  even  a  leaf  of  a  plant, 
may  reproduce  the  whole  plant.  It  is  as  if  each  cell  in  these  lowly 
forms  carried  within  it  the  plan  of  the  complete  organism,  from  which 
it  built  up  the  perfect  plant  or  animal. 

Reproduction  in  the  Higher  Animals. — In  all  the  higher  animals 
reproduction  is  sexual,  and  the  sexes  are  separate. 

In  regard  to  the  secretions  of  the  reproductive  glands,  all  that 
is  necessary  to  be  said  here  is  that,  unlike  other  secretions,  their 
essential  constituents  are  living  cells.  The  spermatozoa  in  the 
male  have,  indeed,  diverged  far  from  the  primitive  type.  Certain 
cells  (spermocytes)  in  the  tubules  of  the  testicle  divide,  each  forming 
two  daughter  spermocytes.  Each  of  the  daughter  spermocytes  in 
turn  divides,  so  that  four  cells  (spermatids)  are  formed  from  each 
spi  rmocyte.  In  the  final  division  which  produces  the  spermatids  a 
ied action  of  the  chromosomes  (p.  5)  occurs,  so  that  the  spermatid 
possesses  only  onedialf  the  number  characteristic  of  the  somatic  cells 
of  the  species.  The  spermatids  elongate  and  become  spermatozoa,  the 
head  of  the  latter  representing  the  nucleus  of  the  former  ;  and  it  is 
this  nucleus  (with  the  middle  piece  originally  containing  the  male 
centrosome  and  attraction  sphere)  which  is  the  essential  contribution 
of  the  male  to  the  reproductive  process.  The  tail  of  the  spermatozoon 
is  simply,  from  the  physiological  point  of  view,  a  motile  arrangement, 
whose  function  it  is  to  carry  the  nucleus  of  the  male  element,  freighted 
with  all  that  the  father  can  transmit  to  the  offspring,  into  the  neigh- 
bourhood of  the  female  reproductive  element  or  ovum.  After  the 
spermatozoon  has  penetrated  the  ovum  its  tail  disappears,  being 
probably  absorbed. 

The  ovum  also  begins  as  a  typical  cell  with  nucleus  (germinal 
vesicle), nucleolus  (germinal  spot),  centrosome  and  attraction  sphere 
(p.  5),  and  it  forms,  by  its  repeated  subdivision,  all  the  cells  of  the 
fcetal  body.  But,  except  in  some  (parthenogenetic)  forms,  it  never 
awakens  to  this  reproductive  activity  till  fecundation  has  occurred  ; 
and  fecundation  essentially  consists  in  the  union  of  the  male  with  the 
female  element,  or  rather  in  the  union  of  the  male  and  female  nucleus 
From  time  to  time  a  Graafian  follicle,  overdistended  by  its  liquor 
lolliculi,  bursts  on  the  surface  of  the  ovary  and  discharges  an  ovum. 
11  was  formerly  believed  that  the  frayed"  or  fimbriated  end  of  the 
Fallopian  tube,  rising  up  fingerdike  from  the  dilatation  of  its  blood- 
vessels, grasps  the  ovum.  But  it  is  more  than  doubtful  whether  this 
occurs.  It  is  more  probable  that  the  ovum  is  first  discharged  into 
the  pelvic  cavity,  and  is  guided  to  the  orifice  of  the  Fallopian  tube, 
not  necessarily  that  of  its  own  side,  by  the  movements  of  the  cilia 
around  the  orifice,  and  then  passed  slowly  along  the  tube  by  the 
downward  lashing  cilia  which  line  it.  If  not  impregnated,  it  soon 
perishes  amid  the  secretions  ol  the  uterus  how  soon  has  been 
matter  ot  discussion,  and  can  hardly  be  considered  as  settled.  It. 
however,  impregnation  occurs,  the  ovum  penetrating  the  superficial 


Kl  PRODI  <    I  ION 

epithelium  into  the  subepithelial  connective  tissue  becomes  fixed  In 
one  ol  the  crypts  or  pouches  of  the  uterine  mucous  membrani 
{dscidua  serotina),  which  grows  round  Li  .is  the  decidua  reflexa. 

Menstruation.  In  the  mature  female,  from  puberty,  the  age  at 
which  the  reproductive  power  begins  (thirteenth  to  fifteenth  year), 
on  till  the  time  ol  the  menopause  (fortieth  to  fiftieth  year),  at  which 
11  ceases,  an  ovum  or  it  may  be  in  some  cases  more  than  one — is 
discharged  at  regular  intervals  of  about  tour  weeks.  This  discharge 
is  accompanied  by  certain  constitutional  symptoms  and  local  signs 
thai  last  for  a  variable  number  of  days."  The  genital  organs  are 
congested,  and  a  quantity  of  blood,  which  varies  in  different  indi- 
viduals, but  is  usually  not  over  50  C.C.,  is  shed.  It  more  than  60  c.c. 
is  lust  the  flow  is  copious.  Over  100  c.c.  it  is  abnormally  great 
(G.  I  loppe-Seyler).  At  the  same  time,  the  whole  or  a  portion  of  the 
mucous  membrane  of  the  uterus  is  cast  off. 

As  to  the  physiological  meaning  of  this  menstruation,  as  it  is 
called,  opinion  is  divided.  Two  chief  theories  have  been  proposed 
to  account  tor  it.  both  of  which  agree  in  considering  the  phenomenon 
to  be  connected  with  a  preparation  of  the  uterus  for  the  reception 
of  the  ovum.  Hut  according  to  the  theory  of  Pfli'iger  the  mucous 
membrane  is  stripped  ofl  (by  a  process  analogous  to  the  '  freshening  ' 
or  paring  of  the  indurated  edges  of  a  wound  by  the  surgeon,  in 
order  that  union  may  occur  when  they  arc  brought  together)  on 
the  chance,  so  to  speak,  that  an  impregnated  ovum  may  arrive.  On  the 
alternative  theory,  this  change  takes  place  because  the  ovum  has  not 
been  impregnated,  and  tin-  bed  prepared  for  it  not  being  required, 
the  swollen  and  congested  uterine  mucous  membrane  undergoes 
degeneration,  and  is  in  part  cast  off  (Reichert,  Williams,  etc.). 

The  process  of  menstruation,  and  the  nutrition  of  the  genital 
ins,  especially  the  uterus,  are  intimately  dependent  upon  the 
ovaries.  There  is  good  evidence  that  the  influence  is  exerted  through 
an  internal  secretion  formed  by  some  portion  of  the  ovarian  sub- 
stance. When,  for  instance,  the  ovaries  of  young  animals  (guinea- 
pigs)  are  removed  from  their  normal  situation  and  transplanted  to 
a  distant  part  of  the  body,  the  external  genitals,  vagina,  and  uterus 
undergo  the  normal  development  instead  of  being  arrested  in  their 
growth,  as  is  the  case  when  the  ovaries  are  removed  altogether.  The 
removal  of  the  ovaries  in  adult  animals  leads  to  fibrous  degeneration 
of  uterus  and  Fallopian  tubes.  On  the  other  hand,  removal  of  the 
uterus  has  no  effect  on  the  development  of  the  ovaries  in  a  young 
animal,  and  does  not  cause  degeneration  of  the  ovaries  of  an  adult 
animal.  In  monkeys,  in  which  a  menstrual  flow  comparable  to  that 
in  the  human  female  occurs,  it  was  found  that  menstruation  took 
place  alter  the  ovaries  had  been  transplanted  from  their  original  seat, 
and  the  flow  stopped  when  the  transplanted  ovaries  were  removed. 
It  has  been  stated,  too,  that  in  a  young  woman  suffering  from 
amenorrhcea  (lack  of  menstruation)  a  regular  flow  appeared  after 
the  transplantation  of  an  ovary  from  another  woman  into  her  uterus. 
Recently  the  view  has  been  put  forward  that  the  important  part  of 
the  ovary  for  these  functions  is  the  corpus  luteum,  which  is  by  some 
investigators  considered  to  be  a  gland  with  an  internal  secretion 
(Born).  This  secretion  seems  to  be  connected  with  the  implantation 
of  the  ovum  and  the  subsequent  growth  of  both  ovum  and  uterus. 
According  to  Fraenkel,  the  absence  of  the  corpus  luteum  prevents 
implantation.  When  the  ovum  has  not  been  fertilized  the  corpus 
luteum  brings  about  menstruation.     Where  fertilization  has  occurred 


ioo6  A   MANUAl    OF  PHYSIOLOGY 

it  prepares  the  uterus  Eor  the  implantation  oi  the  ovum.  He  con- 
siders tli;it  there  is  no  difference  between  the  true  and  the  false 

corpora  lulea.  '  lutein.'  the  dried  extract  of  the  corpora  lutea  of 
cows,  is  recommended  for  the  treatment  of  suppressed  menstruation, 
and  the  troublesome  symptoms  arising  from  the  premature  pro- 
duction of  the  menopause  by  removal  of  the  ovaries. 

The  mode  oi  origin  of  the  corpus  lutcum  has  given  rise  to  much 
discussion.  Two  chief  views  have  been  put  forward  :  (i)  That  it  is 
a  structure  derived  from  the  connective-tissue  wall  (theca)  of  the 
discharged  follicle  (v.  Baer,  etc.)  ;  (2)  that  it  is  developed  from  the 
follicular  epithelium  (membrana  granulosa)  (Sobotta,  etc.).  The 
second  view  seems  to  be  best  established.  The  granulosa  cells 
enlarge,  it  is  said,  without  becoming  more  numerous.  In  certain 
animals  (guinea-pig),  however,  mitotic  division  of  cells  of  the 
membrana  granulosa  has  been  observed  (L.  Loeb). 

The  influence  of  the  ovary  on  the  formation  of  the  decidual  has 
been  illustrated  in  a  very  interesting  way  by  the  investigations  of 
L.  Loeb  on  the  artificial  production  of  deciduomata.  He  has  shown 
that  if  a  number  of  incisions  are  made  into  the  uterus  of  a  rabbit  or 
guinea-pig  within  a  certain  interval  after  the  cestral  period  (period  of 
heat),  a  structure  with  the  histological  characters  of  the  decidua 
develops  at  each  wound.  Impregnation  does  not  appear  to  be  a 
necessary  factor,  nor  even  contact  of  the  ovum  with  the  uterine 
mucous  membrane.  On  the  other  hand,  ovulation,  the  discharge  of 
an  ovum  or  ova,  or  at  any  rate  the  condition  of  the  ovary  associated 
with  this  discharge,  seems  to  be  indispensable,  lor  extirpation  of 
the  ovaries  in  a  large  number  of  guinea-pigs  prevented  the  formation 
of  deciduomata  from  wounds  of  the  uterus  made  at  the  most  favour- 
able period  after  copulation.  The  uterus  then  appears  to  have  an 
inherent  power  of  responding  to  such  a  stimulus  as  a  mcchanica 
injury  by  the  production  of  a  decidual  structure,  but  only  under  the 
influence  of  the  ovary.  The  ovarian  factor  is  probably  not  nervous 
but  chemical,  some  specific  substance  which  acts  on  the  uterus  being 
liberated  periodically  in  connection  with  the  sexual  rhythm. 

Development  of  the  Ovum. — Before  fecundation,  and  apparently 
as  a  preparation  for  it,  the  ovum  is  the  seat  of  remarkable  changes, 
similar  upon  the  whole  to  those  seen  in  the  mitotic  or  indirect 
division  of  ordinary  cells.*  They  have  been  most  fully  studied  in 
the  eggs  of  certain  invertebrate  animals.  The  division  of  the  cell  is 
initiated  by  changes  in  the  centrosomc  and  attraction  sphere.  The 
centrosome  divides  into  two  daughter  centrosomes.  These  take  up 
a  position  one  at  each  pole  of  the  nucleus.  Each  daughtcr-centro- 
somc  is  surrounded  by  a  system  of  radiating  lines  or  filaments,  which 
are  less  conspicuous  than  the  chromatin  filaments  of  the  nucleus, 
since  they  do  not  stain  as  these  do.  .Meanwhile  the  nuclear  mem- 
brane and  the  nucleoli  disappear,  or  at  any  rate  become  indistinguish- 
able from  the  rest  of  the  chromatin  skein.  The  skein  breaks  up  into 
chromosomes,  the  number  of  which  is  constant  for  a  given  species, 
but  is  not  the  same  in  all  species  of  animals. 

The  daughter  centrosomes  or  astrosphcres  are  united  by  meridional 
achromatic  fibres,  which  form  a  spindle  running  through  the  nucleus 
from  one  pole  to  the  other.  The  chromosomes  arrange  themselves  at 
right  angles  (equatorially)  to  the  spindle,  and  then  each  chromosome 
divides  longitudinally  into  two.  The  halves  of  the  chromosomes 
now  pass  toward  their  respective  centrosomes,  being  perhaps  guided 

*  For  figures  illustrating  the  changes  see  any  good  textbook  of  Histology. 


REPRODUi  I  ION  [007 

by  the  fibres  oi  the  spindle.  It  results^from  tins  thai  two  daughter 
nmlci  ,uc  formed,  each  with  the  same  number  of  chromosomes 
as  the  original  nucleus,  although  with  only  half  the  amount  of 
chromatin,  ["he  cytoplasm  divides  also,  so  that  the  parent  cell  is 
now  represented  by  two  daughter  cells.  Jn  ordinary  cell  division 
the  two  daughter  tells  are  of  equal  size,  but  in  the  division  of  the 
ovum  which  occurs  before  fertilization  the  two  resulting  cells  are 
verj  unequal.  The  large  cell  continues  to  be  known  as  the  ovum  ; 
the  small  one  is  the  first  polar  body.  After  extrusion  of  the  Inst 
polar  body  the  ovum  again  divides  unequally.  A  new  spindle  forms, 
and  a  second  polar  body,  again  much  the  smaller  of  the  two  daughter 
cells,  is  cast  oil.  There  is  a  difference,  however,  between  the  process 
of  division  which  gives  rise  to  the  first  and  that  which  gives  rise 
to  the  second  polar  body.  In  the  case  of  the  latter  a  so-called 
reduction-division  occurs ;  the  chromosomes  do  not  split  longi- 
tudinally, but  half  of  the  original  number  pass  into  each  daughter 
nucleus  \s  to  the  significance  of  these  changes  there  has  been: 
much  discussion.  It  is  agreed  that  the  result  of  the  process  is  the 
expulsion  of  a  portion  of  the  chromatin,  the  ovum  now  possessing 
only  half  the  original  number  of  chromosomes,  although  nearly  all 
the  original  cytoplasm.  In  fertilization  the  original  number  is 
restored  by  the  male  element  when  it  arrives  and  penetrates  the 
ovum.  For  in  the  final  cell-division  by  which  the  mature  sperma- 
tozoon is  formed  the  chromosomes  of  its  nucleus  are  also,  after  two 
divisions  essentially  similar  to  those  occurring  in  maturation  of  the 
ovum,  reduced  to  half  the  normal  number. 

The  two  reduced  nuclei  in  the  fertilized  ovum  are  spoken  of  as 
the  male  and  female  pronuclei.  By  their  union  a  single  nucleus  is 
formed  with  the  number  of  chromosomes  normal  to  the  species. 

An  enormous  amount  of  interesting  work  has  been  done  with  the 
view  of  illustrating  the  connection  of  the  complicated  phenomena 
described  with  the  structure  of  the  ovum.  Only  a  bare  reference 
to  one  or  two  of  the  experiments  is  possible  here.  Driesch  and 
Hertwig  find  that  the  nucleus  can  be  made  artificially  to  change  its 
place  with  reference  to  the  yolk,  without  hindering  the  development 
of  a  normal  animal.  Lillie  has  shown  that  centrifugalization  of  the 
eggs  of  annelids,  although  it  markedly  alters  the  distribution  of  the 
yolk  and  other  substances,  does  not  affect  the  form  of  cleavage. 
The  polar  bodies  appear  in  the  position  which  they  would  normally 
occupy.  In  other  words,  no  redistribution  of  the  granules  or  nucleus 
affects  the  polarity  of  the  egg,  which  therefore  is  a  function  or 
property  of  the  ground  substance  of  the  protoplasm.  The  whole 
of  the  protoplasm,  however,  is  not  necessary  for  complete  develop- 
ment. Even  in  Amphioxus,  the  lowest  of  the  vertebrates,  the 
eggs  have  been  broken  up  by  shaking,  and  a  complete  animal 
evolved  from  as  little  as  one-eighth  of  an  ovum.  If  the  separation 
was  incomplete  a  kind  of  Siamese  twins,  or  even  triplets,  could  be 
obtained  (Wilson  and  Mathews).  Nor  is  it  always  indispensable 
that  both  pronuclei  should  be  present. 

Whatever  it  is  that  the  spermatozoon  supplies,  the  process  of 
Icrtilization  can  in  certain  forms  be  started  artificially.  The  studies 
of  Loeb  and  his  pupils  on  artificially  induced  parthenogenesis  are  of 
special  importance.  When  the  unfertilized  eggs  of  the  sea-urchin  are 
exposed  for  one  or  two  minutes  to  50  c.c.  of  sea-water,  to  which 
3  or  4  c.c.  of  decinormal  acetic  acid  has  been  added,  the  majority  of 
the  eggs  form  the  membrane  characteristic  of  the  entrance  of  the 


A    MANUAL  hi    I'll)  SIOLOG  ) 

spermatozoon.     When  thesi  re  afterwards  exposed  for  thirty 

i'>  fortj  minutes  to  i  ■  ea-water,  to  which  [4  or  1 5  c.c. 

strong  solution  ol  sodium  chloride  (two  and  a  hall  tunes  the  strength 
ol  a  aormal  solution,  or  aboul  i  ['6  per  cent.)  has  been  added,  th 
•  it  the  eggs  which  have  formed  membranes  develop  into  swimming 
larvas  that  rise  to  the  surface.  These  larvas  develop  into  perfect 
sea-urchin  larvas  or  '  plutei  '  as  fast  as  the  larvas  of  eggs  fertilize  d 
with  sperm. 

The  facts  ol  parthenogenesis  show  that  it  is  not  absolutely  nee 
for  development  that  the  ovum  should  have  the  normal  number  ol 
chromosomes  restored.  It  can  develop  with  half  the  number,  the 
mosomes  ol  the  female  pronucleus  being  sufficient  for  growth, 
although,  ol  course,  in  this  case  for  a  growth  uninfluenced  by  the 
properties  of  the  male  element.  In  like  manner  it  is  stated  that 
portions  of  the  maturated  ovum  devoid  of  a  nucleus  can  und< 
development  if  penetrated  by  a  spermatozoon,  the  chromosomes  ol 
the  male  pronucleus  being  sufficient  for  growth. 

Not  till  all  these  events  have  taken  place — extrusion  of  the  two 
polar  bodies,  or  maturation;  penetration  of  the  spermatozoon,  and 
blending  of  its  head  (the  male  pronucleus)  with  the  remnant  of  the 
nucleus  of  the  ovum  (female  pronucleus),  or  fecundation  -not  till 
then  does  the  ovum  begin  the  process  of  repeated  division  by  which 
the  whole  body  is  reproduced.  The  fused  or  segmentation  nucleus 
divides  into  two,  each  containing  the  normal  number  of  chromos< 
derived  from  the  splitting  of  those  contributed  by  both  the  male 
and  female  elements.  It  is  believed  that  the  division  takes  place  in 
such  a  way  that  both  male  and  female  chromosomes  are  represented 
in  each  nucleus.  The  cytoplasm  being  also  cleft  by  a  corresponding 
furrow,  two  complete  nucleated  cells  make  their  appearance.  Th 
divide  in  turn,  till  at  length  (in  the  mammal)  the  embryo  is  repre- 
sented by  a  hollow  sphere  or  vesicle,  with  a  cellular  crust.  During 
division  the  upper  or  outer  cells  have  always  been  larger  than  the 
inner  and  lower,  and  have  multiplied  more  rapidly  ;  and  thus  it 
comes  about  that  the  hollow  sphere  of  large  cells  encloses  a  mass  of 
smaller  cells,  along  with  remnants  of  broken-down  yolk  and  of  fluid 
derived  by  absorption  from  the  contents  of  the  uterus.  The  smaller 
cells  continue  to  multiply  and  arrange  themselves  as  a  lining  to  the 
sphere  already  formed,  so  that  in  a  short  time  it  becomes  double, 
and  we  have  already  differentiated  two  of  the  primary  embryonic 
layers — the  ectoderm,  also  called  the  epiblast,  or  superficial,  and  the 
endoderm,  also  called  the  hypoblast,  or  deep  layer.  The  whole  sphere 
is  called  the  blastoderm,  or  the  blastodermic  vesicle. 

While  this  mner  shell  of  endodermic  cells  is  gradually  creeping  on 
to  completion,  there  appears  at  a  part  where  it  is  already  tully 
formed  a  small  opaque  whitish  disc,  the  germinal  area  or  embryonal 
shield.  This  represents  the  stocks  on  which  the  framework  ol  the 
embryo  is  to  be  laid  down.  The  area  elongates  ;  .it  its  posterior 
end  appears  a  thickened  line,  the  primitive  streak,  soon  furrowed  by 
a  longitudinal  groove,  the  primitive  groove,  that  marks  the  direc- 
tum in  which  the  long  axis  ol  the  future  embryo  will  lie.  but  is  not 
Ltseli  a  perm. i.n<  ut  hue  in  the  building,  and  ultimately  vanishes. 
I  lie  appearance  ol  the  primitive  streak  is  the  signal  that  a  rapid 
proliferation  ol  the  cells  of  the  germinal  area,  and  especially  of  the 
ectoderm,  has  begun  ;  and  this  goes  on  until  a  third  layer  is  tunned. 
intermediate  in  position  to  the  original  two.  and  therefore  named 
the  mesoderm.     While  this  is  pushing  its  way  over  the  germinal 


REPRODUCTION  1009 

area  and  into  the  res*  <>i  the  blastodermii  vesicle,  the  ectoderm  in 
front  "t  the  primitive  streak  rises  up  in  two  lateral  ridges,  em  Losing 
'••■11  them  the  medulla*  M"    medullary  groove  Is  the 

beginning  of  the  c<  rebro-spinal  axis  ;  its  walls  first  come  to  overhang 
the  furrow,  and  then  to  coalesce  ;  and  the  medullary  groove  has  now 
become  the  neural  canal.  Immediately  under  it  the  mesoderm 
forms  .1  rod  ot  cells,  the  notochord,  which  is  the  forerunner  of  the 
vertebra]  column  ;  around  tins  the  bodies  of  the  vertebrae  are  after- 
wards developed  from  cubical  masses  oi  mesodermic  cells,  arranged 
in  pairs  .don-  the  notochord.  and  called  the ~  protovertebrcz.  The  rest 
of  the  mesoderm,  running  out  on  each  side,  from  the  protovertebrae, 
splits  into  two  layers,  an  upper  or  somatic  layer,  which  unites  with 
the  ectoderm,  and  a  lower  or  splanchnic  layer,  which  unites  with  the 
endoderm.  Between  the  two  layers  is  a  space  called  the  ccelom,  or 
pleuro-peritoneal  cavity  (Fig.  445). 

I  p  to  the  present,  apart  from  the  enclosure  of  the  neural  canal, 
all  this  formative  activity  is  buried  beneath  the  surface  of  the 
blastoderm,  and  has  not  showed  itself  by  any  external  token  ; 
the  embryo  still  appears  as  a  portion  of  the  germinal  area,  and  lies 
in  its  plane.  Hut  now  a  pocket,  or  crease,  or  moat,  beginning  at 
the  head  as  the  head-fold,  then  pushing  under  the  tail,  gradually 
creeps  round  and  undermines  the  whole  embryo,  which  is  raised 
above  the  general  level,  and,  as  it  were,  scooped  out  from  the  rest 
of  the  blastoderm  ;  till  at  length  it  lies  on  the  latter,  something  like 
an  upturned  canoe,  enclosing  a  tube,  complete  in  front  and  behind, 
but  still  open  in  the  middle,  where  it  communicates  with  the  interior 
of  the  yolk-vesicle.  Since  this  tube  has  been  formed  by  the  tucking 
in  of  the  three  ancestral  layers  of  the  blastoderm,  it  follows  that  it 
is  lined  by  endoderm,  supported  externally  by  the  splanchnic  sheet 
of  mesoderm.  So  that  now  the  body  consists  of  a  dorsal  tube  (the 
neural  canal),  essentially  of  ectodermic  origin,  a  ventral  tube  (the 
alimentary  canal),  essentially  of  endodermic  origin,  and  between 
the  two  a  massive  double  layer  of  mesodermic  tissue,  which  con- 
tributes supporting  elements  to  both.  At  this  point  it  may  be  well 
to  emphasize  the  fact  that  this  embryological  distinction  of  the 
three  primitive  layers  has  a  deep  and  fundamental  meaning,  and 
corresponds  to  a  physiological  distinction  that  endures  throughout 
life.  The  endoderm,  the  lowest  layer  in  position,  may  also  be 
described  as  the  lowest  in  the  physiological  hierarchy.  It  furnishes 
the  epithelial  lining  of  the  alimentary  canal  from  the  beginning  of 
the  oesophagus  to  near  the  end  of  the  rectum,  as  well  as  the  epithelium 
of  the  organs  which  arise  from  diverticula  of  the  primitive  intestine 
— viz.,  the  digestive  glands  (with  the  exception  of  the  salivary  glands), 
the  lungs,  and  the  passages  leading  to  them,  the  thyroid,  and  the 
greater  part  of  the  thymus  gland  in  its  primitive  condition  before 
the  lymphoid  tissue  derived  from  the  mesoderm  has  as  yet  grown 
into  it.  According  to  some  authorities,  the  notochord  is  also 
derived  from  the  endoderm. 

Upon  the  whole,  it  may  be  said  that  the  tissues  of  endodermic 
origin  are  essentially  concerned  in  chemical  labours,  in  the  absorp- 
tion of  food  material  and  excretion  of  waste  products.  The  meso- 
dermic tissues  are  essentially  concerned  in  mechanical  labour  ;  they 
are  the  tissues  of  movement  and  of  passive  support.  The  ectodermic 
tissues  are  at  the  top  of  the  pyramid  ;  they  govern  the  rest. 

From  the  mesoderm  arise  the  muscles,  the  entire  vascular  system, 
with  its  blood-  and   lymph-corpuscles,   the  bones  and  connective 

64 


loio  A  MANUAL  OF  PMYSIOLOG 

tissues  .  and  the  Wolffian  body  and  its  appendages,  which  arc  the 
predecessors  oi  the  genital  glands  and  ducts,  and  of  the  clued  portion 
"i  the  renal  apparatus. 

The  ectoderm  forms  the  epidermis  and  its  appendages,  the  epithelial 

end-organs  of  the  nerves  of  special  sense,  and  the  nervous  system, 
I  i  rebro-spinal  and  sympathetic.  The  salivary  glands  and  the 
mucous  lining  of  the  mouth  and  anus  are  developed  from  the  ecto- 
derm, which  is  indented  to  meet  the  intestinal  canal  and  give  it 
access  to  the  exterior  at  either  end. 

It  is  not  possible  here  to  trace  in  detail  the  development  of  all  the 
organs  of  the  embryo.  Its  nutrition  and  metabolism  not  only 
distinctly  belong  to  the  physiological  domain,  but.  carried,  on  as 
they  arc  under  conditions  that  seem  so  strange,  and  even  so  bizarre, 
to  one  acquainted  only  with  adult  physiology,  .ire  calculated  to 
throw  light  on  the  metabolic  processes  of  the  fully-developed  body. 
And  they  cannot  be  understood  without  reference  to  the  peculiarities 
of  the  vascular  system  in  fcetal  life.  These  we  shall  accordingly 
describe,  but  for  further  details  as  to  the  anatomy  of  the  embryo  the 
student  is  referred  to  some  standard  anatomical  text-book,  such  as 
Quain's  '  Anatomy.' 

Physiology  of  the  Embryo.     In  the  first  period  of  its  development 

the  ovum,  nestling  in  the  pouch  formed  by  the  decidua  serotina  and 

reflexa,  is  fed  from  the  maternal  blood  and  tissues  directly,  without 

the  mediation  of  foetal  bloodvessels,  through  the  finger-like  processes 

or  villi  with  which  its  external  layer,  the  zona  pellucida,  becomes 

studded.     At  the  earliest  stage  at  which  a  human  ovum  has  been 

studied  after  implantation  it  is  already  enveloped  by  a  thick  ecto- 

dermic  covering  (the  trophoblastic  envelope),  consisting  of  two  layers 

of  cells,  one  unquestionably  of  fcetal  origin,  the  so-called  cells  of 

Langhans,  and  the  other  the  syncytium,  the  origin  of  which  is  assigned 

by  some  authorities  to  the  ovum,  by  others  to  the  maternal  tissues. 

The  trophoblastic  covering  is  everywhere  in  contact  with  the  maternal 

blood,  which,    pushing  its   way   into  the  trophoblast   at  intervals, 

divides  it  into  columns.     Later  on  the  fcetal  mesoderm  grows  into 

these,  and  so  the  primary  villi  are  formed.     It  is  not  till  after  the 

first  three  weeks  that  bloodvessels  make  their  way  into  these  villi. 

although  the  mesoderm  of  the  foetus  begins  to  enter  the  villi  about 

the  end  of  the  first,  or  the  beginning  of  the  second,  week.     The 

scanty  yolk  of  the  human  ovum  is  totally  inadequate  to  supply  it 

with  nutriment  for  the  time  that  elapses  before  the  bloodvessels  are 

developed,  and  food  substances  must  be  obtained  from  the  maternal 

liquids  by  imbibition,  osmosis,  diffusion,  or  filtration,  aided,  perhaps, 

by  more  special  absorptive  processes  on  the  part  of  the  fcetal  tissues. 

Soon  the  heart  appears  as  a  tube  (at  first  double),  formed  by  cells 

belonging  to  the  splanchnic  layer  of  the  mesoderm.     It  begins  to 

pulsate  in  the  chick  as  early  as  the  middle  of  the  second  day.  although 

it  as  yet  contains  neither  nerve-cells  nor  fully-formed  muscular  fibres. 

In  the  mammal  pulsation  is  late  in  making  its  appearance,  in  man 

about  the  beginning  of  the  third  week.     A  bloodvessel  grows  out 

from  the  anterior  end  of  the  heart  and  divides  into  two  primitive 

aortic  arches,  from  each  of  which  a  vessel  (omphalo-mesenteric  or 

vitelline  artery)  runs  out  in  the  mesoderm  covering  the  umbilical 

vesicle,  or  yolk-sac.     The  blood  is  returned  to  the  heart  by  the 

vitelline  veins  coursing  in  on  the  walls  of  the  vitelline  duct.     In  this 

way  the  store  of  nutriment  in  the  umbilical  vesicle  of  the  chick. 

which  is  the  only  solid  or  liquid  food  it  receives  or  needs  during  the 


REPRODUCTION 


whole  period  "t  development,  is  tapped,  and  a  regular  channel  of 
supply  established.  <  bcygen  is  al  the  same  time  absorbed  through 
the  parous  shell  :  bul  later  on  this  respiratory  function  is  taken  over 
by  tl  I  or  allantoic  <  irculation.     In  tlie  mammal  the  circula- 

tion  on  tlu-  umbilical  vesicle  is  of  much  less  consequence,  for  the 
quantity  ol  materia]  1<  it  over  utter  the  formation  of  the  blastoderm 

lingly  small;  it  is  only  with  a  few  days'  provision  in  its 
haversack  that  the  embryo  starts  oul  on  its  developmental  march. 
And  the  vitelline  vessels  deriving  their  further  supply  of  food  and 
oxygen  from  the  tissues  of  the  mother  in  contact  with  the  ovum 

be  of  use  as  soon  as  the  second  and  more  perfect  placental 
circulation  is  es- 
tablished, and 
soon  shrivel  up? 
and  disappear, 
as  the  umbilical 
vesicle  shrinks. 

The  second 
circulation  oithe 
embryo  is  de- 
veloped in  con- 
■n  with  a 
remarkabi 
shoot  from  the 
hind-gut  called 
the  allantois, 
which,  before 
the  fifth  day  in 
the  chick  and 
during  the 
second  week  in 
man,  pushes  its 
way  out  be- 
tween the  so- 
matic and 
splanchn  ic 
layers  of  the 
mesoderm — i.e., 
in  the  pleuro- 
peritoneal  cav- 
ity— and  grows 
through  the  um- 
bilicus, carrying 

bloodvessels  along  with  it  in  its  mesodermic  layer.  Still  earlier, 
and.  indeed,  while  the  embryo  is  being  separated  off  from  and 
raised  above  the  level  of  the  rest  of  the  blastoderm  by  the  deepen- 
ing of  the  ditch  around  it.  the  further  banks  of  this  furrow, 
formed  of  ectoderm  and  somatic  mesoderm,  have  risen  up  on  every 
side,  and,  growing  over  the  back  of  the  embryo,  have  finally 
coalesced  and  enclosed  it  in  a  double-walled  pouch  (Fig.  445". 
The  superficial  layer  of  the  pouch  is  called  the  false  amnion  ; 
it  soon  blends  with  the  tufted  chorion  or  common  outer  envelope 
of  the  ovum.  The  inner  layer  persists  as  the  trite  amnion  ;  a 
liquid,  the  amniotic  fluid,  is  secreted  in  the  cavity  which  it  en- 
closes ;  and  the  embryo,  loosely  anchored  for  the  rest  of  its  intra- 
uterine life  by  the  umbilical  cord  alone,  floats  freely  within  it.     The 

64 — 2 


Fig.  443. 


-Diagram  to  illustrate  Formation  of 
Amnion. 


A.  cavity  of  true  amnion  :  F,  F',  folds  about  to  coalesce 
and  complete  the  amniotic  cavity  ;  tn,  mesodermic  layer  of 
amnion ;  B,  allantois ;  I,  intestinal  cavity  of  embryo  ; 
Y,  yolk-sac  ;  h,  endodermic  layer :  c,  ectodermic  layer  of 
embryo.  The  embryo  is  the  shaded  portion  in  the  middle 
of  the  figure.  E  is  placed  over  the  head  region.  No  attempt 
is  made  to  delineate  its  actual  form.  The  mesoderm  is 
represented  by  the  irterrupted  line. 


1012  A   MANUAL  OF  PHYSIOLOGY 

amniotic  fluid  acts  .is  a  water-jacket  or  cushion,  to  break  the  Eon  i 
of  the  inevitable  shocks  and  jars  transmitted  from  the  mother 
to  the  foetus  and  from  the  fcetus  to  the  mother.  To  some  extent. 
in  addition,  it  may  serve  as  a  nutritive  fluid,  for  substances  can 
pass  from  the  blood  of  the  mother  into  the  amniotic  fluid,  and  the 
amniotic  fluid  can  be  swallowed  by  the  fcetus.  This  is  shown  by 
the  fact  that  sodium  sulphindigotate,  when  injected  into  the  maternal 
circulation,  is  found  in  the  amniotic  fluid  and  in  the  alimentary  canal 
of  the  fcetus,  although  not  in  any  of  the  fcetal  tissues.  Fine  lanugo 
hairs  from  the  fcetal  skin  have  also  been  found  in  the  meconium. 

The  precise  origin  and  manner  of  formation  of  the  amniotic  fluid 
have  not  been  settled.  It  is  probably  in  the  main  a  maternal 
secretion  or  transudation.  But  something  is  contributed  by  the 
fcetus  in  the  form  of  renal,  and  perhaps  of  skin,  secretions.  The  fluid 
is  poor  in  solids.  Its  maximum  content  of  protein,  reached  during 
the  first  half  of  pregnancy,  is  only  07  per  cent.  Later  on  it 
diminishes,  and  at  full  term  is  only  one-tenth  of  this  amount.  The 
specific  gravity  is  1006  to  1009.  Its  osmotic  concentration,  as 
measured  by  the  depression  of  the  freezing-point,  is  less  than  that  of 
the  mother's  blood-scrum. 

The  allantois,  growing  out  at  the  umbilicus,  in  the  manner 
described,  insinuates  itself  between  the  true  and  false  amnion,  and 
soon  blends  with  the  latter.  For  a  time  the  secretion  of  the  primi- 
tive kidneys  continues  to  be  poured  into  the  cavity  of  the  allantois, 
so  that  it  serves  in  part  as  an  excretory  organ,  while  in  the  bird  it 
also  performs  the  function  of  respiration  ;  and  in  the  mammal  both 
food  and  oxygen  are  carried  by  its  vessels  to  the  fcetus  during  the 
greater  part  of  intra-uterine  life.  But  later  on  the  outgrowth 
atrophies  and  disappears,  all  except  its  origin  from  the  alimentary 
canal,  which  dilates  and  persists  as  the  urinary  bladder,  and  its 
bloodvessels,  which  grow  in  the  form  of  tufts  or  loops  into  the 
chorionic  villi.  The  vessels  arc  fed  by  two  umbilical  arteries  which 
arise  from  the  hypogastric  arteries  and  run  out  at  the  umbilicus 
on  the  allantois.  The  blood  is  returned  by  an  umbilical  vein, 
whose  further  course  we  shall  have  soon  to  trace.  The  shrivelled 
stalk  of  the  allantois,  projecting  through  the  umbilicus,  takes  part, 
with  its  bloodvessels,  in  the  formation  of  the  umbilical  cord,  which 
contains  also  the  remains  of  the  yolk-sac  and  is  clothed  externally 
by  a  layer  of  the  amnion.  Continuous  with  the  umbilical  cord,  and 
stretching  from  the  umbilicus  to  the  urinary  bladder,  is  a  portion  of 
the  allantois  which  is  represented  in  extra-uterine  life  by  a  thin 
cord-like  structure,  the  urachus.  The  vascular  tufts  of  the  chorion, 
which  at  first  cover  the  whole  surface  of  the  ovum  and  suck  up 
food  and  oxygen  from  decidua  serotina  and  reflexa  alike,  disappear 
in  the  region  of  the  reflexa,  hypertrophy  all  over  the  serotina — 
that  is,  where  the  ovum  is  in  actual  contact  with  the  uterine  wall — 
and  this  part  of  the  chorion  is  now  distinguished  as  the  chorion 
frondosum.  The  giant  villi  of  the  chorion  frondosum  push  their 
way  into  the  thickened  decidua  serotina,  and  ultimately  penetrate 
into  the  great  capillaries  or  sinuses  of  the  uterine  mucous  membrane. 
At  the  same  time  the  tissue  of  the  villi  external  to  the  vessels  becomes 
reduced  to  a  mere  film,  so  that,  except  for  a  thin  covering  of  decidual 
cells,  the  fcetal  vessels  are  bathed  in  maternal  blood.  By  this  inter- 
weaving of  decidua  and  chorion  frondosum  is  formed  the  placenta, 
which  for  the  rest  of  intra-uterine  life  acts  as  the  great  respiratory, 
alimentary,  and  excretory  organ  of  the  fcetus. 


REPRODUCTION  1013 

Exchange  of  Materials  in  the  Placenta. -The  maternal  blood,  as 
it  streams  through  the  colossal  capillaries  of  the  decidua,  gives  up 
to  the  foetal  blood  oxygen  and  food  substances  and  receives  from  it 
carbon  dioxide  and  in  all  probability  urea.  It  is  true  that  the  blood 
in  the  uterine  sinuses  is  not  itself  fully  oxygenated  ;  it  is  not  bright 
red  arterial  Mood.  But  it  yet  contains  more  oxygen,  and  oxygen  at 
a  higher  partial  pressure  (p.  2  [B),  than  the  purest  blood  of  the  foetus, 
and  is.  therefore,  aide  to  part  with  some  of  the  surplus  to  the  dark 
stream  oi  oxygen-impoverished  blood  brought  by  the  umbilical 
arteries  to  the  placenta.  Thus,  it  has  been  found  that  while  the 
blood  of  the  umbilical  artery  of  the  foetus  of  a  sheep  had  47  volumes 
per  cent  of  carbon  dioxide,  and  only  23  of  oxygen,  that  of  the 
umbilical  veins  had  6-3  volumes  of  oxygen,  and  only  40-5  of  carbon 
dioxide  (/unt/  and  Cohnstein).  In  the  exchange  of  gases  between 
the  placental  and  the  tu'tal  blood  the  same  general  features  present 
themselves  as  in  the  external  and  internal  respiration  of  the  mother, 
with  this  difference,  that  the  exchange  of  oxygen  is  neither  between 
air  and  haemoglobin,  as  in  the  lungs,  nor  between  haemoglobin  and 
tissue  elements,  as  in  the  organs;  but  between  maternal  and  fcetal 
haemoglobin,  of  course,  through  the  mediation  of  the  maternal  and 
fcetal  plasma.  There  is  no  reason  to  suppose  that  the  mechanism 
of  the  exchange  is  essentially  different  from  that  of  the  more  familiar 
forms  of  respiration.  Diffusion  of  the  gases  from  places  of  higher 
to  places  of  lower  tension  unquestionably  plays  an  important 
part.  But  this  does  not  exclude  the  possibility  of  a  more  active 
process  of  some  other  kind,  although  there  is  at  present  no  direct 
evidence  of  such  a  gaseous  secretion  as  has  been  previously  discussed 
in  connection  with  pulmonary  respiration  (p.  258).  The  presence  of 
oxydases  in  the  placenta  does  not  throw  any  light  on  the  question. 
For  there  is  no  proof  that  they  act  in  transferring  oxygen  from  the 
one  circulation  to  the  other,  and  oxydases  are  found  in  the  most 
diverse  tissues.  Their  significance  for  the  combustion  processes  of 
the  body  has  already  been  alluded  to  (p.  264). 

Salts  "soluble  in  water,  including  not  only  those  necessary  for 
nutrition,  like  sodium  chloride,  but  many  foreign  salts,  pass  readily 
from  the  placenta  to  the  foetus,  and  in  general  more  easily  the  lower 
their  molecular  weight.  Such  salts  as  potassium  iodide,  e.g.,  when 
injected  into  the  maternal  circulation,  appear  in  the  foetus  in  a  very 
short  time.  On  the  other  hand,  colloidal  solutions — e.g.,  of  silver 
or  silicic  acid — do  not  pass  over  at  all.  It  is  of  practical  importance 
that  substances  like  chloroform,  ether,  and  other  narcotics,  and  alka- 
loids like  morphine  and  scopolamine,  when  administered  in  obstetrica 
practice,  may  find  their  way  from  the  mother  to  the  child,  although 
more  slowly  and  more  capriciously  than  the  salts.  While  diffusion 
and  osmosis  assuredly  take  part  in  the  passage  of  materials  from  the 
placenta  to  the  foetus,  there  is  no  more  reason  to  conclude  that  the 
whole  exchange,  even  for  the  salts,  depends  upon  such  simple  physical 
processes  than  there  is  in  the  case  of  the  exchange  between  any  one 
of  the  maternal  tissues  and  the  maternal  blood.  The  essential 
similarity  of  placental  and  intestinal  absorption,  to  take  one  instance, 
is  seen  in  the  mechanism  by  which  the  foetus  gains  the  iron  required 
for  the  development  of  its  haemoglobin.  The  haemoglobin  of  the 
mother  appears  to  be  the  most  important  source  of  this  iron. 
Erythrocytes  in  all  stages  of  decomposition  can  be  found  in  con- 
tact with  the  chorionic  villi,  and  even  in  the  epithelium  covering 
the  villi.       These    corpuscles    come  partly  from  extravasations  in 


km  l  /    1/  /  vr  //    OF  PHYSIOLOGY 

the  maternal  portion  oi  the  placenta,  bu1  it  is  possible  thai  the 
villi  also  possess  the  power  oi  haemolyzing  intacl  corpuscles  in  the 
circulating  placental  blood.  Iron  can  be  demonstrated  by  micro- 
chemical  reai  tions  in  the  epithelial  cells  oi  the  i  horionic  villi  as  fine 
granules,  which  in<  rease  in  size  towards  tin-  base  of  the  i  ells.  As  we 
pass  deeper  into  the  villus  towards  its  central  bloodvessel,  the  granules 
again  diminish  in  size  I  he  pit  ture  is  very  like  that  seen  in  the  ab- 
sorption of  iron  from  the  intestine  And  if  the  microchemical  picture 
is  practically  the  same,  the  process  by  which  the  iron  is  absorbed  is 
not  likely  to  be  fundamentally  different  in  the  two  cases  (p.  417). 

The  same  is  true  of  the  passage  oi  fal  across  the  placenta.  Fat 
can  always  be  demonstrated  microchemically  in  the  chorionic  villi. 
The  most  superficial  layer  of  the  villi  is  free  from  visible  fat  droplets. 
They  increase  in  number  towards  the  base  of  the  epithelial  cells. 
\s  in  the  case  of  the  intestine,  these  appearances  agree  well  with 
the  \  iew  that  the  fat  is  split  before  being  absorbed  by  the  villi,  and 
undergoes  resynthesis  in  the  epithelium.  That,  as  a  matter  of  fact, 
fat  passes  from  the  mother  to  the  foetus  is  shown  by  the  observation 
that  when  pregnant  guinea-] >igs  were  fed  with  a  foreign  fat  (from 
cocoanuts),  the  characteristic  fatty  acid  (lauric  acid)  was  found  in 
the  fcetus.  This,  however,  does  not  exclude  the  possibility  that  the 
foetus  may  form  fat  in  its  own  tissues  from  carbo-hydrates,  and 
perhaps  from  proteins,  as  it  is  destined  to  do  in  extra-uterine  life. 

Among  the  carbo-hydrates  the  passage  of  dextrose  from  the 
maternal  to  the  fcetal  blood  has  been  experimentally  demonstrated. 
A  specially  interesting  proof  is  afforded  in  cases  where  the  mother 
sutlers  from  diabetes  mellitus.  In  one  case  in  which  the  mother, 
during  diabetic  coma,  was  delivered  of  a  stillborn  child,  the  blood 
of  the  child  contained  22  per  cent,  of  sugar,  its  urine  5*24  per  cent., 
and  the  amniotic  fluid  0^47  per  cent.  The  blood  of  the  mother  had 
a  sugar  content  of  o"8  per  cent.,  and  her  urine  a  content  of  694  per 
cent.  The  sugar  of  the  maternal  blood  is  not  the  only  source  of  the 
carbo-hydrates  of  the  fcetus.  The  glycogen  store  of  the  placenta  is 
to  be  regarded  as  a  second  source,  which  is  rendered  available  on 
conversion  into  dextrose  by  the  placental  diastatic  ferment.  This 
store  of  easily  available  food  material  is  especially  important  in  the 
early  stages  of  development  of  the  ovum  before  a  circulation  has 
been  established  in  the  villi.  In  the  youngest  ova  investigated  the 
decidual  covering  has  been  found  rich  in  glycogen. 

While  it  is  to  be  supposed  that  the  products  of  the  hydrolytic 
decomposition  of  proteins  can  be  absorbed  by  the  foetal  blood  in  its 
passage  through  the  placenta,  to  be  synthesized  to  the  appropriate 
tissue  proteins  in  the  total  organs,  there  is  evidence  that  certain 
proteins  can  be  taken  up  without  change.  In  this  connection  it 
must  be  remembered  that  the  mother  is  much  more  closely  related 
to  the  foetus  as  regards  her  protein  composition  than  any  ordinary 
protein  food  can  be  to  an  animal  in  extra-uterine  life.  In  some 
respects,  indeed,  the  fcetus  may  be  considered,  especially,  perhaps, 
in  the  first  stages  of  its  development,  as  a  part  of  the  mother,  an 
additional,  although  very  complex,  organ  rather  than  an  independent 
organism. 

The  blood  of  the  umbilical  artery,  although  far  from  the  level  of 
the  ordinary  arterial  blood  of  the  mother  as  regards  its  gaseous 
content,  is  vet  the  best  f  he  lot  us  e\  er  gets  :  and  by  a  series  of  con- 
trivances it  is  assured  that  this  best  should  go  first  to  the  most 
important  parts— the  liver,  the  heart,  and  the  head — while  the  legs 


REPRODUCTION  1015 

and  most  of  the  abdominal  organs  have  to  put  up  with  an  inferior 
supply.  This  is  brought  about  mainly  by  the  existence  oi  three 
sh(  1 1  i  ut  3  for  the  blood,  which  disappear  in  the  adult  1  Lr<  ulation,  the 
du<  tus  venosus,  the  ductus  arteriosus,  and  the  foramen  ovale. 

The  blood  oi  the  umbilical  vein,  rich  in  oxygen  for  festal  blood, 
passes  partly  through  the  1  ir<  ulation  oJ  the  liver,  bu1  a  pari  takes 
the  route  oi  the  du<  tus  venosus,  and  empties  itseli  into  the  inferior 
vena  cava.  [*he  latter  gathers  up  the  more  or  less  vitiated  blood 
from  the  inferior  extremities  and  the  renal  and  hepatic  veins,  and 
pours  its  mixed,  but  still  fairly  oxygenated,  contents  into  the  right 
auricle.  I  \  means  "i  the  Eustachian  valve,  the  jet  coming  from 
the  mouth  of  the  inferior  vena  cava  is  directed  into  the  left  auricle 
through  the  foramen  ovale  in  the  inter-auricular  septum.  There 
it  is  joined  by  the  trickle  of  blood  which  is  creeping  through  the 
unexpanded  lungs.  The  left  ventricle  propels  its  contents  through 
the  aorta,  and  thus  a  large  part  cf  this  comparatively  pure  or 
second-best  blood  is  sent  to  the  head  and  upper  extremities.  It 
returns  in  a  vitiated  state  by  the  superior  vena  cava  into  the  right 
auricle,  and  owing  to  the  position  of  the  Eustachian  valve  and  the 
direction  of  the  current,  it  flows  now,  not  through  the  foramen  ovale, 
but  into  ihc-  right  ventricle.  Thence  it  is  driven  through  the  pul- 
monary artery,  but  only  a  small  quantity  of  it  finds  its  way  through 
the  lungs  ;  the  main  stream  is  short-circuited  through  the  ductus 
arteriosus,  and  mingles  with  the  contents  of  the  thoracic  aorta 
below  the  origin  of  the  cephalic  and  brachial  vessels. 

We  may  now-  give  something  more  of  precision  to  the  statements 
that  different  parts  of  the  body  receive  blood  of  different  quality  ; 
and  it  is  possible  roughly  to  divide  the  organs  in  this  respect  into 
four  categories  :  (1)  The  liver,  which  partakes  both  of  the  best  and 
the  worst,  the  purified  blood  of  the  umbilical  veins  and  the  vitiated 
blood  of  the  intestines  and  spleen  ;  (2)  the  heart,  head,  and  upper 
limbs,  which  receive  the  blood  from  the  inferior  extremities  and 
kidneys,  mixed  with  the  pure  blood  of  the  venous  duct  ;  (3)  the 
legs,  trunk,  intestines,  and  kidneys,  which  are  fed  chiefly  by  the 
off-scourings  of  the  cephalic  end,  mitigated,  however,  by  a  pro- 
portion of  mixed  blood  from  the  inferior  cava  ;  (4)  the  lungs,  which 
receive  only  a  feeble  stream  of  unmixed  venous  blood. 

These  peculiarities  of  the  embryonic  circulation  are  in  obvious 
correspondence  with  the  physiological  events  taking  place  in  the 
fcetal  body.  The  liver  is  not  only  the  greatest  gland  in  the  embryo, 
as  it  continues  to  be  in  the  adult,  but  its  activity  seems  to  dwarf 
that  of  all  the  other  glands  put  together,  and  is  in  striking  contrast 
with  the  functional  torpor  of  the  lungs.  From  the  third  month  of 
intra-utenne  life  the  secretion  of  bile  begins  and  the  intestines 
gradually  fill  with  meconium,  of  which  the  principal  constituent  is 
bile.  Accordingly  the  liver  is  most  lavishly  supplied  with  blood, 
while  the  lungs  are  stinted.  And  since  the  liver  has,  as  we  have 
already  learnt,  other  and,  in  the  adult  at  least,  even  more  important 
labours  than  excretion,  a  large  portion  of  the  blood  it  receives 
is  of  the  best  quality  :  it  enters  the  gland  comparatively  rich  in 
oxygen,  and  passes  out  comparatively  poor  ;  while  the  lungs,  which 
have  to  be  nourished  only  for  their  own  sake,  and  are  of  no  use 
whatever  till  the  child  is  born  and  respiration  has  begun,  must  be 
content  with  the  poorest  fare — with  the  crumbs  that  fall  from  the 
table  of  fcetal  nutrition.  The  full-fed  cephalic  end  of  the  embryo 
grows  far  more  rapidly  than  the  half-starved  inferior  extremities, 


ioi6  A  MANUAL  OF  PHYSIOLOGY 

and  the  head  of  the  nev  born  child  is  large  in  proportion  to  the  rest 

Of  the  body. 

I  here  are  some  other  ])oints  in  the  physiology  of  intra-uterine 
life  which  call  for  remark  ;  and,  to  sum  up  in  a  few  words  the  grand 
distinction  between  fcetal  and  adult  life,  we  may  say  that  growth 
is  the  keynote  of  the  former,  work  (functional  activity)  of  the  latter. 
Thus,  the  muscles  at  an  early  period  in  their  development,  long  before 
any  glycogen  can  be  found  in  the  liver,  become  the  seat  of  an  accumu- 
lation of  glycogen,  which,  since  it  cannot  be  used  up  in  contraction 
as  in  the  adult  muscles,  seems  to  be  intimately  connected  with  their 
own  growth,  and  perhaps  also  with  the  growth  of  other  tissues.      It  is 
true  that  the  foetal  tissues  as  a  whole,  including  the  muscles,  are  not 
richer,   as  used  to  be  taught,   but   poorer  in   glycogen  than  adult 
tissues,  and  therefore  the  old  doctrine  that  the  fcetal  glycogen  fulfils 
a  special   '  formative  '  function  in  the  development  of  the  tissues, 
has    lost   its  experimental   basis.      Nevertheless,   there   is   a  paral- 
lelism between  the  growth  of  the  foetus  and  its  glycogen  content. 
Tn   cases  where  the  growth  of  the  foetus  has  been  spontaneously 
arrested,  the  percentage  amount  of  glycogen  in  its  organs  has  been 
found  to  be  diminished  out  of  proportion  to  the  diminution  in  weight. 
A  similar  retardation  of  development  can  be  produced  by  repeatedly 
injecting  phloridzin  into  the  mother,  and  thus  reducing  the  glycogen 
store  of  the  foetus  (I.ochead  and  Cramer).     Probably,  then,  the  fcetal 
glycogen  assists  the  growth  of  the  embryo,  which  is  known  to  be 
accompanied  by  an  intense  carbo-hydrate  metabolism,  by  furnishing 
a  store  of  easily  oxidized  material  for  the  nutrition  of  the  developing 
tissues.     When  the  muscles  have  been  formed,  their  glycogen  is 
still  consumed  in  growth,  and  their  functional  powers  lie  dormant, 
but  for  the  infrequent  and  feeble  movements,  generally  regarded  as 
reflex,  but  possibly  to  some  extent  originated  in  the  cerebral  cortex, 
which  give  the  mother  the  sensation  of  '  quickening.'      It  is  only 
late  in  development  that  the  embryonic  liver  takes  on  its  glycogenic 
function.     In  the  earlier  stages  it  is  entirely  free  from  glycogen.     It 
is  an  interesting  illustration  of  that  exact  adaptation  of  means  to 
ends  which  so  constantly  impresses  the  investigator  of  the  animal 
mechanism  that  the  ferment  which  converts  glycogen  into  dextrose 
(glycogenase)  is  also  either  entirely  absent  from  the  liver  early  in 
gestation,  or  present  only  in  traces  ;  and  that  as  the  glycogen-forming 
and  glycogen-storing  functions  of  the  organ  increase  in  importance,  it 
becomes  richer  in  glycogenolytic  ferment.     It  cannot  be  doubted  that 
the  glycogen  found  in  the  placenta  is  also  deposited  there  in  the  interest 
of  the  rapidly  growing  fcetal  tissues,  perhaps  as  a  kind  of  current 
account  on  which  they  can  operate  at  any  moment  of  emergent  \ . 
when  the  more  distant  maternal  reserves  cannot  be  drawn  upon  in 
time.     The  glycogen  is  formed  in  the  placenta,  probably  from  tin- 
dextrose  of  the  maternal  blood.     By  means  of  a  glycogen-splitting 
ferment,  which  can  be  extracted  by  glycerin  from  the  placenta,  the 
glycogen  appears  to  be  reconverted  into  dextrose  for  absorption  by 
the  foetus.      In  the  earlier  period  of  gestation  the  placenta  seems 
to  perform  vicariously  the  glycogenic  function  of  the  liver,  and  as 
the  glycogen  content  of  the  liver  increases  in  the  later  stages  of  intra- 
uterine life,  that  of  the  placenta  diminishes  proportionally. 

The  excretory  glands  of  the  embryo,  except  the  liver,  scarcely 
awaken  to  activity  during  fcetal  life.  Urine  may  indeed  be  some- 
times found  in  the  bladder  at  birth,  but  it  is  often  absent.  It  is  a 
dilute  urine,  with  a  molecular  concentration  only  about  half  as  great 


REPRODIH  l  TON  1017 

as  that  oi  the  blood,  and  although  a  portion  oi  the  amniotic  fluid, 
which  contains  traces  oi  urea  and  salts,  in  addition  to  small  quantities 
of  albumin,  may  be  secreted  by  the  renal  tubules,  and  find  its  way 
through  the  still  open  urachus  into  the  amniotic  sac,  this  contribution 
cannot  imply  more  than  a  slight  degree  of  glandular  action.  Under 
certain  experimental  conditions,  however,  it  can  be  largely  increased. 
Thus,  extirpation  of  the  kidneys  in  a  pregnant  animal  causes  an 
inciease  in  the  amount  of  amniotic  thud  divdramnios)  through  the 
stimulation  of  the  foetal  kidneys  to  increased  activity  by  the  passage 
of  the  unexcreted  urinary  constituents  of  the  mother's  blood  into 
tli.it  ot  the  lotus.  After  the  injection  of  phloridzin  into  the  foetus 
sugar  has  been  found  in  abundance  in  the  amniotic  fluid,  although 
the  injection  of  that  drug  into  the  mother  caused  no  such  effect.  On 
the  other  hand,  after  injection  of  sodium  sulphindigotate  into  the 
circulation  of  the  foetus  in  the  sheep,  the  foetal  kidneys  contained 
particles  oi  the  pigment,  while  the  amniotic  fluid  remained  un- 
coloured.  Tong  before  full  term  the  sebaceous  glands  have  begun 
their  work  by  the  secretion  of  the  vernix  caseosa,  an  oily  material 
which  (.oxers"  the  skin  and  serves  to  protect  it  from  the  continual 
irritation  of  the  fluid  in  which  the  embryo  floats. 

The  nervous  system  is  even  less  active  than  the  glandular  tissues, 
and  not  more  active  than  the  muscles.  There  is  evidently  no  scope 
for  the  exercise  of  the  special  senses.  Psychical  activity  of  every 
kind  must  be  at  its  lowest  ebb.  Consciousness,  if  it  exifts  at  all, 
must  be  dull  and  muffled.  And  if  motor  impulses  are  discharged 
from  the  cortex,  the  psychical  accompaniments  of  such  discharge  are 
doubtless  widely  different  from  those  which  we  associate  with 
voluntary  effort. 

It  is  a  remarkable  fact  that  this  functional  calm,  broken  only  by 
the  beat  of  the  heart,  is  accompanied  by  a  relatively  intense 
metabolism  of  the  same  order  of  magnitude  as  that  of  the  adult. 
In  the  hen's  egg  at  all  stages  of  development  the  consumption  of 
oxygen  and  production  of  heat  (per  kilogramme  and  hour)  are  the 
same  as  in  the  adult  hen.  The  oxygen  consumption  and  carbon 
dioxide  production  of  pregnant  guinea-pigs  were  determined  before 
and  during  compression  of  the  umbilical  cord  of  a  foetus,  and  a  distinct 
diminution  was  observed  when  the  respiratory  exchange  of  the  foetus 
was  eliminated.  From  the  results  of  a  number  of  observations  it 
was  calculated  that  the  carbon  dioxide  produced  by  the  mother 
was  4<>2  c.c,  and  by  the  foetus  509  c.c.  per  kilogramme  of  body- 
weight  per  hour  (Bohr  and  Hasselbach) .  A  similar  comparison 
between  women  before  and  during  pregnancy  never  showed  any 
diminution  in  the  respiratory  exchange  reckoned  on  the  unit  of  body- 
weight  in  the  pregnant  condition.  In  one  case,  indeed,  and  that 
the  most  exactly  observed,  there  was  an  increase  in  pregnancy. 
Now,  in  the  pregnant  woman  a  considerable  part  of  the  increase  of 
body-weight  is  due  to  the  amniotic  fluid,  in  which,  of  course,  meta- 
bolism does  not  go  on.  It  is  evident,  then,  that  in  the  human  foetus 
also  the  intensity  of  metabolism  is  at  any  rate  not  of  a  lesser  order  of 
magnitude  than' in  the  mother,  in  spite  of  the  much  smaller  amount 
of  muscular  contraction  taking  place.  The  heat  production  of  mother 
and  child  together  Iras  been  directly  estimated  in  several  cases  in  a 
respiration  calorimeter  provided  with  a  bed  just  before  parturition 
and  just  after  it.  After  parturition  the  heat  production  of  the 
mother  was  also  separately  determined.  From  the  difference  it  was 
concluded  that  the  heat  production  of  the  child  per  kilogramme  of 


iois  /    MANUAL  OF  PHYSIOLOGY 

body-weight  per  hour  is  approximately  two  and  a  half  limes  that  of 
the  mother  under  the  same  conditions.     ((  arpenter  and  Murlin.) 
[Tie  foetal  heart  beats  a1  the  rate  of  aboul   [40  times  a  minute  at 

full  term.*  The  blood-pressure  in  the  umbilical  artery  of  the 
mature  embryo  (sheep)  varies  from  60  to  So  mm.  of  mercury  ; 
but  at  the  beginning  of  the  aorta  it  will  be  more.  The  pressure  in 
the  pulmonary  trunk  must  be  about  equal  to  that  in  the  aorta,  since 
the  comparatively  short  and  easy  circuit  through  the  lungs  does 
not  as  yet  exist  .  and  in  accordance  with  this  equality  of  pressure 
(of  work  to  be  done)  is  the  equality  of  thickness  (of  working  power) 
in  the  walls  of  the  two  sides  of  the  heart. 

Suppose,  now.  that  the  embryo  contains  60  grammes  of  blood  for 
every  kilo  of  body-weight,  and  that  the  whole  of  the  blood  passes 
through  the  circulation  in  twenty  seconds.  Then  in  twenty-four 
hours  250/2  kilos  of  blood  will  be  forced  through  the  heart  for  every 
kilo  of  body-weight  against  a  pressure  of,  say,  80  mm.  of  mercury, 
or  1  metre  of  blood.  This  is  equivalent,  in  round  numbers,  to  260 
kilogramme-metres  of  work,  or  o"6  calories.  Now,  taking  the  total 
heat-production  of  the  heart  at  three  times  the  equivalent  of  its 
mechanical  work,  we  get  1  8  calories  per  kilo  of  body-weight  in 
twenty-four  hours  (see  p.  585),  or  about  ^  of  the  heat-production 
of  a  resting  adult. 

Such  movements  of  the  skeletal  muscles  as  occur  cannot  account  for 
any  large  proportion  of  the  total  metabolism,  since  they  are  executed 
in  a  medium  (the  amniotic  fluid)  of  nearly  the  same  specific  gravity 
as  that  of  the  body,  and  therefore  require  the  expenditure  of  a  very 
limited  amount  of  energy.  The  ordinary  functional  activity  of  the 
embryo,  then,  is  quite  incapable  of  accounting  for  the  intensity  of 
the  foetal  metabolic  processes.  Still  less  can  it  be  due  to  an  active 
combustion  in  the  tissues  to  compensate  for  a  rapid  loss  of  heat, 
for  the  foetus  lies  sheltered  in  the  uterus  as  in  a  thermostat  at  its 
own  temperature,  and  can  lose  practically  no  heat  unless  its  tempera- 
ture be  kept  a  little  above  that  of  the  maternal  blood.  The  only 
remaining  explanation  of  the  magnitude  of  the  foetal  metabolism 
is  that  the  growth  processes  are  associated  with  a  large  amount  of 
oxidation  (and  cleavage). 

Notwithstanding  the  intensity  of  metabolism  in  the  embryo,  not 
only  is  even  the  purest  blood,  as  has  already  been  stated,  far  from 
saturated  with  oxygen,  but  the  relative  proportion  of  haemoglobin, 
the  oxygen-carrier,  is  less  than  in  the  adult  ;  and  although  constantly 
increasing  in  amount  from  the  moment  of  its  first  appearance,  it  is 
still  somewhat  deficient,  even  at  full  term,  but  leaps  sharply  up  at 
birth.  At  an  early  period  of  development  the  embryo  also  contains 
much  more  water  than  the  adult  ;  the  specific  gravity  of  its  tissues 
increases  as  development  goes  on. 

The  remarkable  vitality  of  the  foetus,  and  its  resistance  to  asphyxia, 
are  related  not  to  the  feebleness  of  its  metabolism,  but  to  the  com- 
paratively slight  excitability  and  high  endurance  of  nervous  centres 

*  It  has  not  been  finally  determined  whether  the  rate  of  the  heart 
varies  with  the  size  or,  what  probably  comes  to  the  same  thing,  with  the 
sex  of  the  foetus.  As  we  have  seen,  the  variation  of  the  rate  in  the  adult 
with  the  size  of  the  body  is  associated  with  a  corresponding  variation  in 
the  metabolism  and  heat-loss,  which  are  proportionally  greater  in  a  small 
than  in  a  large  animal.  If  this  is  a  causal  connection  we  should  not 
expect  that  in  the  embryo  in  uteto,  where  die  conditions  as  regards  heat- 
loss  are  entirely  different,  such  a  relation  should  exist,  at  any  rate  within 
the  same  species. 


REPRODUCTION  toiQ 

like  the  respiratory,  vaso-motor,  and  cardio-inhibitory.  Even  when 
totally  deprived  of  oxygen,  .is  by  pressure  on  the  umbilical  cord 
during  delivery,  t  he  child  does  not  perish  in  the  two  or  three  minutes 
which  decide  the  fate  oi  the  asphyxiated  adult;  nor  are  the  con- 
vulsions, rise  oi  blood-pressure,  and  slowing  of  the  heart-beat, 
associated  with  asphyxia  in  the  latter,  so  readily  induced,  nor 
premature  and  fatal  efforts  at  respiration  easily  excited  in  uiero. 
But  although  in  such  a  case  the  embryo  behaves  as  a  separate 
organism,  governed  l>v  its  own  laws,  there  are  circumstances  in 
which  it  becomes  merel]  a  part  of  the  mother  and  participates  in  her 
fate.  Thus,  the  stream  oi  oxygen  which  normally  passes  from  the 
maternal  to  the  foetal  blood  is  turned  back  if  asphyxia  threatens 
the  mother;  the  blood  of  the  umbilical  arteries,  instead  of  being 
purified  in  the  placenta,  loses  the  little  oxygen  it  holds  to  the 
blood  of  the  uterine  sinuses,  and  the  tissues  of  the  embryo  are 
impoverished  to  support  the  metabolism  of  the  maternal  organs. 
In  the  same  way,  the  phenomena  of  starvation  have  taught  us 
that  the  nutrition  of  the  organism  is  not  subject  to  the  rules  of 
red  tape.  In  normal  circumstances  the  flow  of  nutriment  follows 
definite  lines  :  the  blood  feeds  the  tissues  through  its  intermediary, 
the  lymph,  and  recoups  itself  from  the  contents  of  the  alimentary 
canal.  But  when  the  normal  sources  of  nutrient  material  fail,  the 
body  falls  back  upon  its  stores.  The  organs  immediately  necessary 
to  life  are  kept,  as  far  as  possible,  on  full  diet  ;  organs  of  secondary 
importance  have  to  be  content  with  half-rations  ;  organs  less  im- 
portant still  are  drawn  upon  for  supplies. 

Parturition.— The  period  of  gestation  is  abruptly  closed  about 
280  days  after  the  last  menstruation,  usually  in  what  would  have  been 
the  tenth  intermenstrual  period  had  menstruation  been  occurring. 
There  is  necessarily  a  considerable  variation  in  the  time  when 
reckoned  in  this  way,  since  the  cessation  of  the  menses  merely  an- 
nounces that  conception  has  occurred  some  time  after  the  last 
period.  It  may  even  be  disputed  whether  the  fertilized  ovum 
corresponds  to  the  last  menstruation  or  to  the  first  absent 
period.  Parturition,  or  the  expulsion  of  the  foetus,  is  accom- 
plished by  periodical  contractions,  the  '  pains  '  of  labour,  at  first 
confined  to  the  uterus.  Soon  the  os  uteri  begins  to  soften  and 
dilate,  the  walls  of  the  vagina  become  congested,  and  its  secretions 
are  augmented.  The  uterine  contractions  increase  in  frequency 
and  force,  and  are  now  accompanied  by  reflex  contractions  of  the 
abdominal  muscles,  and,  if  the  woman  is  not  anaesthetized,  also  by 
voluntary  contractions  of  these  and  of  other  muscles,  which  can 
increase  the  intra-abdominal  pressure.  The  uterine  contractions 
can  be  initiated  and  modified  by  impulses  coming  from  the  central 
nervous  system  by  way  of  the  extrinsic  nerves  of  the  organ.  It  is 
known,  e.g.,  that  the  gravid  uterus  can  be  excited  to  contraction  by 
the  stimulation  of  various  sensory  nerves.  Powerful  mental  impres- 
sions, such  as  fright,  may  bring  on  premature  labour.  Converselv, 
sudden  cessation  of  labour  pains  during  parturition  is  not  uncom- 
monly observed  to  be  produced  by  emotional  disturbances — for 
instance,  the  entrance  of  a  stranger  into  the  room.  Yet  the  con- 
tractions of  the  uterus  are  not  essentially  dependent  upon  extrinsic 
impulses.  For  not  only  do  rhythmical  contractions  occur,  but  the 
whole  process  of  parturition  has  been  seen  to  take  place  in  a  uterus 
whose  nerves  have  all  been  cut.  Even  the  excised  uterus  may  be 
kept  alive  for  as  long  as  forty-eight  hours,  and  may  go  on  executing 


1020  A   MANUA1    OF  PHYSIOLOGY 

periodical  contractions  when  its  bloodvessels  are  perfused  with  such 
an  artificial  fluid  ;ls  Locke's  solution,  or,  indeed,  when  it  is  simply 

immersed  in  the  oxygenated  solution  (Kurdinowski)  (Practical 
Exercises,  p.  1 025). 

It  is  a  question  of  great  interest  how  the  uterine-  contractions  are 
started  so  abruptly  at  full  term  after  so  long  a  period  of  quiescence. 
It  can  hardly  be  that  the  increasing  mechanical  distension  of  the 
uterus,  tolerated  for  so  many  months,  should  suddenly,  in  an  hour, 
become  intolerable.  For  if  the  foetus  dies  before  full  term  it  is 
expelled  without  reference  to  the  bulk  which  the  uterus  has  reached. 
It  is  more  likely  that  some  chemical  change  associated  with  the 
completion  of  intra-uterine  development,  a  change  which  leads, 
perhaps,  to  the  production  of  some  specific  substance  in  the  placenta 
or  the  foetus,  is  the  determining  event.  The  placenta  is  a  structure 
whose  function  is  strictly  limited  to  the  term  of  intra-uterine  develop- 
ment. The  foetus  is  to  live  on,  and  so  is  the  mother.  May  it  11  "1 
be  that  the  placenta  or  essential  elements  in  it  are  timed  to  die,  or 
to  begin  to  die,  at  full  term,  and  that  in  their  death  or  degeneration 
the  substance  or  substances  are  produced  which  start,  and  later 
sustain,  the  uterine  contractions  ?  And  may  not  the  contractions  of 
tlie  uterus,  by  exciting  its  afferent  nerves,  or  through  the  pressure 
of  the  foetus  the  afferent  nerves  of  the  vagina,  in  turn  evoke  the 
associated  reflex  contractions  of  the  abdominal  walls  ?  These  are  ques- 
tions which  have  been  asked,  but  not  as  yet  satisfactorily  answered. 

At  birth,  great  changes  take  place  in  the  foetal  circulation,  and 
these  are  intimately  connected  with  the  commencement  of  the 
respiratory  activity  of  the  lungs.  The  causes  of  the  first  respiration 
are  :  (1)  The  increasing  venosity  of  the  blood  circulating  in  the  bulb, 
which  stimulates  the  respiratory  centre  when  the  umbilical  cord  has 
been  cut  or  tied  and  the  placental  circulation  thus  interfered  with  ; 
(2)  the  stimulation  of  the  skin  by  the  air,  which,  as  we  have  seen, 
acts  reflexly  upon  the  respiratory  centre.  That  both  of  these  factors 
may  be  involved  is  shown  by  the  fact  that  cither  compression  of  the 
umbilical  cord  alone,  or  exposure  of  the  foetus  by  opening  the  uterus 
of  an  animal  without  interference  with  the  circulation,  has  been 
observed  to  be  followed  by  attempts  at  breathing.  Once  distended, 
the  lungs  never  again  completely  collapse — not  even  after  death, 
nor  when  the  chest  is  opened.  The  aspiration  caused  by  the  eleva- 
tion of  the  chest-walls  in  inspiration  (for  the  respiration  of  the  new- 
born child  is  mainly  costal)  sucks  blood  into  the  thorax,  and  expands 
the  vessels  of  the  lungs  for  its  reception  ;  and  in  the  measure  in  which 
the  blood  passing  through  the  pulmonary  trunk  finds  an  easy  way 
through  the  lungs,  the  quantity  which  takes  the  route  of  the  ductus 
arteriosus  diminishes.  The  pulmonary  veins,  and  consequently  the 
left  auricle,  are  better  filled  ;  and  the  increasing  pressure  on  this 
side  of  the  septum  tends  to  oppose  the  passage  of  the  blood  through 
the  foramen  ovale,  to  approximate  its  valve,  and  to  close  its  orifice. 

By  the  second  or  third  day  the  ductus  arteriosus  has  usually 
become  obliterated.  The  umbilical  arteries  and  veins  and  the  ductus 
venosus  become  impervious  soon  after  the  interruption  of  the 
placental  circulation.  The  vein  and  venous  duct  remain  in  the 
adult  as  the  round  ligament  of  the  liver,  the  arteries  as  the  lateral 
ligaments  of  the  bladder. 

Although  from  birth  onwards  the  young  mammal  obtains  its 
oxygen  and  gets  rid  of  its  carbon  dioxide  through  its  own  pulmonary 
surface  instead  of  through  the  placenta,  it  still  lives,  as  regards  its 


REPRODUCTION, 


food  proper,  on  the  tissues  oi  the  mother,  and  thai  in  as  literal  .1 
snis, ■  ,,s  when  it  'lu'u  its  supplies  directly  from  the  maternal  blood. 

Milk.  The  milk  secreted  during  the  firsl  few  days  of  each  lacta- 
tion, the  colostrum,  as  it  is  called,  indeed  may  represent  in  part  the 
fragments  oi  cells  lining  the  alveoli  of  the  mammary  glands,  which 
have  undergone  .1  tatty  <  hange  and  been  bodily  bmken  down.  The 
colostrun  re  leucocytes  filled  with  fat  globules  taken  up 

from  the  contents  oi  the  alveoli.  The  chief  chemical  difference 
between  colostrum  and  ordinary  milk  is  the  greater  richness  of  the 
formei  in  protein.  It  has  been  supposed  that  it  is  of  special  impor- 
tance tor  the  nutrition  of  the  suckling,  perhaps  in  virtue  oi  the 
enzymes  contained  in  it.  and  it  is  said  thai  young  animals  bear 
,11 1  iii,  1.1I  feeding  much  better  it  they  have  been  allowed  to  suckle  the 
in, Mini  foi  the  colostrum,  [n  addition  to  the  fat,  which  when  milk  is 
allowed  to  stand  rises  to  the  top  as  cream,  milk  contains  a  consider- 
able quant  ity  of  cascinogen,  tow  hose  coagulation,  under  the  influence 
oi  the  lactic  acid  produced  from  the  lactose,  or  milk-sugar,  by  certain 
bacteria,  spontaneous  curdling  is  due.  Another  protein,  lact-albumin 
1 1  lalhlnirtoni.  a  large  amount  of  water,  and  some  inorganic  salts,  are 
the  most  important  of  its  remaining  constituents.  The  molecular 
concentration  (p.  398)  of  milk,  as  measured  by  its  freezing-point,  is 
almost  exactly  the  same  as  that  of  blood-scrum.  Its  electrical 
conductivity  varies  extremely,  since  it  depends  on  the  quantity  of 
fai  present,  the  fat  globules,  like  the  blood-corpuscles,  being  practi- 
cally non-conductors. 

The  inorganic  composition  of  milk  is  particularly  interesting  when 
compared  with  that  of  the  blood  on  the  one  hand  and  that  of  the 
suckling  on  the  other.  Thus,  100  grammes  of  ash  from  each  source 
gave  the  following  values  for  the  rabbit  (Abderhalden)  : 


Rabbi's  (14  Days 

Rabbit's  Milk. 

Rabbit  s  Blood. 

Rabbits  Blood- 

old). 
IO'84 

serurn. 
3-19 

KaO 

IOT>6 

23  75 

Na.,0 

5  -96 

7  "92 

3I-38 

54-72 

CaO 

3S-02 

35-65 

o-8i 

1-42 

MgO 

2"I9 

2*20 

0*64 

0-56 

Fe,0:)       . . 

0-23 

0-08 

6-93 

000 

p,o5       .  . 

41 '94 

39-86 

1 1  -i  1 

2-98 

CI    .. 

4-94 

5  "42 

32-66 

47-83 

The  richness  of  the  milk  (and  of  the  suckling)  in  calcium,  phos- 
phorus, and  magnesium,  as  compared  with  the  serum,  is  to  be 
especially  remarked.  This  is,  of  course,  essential  for  the  develop- 
ment of  the  bones.  Whereas  sodium  predominates  greatly  over 
potassium  in  the  serum,  the  opposite  is  the  case  in  the  milk  (and  the 
suckling) .  This  is  connected  with  the  development  of  the  tissue  cells, 
which  are  richer  in  potassium  than  in  sodium.  The  high  chlorine 
content  of  the  serum  is  in  sharp  contrast  with  the  relative  poverty  of 
the  milk  in  that  element,  which  preponderates  in  the  tissue  liquids 
and  is  relatively  scanty  in  the  cells. 

In  addition  to  substances  susceptible  of  chemical  analysis,  milk 
contains  enzymes  like  those  present  in  blood-serum,  including 
oxydases  and  various  hydrolytic  ferments  (proteolytic,  diastatic, 
and  perhaps  lipolytic).     It  is  now  universally  acknowledged  that 


W22  A  MANUAL  OF  PHYSIOLOGY 

mother's  milk  is  incomparably  superior  for  the  feeding  oi  1 1 1  -  -  mtant 
to  any  artificial  substitute,  and  one  factor  m  this  superiority  may 
be  the  present  e  ol  ferments  specifically  adapted  for  the  dig  sstion  oi 
the  human  suckling.  More  important  is  the  practical  sterility  of 
the  human  milk  and  the  necessarily  finer  adaptation  "I  Its  quanti- 
tative and  qualitative  composition,  particularly  the  closer  relation- 
ship of  its  proteins  with  those  of  the  child.  In  addition,  there  is 
some  evidence  thai  the  maternal  milk  contains  immune  bodies  (anti- 
bodies) which  may  increase  the  resistance  of  the  suckling  to  infections. 

However  this  may  be,  there  is  no  question  that  much  of  the  high 
infant  mortality  associated  with  the  industrial  conditions  of  our 
great  cities  could  be  prevented  if  breast-feeding  were  carried  out  by 
every  mother  physically  capable  of  it. 

As  to  the  in  inner  in  which  milk  is  sscretsd,  there  is  no  doubt 
that  its  chief  constituents  are  formed  in  the  gland-cells.  Caseinogen 
and  lactose  do  not  exist  in  the  blood  or  lymph.  The  former  is 
probably   produced   by  an  alteration   in   one  or  other  of  the  scrum 

J)rotcins.  the  latter  by  a  change  in  the  dextrose  of  the  blood.  The 
at  of  the  milk  may  come  partly  from  the  fat  of  the  blood,  but  it 
may  also  be  formed  in  the  gland-cells  from  proteins  and  carbo- 
hydrates. The  precise  manner  in  which  the  fat  globules  are  extruded 
from  the  cells  into  the  lumen  of  the  alveoli  is  not  clear,  but  there  is 
no  good  ground  for  believing  that  the  cells  or  their  free  ends  break 
up  bodily  in  the  |"  '  »cess. 

Little  is  known  as  to  the  influence  of  the  nervous  system  on  the 
secretion  of  milk,  and  no  definite  secretory  fibres  have  as  yet  been 
clearly  demonstrated,  although  the  fact  that  marked  changes  may 
be  produced  in  the  milk  of  nursing  women  as  the  result  of  emotional 
disturbances  indicates  that  such  nerves  do  exist. 

Pregnancy  is  accompanied  with  vascular  dilatation  and  hyper- 
trophy of  the  mammary  glands,  but  the  mechanism  by  which  these 
changes  are  produced  is  unknown.  It  is  probable  that  they  depend 
upon  some  internal  secretion  of  the  ovary  or  some  other  of  the 
organs  of  reproduction.  Pregnane}'  is  not  an  absolutely  indispens- 
able condition,  and  therefore  it  would  seem  that  the  exciting 
substance,  if  any  specific  substance  exists,  is  not  a  product  of  the 
foetus  or  of  the  placenta,  Precisely  similar  phenomena  are  occasion- 
ally seen  in  animals  which  have  not  been  impregnated  ami  even  in 
men.  Humboldt  relates  the  case  of  an  Indian  father,  who  so  well 
understood  the  responsibilities  of  paternity,  and  was  so  capable 
of  fulfilling  them,  that  he  suckled  his  child  for  five  months  on  the 
death  of  the  mother.  Virgin  bitches  arc  frequently  known  to 
produce  milk,  occasionally  even  in  quantity  sufficient  to  rear  pups, 
the  flow  occurring  about  the  time  when  they  would  have  whelped 
had  they  conceived  during  the  previous  oestrus  (period  of  heat  . 
Bitches  which  after  copulation  have  'missed'  having  pups  have 
been  known  to  pr<  duce  so  much  milk,  beginning  at  the  time  they 
were  due  to  whelp,  that  they  were  able  to  rear  litters  of  puppies 
belonging  to  other  bitches.  Mules,  which  are  themselves  sterile, 
may  have  enough  milk  to  suckle  a  foal.  The  nipples  of  certain 
monkeys  becomv  swollen  and  congested  at  each  menstruation 
(Heape),  and  in  women  som?  development  of  the  mammary  glands 
is  often  associated  with  the  menstrual  period.  The  stimulus  to  the 
development  of  the  gland  in  these  cases  appears  to  be  some  change 
correlated  with  oestrus,  and  cannot  be  a  change  correlated  with 
pregnane}-. 


REPRODUCTION 


1023 


Transplantation  of  Tissues.  Besides  the  growth  and  regi  m  ration 
<»t  tissues  or  organs,  the  simple  displacement  of  them  from  their 
norma]  situ.u ion  and  their  implantation  in  a  new  environment  have 
been  studied.  Normally,  .1  migration  <>i  tissue  elements  is  only 
witnessed  in  the  adull  in  the  case  <>i  cells  moving  with  the  circulating 
liquids,  or  endowed  with  the  power  of  amoeboid  movement.  Under 
pathological  con. lit  ions  fragments  of  tissue,  such  as  tumour  cells, 
may  be  can  ied  by  the  blood  or  lymph  to  distant  parts,  and,  settling 
there,  may  undergo  development  (forming  metastases).  En  the 
embryo  the  slo\*  migration  of  tissue  elements  is  a  process  which 
is  responsible  for  some  of  the  anatomical  peculiarities  of  the  adult. 
The  migration  oi  the  ovum  from  the  ovary  is  the  starting-point  of 
the  process  of  reproduction.  The  artificial  displacement  of  tissues 
within  tli«    body  oi  one  and  the  same  animal  (auto-  or  homo-trans- 


Fig.    446. — Method   of  Transplantation   (of   both    Kidneys)   in   Mass. 
(After  Guthrie.) 

Segments  of  die  inferior  vena  cava  and  abdominal  aorta  are  removed  with  the 
kidneys  and  renal  vessels,  and  interposed  in  the  course  of  the  vena  cava  and  aorta 
of  another  animal,  according  to  the  method  of  Carrel  and  Guthrie. 


plantation,  or  graft),  or  from  one  animal  to  another  of  the  same 
species  (iso-transplantation,  or  graft)  has  been  successfully  accom- 
plished in  many  cases.  But  heterotransplantation,  or  grafting 
between  animals  of  different  species,  is  in  general  not  permanently 
successful,  the  graft  undergoing  cytolysis  (p.  29)  in  the  alien  en- 
vironment. 

Transplantation,  or  engrafting,  may  be  done  either  with  or  without 
anastomosis  of  bloodvessels.  In  the  second  method  a  portion  of 
tissue,  usually  small,  or  a  small  organ,  is  simply  inserted  in  its  new 
situation  without  provision  tor  the  immediate  establishment  of  a 
circulation  in  it.  Strips  of  cuticle  may  easily  be  grafted  in  this  way 
to  restore  deficiencies  in  the  skin  after  burns  or  extensive  opera- 
tions. The  ovary  can  also  be  grafted  by  simple  implantation  with 
success.     Guthrie  has  thus  shown  that  hens  whose  ovaries  have  been 


1024 


A    1/  I  xr  li.  OF  PHYSIOLOGY 


interchanged   are  capable   <>i    Laying   c^ks-     When    the   lien-,   were 

impregnated  and  tin-  eggs  hat<  tied  out  the  colour  characters  of  the 
resulting  offspring  seemed  to  have  been  influenced,  not  only  by  the 
hen  to  which  the  ovary  originally  belonged,  but  also  by  the  hen  to 
which  it  had  been  transferred.  Grafts  of  the  thyroid  and  para- 
thyroid have  also  been  shown  to  '  take.' 

In  transplantation  with  anastomosis  of  bloodvessels  the  main 
vessels  of  the  engraft ed  organ  are  sutured  to  suitable  arteries  and 
veins  in  the  '  host,'  so  that  the  circulation  is  at  once  effective.  Con- 
sequently there  is  practically  no  limit  to  the  size  of  the  grafts.  The 
kidney,  spleen,  and  even  a  limb,  have  been  successfully  transplanted 
in  this  way  from  one  clog  to  another.  Segments  of  arteries  preserved 
in  cold  storage  for  a  few  days  or  even  weeks,  and  even  portions  of 
arteries  fixed  by  formaldehyde,  have  been  transplanted  so  as  to  take 
the  place  of  segments  removed  from  arteries  of  living  animals,  and 
have  continued  to  function  perfectly  for  long  periods.  Portions  of 
veins  have  also  been  used  to  fill  up  gaps  in  arteries.  Even  hetero- 
plastic vascular  grafts  have  been  found  to  succeed,  portions  of  dog's 


Fig.   447. — Suturing  Bloodvessels.     Preliminary  Fixation  of  Ends  of 
Divided  Vessels  (After  Guthrie). 

Three  fixing  ligatures  are  placed  at  equidistant  points  on  the  circumference  of 
the  cut  ends,  each  ligature  being  passed  through  corresponding  points  of  the  two 
vessels.  The  ends  of  the  vessels  are  approximated  by  drawing  on  the  ligatures, 
which  are  then  tied,  and  the  margins  of  the  vessels  sewed  together  by  continuous 
stitches  in  the  intervals  between  the  fixing  ligatures,  as  in  Fig.  449.  (Carrel's 
method.) 

arteries,  e.g.,  grafted  into  a  cat,  and  portions  of  rabbit's,  cat's,  or 
human  arteries  grafted  into  a  dog.  Doubtless  the  favourable  result 
is  largely  due  to  the  fact  that  the  function  of  the  large  arteries  is 
mainly  a  passive,  mechanical  one,  which  can  be  discharged  even  by 
a  dead  tube  of  the  requisite  strength,  and  with  the  smooth  interior 
presented  by  a  dead  endothelial  lining  (Carrel.  Guthrie). 

Parabiosis. — Not  only  may  an  organ  or  a  portion  of  tissue  from 
one  individual  be  engrafted  on  another,  but  two  individuals  may  be 
so  united  that  a  greater  or  smaller  degree  of  physiological  intimacy 
is  produced  between  them.  Occasionally,  as  in  the  famous  Siamese 
twins,  an  anomaly  of  development  results  in  such  close  anatomical 
union  of  the  circulatory  and  other  systems  that  in  certain  respects 
the  two  individuals  constitute  almost  a  single  organism,  and  cannot 
be  separated  by  surgical  interference.  A  less  intimate  union  can 
be  established  experimentally  by  opening  the  peritoneal  cavities 
of  the  two  animals,  and  suturing  the  skin  and  connective  tissue 
together  so  as  to  permit  of  permanent  communication.     Pairs  of 


/,7  PR0DUC7  TON 


[025 


animals  living  in  this  condition  (so-called  parabiosis)  have  boon 
utilized  for  the  study  ol  certain  questions  in  immunity.  White  rats 
have  been  kepi  alive  in  parabiosis  for  as  long  as  thirty-four  days  in 
order  to  tesl  the  question  whether  destructive  antibodies  for  cancer 
■  uc  present  in  the  circulation  (Rous),  since  it  has  been  shown  that 
circulating  antibodies  easily  pass  from  one  to  the  other  of  such  a 


Fig.  448.  -Suti  ring  Bloodvessels.     Method  of  Approximating  Edges  and 
11  iiin'g  i\-  Continuous  Suture  (after  Guthrie). 

The  needles  arc  very  fine  cambric  sewing-needles,  and  the  threads  single  strands 
ol  Chinese  twist  silk  <>r  human  hair.  Needles  and  threads  are  sterilized  in 
paraffin-oil.     (Method  of  Carrel  and  Guthrie.) 

pair  of  animals  (Ehrlich).  One  of  each  pair  of  rats  had  a  growing 
tumour  produced  by  transplantation,  while  the  other  had  been 
proved  resistant  to  the  same  type  of  tumour.  No  evidence  of  the 
passage  of  an  antibody  was  found  in  this  case. 


PRACTICAL  EXERCISE. 

Contractions  of  Isolated  Uterine  Rings. — Kill  a  female  adult 
rabbit  bv  striking  it  at  the  back  of  the  neck.  A  rabbit  which  is 
not  pregnant,  or  only  at  the  beginning  of  pregnancy,  should  be 
selected.  Open  the  abdomen,  and  carefully  remove  the  uterus. 
While  separating  the  organ  from  the  broad  ligament  and  vagina, 
support  the  horns  of  the  uterus  on  soft  threads.  Ligature  the 
vagina  before  cutting  through  it,  and  cut  below  the  ligature,  which 
can  then  be  used  to  manipulate  the  uterus.  Do  not  pinch  the  uterus 
with  forceps,  and  handle  it  as  little  as  possible.  At  once  place  it  in 
Ringer's  solution  (p.  186),  kept  at  body  temperature  (380  C.)  in  a  small 
beaker  immersed  in  a  water-bath.  Cut  a  ring  of  tissue  about 
i£  centimetres  in  width  from  one  of  the  horns.  Tie  a  loop  with  a 
fine  silk  thread  at  each  end  of  a  diameter  of  the  ring,  pinching  up  a 
little  of  the  external  coat  to  do  so  with  fine  forceps.  Make  the 
arrangements  necessary  for  recording  contractions  of  the  ring  while  it 
is  immersed  in  a  very  small  beaker  or  a  glass  cylinder  in  the  bath,  as 
in  Experiment  12,  p.  185,  but  do  not  divide  the  ring.  A  narrow- 
glass  tube  connected  by  a  rubber  tube  with  a  cylinder  of  oxygen 
must  be  arranged  to  dip  down  to  near  the  bottom  of  the  beaker. 
The  valve  of  the  cylinder  is  turned  cautiously,  s  >  as  to  permit  oxygen 
t<>  bubble  slowly  through  the  solution.  After  a  longer  or  shorter 
interval   spontaneous   rhythmical  contractions   of  the   uterus   ring 

65 


102  i 


I   M  l.xr.ii    OF  PHYSIOLOGY 


commence.  As  soon  as  they  are  well  established,  and  while  the 
contractions  are  being  recorded  on  a  very  slow  drum,  adrenalin 
solution  should  be  run  into  the  beaker  from  a  graduated  capillary 
pipette  in  such  amount  as  will  make  the  concentration  of  it  in  the 
beaker  i  :  1,000,000.  Run  the  adrenalin  solution  in  at  a  point  as 
far  as  possible  from  the  uterus  ring,  so  that  it  does  not  reach  it  till 
mixture  has  occurred.  Mix  carefully  with  a  thin  glass  rod  without 
disturbing  the  preparation.  Note  whether  the  tone  of  the  ring 
(as  shown  by  its  permanent  shortening)  or  the  rate  and  strength  of 
the  contractions  are  increased.     If  not,  remove  the  solution  from 


Fig.  449. — Contractions  of  Rabbit's  Uterus  Ring. 

1,  Spontaneous  contractions  in  Ringer's  solution  ;  2,  contractions  in  human 
serum  from  a  case  of  persistent  high  arterial  pressure  ;  3,  contractions  in  the 
same  serum  diluted  with  its  own  volume  of  Ringer's  solution  ;  4,  contractions  in 
Ringer's  solution  after  washing  away  the  serum.  Tracings  1  to  4  were  obtained 
from  the  same  ring  ;  5,  increase  of  tone  produced  in  another  ring  by  the  addition 
of  a  little  adrenalin  solution  to  the  Ringer's  solution,  in  which  the  ring  had  bet  a 
executing  spontaneous  contractions.  These  ceased  for  a  time  after  addition  of  the 
adrenalin,  but  later  rcenmmeiu  ed. 

the  beaker  with  a  pipette  or  siphon,  replace  it  by  fresh  warm 
Ringer's  solution,  and  start  the  oxygen  current  again.  While  a 
tracing  is  being  taken  repeat  the  observation,  adding  a  larger  pro- 
portion of  adrenalin.  Determine  in  what  concentration  a  distinct 
effect  is  produced.  This  is  the  basis  of  a  method  said  to  be  capable 
of  detecting  such  minute  quantities  of  adrenalin  as  can  be  suppose.  I 
to  be  present  in  blood-serum  (Fracnkcl).  A  sufficient  number  of 
uterus  rings  can  be  obtained  from  one  animal  for  a  considerable 
number  of  experiments. 


AI'l'IiNDIX 


COMPARISON  OF  METRICAL  WITH  ENGLISH  MEASURES 


Measures  of  Length. 

i  millimetre  =003937  inch. 

1  centimetre  =039371 

1  decimetre    =3'937o8  inches. 

1  metre  =  39'37°79 

1   inch  =  ~5'3995  millimetres. 

Measures  of  Weight. 

1  gramme  =15-432349  grains. 

1  kilogramme    =2-2046213  pounds. 

1  ounce  =28-3495  grammes. 

1  pound  =453-5926 

Measures  of  Volume. 

1   cubic  centimetre  =  0061027  cubic  inch. 

1   litre  (1,000  cubic  centimetres)  =61-027052  cubic  inches. 

=  1-760773   English  or   211 
American  pints. 

=0-22009668  gallon. 

1  cubic  inch  =16-3861759  cubic  centimetres. 

1  cubic  foot  =28-3153119  cubic  decimetres  (or  litres). 

1  pint  =0-567932  litre. 

1  gallon  =4-5434579  litres. 

Measures  of  Work. 

1   kilogrammetre  =about  7-24  foot-pounds. 

1  foot-pound  =0-1381  kilogrammetre. 

1   (kilo)calorie  of  heat  =425-5  kilogrammetres  of  work. 

Temperature  Scales. — To  convert  degrees  Fahrenheit  into  degrees 
Centigrade,  subtract  32,  and  multiply  the  remainder  by  j>.  To 
convert  degrees  C.  into  degrees  F.,  multiply  by  |,  and  add  32  to  the 
result. 

1027  65 — 2 


INDEX 


References  to  the  Practical  Exercises  are  in  black  figures. 


\  bdominai  breathing,  214 
muscles  in  expiration)  - 1  ; 

Abducens  or  sixth  nerve,  822 
inhibition  by,  8  j8 

Aberration,  chromatic,  913,  992 
spherical,  912,  991 

Absinthe  convulsions,  857 

Absorption,  .198 

from  the  peritoneal  cavity,  406 
from  the  stomach,  391,  403,  433 
in  different  animals,  402 
intra-  and  inter-epithelial,  417 
of    bile-constituents    in    jaundice. 

355 

of  cane-sugar,  405,  416,  433 

of  carbo-hydrates,  416 

of  fat.  412.  432,  433 

of  light,  897 

of  proteins,  418 

of  the  food,  401 

physical  introduction  to,  398 
theories  of,  404-406 

of  water  and  salts,  395,  417 

parenteral,  418 
Acapnia  and  blood-pressure,  168 

and  mountain  sickness,  275 

and  shock,  175 
Acceleration  of  heart  by  sipping  water, 

155.  195 
Accelerator  nerves  of  heart,  143,  147, 

184 
Accessory  auditory  nucleus,  824 

vagus  nucleus,  825 
Accommodation,  905,  987,  988 

mechanism  of,  907 

pupil  in,  909 
AC.  E.  mixture,  55,  471 
Acerebral  tonus,  836,  847 
Aceto-acetic  acid  in  diabetes,  520 
Acetone  in  diabetes,  520,  492 
Acid  albumin,  2,  9,  325,  426 
Acidity  of  gastric  juice,  323,  390,  391 
Acidosis,  521 
Acrolein,  12 
Acromegaly  and  pituitary,  568 


Action   currents,  718,    719.   720,   726, 

739 

diphasic,  720 

double  conduction  of,  688 

electromotive  force  of,  722 

in  polarized  nerves,  727 

monophasic,  722 

of  eye,  735 

of  glands,  734 

of  heart,  78,  720,  73°,  733-  74° 

of  human  muscles,  662,  724 

of  phrenic  nerves,  724 

of  spinal  cord,  688,  733,  746,  793 

of  vagus,  225 

of  veratrinized  muscles,  726 

reflex,  809 

theories  of,  725 

velocity  of  propagation  of  varia- 
tion, 723 
Adaptation  of  digestive  juices  to  food, 
340,  369.  376,  381.  387 

of  retina,  935,  946 
Adenase,  507 
Adenin,  441,  507 
Adequate  stimuli,  798,  870,  891 
Adipocere,  527 
Adrenal  glands.     See  Suprarenal  cap  • 

sules 
Adrenalin,  157,  201,  564 

action  of,  on  heart,  156,  564 
on  pupil,  911,  912 
on  uterus,  563,  1025 
on  vasomotors,  157,  163,  201, 
563 

artificial,  565 

glycosuria,  522,  566 
Aerotonometer,  256 
.Esthesiometer  compasses,  1000 

hair,  970,  999 
Afferent  impulses,  decussation  of,  792 

paths  of,  779,  791,  794 
After-images,  943.  997 
Agglutination,  29,  63 
Agglutininogens,  30 
Agraphia,  862 


1029 


1030 


INDEX 


Alaniii,  2. 

f( >nn.it: i  dexti    •'  from,  514 

Albinos.  intra>  as<  ulai  1  I  it  ting  in 
Albumins,  -\  8 

heat-coagulation  of,  8 

in  urine,  1 1  1,  1  1 1 .  i'">,  462,  486 
488 
Albuminates  or  derived  albumins,  9 
Albuminoids,  2, 

All  mini 1-  glands,  $19 

Albumoses,  .? 

.n  tion  of,  "ii  blood-pressure,  157, 
201 
■  hi  coagulatii  in,  35,  p>.  55 

in  peptic  digestion,  325 

tests  for,  10.  426 

in  urine,  486 

Alcohol,     .u  tion     of,    <>n    respiratory 
centre,  1 75.  236 
on  gastric  sei  retion,  vSN 
in  diet,  551 
poisoning,  blood-pressure  curve  in, 

175 
prei  ipitation  of  proteins  l>v.  8 
Alcohols,      relation      of,      to      carbo- 
hydrates, 3 
Aldehydasi 

Aldehyde  groups  in  Living  protein,  499 
Aldehydes,     relation     of,     to     carbo- 
hydrates, 3 
Alexins,  53 
Algometer,  979 

Alimentary  canal,  anatomy  of,  2^7 
length  of,  297 

time  of  passage  through,    ;  1  1 
glycosuria,  510,  610 
Alkali-albumin,  9,  333,  429 
Alkalinity  of  blood,  etc.,  titratable,  24 
Alkaptonuria,  1  1  1 
Allantois,  formation  of,  ion 
'  All  <>r  nothing  '  law.  141 
Alloxuric  bodies.  1  1 1 .  507 
Amblyopia  after  o<  1  ipital  lesion,  \vi 
Amboceptors,  27.  63 

Amide-nitrogen  in  proteolysis,  332 
Amino-, net  ic  ai  id.  2 
Amino-acids,  t,  325,   1 

absorption  of.  420 

conversion  of,  into  glycogen  and 

dextrose,  514 

formation  oi  urea  from,  501,  50 ;, 
505, 

in  liver  diseases,  so  ■; 

in  phosphorus -poisoning,  526 

in  urine,  441.  450 

reaction  for.  450 
Amino-A  alerianic  acid. 
Ammonia,   action   of,   on    muscle  and 
nerve,  6  j  , 

impermeability  of  lungs  (or.  2\2 

in  proteolysis,  332 


Ammonia  in  urine,  t  \o 

after  Kck's  fistula,  502 
n  Ilex  inhibition  of  heart   by,   154, 
195 

Ammonium   salts,   formation   of   urea 
from,  501,  504,  505 
sulphate,  precipitation  of  proteins 

by,  8,  1-1. 

Amnion,  ion 

Amniotic  fluid,  ion,  1012,  1017 

Aniob.i,  (>,  1  j,    55<j,  627 

Amoeboid  movement,  17,  18,  53,  627 
\nipi  1  e,  616 
Amylase,  321 

Amy]  nitrite,  action  on  pulse,  97,  192 
formation   of   methaemoglobin 
by,  46 
Amylolytic  stage  of  gastric  digestion. 

322,  390,  403 
Amylopsin,  331.  333.  429 

influence  of  bile  on,  340 
Anabolic  changes  in  living  matter,  6 
Anacrotic  pulse.  97 
Anaesthesia  by  A.C.E.  mixture,  55 
by  chloral,  204 
by  chloroform  (Grehant's  method), 

186 
by  morphia,  55,  186 
\i\  pressure  > m  brain.  .N7.s, 
Anelectrotonus,  683,  742 
Angular  gyrus  and  vision,  859 
Animal  heat,  572 
Ani  ins,  401 
Ankle-clonus,  811,  813 
Annulus  of  Vieussens,   143.   147.    102. 

it,.  190 
Anode.  401,  615 
Anterior  c  iiuinissiire.  817 
horn,  cells  of,  748,  762 
connections  of,  775 
roots,  775 
Antero -lateral    ascending    tract,    764, 
772.  781 
11  innections  of,  77.5 
descending  tract,  765,  776 

connections  of,  776 
ground  bundle.  765 

Anti-bodies,  30,  .}  I  >s 

'Antidromic  '  nerve-impulses,  105,  688. 

701 
Antiferments,  31s.  361 
Ant igens,  30 
Antikinase,  36,  39,  361 
Antilytic  secretion,  369 

\ nt mi. m \  and  protein  metabolism,  526 

tatiperistalsis,   108,  194 
Ant  ip\  retics,  597 
Antiseptii  s  t>  u  operations,  202 
Antithrombin,  35  .  16,  p..  41 
Antitrypsin,  31  8,   |6i 
Ant  ruin  pyli  >ri.   io.i,  305 


TNDl  X 


10  :  i 


\"i  i  f(  ompressi t.  188 

Aortic  insufficiency,  effect  of,  on  pulse, 

uot(  b,  89,  96 

stenosis,  effecl  of,  on  pulse,  98 

vah  es,  79,  89,  tgj 

.uul  dicrotic  wax  e,  96 
Apex-beat,  82,  191.  193 
Ap  sx  preparation  ol  heart,  [31,  178 
Aphasia,  motor,  862 

sensory,  s"  1 

temporary .  86  1 

\\  ernicke's,  86 1 
Aph  -iiii.i.  86  1 
A I'n  ea,  231,  -'  j8,  288 

vagi,  2  J2 

1  era,  232 
ideine,  action  of,  on  vaso-motors, 

157 
Apomorphine  as  emetic,  313,  427.  432 
Aqueduct  ol  Sj  Ivius,  819 
Aqueous  humour,  901 
Arachnoid,  758 

Arachnolysin,    action    of,    on    erythro- 
cytes, 27 
Annate  fibres,  internal,  772 
Arginase,  503 
Arginin,  331,  312.  503 
Argyll- Robertson  pupil,  910 
Arhythmia,  respirator}',  270 
Aromatic  sulphates  in  urine.  445.  479 
Arsenic  and  protein  metabolism,  526 
Arteries,  structure  of,  74 

to  insert  cannula  into,  55 

tone  of,  169,  813 
Arterioles,  resistance  in,  no,  119 
Arteriosclerosis,  velocitv  of  pulse  in,  99 
Articulation,  positions  of,  283 
Artificial  respiration,  187,  214 

with  oxygen,  189 
Ascending  degeneration,  7113 
Aspartic  acid,  332 

formation  of  dextrose  from,  414 
Asphyxia.  231,  269,  274 

condition  of  haemoglobin  in,  44 

effect  of,  on  circulation,  171,   172, 
189,  198 

glycosuria  caused  by,  518 

in  the  foetus,  1019 
Association  fibres,  761,  7S3,  785 

centres,  855,  865,  866 
Astatic  system  of  magnets,  619 
Asthma,     spasmodic,     and     bronchial 

muscles,  238 
Astigmatism,  irregular,  914 

regular,  917.  989 
Astrospheres,  1006 
Atelectasis,  222 

Atheroma,  effect  on  prise,  97,  98 
Atrio-ventricular   bundle.     See  Auric- 
ulo-ventricular  bundle 


Atropine,  action  of,  on  heart,  149,  183 
on  digestive  secretions,  587 

on  pupil,  'i  1 1 

on    salivary    secretion, 

i&7.  425 

\i traction  sphere,  5,  1 

in  nerve-cells,  748 
Auditory  centre,  82  |,  860 
nerve,  S2$,  828 

vestibular  branch  of,  82  1 
ossicles,  954,  955»  959 
path,  scheme  of,  823 
Auerbach's  plexus,  298,  307,  308 
Augmentation  of  heart-beat,  143,  145, 
148,  156,  184 
nature  of,  151 
primary,  145 
secondary,  145,  147 
Augmentor     nerves,     effect     of,     on 

quiescent  heart,  152 
Aura,  865 

Auricular  canal,  72,  73 
pressure  curve,  90 
Auric  ulo-ventricular   bundle,    7],    1 3  4— 
137 
pulse  tracings  in  disease  of,  137 
Auric  ulo-ventricular  junction,  stimula- 
tion of,  183 
node,  73 
valves,  80,  190 

moment  of  opening  of,  89 
Auscultation  of  heart-sounds,  191 

of  breath-sounds,  291 
Auto-digestion  of  stomach,  360,  434 
Autogenetic  theory  of  nerve  regenera- 
tion, 697 
Autolysis,  509 
Automatic  actions  of  spinal  cord,  812- 

814 
Autonomic  nervous  system,  790,  883, 

884 
Avalanche  theory,  682 
Axial  strand  fibrils,  696 
Axis-cylinder  or  axon,   677,   748,   749, 
755 
bifurcation  of,  697 
fibrils  in,  748 
Axon-reflexes,  372,  697,  809 

Babinski's  sign,  8n 
Bacteria  in  faeces,  397 

in  intestine,  318,  393,  394,  395 
Bactericidal  action  of  gastric  juice,  32S 

ferments,  510 
Balloon  ascents,  deaths  in,  275 
Banting  cure  for  obesity,  534 
Baryta,   absorption   of  carbon  dioxide 

by,  241 
Basal  ganglia,  777,  828 
Basilar  membrane,  956,  958,  963 
Bat's   wing,  contractile  vessels  of,  73,16 


1032 


INDEX 


Batteries,  182.  6 
Beats,  999 

Beaumont  on  digests  >n, 
Bechterew's  aucleus,  s-;i 
Beckmann's  a]  ;  1  492 

Bellon's  record*  r,  290 
Bell's  experiments  on  □  ■  790 

Benzoic  acid,  441,  508 
Bert  on  double  conduction  in  nerves, 
688 

on  effects  of  oxygen  at  high  | 
sure,  274 
Betz  cells  in  the  cortex,  774-  s5- 
Bichromate  cell,  182 
Bidder's  ganglia,  129 
Bile,  334-341.43° 

absorption  of,  355,  383 

a<  ids,  336,  43" 

formation  of,  355 
Hay's  test  for,  430.  491 

adaptation  of,  to  fund.  386 

as  an  excretion,  396 

i  irculation  of,  383 

i  omposition  of,  335 

curve  oi  se<  r<  tion  of,  383.  385 

digestive  action  of,  3) ' 

freezing-point  of,  358 

gases  of,  260,  337 

in  emulsification  of  fats,  338 

influence  of  nerves  on  secretion  of, 
383 

mucin,  335.  430 

pigments,  335-  355.  431 

relation  of,  to  spleen,  571 

precipitation  of  gastric  digest  by, 

34i 

quantity  of,  338 

rat.-  of  flow  of,  into  gut,  385,  392 

reactions  of,  430 

salts,  action  of,  on  blood,  27.  62 
decomposition  of,  337 

secretory  pressure  of,  386 

spectrum  of,  336 
Biliary  fistula,  339,  383 
Bioplasm.     See  Protoplasm  and  Living 

matter 
Bipolar  ganglion  cells,  747.  753 
Bird's  blood,  coagulation  of,  }4.  39 
Biuret  reaction,  7,  426 
Bladder,  472 
Blastoderm,  1008 
Blind  spot,  931,  992 
Blood,  carbon  dioxide  in,  - 1 

coagulation  of,  30-  3".  54 

composition  of,  41 

conductivity  of,  25,  60 

distribution  of,  4"-  49.  I~- 

flow  through  organs,  173 

freezing-point  of,  26,  358 

influence    of    carbon    dioxide 
on,  255 


Blood,  functions  of,  si 

gases  of,  246 

analysis  of,  251 

distribution  of,  252 
in  embryo,  1013,  10 17 
tension  of,  256 
guaiacum  test  for,  68 
kinetic,    and    potential    energy   of 

(  in  ulating,  in 
hiking  of,  26,  61 
opacity  of,  26,  61 
oxygen  dissociation  curve  of,  255 
pre<  ipitin  test  for,  30 
quantity  of,  47.  4s 

in  lungs,  208 
reaction  of,  23,  54.  255 
regeneration  of,  2  r 
specific  gravity  of,  25,  54 
stains,  examination  of.  71 
sugar  in,  41,  462,  511,  516.  519 
velocity  of,  108-119 
in  arteries,  116 
in  capillaries,  77,  119,  177 
in  veins,  122 

measurement  of,  m-113,  204 
viscosity  of,  22,  464 
volume  of  corpuscles  and  plasma, 

26,59 
why  it  does  not  clot  in  the  vessels, 
40 
Klood-rorpuscles,  coloured,  15 
composition  of.  42 
crenation  of,  16 
destruction  of,  21,  29 
enumeration  of,  18,  58 
formation  of,  in  embryo,  20 
gaseous  metabolism  of,  252 
life-history  of,  19 
osmotic  resistance  of,  64 
potassium  in.  255 
rouleaux  formation  of,  16 
shadows  or  ghosts  of,  61 
size  of,  15 
structure  of,  15 
white,  16 

enumeration  of,  19 
Blood-plates,  18 

in  coagulation,  36 
Blood-pressure  and  acapnia,  168 

curves  with    elastic    manometers, 
J02 
with     mercurial     manometer, 
ioi,  103.  195 

■  tracts  of  bone-marrow 

oil,   570 

of  kidney  on,  570 

1  if  nervous  tissue  on,  569 

of  pituitary  on,  568 

of  suprarenal  on,  201, 563 

of  testicle  on,  557 

ol  thymus  on,  558 


/  \Dt  A 


i<>33 


Blood-pressure,  effe<  1  oi   freezing   the 
d  '>n,  168 

>>t  hamorrhagt ,  1  74.  200 

ol  muscular  exercise  on,  to6, 
198 

Of  peptone  (in.  157.  201 

of  posture  on,  [06,  1 73,  199 
■  ii  transfusion  on,  174,  200 

factors  which  maintain,  107 

tall  dt,  in  sleep,  87b 

hydrostatic      and      li  ydrodvnamir 

factors  in,  173 
in  capillaries,  1 1 8,  120 
in  pulmonary  artery.  108 
in  right  and  left  ventricles,  85,  108, 

127 
mean  arterial,  100-107 
measurement  of.  100,  195 
in  man,  104,  175,  198 
permanent  element  in,  103 
respiratory  variations  in,  104,  265- 

-72 

systolic  and  diastolic,  105,  106, 198 
Blood-pump,  250 

Blood-serum,  freezing-point  of,  357 
Blood-supply,  regulation  of,  172 
Bloodvessels,  anastomosis  of,  1024 

rhythmically  contractile,  73,   160, 

164 
structure  of,  74 
tone  of,  169,  886 
Body,  composition  of,  529 
Bohr,  on  tension  of  blood-gases,  256 
Bone-marrow  and  blood-formation,    o, 
22 
action  of  extracts  of,  570 
Bones,  composition  of,  529 

effect  of  deficiency  of  lime  salts  on, 
542 
of  various  salts  on,  542 
influence  of  pituitary  on,  569 
of  testicles  on,  557 
'  Boot  '  electrodes,  739 
Brain,  ana?mia  of,  876 

chemistry  of,  880,  88 r 
circulation  in,  878 
condition  of,  isolated,  867 

in  sleep,  874 
development  of,  746 
functions  of,  827-878 
heat-production  in,  586 
respiratory  changes  in  volume  of, 

271 
resuscitation  of,  879,  880 
size  of,  at  different  ages,  878 
and  intelligence,  878 
Bread,  chemistry  of,  612 
Break-contraction,  Tigerstedt's  theory 

of,  727 
Breast-feeding,  superiority  of,  1022 
Breath,  holding,  219 


Broca's  area.  855,  86  ;. 
aphasia,  862,  864 

Brominei   reflex   inhibition     by  inhala- 
tion of,  235 

Bronchi,  207 

movements  of,  in  respiration,  216 
nerves  of,  237 

Bronchial  breathing,  216,  291 

Brown-Sequard's  syndrome,  793 

Brunner's  glands,  298,  343,  345,  354 

'  Bully  '  coat,  29 

Bulbus  arteriosus,  72 

'  Bull-dog  '  forceps,  55 

Burdacfvs   column.      See   Postero-me- 
dian  column 

Burdon-Sanderson  on   negative  varia- 
tion, 720-722 

Burns,  superficial,  death  from,  276 

Caffeine,  441,  552 

diuretic  action  of,  470 
Caisson  disease,  274 
Calcium  salts,  action  of,  on  heart  strips, 

185 

in  milk-curdling,  327 
and  bone  formation,  542 
and  glycosuria,  520 
deficiency  of,  542 
in  bone,  529 
relation  of,  to  heart-beat,  139, 

183 

Calorie,  definition  of,  574 
Calorimeter,  air,  576 

respiration,  579,  613 
Atwater's,  575 

water  equivalent  of,  613 
Calorimetry,  573,  613 
Cancer,  autolytic  ferments  in,  510 

gastric  juice  in,  324 
Cane-sugar,  3,  10 

absorption  of,  405,  416,  433 

inversion  of,  10,  315 

by  gastric  juice,  328 
Cannula,  three-way,  196 

to  put  into  artery,  55 
trachea,  186 
vein,  200 

gastric,  427 
Capillaries,  blood-pressure  in,  120 

changes  in  lumen  of,  109,  157 

circulation  in,  109,  in,  177 

pulse  in,  120 

resistance  in,  nr,  119 

structure  of,  74 

total  cross-section  of,  119 

velocity  of  blood  in,  119 
Capillary  electrometer,  621,  622,  739 
records,  720,  721,  730 

tubes,  flow  of  liquid  through,  77 
Carbo-hydrates,  absorption  of,  403,  416 

classification  of,  3 


ro34 


INDEX 


Cai  l"  i-h)  drates,  composition  of,  i .  ; 
constitution  oi 
in  urine.   |  ;  2 
metabolism  of,  51; 
passage  of,  tbrou  fh  pla<  enta,  mi  1 
protein-sparing  a<  tion  of,  5  m 
reactions  of,  10 
s<  heme  for  testing  for,  13 
Carbon  balance,  5  jg 

distribution  of,  in  body,  520 

equilibrium,  539 

dioxide,  actii t.  on  respiratory 

centre,  2  jo 

and  blood-flow  in  heart.  16  j 

estimation  of,  24 1.  251,  293. 

2  94 
formation   of,    From    proteins, 
509 

in  Iuiilis.  240 
in  alveolar  air.  242.  257 
in  blood,  24,  25  1 
hi  foetal  blood,  mi  j 
in  serum,  253,  255 
parti. il   pressure  of,  in  blood, 

257 

in  tissues  and  liquids, 
260 
production     of,    in     different 
animals,  246 
in   muscular   work.    213. 

294 
in     relation     to     body- 
weight,  245 
in  rigor  mortis,  263,  673, 
674 
washing  out  of,  242.  246 
monoxide  ha  moglobin.   15,  66 

method  for  partial  pressure  of 
oxygen,  258 
for  quantity  of  blood.  48 
Cardiac  cycle,  78 

changes  in  endocardiac  pres- 
sure during,  90 
death,  156,  235 

impulse.  82,  191.  193 

nerves,    143,    146,    147,   182.   184. 
187.  190 
ii'  irmal  excitation  of,  152 
sound  (Chauveau  and  Marey's),  87 
sphincter,  302,  $09,  313 
Cardiogram,  8  |,  191 
inversion  of,  B 1 
Cardiograph.  82,  191 

Cardio  -  inhibitory      and      augmentoi 
centres,  15  j 

t •  of,  I  S3.  IS  ( 

Cardio-pneumatic  movements,  1 1  7,  291 

Cardio -vascular  nerves.  1  ^n 
Casein.  327.  503.  535 
Caseinogen.  2.   (27.  spi.6ll 
Castration,  effects  of,  556 


l    .U. liases.    JO| 

in  blood-corpuscles,  68 

l   iii  Users,  315 

Cataract    ami    physical    chemistry    of 

lens,  901 
Catheter,  pulmonary,  z=,t 
1  atheterism,  609 
(  ells,  structure  of,  4 

Cellulose,  digestion  of,    J96 

Central  canal  of  cord,  746,  759 
Central  nervous  system,  development 
of,  746 
electromotive  phenomena  of, 

732,  733 
functions  of,  786 
general  arrangement  of,  7s<) 
histology  of,  747-758 
localization     of     function     in, 

867,  872 
methods  of  study  of.  745 
resuscitation  of,  879,  880 
grey  axis,  759 
Centre  of  gravity  of  body,  839 
Centres  of  cord  and  bulb,  814 

cardio-inhibitory  and   augmentor, 

153.  i54 

heat-,  595,  597 

'  motor,'  of  cortex,  846   858 

musical,  861 

sensory,  of  cortex,  85*   86l 

vaso-motor,  166-169 
Centrifuge,  56 
Centrosome,  5 

in  nerve-cells,  7  \.8 

in  the  ovum,  1004,  1006 
Cerebellar  ataxia,  832,  836 
Cerebellum,   connections   of, 
•s  (2 

with  auditory  nerve 
development  of,  747 

effects  of  renio\   il   , 
functions  of,  830,  835 
inferior     peduncles    of.     760 

779.  832 
inhibition  from.  836 
middle    peduncles    of.    760 

780,  832 
structure  of,  830 

superior    peduncles    of,    760,    772, 

780 
worm  of,  7/1.   772,   77 
836 
Cerebral  ana>mia,  172,  174- 

resuscitation  after.  879,    5 
circulation.  878,  879 
cortex,  and  respiration.  225 

developmental  differentiation 

of.  854,  855 

functions  of.  840 
histological  differentiation  of, 
SS  1-853 


780 


771. 


INDEX 


1035 


*  erebral  <  >  >rt f.x.  inhibition  from,  8  \6 

laj  1  1 

•  motor     ire  is  of,  s  1 1 
sensoi  j  ai  ea    of,  858 
vesi<  les,     1 
(  ei ebi  mis.  cerebrosides,  691 
(  erebi  o-spinal  Quid,  75*.  's,s- 
displacemenl  of,  272 
1  inn.  excision  of,  8  p>.  888 
Cervical    sympathetic,     See    Sympa- 
thetic cervical 
Chalk  stones 

Cheese,  1  hemistry  of,  g  \<<.  611 
Chemiotaxis,  5 1 

in  nen e  regeneration,  695 
Cheyne-Stokes    respiration,    238,    27s. 

288 
Chiasms.,  818 
Child,  food  requirement  of,  549 

gasei  ius  exchange  in,  244 
Chloral,  anaesthesia  by,  174,  199 
Chlorides,  estimation  of,  477 
Chloroform,  absorption  of,  i>v  erythro- 
cytes, ->  55 
action     of,     on     cardio-inhibitory 
•  entre,  235 
on  respirati  >ry  centre.  2.54 
■  m  urine  secretion.  471 
on    vaso-motor    centre.    174, 
199,  234,  235 
anaesthesia,  dangers  of,  234 
taking  action  of,  61 
passage  of,  through  placenta.  1013 
reflex  inhibition  of  heart  by,  154 
Chlorosis,   absorption   of  iron    in,    396, 
418 
blood-count  in,  23,  25 
quantity  of  blood  in,  40 
Cholagogues,  385,  388 
1  h  .lesterin,  4-  42.  47.  335-  337-431 
in  haemolysis,  28 
in  serum,  41 
Cholic  acid,  337 
(holm.  4,  366,  882 
Cholohaematin,  336 
Chorda  tympani,  362,  363,424 

antagonism     of     sympathetic 

with,  365,  368,  425 
hypothetical  fibres  in,  366 
taste  fibres  in.  821,  822 
Chorda1  tendineae.  70 
Chorion,  1012 

Choroidal  epithelium,  900,  934 
and  visual  purple,  u  |6 
Choroid  plexus,  882 
Chromaffin  tissue  of  adrenals,  565 
Chromatin,  5.  749,  873 

changes    in,    in    nerve-cells,    369. 

745.  756,  77o,  775,  874 
extranuclear,  874 
Chromogens,  336,  443 


(  broniophanes,  936 
Chromo-proteins,  2 
1  Chromosomes,  5,  roo6 
(  hrysotoxin,     action     "f.     on     blood- 
pressure,  157 
Chyle,  com  pi  »si1  ion  of,  1  1,  50,  1 1  1 

tat  in,  340 
fistula,  50 
Chyme,  305.   ;8o 

to  obtain,  427 
Chymosin.     See  Rennin 
Cilia.  628,  705 
Ciliary  ganglion,  820 

muscle,  819,  898,  1)07.  908 
nerves,  819,  820,  908,  985 
processes,  898.  986 

and     secretion     of     aqueous 
humour,  901 
Ciliated      membranes,      electromotive 

phenomena  of,  734 
Cinematograph,  928 
Circulating  liquids,  the.  1  | 
Circulation,  artificial,  262 

changes  in,  at  birth,  1020 

comparative,  72 

cross,  through  brain,  232,  867 

general  view  of,  7^ 

in  brain,  878 

in  the  capillaries,  109,  1 1 1 

in  the  embryo,  1010,  ion,  1015 

in  the  frog's  web,  15.  177 

in  the  lungs,  207 

in  the  veins,  109,  11 1,  121 

influence  of  posture  on,  173 

of  respiration  on,  265 
of  lymph,  176 
time,  123,  203,  208 

electrical  method,  123,  203 
Hering's  method,  123 
methylene  blue  method,  125, 
203 
Circus  movements,  837 
Clarke's  column,  762 

connections  of,  770 
Climate  and  food,  590 
Coagulated  proteins,  reactions  of,  9 
Coagulation  of  blood,  30,  54 
factors  in,  38 
influences  restraining,  39 
intravascular,  38,  39 
of  crayfish,  36 
of  Limulus,  36 
prevention  of,  31,  54 
of  lymph,  49 

temperature,  to  determine,  8 
Coagulins,  33 
Coal-gas  poisoning,  45,  66 
Cobra-venom  and  coagulation,  39 
Cocaine,  action  of,  on  intestinal  mow. 
ments,  307 
on  nerve-fibres,  687 


1036 


IX hi  X 


Cocaine,  action  of,  on  tin-  pupil,  911 

fever,  586 
Cochlea,  823,  956,  957. 
1  o<  hleai  rool  of  eighth  nerve,  773,  823 

••  hi.  550,  551 
I  oeli 'in.  1 

Coffee,  441,  550,  551 
Cold   sensations,    968,    969,    971,    972, 
1001 
after    section    of    cutaneous 

nerves,  975,  977 
paths  for,  795 
Collaterals,  678,  749,  785 

ol   posterior  root  fibres,  769.   792. 
797 
Colloids    of    Grimaux,    effect    1 

coagulation,  39 
Colon,  movements  of,  308 

innervation  of,  310 
Colostrum,  102 1 
Colour,  body-  and  surface-, 
blindness,  948,  998 
temporary,  949 
mixing,  940,  996 
triangle,  942 
vision,  939 

Hering's  theory  of,  945 
Young-Helmholtz    theory   of, 
941 
('■.loured  shadows,  944 
Colours,  complementary,  940,  996 

primary,  g  |  r 
O  >iiia.  congestion  of  brain  in,  875 

diabetic,  521 
Comma  tract,  765,  769 
Commissural  fibres,  701 
Common   path,  principle  of  the,   797, 

Commutator,  Pohl's,  625 

Compensator,  620 

Compensatory  pulse  of  heart,  141,  142 

Complement.  27,63 

Compleiueutal  air,  220,  291 

Complementary  colours,  940,  996 

Condensed    air,    effects    of    breathing, 

272-274 
Condensor  discharges,  ha?molytic  action 

of,    27 

as  stimuli  for  nerves,  658 
Conduction,  double,  687 
irreciprocal,  688 
isolated,  689 
loss  of  heat  by,  578,  579 
Conductivity,  molecular,  401 

'I  nerve,  effect  of  temperature 

on,  687 
effect  of  electrif  al  currents  on. 
658.  741 
specific,  401 

■red  as  test  lor  acids.  324 
Conjugate  deviation,  S3S,  845,  858 


srvation  of  energv,  law  of,  in  body, 

580 
(  onsonants,  282 

1  ■  >ut r  i-  tion,  idio-muscular,  659 

law  of,  68  1,  742 

for  nerves  in  situ,  686,  743 

paradoxical,  729,  741 

secondarv,  729,  738 

without  metals,  717 
Contrast,  944,  996,  997 
Co-ordination  "t  movements,  778,  831, 

837 
Core-models  and  electrotonic  currents, 

728,   72') 

Cornea,  radius  of  curvature  of,  902 

<  orona  radiata,  768,  774,  776 

<  orpora  Arantii,  79 

quadrigemina,  772,  773 
and  respiration,  225 
anterior,  818,  829 
posterior,  824,  828,  861 

striata,  747,  759.  768,  785,  892 

and    temperature    regulation. 

595 
Corpus  callosum,  760,  784 

luteurn,  and  menstruation,  1005 
haematoidin  in,  356 
internal     secretion     of,     557, 

1006 
origin  of,  1006 
Cortex  of  brain,  functions  of,  840.     See 
also  Cerebral  cortex 
'  motor  '  areas  of,  844 
sensory  areas  of,  858 
Corti,  ganglion  of,  823 

organ  of,  958,  961,  963 
Costal  breathing,  214 
Coughing,  239 

Cranial  conduction  of  sound,  960,  999 
nerves,  815 

bifurcation  of  afferent  fibres, 

of,  820,  822,  823,  825 
homologies  of,  816 
nuclei  of,  816,  817 
Crayfish  blood,  clotting  of,  36 
Cream,  611 
Crista  acustica,  833 
Cross-circulation  through  brain,  232 
Crossed  pyramidal  tract,  765,  774,  777 

connei  tions  of,  774.  778 
Crura  cerebri,  768,  783 
Crusta,  768 

Cuneate  funiculus,  767 
nucleus,  767 

relation  of,  to  fillet,  772 
Cuneus  and  vision,  859 
Curara,  action  of,  on  skeletal  muscle, 
633,  706 
on  gaseous  exchange,  245,  51  7 
on  heat-production,  590,  596 
on  vomiting,  313 


INDEX 


1037 


Curdling  of  milk  bj    rennin,  )s6, 

427 
(  urrenl  Lntensit  j  and  stimulation,  6  [6, 

"t  .11  tion.     Set    \<  tion  current 
■  1  rest.     Sei  I  lemari  ation  1  urrenl 
<.  utaneous  burnsi  death  from,  276 
excretion, 
aerves,  phenomena  after  section  of, 

respiration.  275 
(.  yanogen  groups  is  h\  ing  protein,  499 
Cybulski's  method  for  velocity  of  blood, 

1 1  1 
Cystin,  332,  337,  450.  5 \\ 
Cytolysins,  29 
Cytoplasm,  5 
Cytosine,  507 

Dancing  mice,  labyrinth  in,  837 

Daniell  cell,  182.  615 

Daphnia,  Metschnikoff's  researches  on, 

52 

action  of  muscarine  on  heart  of.  1  5  1 
Dark-adapted  eye,  934,  936,  946 
Daturine,  action  of,  on  heart,  150 

on  pupil,  911 
'  Dead  space,'  respiratory,  221 
Deaf-mutes,  equilibration  in,  835 

atrophy  of  temporal  convolutions 
in,  860 
Decerebrate  rigidity,  836,  847 
Decidua,  1005,  1010 

absorption  of,  by  leucocytes,  52 
artificial  production  of,  1006 
Decinormal  solutions,  439,  483 
Decussation  of  afferent  impulses,  792 
of  efferent  impulses,  792 
of  fillet,  772 

of  optic  nerve,  818,  859 
of  pyramids,  768,  774,  yyy 
1  >rt. 1  ration,  310,  311 
Deficiency  phenomena,  786 
Degeneration  of  muscles,  698 
of  nerves,  691 

chemistry  of,  693 
reaction  of,  698 
Deglutition,  301 
centre,  303 
nerves  of,  303 
sounds,  303 
Deiters'  nucleus,  780,  781,  792,  Sj  ^ 
Demarcation  current,  718,  739 

electromotive  force  of,  7Z2 
theories  of,  724 
Dendrites,  749 

amoeboid  movements  of,  749 
and  sleep,  876 
Dentate    nucleus   of   cerebellum,    760, 
77i,  779 
of  olive,  767 


Depressor  nerve,  154,  ""' 

pi  essor  actit I 

I  »esi  emliug  degeneration.  764,  77  I 
I  '.liter, .. proteose,  3,  10,  3-=> 
I  >evelopment  of  embryo,  1006 
I  'exirin.   j,  II.   1  (J.  608 

formed  in  salivary  digestion.    ,.1. 
423 
Dextrose,  3.  315,  316.  442.  1  13 

estimation  of,  in  urine,  489 

in  Mood,  41,  417,  462,  516 

in  Lymph,  4'),  417 

Trommer's  test  for,  10.  451 
Diabetes,  518 

dextrose-nitrogen  ratio  in,  522 

duodenal,  555 

levulose  used  up  in,  520 

oxygen  consumption  in,  243 

pancreatic,  520,  553 

phloridzin,  521,  610 

reaction  of  blood  in,  23 

respiratory  quotient  in.  243 

sugar-destroying    power    of    blood 
in.  519 
Diabetic  coma,  521 
Diapedesis,  53,  177 
Diaphragm  in  respiration,  211,  223 

recording  movements  of,  21S 
Diastases,  321,  355,  512 
Diastole  of  heart,  80 
Dichromatic  vision,  94S,  949,  998 
Dicrotic  wave,  94,  10 1 
Dietaries,  standard,  543-54S 
Dietetics,  543 
Differential  rheotome,  723 
Diffusion,  398 

circles,  912,  950 

of  gases,  247 
Digestion  as  a  whole,  389 

bacteria  and,  318,  395 

chemical  phenomena  of,  319-344 

comparative,  296 

gaseous  exchange  during,  245 

in  intestine,  391 

in  stomach,  389 

mechanical  phenomena  of,  300 

of  carbo-hydrates,  322,  389 

of  fats,  328,  334,  338,  427,  432 

of  proteins,  390,  391 

significance  of,  299 

time  required  for,  391,  432 
Digestive  glands,  structure  of,  345 

juices,  action  of  drugs  on.  387 

adaptation  of,   to  food,   340, 

369,  376,  381,  387 
protection  of  gut  against,  359 
secretion  of,  344,  354 
summary,  388,  389 

organs  in  different  animals,  296 
Digitalis,  diuretic  action  of,  470 
Dilator  of  pupil,  911 


]..;* 


I\l>l  X 


l  lioptei .  906 

I  diphtheria  toxin.  ■>'  tion  "t  enzymes  on, 

342 

I  tiplopia,  820,  923,  92  1 
l  lirecl  cerebellar  tract,    6  1 

connei  t i<  >ns  of,  770.  ;;<) 

pj  r. uiii.l.il  tract,  765.  774,  778 
Disaccharides,  ;.  ;  ij 

absoi'i'ticii  .1!.  1 1 1.. 
1  tischai  ge    ol    ventricle,  pet  iod  of,  79, 

90 
I  dispersion  in  ej  e,  91  1 

i>\  .1  prism,  875 
I  liuresis  b)  salts,  (.63 

1  Miii'rlii  -.    |;u 

I  loremus'  ureomi  tei .  482 
I  ><  >iil  1 1 . ■  1 1  induction  in  aerve,  687 
images,  neglei  t  of,  924 

1 1 graph,  113 

I  'rum.  to  smoke  a,  179 

Dry  cells,  182 

Ductus  arteriosus  and  ductus  venosus, 

mi  s 

Dulcite,  relati f,  to  galactose,  3 

1  duodenum,  glycosuria  after  removal  of, 

555 
I  »ur.i  mater,  758 
Dyspnoea,  231 

heat,  290 

respirat  iry  quotienl  in,  242 

Ear,  anatomy  of,  95  1 

ossicles  of,  954,  955 
functions  of,  959 

resonance  tone  of,  80,  

Echidnase,  46 
Eck's  fistula,  356,  502 
I  Ectoderm,  6,  1008,  1009 
Ectoplasm,  4 
Effei  tor  "t  reflex  arc-.  797 
Efferent  impulses,  decussation  of,  768, 
774.  777-  7<)i 
paths  of,  792 
Egg-albumin,  absorption  of,  1  [8 
amino-acids  in,  1 
excretion  of,  1.19,  (.62,  609 
reactions  of,  8 
1  gg-j  oik,  ioio,  ioi  - 
Ehrlich's  triacid  stain,  1 7 
Eighth  nerve.     See  Auditory  aerve 
Elasticity  ol  muscle,  6 

1  lei  trical  conductivity,  oi  I '1 1.  25,  60 

ol  gastric  juici  , 
of  milk,  1021 
"I  scrum,  60,  357 
or^.in,  development  .  ] 
response.      See  Action  current 
Electric  fishes,  736 
Electrocardiogram,  human,   730.   731, 

732.  734 
Electrodes,  tinpolarizable,  <>2>  739 


Electrolytes, 

Electrometer,  capillary,  621,  622,  740 

Ivlectroinotive  force,  6x6 
Electrons,  401 

Hlectrotonic     alterations     of     excita- 
bility    and     conductivityi 
683.  68  1 
currents,  728,  740 
Electrotonus,  <>^  ^,  740.  741 
1  le\ enth  aerve,  827 
Emboli,  artificial,  745 
Embrj  0,  asphj  sia  in,  1018 

circulation   in,    1010.    1011,    1 

1020 
development  of,  1006,  1010 
gases  1  >t  bloi  id  in,  1013 
glycogen  in,  514,  1016 
heat-production  in,  1017,  1018 
inverting  enzymes  in,  342,   1014, 

1016 
liver  in,  1015 
metabolism  of,  1017 
physii  ilogy  of,  1010 
Emetics,  313,  427.  432 
Emmetropic  eye,  914.  915 
Emotions,  genesis  of,  866 
Emulsification  of  fats.  12.  338,  431 
Emulsin,  315,  316 
End-brush,  740 
Endocardiac  pressure,  84,  89 
amount  of,  85 
curves  of,  84,  87,  88 
measurement  of,  85 
negative,  92 
I  adoderm,  6,  1008,  1009 
Endogenous  fibres  of  curd.    701,   765, 

795 
Endolymph,  833,  956 
Endoplasm,  4 

lindothermic  reactions,  585 
Enemata,  308,  42 1 

Energy  of  food,  influence  of  hydrolysis 
on,  580 

law  of  conservation  of,  in  body,  580 
Enterokinase,  343,  3*7 
Enzymes.     See  Ferments 
Ependyma,  759 
Epiblast.     See  Ectoderm 
Epicritic  sensibility,  98] 
Epiglottis,  301,  302 
Epilepsy,  cortii  al,  865,  889 

produi  ed  by  absinth  , 
Equilibration,  cerebellum  and.  831 

Deiters'  nucleus  and,  825 

in  dog-fish, 

in  pigeon,  834 

muscular  nerves  and,  835 
ircular  canals  and,  8a 
833 

skin  and,  835 
.  mi  centi  e.  107 


TND1  -V 


1039 


Erepsin,   143,  \ig 

1  tph,  556,  6  i'i.  650,  65a,  708 

•   md  blood-pressure,  157 
Eruci<  acid, 
ErythroblastSj  2 1 
Erythrocj  tes,  15 

enumeration  of,  18, 

gases  of,  252,  253 

life-history  of,  tg 
1  1  \  throdext]  in,  ix,  321, 


58 


423 


578,  579 
if     living 


Esbach's  albuminimeter  and  reagent, 

488 
Eserine,  a<  tion  of,  on  accommodation, 
9o8 

on  pupil,  01 1 

Ether,  at  tion  of,  on  bl l-<  orpuscles, 

27,  28,  61 

on  urine  secretion,  471 
Ethyl  butyrate,  synthesis  of,  by  lipase, 

1  udiometer,  215 

Euglobulin,  1- 

Eustachian  tube,  274.  954 
valve,  1015 

Evaporation,  loss  ol  beat  l>\ 

Exi  itability,     .1     property 
matter,  6 
direct,  of  muscle,  ('.13,  706 
of  nerve,  effect  of  temperature  on, 

I'M,    687 

effect  of  electrical  currents  on, 
^58,741 
Excitable  tissues,  the,  027 
l.v  retion,  4.53 
Exothermic  reactions,  585 
I  Expectoration,  435 
Expiration,  213 

duration  of,  218 
1.  214 
Expired  air.  composition  of, 
Extensibility  of  muscle,  030 
Extension  reflex,  crossed,  800,  887 
Extensor  reflex,  the,  798 

thrust,  the,  799 
Exteroceptive  reflexes,  810 
Extra  contraction  of  heart,  141 

systoles,  in  man,  141,  142 
Exudation,  inflammatory,  53 
Eye,    chemistry    of    refractive 
of,  901 

compound,  of  insects,  897 

currents  of,  734,  735 

defects  of,  912 

development  of,  747 

Ktihne's,  988 

movements  of,  951 

muscles  of,  952 

nerves  of,  818,  908,  909 

optical  constants  of,  902,  903 

reduced,  903,  904 

refraction  in,  902 


-41. 293 


media 


Eye,  strm  ture  of,  898,  985 

1  Miijugate  deviation  of,  838,  845, 

primary  position  <>f.  951 
w  bee!  movements  of, 

l.n  i.il  li.iv  e,  822 

union  of,  with  accessory,  868 

palsy,  822 

bai  teria  in,  397 

composition  of,  396,  432 

odour  of,  396 

storage  "t.  in  sigmoid  flexure,  309 
I  ainting,  1  75 
Fallopian  tubes,  1004 
Falsetto  voice,  281 
Faradic  current,  624 
Far-point  of  vision,  915,  988 
Fasciculus  solitarius,  822,  825 
Fasting  men,  metabolism  in,  532 
F'at,  absorption  of,  412.  432.  433 
function  of  bile  in,  41  1 

composition  of,  1,  3,  11,  523,  529 

digestion  of,  32S.  334,  338 

emulsification  of,  12,  338 

excretion   of,   into   intestine,    354, 

4i5 
formation     of,      from      carbo-hy- 
drates, 524 

from  fatty  acids.  523 
from  proteins,  525 
in  fa'ces  in  jaundice,  340 
influence  of,  on  pancreatic  secre- 
tion, 380 
iodine  value  of,  4,  526 
melting-points  of,  4,  12 
metabolism  of,  522.  527 

in  phosphorus-poisoning.  525, 
526 
migration  of,  522,  525,  526,  ^27 
organized,  526 

passage  of,  through  placenta.  1014 
protein-sparing  action  of,  523,  534 
saponification  of,  II 
solvents  of,  4 

sources  of,  in  body,  523,  52  \ 
stained,  absorption  of,  414.  432 
synthesis  of,  in  intestine,  415 
F'atigue,  muscular,  648,  050.  053.  708 
cause  of,  650 
of  nerve-cells,  873,  874 
of  reflex  arcs,  800 
seat   of   exhaustion    in.    651,    652, 
708.  709 
Fat-splitting  ferment   of  gastric  juice, 
323-  328 
of  intestinal  juice.  342 
of  pancreatic  juice,  331,  334, 

339-  429 
of  tissues,  527 
bacteria  of  intestine,  393.  395 


1040 


TND1  X 


l-.iit  \  .K  ids,  absoi  i'ii i.  1 1  ;. 

tests  for,  ii.  12 
Fei  hner's  law,  g 
Pebling's  solution,  489 
Fenestra  1  otund  1 
Ferments,  314 

gly<  olytic,  517 

mtr.K  ellular,   314,    159,   51 
527 

in  urine,   11 1 

mode  oi  action  of,  3 1<< 

oxidizing,   42,   68,    j<>|.   295.    514, 
507.  509,  1013 

quantitative  estimation  of,  317,422 

reducing,  509 

reversible  action  of,  317,  509,  528 
Ferricyanide  of  potassium,   action  of, 
on  haemoglobin,  46 
estimation  oi  oxygen  in  blood 
by.  251 
Fertilization  oi  ovum,  1007,  1008 
Fever,  597 

effect  of,  on  pulse  99 

metabolism  in,  597,  000.  601 

produced  by  cocaine,  586 
by  puncture,  595 

retention  theory  of,  599 

significance  <>f,  601 
Fibrillar  contraction  of  heart.  138.  190 
Fibrin-ferment,  32 

fi  'rmation  of,  33 

nature  of,  32. 

precursors  of.  33 

preparation  of,  33.  57 

source  of,  36 
Fibrin.  f<  irmation  of,  30 

protein  reactions  of.  9 

quantity  of.  in  blood,  4 1 
Fibrinogen,  32,  3 

Fick  and  YVislicenus'  experiment,  537 
Fifth  nerve.     See  Trigeminus 
Fillet,  772 

decussation  of,  772.  791 

descending  fibres  of,  773 

lower  or  Lateral,  772,  ^:  1 

upper  or  intermediate  772 
Fish-sperm,  proteins  of,  2 
Fistula,  biliary,  339,  383 

double    gastric    and    oesophageal, 
257.  374 

Eck's,  356 

gastric,  373 

intestinal,  341 

pani  reatic,  378 

salivary,  370 
Flavour,  968 
Flechsig's  cortical  fields, 

tract.     Set   l  >ire<  t  cerebellar  tra<  t 
Flour,  chemistry  of.  612 
Flow  ot  liquids,  75 

with  intermittent  pressuri 


Fluorides,  influence  of.  on  coagulation, 

FOI     ll    lllllllilll.lt  loll    ol   '   J    \    <i2'i 

lot  11, .     See  Embryo 

Folin's  method  ot  estimating  indican, 

480 
kreatmiu.  485 
uric  acid,  485 
Fontanelle,  sinking  of,  in  sleep,  875 
Food  and  climate,  590 

relation  of,  to  surf.u  e,  540.  593 
time  of  passage  ot.  along  gut,   ;n 
I  oods,  composition  of,  546,  611,  612 

isodynamic,  670 
Foot-jerk,  <si  1 
Foramen  of  Magendie.  882 
ot   Monro.  747 
ovale.  954.  955,  960 
I •■  i '  -  d  movements,  836 
Fore-brain,  747 
Formaldehyde  reaction  for  proteins,  8 

reflex  inhibition  by  inhaling,  235 
Formatio  reticularis.  768 
Formic   arid   in     saliva'  ol  Octopus, 

361 
Fourth  or  trochlear  nerve,  820 
Fovea  centralis,  899,  900.  935,  946 

representation  of,  on  cortex, 

859 
Freezing  and  thawing,  haemolysis  by,  27 
Freezing-point    and   osmotic  pres 
398 
determination  of,  399,  492 
of  solid  tissues,  411 
of  urine  446,  492 
Frontal  lobes,  function  of,  865.  866 
Fundus  of  stomach,  in  digestion.  304, 

305 
Funiculus  gracili>  and  1  uneatus,  767 
Furfuraldehyde   in   Pettenkofer's   test, 

H7.  430 
Furunculosis,   opsonins  and   treatment 
of.  53 

Galactose.  3,  316 

<  rail-bladder,  action  oi  peptone  on,  411 

nerves  of,  384 
( ..il\  anic  rotation 
1  ,.il\  ani's  experiment,  71  7.  738 

<  ralvanometer,  617,  740 

'  string."  <>i<) 
I ,.il\  anotonus,  636 

Ganglion-cells,   changes  in,    with   age, 
755 

bipolar,  753 
1  ranglii  'U  jugulare,  825 

nodosum,  825 

petrosum,  B22, 

spirale,  ^23 

super  ius, 

vestibular* 


INDEX 


ir>4  r 


Gaseous  exchange.  2  11.  293 
1  in  umstances  afta  1  i n^.  24  \ 
relation  of,  to  external  tempera- 
ture, 1  |S 

Gases  ..i  blood,  .  ('• 
diffusion  of,  -ir 
partial  pressure  of,  248,  *49<  -5,j 

S'.lnti"ii  of,  248 

Gas-pump,  250 
Gasserian  ganglion 
developing,  752 

<  i.istrii'  diyi'Sti'iii.  amylolytic  stage  of, 

33*.  390 

testing  for  products  of,  426 
-lands,   changes  in.  during  secre- 
tion, 347,  349 
influence  of  nerves  on,  372 
structure  of,  345,  350 
juice.  j,22.  427 

acidity  of,  323,  324,  428 
adaptation  of,  to  food,  376 
antiseptic  function  of,  328 
artificial,  426 

Beaumont's  researches  on,  323 
composition  of,  323 
formation      of      hydrochloric 

acid  of,  351 
freezing-point     and     conduc- 
tivity of,  357.  358 
in  cancer,  324 
lactic  acid  in,  324 
organic   and   inorganic    acids 

in,  324 
psychical  secretion  of,  374 
quantity  of,  324 
secretion  of,  350 
to  obtain,  323,  374.  427 
lipase,  323,  328 
secretin,  374 
Gastro-enterostomy,     assimilation     of 

protein  after,  330 
Gelatin,  2,  690 

cleavage  products  of,  2,  534 
protein-sparing  action  of,  534 
reactions  of,  9 
Gelatose,  3,  416 
Gemmules,  749 
Geniculate  bodies,  lateral,  818,  829 

mesial  or  internal,   773,   819, 
828,  861 
and  auditorv  nerve,  773, 
824,  828 
ganglion,  822 
Germinal  area,  1008 
cells,  754 
vesicle,  1004 
Ghosts  of  erythrocytes,  61 
Giant  pyramidal  cells,  774,  852 
Gianuzzi,  crescents  of,  345,  353 
Gigantism    and   disease   of    pituitarv, 
568 


Glands,  electromotive  phenomena  of, 

734 

beat -production  in,  585 

racemose.  345 
serous  and  mucous,  319 
Glaucoma,  tntra-ocular  tension  in,  902 
Gliadin,  influence  of,  on  serum  proteins, 

498 
Globin,  2,  47 
( rlobulins,  2,  47 
in  urine,  486 
reactions  of,  9 
Globulose,  3 
Glomeruli,  452,  455.  458,  465,  469 

olfactory,  816,  818 
Glosso-labio-laryngeal  palsy,  825 
Glosso-pharyngeal  nerve,  821,  825 
and  taste,  821,  822,  825 
in  deglutition,  304 
Glottis,  2i6,  277,  282,  302 

movements  of,  in  respiration.  215 
Gluco-proteins,  3 
Glucose.     See  Dextrose 
Glutamic  acid,  332 

formation   of  dextrose   from, 

514 
in  serum  proteins,  498 
Gluten,  6l2 
Gluten-fibrin,  503 

Glycerin,  formation  of  glycogen  from, 
513 
in  blood,  441 
test  for,  12 
Glycin  or  glycocoll,   2,   332,   337,   441, 
510,  526 
formation  of  dextrose  from,  514 
of  hippuric  acid  from,  508 
of  urea  from,  501 
hydrolysis  of,  322 
Glycocholic  acid,  336 
Glycogen,  3,  13,  511,  527 

disappearance  of,  in  fasting,  515 
extra-hepatic,  514 
formation  of.  512 
formers,  513 
function  of,  515 
in  diabetes,  519 
in  embryo,  514,  1016 
in  leucocytes,  47 
in  liver-cells,  512 
in  muscles,  514,  515,  667 
in  placenta,  514,  1014,  1016 
in  strychnine -poisoning,  595,  596 
preparation  of,  511,  608 
used  up  in  muscular  contraction, 
515 
Glycogenase,  510,  554,  1016 
Glycogenolysis,  512,  515,  1016 

splanchnic  nerves  and,  519 
Glycolysis,  516,  554,  555 

bv  pancreas  and  muscle,  517,  554 

66 


1042 


INDEX 


I  rlycosuria,  516 
adrenalin,  522 
after  injection  oi    ugar  into  blood, 

609 
alimentary,  516,  610 
duodenal,  555 
in  diabetes,  518 
pancreatic,  520,  553 
phloridzin,  521,609 
puncture,  518,  555 
Glycuronic  acid,   1  1  • 
Glycyl-glycin.  503 

Glyoxylic   acid   in   Adamkiewicz's  re- 
action, 8 
Gmelin's  test  for  bile-pigments,  431 
Golgi's  method,  749 

second  type,  cells  of,  754,  869 
Goll's   column.      See    Postero-median 

column 
(niltz  on  dog's  brain,  842 
on  monkey's  brain,  850 
on  removal  of  spinal  cord,  787 
Gout,  uric  acid  in,  449,  505 

uricolytic  ferment  in,  508 
Gowers'  tract.     See  Antero-lateral  as- 
cending tract 
Graafian  follicle,  1004 
Gracile  and  cuneate  nuclei,  767,  772 
Gracilis  experiment,  Kuhne's,  688 
Grafting  of  tissues,  1023 
Gramme-molecular  weight,  398 
'Granule-cell,'  754,  817 
Gravity,  centre  of,  in  standing,  839 
influence  of,   on  circulation,    173, 
199 
Grehant's  method  of  anaesthesia.  186 
Ground-bundle,  antero-lateral.  765 
Guaiacum  test  for  blood,  68,  264 
Guanase,  507 
Guanin,  441,  504,  507 
Gudden's  commissure,  819 
Giinzburg's  reagent,  428 
Gymnotus,  737 

Habits,  effect  of  cortical  lesions  on,  866 

Haematachometer,  113 

Hacmatin,  47,  67 

Haematoblasts,  21 

Haematocrite,  25,  59 

Haematoidin,  356 

Haematoporphyrin.  47,  67 

in  urine,  443 
Haemautographic  tracing,  102 
Haemin,  47 

test  for  blood.  71 
Haemochrome,  16,  28,  252 
Haemochromogcn.  47.  67 
Haemocytometer,  58 
Haemoglobin,  42 

composition  of,  2,  43 

crystals  of,  3,  41,  65 


Haemoglobin,  derivatives  of,  45-47.66. 
67 
dissociation  of,  43,  248,  252,  254 
in  foetus,  1018 
intracorpuscular  crystallization  of, 

44,  62 
iron  and  sulphur  in,  3,  43 
quantitative  estimation  of,  69 
relation  of,  to  bile  pigment,  388 
spectrum  of,  44,  65 
Haemoglobinometer,    Gowers-Haldane, 

68 
Hemoglobinuria.  46,  444 
Haemolysis,  26,  61,  63 
in  placenta.  1014 
mechanism  of,  28 
Haemolysinogens,  30 
Haemometer,  Fleischl's,  69 
Haemophilia,  34 

Haemorrhage,     effect     of,     on     blood- 
pressure,  174,  200 
Hair  aesthesiometer,  970,  999 
Hair-cells  of  vestibule,  833 
of  Corti,  958,  961,  963 
Haldane     and     Smith's     method     for 

quantity  of  blood,  48 
Harmonics  or  overtones,  280 
Hay's  test  for  bile-salts,  491 
Hayem's  solution,  18 
Head,  grafting  of  the,  867 
Head  on  referred  pain,  790 
on  sensory  nerves,  981 
Hearing,  953 

centre  for,  824,  860 
impairment  of,  in  facial  palsy,  822 
range  of,  964 
Heart,  action  current  of,  78,  730.  740 
action  of  drugs  on,  152,  183 
'  all  or  nothing  '  law  in,  141 
anatomy  of  frog's,  129,  177 
automatism  of,  129,  130 
beat,  78,  178,  186 
cause  of,  129 
chemical    conditions   of,    139, 

185 

voluntary  acceleration  of,  156 
conduction  and  co-ordination  in, 

129,  134 
discharge  of,  90 

embryonic,  132,  1010,  1015,  1020 
excitability  of,  130 
extra  contraction  of,  141 
fibrillar  contraction  of,  138,  190 
filling  of,  90 
ganglion-cells  of,  129 
gaseous  metabolism  of,  264 
glycogen  in.  515 
haemorrhage  from.  189 
heat  produced  by,  585.  670,  10 18 
heat  standstill  of,  152,  178 
impulse  of,  82,  191 


TNDEX 


i«>43 


Heart,    influence  of   temperature  on, 
178,  181 
mammalian,  action  of,  186 
muscle,  m 

a<  tion  of  salts  on,  139.  185 
nature  oi  contraction  of,  142 
nerves  of,   distribution  in   heart, 
148,  1 1 'i 
augmentor,  143,  146,  147.  184. 

190 
extrinsic,  143 

inhibitory,  143.  i)7.  182.  187 
intrinsic,  120 
normal  excitation  of,  152 
output  of,  127 

ssure  in.  84,  90 
primitive  vertebrate,  70,  72 
refractory  period  of,  1 1 1 
respiratory',  72 
resuscitation  of,  139,  149 
rliythniic.it  y  of,  129.  133 
sounds  of,  80,  191 
source  of  energy  of,  670 
suction  action  of,  92,  121 
tonicity  of,  130 

tracings,  145,   147.   151.   152,   155. 
178,  180,  185,  188 
simultaneous,     from     auricle 
and  ventricle,  180 
valves  of,  78,  190,  191 
insufficiency  of,  191 
moment  of  closure  of,  89 
wurk  of,  127 

in  foetus,  1018 
Heart-strips,  contraction  of,  139,  185 
Heat-centres,  595,  597 
Heat-dyspncea,  290 
Heat,  distribution  of,  602 

equivalent  of  food-substances.  581 
of  cleavage  products  of  food, 

580 
of  work  of  heart,  585 
given     off     in     respiration,     579, 

613 
involuntary  regulation  of,  587 

voluntary  regulation  of,  589 
loss  from  body,  578 

after    varnishing    skin,     276, 

476,  594 
by  evaporation,  578,  579 
mechanical    equivalent    of,     581, 
1027 
Heat-production,   effect  of  curara  on, 
590 
and  size  of  body,  593 
in  brain,  586 
in  fever,  598,  599 
in  glands,  585 
in  heart,  585 
in  muscles,  583 
in  sleep,  582 


Heat-production,    involuntary   regula- 
tion of,   590 

"i  different  classes,  582 

of  man,  581 

relation   to   muscular   work,    583, 
664 
to  surface  of  body,  593,  595 

seats  of,  583 

sources  of,  580 

voluntary  regulation  of,  589 
Heat-rigor,  263,  674,  715 
Heat-sensations,  972,  974,  1001 

after  section  of  cutaneous  nerves, 
975.  978 
Heat-units,  574 
Heidenhain's    experiments     on     renal 

secretion,  458 
Heller's  test  for  albumin,  486 
Helmholtz's  wire,  624 
Hemeralopia,  948 
Hemianesthesia,  capsular,  783 
Hemianopia,  819,  829,  858 

nasal,  819 
Hemiplegia    after    removal    of    motor 
cortex,  848 

and  motor  aphasia,  863 

cutaneous  reflexes  in,  807 
Hemisection  of  cord,  793 
Hering's  theory  of  colour  vision,  945 
Herpes  zoster  and  trophic  nerves,  701 
Hetero-proteose,  3,  10 
Hexone  bases,  331,  332 
Hexoses,  3 

Hibernation,  respiratory  quotient    in, 
242 

temperature  regulation  in,  596 
Hiccup,  239 
Hippocampal  convolution  and  olfactory 

tract,  817,  862 
Hippuric  acid,  441,  486 

synthesis  of,  441,  508 
Hirudin,  36 

Histidin  in  tryptic  digestion,  331,  332 
Histones,  2 

Holder  for  animal,  186 
Holmgren's  wools,  998 
Homogentisinic  acid,  444 
Homoiothermal  animals,  572,  577,  587 
Homolateral  fibres  of  pyramidal  tracts, 

774.  778 
Hopkins's  method  of  estimating  uric 
acid,  484 

test  for  lactic  acid,  716 
Hormones,  375,  571 
Horopter,  924 
Humidity  of  air,  and  body  temperature, 

588 
Hunger,  sensation  of,  826 
Hyalomucoid,  701 
Hydra,  structures  of,  6 
Hvdramiic  plethora,  462 

66—2 


1044 


IX hi  X 


Hydramnios,  1017 
Hydrobilirubin,  3  \(< 
Hydrocele  fluid)  clothing  ol 
Hydrochloric  acid,  action  of,  on   pro- 
teins, 326 
in  gastric  juice,  323,  326,  428 
formation  of,  351 
Hydrogen  balance,  540 

in  expired  air,  2  1 2 

ions  in  blood,  etc.,  23 

percentage  of,  in  tissues,  529 
Hydrolysis  by  u  ids,  1,  322 

by  ferments,  314 

and  energy  value  of  food,  580 
Hydrostatic    and    hydrodynamic    ele- 
ments in  blood-pressure,  173 
Hydrostomia,  372 
Hydroxylions  in  blood,  etc.,  23 
Hyoscyamine,  action  of,  on  pupil,  91 1 
Hyperalgesia  after  nerve  section,  793, 

979 
Hyperchromatism,  874 
Hyperglycemia,  518,  310 
Hypermetropia,  916 
Hyperpnoea,  231 

in  mountain  sickness,  275 
Hypnosis,  877 
Hypoblast.     See  Endoderm 
Hypobromite    method    of    estimating 

urea,  440,  480 
Hypogastric  nerves,  310,  311 
Hypoglossal  nerve,  827 

and  lingual,  union  of,  688 
Hvpoisotonic  solutions,  400 
Hypophysis,  830 

action  of  extracts  of/566 
Hypoxanthin,  441,  504.  5°7>  691 

Identical  points,  theory  of,  923 
Idio-muscular  contraction,  659 
Ileo-ca-cal  valve,  307,  308,  394 
Ileo-colic  sphincter,  308,  310,  394,  421 
Illusions,  visual,  928 
Image  on  retina,  formation  of,  902.  903, 
986 
size  of,  904 
Imbibition,  398,  405,  474 
Immunity,  30 

Income  and  expenditure  of  body,  528 
Iih  us,  954,  955i  959 
[ndii  ators,  2  i-   ;'^-,.  l<>i, 
Indigo-carmine,  excretion  of,  by  kid- 
ney, 458 
Indol,  333 

formation  of,  in  intestine.  395 
Indophenyloxydase,  260,  265 
Indoxyl  in  urine,  445,  449.  479.480 
Induced  currents,  623 
Induction  machine,  62 

arranged  for  single  shocks.  703 
for  tetanus,  184 


Induction   machine,    make   and   break 

shocks  from,  702 
Infant,  food  requirement  of.  549 
Inferior  peduncle  of  cerebellum.     See 

Restiform  body 
Inflammation,  diapedesis  in,  53,  177 
Infra-proteins,  2 
Infundibulum,  830 
Inhibition  in  reflex  action,  800 

from  the  cortex,  846 
Inhibition  of  heart,  143,  144,  182.  187 
nature  of,  151 
reflex,  154 

bv    vapours,     154,     155, 

195 

Injury-current.      See    Demarcation 

current 
Inorganic  salts.     See  Salts 
Inspiration,  210 

duration  of,  218 
forced,  214 
Insufficiency  of  cardiac  valves,  81.  96, 

191 
Intellectual  processes,  seat  of,  865 
Intercostal  muscles,  212 
Intermediary  body.  27 
Intermedio-Iateral  tract,  762 
Internal  capsule,  760,  768,  776,  779 

arrangement  of  fibres  in,  782 
respiration,  206,  259 
Internal  secretion.     See  Secretion 
Intestinal   contents,   reaction  of,    392, 
393 
juice,  341 

action  of,  in  digestion,  342- 

344 
adaptation  of,  to  food,  387 
influence  of  nerves  on,  386 
Intestine,  large,  absorption  in,  421 
Intestines,  bacteria  in,  318,  328,  393, 

394.  395 
digestion  in,  391 
movements  of,  306,  308 
nerves  of,  309 

reaction  of  contents  of,  392.  303 
relative  length  in  different  animals, 

297 
resection  of,  421 
Intracranial  pressure,  effects  of  increase 

of,  875 
Intra-ocular  tension,  880,  902 
Intrathoracic  pressure,  209,  221 

in  foetus,  222 
Intravascular  dotting,  38 

influences  restraining,  39,  40 
Inversion  of  carbo-hydrates,  328,  342, 

433 

in  thyroid,  561 

[1  'lis.  25,  400 

Iris,  centre  for  movements  of,  815,  820, 
909 


INDEX 


1045 


Iris,    effect  of   stimulation  oi  sympa- 
theti(  on.  'ii  i.996 

functions  oft  91  - 

m  ac<  ommodation,  909 

local  mechanism  of,  9]  1 

nerves  of,  BiOi  820,  908,  909 

sphincter  of,  820.  >><>s 
li  'ii.  absorption  of,  4^ 

m  In  I- 

111  l>r.m.  s  1  1 

in  foetus,  543,  1013 

in  liver,  si,  355, 432 

in  milk.  543 

m  ordinary  dietary.  543 

in  placenta,  1014 

111  spleen.  -  i 
Iron-ammonia  alum  as  indicator,  477 
Irradiation,  950 

of  reflexes,  802,  885 
Island  of  Reil.  855,  865 
Isodynamic  relation  of  foods,  670 
Isomaltose,  315.  320,  442 
Isotonic  solutions,  400 

and  isometric  contraction,  645 
Itching,  968,  975 

Jacksonian  epilepsy,  865 

Jacobson's  nerve,  363 

Japanese  dancing  mice,  internal  ear  of, 

837 
Jaundice,  absorption  of  bile  in,  355 
fat  in  faeces  in,  340 
hematogenic  and  obstructive,  356, 
386 
Jaw-jerk,  811 
J  udgment,  false,  as  explaining  contrast, 

945 
Judgments,  visual,  926 
Jugular  pulse,  91 

tracings,  137,  193 

Karyokinesis,  5 

Karyosome.     See  Nucleolus 

Katabolic  changes  in  living  matter,  6 

Kathode,  401,  615 

Rations,  401 

Kephalin,  690 

Keratin,  2 

Ketones,  relation  of,  to  carbo-hydrates, 

3 
Key,  short-circuiting,  625 
Kidney,  absorption  in,  457 
bloodvessels  of,  452,  468 
execretion  of  pigments  by,  458 
formation  of  hippuric  acid  in,  508 
gaseous  metabolism  of,  264 
'  internal  secretion  '  of,  569 
nerves  of,  161,  468,  469 
removal  of  only,  447 

greater  part   of  renal   tissue, 
569 


Kidney,  secretory  pressure  in,  466  - 
tubules  of,  453,  454 
transplantation  of,  1023 
Km. esthetic,  function  of  Rolandic  area, 

856 
Kjeldahl's  method  for  total  nitrogen, 

482 
Knee-jerk,  801,  802,  811,  813.  888 

reinforcement  of,  807 
Kreatin,  41,  442,  504,  666 
Kreatinin,  437.  442,  485,  497-  505,  509 
excretion  of.  after  muscular  work, 
538 
in  starvation,  530 
Kresol  in  urine.  445 
Kulme's  eye,  988 
Kymograph.  10 1 

Labyrinth  of  ear,  833,  956,  957,  960 

as  a  proprio-ceptive  organ,  833 
extirpation  of,  835 
Laccase,  264,  314 
Lachrymal  glands,  435 
Lactase,  316,  342,  416 
Lactation,  relation  of,  to  ovary,  1022 
Lacteals  and  fat  absorption,  4r4,  433 

and  sugar  absorption,  417 
Lactic  acid,  action  of,  on  bloodvessels, 
162 
on  respiratory  centre,  230, 
275 
Hopkins's  test  for,  716 
in  gastric  juice,  324,  329 
in  intestine,  393 
in  muscle,  162,  658,  667,  668, 

716 
Uffelmann's  test  for,  428 
Lactose,  3,  316,  549 

absorption  of,  405,  416 
supposed  adaptation  of  pancreas 
to,  382 
Laking  of  blood,  26,  6l,  63 

of  nucleated  corpuscles,  62 
Langerhans,  islets  of,  347,  368,  554 
Langley's    experiments    on    union    of 
vagus  and  cervical  sympathetic,  868 
Lanolin,  absorption  of.  413 
Lanugo,  1012 
Laryngoscope,  280 
Larynx,  anatomy  of,  277 

abductors  and  adductors  of,  277, 

285 
movements  of,  in  respiration,  215 
nerves  of,  285,  286 
paralysis  of,  286,  826 
Lateral  horn,  762 

nucleus  of  bulb,  772 
Laurie     acid,     passage     of,     through 

placenta,  1014 
Lavoisier  and  carbon  dioxide,  240 
Law  of  contraction,  684,  686,  742,  743 


1046 


INDEX 


Lecithin.  |,  1 1.  ,.-.   ,  M7 

in  bile,  337 

in  haemolysis,  28 

in  ni;r\  es,  69a 
I.eelanehe  eel].  182 
Leech  extracl  and  coagulation,  35 
Legal's  test  for  acetone,  492 
Lens,  900,  986 

alteration    of,  in  accommodation, 
905,  906 

chemistry  "t.  001 

radii  of  curvature  "t.  <»>._• 

refractive  indices  of,  903 

regeneration  of,  1003 
Lenses,  refrai  tion  by,  895,  896 
Leucin,  2,  526 

formation  >>f  urea  from,  501 

and    tyrosin     formed    in    tryptii 
digestion,  332,  430 
in  urinary  sediments,  450,  452, 

495 

Leucocytes,  16 

and  absorption  of  fat.   ji| 

ptone,  420 
and  coagulation,  36 

1  lassiln  .it  i>  m  ..I.    17 

composition  of,  47 

destruction  of,  22 

emigration  of,  54,  177 

enumeration  of,  19,  58 

ferments  in,  47,  355,  359,  510 

formation  of,  22 

glycogen  in,  47 
Leucocytosis,  19 
Leucyl-leucin,  503 
Leukaemia,  blood-corpuscles  in.   ig 

uric  acid  in,  449 
Levatores     costarum,     action     of.     in 

respiration,  211 
Levulose,  3,  315.  510.  520 
Levulosuria,  516,  s^'> 
Liben's  test  for  acetone,  492 
Lieberkiihn's  crypts,  345,  421 
Light  bath,  ai  tior  of,  on  blood,  275 

reflex,  path  of,  81 8,  829 

consensual,  910 

Lime-juice  as  antisi  orbutic,  552 

Limulus  blood,  coagulation  of,  36 

heart,  cause  of  beat  of,  130 
action  of  drugs  on,  151 
Lipases,  42,  315,  334,  510,  527 

gastric,  323,  328 

in  succus  entericus,  342 

pancreatic,  331 
Lipoids,  4,  690 

of  erythrocytes  in  haemolysis,  28 
Lissauer,  tract  of,  764 
Listing's  law,  951 
Litmus  as  indicator.  _- 1 

paper,  glazed,  54 
Liver  and  coagulation  of  blood     {0 


Liver  and  destruction  oi  ei 
21 

ferments  in,  510 

formation    of    bile-pigments    anil 
acids  in,  355 

of  glycogen  in,  511,  512,  513, 
519,  608 

igar  in,  511.  515 
of  urea  in.  501.  505 
heat-produi  tion  in,  585 
internal  set  retion  of,  552 
iron  in,  21,  355,  432 
Minkowski's  experiments  on,  502 
structure  of,  14,  345 
Living  and  dead  proteins,  499 
Living  matter,  composition,  1 
functions,  6 
structure,  4 
'  Living  test-tube  '  experiment,   {I 
Localization  of  function  in  brain,  867, 
872 
degree  of,  in  different  animals, 

872 
of  sensations,  980,  982 
Locke's  solution,  139 
Locomotion,  839 

Locomotor    ataxia,     equilibration    in, 
835 
knee-jerk  in,  811 
pupil  in,  910 
tactile  sensations  in,  795 
Loeb  on  artificial  parthenogenesis,  1007 
Loewenthal's  tract.     See  Antero-lateral 

descending  tract 
Lungs,  circulation  in,  208 
elastic  tension  of,  209 
influence  of,  on  coagulation,  40 
quantity  of  blood  in,  208,  268 
sei  retory  action  of,  258 
structure  of,  207 
vaso-motor  nerves  of.  11,3 
Lutein,  1006 
Luxus-consumption,  535 
Lymph,  circulation  of.  176 
composition  of,  49 
dextrose  in,  49,  4  1 7 
formation  of,  406 

and  activity  of  organs,  410 
and  blood-pressure,  408,  409 
functions  of,  si 
gases  of,  260 

osmotic  pressure  of.  410.  411 
post-mortem  flow  of,  412 
l.vuiphagogues,  406 

hatic  glands,  formation  of  lymph- 
t es  in.  23 
i    mphatics,  407 

absorption  of  bile  by,  355 
Lymph-hearts,  177 
Lymphocytes,  17.  22,  47 


INDEX 


1047 


istii  1.  833 
lute  1  993 

Magendie,  foramen  1  >fc 

experimenta  on  nerve-roots,  790 
nation  oi  fat  in,  526 

Magnesium  sulphate  solution  for  bl I- 

ure  ti acings,  195 
Make  and  break  shocks,  702 
Malapterurus,  7\> 

al  nerve  of,  737<  758 
double  conduction  in,  688 
Malleus,  954,  uss.  959 
Maltase,  315,  334,  34«.  4*6.  5i« 
Mali 

absorption  of,  1 16 
Mammary  glands,  537.  1021 
Manganese  in  bile,  337 

absorption  of,  n 7 
Mannite,  relation  of,  to  levulose,  3 
Manometer,  differential,  89 

Fick's  (.'-spring,  85 

Pick's  elastic,  86 

Hiirthel  s  elastic,  86 

m.ixiinuin  and  minimum,  85 

mercury,  cox.  195 

solutions  for  tilling  tubes  of,  195 
Man  his  solution,  693 
Marginal  veil,  746 
Mariotte's  experiment,  932 
Massage  of  muscles,  effect  of,  on  blood- 
pressure.  171 
'  Mast  '  <ells,  18 
Mastication.  300 
Maturation  of  ovum,  1008 
Maxwell's  spot.  994 
Meconium,  396,  1012,  1015 
Mediastinum,  209 

Medulla  oblongata,  anatomy  of,  767 
centres  of,  814,  815,  816 
development  of,  748 
Medullary  groove,  746,  1009 

sheath  of  nerve,  677 

development  of,  748 
Megaloblasts,  21 
Meissner's  plexus,  298 
Membrana  tectoria,  958,  961 
Memories,  storage  of,  866 
Meniere's  disease,  834 
Menopause,  1005 
Menstruation,  1005 
Mental  processes,  seat  of,  865,  866 
Mesenteric  ganglion,  inferior,  473 
Mesoblast,  mesoderm,  1008,  1009 
Metabolism,  endogenous,  497,  504,  505, 

exogenous,  497 

in  fever,  530.  596,  597,  600 

in  muscular  work,  537,  583,  584 

in  plants.  6 

nitrogenous,  laws  of,  535-539 

of  carbo-hydrates,  511 


Metabolism  of  embryo,  1017 
oi  fat,  522 
oi  living  matter,  6 
oi  proteins,  1.96 

Metamorphosis  of  larva',    phagocytosis 
111.  52 

Meta-proteinSi  2.  j,  9 
Methaamoglobin,  46,  67 

in  urine,  444 
Methylene     blue,     reduction     of,      in 

tissues,  205 
Methyl  orange  as  indicator,  24,  393 
Methyl  violet  as  test  for  acids,  324 
Metronome.  179 
Metschnikoff's  theory  of  phagocytosis, 

52 
Mett's  tubes,  318,  422 
Microblasts,  21 
Micturition,  471 

centre,  472 
Mid-brain,  747 
Milk,  assimilation  of,  549 

calcium  and  phosphorus  in,  542 

carbon  and  nitrogen  in,  546 

chemistry  of,  610.  611 

composition  of,  546,  549,  1021 

formation  of  fat  in,  527 

iron  in.  543,  102 1 

salts  of,  102  r 

secretion  of.  1022 

without  pregnancy.   1022 
Milk-curdling  ferment,  323,  327,  61 1 
Millon's  reagent  8 
Miniature  stomach,  373 
Miotics,  911 

Mirrors,  reflection  from,  892,  893 
Mitosis,  5,  1006 
Mitral  cells  of  olfactory  bulb,  816 

valve,  7S,  190 
Moist  chamber.  704 
Molecular  concentration,  398 

layer  of  cerebellum,  830 
of  olfactory  bulb,  816 
Molisch's  test  for  carbo-hydrate,  11 
Monakow's  tract,  765,  781,  848 
Monobutvrin,    splitting   of,    bv   blood, 

528 
Monochord.  998 
Mono -saccharides,  3 

absorption  of,  4 id 

as  glycogen-formers,  513 
Moreau's     experiment     on     intestinal 

juice,  386 
Morphine,  action  of,  on  motor  centres, 
858 

quantity  of,  for  dog.  55,  186 
Mother -substances    of    ferments,    328, 

33i.  353-  354 
'  Motor-areas,'  843.  844 

in  dog.  843,  889 

in  hedgehog,  872 


[048 


INDEX 


'Motor-areas'  In  man.  844,  851,  855, 
860 
in  monkey,  8  1 1 
in  opossum,  872 
in  1  irnithorh)  ai  bus,  872 
in  rabbit,  87a 
path,  774,  77''.  7<i- 
recovery    alter   ablation    of,    848, 

850,  851 
sensory  functions  of,  844,  856 
Mountain  sickness,  275 
Movements,  co-ordination  of,  798,  831, 
837 
forced,  836.  837 
Mucin,  3 

of  bile,  335 
Mucous  glands,  319,  345 

1  hanges  in  activity,  352.  425 
membranes,    sensibility   of,    981, 
1002 
Midler's  experiment,  273 
Murexide  test  for  uric  arid.  484 
Muscae  volitantes,  914 
Muscarine,     action    of,    on    digestive 
secretions,  387 
on  heart,  150,  183 
mi  pupil,  911 
Muscle,  afferent  impressions  from,  835, 

983 
path  for,  984 
composition  of,  (>(>(),  713 
degeneration  of,  698,  700,  814 
diffraction  spectrum  of,  642 
direct  excitability  of,  633,  706 
elasticity  and  extensibility  of,  030 
gases  of,  260 

general  physiology  of,  627 
glycogen  in,  514,  515 
heat-production  in,  583 
heat -shortening  of,  673 
lactic  acid  production  in,  667,  668, 

716 
oxygen   consumption  and  carbon 

dioxide  production  of,  263 
permeability  of,  671 
polarization  of,  726 
proteins  of,  672,  714 
reaction  of,  667,  716 
respiration  of,  261 
rigor  of,  263,  715 
smooth,  contraction  of,   645,  647, 

713 

sound,  660 

stimulation  of,  632,  704,  707 

by  voltaic  current,  636.  704 
structure  of,  6 

in  polarized  light,  641 
Muscles,  antagonistic,  co-ordination  of, 

838 
Muscle-interruptor,  automatic  648 
Muscle-nerve  preparation,  to  make.  703 


Muscle  spindles,  229,  983,  984 
Muscular    contraction,    chemical    phe- 
nomena of,  666 

durati >f.  642 

formula  of,  684,  686,  742.  743 

lie, u  produced  in,  583,  663 

idio-museular,    (>=,<) 

in  absence  of  oxygen,  201,  295 

intliieni  r   ol    fatigue    on.    648, 
652,  708.  709 
of  load  on.  645,  708 
of    mental     fatigue     on. 

654 
of  temperature  on.   647, 

706 
of  veratrine  on,  654*  709 
isometric  and  isotonic.  645 
lactic  acid  formed  in.  667,  668, 

716 
latent  period  of,  642,  710 
mechanical     phenomena     of. 

643 
mechanism  of,  640 
of   smooth    muscle,  645,  647, 

713 

optical  phenomena  of,  638 
physico-chemical      conditions 

of,  671 
recording  of,  706.  707 
reversal  of  stripes  in,  640 
seat  of  fatigue  in,   651,    652, 

708,  709 
source  of  energy  of,  537,  586, 

669 
superposition  of,  656,  711 
velocity  of  wave  of,  659,  719 
voluntary,  660 

seat  of  fatigue  in,  652 
work  done  in,  646 
Muscular  fatigue,  650 

influence    of    stimulants    on. 

552 
seat  of  exhaustion  in.  (151.  052 
exercise,   effect  of,   on   pulse,    97, 

192 
sensations,  835,  856,  862,  869,  968, 

982 
sense,  983 

tetanus,  656,  657,  711 
tissue,  action  of  extracts  of,  569 
tone,  813,  886 

work,  nitrogen  metabolism  in,  .^37 
relation  of,  to  energy  expended, 
583,  665,  666 
Musical  centres,  861 
M\  dratics,  911 
Myelination,   time  of,   in   cortex,   854, 

855 
M  \  ocardiogram,  155 
Myocardiograph,  188 
Myogenic  hypothesis  of  heart-beat,  132 


TND1  A 


1049 


1  iph.  pendulum.  64  1 

-inipN-.  179.  707 
1  I.  7'3 

7*5 
7J5 
Myotatii  irritability,  802,  813 
j.  ma  .mil  thyroidectomy, 


560 


.1  s«  ration,  435 

\'-.ir-| it  "i  vtsiodi!  915,  9*7.  987 

S'ecturus,  ablation  of  cerebral   hemi- 
spheres in.  s 1 1 
equilibration  in,  after  destruction 

oi  intern. il  ear.  836 
intracorpuscular  crystallization  in 
erythrocytes  of,  62 
e  ph.i-e  iii  coagulation.  38 
ttive  variation.   See  Action  current 
Neo  e-eells.  677 

1  banges  in,  after  section  of  axon, 
i"i  1 
in  fatigue,  874 
with  age,  755 
growth  of,  754 
number  of,  in  brain,  757 
Nerve,  chemical  changes  in,  68o,  881 
1 'imposition  of,  690,  881 
1  ondnctivity  of,  686 

1  n  >ssing,  694,  867,  868 
degeneration  of,  691 

chemistry  of,  692 
double  conduction  in,  687 

*    of   temperature   on   excita- 
bility and  conductivity  of,  681 
effect  of  voltaic  current  on,   683, 

741 
fatigue  of,  680 
isolated  conduction  in,  689 
minimum  stimulus  of,  681 
pattern  in  regeneration,  695 
polarization  of,  726 
refractory  period  of,  680 
regeneration  of,  694 

chemistry  of,  693 
stimulation  of,  680. 
structure  of,  677 
Nerve-ending,  motor,  634,  635 
Nerve-fibres,  enumeration  of,  775 

size  of,  745,  758 
Nerve  impulses,  '  antidromic'  165,  688, 
701 
nature  of,  679 
velocity  of,  689,  713 
in  reflex  arcs,  800 
temperature     co-efficient 
of,  679 
Nerve-muscle  preparation,  to  make,  703 
Nerves,  classification  of,  702 

cutaneous,    phenomena   after  sec- 
tion of,  975-981 


Nerves  in  titu,  law  of  contraction  for 

686.  743 
trophic  699 
Nervous  activity,  chemistry  of,  880.  881 
1  issue,  effects  of  extracts  of,  569 
reaction  of,  691 
Nervus  erigens,  [64,  i ' > 5 .  167,  501,473, 
884 
pudendus,  vaso-motors  in,  [64,  167 

Neural  axis,  primitive,  759 

<  anal,  development  of,  746 
Neuroblasts,  746,  754 
Neurofibrils,  748,  750 

theory  of  continuity  of,  751 
Neurogenic   hypothesis   of    heart-beat, 

130 
Neuroglia.  758,  817 
Neurokeratin,  690 
Neurons,  677,  748-757 

development  of,  747,  752.  754 
fibrils  in,  748 
nutrition  of,  756 
processes  of,  749,  752 
scheme  of  motor,  753 
varieties  of,  753 
Nicotine,  action  of,  on  ganglion  cells  of 
heart,  150 
of   salivary   glands,    363, 
365 
on  intestinal  movements,  307 
on  skeletal  muscle,  634,  635 
on  sympathetic  cells,  165 
Night-blindness,  948 
Ninth  nerve.     See  Glosso-pharyngeal 
Nissl's  bodies  in  nerve-cells,  749,  755, 
873 
chromatolysis    of,    369,     745. 

756,  873,  874 
method  of  staining,  749 
Nitrogen,  execretion  of,  in  starvation. 
532 
after  muscular  work,  538 
variation  of,  with  protein  in 
food,  535,  612 
estimation  of  total,  482 
in  proteins,  1,  529 
of  body,  528 
requirement,  minimum,  533,  544, 

539 
starvation,  531 
Nitrogenous  equilibrium,  529,  533 
metab  lism,  496 

influence   of   fat    and    carbo- 
hydrates on,  523,  534 
of  muscular  work  on,  537, 
538 
in  starvation,  530,  532 
laws  of,  535,  537 
Nceud  vital,  814 
Normal  solutions,  439^ 
Normoblasts,  21 


I<>;0 


INDEX 


Notochord.  1009 
Nuclease,  507.  5x0 
Nucleic  acid,  1.  2.  5 

Nucleins.  1,  2,  506 

formation  of  iirii  <n  id  from,  506 
Nuclei  pontis,  76*.  777.  7-1 
Nucleolus,  874,  1 
Nucleo-proteins,  1,  2.  5,  42,  47.  506 

hydrolysis  of,  507 

influence  ■ 't.  on  coagulation,  34,   (8 
Nucleus  ambiguus.  825 

cuneatus  and  gracilis.  767,  772 

dentatus,  760,  780 

globosus,  780 

of  Deiters,  780,  781,  7g2,  824 

tei  ti.  780,  824 
Nucleus,  function  of,  5 

daughter,  5,  1007 

influence  of,  on  oxidation,  260 

structure  of,  5 
Nucleus-plasma  relation.  874 
Nussbaum's     experiments     on     renal 

excretion,  460 
Nystagmus,  831 

Oatmeal  as  a  food.  546,  547 
Obermayer"s  reagent,  479 
Obesity,  Banting  cure  for,  534 
Occipital  cortex  and  vision,  858,  859 
Octopus  macropus,  saliva  of,  361 
Oculo-motor  or  third  nerve,  819 
Odours,  classification  of,  965 
OZdema,  408 
OZsophagus,   contraction  of,    302,    303, 

713 
successive  combination  of  reflexes 
in.  806 
(Estrus,  1006,  1022 
Ohm.  616 

re  1  iprocal,  26 
Ohm's  law,  616 
Oleic  acid.  12 
Olein.  4,  12 
Olfactometer,  966 

Olfactory  bulb,  structure  of,  816,  818 
glomerulus.  816 
n<r\  1 

sensations.  965 
trad 

development  1  I 
Olive.  767,  771 

connections  of  cerebellum  with.  780 
superior,  824 
Oncometer,  117,  467 
Opacities  inthe  eye.  914-  929 
Ophthalmometer,  906.  990 
Ophthalmoscope,  direct   method.    010. 
920.  994 
indirect  method,  919.  994 
testing  errors  of  refraction  by.  804, 
919.  994 


Opitz  on  velocity  of  blood  in  veins,  121. 

122 
Opsonic  index,  53 
Opsonins,  53 
Optical  constants  of  the  eye,  902 

of  reduced  eye,  904 
Optic  axis,  898,  914 
disc,  900,  902,  932 
lobes,  829 
nerve,  818 

efferent  fibres  of,  819 
radiation,  785,  818 
thalami,   747,   768,    772,    781,    784, 
818,  820 
and  tegmental  path,  773,  779. 

784 
functions  of,  829 
Optimum  temperature,  315 
Optogram.  935 
Orbicularis     oculi.      displacement     of 

centre  for,  872 
Orcin  reaction  for  pentoses.  491 
Ornithin,  503 
Osmic  acid  test  for  fat,  12 
Osmosis,  398 

Osmotic  pressure,  398,  492 
of  proteins,  406 
of  solid  tissues,  411 
resistance  of  erythrocytes.  64 
( otoconia,  833 
Otoliths,  833 
Output  of  heart,  127 
Ovary,  grafting  of,  1023 

influence  of  uterus  on,  1005,  1006 
internal  secretion  of,  556,  1005 
Overtones,  280 
Ovulation,  1004,  1006 
Ovum,  development  of,  1006 
Oxalates  and  coagulation,  34,  55 

in  urinary  sediments.  442.  495 
Oxidation,  seats  of,  259 

nature  of,  in  body.  264 
Oxidizing   ferments.    42.   68.    2^4.  295. 

314,  507,  509.  5io 
I  >  walaniu,  332 

Oxybutyric  acid  in  diabetes,  520 
Oxvdases.     See  Oxidizing  ferments 

•  n.   amount  consumed.   241.   243. 

293 
artificial  respiration  with.  189 
balance,  540 
deficit.  242.  mi 

dissociation  curve  of  blood,  255 
estimation,  251 
in  blood,  252 
inhalation,  46 
in  heart.  585 
in  resting  musch 
partial  pressure  of,  in  blood  and 

alveolar  air.  258 
toxie  effects  of.  271 


INDEX 


105 1 


!,    used   up  in   muscular   work, 
26l,  26  ; 
Oxyntii  or  acid-forming  cells.  1 1  5,  in 

350 

I  Kvplieiivl.il.min.  2 
<  txyprolin, 

11  in.  608 

Pa<  ini.iii  corpuscles,  <k> 

Pain,  9,69,  968,  973,  1000.  1001 

r.iitrc  for.  856 

referred,  790,  982,  980 
sensations   after    section    of    cu- 
taneous aerves,  975-  979 
Painful  impressions,  paths  of,  795 
decussation  of,  793 
from  internal  organs,  799.  97.; 
Palmitin,  4 

Pani  teas,  changes  in.  during  secretion, 
W" 

internal  secretion  of,  553 

nerves  of,  378 
relation  of  spleen  to,  382 
Pancreatic  juice,  artificial,  428 

adaptation  of.  to  food,  381 

to  lactose,  382 
composition  of,  330 
ferments  of,  331,  428 
freezing-point  of,  357 
quantity  of,  331 
rate  of  secretion  of,  380,  381, 

382 
secretory  pressure  of,  382 
t.>  obtain.  330.  429 
Papillary  muscles.  78,  79 
Parabiosis,  1024 

Paradoxical  contraction,  729.  741 
Paralysis,  crossed,  822 
Paralvtic  secretion  of  intestinal  juice, 
386 
of  saliva,  369 
Paramyosinogen,  672,  715 
Paraphasia,  864 

Paraplegia,  reflex  movements  in,  812 
Parasternal  line,  82 
Parathyroids,  558 

effect  of  excision  of,  559 
Parenteral  absorption.  418 
Parotid,  changes  in,  during  secretion, 

346 
Pars  intermedia  of  seventh  nerve,  821, 
822 
of  pituitary,  566 
Parthenogenesis,  1004 

artificial,  1007 
Partial  pressure,  248 

measurement  of,  249,  256 
of  air  of  alveoli,  242,  257 
of  blood-gases,  256 
Parturition,  1019 
Pause  of  heart,  79,  80 


Peduncle,  inferior  cerebellar.     See  Res- 
tiform  body 
middle  cerebellar,    760,    768,    780, 
83a 

superior  cerebellar,  760.  772,  780 
Pelvic  nerve,  164,  165,  310,  884 
Pendulum  myograph,  644 

movements  of  intestine,  306 
Pentoses,  tests  for,  490 
Pentosuria,  450,  520 
Pepsin,  323,  326,  426 

secretion  of,  349,  350 
rate  of,  377,  378 
Pepsinogen,  353 
Peptones,  2,  3 

absorption  of,  419 

effect  of,  on  coagulation,   35,   40, 

55 
on  blood-pressure.  201 

in  diet,  534 

reactions  of.  10,  487 
Percussion  of  lungs,  217 
Pericellular  basket,  754 
Perikaryon  or  cell-body,  748 
Perilymph,  954,  956 
Perimeter,  946 
Perimetric  chart,  947,  991 
Periodic  breathing,  238,  275,  288 
Peripheral  nervous  centres,  808 

reference  of  sensations,  980 
Peristalsis,  302,  303,  306,  659 
Peristaltic  rush,  308 
Peritoneal  cavity,  absorption  from,  406 
Peritoneum,  sensibility  of,  973,  981 
Pernicious  anosmia,  blood-count  in,  19 

quantity  of  blood  in,  49 
Peroxydase  in  blood-corpuscles,  68 
Personal  equation,  873 
Perspiration.     See  Sweat 
Pettenkofer's   test   for   bile-acids,  377, 

430 

Peyer's  patches,  formation    of    lympho- 
cytes in,  22,  298 

Phagocytosis,  51 

Phakoscope,  906,  987 

Phenol,  formation  of,  in  intestine,  395 
in  urine.  445.  532 

Phenolphthalein  as  indicator.  24,  393 

Phenyl-alanin,  1.  332 

Phenvl-hvdrazine   test   for  sugar.   320. 
488 

Phlorizidin  and  fat  migration,  527 
diabetes,  521,  609 
effects  of,  on  foetus,  1016,  1017 

Phloroglucin  reaction  for  pentoses,  490 

Phonograph,  analysis  of  vowel  sounds 
by,  284 

Phosphates  in  urinary  sediments,  439, 

494 

in  urine,  444.  486 
Phosphatides,  337,  526,  690 


1 052 


INDEX 


Phosphenes,  924 

Phosphorescence,  oxidation  in,  260 
Phosphorite  acid,  estimation  of,  478 
Phospho-proteins,  3 
Phosphorus  in  milk.  5  \z 

influence  of.  on   pn  tein   metabo- 
lism. 526 
poisoning,  fat  metabolism  in,  525 
Photo-chemical  substam  es,  735,  9 ;  1 
Photo-electric  reactions,  735 
Phrenic  nerves,  223,  224,  289 
.ii  1  [on  current  <>f,  724 
union  of,    with   sympathetic, 
696 
nuclei,  connections  of,  22? 
Physiological  salt  solution.  178 
Physostigmine,  action  of,  ondigestive 
secretions,  387 
on  pupil,  91  1 
I'm  mater,  758 
Pigmented   epithelium   of  retina,    900. 

934 

and  visual  purple,  936 

Pigments,  excretion  of,  by  kidney,  438 

Pigment  spots  and  light  sensation,  897 

Pilocarpine,     action    of.    on    digestive 

secretion  •,  387 

on  heart  nerves,  150,  183 

on  lymph  formation,  408 

on  pupil,  911 

.mi  salh ary  secretion,  425 
Pilo-motor  nerves,  165,  695,  884,  975, 

979 
Pineal  body,  571,  830 
Piotrovvski's  reaction  for  proteins.  7 
Pitch,  280 

appreciation  of,  962 
sensitiveness  of  ear  for  sounds  of 
different,  965 
Pithing  a  frog,  177 
Pitot's  tubes,  113 
Pituitary  body,  819,  H30 

action  of  extracts  of,  568 
effects  of  removal  of,  567 
internal  secretion  of,  566 
Placenta,  autolysis  in,  510 
bile-pigment  in,  350 
exchanges  in,  1013 
glycogen  in,  514,  1014,  1016 
passage      of       blood  -  substances 
through,  1014 
Plants  and  animals  compared,  6 
Plasma,  blood-,  15,  25,  31,  41 
Plasmine  of  Denis,  31 
Plasmolysis,  400 
Plasmon,  535 
Plethora,  hydra?mic,  462 
Plethysmograph,  117,  159.  194 
Pleural  cavity.  209 
Pneumonia  after  section  of  vagi,  237 
Pneumothorax,  209 


Poikiloderma]  animals,  ^72,  577 
I'oiseuille's  space,  100.  177 

laws  for  capillary  flow,  77 
Polar  bodies,  1007 
Polarimeter,  489 
Polarization  of  light.  641 

ot  muscle  -ind  nen  e,  726 
positive,  727 
Pole-changer,  625 

Poliomyelitis,     anterior,     degeneration 
in.  77i 
knee-jerk  in,  Mi  2 
nerve  anastomosis  in,  868 
Polycythemia,  19,  23 
Polygraph,  94,  193 
Polypeptides,  2,  3,  535 
Polysaccharides,  3 

absorption  of.  416 
Pons,  747.  768,  777,  784 

functions  of,  828 
Portal  vein,  dextrose  in,  417 
vaso-motors  of,  164 
Posterior    corpora    quadrigeinina   and 
auditory  nerve,  824,  828 
horn,  cells  of,  762 
longitudinal  bundle,  77^,  824 
root-fibres,  branching  of,  769 
overlapping  of,  790,  857 
roots,  degeneration  after  section  of, 
693,  768,  769 
loss  of  movement  after  section 

of.  857 
loss  of  sensation  after  section 
of,  790 
Postero-exteraal    and    postero-median 

columns,  763,  768 
1'ost-ganglionic  fibres,  868,  883 
Post-sphygmic  period  of  cardiac,  cycle, 

90 
Posture,    influence    of,    on    blood-pres- 
sure, 173,  199 
on  pulse-rate,  99.  195 
Potassium  in  nerves,  961 
in  erythrocytes,  255 
in  nuclei,  5 

microchemica]  test  for,  5 
relation  of,  to  heart-beat,  139,  185, 
186 
Potassium    ferrocyanide   test   for  pro- 
teins, 8 
Potential,  615 

differences  of,  in  tissues,  718 
Precipitins,  30,  418 
Predicrotic  wave,  95 
l'refrontal  region  of  cortex,    function 

of,  866 
Preganglionic  fibres,  868,  883.  884 
Prepyramidal    tract.     See    Monakow's 

tract 
Presbyopia,  916 
IYesphygmi<  period  of  cardiac  cycle  90 


l.\hi  X 


1053 


r  ind  depressor  nesves,  157-  '/""•'• 

u  t'-n.ii.  too,  i"  ;.  195.  198 
end  1.  90 

intr.i"  r.mi  ll 

intrathorai  i< .  -•!".  --1 

itive  in  heart-.  92,  96 
respirator] 

:  saliva,  363 

sensations,  <)<>s.  <>7i.  981,  1000 
Primary  colours,  94 1 

ion  "f  eyes,  951 
Primitive  streak  and  groove,  1008 
Pnx  hromatin.  s 

Projection  >>f  image  into  space,  923,  928 
Prolin,  3  )a 

Pronucleus,  1007 
Proprio-ceptive  reflexes,  810 

m  and  cerebellum,  831,  832 
Proprio-spinal  fibres,  761.  765 
Pro-secretin.  380 
Prosthetic  groups.  2 
Protagon,  47,  691 
Protamins,  2 

influence  of,  on  coagulation.  41 
Proteins,  absorption  of,  41S 

circulating,  536 

classification  of,  2 

cleavage  products  of,  1,  332 
in  diet,  535 

composition  of,  1,  525 

conjugated,  2 

derivatives  of,  3 

formation  of  carbon  dioxide  from, 

509 
of  fat  from,  515 
of  glycogen  from,  512 

in  urine,  443,  486 

living  and  dead,  499 

metabolism  of,  496 

endogenous,  497,  534,  536.  545 
exogenous,  497,  535 
influence  of  poisons  on.  526 

minimum    requirement     in    food, 

533.  544,  545-  583 
muscular  energy  from,  538 
passage  of,  through  placenta,  1014 
reactions  of,  7 
scheme  for  testing  for.  13 
specificity  of,  3,  418 
synthesis  of,  2,  420,  497,  510 
Protein-sparing   action   of   other   food 

substances,  523,  534.  531 
Proteolysis,  332 

difference  between   acid  and   fer- 
ment, 535 
Proteoses,  2,  3,  325.  421 

action  of,  on  blood-pressure,  157, 

201 
influence  of,  on  coagulation,  35.  40, 
55 


es,  tests  for,  10.  486 
Pi  otopal  tiii  sensibility,  981 
Pn iti iplasm,  composition  •*!.  1 

functions  of,  6,  628 

structure  of,  4 
Prothrombin,  33 
Protovertebrae,  1009 
Pseudo-fatigue,  653 
Pseudo-globulin.  42 
Pseudopodia,  16,  627 
Pseudo-reflexes,  802 
Psychical  secretion  of  gastric  juice,  374 
of  saliva,  371 

processes,  seat  of,  865.  866 
Ptosis,  820 
Ptyalin.  320.  422 
Pulmonary  catheter.  257 
Pulse,  the,  92 

anacrotic,  97 

aortic,  95 

characters  of,  94.  192 

dicrotic  wave  of,  94,  95 

frequency  of,  98.  195 

influence  of  posture  on,   99,    156, 
192 

in  foetus,  1017 

respiratory  variation  in   269 
of  swallowing  on,  155,  195 

jugular,  91,  193 

venous,  91,  120,  122,  193 
Pulse-tracings,  94.  192 

effect  of  amyl  nitrite  on,  97,  192 
of  muscular  exercise  on,  97, 
192 

from  different  arteries,  97.  193 

from  jugular  vein,  137,  193 

secondary  waves  of  oscillation  in, 

95 
Pulse-wave,  disappearance  of,  in  capil- 
lary region,  103 
reflexion  of,  95,  96 
velocity  of,  99 
Pulsus  alternans,  142 

bigeminus,  142 
Pulvinar,  818,  829 
Puncture  fever,  595.  596,  597 

glycosuria,  518,  555 
Pupil,  Argyll-Robertson,  910 

changes    in,    during    accommoda- 
tion, 909 
constrictor  nerves  of,  883.  908 
dilator  nerves  of,  908,  996 
eccentricity  of,  914 
influence  of  drugs  on,  911 
of  adrenalin  on,  563 
of  light  on,  818,  829 
photography  of,  910 
Purin  bases,  2,  397,441,  538,  507 

in  fever,  601 
Purkinje's  cells  in  cerebellum,  753,  754 
figure,  930,  998 


1054 


INDEX 


Purkinje-Sanson  images,  906,  987 
Pus  cells,  origin  of,  .  1 

gly<  ogen  in,  \r 

Putrefaction.    ,unl    1 1  \ stallization     oi 
haemoglobin,  1 1 
1 1 .1 1  nr >] \- 1  i-  effect  of,  zj,  62 
pri ducts  of  proteins,  action  of,  on 

blond-pressure.  570 
Pycnometer,  57 
Pyloric  sphincter,  305.  309 

regulation  of  opening  of,  305, 
380,  392 
Pyramidal  cells,  751 
giant.  774 
tracts,  765,  777 

connections  of.  774,  77s.  852 
in  different  animals,  776 
relations  of,  to  pons.  828 
Pj  ramids,  767 

connections  of,  774 
decussation  of,  70s.  774.  777,  7(12 
Pyrimidin     bases     from     uucleiu    sub- 
stances, 507 
Pyrocateohin  in  urine,  436,  445 
Pyrogallic  acid,  absorption  ol  oxygen 
by,  251 

Quadratus    lumborum,    action    of,    in 
respiration,  211 

Radiation,  loss  of  heat  by,  578 
Radium  rays,  visibility  of,  950 
Raftinose,  316 

Reaction,  in  physico-chemical  sense,  23, 
439 
of  blood,  23,  54.  57 
of  degeneration,  698 
of  intestine,  392,  393 
of  tissue  liquids,  23 
of  urine,  439 
regulation  of,  24 
time,  872 
Receptive  substances,  150,  166,  635 

field  of  reflexes,  801 
Receptor  of  reflex  arc,  796,  798,  871 
Reciprocal  innervation,  in  reflex  move- 
ments, 801 
in  volitional  movements,  838, 

846 
of  bloodvessels,  171 
Recurrent  fibres,  372,  693,  79] 

sensibility.  791 
Red  nucleus,  781,  784 
Reduced  eye,  903 
Reductases,  509 

Reference  of  sensations,  peripheral,  980 
Referred  pain,  790,  980,  982 
Reflection  of  light,  892,  893 
Keflex  action.  796,  885,  887 

anatomical  basis  of.  707 
inhibition  iu,  boo,  801 


Reflex  arcs,  irreciprocal  conduction  in. 

688,  799 
pei  uliarities  oi  1  onduction  in, 

799,  800 
refractor)  state  in,  800 
summation  of  stimuli  in,  800 

'  cardiac  death,'    I  =>(>.  235 
centres  in  cord,   s  1  1 
peripheral,  808 

figure,  804 

time,  809,  886 
Reflexes,  action  oi  stry<  hnine  on,  801 
of  tetanus  toxine  on 

iitcr-discharge  of,  800 

axon-,  372,  809 

combination  of,  805 

1  ommon  pal  h  of,  rg;.  7>>% 

compounding  of,  798 

co-ordination  of.  .sos. 

1  r<  issed,  793 

differences        between        a  irl  i'  a 
reactions  and,  X47 

extero-  and  proprio-ceptive,  Bio 

facilitation  of.  805.  807 

from    sympathetic    ganglia,     $71, 
809 

in  disease,  810 

inhibition  of,  800,  801,  806.  886 

irradiation  of,  802,  885 

'  purposive  '  character  of,  805 

reinforcement  of,  805,  807 

resuscitation  of,  880 

spinal  relation  of,  to  brain.  806 

superficial  and  deep,  810.  81 1 
Refraction  of  light,  894-896 

in  eye,  902 
Refractive  index,  894 

of  media  of  eye,  903 
Refractory  period  of  heart.  141 

in  reflex  arc,  800 
Regeneration  of  nerve,  694-698 
autogenetic  theory  of, 
chemistry  of,  694 

of  nerves  after  anastomosis,  867 

of  tissues,  1003 
Reil,  island  of,  855,  865 
Renal  nerves,  161,  468,  469 

secretion,  theories  of,  455 

tubules,  453.  454 

vein,  ligation  of.  468 
Renin,  570 

Rennin,  323,  326,  327.  353.  427 
Reproduction,     a    property    of    living 
matter,  /. 

sexual,  1004 
Reserve  air,  220,  291 
Residual  air.  220.  291 
Resistance,  ele<  meal.  615 

measurement  of.  60.  617 

osmotic,  oi  erythrocytes,  64 

thermometer,  574,  664 


INDEX 


1055 


ini  e,  999 

,,l  ,..,r.  80,  660 

.   .,,    .,.  essory  phenomena  of, 

afferent  aerves  of,  233,  289 
.ni.l  pulse,  relation  in  frequency  of, 
■ig 

apparatus,  241 
artificial,  187.  n  1 

influence   of,    on   blood-pres- 
sure, -"■> 

with  oxygen,  189 
calorimeter,  a  1  c,  579>  613 
chemistry  of,  jjo,  292-295 

in  -Stokes,  238 
comparative  physiology  of,  206 
cutaneous,  206,  275 
,  fferent  aerves  of,  223 
external  and  internal,  206 
forced,  214.  2iu,  246 
frequency  of,  21.^ 
gaseous  changes  in,  241,  251 
beat  lost  in,  579.  578,  613 
in    condensed    and    rarefied    air, 

272-275 
influence    of    vagi    on,    224-229. 
289 
of  cutaneous  nerves  on,  229 
of  '  higher  paths  '  on,  224 
of  muscular  exercise  on,  229 
on  blood-pressure,  265 
on    capacity    of    pulmonary 

vessels,  266 
on  pulse-rate,  269 
internal,  206,  257,  259 
mechanical  phenomena  of,  200 
of  muscle,  261-264 
of  tissues,  264 
reflex  inhibition  of,  229 
regulation  of,  230 
types  of,  213 
Respiratory  arhythmia,  270 
automatism,  233,  814 
capacity,  220,  291 
centre,  223 

action  of  alcohol  on,  175,  236 
of    carbon     dioxide     on, 

230.  242 
of  chloroform  on,  234 
of  deficiency   of  oxygen 

on,  230,  275 
of  venous  blood  on,  230- 
232 
initial  rate  of  discharge  of,  in 
resuscitation,  234 
centres,  spinal,  236 
'  dead  space,'  221 
exchange,  241 
impurity,  permissible,  243 
movements,  21 1-2 13 
duration  of,  218 


Respiratory  organs,  anatomy  of,  207 
pressure!  222 
pump,  121 

quotient.  242,  295 

in  different  animals,  246 
in  muscular  work,  242 
sounds,  2i(>,  291 

tracings,  218,  226,  227,  228,  287, 
288 
Restiform   body,    760,    767,    771,    779, 
780,  823 
and  direct  cerebellar  tract,  771 
and  olive,  780 
constituents  of,  779,  780 
Restitution  processes,  585 
Resuscitation      of      central      nervous 
system,  879,  880 
of  heart,  130,  159 
of  reflexes,  880 
of    respiratory    mechanism,     233, 

880 
scratch-reflex  in,  805 
Reticular  formation,  768 

posterior,  763 
Retina,  adaptation  of,  935.  946 
curves  of  excitation  of,  1)4.' 
development  of,  747 
electromotive  phenomena  of,  734, 

735.  934 
fatigue  of,  944,  997 
intermittent    stimulation   of,    937 

938,  998 
photography  of,  910 
pigmented  epithelium  of.  900,  932, 

934.  936 
sensibility  of  different  parts  of.  946 

of,  for  colours,  947 
structure  of,  899 

time   necessary   for   excitaton    of, 
937 
Retinal  bloodvessels,  shadows  of,  930, 
932,  998 
image,  formation  of,  902,  986 
size  of,  904 
Retinoscopy,  920,  994 
Rheocord,  619,  620 

simple,  620,  705 
Rheotome,  differential,  723 
Rhinencephalon,  817,  862 
Rhodopsin.     See  Visual  purple 
Ribs  in  respiration,  212 
Rigor  mortis,  608,  671 

analogies  of,  to  muscular  con- 
traction, 673 
influence  of  labyrinth  on.  835 

of  nerves  on,  675 
production  of  carbon  dioxide 
in,  263,  673 
of  lactic  acid  in.  669,  711 
removability  of,  676 
time  of  onset  of,  675 


ic>5fi 


INDl  X 


Rigor,  beat-,  26  |,  67 1 

production  >>f  carbon  dioxide 

in.  . 
Ringer's  solution.  186 
Ritter's  tetanus,  636.  662,  7-7-  743 
Ritter-Valli  law, 
R.kIs  ami  cones  111  \  ision,  932.  935,  936, 

948 

Rolando,  fissure  "t.  9  \\,  856 

substance  of,  759.  763 
Rontgen    rays,    for    study    of    gastrii 
movements,  306.  31 1 
of  lungs,  217 
of  vomiting.  312 
visibility  of.  950 
Root -fibres,    posterior,    course    of,    in 

cord,  769,  791 
Roots  of  spinal  nerves,    functions  of, 
79O,   7')-'.  884 
section     and    stimulation    of 
884.  885 
Rosolic  acid  as  indicator,  24 
Rubro-spinal    tract.     See    Monakow's 
tract. 

Saliva,  action  of,  in  the  stomach,  322 
adaptation  of,  to  food,  369 
amylolytic  action  of,  319,  423 
chemistry  of,  319.  422 
freezing-poin    of,  358 
functions  of,  320 
influence  of  nerves  on  secretion  of, 

363-371 
paralytic  secretion  of,  369 
reflex  secretion  of,  369 

in  vomiting,  312,  369 
secretory  pressure  of.  363 
Salivary  centre,  371 
corpuscles,  320 

fistula,  370  i 

glands,  319.  345 

action  currents  of.  734 
blood-flow  in,  during  activity, 

364 
changes  in,  during  secretion, 

346,  347.  352 
cranial  nerves  of.  362.  424 
heat  production  in.  364.  586 
removal  of,  571 
svmpathetic    nerves    of,    363, 

425 

'  trophic -secretory  '   fibres  of, 

366 
Salmin,  2,  503 

Salol,  action  of,  on  bile  secretion,  388 
Salt-hunger,  542 

gastric  secretion  in.  351 
Salt  solution,  physiological,  178 
Salts,  absorption  of,  417 

action  of,  on  heart  muscle,  185 

in  diet,  549 


S.ilis  in  metabolism,  5 1 1 
of  bile,  337 
"t  bone,  sz<) 
■  it  erythro<  ytes,  43 

17 

of  living  matter,  1 

of  lymph,  50 
of  milk.  542.  550 
<>f  must  le,  667 
oi  serum,  42 
of  urine,  \  j6,  \\\.  \\  g 
passage  of,  through  placenta,  1013 
Saponification  of  fats,  II,  12,  338 
Saponin,  action  of,  on  blood-corpuscles. 

27,  28,  62 
Sarcolactic  acid.     See  Lactic  acid 
Sarkin.     See  Hypoxanthin 
Scalene  muscles,  in  inspiration,  21 1 
Scarpa's  ganglion.  823 
Scheiner's  experiment,  917.  987 
Si  hmidt's  fibrin-ferment,  32.  57 
Schiitz's  law  of  ferment  action,  317 
Sciatic  nerve,  to  expose.  198 
Scleroproteins,  2,  529 
Scopolamine,      passage     of,      through 

placenta,  1013 
Scratch-reflex,  the,  799,  800,  804,  805, 

806,  887 
Scurvy,    prevention   of,    by    vegetable 

acids.  552 
Sebaceous    glands,    sebum,    435,    473, 

527.  737 
Secondary  contraction,  729.  738 

with  heart.  188 
Secretin.  347,  379,  384.  429 

gastric,  375 
Secretion,  electromotive  changes  in,  734 
internal,  552 

of  corpus  luteum.  557 
of  kidney,  569 
of  liver,  552 
of  ovary.  556 
of  pancreas.  553 
of  parathyroid,  559 
of  pineal  gland.  571 
of  pituitary  body,  566 
of  spleen,  571 
of  suprarenals.  563,  201 
of  testes,  556 
of  thymus,  557 
of  thyroid,  558.  560 
paralytic,  369 
psychical,  371,  374 
Secretory  pressure  of  bile,  386 

of  pancreatic  juice,  382 
of  saliva,  363 
of  urine.  466 
Segmentation  of  food  in  intestine,  307 
Self-digestion  of  stomach,  360.  434 
'  Self-steering  '    of    respiratory  move- 
ments, 226 


/\  I'l  X 


1057 


Semii  ii'  ulac  i  anals,  8 

.unl  equilibration,  B  .  i 
and  ion  ed  in.  .\  ements,  - 
Semilunar  val\  es,  70.  191 
.uid  dicrotii  u.r> 
moment  ol   1  losui 
point 
Semisectioa  oi  cord,  793 

!  11  iatii  .11  of,  795,  796 
localization  of, 

after    section    of    cutaneous 

nerves.  980 
relation  of,  to  stimulus,  98  1 
Senses,  the,  B9] 

Sensibility  of  internal  organs,  97 
Sensori-motor    functions    oi    '  motor  ' 

cortex,  856 
Sensory  areas,  857 

paths  to  brain,  791,  7. 14.  77.) 
decussation  of, 
Serin,  332 

Serous  glands.  319,  340 
Serum,  24,  26,  27,  30,  41.  57 
composition  of,  41,  57 
conductivity  of,  317 
ferments  in,  42 
freezing-point  of,  26,  357 
specific  gravity  of,  25.  57 
reaction  of,  57 
Serum-albumin,    41,    42,    49.    57.   487, 
498 
amino-acids  in,  1 
crystallization  of,  3 
Serum-globulin,  32,  41.  42.  49,  57.  487 
Serum-proteins,  in  starvation,  498 

source  of,  498 
Serratus  posticus,  action  of,  in  respira- 
tion, 211 
Seventh  nerve,  822 
Sexual   organs,    internal    secretion   of, 

556 
Shadow  test.     See  Skiascopy 
Sham  feeding,  324.  352,  374 

in  puppies,  37.^ 
Shivering  and  temperature  regulation, 

59i 
Shock,  spinal,  7S6,  800,  808 
surgical,  175 

acapnia  as  a  factor  in,  169,  175 
Side-chains,  635 
Sighing,  239 

Sigmoid  flexure,  309,  311 
Signal,  electric,  626 
Silent  areas  of  cortex,  865 
Single  vision,  theories  of,  923 
Sino-auricular  junction,  stimulation  of, 
183 
node,  72 
Sinus  venosus,  72 

stimulation  of.  144 


Sixth  nerve  or  abdui  en 
Skate,  elei  tm  .il  organ  of, 

Sk.it. . I.    u  I 

Skatozyl  in  urine.  1  |6,  1 1 , 
Skm.  currents  ol 

exi  ration  i>v.  17  ; 

impulses    from,    in    equilibration, 

respiration  by,  275 

varnishing  "t,  270.  47 1 

Sleep.    S73 

amount  necessary,  876 
cerebral  circulation  in, 
depth  of,  876 

•  tie.  t  .>t.  on  pulse,  99 
g  iseous  exchange  in.  2 15 
intrai  ranial  pressure  in.  875 
plethysmography    tracings    from 

arm  in,  875 

theories  of  causation  of,  875 
Smell.  965,  999 

centre  for.  817,  861 
Snake  venom,  effect  of.  on  coagulation, 

39 
on  blood -corpuscles,  27 
Sneezing,  239 

Soda-lime,    absorption    of    carbon    di- 
oxide by,  241.  294 
Sodium,  relation  of,  to  heart-beat,  139 
chloride,     action     of,     on     heart- 
strips,  185 
amount  needed  in  food,  550 
influence    of     potassium 
salts  on,  550 
citrate  solution  for  blood -pressure 

tracings,  195 
hydrosulphite,  absorption  oi  oxy- 
gen by,  251 
Solidity,  judgment  of,  925,  926 
Sorbite,  relation  of,  to  dextrose,  3 
Soret's  hemoglobin  band  in  violet,  45, 

47 
Sound,  cranial  conduction  of,  960.  999 

pictures,  964 
Sounds,  complex,  analysis  of,  962 
Specific  energy,  870,  980 

sensibility,  980 
Spectroscope,  43,  65 
Speech,  282 

centre  for,  862-864,  872 
Spermaceti,  absorption  of,  414 
Spermatozoa,  development  of,  1004 
Spermin,  556 

Spherical  aberration,  912,  991 
and  irradiation,  950 
Sphincter  ani,  311,  B13 
cardiac,  302.  309 
ileo-colic,  308.  310 
pylori,  305,  309 
Sphvgmic  period  of  cardiac  cvcle.  90 
67 


INDEX 


Sphygmograms,  spbygmograph,   . 

192 
Sphygmonian  >iint' 1   "t  Krlanger.    10  p 
198 
of  Riva-Ro<  ci,  198 
Sphygmometer  oi   1 1 1 1 1   and    Barnard, 

106 
Spider-poison,     action    of,    on    blood- 
corpuscles,  27 
Spinal  canal.  746,  754 
Spinal  cord,  action  currents  of,  7  , 

action  of  strychnine  on,  707. 
801 
of  tetanus  toxine  on,  797, 
801 
anatomy  of,  762 
ascending  tracts  of,  763 
automatic  functions  of,  813 
centres  of,  811,  814 
complete  section  of,  786 
conduction    of    impulses    by, 

788 
descending  tracts  of,  764 
endogenous  fibres  of,  761,  765, 

795 
excitability  of  fibres  of,  788 
functions  of,  788 
grey  matter  of,  762 
removal  of,  787 
semisection  of,  793 
white  matter  of,  763 
Spinal  frog,  experiments  on,  885.  886 
ganglion,  cells  of,  747.  753 
fatigue  of,  809,  875 
tibres,  bifurcation  of,  7'") 
relation  of,  to  posterior  root- 
fibres,  693,  808 
preparation.      mammalian,      886, 

887 
reflexes,  796,  79a 
centres  for,  811 
inhibition  of,    800,    801,    806, 

886 
long,  ^01 

relation  of,  to  brain,  806 
^hort,  803 
respiratory  centres,  236 
roots,  functions  of,  790 

section    and    stimulation    of, 
884 
shock,  7.86 
Spindle,  nuclear,  1007 
Spino-tei  tal  tibres.  77- 
Spino-thalamic  fibres,  772 
Spirometer,  219,  291 
Splanchnic  nerves,  161,  309,  470,  518 
and    gastro-intestinal    move- 
ments 
and  glycogenolysis,  5*9 
and  iko-<  olic  spbin<  ter,  }io 


Spleen  and  blood-formation,  21,  571 
and  blood-destrw  tion,  21,  171 
and  formation  ol  buV-pigment,  s;i 
and  formation  oi  trypsin.  383 

proteolytic  ferment  of,  383 
relation  of,  i"  pani  reas,  },X2.  571 
removal  of.  571 
Spongioblasts,  746 

Spring  myograph,  643 

'  Staircase  '  or  '  treppe.'  1 »  ,.  op,.  631 

Standard  dietaries.  54  , 

solution     of    ammonium     sulpho- 
<  j  anide,  478 
of  sil\  er  nitrate,  478 
oi  uranium  nitrate,  478 
Standing,  ^37 

Stannius'  experiment,  132,  151,  183 
Stapedius,  822,  955,  961 
Stapes,  954,  055-  959 
Starch,  3 

action  of  acids  on,  II 

digestion  by  saliva,  320,  423 

tests  for.  10 
Starvation,  excretion  of  salts  in,  5 1-: 

loss  of  weight  of  organs  in,  530 

metabolism  in.  530,  532 

premortal  rise  in  urea  excretion  in. 

53i 

respiratory  quotient  in,  243 

serum  proteins  in,  498 
Stasis,  53-  177 
Stationary  air,  220 
Steapsin.  331,  334 
Stearin,  4 

Stenson's  experiment.  676 
Stercobilin.  336.  396 
Stereognosis,  856 
Stereoscope.  925 
Stereoso  >pi<   \  ision,  92  ( 
Stethograph.  287.  289 
Stethoscope.  191 

Stillmg's  sacral  and  cer\  i<  al  nu<  lei.  76a 
Stimulants,  550 
Stimulation,  law  of  polar,  1^7 

chemical,  of  nerve, 

el.  ctrical,  638,  68i,  685 
Stimuli,  adequate, 

smnmation  of,  655,  71 1 
Mokrs-Adanis    disease    ami    auriculo- 

ventricular  bundl  :,  137 
Stomach,  absorption  from,  191 

auto-digestion  of,  360,  434 

glands  ot. 

changes  in,  during  sei  retion, 
347 
movements  of,  304 
nerves  of,  309 

protection  of,   from  gastric  juice. 
359 


/  WDEX 


Stomach,  trans\ erse  band  of,   |i 

Strabismus,  8ao,  sj.-,  .,.- . 

Strawberry  extract,  effect  of,  do  lymph- 
flow,  |  I -• 

Sti  ia  a<  n-; 

String  galvanometer,  6x9 

Stroma  >>t  coli  mred  i  orpuscles,  1 5 

Str< imuhr,  1 1  j.  i  2-\  17? 

Strontium  and  bone  formation,  sij 

Strychnine,  action  of,  "ii  cord,  797,  801, 
886 
tetanus,  rhythm  of,  66a 

St min.  2 

Sublingual  ganglion,   |i 

Submaxillary    gland,    gaseous    metab- 
olism of,  -•<>  1 

Substance  oi  Rolando,  759,  76 ) 

Substantia  nigra,  768,  777 
is  entericus,   1 1 1 

action  of,   in  digestion,   342- 

344 

adaptation  of,  to  food,  387 
influence  "i  aerves  on,  Vs'1 
Suckling,  food  requirement  of,  549 
Sucrase.     Ste  Invertase 
Su<  rose.     See  Cane-sugar 
Sudo-motor  nerves.     See  Sweat-nerves 
Sugar,  absorption  of,  405,  |i<>.  433 
and  muscular  contraction,  5 17 
'  centre  '  in  bulb,  5 18,  555 
destruction  of,  in  blood,  517 
estimation  of,   by   Fehling's  solu- 
tion. 489 
by  polarimeter,  490 
excretion  of,  by  kidneys,  516,  609 
fate  of,  in  organism,  516 
t<  Tin. it  ion  of,  in  liver,  5  1 5 
in  blood,  41,  462.  511,  516.  519 

regulation  of,  554 
in  urine.  451,  488.  g  16 
phenyl-hydrazine,  test  for.  488 
Trommer's  test  for,  10.  488 
j  east,  test  for,  489 
Sulphates  in  urine.  437.  444.  415 

estimation  of,  479 
Sulphocyanide  in  saliva.  319,  422 

in  urine.  445 
Sulphur,  '  neutral.'  497 
Summation  in  reflex  arc,  800 

of  stimuli,  655,  711 
Superior  laryngeal  nerve.  825 

and  deglutition,  304 
and  respiration.  227.  289 
Superposition  of  contrai  tions,  656,  711 
Supplemental  air,  220,  291 
Suprarenal  capsules,  secretion  of,  563 
cholin  in  cortex  of,  556 
extract,   action  of,  157,    163,  201. 
563.  564 
secretion  of,  563 


Suprarenin,  56 1.     See  also  Adrenalin 
Surfai  ■■  "i  body,  rolai  ion  t"  mas 

149 

tens Influent  e  ol  bile  on,   ,  \o 

in  muscular  1  ontrai  t  ii  in,  640 
Suspensory  ligamt  nt,  900 

in  .n  c  ommodation,  907,  008 
Sul  Hi'  5,  203 
Sunning  nt  bloodvessels,  102  1 

oi  nerves. 
Swallowing,    effecl    of,    on    pulse-rate, 
155.  195 

Sweat.  473 

.  entres,  475 

nerves,  474,  17s.  979>  '>7'-~ 
quantity  of,   17  1.  588 
Swim-bladder,  gases  of,  2,y> 
Sylvian  aqueduct,  819 
Sympathetic,     abdominal,     reflex     in- 
hibition through,  15  t 
cardiac  fibres  of,  in  frog,  143,  146, 
184 
in    mammals,    147,     148, 
190 
cervical,  vaso-motor  fibres  in,  159. 
202 
dissection  of,  in  dog,  190 

in  frog,  1  Si 
fibres  for  salivary  glands,  367. 

160,  363.  424 
pilo-motor  fibres  in,  695 
pupillo-dilator,  fibres  of,  695 
regeneration  of,  693,  695 
union  of,  with  phrenic,  696 
course    of    vaso -motor    fibres    in, 

165 
ganglia,    action     of    nicotine    on. 

165 
development  of,  754 
supposed  reflexes  from.  809 
ganglion  cells,  754 
vibration,  999 
Synapse,  749,  785,  797,  800 

membrane  theory  of,  749,  751 
S3  ncope,  173 
Syncytium,  6,  1010 

Synergic    muscles    innervated    in    re- 
flexes. 803 
Syringomyelia,    dissociation    of  sensa- 
tions in,  795 
Systole  of  heart,  78 

Tachograph  gas,  115 
Tachycardia  in  disease,  826 
Tactile  impressions,   path   of,    in   cord, 
795 
sensations,  968 

centres  for,  856,  842 
Taenia  terminalis,  78 
Talbot's  law,  938.  998 

67 — 2 


lOfin 


INDEX 


Tallquist's  method  "i  estimating  harrno- 

^l"bin.  70 
Tambour  receh  iux.  3 ;.  2 1 7 

recording,  8  i.  192 
Taste,  966,  999 

I1ITVI-S   r,f.    Ba  I.    822,    825,    966 

1!  ions,    1  lassifii  ation    of,    967, 
999 
1  aste-buds,  966 
Taurin,  n; 
Taurocbolic  acid,  336 
Tea,  hi.  550.  551 
Tears.  435.  902 
Teeth,  300 

Tegmenta]  afferent  path.  772,  779 
Tegmentum,  768 
I  elodendrion,  749 
Temperature  in  axilla.  603 
in  cavities  of  heart,  503 
in  different  animals.  377 
influence  of  age  on.  607 
of  humidity  on,  588 
in  mouth,  603 
in  rectum,  577,  603 
of  blood,  577,  602,  604 
of  body,  daily  variation  of.  605 
of  brain.  585,  604 
of  skin.  574,  605 
post-mortem  rise  of,  607 
regulation  of,  587 

'  chemical '     and     '  physical,' 

590 
effect    of    thyroidectomy    on, 

593 
in  hibernating  animals,  596 

sensations,  paths  for,  793.  795 

t"|»>L;raphy,  602 
Temporo-sphenoidal  convolutions  and 

hearing,  824,  860 
'  Tendon-reflex,'  802 
Tendons,  nerve-endings  in,  983 
Tension  of  blood-gases,  256 

of  oxygen  in  human  blood,  258 
Tensor  tympani,  820,  955,  961 
Testicles,  action  of  extracts  of,  557 

effect  of  removal  of,  556 
Tetanolysin,  hemolytic  action  of.  27 
Tetanus,  composition  of,  657,  711 

electrical,  656,  711 

frequency  of  stimulation  necessary 
for.  657.  658 

negative  variation  in.  721,  722 

Ritter's,  636,  662,  727.  743 

secondary.  730,  738 

toxin,  action  of,    on  spinal    cord. 
797.  801 
Tetany  after  parathyroidectomy,  559 
Thalamencephalon,  747 
Thalamo-bulbar  tract,  773 
Thalamus,     See  Optic  thalamus 


Theobromine,  1 1 1 
Theophyllin,  1 1 1 
I  tiermo-elei  trie  juni  tions,  S73.  <  ■ 
'Thermogenic'  nerves,  701 

Thermometers,  572 

resistant  e,  <><<  >,.  064 
Thermopile, 
Thermotaxis,  587,  590 
1  hiosulphurii  at  id  in  urine 
Third  nerve,  819 
Thirst,  sensation  "f.  826 
Thiry's  fistula,   ;  1 1 
Thoracic  dui  t.  1 70 

absorption  o  415 

proteids  by,  1 1 9 
and  jaundice,  3=15 
glycosuria    after    ligation  <>f. 
555 

respiration.  214 
Thrombin.  32 

specificity  of,  37 
Thrombogen,  33,  36.  37 
Thrombokinase,  33,  37.  57 

sources  of,  34,  36 
Thymine,  507 
Thymus,  feeding  with,  506 

formation  of  lymphocytes  in,  22 

nucleo-proteins    of,  and    coagula- 
tion, 38 

removal  of,  557 
Thyroid,  effects  of  excision  >>i.  560 

on  heat-regulation,  593 

feeding  and  metabolism. 

grafting,  561 

iodine  in,  561,  562 
Thyroiodin,  561 
Tickling,  968,  975 
Tidal  air.  2211.  291 
Timbre,  280 
Time-markers,  179,  625 
Tissue  liquid,  407,  408 

respiration,  2'' t 
Titratable  aciditv  of   urine.    j-;S,   4  v». 

477 

alkalinity  of  blond,  24 
Tone,  muscular.  632.  81  j,  886 

trophic  813,  M14 
Tonsils,  formation  of,  lymphocytes  in, 

22 
Tonus,  acerebral,  836,  B47 
Topognosis,  856 
Torpedo,  736,  737 
Torricelli's  theorem,  75 
Touch,  acuity  of,  970,  1000 

after  section  of  cutaneous  nerve. 
975.  976 

corpuscles,  968 

spots,  969,  970,  1000 
Trachea,  to  put  a  cannula  in,  186 
Tracheal  cannula,  to  make,  186 


INDEX 


:  Olsb,   179 

ts  in  <  '>rii.  76  1 
tfusion,  tc  1 7 1-  200 
plantation  ol  tissues,  1 

band    oi    stomach, 

Traube •  Her ing  curves,  270,  j  r  1 

-piil  valve. 
Trigeminus  nert  1 

1  il   as<  ending  bundle  of, 

'  trophic '  effe<  ts  "i  l(  sions  of, 
699, 

Triple  phosphate,  1  jg 

Tristearin,  1 

Trochlear  or  fourth  nerve, 

Trommer's  tesl  for  reducing  sugar,  10 

Trophic  nerves.  690.  sjj 
tone,  81  - 

Trophoblast,  1010 

Trypsin,  331 

influence  of  bile  on,  340 
relation  of,  to  spleen,  382.  571 

Trypsinogen,  331,  343.  353.  571 

Tryptic  digestion,  331,  340,  343,  391, 
428 
products  of,  332 

Tryptophane.  2,  $32.  430.  510.  534 
and  Adam  Kiewicz's  reaction,  8 
and  the  formaldehyde  reaction  for 

proteins.  8 
as  a  precursor  of  indol,  449 

Tubercle   bacilli,    absorption    of,    from 
intestine,  413 

Tuberculum  acusticum,  824 

Twelfth  nerve,  827 

'  Twitch,'  the.  706 

Tympanic  membrane,  954,  960,  961 
fundamental  tone  of,  961 

Tympanum.  954 

sin,  2.  430,  526,  534 

and  Millon's  reaction.  8 

in  pancreatic  digestion,  332,  430 

in  serum  proteins,  498 

in  urinary  sediments.  450.  495 

production  of,  in  liver,  510 

Tyrosinase.  265 

Uffelmann's  test  for  lactic  a<  id.  428 
Umbilical  cord,  1012.  1020 

vesicle.  10 10 
Uncinate  gyrus,  817,  861 
Unicellular  organisms.  6 
Unipolar  stimulation,  843 
Unpolarizable  electrodes,  625,  739 
Urachus,  10 12 
Uracil,  507 
Uraemia,  447 
Urates  in  urinary  sediments,  438,  494 


II.   I'l.  \^>.  I  10, 
.u  tion  of,  on  blo<  •!  62 

after  Bck'a  fistula, 

decomposition  of,    1  [O,  480.  585 

diuretic  action  of,  171 
estimation  of,  481 
formation  of, 

l>v  oxidation. 
in  liver.  501 
in  blood,   162,  500 
in  fever,  4  yg 
in  starvation.  531 
premortal  riv  in  excretion  ■ 
substances  which  form,  501 
variations  with   proteins   in  food, 
437-  44'>,  497.  500,  6l2 
1  rreometer,  I  ►oremus',  482 
Ureter,  contractions  of,  659 
Uric     acid,    437,    440,    449.     504,     507, 
538 
destruction  of,  508 
endogenous,  441.  507 
estimation  of,  484,  485 
exogenous,  507 
formation    of,    in    birds,    502. 
505 
in  mammals.  505 
from  nuclein  substances. 

504,  506,  507 
from  nucleo-proteids,  506 
hydrolysis  of,  508 
in  blood,  505 
in  gout.  449.  505 
in  leukaemia,  449,  505 
in  urinary  sediments,  438,  494 
Uricolytic  ferment,  508 
Urine,  acidity  of,  437.  438.  439.  477 
acetone  in.  492,  520 
aceto-acetic  acid  in.  520 
acid  fermentation  of,  438 
alkaline  fermentation  of,  439 
amino-acids  in.  441,  450 
in  liver  diseases.  505 
ammonia  in,  440 

after  Eck's  fistula.  502 
aromatic  bodies  in,  445.  449.  479 
bile  in.  451,  491 
carbohydrates  in,  442 
chlorides  in,  444.  477 
collection  of,  476.  609 
composition  of,  436,  437 
cystin  in.  450 

ethereal  sulphates  in,  445,  479 
examination  of.  494 
ferments  in,  443,  444 
freezing-point   of,    446,    447,    465, 

492 
haematoporphyrin  in,  443 
hippuric  acid  in,  441,  486 
incontinence  of,  473 


[062 


INDEX 


i  Frine  in  disease,  1 1 

indoxyl    in.    i  ;'..    i  i;.    445,    440. 

479 
in  foetus,   tOl6,  mi  7 

in  starvation,  5  jo,  532 

kreatinin  in.  4  \z,  485 

leucin  and  1 5  rosin  in,  1  so.  495 

methsemoglobin  in.  144,  psr 

1  Kim  it  ic  pressure  1  if,  ins 

1  ixalic  acid  in.  11 1 

pentoses  in.  450,  491 

phenol  in.  (is 

phosphi  'in  .11  id  in.  hi.  478 

physico-chemical  analysis  of,  1  in 

pigments  of,  11  | 

proteins  in.  1.43,  451,  486 

proteoses  in.  451,  486 

purin  bases  in.  441 

quantity  of,  436,  437 

reabsorption  of.  457 

reaction  of,  436,  438,  439,  477 

secretion  of,  451 

action  of  glomeruli  in,  455,  458, 

465 
1  >f    '  rodded  "   epithelium 
in,  458,  460.  466 
Beddard's     experiments     mi. 

460 
Heidenhain's  experiments  on, 

458 
Xnssbaum's   experiment   on, 

460 
influence    of    circulation    on. 

I'T 
of  drugs  on,  470 
.>i  nerves  on,  467-470 
relation  to  blood-pressure.   |.6g 
theories  of,  455 
work  done  by  kidney  in.  465 
secretory  pressure  of,  466 
sediments  of,  438,  439,  494 
skatoxyl  in.  445,  480 
specific  gravity  of,  436,  448.  477 
sugar  in.  4 si.  488 
sulphuric  acid  in,  444.  479 
total  nitrogen  in.  482 
urates    in,      1  {8,     439,     440,     449, 

494 
urea  in,  436,  440.  480 
uric  acid  in,  440.  4  pi.  480 
xanthin  bases  in.   |  |  1 

i  rrinometer,  477 

Urobilin,  33G,  306,   1  1  3 

Urochrome,  443 

Uroerythrin.  443 

I  rrohypertensine,  570 

Urorosein,  443 

Urea  and  secretion  of  aqueous  humour, 
901 

Utricle,  833,  957 


.rr  tion  "t  both,  2  16,  ;oo 

effei  1  of,  'Hi  respiration.  ^.'  1 

Vagus,   cardiac   fibres  of.  in    fro. 
181.  182 
centre,    effect    of    suprarenal    >\- 

tract  on.  201 
in  mammals.  147,  187.  197 
in  tortoise,  181 
[legal  ive  \  ariation  of.  22s 
relation  of,  to  respiration,  22  (.  22*). 
289 
to  deglutition,  304 
to  gastric  secretion,  374 
to     gastrointestinal      move. 

ini'iii  - 
to  pancreatic  secretion,    $78, 
380 
tracings.  182.  197 
Vagus  nerve,  825 

and    cervical    sympathetic,    union 
of.  868 
Valsalva's  experiment,  273 

sinuses,  191 
Valves  of  heart,  action  of,  190.  191 

moment     of     opening     and 
closure  of.  88, 
of  veins,  74 
Valvulae  conniventes,  403 
Varnishing  skin,  276.  4  74 

tracings,  179 
Vaso-constrictors   and   dilators,    differ- 

ences  between,  159 
Vaso-dilator  fibres,  163,  164 

of  chorda  tympani,  t6  j 
of  limbs.  165 
nervi  erigentes,  163,  165 
Vaso-motor  cells  in  the  cord,  169 
Vaso. motor  centres,  166 
in  sleep,  875 
peripheral,  168,  979, 
spinal,  167,  763 
nerves,  157-172,  763,  975.  479 

methods  of  investigating,  158 
nerves  of  brain.  160 

cervical     sympathetic,      159 

202 
course  of,  165,  884 
in  splanchnics,  161 
in  trigeminus,  161 
"t  car.   16Z,   ISO.  202 
of  heart.  162 
of  kidney,  161.  467 
of  limbs.  161 
ot  lungs.  163 
of  muscles,  162 

nt  veins.  157,  164 
reflexes,  169,  171,  198 
tone,  nature  of,  168 
Vein,  to  put  a  cannula  in.  200 


WDl  X 


1063 


Vein   oi    rabbit's    ear,    injection    into, 

610 
Veins,  <  Irculation  In,  [09,  mi.  ui 

I'ulx-  111.  g  1 

structure 
valves  oi 

\  aso-motor  nerves  of,  [6 1 
velocity  oi  blood  In,  1  -•  1 
Vella's  fistula,  ;  1 1 

1  \ -ui  blood,  to8 
in  arteries,  1 i<> 
in  capillaries,  77,  1  [9,  177 
in  \  eins,  1  aa.  1  a  1 
measurement     of,     111  —  113, 
204 
Velocity    ol    the    nerve-impulse,    689, 

Velocity-pulse,  curves  of,  114,  115 
Venous  pulse,  91,  un 

tra<  ings  of,  1  ;;.  193 
Ventilation,  2 1  ; 
Ventricles  oi  brain,  7  17 
\  1  1  atrine,  action  of,  "n  muscle,  654 
Vernix  1  aseosa,  1017 
\  1  rtigo,  8  \6,  <s.i7 
Vesicular  murmur,  210,  291 
Vestibular  branch  of  auditory  nerve, 

i2A 
Vestibule,  823,  956 

aud  equilibration 
Vieussens,  annulus  of,  147.  190 
\*illi,  408,  413 
Viscosity  of  blood,  22 
Vision,  central  and  peripheral,  925,  935, 
946 
colour,  939 
far-point  of,  915,  988 
111  congenitally  blind,  after  opera- 
tion. 927 
near-point  of,  915,  917 
physical  introduction  to,  892 
steri  oscopic,  925 
Visual  acuity,  997 
angle,  904 
axis,  898,  914 
centres,  819,  857,  858 
field,  819,  n  (.6,  992 
illusions, 
judgment,  926 
path,  scheme  of,  819,  .S57 
purple,  736,  934 

regeneration  of,  935,  936 
Visuo-psychic  and  visuo-sensory  areas, 

860 
Vital  capacity,  220,  291 
Vitellm.  2 

Vitelline  a  tery  and  veins.  1010 
Vitreous  humour.  901,  902,  985 
opa<  Lties  in  ,  929,  914 
V  "  al  cords,  277.  282 


Voi  al  cords,    ^  emeui  ■>   ■  if,    in    1  es- 

piral  ion, 

in  von  c  po  11  Im,  1  ion,  271) 

paralysis  of,  286 
prodw  tiou  of,  276,  2~* 
pressure  in  trachea  in,  27'i 
falsetto,  281 
in  1  hildren,  27'/ 
Volkmann's  method  for  blood  velocity, 

1 1 1 
Volt,  616 
Volume  oi  corpuscles  and  plasma  in 

blood,  26,  59 
Volume-pulse,  116 

Voluntary  contraction,  fatigue  in,  652. 
709 
nature  of,  660 
Vomiting,  312 

caused  l>v  apoiiiorpliine,  312,  31;, 

427.  432 
centre,  313 
Vowel  cavities,  28  1 
Vowels,  Helmholtz's  theory  of,  283 
Hermann's  theory  of,  284 

Wallerian  degeneration,  692 

Warmth  sensations,  968,  969,  791,  972, 

IOOI 

after     section     of     cutaneous 

nerves,  975,  977,  978 
paths  for,  795 
Water,  absorption  of,  395,  417 

equivalent  of  calorimeter,  613 
in  diet,  549 

production  of,  in  body,  541 
valve,  614 
Weber's  law,  984 
Weigert's  method,  757 
Welcker's    method    for    quantity    of 

blood,  47 
Weyl's  test  for  kreatiuin,  485 
Wharton's  duct,  362,  363,  424 
Wheatstone's  bridge,  617 
Wheat  flour,  546,  547,  612 
Wheel-movements  of  eyes,  951 
Whey-protein,  327 
Whispering  voice,  28  j 
White  blood-corpuscles,  16 
Wolffian  body.  1010 
Wooldridge's  tissue  extracts  and  coagu- 
lation. 38 
Word-blindness.  864 
deafness,  866 
pictures,  866 
Work -adder,  664 
Work,  muscular.  5S3.  664,  646 

relation    of,    to    heat-produc- 
tion, 582.  583,  665 
source  of  energy  of,  669 
ol  heart,  127 


IIP'.  I 


INDEX 


Worm   "i   cerebellum, 
\\  risberg,  um  e 


771.    772.    779. 


825 


Xanthin 

fever  produi  ed  b 
Xanthin-bases  in  urine,  1 1 1 
Xanthro-pot<  ic  rea<  tion,  7 

■  nil. 1.  372 


Pawning, 

Velio  w -spot  993 

">  east-tesl  for  sugar,  489 
Yohimbine,  action  of,  on  aerve,  < 
Volk-sai .' 

/c|1ii,t'>  illusion  oi  parallel  lint  - 

Zonule  "i  Zinn,  900 

Zymogens,  328,  331,  353.  354.  360 


THE    END 


Bail  It!  re,   Tindall  and  Cox,  8,  Henrietta  Street,  C event  Garden 


rart 


St4 
1910 


[ 


